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Vetiver grass hedgerows significantly trap P but little N from sloping land: Evidenced from a 10-year field observation

Huang, Zhigang, Oshunsanya, Suarau Odutola, Li, Yong, Yu, Hanqing, Are, Kayode Steven
Agriculture, ecosystems & environment 2019 v.281 pp. 72-80
Chrysopogon zizanioides, agricultural land, clay, crop yield, field experimentation, land degradation, nutrients, particle size distribution, silt, soil, solubility, surface water, topographic slope, trapping, water erosion, water pollution
The removal of soil N and P nutrients from sloping land by water erosion can cause land degradation and surface water pollution if not prevented. Vetiver grass hedgerows (VGH) established across the slope could help in trapping and stocking nutrients but its long-term impacts on N and P have not been studied. A 10-year field experiment was conducted to i) determine the effectiveness of different spacing of VGH to trap N and P discharged from sloping land, and ii) clarify the underlying mechanisms causing differences in N and P stocks by the establishments of VGH. Treatments consist of three VGH established at 5 m (VGH5m), 10 m (VGH10m), 20 m (VGH20m) intervals and a control (plot without VGH). Trapped sediment N, P and particle size distribution were determined. VGH significantly (p < 0.01) trapped P but little N when compared to control. P trapped under different spacing of VGH relative to control decreased in the following order: VGH5m (0.84 kg m−2), VGH10m (0.59 kg m−2) and VGH20m (0.48 kg m−2), with the P trapped efficiencies of 62.7%, 44.0% and 35.8% respectively. Clay trapped were significantly (p < 0.05) higher in VGH5m (1.30 kg m−2), VGH10m (1.13 kg m−2) and VGH20m (1.01 kg m−2) plots than control with clay trapped efficiencies of 55.1%, 48.3% and 43.0% respectively. Also, silt trapped were significantly (p < 0.05) higher in VGH5m (0.99 kg m−2), VGH10m (0.86 kg m−2) and VGH20m (0.55 kg m−2) plots than control with silt trapped efficiencies of 28.4%, 24.7% and 15.9% respectively. P trapped efficiency by VGH was significantly (p < 0.01) positively correlated to silt + clay trapped efficiency indicating that clay + silt trapped by VGH can retain P. But there was no significant relationship between N trapped efficiency and silt + clay trapped efficiency due to high solubility of N. Increased maize yields were significantly positively related to N (r2 = 0.96; p < 0.01), P (r2 = 0.97; p < 0.01) and C (r2 = 0.98; p < 0.01) trapped by VGH. Our results imply that VGH trapped fine soil particles (silt + clay particles) that retained P but could not retain significant amount of N. The establishment of VGH across the sloping land will significantly reduce nutrient loss within eroded agricultural landscape and consequently increase crop yields.