Effectiveness of the application of rice straw mulching strips in reducing runoff and soil loss: Laboratory soil flume experiments under simulated rainfall

The use of mulch as a management tool has shown one of the highest effectiveness/cost ratios for improving agricultural soil fertility, crop productivity, soil restoration in badlands and post-fire soil erosion mitigation. Some researchers have suggested that mulching costs can be reduced by applying it in strips rather than over the entire area. However, the implications of strip-wise mulching on the effectiveness to reduce soil erosion are poorly known. This study aimed to evaluate, in laboratory experiments, the effectiveness of strip-wise mulching with rice straw in reducing runoff and soil loss for a highly erodible sandy loam soil at a steep slope of 40%. Six mulching application schemes were compared against a bare soil. The six schemes combined two surface cover rates of 50 and 70% and three spatial patterns: mulch over the entire flume length and two strips of 1/3 and 2/3 of the flume length, both located at the bottom part of the flume. The runoff-erosion experiments involved the simulation of a sequence of three rainfall events, the latter one combining the application of concentrated flow from upslope of the soil flume. Overall, mulching was more effective in reducing soil loss than runoff (50 vs. 25%) and was significantly more effective during the first rainfall event than during the following two events (83 v. 16% for runoff and 92 vs. 53% for soil loss). During the third event, mulching effectiveness dropped significantly with increasing rates of upslope concentrated flow. Overall, mulching was more effective when applied over the entire flume length than over the 1/3 and 2/3 flume's length strips, both in terms of runoff (24 vs. 21 and 13% at 50% soil cover and 41 vs. 33 and 16% at 70% soil cover) and of soil loss (44 vs. 50 and 33% at 50% soil cover and 71 vs. 60 and 39% at 70% soil cover). Even so, these differences were not significant. Therefore, strip-wise mulching can be an effective approach to substantially reduce costs or to maximize the area that can be treated. Its main disadvantage may be that it does not avoid runoff generation and associated transport process in the slope areas where no mulch is applied.