A sensitivity analysis is critical for determining the relative importance of model parameters to... more A sensitivity analysis is critical for determining the relative importance of model parameters to their influence on the simulated outputs from a process-based model. In this study, a sensitivity analysis for the SPACSYS model, first published in Ecological Modelling (Wu, et al., 2007), was conducted with respect to changes in 61 input parameters and their influence on 27 output variables. Parameter sensitivity was conducted in a ‘one at a time’ manner and objectively assessed through a single statistical diagnostic (normalized root mean square deviation) which ranked parameters according to their influence of each output variable in turn. A winter wheat field experiment provided the case study data. Two sets of weather elements to represent different climatic conditions and four different soil types were specified, where results indicated little influence on these specifications for the identification of the most sensitive parameters. Soil conditions and management were found to af...
There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estima... more There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estimation of unsaturated soil properties. The pedo-transfer functions can be used for the estimation of the soil–water characteristic curve (SWCC) which in turn is used for the estimation of other unsaturated soil properties. The accuracy of the indirect pedo-transfer function method for the estimation of the SWCC depends on the PTF and the equation used to best-fit the particle-size distribution (PSD) data. The objectives of this study are to: (1) evaluate the performance of the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation for best-fitting the particle-size distribution, (PSD) data, and, (2) compare the predictions made by two of the commonly used PTFs; namely, Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) and Fredlund et al. (Can Geotech J 39:1103–1117, 2002), for estimating the SWCC from the PSD. The authors used 258 measured PSDs and SWCC datasets from the Loess Plateau, China, for this study. The dataset consisted of 187 silt–loam soils, 41 loam soils, 11 silt–clay–loam soils, 10 sand–loam soils, 6 silt–clay soils, and 3 loam–sand soils. The SWCC and PSD datasets were measured using a Pressure Plate apparatus and the pipette method, respectively. The comparison between the estimated and measured particle-size distribution curves showed that the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation closely prepresented the PSD for all soils in the Loess Plateau, with a lower root mean square error (RMSE) of 0.869%. The comparison between the estimated and measured water contents at the same suction showed that the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF performed somewhat better than the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) function. The Fredlund et al. method had RMSE value of 0.039 cm3 cm−3 as opposed to 0.046 cm3 cm−3 for the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) method. The Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF produced the closest predictions for sand–loam, loam–sand, and loam soils, with a lower RMSE for gravimetric water content ranging from 0.006 to 0.036 cm3 cm−3. There were consistent over-estimations observed for silt–loam, silt–clay–loam, and slit–clay soils with RMSE values for gravimetric water content ranging from 0.037 to 0.043 cm3 cm−3. The measured and estimated air-entry values were closest when using the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF. The measured and estimated maximum slopes on the SWCC were closest when using the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) PTF.
The objective of this study is to evaluate the potential utility of the USGS Global Data Assimila... more The objective of this study is to evaluate the potential utility of the USGS Global Data Assimilation System (GDAS) 1-degree, daily reference Evapotranspiration (ET0) products by comparing them with observed Oklahoma mesonet daily ET0 over a 2 year period (2005–2006). The comparison showed a close match between the two independent ET0 products, with bias within a range of 10% for most of the sites and the overall bias of − 2.80%. The temporal patterns are strongly correlated, with a correlation coefficient above 0.9 for all groups. In summary, we conclude that (1) the consistent low bias shows the original GDAS ET0 products have high potentials to be used in land surface modeling; (2) the high temporal correlations demonstrate the capability of GDAS ET0 to represent the major atmospheric processes that control the daily variation of surface hydrology; (3) The temporal and spatial correspondences in trend between independent datasets (GDAS and MESONET) were good. The finding in Oklahoma, a different hydro-climate region from a similar regional study conducted in California by Senay et al. (J Am Water Res Assoc 44(4):969–979, 2008), reconfirms the reliability and potential of using GDAS reference ET for regional energy balance and water resources management in many parts of the world.
Evapotranspiration (ET) is deemed critical for water resources management. Even in the same clima... more Evapotranspiration (ET) is deemed critical for water resources management. Even in the same climatic and meteorological conditions, actual ET (ETa) may exhibit remarkable spatial variability across different vegetation covers, agricultural land use practices, and differing types of urban land development. The main objectives of this study are (1) to evaluate the possible closure of the heat balance equation using Oklahoma's unique environmental monitoring network; and (2) to estimate ETa and determine the variation with regards to varying types of land use and land cover in urban settings. In this study, a Surface-Energy-Balance ET algorithm was implemented to estimate ETa at a higher spatial resolution using Landsat 5 satellite images while the Oklahoma Mesonet observations can be used as our ground truth data. Accuracy of the estimated ETa was assessed using latent heat flux measurements provided by AmeriFlux towers. The associated bias ratios of daily mean ETa with respect to both burn and control sites are -0.92%, and -8.86% with a correlation of 0.83 and 0.81, respectively. Additionally, estimated ETa from a water balance budget analysis and the remotely sensed ETa are cross-validated with a low bias ratio of 5.2%, and a correlation coefficient of 0.7 at the catchment scale. The lowest ETa was observed for developed urban areas and highest for open water bodies. The ETa difference is also demonstrated from two contrasting counties. The results show Garfield County (agricultural) has higher ETa values than Oklahoma County (urban) for all land cover types except open water bodies.
