Nitrogen Fertilization

Nitrogen isotopic studies have the potential to shed light on the structure of ancient ecosystems, agropastoral regimes, and human-environment interactions. Until relatively recently, however, little attention was paid to the complexities of nitrogen transformations in ancient plant-soil systems and their potential impact on plant and animal tissue nitrogen isotopic compositions. This paper discusses the importance of understanding nitrogen dynamics in ancient contexts, and highlights several key areas of archaeology where a more detailed understanding of these processes may enable us to answer some fundamental questions. This paper explores two larger themes that are prominent in archaeological studies using stable nitrogen isotope analysis: (1) agricultural practices (use of animal fertilizers, burning of vegetation or shifting cultivation, and tillage) and (2) animal domestication and husbandry (grazing intensity/stocking rate and the foddering of domestic animals with cultigens). The paucity of plant material in ancient deposits necessitates that these issues are addressed primarily through the isotopic analysis of skeletal material rather than the plants themselves, but the interpretation of these data hinges on a thorough understanding of the underlying biogeochemical processes in plant-soil systems. Building on studies conducted in modern ecosystems and under controlled conditions, these processes are reviewed, and their relevance discussed for ancient contexts.

Eutrophication is a major driver of species loss in plant communities worldwide. However, the underlying mechanisms of this phenomenon are controversial. Previous studies have raised three main explanations: 1) High levels of soil resources increase standing biomass, thereby intensifying competitive interactions (the “biomass-driven competition hypothesis”). 2) High levels of soil resources reduce the potential for resource-based niche partitioning (the “niche dimension hypothesis”). 3) Increasing soil nitrogen causes stress by changing the abiotic or biotic conditions (the “nitrogen detriment hypothesis”). Despite several syntheses of resource addition experiments, so far, no study has tested all of the hypotheses together. This is a major shortcoming, since the mechanisms underlying the three hypotheses are not independent. Here, we conduct a simultaneous test of the three hypotheses by integrating data from 630 resource addition experiments located in 99 sites worldwide. Our results provide strong support for the nitrogen detriment hypothesis, weaker support for the biomass-driven competition hypothesis, and negligible support for the niche dimension hypothesis. The results further show that the indirect effect of nitrogen through its effect on biomass is minor compared to its direct effect and is much larger than that of all other resources (phosphorus, potassium, and water). Thus, we conclude that nitrogen-specific mechanisms are more important than biomass or niche dimensionality as drivers of species loss under high levels of soil resources. This conclusion is highly relevant for future attempts to reduce biodiversity loss caused by global eutrophication.

Chlorophyll meters are widely used to guide nitrogen (N) management by monitoring leaf N status
in agricultural systems, but the effects of environmental factors and leaf characteristics on leaf N
estimations are still unclear. In the present study, we estimated the relationships among SPAD
readings, chlorophyll content and leaf N content per leaf area for seven species grown in multiple
environments. There were similar relationships between SPAD readings and chlorophyll content per
leaf area for the species groups, but the relationship between chlorophyll content and leaf N content
per leaf area, and the relationship between SPAD readings and leaf N content per leaf area varied
widely among the species groups. A significant impact of light-dependent chloroplast movement on
SPAD readings was observed under low leaf N supplementation in both rice and soybean but not
under high N supplementation. Furthermore, the allocation of leaf N to chlorophyll was strongly
influenced by short-term changes in growth light. We demonstrate that the relationship between
SPAD readings and leaf N content per leaf area is profoundly affected by environmental factors and
leaf features of crop species, which should be accounted for when using a chlorophyll meter to guide
N management in agricultural systems.

1. Nitrogen (N) and phosphorus (P) often limit biological processes in terrestrial ecosystems. Based on previous studies mainly focusing on plants, the concept of resource limitation has evolved towards a theory of (co)limitations by multiple resources. However, this ecological framework has not been applied to analyse how soil microorganisms and plants concurrently respond to N and/or P addition, and whether these responses are constrained by phylogenetic relatedness.
2. Here, we applied this framework to analyse microbial and plant responses at community and taxon levels to different fertilization treatments (four N levels without P; four P levels without N and four NP levels) in Tibetan grasslands.
3. Total plant biomass showed serial limitation by N then P, and most plant species were limited by N only. Total archaeal abundance decreased with P addition, but diverse nutrient limitation types were observed for archaeal taxa. Closely related archaeal taxa tended to similarly respond to N, and functional similarity between distant archaeal groups was observed for response to P, possibly due to functional convergence. In contrast, total bacteria slightly increased with P addition only when plants remained N limited, whereas without N limitation, plants rather than bacteria benefited from P addition. Most bacterial taxa were limited by other resources than N and P, and no clear phylogenetic signals were observed regarding bacterial responses to N/P additions.
4. Synthesis. We propose a novel approach for characterizing microbial response types to nutrient addition. It demonstrates that in Tibetan meadows, most dominant plant species, archaea and bacteria, respectively, depend on N, both N and P and other resources.

Porous soils are characterized by high infiltration, low moisture retention and poor fertility due to limitation of organic matter and nitrogen (N). However, wherever irrigated and properly managed, these are among the most productive soils in the world. For sustained productivity and prevention of N related pollution problems, fertilizer N management in porous soils needs to be improved by reducing losses of N via different mechanisms. Losses of N through ammonia volatilization are not favoured in porous soils provided fertilizer N is applied before an irrigation or rainfall event. Ammonium N transported to depth along with percolating water cannot move back to soil surface where it is prone to be lost as NH3. Under upland conditions nitrification proceeds rapidly in porous soils. Due to high water percolation rates in porous soils, continuous flooding for rice production usually cannot be maintained and alternate flood and drained conditions are created. Nitrification proceeds rapidly during drained conditions and nitrates thus produced are subsequently reduced to N2 and N20 through denitrification upon reflooding. Indirect N-budget estimates show that up to 50% of the applied N may be lost via nitrification-denitrification in irrigated porous soils under wetland rice.

Understanding how intra-specific differences in plant traits mediate vulnerability to herbivores of relevant habitat-forming plants is vital to attain a better knowledge on the drivers of the structure and functioning of ecosystems. Such studies, however, are rare in seagrassmesograzer systems despite the increasingly recognized relevance of mesograzers as seagrass consumers. We investigated the role and potential trade-offs of multiple leaf traits in mediating the vulnerability of the seagrass Zostera noltei to different mesograzer species, the amphipod Gammarus insensibilis and the isopod Idotea chelipes. We worked with plants from two different meadows for which contrasting chemical and structural traits were expected based on previous information. We found that plants with high vulnerability to mesograzers (i.e. those preferred and subjected to higher rates of leaf area loss) had not only higher nitrogen content and lower C:N, fibre, and phenolics, but also tender and thinner leaves. No trade-offs between chemical and structural traits of the seagrass were detected, as they were positively correlated. When leaf physical structure was removed using agarreconstituted food, amphipod preference towards high-susceptibility plants disappeared; thus indicating that structural rather than chemical traits mediated the feeding preference. Removal of plant structure reduced the size of isopod preference to less than half, indicating a stronger contribution of structural traits (> 50%) but combined with chemical/nutritional traits in mediating the preference. We then hypothesized that the high environmental nutrient levels recorded in the meadow exhibiting high susceptibility modulate the differences observed between meadows in seagrass traits. To test this hypothesis, we exposed lowvulnerability shoots to eutrophic nutrient levels in a 6-week enrichment experiment. Nutrient enrichment increased Z. noltei nitrogen content and lowered C:N, fibre, and phenolics, but had no effect on structural traits. Overall, our findings help to better understand the traitmediated seagrass susceptibility to mesograzers and reinforce the increasingly recognized role of structural defences against herbivory.

