Effect of Staggered Contour Trenches and Hillside Ditches on surface runoff and soil loss on steep slopes in shaded coffee, Costa Rica.
Different types of soil and water conservation measures (SWCM) have been implemented in many regions of the world to control soil loss; one of the types of SWCM are engineering techniques such as Staggered Contour Trenches (SCT) and Hillside ditches (HD) . This study measured the effects of STC and HD, on surface runoff, soil loss, exposure of organic matter and soil moisture content, in a shaded coffee crop with steep slopes in an Entisol soil. Nine runoff plots (three plots by each treatment and three plots of control) were installed in Llano Brenes, Costa Rica, in the upper basin of the Jesus Maria River. The data was collected between May 2018 and November 2019. Surface runoff and soil loss were measured in each plot while soil moisture content was measured in representative treatment plots. Due to the non-compliance of the normal data distribution assumptions, a logarithmic transformation of the data was used, and they were evaluated using the Kruskal-Wallis one-way nonparametric analysis of variance test. Spearman correlation and linear regressions were used to assess the effect of the precipitation and intensity in the soil loss and runoff in each treatment. The amount of organic matter exposed by soil removal was not statistically different between HD and SCT, but both were different in comparison with the control (R2=0.81, P<0.05). HD generated the lowest mean surface runoff and mean soil loss (p<0.0001). Spearman correlation analysis showed the rainfall depth contributed more to runoff depth (HD R=0.62; SCT R= 0.62; Control R=0.60; p<0.001) and soil loss (HD R=0.50; STC R= 0.53; Control R=0.50; p<0.001) than other variables. Regression analysis showed that runoff and soil loss were significant (p<0.05) and positively correlated with rainfall depth for each treatment. With an increase of one mm of precipitation, on average the runoff increases 0.02 mm for HD, 0.04 mm for SCT and 0.04 for the control. An increase of one mm of precipitation, on average the soil loss increases by 0.01 g m-2 for HC, 0.18 g m-2 for SCT and 0.54 g m-2 for the control, with the constant average intensity variable. In this study, HC was shown to be efficient in erosion control on steeper slopes. HC helped reduce soil loss compared to the control, by 88 % in 2018 and 83 % in 2019. HC also reduced runoff generation by 55 % in 2018 and 60 % in 2019 compared to the control. While SCT was not statistically different in the generation of surface runoff and soil loss compared to the control.