Soil texture and evaporative demand have been reported to be the main factors which influence the... more Soil texture and evaporative demand have been reported to be the main factors which influence the transpirational response to soil water deficits. However, experimental evidences are not enough. The objective of this study was to investigate the transpirational response to soil water availability in soils of different textures under different evaporative demand levels. The three main soils of the Loess Plateau of China (loamy clay, clay loam and sandy loam) were selected and six constant soil water treatments were applied for winter wheat (Triticum aestivum L.) grown in pots. In order to reduce the influence of environmental conditions and plant factors, a normalized daily transpiration rate was used to develop the relationships with volumetric soil water content and soil water suction. Results showed that, under various levels of evaporative demand, a linear-plateau function with a critical value could be used to describe the dynamic change of the normalized transpiration rate with soil drying. Soil texture significantly influenced both the critical and the slope values of the linear-plateau equations, however, evaporative demand significantly affected the critical values of volumetric soil water content and soil suction for the loamy clay and clay loam only. Therefore, for saving water, different strategies are needed for these three soils.
High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum ae... more High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum aestivum L.) grown in the Loess Plateau of China under semiarid climatic conditions. Grain yield can be improved by effective water management practices. A 13-year field experiment was conducted at the CERN Changwu Agro-ecological Experimental Station of the Loess Plateau to determine optimal irrigation strategies under limited water supply and to develop relationships among grain yield (Y), seasonal evapotranspiration (SET) and water-use efficiency (WUE). The experiment consisted of five irrigation treatments and three blocks. Measurements included grain yield, soil water content at various depth intervals in the 0–3,000 mm layer, irrigation amount, and precipitation. Results showed that winter wheat grown in this area experienced serious water stress during critical growth stages for the no-irrigation treatment. The amount and timing of irrigation had an important effect on grain yield, but significant differences in yield were not observed between the three-irrigation and the four-irrigation treatments. Grain yield was linearly related (R 2=0.66) to SET, but differences in WUE were not significant for any of the treatments. The relationship between WUE and Y was best represented by a second order polynomial (R 2=0.65) consisting of a nearly linear portion between 1.5 and 5.0 Mg ha−1. Optimum water management of winter wheat in the Loess Plateau should consist of three 87.5 mm irrigations applied at stem elongation, booting, and anthesis.
The Soil Conservation Service curve number (CN) method is widely used for predicting direct runof... more The Soil Conservation Service curve number (CN) method is widely used for predicting direct runoff from rainfall. However, despite the extent of cultivation on hillslope areas, very few attempts have been made to incorporate a slope factor into the CN method. The objectives of this study were (1) to evaluate existing approaches integrating slope in the CN method, and (2) to develop an equation incorporating a slope factor into the CN method for application in the steep slope areas of the Loess Plateau of China. The dataset consisted of 11 years of rainfall and runoff measurements from two experimental sites with slopes ranging from 14 to 140%. The results indicated that the standard CN method underestimated large runoff events and overestimated small events. For our experimental conditions, the optimized and non-optimized forms of the slope-modified CN method of the Erosion Productivity Impact Calculator model improved runoff prediction for steep slopes, but large runoff events were still underestimated and small ones overpredicted. Based on relationships between slope and the observed and theoretical CN values, an equation was developed that better predicted runoff depths with an R2 of 0.822 and a linear regression slope of 0.807. This slope-adjusted CN equation appears to be the most appropriate for runoff prediction in the steep areas of the Loess Plateau of China.
The objective of this study was to examine the trends of changes in streamflow in a watershed of ... more The objective of this study was to examine the trends of changes in streamflow in a watershed of the Loess Plateau, where a series of soil conservation measures were implemented since the late 1950s. Both parametric and non-parametric Mann–Kendall test were used to identify the trends in hydrologic variables over the last 50 years, and it showed significant downward trends in annual runoff, surface runoff and baseflow. The Pettitt’s test was used to detect the change points of runoff, which occurred in 1973, and the whole 50-year records could be divided into contrast (from 1957 to 1973) and treated (from 1974 to 2006) periods. It was observed that the average annual runoff during treated period reduced by 60%, surface runoff and baseflow reduced by 65% and 55%, respectively in comparing with the contrast period. But the proportion of baseflow to total runoff showed a significant increasing from 0.57 to 0.63. Seasonal runoff also showed decreased trend with the highest reduction occurring in summer and lowest in winter. Annual precipitation in whole period showed no significant trend, so the changes in hydrologic variables were induced by conservation measures. Comparison of the flow duration curves for the two periods showed that reductions in high and low flows varied greatly. Results showed that conservation measures have resulted obvious changes in the hydrologic variables in a watershed of Loess Plateau.
Journal of The American Water Resources Association, 2003
ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental qual... more ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental quality on the Loess Plateau of China. The annual total sediment load of the Yellow River is 1.6 billion tons, with about 90 percent coming from soil erosion from the Loess Plateau. To reduce soil erosion from the Loess Plateau, conservation practices, including tree planting, ridge construction between fields and around gullies, terrace and ditch construction perpendicular to the main slope, and dam construction are being implemented. An evaluation of these conservation practices is required before they are implemented at the large scale. The objective of this study is to evaluate the effectiveness of conservation practices to control runoff and sediment yield from paired watersheds in the hilly gully region of the Loess Plateau. The advantage of the paired watershed approach is its sensibility in detecting differences in runoff and sediment transport by monitoring both watersheds during two periods, an initial period with no conservation practices and a treatment period with only one watershed subjected to conservation practices. Implementation of the conservation practices resulted in (1) cumulative runoff and sediment yield that were, respectively, 25 and 38 percent less from the treatment watershed than from the control, (2) a decrease in the number of rainfall events producing runoff and sediment transport (94 in the control versus 63 in treatment), and (3) a reduction in the maximum discharge and maximum suspended sediment concentration.
