How to model the effect of mechanical erosion control practices at a catchment scale?

Conservation agriculture practices are a crucial factor in mitigating and controlling erosion by water.To address water erosion estimates,most environmental models use the USLE,RUSLE,and MUSLE models.Management practices that affect soil erosion by modifying the flow pattern,such as contour farming,strip farming,or terracing,are represented within these models as a support practice(P)factor.However,due to the difficulty in accurately mapping the P-factor,many studies choose to ignore it,using only the default value P-factor 1 which represents the absence of sowing at the level or cultivation in strips.This study proposes a methodology that evaluates the current P-factor based on the angle between the crop row orientation and the elevation contour lines.The method was tested in four areas under soybean crop fields in southern Brazil,totaling 25 km^(2).The reason for choosing four areas is to select different characteristics of rural properties and topographic conditions.The ideal values of the P-factor are expected to be between 0.5 and 0.6;however,in our case,a P-factor greater than 0.8 was obtained in 60%of the area,indicating the low occurrence of contour farming reduces erosion rates.The results show that policymakers could potentially use this methodology(angle between the crop rows and contour lines)to run soil-erosion risk scenarios for a broader application of contour farming.This allows the P-factor to be quantified via a thematic map instead of assigning uniform P-factor values.With a detailed study of the P-factor on the slopes,there is a better understanding of where to target support practices to reduce erosion.