In soils, nitrogen (N) addition typically enhances ammonia oxidation (AO) rates and increases the population density of ammonia-oxidizing bacteria (AOB), but not that of ammonia-oxidizing archaea (AOA). We asked if long-term inorganic N addition also has similar consequences in arid land soils, an understudied yet spatially ubiquitous ecosystem type. Using Sonoran Desert top soils from between and under shrubs within a long-term N-enrichment experiment, we determined community concentration-response kinetics of AO and measured the total and relative abundance of AOA and AOB based on amoA gene abundance. As expected, N addition increased maximum AO rates and the abundance of bacterial amoA genes compared to the controls. Surprisingly, N addition also increased the abundance of archaeal amoA genes. We did not detect any major effects of N addition on ammonia-oxidizing community composition. The ammonia-oxidizing communities in these desert soils were dominated by AOA as expected (78% of amoA gene copies were related to Nitrososphaera), but contained unusually high contributions of Nitrosomonas (18%) and unusually low numbers of Nitrosospira (2%). This study highlights unique traits of ammonia oxidizers in arid lands, which should be considered globally in predictions of AO responses to changes in N availability.

This research was carried out to study the effect of nitrogen rate application (0, 120, 240 and 360 kg Nitrogen ha-1) and nitrogen timing on grain yield, yield components, grain quality and protein banding pattern in different growth stages of wheat (Shiraz cultivar) which was grown at research station of the School of Agriculture, Shiraz University at Bajgah in the 2008-2009. Results indicate that the highest value for grain yield was obtained at 240 kg N ha −1 when it was applied through vegetative growth stages (8230 kg ha-1). Yield components were significantly increased with enhancing the level of nitrogen with no significant difference between 240 and 360 kg N ha-1. Results show that no N application at tillering stage decreased spikes number/m 2 and seeds spike-1 , and the minimum value of 1000 grain weight was observed when we remove N application in grain filling period. Leaf protein did not influenced by N treatments. However, the sharpness of a band with molecular weigh about 51 kDa, related to Rubisco enzyme, was increased in some treatments. Furthermore, 240 kg N ha-1 application in all timing treatments resulted in maximum seed protein content (5.5 mg protein g-1 grain). At the same time, seed water soluble proteins, Albumin and Globulin, showed no polymorphism. While different N rate treatments had no significant effect on seed gluten content, no N application in grain filling period declined it significantly. All in all, obtaining high wheat grain yield beside a suitable bakery quality are possible in a proper farming management system without environmental impact of N over application. These goals may be achieved with sufficient N application during vegetative growth for yield and late season N application for protein quality.

Photosynthesis in C3 plants is significantly limited by mesophyll
conductance (gm), which can vary with leaf anatomical
traits and nitrogen (N) supplements. Several studies have
investigated the response of gm to N supplements; however,
none examined the implications of N supplements on the
response of gm to rapid environmental changes. Here we
investigated the effect of N supplement on gm and the
response of gm to change of CO2, temperature and irradiance
in rice. High N supplement (HN) increased mesophyll cell
wall surface area and chloroplast surface area exposed to
intercellular airspace per leaf area, and reduced cell wall
thickness. These changes resulted in increased gm. The gm of
leaves with HN was more sensitive to changes in CO2 concentration,
temperature and irradiance.The difference in leaf
structural features between low N supplement and HN indicates
that a rapid change in gm is related to the regulation of
diffusion through biological membranes rather than leaf
structural features. These results will contribute to an understanding of the determinants of gm response to rapid changes in environmental factors

Plant nitrogen isotopic compositions are highly variable and are influenced by a diversity of environmental and anthropogenic factors, including the application of animal-derived fertilizers. Legumes that acquire most of their nitrogen from atmospheric N2 (rather than mineralized soil nitrogen) tend to have relatively low δ15N values (consistently around 0 ‰), and it has been presumed that their δ15N values are largely or wholly unaffected by fertilization. This study presents nitrogen isotopic data from leguminous (garden bean, Phaseolus vulgaris) and non-leguminous (summer squash, Cucurbita pepo) plants subjected to seabird guano fertilization while growing under controlled conditions. Both bean and squash tissue δ15N values were substantially increased by seabird guano fertilization: +16.3 to +19.2 ‰ for bean and +19.6 to +24.5 ‰ for squash. The results of this study demonstrate that the enrichment in plant 15N resulting from seabird guano fertilization occurs consistently in non-maize species. Moreover, it demonstrates that under conditions of high soil nitrogen availability, leguminous plants may obtain a substantial portion of their nitrogen through the uptake of inorganic soil nitrogen (ammonium and nitrate), rather than atmospheric N2. In general, where the δ15N values of fertilizers differ substantially from that of endogenous soil nitrogen and mineralized nitrogen derived from the fertilizer is readily available, a significant manuring effect can be expected in leguminous plants.

Nitrogen deficiency influences importantly the plant photosynthetic capacity and crop productivity. Here, we employed the rapid, non-invasive measurements of chlorophyll a fluorescence kinetics for calculation of the integrative fluorescence parameters related to the leaf photosynthetic performance. In pot experiments with winter wheat (Triticum aestivum L.) we cultivated plants during the whole growing period in the soil substrate supplied with four different doses of nitrogen. The leaf nitrogen and chlorophyll content as well as the plant dry mass were analyzed after chlorophyll fluorescence records in three growth stages. Our results indicate that the commonly used parameter Fv/Fm (the maximum quantum yield of photochemistry) was almost insensitive to nitrogen treatment. In contrary, the performance index (PIabs) and total performance index (PItot) were much more responsive and significant differences among plants of different nitrogen treatments as well as between the youngest and third leaf from the top were observed. Parameter PItot was shown to express only small diurnal changes, thus being more reliable and more useful for comparison of different samples in field conditions than more frequently used parameter PIabs.

In precision farming, accurate estimation of canopy nitrogen concentration (CNC) is valuable for effective crop growth monitoring and nitrogen (N) fertiliser management. To date, many canopy multispectral indices have been proposed as indicators for CNC; however, many of these indices have also shown sensitivity to biomass and their performance drops at high biomass levels. Dependence on growth stage, season, or other environmental conditions limits their efficacy as generalized CNC indices. The objectives of this study were to assess the robustness of popular CNC indices across a wide range of biomass levels and fertiliser application levels; and for two contrasting seasons-winter and summer. To achieve this, we analysed the efficacy of seven canopy nitrogen indices, including canopy chlorophyll content index (CCCI), together with eleven other commonly used spectral indices. We used canopy level solar-induced hyperspectral reflectance data acquired using a hand-held optical spectroradiometer across four growth stages in winter (May-June 2018) and four in summer (January-February 2019) from an experimental field of irrigated perennial ryegrass with variable N application in Victoria, Australia. The field contained 40 plots, each with one of eight different N treatments. Almost all the indices exhibited similar correlation to CNC (%) when applied to individual stages (days) in both winter and summer; however, relationships between CNC and individual indices varied significantly between stages. We obtained similar results for canopy biomass. When the data across the entire range of growth stages and seasons were combined, the correlations between most canopy nitrogen indices and CNC became weak (R 2 < 0.25, 0.9% ≤ RMSE ≤ 1.0%). PRI exhibited the highest correlation with CNC (R 2 = 0.58, RMSE = 0.7%) for the combined data set. Even so, PRI's association with CNC and canopy biomass changed with the season. Most indices responded to both CNC and biomass simultaneously, and this confounds the estimation of CNC due to strong but growth stage-specific relationships between CNC and canopy biomass. This study shows that it is important to consider a wide range of conditions when evaluating multispectral CNC indices.

