Nitrogen application favors soil organic phosphorus accumulation in calcareous vegetable fields.

Understanding soil P transformation is critical to optimizing P supply to crops while minimizing P loss to water. Nitrogen application in agricultural fields can cause acidification, changing soil chemistry and altering P cycling. In a calcareous vegetable field in China, 13 years of N application (1172 kg N ha−1 year−1) significantly decreased soil pH, CaCO3, and Mehlich-3 extractable (M3) Mg and increased M3-Fe and M3-Al. Nitrogen addition also increased microbial biomass C (MBC), decreased alkaline phosphomonoesterase (ALP) activity, and changed the total bacterial and phoD-harboring bacterial community composition. Soil total P, Olsen-P, and M3-P were not affected by N fertilization, but there were significant increases in soil total organic P (Po), NaOH-extractable Po, and the proportion of orthophosphate diesters. Redundancy analysis showed that soil pH, organic C, CaCO3, and ALP activity had significant effects on the compositions of soil P form (P < 0.05) and could explain 36.4, 13.3, 27.5, and 10.6% of the total variances observed in the composition of P forms. This suggests that soil acidification from N application in this P-rich calcareous soil altered soil abiotic P cycling processes through increasing the chemical adsorption of Po by Fe and Al. It also altered biotic P cycling processes by increasing microbial P uptake and immobilization and decreasing P biochemical mineralization, resulting in Po accumulation. [ABSTRACT FROM AUTHOR]