Papers by Cristian Youlton
Ciencia E Investigacion Agraria, 2016
Plant Disease
English (Persian) walnut (Juglans regia) trees affected by root and crown rot were surveyed in fi... more English (Persian) walnut (Juglans regia) trees affected by root and crown rot were surveyed in five regions of central Chile between 2015 and 2017. In each region, nine orchards, ranging from 1 to 21 years old, were randomly selected and inspected for incidence and severity of tree decline associated with crown and root rot. Soil and symptomatic crown and root tissues were collected and cultured in P5ARP semiselective medium to isolate potential oomycete pathogens, which were identified through morphology and molecularly using ITS sequences in the rDNA gene and beta tubulin gene. The most frequently isolated species was Phytophthora cinnamomi. Pathogenicity tests were conducted with representative oomycete isolates. P. cinnamomi, P. citrophthora, and Pythium ultimum were all pathogenic in J. regia. Nevertheless, only P. cinnamomi and P. citrophthora were pathogenic to English walnut. Py. ultimum caused limited levels of root damage to English walnut seedlings. Our research indicates...
Hydrology and Earth System Sciences Discussions
Farmland expansion in the Brazilian Cerrado, considered one of the largest agricultural frontiers... more Farmland expansion in the Brazilian Cerrado, considered one of the largest agricultural frontiers in the world, has the potential to alter water fluxes on different spatial scales. Despite some large-scale studies being developed, there are still few investigations in experimental sites in this region. Here, we investigate the water balance components in experimental plots and the groundwater table fluctuation in different land covers: wooded Cerrado, sugarcane, pasture and bare soil. Furthermore, we identify possible water balance trade-offs due to the different land covers. This study was developed between 2012 and 2016 in the central region of the state of São Paulo, Southern Brazil. Hydrometeorological variables, groundwater table, surface runoff and other water balance components were monitored inside experimental plots containing different land covers; the datasets were analyzed using statistical parameters; and the water balance components uncertainties were computed. Replacing wooded Cerrado by pastureland and sugarcane shifts the overland flow (up to 42 mm yr-1), and soil water storage (up to 504 mm yr-1). This fact suggests significant changes in the water partitioning in a transient land cover and land use (LCLU) system, as the evapotranspiration is lower (up to 719 mm yr-1) in agricultural land covers than in the undisturbed Cerrado. We recommend long-term observations to continue the evaluations initiated in this study, mainly because tropical environments have few basic studies at the hillslope scale and more assessments are needed for a better understanding of the real field conditions. Such efforts should be made to reduce uncertainties, validate the water balance hypothesis and catch the variability of hydrological processes.
Journal of Plant Nutrition and Soil Science
The structural stability of soil is a physical characteristic that affects soil degradation proce... more The structural stability of soil is a physical characteristic that affects soil degradation processes. Calcium‐based amendments, such as calcium carbonate, calcium sulfate, and calcium oxide/hydroxide, have been shown to improve the stability of soil aggregates. This study seeks to determine which calcium‐based soil amendments, and at what concentration, are the most efficient in improving aggregate stability of sandy topsoils derived from granitic and metamorphic parent materials, and to analyze the mechanisms involved. In the pot experiment, soils amended with CaCO₃, CaCl₂, and CaSO₄ did not present significant differences in aggregate stability compared to the control or among each other. In contrast, Ca(OH)₂ soil amendment brought the greatest stability to the soil aggregates. A dose of 1% Ca(OH)₂ significantly increased the stability of soil aggregates. This effect is due to the reaction of Ca(OH)₂ with atmospheric CO₂ which leads to the formation of CaCO₃, a delayed reaction not showed by the other soil amendments tested. Likewise, the greater solubility of Ca(OH)₂ compared to CaCO₃ exerts a greater aggregation effect on soil. Thus, the mechanism of action of Ca(OH)₂ is related to cementation, rather than flocculation. Future studies should be carried out to demonstrate the effectiveness of Ca(OH)₂ under field conditions.