The nitrogen (N) cycle is an important part of earth's biogeochemical cycles and N is a critical element for all life. Whereas the response to N-and more rarely phosphorus, P-fertilization of some microbial groups involved in soil N cycling has been studied, a comprehensive view of how the major microbial groups involved in soil N dynamics respond to combined N and P fertilization is lacking, which restricts our understanding of ecosystem responses to fertilization. Here we investigated the effects of different N, P and NP fertilizer levels (4 N levels without P; 4 P levels without N; and 4 P levels with constant N addition) on the abundances of 9 microbial groups involved in N dynamics. Real time PCR was used to target free N 2 fixers, nitrifiers (bacterial and archaea ammonia oxidizers, AOB and AOA, respectively; and the nitrite oxidizers Nitrobacter and Nitrospira), nitrate reducers, nirK-and nirS-nitrite reducers, and nitrous oxide reducers. Soil physical-chemical characteristics and potential nitrification, PNR, were also measured. N fertilization increased the abundances of AOB and Nitrobacter but did not affect the abundances of the other groups. P fertilization decreased the abundances of N 2 fixers, nitrate reducers and AOA, and increased the abundances of Nitrobacter and nitrous oxide reducers. NP fertilization decreased the abundances of AOA and nirK-nitrite reducers. Using a correlation network analysis, we demonstrate the strong coupling generally observed in these grasslands between N 2 fixers, AOA, Nitrospira, narG-nitrate reducers and nirK-denitrifiers (most of them responding to N/P availability, and being known to be favored by low oxygen availability); and between AOB and Nitrobacter (known to be favored by high oxygen and high N levels) that controlled changes in PNR. The observed (de)coupling between the responses of the different microbial groups may have major consequences for N cycling and N losses from fertilized Tibetan alpine meadows.

In a time of resource reduction and climate variability, water conservation is critical to improve agroecosystem sustainability. Non-ionic surfactants were recently hypothesized as irrigation adjuvants, but so far researchers obtained contrasting results. The first objective of this work was to evaluate the capillary adsorption properties of organosilicone surfactants by providing two robust tests on standard porous media. Results showed smaller capillary mobility and higher wetting power (" superspreading ") compared to pure water. An innovative non-ionic surfactant formulation, the organosilicone PET (PolyEther-modified Trisiloxane), was then investigated as irrigation adjuvant in a pot trial on lettuce in absence of fertilization. Overall, the system was characterized by an improvement in the processes of resource acquisition, i.e. water and nutrients. Results indicated higher lettuce leaf area, reduced root dry weight and root:shoot ratio and a positive main effect on the uptake, availability and/or use efficiency of P, K and some micronutrients. The N use efficiency and recovery increased 3–15%, with higher N concentration and content against changes in plant weight. Fresh yield data showed a particularly high irrigation use efficiency (+77–60%), and the adjuvant productivity (variation of lettuce yield due to PET) increased by 12–26%. Our experimental findings can be explained by hypothesizing that PET affected both capillary and adsorption processes during water diffusion along concentration gradients, which constitute the main driving force for solutes movement towards the roots. A theoretical model is provided to explain how PET improved the thickening and interconnection of conductive adsorbed water film in soil.

A 15 N labeling and lysimeter experiment was conducted with mesocosms of a semi-arid Leymus chinensis grassland. The aim of the study was to evaluate the effects of N fertilization timing (fertilization in fall or spring) and rate (0, 56, and 112 kg-N ha −1 year −1) on ecosystem services (seed yield and forage yield), ecosystem disservices (N leaching surveyed during 1 year and emissions of NH 3 and N 2 O integrated over 76 days after fertilization), and recovery of added fertilizer N in plants and soil. Seed and forage yields increased more under fall than spring N fertilization. Further, N fertilization was linked to higher soil NH 3 and N 2 O emissions, particularly under high N rate for both NH 3 (2.0 and 1.6 kg-N ha −1 under fall and spring N fertilization, respectively) and N 2 O (0.24 and 0.21 kg-N ha −1 , respectively). N leaching was never observed. A significant N fertilization timing × rate interaction effect was observed on plant recovery efficiency of added fertilizer N (Plant-NRE). Plant-NRE was higher for high than moderate N rate, with + 13.2% (from 22.8 to 36%) and + 16.4% (from 28.2 to 44.7%) for fall and spring fertilization, respectively. Fertilizer N recovered in soil was highest for moderate N rate in fall (68% of total N fertilizer) and lowest for high N rate in spring (46%). Our results show synergies among the ecosystem services (seed and forage yields) and among the disservices (NH 3 and N 2 O emissions), and trade-offs between the services and disservices, some of these synergies and trade-offs being modulated by N fertilization timing and rate. Our study is the first one analyzing the possibly interactive effects of the N fertilization timing and rate on this range of ecosystem services and disservices in semi-arid perennial grasslands, which can be useful for N risk: benefit analysis when evaluating N fertilization strategies.

Efficient nitrogen (N) fertilizer management is critical for wheat production and the long-term protection of the environment. Given the importance of durum wheat for the Italian economy, its environmental implications need to be investigated for designing sustainable production system. Three concurrent experiments were carried out in Gravina in Puglia (Apulia, southern Italy) to investigate the agronomic and environmental response of rainfed durum wheat (Triticum turgidum L., var. durum) to different N rates, N source and application time over three years (2010e2012). In the three experiments, the following parameters were analyzed: grain yield, yield components (i.e. harvest index, spikes m À2), quality traits (i.e. hectoliter weight, protein content), energy input/output analysis including the calculation of energy indexes and greenhouse gas (GHG) emissions. The N rate experiment included rates of 45, 90 and 135 kg N ha À1. Each rate was split in various proportions between sowing, tillering and stem elongation. For the experiment on N timing and splitting, a single dose of 90 kg N ha À1 was split between sowing, tillering and stem elongation at different fractions (0-90-0; 40-50-0; 10-40-40). The N fertilizer source experiment tested the effect of the application of 90 kg N ha À1 of urea split at sowing and tillering (12-78-0) on the investigated parameters, and compared to Entec ® 26 and Sulfammo 23 with the same does and application time. Nitrogen agronomic efficiency (NAE) was also calculated to assess the potential yield increase in response to different N fertilizer rates and types. The results showed that N rate, N source and the application time had a significant impact on grain yield, grain protein content, energy output and GHG emissions under normal weather conditions. Considering the site-specific condition, the overall results revealed that the split application of 90 kg N ha À1 during three growth stages gave favorable results in terms of grain yield and quality, and optimizes NAE with less environmental impact. The effectiveness and efficiency of this strategy was more pronounced when two-third of the full N dose was applied at later stages (tillering and stem elongation). This strategy found to be more effective in improving wheat yield and quality than the increase in the N rate, which could offer the potential to decrease N fertilization rate in wheat production. This study provides useful information for farmers on how to manage the N fertilization of wheat for sustainable production system.

We studied the relative importance of several environmental factors for tundra plant communities in five locations across Svalbard (High Arctic) that differed in geographical location, oceanographic and climatic influence, and soil characteristics. The amount of marine-derived nitrogen in the soil supplied by seabirds was locally the most important of the studied environmental factors influencing the tundra plant community. We found a strong positive correlation between δ 15 N isotopic values and total N content in the soil, confirming the fundamental role of marine-derived matter to the generally nutrient-poor Arctic tundra ecosystem. We also recorded a strong correlation between the δ 15 N values of soil and of the tissues of vascular plants and mosses, but not of lichens. The relationship between soil δ 15 N values and vascular plant cover was linear. In the case of mosses, the percentage ground cover reached maximum around a soil δ 15 N value of 8‰, as did plant community diversity. This soil δ 15 N value clearly separated the occurrence of plants with low nitrogen tolerance (e.g. Salix polaris) from those predominating on high N content soils (e.g. Cerastium arcti-cum, Poa alpina). Large colonies of planktivorous little auks have a great influence on Arctic tundra vegetation, either through enhancing plant abundance or in shaping plant community composition at a local scale.

With that diet, you will go far: trait-based analysis reveals a Supplementary data tml (1255 articles) ecology Articles on similar topics can be found in the following collections Email alerting service here right-hand corner of the article or click Receive free email alerts when new articles cite this article -sign up in the box at the top http://rspb.royalsocietypublishing.org/subscriptions go to: Proc. R. Soc. B To subscribe to on February 5, 2013 rspb.royalsocietypublishing.org Downloaded from rspb.royalsocietypublishing.org Research Cite this article: Betzholtz P-E, Pettersson LB, Ryrholm N, Franzén M. 2012 With that diet, you will go far: trait-based analysis reveals a link between rapid range expansion and a nitrogen-favoured diet. Proc R Soc B 280: 20122305. http://dx.

