Under extreme rainfall and cropping practices, the runoff-induced loss of nitrogen (N) and phosphorus (P) becomes a primary non-point pollution source, threatening water quality and ecosystem integrity. The hedgerow-grass ditch systems (HGDS) are a recognized soil erosion control measure on slopes. However, its efficacy in reducing N and P losses across varying rainfall magnitudes (RMs) and cropping systems remains unclear. In this 3-year field study (2022–2024) in a Regosols citrus orchard, we evaluated clean-tilled citrus orchard control (CK) and 5 treatments (T1-T5), namely Trifolium repens L. HGDS in citrus orchard (T1), Chrysopogon zizanioides (L.) Roberty HGDS in citrus orchard (T2), agroforestry citrus orchard (citrus intercropping with vegetables) (T3), Trifolium repens L. HGDS in agroforestry citrus orchard (T4), Chrysopogon zizanioides (L.) Roberty HGDS in agroforestry citrus orchard (T5), across 26 erosive events spanning four RM categories (moderate rain, heavy rain, rainstorm, and large rainstorm). Runoff depth (RD), sediment yield (SY), and the concentrations and losses of total, dissolved, and particulate N and P (TN, DN, PN, TP, DP, PP) were measured. Surface runoff was initiated at 24‑h rainfall above 20 mm. Compared to CK, 5 treatments (T1–T5) significantly reduced RD (26–71%), SY (62–89%), TN loss (57–86%), and TP loss (58–81%). Treatment DN comprised 57–75% of TN loss, whilst DP accounted for 43–50% of TP loss. As RM increased from moderate to large rainstorm, RD, SY, and N and P losses increased sharply, with strong positive correlations observed in CK. These responses were significantly attenuated under HGDS treatments. The results demonstrate that HGDS, especially when integrated with agroforestry, can effectively buffer rainfall impacts and substantially lower nutrient exports from sloping orchard systems. This study provides mechanistic insight and empirical support for adopting HGDS as a sustainable management practice to mitigate non-point source pollution and enhance the ecological resilience of hillslope agriculture. • Daily rainfall threshold > 20 mm triggered runoff in citrus orchards. • Hedgerow-grass ditch systems (HGDS) consistently reduced runoff and sediment yield. • HGDS always reduced nitrogen (N) and phosphorus (P) loss across rainfall intensities. • Heavy rainfall raised dissolved N and particulate P shares in total losses. • In intercropped orchards, HGDS cut both N and P losses by over 60%.
Zhao et al. (Fri,) studied this question.