Ciencia e investigación agraria, 2016
R. Petitpas, J.T. Ibarra, M. Miranda, and C. Bonacic. 2016. Spatial patterns in a 24year period s... more R. Petitpas, J.T. Ibarra, M. Miranda, and C. Bonacic. 2016. Spatial patterns in a 24year period show a case of increase forest cover and decrease fragmentation in Andean temperate landscapes, Chile. Cien. Inv. Agr. 43(3):384-395. Changes in landscape pattern were studied in a temperate landscape of the La Araucanía Region, Chile. Using aerial photographs from 1983 and 2007, we created land use/land cover maps. We then quantified the changes in composition and configuration by using landscape metrics and an adjacency matrix. By 2007, the dominant land cover had changed from agriculture to native vegetation. Residential areas showed the largest relative increase (670%) and had significant adjacency with native vegetation. The native vegetation increased by 375 ha, but the number of patches decreased by 45% and the mean patch area increased by 124%, which indicated that fragmentation decreased. The growth of tourism and the preference for "natural" spaces by new residents are suggested as the main drivers of this native vegetation recovery. Understanding the process of forest recovery may be helpful for reversing the general trend of forest loss in temperate forests of South America. This research is a first approach in exploring specific cases of native vegetation recovery and decreases in fragmentation in this Global Biodiversity Hotspot.
Bosque (Valdivia), 2016
Chilean palms (Jubaea chilensis) are endemic of central Chile and are classified as vulnerable ac... more Chilean palms (Jubaea chilensis) are endemic of central Chile and are classified as vulnerable according to the category of conservation. Even though the population of palms has gone down, there are still some groups (palmar) that remain in locations such as Petorca, Chile. In Petorca, the site "Las Palmas" was declared "Priority Site for the Biodiversity Conservation". However, the number of palms, their age and spatial distribution in "Las Palmas" are still unknown. Thus, in order to describe the conservation status, a population survey of palms was done. Location and age of every palm (infantile, child, adult or old, according to morphological features) were noted and their position georeferenced. Data were analyzed using a geographic information system that included maps and satellite imagery (Quickbird II). To assess the spatial distribution of palms, a Complete Spatial Randomness (CSR) test was applied using an L-function. Main results showed that 1,300 palms are present in "Las Palmas". Among those palms, 41 % are infantile, 45 % are young, 14 % are adults and 0.5 % are old plants. Infantile, young and adult palms have an aggregated distribution in high and inaccessible areas of the watershed headwater, while old palms have disaggregated distribution. The palmar is crossed by route E-37-D, where some adult palms that produce seeds are commonly present. However, if any seed gets to infantile palm, it does not reach the juvenile stage. There is no regeneration in lowland and in the proximity of communities. Thus, the palmar is reducing its extension.
Sustainability, 2016
The planting of sugarcane crops has expanded in the last decade in the southeast of Brazil, mainl... more The planting of sugarcane crops has expanded in the last decade in the southeast of Brazil, mainly due to its use for biofuel production, such as ethanol. This expansion in the State of São Paulo has occupied land that was previously used for cattle production. The change in land use affects soil and water through changes in ground cover and disturbance associated with farming practices. The objective of the following study was to determine the impact on runoff and erosion resulting from the conversion of pastureland to sugarcane for biofuel production. Erosion plots measuring 100 m 2 were built on a farm in Itirapina-SP, Brazil, on land with a slope gradient of 9% and soil composed of Quartz-sand Neosols (Typic quartzipsaments). The treatments were an 18-year old pasture and a new sugarcane plantation, with three replicates for each. After each rainfall episode, erosion and runoff were monitored during the first and second years after sugarcane was planted. The results show increased runoff and soil loss during the first year, though levels decreased in the second year when the sugarcane residue mulch ground cover increased. In addition, the necessary rainfall characteristics (e.g., intensity, duration) required to produce runoff and soil erosion were identified.
Revista Brasileira de Engenharia Agrícola e Ambiental, 2016
The low reliability of evaporation estimates in reservoirs challenges the management of water res... more The low reliability of evaporation estimates in reservoirs challenges the management of water resources, especially when drought occurs. The evaporation rates measured in buried tanks (20 m2 evaporimeters) are close to that of lakes. However, there are few studies in Brazil using long data sets with this type of tank. In this context, this study aimed to evaluate evaporation estimates of free water surface using the method of Penman (1948) and other five empirical equations in comparison with data from a 20 m2 tank observed during 10 years. The annual relationship between rainfall and evaporation was 1.0, showing variations in dry years (0.7) and rainy years (1.3). Among all evaluated methods, Linacre (1993) shows the best performance. Camargo et al. (1999) has very good estimates using air temperature as input variable and is a simple and reliable alternative when data are missing.