It has been suggested that grazing could stimulate the aboveground dry mass and/or nitrogen yields available to grazers (i.e., the grazing optimization hypothesis, GOH), but the actual importance of this effect is still controversial. The GOH has only been tested for a few grasslands and one savanna ecosystem, but not for the moistest and warmest grasslands and savannas of the world. The objectives of this study were to test the GOH in the humid savanna of Lamto (West Africa) by analyzing the growth of grasses in response to a field trial with three levels of clipping two levels of fertilization. We quantified the effects of clipping and fertilization on the dry matter and nitrogen yields to grazers (i.e., mass or nitrogen amount in clipped-off tissues during the experiment) and on the remaining yield (i.e., mass or nitrogen amount in residual phytomass at the end of the experiment) over a three-month period. Total phytomass yield, the sum of yield to grazers, and the remaining yield was maintained under moderate clipping frequency and fertilization as compared to control conditions. Both clipping frequencies decreased the remaining phytomass yield as compared to control plots. Clipping frequency significantly increased nitrogen concentrations in the total yield, in the remaining yield, and in the yield to grazers. Total nitrogen yield and nitrogen yield to grazers were 65% and 91% higher on the plots experiencing moderate clipping frequency with fertilization as compared to control plots. The study shows that grazers in this humid savanna system could potentially modify ecosystem processes in such a way as to partly alleviate nutritional deficiencies, but only in the presence of increased nitrogen availability.

Drought is a multidimensional stress that results in economic mislays. Allometric features of drought stressed cotton plants were investigated during two separate experiments. In the first experiment, susceptibility of the cotton seed germination stage towards decrease osmotic potential was evident under PEG-8000 induced drought stress. While changes in growth and biochemical constituents were studied from the field experiment and were explained on the basis of developmental plasticity under water deficit growth conditions. Potassium nitrate was applied as the seed pre-treatment and its influence on the morphological and structural development was marked with prime reference to cotton growth and productivity under water limited environment. A shift in the biochemical attributes of drought stressed cotton plants showed reduction in the chlorophyll contents occurred. Cotton stress response was obvious from the shift in the chlorophyll a/b relative ratio which was also influenced by seed pre-treatment. It is concluded that structural modifications under water scarce environment play a vital role in determining the morphological and physiological status of cotton.

This study investigated the effects of a commercial biofertilizer containing the mycorrhizal fungus Rhizophagus irregularis and the diazotrophic N-fixing bacterium Azotobacter vinelandii on root and shoot growth, yield, and nutrient uptake in common wheat (Triticum aestivum L.) in order to improve the sustainable cultivation of this widespread crop. The trials were carried out in controlled conditions (rhizoboxes) and in open fields over two years to investigate the interaction between inoculation and three doses of nitrogen fertilization (160, 120 and 80 kg ha −1) in a silty-loam soil of the Po Plain (NE Italy). In rhizoboxes, efficient root colonization by R. irregularis was observed at 50 days after sowing with seed inoculation, together with improved root tip density and branching (+~30% vs. controls), while the effects of post-emergence inoculation by soil and foliar spraying were not observable at plant sampling. In the open, field spraying at end tillering significantly increased the volumetric root length density (RLD, +22% vs. controls) and root area density (+18%) after about two months (flowering stage) in both years under medium and high N fertilization doses, but not at the lowest N dose. In absence of inoculation, RLD progressively decreased with increased N doses. Inoculation had a negligible effect on grain yield and N uptake, which followed a typical N dose-response model, while straw Zn, P, and K concentrations were seldom improved. It is concluded that medium-high N fertilization doses are required to achieve the target yield and standards of quality (protein contents) in wheat cultivation, while the use of this mixed VAM-PGPR biofertilizer appears to be a sustainable mean for minimizing the adverse effects of chemical N fertilizers on root expansion and for improving the uptake of low-mobility nutrients, which has potentially relevant environmental benefits.

Our understanding of the response of vascular, terrestrial plants to nitrogen (N) addition is advanced and provides the foundation for modern agriculture. In comparison, information on responses of marine macroalgae to increased nitrogen is far less developed. We investigated how in situ pulses of nitrate (NO3 −) affected the growth and N physiology of Macrocystis pyrifera by adding N using potassium nitrate dissolution blocks during a period of low seawater N concentration. Multiple parameters (e.g. growth, pigments, soluble NO3 −) were measured in distinct tissues throughout entire fronds (apical meristem, stipe, adult blade, mature blade, sporophyll, and holdfast). Unexpectedly, N fertilisation did not enhance elongation rates within the frond, but instead thickness (biomass per unit area) increased in adult blades. Increased blade thickness may have enhanced tissue integrity as fertilised kelp had lower rates of blade erosion. Tissue chemistry also responded to enrichment; pigmentation, soluble NO3 −, and % N were higher throughout fertilised fronds. Labelled 15N traced N uptake and translocation from N sources in the kelp canopy to sinks in the holdfast, 10 m below. This is the first evidence of long-distance (>1 m) transport of N in macroalgae. Patterns in physiological parameters suggest that M. pyrifera displays functional differentiation between canopy and basal tissues that may aid in nutrient-tolerance strategies, similar to those seen in higher plants and unlike those seen in more simple algae (i.e. non-kelps). This study highlights how little we know about N additions and N-use strategies within kelp compared to the wealth of literature available for higher plants.

BACKGROUND: In a field experiment conducted in a Mediterranean area of inner Sicily, durum wheat was inoculated with plant growth–promoting rhizobacteria (PGPR), with arbuscular mycorrhizal fungi (AMF), or with both to evaluate their effects on nutrient uptake, plant growth, and the expression of key transporter genes involved in nitrogen (N) and phosphorus (P) uptake. These biotic associations were studied under either low N availability (unfertilised plots) and supplying the soil with an easily mineralizable organic fertiliser. Regardless of N fertilisation, at the tillering stage, inoculation with AMF alone or in combination with PGPR increased the aboveground biomass yield compared to the uninoculated control. Inoculation with PGPR enhanced the aboveground biomass yield compared to the control, but only when N fertiliser was added. At the heading stage, inoculation with all microorganisms increased the aboveground biomass and N. Inoculation with PGPR and AMF+PGPR resulted in significantly higher aboveground P compared to the control and inoculation with AMF only when organic N was applied. The role of microbe inoculation in N uptake was elucidated by the expression of nitrate transporter genes. NRT1.1, NRT2, and NAR2.2 were significantly upregulated by inoculation with AMF and AMF+PGPR in the absence of organic N. A significant down-regulation of the same genes was observed when organic N was added. The ammonium (NH4+) transporter genes AMT1.2 showed an expression pattern similar to that of the NO3- transporters. Finally, in the absence of organic N, the transcript abundance of P transporters Pht1 and Pht2;1 was increased by inoculation with AMF+PGPR, and inoculation with AMF upregulated Pht2 compared to the uninoculated control. These results indicate the soil inoculation with AMF and PGPR (alone or in combination) as a valuable option for farmers to improve yield, nutrient uptake, and the sustainability of the agro-ecosystem.

SUMMARY Multilocation experiments were established to determine the best strategy for using inorganic fertilizer in conservation agriculture (CA) systems that use green manure cover crops, namely sunhemp, velvet bean and cowpea grown in rotation with maize. The objectives of the study were to determine (i) the effect of half and full rates of basal fertilizer on maize and legume biomass yields, (ii) the residual effects of unfertilized, half and fully fertilized green manure legumes on maize grown after the legumes, and (iii) the residual effect of unfertilized, half and fully fertilized green manure legumes combined with basal and topdressing fertilizer on maize yields. Experimental design was a randomized complete block with basal fertilizer as a treatment in the green manure legumes phase. Previously, in the maize phase, green manure legume species were the main treatment with basal fertilizer as a subtreatment (sunhemp, velvet bean and cowpea: 0, 75, 150 kg ha −1 and 0, 50, 100 kg ha −1 , respectively). Nitrogen was applied in the maize phase at 0, 23, 46, 69 kg N ha −1 as a sub-subtreatment in Malawi. Results showed that inorganic fertilizer is the most effective when applied to the maize, not green manure legumes. Biomass of green manure legumes, sunnhemp 8084 kg ha −1 , velvet bean 7678 kg ha −1 and cowpea 4520 kg ha −1 , was not significantly affected by application of basal fertilizer. Maize production increased after the application of green manure legumes with maize-after-maize, maize-after-velvet bean, maize-after-sunnhemp and maize-after-cowpea, yielding 3804, 5440, 5446 and 5339 kg ha −1 , respectively. Nitrogen increased maize yield regardless of the previously used green manure legumes species. Our results suggest that farmers should apply fertilizer to maize and grow green manure legumes on residual soil in CA systems. Despite growing green manure legumes, smallholders should apply nitrogen topdressing to maize grown using the green manure legumes in some agro-ecologies.

