Hedgerow-grass ditch system effectively reduces sediment yield and nitrogen loss with surface runoff during simulated rainfall

Abstract

Hedgerow-grass ditch systems combine the advantages of contour planting and ecological grass ditches and have better soil and water conservation (SWC) benefits; however, there is a lack of a comprehensive understanding of their combined effects on sediment yield (SY) and N loss with surface runoff. To study the efficient management of hedgerow-ditch system runoff and nutrient loss in sloping farmland, an adjustable slope with a gradient of 15° and a drainage ditch with a gradient of 16° were used under typical erosive rainfall of 60 mm h⁻¹. Four treatments, including control check (CK), bare slope (a slope without hedgerow and ditch system); T1, hedgerow slope (a hedgerow slope without a ditch system); T2, bare slope-soil ditch system (a bare slope with a soil ditch system); and T3, hedgerow-grass ditch system (a slope with hedgerow and a grass ditch system), were used to assess their impacts on runoff depth (RD), infiltration rate, sediment yield, and the concentration and loss quantities of total nitrogen (TN), dissolved nitrogen (DN), and particulate nitrogen (PN) and DN/TN in runoff. The results indicated that, compared with CK, the RD under T1, T2, and T3 were significantly decreased by 16.6 %, 14.4 %, and 54 %, respectively. The infiltration amounts under T1, T2, and T3 were significantly increased by 52.9 %, 45.7 %, and 171.9 %, respectively. The sediment concentration and SY rate were significantly reduced by 69.9 % and 94.9 %, and 22.1 % and 93.3 % under T1 and T3, respectively, but increased by 43.9 % and 274.7 % under T2 relative to CK. The diverse forms nitrogen (TN, DN, and PN) concentrations and losses under T3 were significantly reduced by 21 %, 10.4 %, 30.2 %, and 64.6 %, 57.6 %, and 67.1 %, respectively. The runoff DN/TN ratio was 53 %, revealing that DN was the primary type of N loss. Regression analysis showed that the RD exerted a more pronounced influence on TN loss across the four treatments, and a power function (R² > 0.98, p < 0.01) of the cumulative RD could be used to predict TN, DN, and PN losses. Principal component analysis demonstrated that the hedgerow-grass ditch system affected slope nitrogen loss by changing the infiltration rate and DN/TN ratio. Our study demonstrates that the hedgerow-grass ditch system effectively reduced the sediment yield and N loss and could be used as an effective means of N control on sloping farmlands.