Qiong Wang

Understanding soil phosphorus (P) distribution and its key drivers is fundamental for sustainable P management. In this study, a 21-year fertilization experiment on black soil was carried out, setting up five fertilization treatments: unfertilized control (CK), nitrogen and potassium (NK), nitrogen, P and potassium (NPK), NPK plus straw (NPKS), and NPK plus manure (NPKM). The distribution and effecting factors of P pools within soil aggregates were investigated. Compared to CK, the NK and NPK treatments decreased calcium-associated P concentration in all aggregate fractions. Meanwhile, the NPK treatment significantly increased the organic P extracted from NaOH in unaggregated particles (3, and NaOH increased as aggregate size increased. This was mainly because straw or manure addition promoted soil organic carbon (SOC) storage in aggregates, creating more sorption sites via association with amorphous metallic minerals, and, thus, facilitating P accumulation. In conclusion, decreasing soil pH by chemical fertilizers is an effective strategy for mobilizing soil P, whereas increasing SOC by straw or manure facilitates P accumulation.

Phosphorus (P) leaching from excessive P application is the primary pathway of P losses in agricultural soils. Different P fertilizer practices have mixed effects on P leaching. We conducted a meta-analysis of the relevant literature regarding the response of crop yields, soil-available P (AP), and total P (TP) leaching to reduced P input (RP) and an inorganic-organic combination fertilizer (NPKM) for different agricultural land-use types. Compared to conventional P application (CP), RP (10~90% reduction) did not reduce crop yields in vegetable fields (experiments were 1~4 years) but significantly reduced cereal yields by 4.57%. Compared to chemical fertilizer (NPK), NPKM significantly increased cereal yields by 12.73%. Compared to CP, RP significantly reduced AP at 0~60 cm in vegetable and cereal fields. The greatest reduction occurred at 20~40 cm in vegetable fields (40.29%) and 0~20 cm in cereal fields (34.45%). Compared to NPK, NPKM significantly increased the AP at 0~60 cm in vegetable fields, with the greatest increase (52.44%) at 20~40 cm. The AP at 0~40 cm in cereal fields significantly increased under the NPKM treatment, with the greatest increase at 0~20 cm (76.72%). Compared to CP, RP significantly decreased TP leaching by 16.02% and 31.50% in vegetable and cereal fields, respectively. Compared to NPK, NPKM significantly increased TP leaching in vegetable fields (30.43%); no significant difference in leaching occurred in cereal fields. P leaching, in response to RP, was influenced by the P amounts applied (34.49%); soil organic matter (14.49%); and TP (12.12%). P leaching in response to NPKM was influenced by multiple factors: rainfall (16.05%); soil organic matter (12.37%); soil bulk density (12.07%); TP (11.65%); pH (11.41%). NPKM was more beneficial for improving yields in cereal fields with low soil fertility and lower P-leaching risks.

Understanding the effects of a fertilization regime on the long-term accumulation and transformation of soil phosphorus (P) is essential for promoting the development of sustainable management of soil P. Based on a 29-year field experiment in Mollisol, the compositions and changes of P forms using a modified Hedley sequential extraction method, solution ³¹P-NMR and P K-edge XANES and soil properties were investigated under continuous mono maize with and without manure (NPKM and NPK). Results showed a stronger positive related coefficient between soil total P and labile P, and mid-labile P fraction was found in NPKM than in NPK treatment. It indicated NPKM could improve the availability of soil accumulated P and reduce its transformation to stable P. Accumulated inorganic P (Pi) was dominated by aluminum phosphate (Al-P) and monobasic calcium phosphate monohydrate (MCP) for NPK treatment, Al-P, MCP, and tricalcium phosphate for NPKM treatment with XANES analysis, which contributed to the P availability in Mollisol. Moreover, the proportion of IHP with XANES and ratio of orthophosphate diesters to monoesters in NPK compared to NPKM indicated the higher Po lability with NPK treatment. Pi, especially NaHCO₃-Pi and NaOH-Pi, were the potential sources of resin-Pi. Soil organic matter (SOM), organic-bound iron, and alumina oxide (Fe_p + Al_p) showed significant influence on the transformation of P forms. Our research suggested that due to the rise in SOM and Fe_p + Al_p, the fertilization regime significantly increased most highly active soil P fractions, especially in NPKM treatment. This work gives new insight into sustainable P management, which benefits the reduction in soil P accumulation.

Phosphorus is an essential macronutrient, both as a component of several important plant structural compounds and as a catalyst in the conversion of numerous important biochemical reactions in plants. The soil Olsen P (OP) level is an important factor affecting crop production and P-use efficiency (PUE). We tested the effect of six OP levels and P doses on maize yield, where the P doses were 0, 22, 44, 59, 73, and 117 kg P₂O₅ ha⁻¹, with three replications, from 2017 to 2019. The response of crop yield to the OP level can be divided into two parts, below 28 mg kg⁻¹ and above 28 mg kg⁻¹. The change point between the two parts was determined as the agronomic critical level for maize crops in the study area. The PUE (%) increased with soil OP levels and decreased with P fertilizer application rates. In addition, results for the low P application rate (P2), 22 kg P₂O₅ ha⁻¹, showed that PUE significantly increased with an increase in the soil OP level compared with PUE at a low OP level (OP1), 0 kg P₂O₅ ha⁻¹. The PUE value increased by 49.5%, 40.1%, and 32.4% at a high OP level (OP6) in 2017, 2018, and 2019, respectively, compared to that at a low OP level (OP1). At the same OP levels, in all three years, the PUE at a high P application rate (P6) decreased significantly, in the range of 62.8% to 78.7%, compared to that at a low P application rate (P2). Under an average deficit of 100 kg ha⁻¹ P, the OP level of the soil in all three years decreased by 3.9 mg kg⁻¹ in the treatment without P addition (P1) and increased by 2.4–3.5 mg kg⁻¹ in the P treatments for each 100 kg ha⁻¹ P surplus. A phosphorus application rate of 44 kg P₂O₅ ha⁻¹ and an OP level of 28 mg kg⁻¹ are sufficient to obtain an optimum yield, increase the PUE, and reduce environmental hazards in the study area in northeastern China.