Aflatoxin accumulation in maize is strongly influenced by the environment in which the crop is grown. To gain insights into the ways in which soil fertility influences aflatoxin, we investigated the relationships between agronomic traits and aflatoxin in diverse maize testcrosses that were grown under two nitrogen treatment levels. The experiment was conducted in Eastern Kenya, an aflatoxin-endemic area, with natural Aspergillus flavus inoculum. A panel of 205 maize lines was grown under low soil nitrogen (N low = 26 kg/ha applied N) in the long season of 2011 and a subset of the genotypes (n = 123) was grown under high soil nitrogen (N high = 114 kg/ha applied N) in the short season of 2010 and long season of 2011. Kernel traits, grain yield, days to anthesis, ear rot, and aflatoxin were analyzed for the panel. Grain yield, protein, and kernel bulk density were higher in maize grown under N high compared to maize grown under N low , with grain yield twice as high under N high. A higher proportion of plots had grain with detectable aflatoxin under N low than under the N high. When the maize testcrosses were grouped into three maturity categories based on days to anthesis, aflatoxin accumulation was twice as high in the late-maturing group than in the other two categories under N low. The proportion of aflatoxin contamination was higher in dent than in flint maize. However, the extent of aflatoxin accumulation did not differ significantly (P > 0.05) over the entire testcross panel, among maize genotypes within the maturity groups or among kernel texture groups within the maturity groups. Kernel bulk density and protein content were higher in early and intermediate groups than in the late maturity group. Grain yield did not differ among the maturity groups (P > 0.05), but significant positive correlations were observed between the proportion of grain yield reduction due to low soil nitrogen stress and aflatoxin in early and late maturity groups. Kernel bulk density was negatively correlated with aflatoxin in grain. No significant association was observed between aflatoxin and ear rot or kernel size. We conclude that aflatoxin mitigation strategies should include soil nitrogen amendment and breeding approaches that include selection for the correlated agronomic traits.

Woody plant encroachment is a common consequence of disturbance in savannas. Grazers and browsers
interfere with sapling establishment dynamics by direct consumption of plant tissue, changing soil nutrient
status (through fertilization and trampling) and grass competition. Studies evaluating the effects of
herbivory on sapling establishment have mostly been extrapolated from single species. In a controlled
field experiment, we studied the effects of clipping (simulating grazing and browsing), nutrients, grass
competition, and their interactive effects on sapling survival and growth of four dominant humid and
four dominant mesic savanna species. We conducted this experiment in a humid South African savanna.
We found no effects on sapling survival by the treatments provided. However, clipped saplings of all
species increased their investment in relative growth rate of stem length (RGRL). Clipping had a greater
negative impact on relative growth rate of more humid than mesic species in terms of stem diameter
(RGRD), total dry biomass and proportion of leaf biomass. Nutrients had a positive effect on the RGRL and
sapling biomass of three mesic species. Positive effects of nutrients on RGRL of one humid and two mesic
species were observed in their clipped saplings only. Grass competition had a strong negative impact on
all growth parameters measured. Clipped saplings of one humid and two mesic species had lower RGRL
with grass competition whereas intact saplings showed no significant response. After clipping, humid
savanna species were more vulnerable to grass competition than mesic species, with reduced ability to
use nutrients. In conclusion, herbivory increases sapling vulnerability to grass competition, with humid
species being more susceptible than mesic species, indicating that woody-plant control strategies are
more likely to be effective in humid savannas.

Biogas digestate (BD) is increasingly used as organic fertilizer, but has a high potential for NH3 losses. Its proposed injection into soils as a countermeasure has been suggested to promote the generation of N2O, leading to a potential trade-off. Furthermore, the effect of high nutrient concentrations on N2 losses as they may appear after injection of BD into soil has not yet been evaluated. Hence, we performed an incubation experiment with soil cores in a helium–oxygen atmosphere to examine the influence of soil substrate (loamy sand, clayey silt), water-filled pore space (WFPS; 35, 55, 75 %) and application rate (0, 17.6 and 35.2 mL BD per soil core, 250 cm3) on the emission of N2O, N2 and CO2 after the usage of high loads of BD. To determine the potential capacity for gaseous losses, we applied anaerobic conditions by purging with helium for the last 24 h of incubation. Immediate N2O and N2 emissions as well as the N2 / (N2O+N2) product ratio depended on soil type and increased with WFPS, indicating a crucial role of soil gas diffusivity for the formation and emission of nitrogenous gases in agricultural soils. However, emissions did not increase with the application rate of BD. This is probably due to an inhibitory effect of the high NH4+ content of BD on nitrification. Our results suggest a larger potential for N2O formation immediately following BD injection in the fine-textured clayey silt compared to the coarse loamy sand. By contrast, the loamy sand showed a higher potential for N2 production under anaerobic conditions. Our results suggest that short-term N losses of N2O and N2 after injection may be higher than probable losses of NH3 following surface application of BD.

BACKGROUND: With the increasing demand for high-quality foodstuffs and concern for environmental sustainability,
late-season nitrogen (N) foliar fertilization of common wheat is now an important and widespread practice. This study
investigated the effects of late-season foliar versus soil N fertilization on yield and protein content of four varieties of durum
wheat, Aureo, Ariosto, Biensur and Liberdur, in a three-year field trial in northern Italy.
RESULTS: Variations in low-molecular-weight glutenins (LMW-GS), high-molecular-weight glutenins (HMW-GS) and gliadins
were assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). It was found that N applied to the
canopy did not improve protein rate compared with N application to the soil (general mean 138mg g−1), but moderately
increased productivity in the high-yielding varieties Liberdur and Biensur (three-year means 7.23 vs 7.13 and 7.53 vs 7.09 t
ha−1 respectively). Technological quality was mainly related to variety choice, Aureo and Ariosto having higher protein rates
and glutenin/gliadin ratios. Also found was a strong ‘variety × N application method’ interaction in the proportions of protein
subunits within each class, particularly LMW-GS and gliadins. A promising result was the higher N uptake efficiency, although
as apparent balance, combined with higher HMW/LMW-GS ratio in var. Biensur.
CONCLUSION: Late-season foliar N fertilization allows N fertilizer saving, potentially providing environmental benefits in the
rainy climate of the northern Mediterranean area, and also leads to variety-dependent up-regulation of essential LMW-GS and
gliadins. Variety choice is a key factor in obtaining high technological quality, although it is currently associated with modest
grain yield. This study provides evidence of high quality in the specific high-yielding variety Biensur, suggesting its potential as
amono-varietal semolina for pasta production.