The hydrology of the Earth's surface is quite dynamic. Attempts to model the hydrology have been ... more The hydrology of the Earth's surface is quite dynamic. Attempts to model the hydrology have been only partially successful. Many of the existing detailed numerical models require so many input parameters that they are not practical for use at speci®c locations, and the simpli®ed models do not well describe the dynamic surface hydrology. Here, we present a modi®ed statisticaldynamic model that is simple to use. We evaluate how well the modi®ed statistical-dynamic model describes surface hydrology by comparing it to a more advanced numerical model and to ®eld measurements. Our model is developed by making speci®c modi®cations to the Eagleson statisticaldynamic water balance model. Speci®c modi®cations to the earlier model include: the addition of precipitation periods that can account for seasonal variations in precipitation and water balance, a change in how soil water properties and¯ow are computed, and how a limited water supply in¯uences plant transpiration so that transpiration rates can be less than the potential transpiration rates. Mass conservation and a step by step prediction-correction algorithm are used to calculate the mean water balance and its partitioning as well as the average soil moisture in the precipitation periods. All of these modi®cations improve the statistical-dynamic model and make it more¯exible and potentially useful. Comparisons of the modi®ed model are made with numerical simulations of the WAVES model and with 10-year ®eld measurements from an eco-hydrological system on the Loess Plateau. The data from a long-term fertility experiment of winter wheat at Changwu Agroecological Station on the Loess Plateau are used to test the modi®ed statistical-dynamic water balance model. In both comparisons the correspondence is remarkably good. The modi®ed statistical-dynamic water balance model accurately predicts the mean water balance components and the dynamic processes of the mean soil moisture for speci®c wheat-fertility-productivity Agricultural Water Management 48 (2001) 21±35 : S 0 3 7 8 -3 7 7 4 ( 0 0 ) 0 0 1 1 1 -6 conditions. The statistical-dynamic water balance model is simple to use, fast and ef®cient, requires less input than complex numerical models, and is shown to be quite accurate in predicting dynamic soil moisture storage. #
Winter wheat monoculture occupies a large area of the Loess Plateau dryland region of China. Its ... more Winter wheat monoculture occupies a large area of the Loess Plateau dryland region of China. Its yield is mainly limited by available water and fertilization. From the mid-1980s, yield of winter wheat increased with fertilizer application, and this increased productivity may increase soil-water depletion and reduce available soil-water at planting. Besides rainfall during the growing season, an important source of water for the crops is stored soil-water at planting. In the long run, increasing fertilization may not be sufficient to maintain higher yield. To develop better dryland crop and water management practices, a 15-year experiment of winter wheat monoculture was conducted at the Changwu Agri-ecological Station of the Loess Plateau from 1984 to 1999. Different levels of productivity were implemented by the application of chemical fertilizers and manure. The experimental design consisted of a control treatment (CTL) and three fertilizer treatments: nitrogen, phosphorus and manure (NPM), nitrogen and phosphorus (NP), and manure (M). Compared to CTL, on average, treatments NPM, NP and M increased yield by 148, 110 and 59%, and decreased soilwater at planting by 102.6, 59.1 and 31.6 mm within the 300 cm profile, and soil-water at harvest by 142.3, 102.5 and 70.2 mm, respectively. There was a decrease of soil-water with time for fertilizer treatments. Crop yield with high fertilization treatments responded more to rainfall variations. Considering the importance of soil-water at planting for crop yield in dryland farming, winter wheat monoculture with high fertilization does not appear to be a sustainable management practice in the Loess Plateau dryland region of China. #
Since the late 1950s a series of soil conservation practices have been implemented in the Loess P... more Since the late 1950s a series of soil conservation practices have been implemented in the Loess Plateau. It is important to assess the impact of these practices on hydrology at the catchment scale. The Jialuhe River catchment, a tributary of the Yellow River, with a drainage area of 1117 km2 in the Loess Plateau, was chosen to investigate the hydrological responses to conservation practices. Parametric and non-parametric Mann-Kendall tests were utilized to detect trends in hydrological variables or their residuals. Relationships between precipitation and hydrological variables were developed to remove the impact of precipitation variability. Significant linear decreasing trends in annual surface runoff and baseflow were identified during the treated period from 1967 to 1989, and the rate of reduction was 1.30 and 0.48 mm/year, respectively. As result, mean annual surface runoff and baseflow decreased by 32% over the period of 1967 to 1989. Seasonal runoff also decreased during the treated period with the greatest reduction occurring in summer and the smallest reduction in winter. The response of high and low daily flow to conservation practices was greater than average flows.
J. Gallichand). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o... more J. Gallichand). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t 0378-3774/$ -see front matter #
The effects of 18 years continuous cropping of irrigated rice on soil and yields were studied in ... more The effects of 18 years continuous cropping of irrigated rice on soil and yields were studied in two long-term fertility experiments (LTFE) at Ndiaye and Fanaye in the Senegal River Valley (West Africa). Rice was planted twice in a year during the hot dry season (HDS) and wet season (WS) with different fertilizer treatments. Soil organic carbon (SOC) under fallow varied from 7.1 g kg -1 at Fanaye to 11.0 g kg -1 at Ndiaye. Rice cropping maintained and increased SOC at Ndiaye and Fanaye, respectively and fertilizer treatments did not affect SOC. Soil available P and exchangeable K were maintained or increased with long-term application of NPK fertilizers. Without any fertilizer, yields decreased by 60 kg ha -1 (1.5%) and 115 kg ha -1 (3%) per year at Fanaye and Ndiaye, respectively. The highest annual yield decreases of 268 kg ha -1 (3.6%) and 277 kg ha -1 (4.1%) were observed at Fanaye and Ndiaye, respectively when only N fertilizer was applied. Rice yields were only maintained with NPK fertilizers supplying at least 60 kg N, 26 kg P and 50 kg K ha -1 . It was concluded that the double cropping of irrigated rice does not decrease SOC and the application of the recommended doses of NPK fertilizer maintained rice yields for 18 years.
