Use of Vetiver Grass for Soil and Water Conservation in Nigeria

摘要

Soil erosion persists on agricultural lands in Nigeria. To curb erosive land degradation requires soil conservation measures that are cheap, replicable and sustainable. The use of vetiver grass ( Vetiveria zizanioides) has offered such prospects in a wide range of climatic environments. Although the grass grows in Nigeria, its potential for soil and water conservation and improved crop yield has not been realzed, let alone quantified.A study was conducted at the Teaching and Research Farm of the University of Ibadan, Nigeria (7°24′ N, 3°54′ E) for three growing seasons to assess:( i ) the effectiveness of vetiver grass on soil and water loss,( ii ) soil moisture retention and,( iii ) crop yields. Vetiver strips were established on 6 % slopes at a surface interval of 20 m on erosion plots measuring 40 m × 3 m each. Plots with and without vetiver strips constituted the treatment and control, respectively. Each was replicated thrice and laid out in a randomized complete block design. Neutron probe access tubes were installed to a depth of 1 m at 10 m from the upslope end of the plots and lm behind the first vetiver strip to enable soil weekly moisture measurements at those points using a neutron moisture meter at 10 cm depth-intervals down to 80 cm depth. The plots, laid bare in the first season to determine the maximum efficiency of the vetiver strips, were sown to cowpea in the second season and maize in the third season when actual runoff and soil loss from each plot were determined using soil and water collecting devices at the end of each plot. In the first season, soil accumulation at the vetiver strips was estimated using calibrated rods. Results showed that first vetiver strip on the slope accumulated 98 % more soil than lower vetiver strips in the first year. Vetiver strips increased cowpea seed and stover yields by 11.1% and 20.6 % , respectively and increased soil moisture storage by a range of 1.9% to 50.1% at various soil depths. Maize yield increased by 50% . Soil loss and runoff water were 70% and 130% higher on non-vetiver plots than vetiver plots. Eroded soils on non-vetiver plots were consistently richer in nutrient contents than on vetiver plots. Nitrogen use efficiency was enhanced by about 40 %.