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.

全球众多地区已实施多种土壤与水保持措施（SWCM），以控制土壤侵蚀；其中一类SWCM为工程技术，例如交错等高沟（SCT）和山坡沟渠（HD）。本研究测量了SCT和HD对具有陡峭坡度的遮荫咖啡作物在Entisol土壤中地表径流、土壤侵蚀、有机物质暴露和土壤含水量影响的效应。在哥斯达黎加的Llano Brenes，耶稣玛丽亚河上游流域安装了九个径流小区（每处理三个小区，对照组三个小区）。数据收集时间介于2018年5月至2019年11月。在每个小区测量地表径流和土壤侵蚀量，同时在代表性处理小区测量土壤含水量。由于数据不符合正态分布的假设，对数据进行对数变换，并使用Kruskal-Wallis单因素非参数方差分析进行评估。Spearman相关分析和线性回归用于评估降水量和强度对每处理土壤侵蚀量和径流的影响。土壤去除暴露的有机物质数量在HD和SCT之间无统计学差异，但与对照相比均有显著差异（R²=0.81，P<0.05）。HD产生了最低的平均地表径流和平均土壤侵蚀量（p<0.0001）。Spearman相关分析表明，降水量深度对径流深度（HD R=0.62；SCT R=0.62；对照 R=0.60；p<0.001）和土壤侵蚀（HD R=0.50；SCT R=0.53；对照 R=0.50；p<0.001）的贡献大于其他变量。回归分析显示，径流和土壤侵蚀与降水量呈显著正相关（p<0.05），每增加1毫米的降水量，HD的平均径流增加0.02毫米，SCT和对照分别增加0.04毫米。在恒定平均强度变量下，每增加1毫米的降水量，土壤侵蚀量分别增加0.01克/平方米（HC）、0.18克/平方米（SCT）和0.54克/平方米（对照）。在本研究中，HC在陡峭坡面侵蚀控制方面表现出高效性。与对照相比，HC在2018年和2019年分别减少了88%和83%的土壤侵蚀。HC在2018年和2019年比对照减少了55%和60%的径流生成。而SCT在产生地表径流和土壤侵蚀方面与对照无统计学差异。