Pots used for experiments conducted on plants grown in them create rooting environments that are ... more Pots used for experiments conducted on plants grown in them create rooting environments that are affected by limited soil volume, which can affect various physiological processes, including transpiration, and plant growth. However, the applicability of results from pot experiments to the field has received limited attention. The objective of this study was to compare the growth and transpiration of maize (Zea mays L.) and winter wheat (Triticum aestivum L.) when grown in pots and field plots under various constant water deficits. The experiments were conducted under similar environmental conditions for both pots and plots. Transpirational responses at both transient (RTTr) and daily (RDTr) time scales to a decreasing fraction of available soil water (FASW) were analyzed. For a comparable FASW, there was a significant reduction in shoot dry weight and total transpiration for plants in pots compared to those in plots. A parabolic relationship between shoot dry weight and total transpiration existed and was not influenced by soil volume or crop type. The plot experiment data for both crops was consistent with pot data for the response of RDTr and RTTr to changes in FASW, which was represented by a linearplateau function. However, the threshold values were significantly different for the two time scales. The threshold values and slopes of the linear-plateau function for maize and wheat were not significantly different in the response of RTTr to FASW, but were significantly different in the response of RDTr to FASW. Therefore, the transpirational responses of the selected maize and winter wheat hybrids to soil drought were different at the daily and transient time scales.
In the dryland region of the Loess Plateau in China, improved soil and water conservation practic... more In the dryland region of the Loess Plateau in China, improved soil and water conservation practices are essential for sustainable agriculture. The prevailing cropping practice in this region, growing winter wheat (Triticum aestivum L.) as a monoculture, carries two major drawbacks which arise during the fallow period from July to September: firstly, an exposure to soil erosion from rainstorms and, secondly, poor water storage efficiency of rain. Alternative cropping systems were therefore investigated. They comprised four rotations, each of 3 or 4 years, involving different combinations of corn (Zea mays L.), wheat, broomcorn millet (Panicum miliaceum), and pea (Pisum sativum L.). The water use efficiencies (WUEs) and sustainability of the rotations were evaluated at Changwu Agri-ecological Station in the Loess Plateau from 1984 to 1996. Results showed that two of the rotations gave significantly improved grain yields and WUE compared to the standard wheat monoculture. The rotation of corn, wheat, and wheat-millet could increase the duration of crop coverage during the rainy season from a low of 38% of the time for wheat to a maximum of 80%, and the crop precipitation interception index (CPII) from 53% for wheat to a maximum of 73%. All the alternative rotations tested did not significantly affect available soil water at wheat planting. Considering all factors, a 3-year rotation of corn, wheat, and wheat-millet was found to offer the best potential for improving cropping practice in the region.
Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caraga... more Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caragana korshinkii Kom is a shrub that is widely planted in this region to control soil erosion and land desertification. The objective of this study was to investigate the fine root distribution of mature C. korshinkii and its water consumption, when grown in either silt loam or sandy soils, in order to understand differences between the water cycles of two such soils found in the transition zone between fertile loess hills and desert of the Northern Loess Plateau. Fine root distributions were measured using the trench-profile method. Soil water dynamics were monitored with a neutron probe during two growing seasons. The results showed that fine root area density (FRAD) declined with increasing soil depth in both soils, with 70.7% and 96.6% of the total fine roots being concentrated in the upper 1-m layer of the silt loam and sandy soils, respectively. Water consumption by C. korshinkii in the silt loam was close to that in the sandy soil. Most water consumption in both soil types was from the upper 1-m layer. Little variation in plant available water (PAW) occurred in the 3–6 m soil layer during the whole study period. However, in this layer, the PAW was significantly lower in the silt loam soil than in the sandy soil. Total actual evapotranspiration (ETa) was slightly higher from the sandy soil plots than from those of the silt loam soil during both growing seasons. Our study indicated that mature C. korshinkii effectively uses about the same amount of water from either the silt loam or sandy soils, but that more soil water at depth was extracted from silt loam soil than from sandy soil.
2011. Water availability and forest growth in coarsetextured soils. Can. J. Soil Sci. 91: 199Á210... more 2011. Water availability and forest growth in coarsetextured soils. Can. J. Soil Sci. 91: 199Á210. A method of evaluating the influence of soil layering and climatic variability on plant available water for forest growth is presented. This method enables species-specific levels of maximum sustainable plant transpiration to be evaluated. A calibrated HYDRUS-1D model was used with a 60-yr meteorological record to simulate actual evapotransipration (ET a ) of dominant tree species with different values of leaf area index (LAI) for three sites in northern Alberta. A probability distribution of ET a was developed for each case. The relationships between LAI, plant above-ground primary production (ANPP), and ET a were used to estimate the minimum water demand to support plant growth at specific sites. The developed frequency curves of ET a and the minimum water demand can be used to determine the maximum sustainable LAI and the risk associated with revegetating a particular site with a dominant tree species. The effect of different tree species on the minimum water demand and the maximum sustainable LAI was also illustrated. The results indicated that layering of coarse-textured soils can provide more plant available water and support a higher maximum sustainable LAI than homogeneous soils of a similar texture.