Postseismic uplift midway along the 1960 Chile rupture appears to be slowing down. We studied the... more Postseismic uplift midway along the 1960 Chile rupture appears to be slowing down. We studied the uplift near Puerto Montt, 70 km east of the Pacific coast. Puerto Montt is located on the boundary between the 1960 earthquake's coseismic and a coseismic and/or postseismic upwarp farther inland. This deformation was mapped by George Plafker in 1968, and the postseismic uplift was checked by him and others in 1989. The postseismic uplift has been attributed to afterslip on the plate interface, stress relaxation in the forearc mantle, or both. We obtained further information about shoreline change before and after the earthquake from the Pacific coast to 120 km eastward inland, about midway along the length of the 1960 rupture. Following in Plafker's footsteps, we used several criteria for distinguishing between coseismic and postseismic movement. We asked eyewitnesses whether sea level changed at the time of the earthquake, and whether it has changed in the decades since. We ...
… e investigación agraria, 2010
Quantification and control of runoff and soil erosion on avocado orchards on ridges along steep-h... more Quantification and control of runoff and soil erosion on avocado orchards on ridges along steep-hillslopes. Cien. Inv. Agr. 37(3): 113-123. Soil erosion increases after building downward ridges along steep hillslopes, in particular during the first winter. This erosion decreases when trees grow, but runoff increases. This study presents results of erosion under five different treatments: (i) soil cover with native vegetation, (ii) bare downward ridges, (iii) downward ridges with six year-old avocado orchard, (iv) downward ridges with plant cover and (v) downward ridges covered with agroindustrial waste sludge. The results revealed 20 t ha-1 of soil erosion during the first year after ridges were built, while mitigation measures can reduce erosion in 90%. Adult orchard showed the largest runoff, which probably is due to the effect of a high and about constant soil moisture during irrigation period and smaller infiltration capacity of eroded soil.
Estimates of evapotranspiration on a local scale is important information for agricultural and hy... more Estimates of evapotranspiration on a local scale is important information for agricultural and hydrological practices. However, equations to estimate potential evapotranspiration based only on temperature data, which are simple to use, are usually less trustworthy than the Food and Agriculture Organization (FAO)-Penman-Monteith standard method. The present work describes two correction procedures for potential evapotranspiration estimates by temperature, making the results more reliable. Initially, the standard FAO-Penman-Monteith method was evaluated with a complete climatologic data set for the period between 2002 and 2006. Then temperature-based estimates by Camargo and Jensen-Haise methods have been adjusted by error autocorrelation evaluated in biweekly and monthly periods. In a second adjustment, simple linear regression was applied. The adjusted equations have been validated with climatic data available for the Year 2001. Both proposed methodologies showed good agreement with the standard method indicating that the methodology can be used for local potential evapotranspiration estimates.
Basado en las observaciones del aumento de la temperatura media global del aire y del océano, en ... more Basado en las observaciones del aumento de la temperatura media global del aire y del océano, en el derretimiento generalizado de nieve y de hielo, y en el aumento global del nivel medio del mar, el último informe del IPCC sobre cambio climático revela que las alteraciones en los patrones climáticos globales son evidentes. Además indica un probable aumento de la frecuencia de precipitaciones intensas en los últimos 50 años, con una tendencia de probable intensificación en el futuro (IPCC, 2007). Estos cambios globales también se manifiestan en los diferentes parámetros climáticos a escala local. Dufek y Ambrizzi (2008) exponen evidencias de las variaciones climáticas en América del Sur y en Brasil, y analizan estadísticamente el registro pluviográfico de 59 estaciones en el estado de Sao Paulo entre los años de 1950 y 1999, constatando un incremento significativo en la precipitación total en mas de un 45% de las estaciones analizadas, asociado al aumento en la frecuencia de lluvias intensas y superiores a 20 mm. Un análisis estadístico de las lluvias a largo plazo-116 años de registro pluviométricoen el municipio de Campinas-SP no encontró variaciones significativas (Blain et al., 2007), concluyendo que los cambios en el patrón de lluvias no es aplicable para el conjunto del estado de Sao Paulo. Uno de los fenómenos que proporciona alteraciones en el clima de América del Sur es El Niño Oscilación del Sur (ENOS), ocasionado por una alteración del sistema océano-atmósfera, en el océano Pacífico tropical. Su fase cálida,
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Papers by Cristian Youlton