Long-term organic substitution management affects soil phosphorus speciation and reduces leaching in greenhouse vegetable production

Excessive phosphorus (P) fertilizer and manure application is widespread in greenhouse vegetable production, causing P accumulation and groundwater pollution. The partial substitution of chemical fertilizer with organic amendments may effectively address this problem; however, little is known about P speciation and transformation at the molecular scale. Here, we combined P K-edge X-ray absorption near-edge structure, 31P nuclear magnetic resonance spectroscopy, and chemical extraction to characterize P speciation and assess P leaching in a 10-year field experiment including chemical fertilizer (4CN) and replacement of half the chemical N fertilizer with manure (2CN+2 MN), straw (2CN+2SN), or combined manure and straw (2CN+1 MN+1SN) treatments. Compared to the 4CN treatment, organic substitution treatments resulted in 10.0–16.3% lower P accumulation and 57.3–102% higher organic P. Newberyite was detected in the organic substitution treatments, making up 6.9–13.0% of the total P, and the hydroxyapatite proportion was 7.3–15.6% lower than that in the 4CN treatment. Moreover, 2CN+2 MN treatment increased the orthophosphate diester content and labile P (Resin-P and NaHCO3–P) proportion, and 2CN+2SN treatment increased the orthophosphate monoester content and moderately labile P (NaOH–P) proportion. The 2CN+1 MN+1SN treatment exhibited the advantages of both manure and straw application. Partial least squares path modeling revealed that labile P was affected mainly by manure application and pH, and moderately labile P was influenced mainly by straw application and alkaline phosphomonoesterase activity. Compared with the 4CN treatment, the organic substitution treatments significantly decreased the total P leaching losses by 21.3–48.8%. Our results provide new insights into soil P transformation in response to different organic amendments. Combined manure, straw, and chemical fertilizer application (2CN+1 MN+1SN treatment) was a more effective practice for developing sustainable P management practices by comprehensively considering soil P transformation, vegetable yields, and environmental losses.