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Water erosion remains a major threat to soil and water conservation in the humid tropics and, thus, requires effective conservation measures to curb it. To quantify the efficacy of vetiver grass (Chrysopogon zizanioides L.) strips and mulch in soil structural quality buildup and in reducing the eutrophic quality index and enrichments ratios of major nutrients, a study was conducted between 2007 and 2009 on eroded landform (8% slope) of a Typic Kanhapludalf in a subhumid region of southwestern Nigeria. Treatments were vetiver buffer strips (10 m vetiver grass strip [VGS]), vetiver mulch (6 Mg ha j1 vetiver grass mulch [VGM]), combined vetiver strips and mulch (10 m VGS + 4 Mg ha j1 VGM), and a control (no buffer strips or mulch). Soil structural quality estimated by water-stable aggregates at 0-to 5-cm depth increased by 36%, 73%, and 64% under 10 m VGS, 6 Mg ha j1 VGM, and 10 m VGS + 4 Mg ha j1 VGM, respectively, more than the control. The corresponding increase in mean weight-diameter under the vetiver systems was 30%, 42%, and 47% higher than the control. The waterstable aggregates and mean weight-diameter at the 5-to 15-cm depth followed a similar trend in the 0-to 5-cm layer. The resistive potentials of the vetiver systems in reducing soil loss, sediment-associated nutrients, total suspended solids, and eutrophic quality index were significantly higher than the control because of an increase in surface hydraulic roughness, which were in the order of 6 Mg ha j1 VGM G 10 m VGS G 10 m VGS + 4 Mg ha j1 VGM. Application of 6 Mg ha j1 VGM appear to be better than 10 m VGS and contributed to the reduction of runoff and enrichment ratios, thus, changing the order to 10 m VGS G 6 Mg ha j1 VGM G 10 m VGS + 4 Mg ha j1 VGM. The results indicate that an integration of vetiver buffer strips and mulch (10 m VGS + 4 Mg ha j1 VGM) had a better control of runoff, soil loss, sediment-associated nutrients, and water quality degradation, as well as improving soil structural quality buildup when compared with vetiver buffer strips or mulch alone.

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This study investigates the influence of vetiver grass strips (VGS), vetiver mulch (VGM) and composted vetiver prunes (veticompost) on soil quality of an eroded land in the Institute of Agricultural Research and Training, Ibadan (7 0 22 ' N; 3 0 50 ' E), Nigeria. The treatments were 3-m wide VGS established at 10-m inter-row spacing, VGM imposed at 5 Mg ha-1 , veticompost applied at 5 Mg ha-1 and a control (no-vetiver grass). All quality indicators including physical, chemical and biological indices and soil erodibility (K) factors were determined between 2008 and 2011. Results show that soil organic matter (SOM) and associated nutrients play a major role in soil quality variation. VGM had the highest impact on soil quality (76.5%) but not significantly different (P<0.05) from veticompost (72.5%). Soil quality ratings were in the order of VGM > veticompost > VGS > control. Significant and positive relationship (r = 0.92*) exist between soil quality ratings and maize yield, with 70% of grain yield variability accounted to the soil quality. K factor ranged from 0.013 to 0.030 Mg h MJ-1 mm-1 with the VGM and control plots having the least and highest K factors, respectively. Although the soil quality under veticompost is lower than vetiver mulch but the SOM and associated nutrients under veticompost enhanced better soil productivity, and thus accounted for higher crop yields than other treatments.