Crops are usually planted on sloping land in mountainous areas due to limited suitable land area. This results in serious soil erosion and loss of nitrogen (N) and phosphorus (P) to land degradation and water eutrophication. It is important to adopt appropriate cultivation practices to change this situation. However, few long-term in situ measurements are available to assess the magnitude of effects of combined cultivation patterns on soil erosion and nutrient loss from sloping farmland with red soil, as well to quantify N and P losses through runoff and sediment transport. A field trial with the cash crop (CC) Nicotiana tabacum was carried out under natural rainfall conditions on sloping farmland with red soil in Yunnan, China during 2014–2017. Four cultivation patterns were applied. They included NVF (No fertilizer application + Vertical ridge + Film covered), OVF (Optimizing fertilizer application + Vertical ridge + Film covered), OHF (Optimizing fertilizer application + Horizontal ridge + Film covered), and OHFR (Optimizing fertilizer application + Horizontal ridge + Film removed). The first two treatments belonged to the vertical ridge (VR) group, and the remaining treatments belonged to the horizontal ridge (HR) group. Results indicated the HR group performed significantly better than the VR group, especially the OHFR treatment, in terms of the HR group producing average runoff (177.12–182.27 mm), sediment loss (2673.33–3309.17 kg·ha⁻¹), and nutrient loss of total nitrogen (TN) (7.58–7.93 kg·ha⁻¹), total phosphorus (TP) (1.00–1.09 kg·ha⁻¹) through runoff, TN (3.53–4.72 kg·ha⁻¹), TP (2.59–2.76 kg·ha⁻¹) through sediment. TN was lost mainly through runoff transport, while TP was lost mainly through sediment transport. On average, the HR group decreased runoff, sediment, total N and P loss by 39% to 73% relative to the OVF treatment, whereas NVF treatment increased 3% to 30% of those (p < 0.05). Under four cultivation patterns, total dissolved nitrogen (TDN) was the dominant form, which accounted for 71–77% of TN. The average percentage of NO₃⁻-N/TN was about 45–52%, much higher than NH₄⁺-N/TN of around 8–10% in runoff. Total dissolved phosphorus (TDP) made up about 48–59% of TP in runoff. Redundancy analysis (RDA) showed that sediment, runoff, and soil pH were the three key factors controlling nutrient loss. In conclusion, OHFR is recommended because it consistently outperformed other patterns in terms of reducing runoff, sediment, and nutrient losses.

Introduction: Evaluation of the changes in phosphorus (P) fractions (various P forms) and their availability at different soil layers is critical for enhancing P resource use efficiency, mitigating subsequent environmental pollution, and establishing a suitable manure application strategy. However, changes in P fractions at different soil layers in response to cattle manure (M), as well as a combined cattle manure and chemical fertilizer application (M+F), remain unclear in open-field vegetable systems. If the amount of annual P input remains the same, identifying which treatment would cause a higher phosphate fertilizer use efficiency (PUE) and vegetable yield while simultaneously reducing the P surplus is especially warranted.Methods: Based on a long-term manure experiment that started in 2008, we used a modified P fractionation scheme to analyze P fractions at two soil layers for three treatments (M, M+F, and control without fertilizer application) in an open-field cabbage (Brassica oleracea) and lettuce (Lactuca sativa) system, and assessed the PUE and accumulated P surplus.Results: The concentrations of the soil P fractions were higher in the 0–20-cm soil layer compared to the 20–40-cm layer, except for organic P (Po) and residual-P. M application significantly increased the inorganic P (Pi) (by 8.92%–72.26%) and the Po content (by 5.01%–61.23%) at the two soil layers. Compared with the control and M+F treatments, M significantly increased residual-P, Resin-P, and NaHCO3-Pi at both soil layers (by 31.9%–32.95%, 68.40%–72.60%, and 48.22%–61.04%), whereas NaOH-Pi and HCl-Pi at 0–20 cm were positively correlated with available P. Soil moderately labile-P was the predominant P component in the two soil layers (accounting for 59%–70%). With the same annual P input amount, M+CF created the highest vegetable yield (117.86 t ha-1), and PUE (37.88%) and M created the highest accumulated P surplus (128.80 kg ha^-1yr^-1).Discussion: Collectively, a combined manure-chemical fertilizer application has great potential to yield a long-term positive outcome both in terms of vegetable productivity and environmental health in open-field vegetable systems. This highlights the methods’ benefits as a sustainable practice in subtropical vegetable systems. Specific attention should be given to a P balance to avoid excessive P input if a rational strategy for manure application is to be attained. This is especially the case for stem vegetables that require manure application and decreases the environmental risk of P loss in vegetable systems.