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.

The effects of different types of phosphate fertilization on the phosphorus (P) adsorption-desorption in low-P red soil remain unclear. A field plot location test was carried out, and fifteen red soil samples were collected at depths of 0–20 cm from five phosphate fertilizers (CK—no-phosphate, SSP—single superphosphate, CMP—calcium magnesium phosphate, MAP—monoammonium phosphate, and DAP—diammonium phosphate) after the maize was harvested to evaluate the soil physicochemical properties, P adsorption, and desorption characteristics. The structural equation model (SEM) and adjacent tree method (ABT) were used to quantitatively analyze the relative contribution of P adsorption and desorption. The yield, P accumulation, and the P use efficiency of maize were the highest under SSP and CMP treatments. The P adsorption amount was CK > DAP > MAP > CMP > SSP, and the P desorption amount was DAP > MAP > CMP > SSP > CK. Compared with the CK treatment, P adsorption of other P treatments reduced by an average of 21.4%, while P desorption increased by 154.8%. The effect of different types of phosphate fertilizers on soil P adsorption was mainly through regulation of soil organic matter (SOM) and Olsen P, and the effect on soil P desorption was mainly through regulation of SOM and CaCO₃. Al₂O₃ had the greatest effect on P adsorption with a relative contribution rate of 31.52%, and SOM had the greatest effect on P desorption with a relative contribution rate of 53.04%. SSP and CMP treatments had an optimal matching with acidic red soil, which can promote P adsorption, effectively slow down P loss, improve P utilization, and increase crop yield.

Phosphorus (P) application can enhance soil P availability and alter P fractions. However, the P accumulation and transformation of different P sources in low-phosphorus red soil remain unclear. Two-year (2018–2019) field experiments were conducted to investigate the effects of five P source treatments (CK—no phosphorus; SSP—superphosphate; MAP—calcium–magnesium phosphate; DAP—monoammonium phosphate; and CMP—diammonium phosphate) on the P accumulation of maize and soil P fractions in low-P red soil using the Hedley Sequential Method. The results showed that P application significantly increased P uptake, Olsen-P, total phosphorus, and most of the soil P fractions. Compared to the CMP, MAP, and DAP treatments, SSP had a relatively higher P accumulation and labile P pool, with a slightly lower moderately labile P pool. The SSP treatment mainly increased soil-available P content and crop P uptake by increasing the labile P pool (resin-P and NaHCO₃-Pi) and reducing the moderately labile P pool and non-labile P pool. The P activation coefficient (PAC%) and Olsen-P were positively correlated with labile P (resin-P, NaHCO₃-Pi, and NaHCO₃-Po) and moderately labile P (NaOH-Pi and 1 M HCl-Pi) and negatively correlated with Fe₂O₃ and Al₂O₃. The results suggest that SSP has a priority effect on the crop P uptake and soil P availability in low-P red soil.