Effects of vetiver grass (Vetiveria nigritana) strips, vetiver grass mulch and an organomineral fertilizer on soil, water and nutrient losses and maize (Zea mays, L) yields

Soil erosion remains a serious problem on most agricultural fields especially in the humid tropics. Experiments were conducted between 2003 and 2005 to test the efficiency and efficacy of using vetiver grass strip (VGS), vetiver grass mulch (VGM) and an agronomic practice of using an organomineral fertilizer (OMF) capable of improving soil structure and a control, as treatments, on soil and water conservation and improvement of maize yields. The treatments, in three replicates, were laid out in a randomized complete block design on 7% runoff plots on an Alfisol in the sub humid region of Southern Nigeria. Soil physical conditions were significantly best under VGM plots and least under VGS plots. Nevertheless, runoff and soil loss were generally in the increasing order of VGS, VGM and OMF. Although mean runoff and soil loss on VGS plots were 36.6% and 28% of the value of the control plot in 2003, when 2 tonnes/ha of vetiver grass mulch was applied to the control plot in 2004, these values were increased to 61.5% and 48.4%, respectively indicating a significant reduction of runoff and soil loss on the mulched plots. Vetiver grass mulch (VGM) at 6 tonnes/ha was more effective than VGS plots in reducing runoff than soil loss. Whereas mean runoff for VGM, VGS and OMF plots were 28.67, 38.44 and 42.44 mm, respectively, the corresponding mean soil losses at 6 tonnes/ha were 980.5 kg/ha, 389 kg/ha and 1251 kg/ha, respectively. Mean soil losses were 629 kg/ha and 591.5 kg/ha higher on VGM than VGS plots at 4 tonnes/ha and 6 tonnes/ha, respectively. Mean No₃-N levels of runoff water on the VGS plots were 40.4% and 65.6% of the levels of the OMF and the control plots, respectively over 2003 and 2004. Nutrient loads of eroded sediments were highest for OMF plots and least for VGS plots. Carbon, Nitrogen and P contents of eroded sediments were 22–23.5%, 12–35.9%, and 20.6–37.6% lower on VGS plots than other treatments.

The significant beneficial effect of OMF in producing the highest yields was dwarfed by the potential danger of water pollution by nutrient loads in the absence of a soil erosion control measure. Although the differences were not significant, grain yields on VGM plots were 4% and 47.4% higher than on VGS plots when 4 and 6 tonnes/ha of grass mulch were applied.