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−1 vetiver grass mulch [VGM]), combined vetiver strips and mulch (10 m VGS + 4 Mg ha−1VGM), 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−1 VGM, and 10 m VGS + 4 Mg ha−1 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 water-stable 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−1 VGM < 10 m VGS < 10 m VGS + 4 Mg ha−1 VGM. Application of 6 Mg ha−1 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 < 6 Mg ha−1 VGM < 10 m VGS + 4 Mg ha−1 VGM. The results indicate that an integration of vetiver buffer strips and mulch (10 m VGS + 4 Mg ha−1 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.
1Obafemi Awolowo University, Institute of Agricultural Research and Training, Moor Plantation, Ibadan, Nigeria. Mr. Kayode S. Are is corresponding author. E-mail: firstname.lastname@example.org
2Agronomy Department, University of Ibadan, Ibadan, Nigeria.
Received August 13, 2010.
Accepted for publication February 23, 2011.