Exploring the resistive impact of vegetative grass strip spacing on soil loss and sediment-bound nutrients in an agricultural hillslope

Abstract

Soil erosion may continue to pose a serious threat to food security, particularly in Sub-Saharan Africa, as arable land continues to expand. Though considerable research has been carried out on the use of vetiver grass strips (VGS) to reduce soil erosion, information on the comparative effectiveness of VGS spacing in a monocropping system is limited. Therefore, a field trial was conducted during the early and late 2013 and 2014 cropping seasons at erosion demonstration site of the Institute of Agricultural Research and Training, Ibadan, to investigate the resistive impact of different VGS spacing on reducing surface runoff, soil and sediment-bound nutrient losses and improving crop yields on Alfisol. The treatments: VGS spaced at 5, 10, and 20 m surface intervals (5m-VGS, 10m-VGS, and 10m-VGS), as well as a control without VGS, were laid out in a randomized complete block design with a 7% slope in three replicates. The results showed that the average runoff from the control plot was significantly higher (p ≤ 0.05) than the VGS plots by 64–195%. 5m-VGS kept back more rainfall water from lost than other VGS (10m-VGS and 20m-VGS) plots. The resistive capacity of 5m-VGS in reducing soil loss and sediment-bound carbon, nitrogen and phosphorus surpassed other treatments by 20–369%, 33–912%, 19–914% and 19–574%, respectively. The VGS spacing had significant (p ≤ 0.05) influence on the yields of maize. The average maize grain yield increased by 75.4 to 342 kg ha-1 across the four cropping seasons. Though there was no significant difference in grain yields between 5m-VGS and 10m-VGS, 10m-VGS surpassed 5m-VGS by increasing grain yield by 5%.  Thus, the conservation benefit of 5m-VGS in reducing soil erosion was negated by its invasiveness and lower grain yield compared to 10m-VGS. From a scientific standpoint, considering an absence of significant differences in erosion control measures between 5m-VGS and 10m-VGS, 10m-VGS may be suggested on agricultural hillslopes ≤ 7% for erosion control and crop production.