Abstract
Cropland area in Uruguay, mostly soybeans, increased 300% during the last decade due to expansion to new areas. Although no-tillage practices are generalized among farmers, soil erosion is still a major environmental and economic issue. A predictive tool as the Water Erosion Prediction Model Project (WEPP), based on soil processes, has never been used in Uruguay. The objective of this research was to evaluate the soil erosion impact of various managements of intensive agriculture on Mollisols of Uruguay, applying the WEPP erosion model. The model was first adjusted and validated for annual erosion estimates of an Abruptic Argiudoll (Nash Sutcliffe (NS)= 0.81 and R2 = 0.89) and a Vertic Argiudoll (NS= 0.86 and R2= 0.90), and later applied to evaluate three Mollisols and one Vertisol with different soil managements. Treatments combined no tillage (NT) and reduced tillage (RT) with different crop rotations. Crop rotations were: continuous soybean (CS), soybean-wheat (SW), soybean-winter cover crop (S-Cover crop), cornsoybean- wheat-3/4 yr pasture (CSW-PPP/PPPP), and corn-soybean-wheat-soybean-wheat-3/4 yr pasture (CSWSWPPP/ PPPP). Soil erosion under RT system or CS was always above 7Mg.ha-1 (T value). Pastures inclusion under NT showed values below 7 Mg.ha-1.WEPP simulated an average erosion rate below T for SW rotation with NT (100m; 3% slope) in three of the four soils studied. However, by varying the slope and the length of the hillslope, the range for which the average annual erosion remains below this level is limited (only 3% - 4%). Moreover, for those hillslopes whose average annual erosion does not exceed the T value, there is still approximately a 25% probability that this may occur any given year. Our work highlights the potential of using WEPP in the development of criteria for assessing sustainability of soil management, alternative to T value of average annual erosion units, including risk analysis.
Highlights
IntroductionCropland area in Uruguay, mostly soybeans, increased 300% during the last decade (1) due to expansion to new areas were soils are more vulnerable to water erosion
For a mean annual precipitation of 1164 mm, the mean annual erosion simulated with Water Erosion Prediction Model Project (WEPP) model ranged from 2 to 67 Mg.ha-1.yr-1
The criterion used in Uruguay hereto to evaluate sustainability of crop rotations and soil management in terms of soil erosion has been the soil tolerance value (T) as a threshold for acceptable mean annual erosion
Summary
Cropland area in Uruguay, mostly soybeans, increased 300% during the last decade (1) due to expansion to new areas were soils are more vulnerable to water erosion. By the end of last century, Uruguayan agriculture was mostly managed alternating with crop-pasture rotations. This management reduced soil degradation produced by continuous crops (2). Soybean crops leave the soil both more susceptible to erosion (due to negative balances of nitrogen and carbon), and more exposed to erosion (because of the scarce residues of low C:N relation, which are an ineffective protection for the rain and runoff impacts) (3). No-tillage practices are generalized among farmers, soil erosion is still a major environmental and economic issue
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