Soil accumulation by VGH serving as barriers to trap eroded soil was significantly (p < 0.05) affected by the spacing. The average depth of soil accumulated per VGH spaced at 5 m, 10 m and 20 m wide intervals over three years were 32.17, 67.21 and 159.7 mm respectively while depth of soil removed on the control plot was 168.0 mm. Gravimetric moisture content increased with wider alley spacing and infiltration characteristics were improved in the alleys. Mean maize grain yield over the three growing seasons was significantly (p < 0.05) higher in vetiver grass alleys of 5, 10 and 20 m than the control by 34.4%, 23.3% and 6.5%, respectively. Cassava tuber yields were higher in vetiver alleys than the control by 1.7 to 4.7% in the first season, 2.8 to 5.1% in the second season and 3.6 to 7.0% in the third season, following the same trend as maize yields. The greater loss of soil under maize and cassava intercropped on plot without vetiver grass resulted in a decrease in the yields of crops as compared to vetiver alley plots. Although crop yields in VGH plots were higher than on the control, areas of land taken out of cultivation by VGH spaced at 5, 10 and 20 m wide intervals were 120, 60 and 30 m2 ha− 1, respectively at the end of the third season when the vetiver was 52 months old. Thus, a balance needs to be struck between the number of hedges with respect to slope and the area of land left for cultivation.
Soil accumulation by VGH serving as barriers to trap eroded soil was significantly (p < 0.05) affected by the spacing. The average depth of soil accumulated per VGH spaced at 5 m, 10 m and 20 m wide intervals over three years were 32.17, 67.21 and 159.7 mm respectively while depth of soil removed on the control plot was 168.0 mm. Gravimetric moisture content increased with wider alley spacing and infiltration characteristics were improved in the alleys. Mean maize grain yield over the three growing seasons was significantly (p < 0.05) higher in vetiver grass alleys of 5, 10 and 20 m than the control by 34.4%, 23.3% and 6.5%, respectively. Cassava tuber yields were higher in vetiver alleys than the control by 1.7 to 4.7% in the first season, 2.8 to 5.1% in the second season and 3.6 to 7.0% in the third season, following the same trend as maize yields. The greater loss of soil under maize and cassava intercropped on plot without vetiver grass resulted in a decrease in the yields of crops as compared to vetiver alley plots. Although crop yields in VGH plots were higher than on the control, areas of land taken out of cultivation by VGH spaced at 5, 10 and 20 m wide intervals were 120, 60 and 30 m2 ha− 1, respectively at the end of the third season when the vetiver was 52 months old. Thus, a balance needs to be struck between the number of hedges with respect to slope and the area of land left for cultivation.
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