Nitrogen fertilizer practices affect nitrous oxide (N2O) emissions from agricultural soils. The “4R” nutrient stewardship framework of using N fertilizer at the right rate, right source, right placement and right time can reduce N2O emissions while maintaining or improving yield of field crops, but understanding of how the various factors affect N2O emissions from irrigated processing potato is lacking. We examined the effects of selected 4R practices on emissions, using results from two irrigated processing potato studies each conducted in 2011 and 2012 in Manitoba, Canada. Experiment 1 examined combinations of source (urea, ESN), placement (pre-plant incorporation [PPI], banding), and rate (100 and 200 kg N ha-1) on a clay loam soil. Experiment 2 examined timing and source treatment combinations (urea PPI, ESN PPI, urea split, urea split/fertigation) on a loamy fine sandy soil. For Experiment 1, use of ESN at 200 kg ha-1 did not reduce area-, yield- and applied fertilizer N- based N2O emissions compared to urea at 200 kg ha-1, irrespective of placement. Emissions from pre-plant banding ESN at 200 kg ha−1, however, were 32% lower than from PPI ESN. For Experiment 2, compared to single pre-plant urea application, fertigation simulated by in-season application of urea ammonium nitrate (UAN) gave lower area-, yield- and applied fertilizer N- based emissions. Split urea (  2/32/3  pre-plant,  1/31/3  hilling) also reduced area- and yield- based N2O emissions compared to single pre-plant urea application. Emissions were generally lower at the site with loamy fine sandy soil than the site with clay loam soil. These results demonstrate that combinations of “4R” practices rather than source alone are best to achieve reductions in N2O emissions from irrigated potato production.

Vigorous interspecific rootstocks increase nitrogen (N) uptake in tomato plants but limited information is available on xylem transport rate. Non-grafted and self-grafted tomato plants cv. Attiya and plants grafted onto an interspecific hybrid, Kaiser, were grown under growth chamber conditions and subjected to two light levels, 400 or 800 µmol PAR m −2 s −1. Plant water uptake, xylem sap NO 3 − content, and stem hydraulic conductance (k s) were measured after two weeks of growth. Xylem vessel number and diameter were evaluated in cross-sectional stem cuts and the theoretical xylem hydraulic conductance (k h) was calculated. Only the light level modified the xylem NO 3 − content. Grafting reduced k s by 84% in comparison to non-grafted plants. The water uptake rate and xylem sap NO 3 − content were 4.02 ± 0.66 g H 2 O kg −1 DW h −1 and 12.78 ± 1.16 mM, respectively, across all grafting treatments. The rootstock has a higher k h because the vessel diameter is 79.3 ± 14.4 µm while in non-grafted plants it is 62.0 ± 10.1 µm. Nitrate concentration and transport rate changes accordingly to the plant's growth rate. The vigorous rootstock relies on larger vessels to supply the required amounts of N.

Ammonia synthesis is the most important step for nitrogen-fertilizer production and consumes approximately 1% of the world’s energy production and energy-related greenhouse gas emissions. In addition to the concomitant emissions caused by ammonia and nitrogen fertilizer synthesis, centrally produced fertilizer that must be distributed to farms also harms the environment because of the embodied energy of transportation. An environmentally-optimal nitrogen fertilizer system would be distributed on farms themselves using only renewable inputs. Recent developments in solar photovoltaic technology and subsystems for ammonia production have made non-organic on-site ammonia production physically possible. This study provides a technical evaluation of the process for on-site nitrogen-fertilization of corn using solar photovoltaic electricity as the energy input. The system consists of a water electrolysis system to generate hydrogen and a membrane system to generate nitrogen needed as material inputs. Total power consumption for syngas preparation to generate a unit of ammonia is calculated. System total energy consumption is calculated while compensating syngas preparation with heat recovery. Five case-study locations are evaluated to determine their suggested nitrogen fertilizer addition (N-rate) for corn growth and the energy consumption for suggested N-rate is calculated. The System Advisor Model (SAM) is then used to simulate the PV system output for those five locations. Finally, the PV land use required as a fraction of the corn field area is determined. The results indicate that because PV is so much more efficient at solar energy conversion than organic methods, even the worst case evaluated in Indiana requires less than 1% of the corn field converted to a PV system to provide enough energy to generate sufficient amounts of ammonia for fertilizer for the remaining corn. The system was modeled to provide ammonia to fertilize for corn fields larger than 1079 acres with the worst soil conditions, the area of which applies to more than half of cropland in the U.S. in 2011. As the finiteness and emissions of fossil fuel production of nitrogen become more important, this renewable system should become economical and future investigations into its overall viability are warranted.

Film mulching is a very common technique in agriculture worldwide, but few studies have focused on the dry matter (DM) and N accumulation of mulched crops. Understanding the grain yield (GY) associated with DM and N accumulation is essential for improving crop production. We conducted a 3-yr field experiment with six N fertilizer rates (0, 100, 200, 250, 300, and 400 kg ha–1) in the semiarid climate of northwest China to determine the GY and DM and N accumulation of film-mulched maize (Zea mays L.). The results showed that relatively high GYs (13.1–15.1 Mg ha–1) were obtained using N fertilizer rates of 200 to 400 kg ha–1 in the 3 yr despite large year-to-year differences in rainfall. When the N rate was below 250 kg ha–1, the GY, DM, and N accumulation increased significantly as the N fertilizer rate increased. A linear-plateau model best described the relationship between the GY and the DM and N accumulation during the pre-silking stage and a linear model the relationship during the post-silking stage. We conclude that optimizing N management to improve DM and N accumulation (especially postsilking)
is the key to ensuring a high yield of film-mulched maize.

Conservative agriculture includes a range of management strategies with low energy inputs such as no-tillage, minimum tillage, and low application of fertilizers. Weed flora in arable fields is strictly affected by agronomic practices such as tillage and fertilization management. This study was conducted seven years after the beginning of a long-term—durum wheat–faba bean—rotation. It analyzes the combined effects on the soil seed bank of three different tillage systems (conservative, reduced, and conventional tillage) and two levels of nitrogen fertilization. The effects were investigated both using stepwise discriminant analysis and analysis of variance in order to find statistical differences among main factors and their interactions. The seed bank of Conyza canadensis, Papaver rhoeas, Solanum nigrum, Fallopia convolvulus, and Fumaria officinalis was higher in conservative or reduced tillage plots. The magnitude of the response to nitrogen supply varied among weed species. Conyza canadensis seemed to be favored by low nitrogen supply, whereas Sinapis arvensis by higher doses of nitrogen. Anagallis arvensis showed the lowest seed bank in conventionally tilled plots, without distinction of nitrogen supply. The results suggest that different tillage systems and, to a lesser extent, different nitrogen supply, produce changes in the seed bank size and composition, along the soil profile.

Nitrogen deficiency strongly influences crop photosynthetic performance and biomass production. In this study, we applied rapid, non-invasive records of chlorophyll a fluorescence kinetics for evaluation of wheat (Triticum aestivum L.) leaf  photosynthetic performance. Plants were grown during the whole season in big pots filled with the soil substrate and they were supplied by different doses of nitrogen nutrition. The plant nitrogen and leaf chlorophyll content as well as the plant aboveground biomass were analyzed after chlorophyll fluorescence records in three growth stages. Our results confirmed that the maximum quantum yield of  hotochemistry frequently used in previous studies was almost insensitive to nitrogen treatment, if measured in young, non-senescent leaves. On the contrary, the performance index was much more responsive. The performance index values derived from
parallel measurements in the youngest and third leaf from the top were used to calculate performance index leaf ratio, which correlated well with the plant nitrogen content. Moreover, this parameter was not sensitive to midday depression, which significantly affected the values of other chlorophyll fluorescence parameters. Although the optimum performance index leaf ratio values decreased continuously in the second part of the growing season, the optimum and critical values for each growth stage can be easily identified. Thus, we suggest performance index leaf ratio as the simple parameter for the rapid evaluation of the wheat photosynthetic performance and an early indicator of insufficient nutrition level. Unlike some other approaches, suggested method seems to be useful alsoin conditions of a moderate nutrient deficiency.

Plasma-assisted nitrogen fixation is a promising sustainable and clean alternative to the classical Haber-Bosch process. However, the high energy consumption and low production rate of plasma-assisted nitrogen fixation limit its application. This study shows that the non-thermal (non-equilibrium) enhancement of the arc plasma significantly reduces the energy consumption of nitrogen fixation. The highest energy efficiency with high NO selectivity is observed with a low specific energy input (SEI). However, the highest production rate is reached at a high SEI. The studied process offers high NO selectivity (up to 95%) with low energy consumption ($48 GJ per tN) at 0.1 kJ L À1 SEI, which is much lower than the previously reported value of plasma-assisted atmospheric nitrogen fixation and is close to that of the Haber-Bosch process.

