Vetiver grass hedgerows significantly reduce nitrogen and phosphorus losses from fertilized sloping lands

Runoff and over-use of fertilizers have been considered as two major factors accelerating the discharge of nitrogen (N) and phosphorus (P) from agricultural fields to surface water. The practice of vetiver grass hedgerows (VGH) can check sediments and runoff pollutants from agricultural fields. However, the efficiency of VGH in reducing N and P losses while maintaining optimum crop yields is still unclear under a recommended fertilization rate. A three-year field experiment was conducted on a 10 ^o sloping land to know how VGH can reduce the discharge of runoff nutrients to surface water bodies and maintain optimum crop yields, and to understand the relationships between changing soil properties and reduction of sediments N and P due to the adoption of VGH. Five fertilization treatments to VGH were examined under VGH plus organic fertilizer (VGH + OF), VGH plus inorganic fertilizer (VGH + IF), sole organic or inorganic fertilizer (OF or IF) and no VGH and fertilizer (Control). Runoff nutrient pollutants PO₄^-, NO₃^--N and NH₄⁺-N were significantly (P < 0.01) reduced by VGH + OF compared to OF by 97%, 94% and 95% and VGH + IF compared to IF by 95%, 88% and 89% respectively for 2012, 2013 and 2014. Sediment nutrients N and P were significantly (P < 0.01) reduced by VGH + OF compared to OF by 98% and 99%, and VGH + IF compared to IF by 94% and 99%, respectively. Improved soil properties by VGH significantly (P < 0.01) reduced runoff pollutants and consequently increased maize yields. Our results imply that runoff erosion, rather than fertilization, is a major driving force for agriculture-derived water pollution. Adoption of VGH with a recommended fertilization rate could significantly reduce N and P nutrient losses from agricultural fields and consequently improve water quality as well as maintaining optimum crop yields on sloping lands.