A sensitivity analysis is critical for determining the relative importance of model parameters to... more A sensitivity analysis is critical for determining the relative importance of model parameters to their influence on the simulated outputs from a process-based model. In this study, a sensitivity analysis for the SPACSYS model, first published in Ecological Modelling (Wu, et al., 2007), was conducted with respect to changes in 61 input parameters and their influence on 27 output variables. Parameter sensitivity was conducted in a ‘one at a time’ manner and objectively assessed through a single statistical diagnostic (normalized root mean square deviation) which ranked parameters according to their influence of each output variable in turn. A winter wheat field experiment provided the case study data. Two sets of weather elements to represent different climatic conditions and four different soil types were specified, where results indicated little influence on these specifications for the identification of the most sensitive parameters. Soil conditions and management were found to af...
There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estima... more There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estimation of unsaturated soil properties. The pedo-transfer functions can be used for the estimation of the soil–water characteristic curve (SWCC) which in turn is used for the estimation of other unsaturated soil properties. The accuracy of the indirect pedo-transfer function method for the estimation of the SWCC depends on the PTF and the equation used to best-fit the particle-size distribution (PSD) data. The objectives of this study are to: (1) evaluate the performance of the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation for best-fitting the particle-size distribution, (PSD) data, and, (2) compare the predictions made by two of the commonly used PTFs; namely, Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) and Fredlund et al. (Can Geotech J 39:1103–1117, 2002), for estimating the SWCC from the PSD. The authors used 258 measured PSDs and SWCC datasets from the Loess Plateau, China, for this study. The dataset consisted of 187 silt–loam soils, 41 loam soils, 11 silt–clay–loam soils, 10 sand–loam soils, 6 silt–clay soils, and 3 loam–sand soils. The SWCC and PSD datasets were measured using a Pressure Plate apparatus and the pipette method, respectively. The comparison between the estimated and measured particle-size distribution curves showed that the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation closely prepresented the PSD for all soils in the Loess Plateau, with a lower root mean square error (RMSE) of 0.869%. The comparison between the estimated and measured water contents at the same suction showed that the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF performed somewhat better than the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) function. The Fredlund et al. method had RMSE value of 0.039 cm3 cm−3 as opposed to 0.046 cm3 cm−3 for the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) method. The Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF produced the closest predictions for sand–loam, loam–sand, and loam soils, with a lower RMSE for gravimetric water content ranging from 0.006 to 0.036 cm3 cm−3. There were consistent over-estimations observed for silt–loam, silt–clay–loam, and slit–clay soils with RMSE values for gravimetric water content ranging from 0.037 to 0.043 cm3 cm−3. The measured and estimated air-entry values were closest when using the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF. The measured and estimated maximum slopes on the SWCC were closest when using the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) PTF.
The objective of this study is to evaluate the potential utility of the USGS Global Data Assimila... more The objective of this study is to evaluate the potential utility of the USGS Global Data Assimilation System (GDAS) 1-degree, daily reference Evapotranspiration (ET0) products by comparing them with observed Oklahoma mesonet daily ET0 over a 2 year period (2005–2006). The comparison showed a close match between the two independent ET0 products, with bias within a range of 10% for most of the sites and the overall bias of − 2.80%. The temporal patterns are strongly correlated, with a correlation coefficient above 0.9 for all groups. In summary, we conclude that (1) the consistent low bias shows the original GDAS ET0 products have high potentials to be used in land surface modeling; (2) the high temporal correlations demonstrate the capability of GDAS ET0 to represent the major atmospheric processes that control the daily variation of surface hydrology; (3) The temporal and spatial correspondences in trend between independent datasets (GDAS and MESONET) were good. The finding in Oklahoma, a different hydro-climate region from a similar regional study conducted in California by Senay et al. (J Am Water Res Assoc 44(4):969–979, 2008), reconfirms the reliability and potential of using GDAS reference ET for regional energy balance and water resources management in many parts of the world.
Evapotranspiration (ET) is deemed critical for water resources management. Even in the same clima... more Evapotranspiration (ET) is deemed critical for water resources management. Even in the same climatic and meteorological conditions, actual ET (ETa) may exhibit remarkable spatial variability across different vegetation covers, agricultural land use practices, and differing types of urban land development. The main objectives of this study are (1) to evaluate the possible closure of the heat balance equation using Oklahoma's unique environmental monitoring network; and (2) to estimate ETa and determine the variation with regards to varying types of land use and land cover in urban settings. In this study, a Surface-Energy-Balance ET algorithm was implemented to estimate ETa at a higher spatial resolution using Landsat 5 satellite images while the Oklahoma Mesonet observations can be used as our ground truth data. Accuracy of the estimated ETa was assessed using latent heat flux measurements provided by AmeriFlux towers. The associated bias ratios of daily mean ETa with respect to both burn and control sites are -0.92%, and -8.86% with a correlation of 0.83 and 0.81, respectively. Additionally, estimated ETa from a water balance budget analysis and the remotely sensed ETa are cross-validated with a low bias ratio of 5.2%, and a correlation coefficient of 0.7 at the catchment scale. The lowest ETa was observed for developed urban areas and highest for open water bodies. The ETa difference is also demonstrated from two contrasting counties. The results show Garfield County (agricultural) has higher ETa values than Oklahoma County (urban) for all land cover types except open water bodies.