Nitrogen fertilization can affect the uptake and accumulation of nutrients, heavy metals and trace elements in plants. The aim of the study was to evaluate the influence of nitrogen application on mineral composition of carrot storage roots. In 2003-2005 field experiment with carrot 'Kazan F 1 ' cv. was conducted in Trzciana (50 o 06' N, 21 o 85' E, South-East Poland), each year on a different site within a single soil complex. The experiment was arranged in a split-plot design with four replications. The following combinations with various nitrogen fertilization regimes (presented as kg N·ha -1 ) were distinguished: 1 -Control, 2 -Ca(NO 3 ) 2 70, 3 -Ca(NO 3 ) 2 70+70, 4 -(NH 4 ) 2 SO 4 70 and 5 -(NH 4 ) 2 SO 4 70+70; where 70 kg N·ha -1 was used pre-sowing, whereas 70+70 kg N·ha -1 was applied in two rates: pre-sowing and as top-dressing. Solid nitrogen fertilizers were added to the soil in the form of: Ca(NO 3 ) 2 (15.5% N) and (NH 4 ) 2 SO 4 (21% N). In carrot storage roots as well as in soil samples collected after carrot cultivation, the content of the following elements was determined: Ag, Sc, Sn, Sr, Ti, Y, Yb and V. Fertilization with nitrogen had significantly influenced the accumulation of Ba, Co, Dy, In, Lu, Mg, Ni, P, Pb, S, Sb, Sc, Sn and Y in carrot roots. In particular combinations, a diverse effect of N application was observed in reference to the content of mentioned elements. Revealed differences in the soil level of tested elements did not correlate (were not reflected) with the rate of its accumulation in carrot storage roots. key words: nitrogen fertilization, heavy metals, trace elements, rare elements, mineral composition of plants

Abstract

Improvement of nitrogen (N) use efficiency is urgently needed since excessive application of N fertilizer has been widespread in small-scale fields in China, causing great losses of N fertilizer and environmental pollution. In the present study, a simple technology, termed the Green Window Approach (GWA), to optimize N strategies for cereal crops is presented. The GWA represents an on-field demonstration site visualizing the effects of incremental N levels and enables farmers to conduct such a trial within their own fields. The lowest N rate that achieves no visible change in plant growth or biomass shows the optimal N requirement of crops. Therefore the objective was to develop the key procedures of GWA and to evaluate the effects of its application in cereal crops on grain yield, N use efficiency and economic benefit. A total of seven GWA trials were performed from 2009 to 2011 on farmers' irrigated wheat fields in the North China Plain. The GWA consisted of eight small plots placed in a compact layout on a well-accessible part of the field. Plot size varied from 2.5x2.5 to 4x4m(2), depending on the size and shape of each field. All GWA plots received basal nitrogen (N), phosphorus (P) and potassium (K) rates of 30 kg N/ha (except for the nil-N plot), 80 kg P2O5/ha and 100 kg K2O/ha. Nitrogen supplies, including residual soil nitrate in 0-90 cm determined at Zadoks growth stages (GS) 21-23 in early spring and the split-topdressing N at GS 21-23 and GS 41-52, were incrementally increased from 0 to 420 kg N/ha. The remaining part of the field still received farmers' customary fertilization (FCF). Optimal N rate could be estimated as the lowest N rate that achieved no visible change in plant growth at GS 60-73. Compared with FCF area, grain yield was increased by 13% to a maximumor near maximum value of 5.8 t/ha, optimal N rate was sharply decreased by 69% to 116 kg N/ha, apparent N recovery was greatly increased from 11 to 46%, whereas the cost of fertilizer input was decreased by 57% to 1045 Chinese Renminbi (RMB)/ha (162 US$/ha), the profit of grain yield was increased by 13% to 12211 RMB/ha (1891 US$/ha) and the net economic benefits were increased by 60% to 7473 RMB/ha (1157 US$/ha). Most importantly, the GWA does not need laboratory facilities, complicated procedures or professional knowledge of N balances, and farmers can easily understand and use GWA by themselves.

Water and nitrogen (N) are two key limiting factors for citrus production. Reported effects of water and N inputs on citrus yield, water use efficiency (WUE) and N use efficiency (NUE) vary greatly, mainly due to differences in cultivars, tree age, climate, soil types, and water and N input levels. So far, no systematic analysis has been performed, and as a result, the interactive effects of water and N inputs on yield, WUE and NUE of citrus orchards are unknown. Also, gaps between attainable and actual yields, WUE and NUE have not been established yet. Here, we report on a global meta-analysis of yields, WUE and NUE of citrus production systems, using 1009 observations from 55 studies, conducted in 11 countries. Median citrus yields ranged from 30 to 60 t ha-1, which were in between average global yields (range 10-30 t ha-1) and attainable yields (range 60-90 t ha-1). Median WUE ranged from 2.5 to 5 kg m-3 and median NUE from 150 to 350 kg kg-1. Citrus yields were related to water and N inputs and tree age. Relationships between water and N inputs and yield, WUE and NUE were also analysed for sub-datasets and quantiles, to examine the relationships near the extremes. There were statistical significant interactions between water and N inputs in yield and NUE, but not in WUE. This indicates that studies aiming at the optimization of water and N inputs must consider interactions and optimize water and N inputs simultaneously. Based on our analyses, we estimated that reducing over-optimal irrigation to optimal irrigation may increase citrus yield by 20%, WUE by 30% and NUE by 15%. Similarly, reducing over-optimal N fertilization to optimal N fertilization may increase yield by 10%, WUE by 15% and NUE by 40%. We concluded that there is room for a significant increase in yield, WUE and NUE through the simultaneous optimization of water and fertilizer N inputs via precision fertigation

Elephant grass is a tropical forage plant widely spread in Brazil, used mainly in the livestock sector and in cattle feeding. Because of its high productivity and photosynthetic capacity, this culture has also been considered an alternative source of renewable energy. Six clones of elephant grass (Pennisetum purpureum Schum.) were evaluated under five levels of nitrogen fertilization (100, 200, 400, 800, and 1600 kg·N·ha-1), in a randomized-block design with a split-plot arrangement with three replicates, from April 2010 to December 2012, in the city of Campos dos Goytacazes— RJ, Brazil. The objective was to obtain estimates of variation in morpho-agronomic traits and biomass quality. We observed that genotypes Cameroon-Piracicaba and Gua?u I/Z2 have great potential to be used, with maximum dry matter yields of 60.97 and 44.10 t·ha-1 per cut for energy purposes among the studied genotypes.

VIS-NIR spectroscopy for estimation of Nitrogen (N) content in olive leaves was studied as a tool for efficient fertilisation in olive (Olea europaea) orchards. Olive leaf samples (cv. Barnea) were taken from orchards which had been fertilised with a wide range of N levels. Dried ground leaves, fresh ground leaves and intact leaves were tested. Reflectance measurements were taken using three spectrometers: USB-2000 for VIS-NIR (450 e1000 nm) and a LIGA, and a Luminar-5030 for SWIR (1100e1700 nm). Nitrogen concentrations of the same samples were measured analytically as a reference for the spectral analyses, which were conducted by means of partial least square regression (PLSR). The best predictive model for comprehensive in-season and between-season samples (160 samples from three seasons, taken on 18 separate days) was obtained using the Luminar spectrometer using thoroughly ground dried leaves (R 2 ¼ 0.91). Classification into three N levels was evaluated and gave an overall accuracy of 0.83 with a kappa of 0.75 (substantial). Intact leaves yielded non-sufficient correlations. The results showed that leaf dehydration improves the model performance significantly and that VIS-NIR spectroscopy might be used for decision-making in fertilisation procedures. Finally, a protocol is suggested for laboratory spectral measurements.

