Soil properties characterization for land-use planning and soil management in watersheds under family farming

Environmental monitoring of small,rural watersheds was one of the components of the Natural Re-sources Management and Rural Poverty Alleviation Program(RS-Rural)in southern Brazil.The purpose of the monitoring was to assess the impact of promoting soil conservation and environment manage-ment practices adopted by farmers and funded by the Program.In four small monitored watersheds,in a total of 95 plots representing distinct land use and soil management,surface soil was collected to characterize ground-zero of the Program by determining several soil physical,chemical and microbio-logical properties.Principal component analysis(PCA)shows soil physical,chemical and biological properties were decisive in defining the agricultural soils in the rural watersheds with family farming.The sensitivity to chemical properties provides an opportunity to improve soil quality if soil management focuses on altering those properties.Soil management practiced by tobacco farmers leads to rapid,intense degradation of some natural soil properties,especially those related to the dynamics of soil organic matter,compared with more conservationist uses(forest,regrowth,and grassland).Thus,soil management must be reoriented to avoid the progress of degradation and recover soil physical and biological quality.Cover crops and by land-abandonment to allow natural vegetation are important management strategies for the degraded soils used for tobacco production,increasing soil organic matter,nutrients and microbial activity and thus allowing further crop production.In conclusion,wa-tersheds with tobacco cropping have soils with lower quality than when under no-tillage grain pro-duction,requiring changes in land use and soil management.

Event-based hydrology and sedimentation in paired watersheds under commercial eucalyptus and grasslands in the Brazilian Pampa biome

Ecological and hydrological impacts are expected when watersheds are under commercial eucalyptus.In this study we evaluated event-based hydrology and sedimentation in paired watersheds under commercial eucalyptus and grasslands cover.Flow,suspended sediment concentration,and sediment production were measured and simulated with the Limburg Soil Erosion Model(LISEM)in paired hydrographic watersheds located in southern Brazil;one occupied with 7-years old Eucalyptus saligna plantation(forest watershed-FW;0.83 km^(2))and another Pampa biome with native and exotic grasses used for beef cattle production(grassland watershed-GW;1.10 km^(2)).The effect of rainfall on hydrological and sedimentological variables was more evident in GW compared with FW.The shape of the hydrograph was steepest in GW,with rapid,marked increase and decrease in flow during rainfall.The parameters changed for model calibration in FW and GW were soil saturated hydraulic conductivity,initial soil moisture,and Manning roughness coefficient,whereby the statistical performance was classified as good(NSE>0.75).Fourteen events different from those used in the calibration process were validated for FW and GW,with NSE index classified as“good”and“very good”for hydrology.Our study shows limitations of LISEM in calibrating and validating the sediment yield for individual events due to the spatial variability of factors controlling soil erosion.The validated modeling results of this study may be applied in simulating soil and crop scenarios in watersheds cultivated with commercial forest and grassland for grazing.