Soil texture and evaporative demand have been reported to be the main factors which influence the... more Soil texture and evaporative demand have been reported to be the main factors which influence the transpirational response to soil water deficits. However, experimental evidences are not enough. The objective of this study was to investigate the transpirational response to soil water availability in soils of different textures under different evaporative demand levels. The three main soils of the Loess Plateau of China (loamy clay, clay loam and sandy loam) were selected and six constant soil water treatments were applied for winter wheat (Triticum aestivum L.) grown in pots. In order to reduce the influence of environmental conditions and plant factors, a normalized daily transpiration rate was used to develop the relationships with volumetric soil water content and soil water suction. Results showed that, under various levels of evaporative demand, a linear-plateau function with a critical value could be used to describe the dynamic change of the normalized transpiration rate with soil drying. Soil texture significantly influenced both the critical and the slope values of the linear-plateau equations, however, evaporative demand significantly affected the critical values of volumetric soil water content and soil suction for the loamy clay and clay loam only. Therefore, for saving water, different strategies are needed for these three soils.
High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum ae... more High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum aestivum L.) grown in the Loess Plateau of China under semiarid climatic conditions. Grain yield can be improved by effective water management practices. A 13-year field experiment was conducted at the CERN Changwu Agro-ecological Experimental Station of the Loess Plateau to determine optimal irrigation strategies under limited water supply and to develop relationships among grain yield (Y), seasonal evapotranspiration (SET) and water-use efficiency (WUE). The experiment consisted of five irrigation treatments and three blocks. Measurements included grain yield, soil water content at various depth intervals in the 0–3,000 mm layer, irrigation amount, and precipitation. Results showed that winter wheat grown in this area experienced serious water stress during critical growth stages for the no-irrigation treatment. The amount and timing of irrigation had an important effect on grain yield, but significant differences in yield were not observed between the three-irrigation and the four-irrigation treatments. Grain yield was linearly related (R 2=0.66) to SET, but differences in WUE were not significant for any of the treatments. The relationship between WUE and Y was best represented by a second order polynomial (R 2=0.65) consisting of a nearly linear portion between 1.5 and 5.0 Mg ha−1. Optimum water management of winter wheat in the Loess Plateau should consist of three 87.5 mm irrigations applied at stem elongation, booting, and anthesis.
The Soil Conservation Service curve number (CN) method is widely used for predicting direct runof... more The Soil Conservation Service curve number (CN) method is widely used for predicting direct runoff from rainfall. However, despite the extent of cultivation on hillslope areas, very few attempts have been made to incorporate a slope factor into the CN method. The objectives of this study were (1) to evaluate existing approaches integrating slope in the CN method, and (2) to develop an equation incorporating a slope factor into the CN method for application in the steep slope areas of the Loess Plateau of China. The dataset consisted of 11 years of rainfall and runoff measurements from two experimental sites with slopes ranging from 14 to 140%. The results indicated that the standard CN method underestimated large runoff events and overestimated small events. For our experimental conditions, the optimized and non-optimized forms of the slope-modified CN method of the Erosion Productivity Impact Calculator model improved runoff prediction for steep slopes, but large runoff events were still underestimated and small ones overpredicted. Based on relationships between slope and the observed and theoretical CN values, an equation was developed that better predicted runoff depths with an R2 of 0.822 and a linear regression slope of 0.807. This slope-adjusted CN equation appears to be the most appropriate for runoff prediction in the steep areas of the Loess Plateau of China.
The objective of this study was to examine the trends of changes in streamflow in a watershed of ... more The objective of this study was to examine the trends of changes in streamflow in a watershed of the Loess Plateau, where a series of soil conservation measures were implemented since the late 1950s. Both parametric and non-parametric Mann–Kendall test were used to identify the trends in hydrologic variables over the last 50 years, and it showed significant downward trends in annual runoff, surface runoff and baseflow. The Pettitt’s test was used to detect the change points of runoff, which occurred in 1973, and the whole 50-year records could be divided into contrast (from 1957 to 1973) and treated (from 1974 to 2006) periods. It was observed that the average annual runoff during treated period reduced by 60%, surface runoff and baseflow reduced by 65% and 55%, respectively in comparing with the contrast period. But the proportion of baseflow to total runoff showed a significant increasing from 0.57 to 0.63. Seasonal runoff also showed decreased trend with the highest reduction occurring in summer and lowest in winter. Annual precipitation in whole period showed no significant trend, so the changes in hydrologic variables were induced by conservation measures. Comparison of the flow duration curves for the two periods showed that reductions in high and low flows varied greatly. Results showed that conservation measures have resulted obvious changes in the hydrologic variables in a watershed of Loess Plateau.
Journal of The American Water Resources Association, 2003
ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental qual... more ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental quality on the Loess Plateau of China. The annual total sediment load of the Yellow River is 1.6 billion tons, with about 90 percent coming from soil erosion from the Loess Plateau. To reduce soil erosion from the Loess Plateau, conservation practices, including tree planting, ridge construction between fields and around gullies, terrace and ditch construction perpendicular to the main slope, and dam construction are being implemented. An evaluation of these conservation practices is required before they are implemented at the large scale. The objective of this study is to evaluate the effectiveness of conservation practices to control runoff and sediment yield from paired watersheds in the hilly gully region of the Loess Plateau. The advantage of the paired watershed approach is its sensibility in detecting differences in runoff and sediment transport by monitoring both watersheds during two periods, an initial period with no conservation practices and a treatment period with only one watershed subjected to conservation practices. Implementation of the conservation practices resulted in (1) cumulative runoff and sediment yield that were, respectively, 25 and 38 percent less from the treatment watershed than from the control, (2) a decrease in the number of rainfall events producing runoff and sediment transport (94 in the control versus 63 in treatment), and (3) a reduction in the maximum discharge and maximum suspended sediment concentration.