The objective of this work was to evaluate the potential of a terrestrial active optical sensor to support
nitrogen fertilization recommendation, in variable rates, for sugarcane crops. Experiments in a randomized
complete block design were carried out with different N rates (0, 50, 100, 150 and 200 kg ha‑1). The response
of sugarcane to N was evaluated by different methods – optical sensor, chlorophyll meter, and leaf N content
–, when the average height of stalks was 0.2, 0.4 and 0.6 m. A low correlation was observed between leaf N
content and the amount of chlorophyll measured by a portable chlorophyll meter. Therefore, these two traits
were insufficient to evaluate the efficiency of the optical sensor, since the measured values increased with the
amount of N applied. The strategy of fertilization recommendation based on crop response, estimated by the
optical sensor in a sugarcane strip that received the appropriate N rate, was more consistent with the obtained
yield. The optical sensor is a useful tool to recommend N for sugarcane crops, taking into account the spatial
variability of N demand.

Currently, the cultivation of sweet potato (Ipomoea batatas (L.) Lam.) is gaining more and more popularity. The aim of the present study was to investigate the effect of different nitrogen (N) fertilization levels on the parameters related to the efficiency of the photosynthetic apparatus, plant photosynthetic productivity, tuber yield and tuber dry matter yield of I. batatas. The study also aimed to identify phenotypic variation in the physiological measures and tuber yield traits of I. batatas. To achieve these objectives, a field experiment was carried out during the period 2013–2015 in Uhnin (51.5833° N, 23.0333° E), central-eastern Poland. The experimental factor was different nitrogen fertilization rates (0, 50, 100, 150 and 200 kg ha-1 N). The conditions in the experimental years had the strongest effect on tuber dry matter content and yield and on minimum chlorophyll fluorescence yield and chlorophyll a content. The fertilization × year interaction had the lowest percentage contribution to the total variance, while its highest contribution was observed for chlorophyll b. Nitrogen fertilization had the lowest percentage contribution to the physiological measures of chlorophyll fluorescence, but a quite high contribution to tuber dry matter content and yield. Nitrogen fertilization up to a level of 150 kg ha-1 N beneficially affected electron flow at successive plant growth stages, beginning from the 6-leaf stage until physiological maturity. Nitrogen fertilization was also shown to have a stimulating effect on the photosynthetic efficiency of I. batatas at the end of the growing season. A decreasing trend was observed in the maximum chlorophyll fluorescence yield (F m) as affected by increasing N rates. A significant increase in actual photochemical efficiency of photosystem (PS) II (Y) and in the photochemical fluorescence quenching coefficient (qP) was observed up to a level of 100 kg ha-1 N. The minimum chlorophyll fluorescence yield (F 0), non-photochemical fluorescence quenching coefficient (qN) and electron transport rate (ETR) were most favourable in the plots fertilized at a rate of 150 kg ha-1 N.

The objective of this work was to assess the performance of corn (Zea maysL.) genotypes as affected by inputs of black oat (Avena strigosa Schreb.) residues applied on the soil surface and nitrogen fertilization under no-tillage system in a Typical Haplustox. The experiment was carried out in a complete randomized block design, arranged in split-split plots with three replicates. The main plots consisted of the amount of crop residues on the soil surface (no crop residue, 5.16 and 10.32 mg ha-1). The split plots were three corn genotypes, and the split-split plots were five nitrogen rates: 0, 60, 120, 180, and 240kg ha-1. An increase in the nitrogen rates decreased nitrogen deficiency and provided an adequate nitrogen supply for corn, under all the amounts of black oat residues. The corn genotypes grown with different amounts of black oat residues and nitrogen rates had different grain yield responses, use of mineralized nitrogen from crop residues, and root growth.

ue rates to be applied, supplying plants with mineral N to at the appropriate time, without leaching losses. Most studies on residue-treated soils use the technique without leaching of mineral forms and the volumetric determination method. The repeatability of the test is however poor and the sensitivity of the determination method low, especially in soils amended with sewage sludge and organic compost. In this study we adopted the not very well-known leaching method, with determination of N-mineral forms by spectrophotometer methods. In columns filled with soil taken from a depth of 0.20 m of an alic, loamy soil Hapludox, the following residues doses (Mg ha-1 - wet basis) were incorporated: Sewage sludge - L 1 = 3.6; L2 = 7.2; L3 = 14.4; and Organic compost (sewage sludge + tree cuttings) - C1 = 7.2, C2 = 14.4, C3 = 28.8. Columns were incubated and periodically leached with a 0.01 mol-1 L KCl solution, and the N-mineral forms were determined colorimetrically. High mineralization rates at lower sludge and compost rates were observed, indicating a priming effect, which is undesirable in soil management under tropical conditions. Lower N-mineralization rates were observed at L2 and C2, close to those suggested by the Brazilian legislation that regulates sewage sludge application to agricultural soils, but falling short of the N requirement, while higher mineralization rates were observed at the lower and higher doses, suggesting that the current legislation should be reviewed. Generally, the N mineralization rates were higher for organic compost than for sewage sludge, while the degradation speed was lower for the organic compost, indicating a greater distribution of the available N forms over time. The mineralization leaching method with determination of mineral-N forms by colorimetry proved to be fast and efficient, and more studies should test different soils and organic wastes for validation for routine use.

Efforts have increased to measure nitrate losses from farmland under different management practices due to environmental and public concerns over levels of nitrate-nitrogen (NO 3-N) in surface and ground waters. This study evaluated the effect of conventional tillage (CT) and strip tillage (ST) practices and three N application rates on NO 3-N concentrations in soil water at a 76 cm depth under irrigated sugar-beet (Beta vulgaris L.) in a clay loam soil. Nitrogen rates were applied as dry urea at 120, 150, 180 kg N ha −1 in 2006; 130, 160, 190 kg N ha −1 in 2007; and 110, 140, 170 kg N ha −1 in 2008. Soil water volumes were measured weekly during each growing season using three ceramic suction cup samplers per plot placed at a 76 cm depth below the soil surface under each tillage. Results indicated that NO 3-N concentrations at the 76 cm depth in the soil profile were not significantly affected by either tillage practice or by N application rate due to soil variability across the field and due to suction cup samplers' biased estimate of soil water. The three N rates under CT and ST practices maintained NO 3-N concentrations below the root zone to levels exceeding the 10 mg L −1 safe drinking water maximum level in all three years. There were large variations in NO 3-N concentrations among replicates within each tillage and N rate that were likely caused by variability in soil physical, hydraulic and chemical properties that impacted water movement through the soil profile, N dynamics and leaching below the root zone of sugarbeet. In conclusion, suction cup samplers are point water measurement devices that reveal considerable variability among replicates within each treatment due to the heterogeneity of field soils. Further, these samplers are not recommended in heterogeneous soils with preferential flow characteristics.

Biofortification of vegetables with iodine can become an alternative method to salt iodization of introducing this element to human diet. Iodine is not an essential nutrient for plants and its effect on plant growth and development has not yet been sufficiently examined. The aim of the study was to assess the influence of soil fertilization with iodine (in the form of Iand IO 3 -) and nitrogen (applied as NO 3 and NH 4 + ) on the effectiveness of iodine biofortification as well as mineral composition of carrot storage roots. Carrot cv. Kazan F 1 was cultivated in a field experiment in 2008 and 2009. Different soil fertilization treatments with iodine as well as nitrogen were tested, including: 1 -control without N

Two sub-blocks were distinguished in a pot experiment with carrot 'Kazan F 1 ' cultivation: with and without plant foliar application. The plants were treated thrice with foliarly applied 2% urea solution, 1% solution of 'Supervit R' multicomponent fertilizer and again with 2% urea solution. Nitrogen fertilization used within the sub-blocks included: the control (unfertilized with nitrogen), Ca(NO 3 ) 2 , NH 4 NO 3 , (NH 4 ) 2 SO 4 and CO(NH 2 ) 2 . The roots of plants fertilized with (NH 4 ) 2 SO 4 contained the largest quantities of Cd and Zn. The forms of fertilizer (N) did not affect carrot Cu concentrations. Foliar application raised Cu contents but had no statistically significant effect on Cd or Zn concentrations in carrot.