How agricultural management practices affect nitrogen transportation and redistribution under the drying-rewetting process of loessial sloping lands?

Abstract

Nitrogen (N) is one of the most common macronutrients applied to soil to promote crop productivity, but no more information can be found in the effect of different management practices on the surface pathways of N loss in the process of drying-rewetting alternation. In this study, the laboratory intermittent rainstorms were adopted to quantify the mechanism and implication of agricultural interventions on slope runoff N fractions. Results indicate that: (i) The threshold ranges of sediment yield rate under 0% and 3% biochar vegetated slopes are generally smaller than that of bare slope while 6% biochar is just the opposite, but all of them increased with increased rainfall intensity. Horizontal ridge and vegetation strips show good performance on reducing sediment and fixing N under 0–3% biochar application, but the sediment and N loss increased dramatically when the biochar application increased from 3% to 6%. (ii) N loss can be aggravated from P3 (conventional flat planting + 3% biochar) to H6 (horizontal ridge planting + 6% biochar) on 10° bare slope and 120 mm·h-1 heavy rainstorm due to the drying-wetting cycle and the redistribution of eroded soil particles, but N loss on 10° vegetated slopes experienced overall significant decreases because vegetation combined with horizontal ridge or appropriate biochar curtail erosion and retain sediment. (iii) The hydrological pathways transporting various N fractions vary with different management practices. e.g., the particulate fractions in H6 of vegetated slope is 90.29% while 44.88% in bare slope under 120 mm·h-1, indicating biochar in excessive application would increase the loss of particulate nutrients under heavy rainstorms even with vegetation and horizontal ridge. The results will be helpful to parameterize from a lower scale or disaggregate from a higher scale in the runoff nutrient management of agroecological systems of the Loess Plateau.