The hydrology of the Earth's surface is quite dynamic. Attempts to model the hydrology have been ... more The hydrology of the Earth's surface is quite dynamic. Attempts to model the hydrology have been only partially successful. Many of the existing detailed numerical models require so many input parameters that they are not practical for use at speci®c locations, and the simpli®ed models do not well describe the dynamic surface hydrology. Here, we present a modi®ed statisticaldynamic model that is simple to use. We evaluate how well the modi®ed statistical-dynamic model describes surface hydrology by comparing it to a more advanced numerical model and to ®eld measurements. Our model is developed by making speci®c modi®cations to the Eagleson statisticaldynamic water balance model. Speci®c modi®cations to the earlier model include: the addition of precipitation periods that can account for seasonal variations in precipitation and water balance, a change in how soil water properties and¯ow are computed, and how a limited water supply in¯uences plant transpiration so that transpiration rates can be less than the potential transpiration rates. Mass conservation and a step by step prediction-correction algorithm are used to calculate the mean water balance and its partitioning as well as the average soil moisture in the precipitation periods. All of these modi®cations improve the statistical-dynamic model and make it more¯exible and potentially useful. Comparisons of the modi®ed model are made with numerical simulations of the WAVES model and with 10-year ®eld measurements from an eco-hydrological system on the Loess Plateau. The data from a long-term fertility experiment of winter wheat at Changwu Agroecological Station on the Loess Plateau are used to test the modi®ed statistical-dynamic water balance model. In both comparisons the correspondence is remarkably good. The modi®ed statistical-dynamic water balance model accurately predicts the mean water balance components and the dynamic processes of the mean soil moisture for speci®c wheat-fertility-productivity Agricultural Water Management 48 (2001) 21±35 : S 0 3 7 8 -3 7 7 4 ( 0 0 ) 0 0 1 1 1 -6 conditions. The statistical-dynamic water balance model is simple to use, fast and ef®cient, requires less input than complex numerical models, and is shown to be quite accurate in predicting dynamic soil moisture storage. #
Winter wheat monoculture occupies a large area of the Loess Plateau dryland region of China. Its ... more Winter wheat monoculture occupies a large area of the Loess Plateau dryland region of China. Its yield is mainly limited by available water and fertilization. From the mid-1980s, yield of winter wheat increased with fertilizer application, and this increased productivity may increase soil-water depletion and reduce available soil-water at planting. Besides rainfall during the growing season, an important source of water for the crops is stored soil-water at planting. In the long run, increasing fertilization may not be sufficient to maintain higher yield. To develop better dryland crop and water management practices, a 15-year experiment of winter wheat monoculture was conducted at the Changwu Agri-ecological Station of the Loess Plateau from 1984 to 1999. Different levels of productivity were implemented by the application of chemical fertilizers and manure. The experimental design consisted of a control treatment (CTL) and three fertilizer treatments: nitrogen, phosphorus and manure (NPM), nitrogen and phosphorus (NP), and manure (M). Compared to CTL, on average, treatments NPM, NP and M increased yield by 148, 110 and 59%, and decreased soilwater at planting by 102.6, 59.1 and 31.6 mm within the 300 cm profile, and soil-water at harvest by 142.3, 102.5 and 70.2 mm, respectively. There was a decrease of soil-water with time for fertilizer treatments. Crop yield with high fertilization treatments responded more to rainfall variations. Considering the importance of soil-water at planting for crop yield in dryland farming, winter wheat monoculture with high fertilization does not appear to be a sustainable management practice in the Loess Plateau dryland region of China. #
Since the late 1950s a series of soil conservation practices have been implemented in the Loess P... more Since the late 1950s a series of soil conservation practices have been implemented in the Loess Plateau. It is important to assess the impact of these practices on hydrology at the catchment scale. The Jialuhe River catchment, a tributary of the Yellow River, with a drainage area of 1117 km2 in the Loess Plateau, was chosen to investigate the hydrological responses to conservation practices. Parametric and non-parametric Mann-Kendall tests were utilized to detect trends in hydrological variables or their residuals. Relationships between precipitation and hydrological variables were developed to remove the impact of precipitation variability. Significant linear decreasing trends in annual surface runoff and baseflow were identified during the treated period from 1967 to 1989, and the rate of reduction was 1.30 and 0.48 mm/year, respectively. As result, mean annual surface runoff and baseflow decreased by 32% over the period of 1967 to 1989. Seasonal runoff also decreased during the treated period with the greatest reduction occurring in summer and the smallest reduction in winter. The response of high and low daily flow to conservation practices was greater than average flows.
J. Gallichand). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o... more J. Gallichand). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t 0378-3774/$ -see front matter #
The effects of 18 years continuous cropping of irrigated rice on soil and yields were studied in ... more The effects of 18 years continuous cropping of irrigated rice on soil and yields were studied in two long-term fertility experiments (LTFE) at Ndiaye and Fanaye in the Senegal River Valley (West Africa). Rice was planted twice in a year during the hot dry season (HDS) and wet season (WS) with different fertilizer treatments. Soil organic carbon (SOC) under fallow varied from 7.1 g kg -1 at Fanaye to 11.0 g kg -1 at Ndiaye. Rice cropping maintained and increased SOC at Ndiaye and Fanaye, respectively and fertilizer treatments did not affect SOC. Soil available P and exchangeable K were maintained or increased with long-term application of NPK fertilizers. Without any fertilizer, yields decreased by 60 kg ha -1 (1.5%) and 115 kg ha -1 (3%) per year at Fanaye and Ndiaye, respectively. The highest annual yield decreases of 268 kg ha -1 (3.6%) and 277 kg ha -1 (4.1%) were observed at Fanaye and Ndiaye, respectively when only N fertilizer was applied. Rice yields were only maintained with NPK fertilizers supplying at least 60 kg N, 26 kg P and 50 kg K ha -1 . It was concluded that the double cropping of irrigated rice does not decrease SOC and the application of the recommended doses of NPK fertilizer maintained rice yields for 18 years.
Pots used for experiments conducted on plants grown in them create rooting environments that are ... more Pots used for experiments conducted on plants grown in them create rooting environments that are affected by limited soil volume, which can affect various physiological processes, including transpiration, and plant growth. However, the applicability of results from pot experiments to the field has received limited attention. The objective of this study was to compare the growth and transpiration of maize (Zea mays L.) and winter wheat (Triticum aestivum L.) when grown in pots and field plots under various constant water deficits. The experiments were conducted under similar environmental conditions for both pots and plots. Transpirational responses at both transient (RTTr) and daily (RDTr) time scales to a decreasing fraction of available soil water (FASW) were analyzed. For a comparable FASW, there was a significant reduction in shoot dry weight and total transpiration for plants in pots compared to those in plots. A parabolic relationship between shoot dry weight and total transpiration existed and was not influenced by soil volume or crop type. The plot experiment data for both crops was consistent with pot data for the response of RDTr and RTTr to changes in FASW, which was represented by a linearplateau function. However, the threshold values were significantly different for the two time scales. The threshold values and slopes of the linear-plateau function for maize and wheat were not significantly different in the response of RTTr to FASW, but were significantly different in the response of RDTr to FASW. Therefore, the transpirational responses of the selected maize and winter wheat hybrids to soil drought were different at the daily and transient time scales.
In the dryland region of the Loess Plateau in China, improved soil and water conservation practic... more In the dryland region of the Loess Plateau in China, improved soil and water conservation practices are essential for sustainable agriculture. The prevailing cropping practice in this region, growing winter wheat (Triticum aestivum L.) as a monoculture, carries two major drawbacks which arise during the fallow period from July to September: firstly, an exposure to soil erosion from rainstorms and, secondly, poor water storage efficiency of rain. Alternative cropping systems were therefore investigated. They comprised four rotations, each of 3 or 4 years, involving different combinations of corn (Zea mays L.), wheat, broomcorn millet (Panicum miliaceum), and pea (Pisum sativum L.). The water use efficiencies (WUEs) and sustainability of the rotations were evaluated at Changwu Agri-ecological Station in the Loess Plateau from 1984 to 1996. Results showed that two of the rotations gave significantly improved grain yields and WUE compared to the standard wheat monoculture. The rotation of corn, wheat, and wheat-millet could increase the duration of crop coverage during the rainy season from a low of 38% of the time for wheat to a maximum of 80%, and the crop precipitation interception index (CPII) from 53% for wheat to a maximum of 73%. All the alternative rotations tested did not significantly affect available soil water at wheat planting. Considering all factors, a 3-year rotation of corn, wheat, and wheat-millet was found to offer the best potential for improving cropping practice in the region.
Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caraga... more Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caragana korshinkii Kom is a shrub that is widely planted in this region to control soil erosion and land desertification. The objective of this study was to investigate the fine root distribution of mature C. korshinkii and its water consumption, when grown in either silt loam or sandy soils, in order to understand differences between the water cycles of two such soils found in the transition zone between fertile loess hills and desert of the Northern Loess Plateau. Fine root distributions were measured using the trench-profile method. Soil water dynamics were monitored with a neutron probe during two growing seasons. The results showed that fine root area density (FRAD) declined with increasing soil depth in both soils, with 70.7% and 96.6% of the total fine roots being concentrated in the upper 1-m layer of the silt loam and sandy soils, respectively. Water consumption by C. korshinkii in the silt loam was close to that in the sandy soil. Most water consumption in both soil types was from the upper 1-m layer. Little variation in plant available water (PAW) occurred in the 3–6 m soil layer during the whole study period. However, in this layer, the PAW was significantly lower in the silt loam soil than in the sandy soil. Total actual evapotranspiration (ETa) was slightly higher from the sandy soil plots than from those of the silt loam soil during both growing seasons. Our study indicated that mature C. korshinkii effectively uses about the same amount of water from either the silt loam or sandy soils, but that more soil water at depth was extracted from silt loam soil than from sandy soil.
2011. Water availability and forest growth in coarsetextured soils. Can. J. Soil Sci. 91: 199Á210... more 2011. Water availability and forest growth in coarsetextured soils. Can. J. Soil Sci. 91: 199Á210. A method of evaluating the influence of soil layering and climatic variability on plant available water for forest growth is presented. This method enables species-specific levels of maximum sustainable plant transpiration to be evaluated. A calibrated HYDRUS-1D model was used with a 60-yr meteorological record to simulate actual evapotransipration (ET a ) of dominant tree species with different values of leaf area index (LAI) for three sites in northern Alberta. A probability distribution of ET a was developed for each case. The relationships between LAI, plant above-ground primary production (ANPP), and ET a were used to estimate the minimum water demand to support plant growth at specific sites. The developed frequency curves of ET a and the minimum water demand can be used to determine the maximum sustainable LAI and the risk associated with revegetating a particular site with a dominant tree species. The effect of different tree species on the minimum water demand and the maximum sustainable LAI was also illustrated. The results indicated that layering of coarse-textured soils can provide more plant available water and support a higher maximum sustainable LAI than homogeneous soils of a similar texture.
Uploads
Papers by Mingbin Huang