Long-term organic fertilization increases phosphorus content but reduces its release in soil aggregates

There is currently limited published information on the coupling correlation between phosphorus (P) redistribution and release in soil aggregates. To fulfill this gap, we conducted a 10-year field experiment of soil amended with organic fertilizer to investigate phosphorus transformation and immobilization during the organic fertilization process. Microbial communities, functional genes and enzymes were analyzed to elucidate the multi-mechanisms of the conversion among phosphorus fractions. Phosphorus content in soil aggregates was determined as follows: FeP (34 % ~ 45 %) > Ca-P (16 % ~ 27 %) > Oc-P (15 % ~ 17 %) > Or-P (13 % ~ 19 %) > Al-P (4 % ~ 5 %) ≈ Ex-P (2 % ~ 4 %). Compared to a control with only chemical fertilizer, a 13 % ~ 38 % increase in P availability of experimental treatments mixed with chemical and organic fertilizers was attributed to the mineralization of Or-P, but not to the dissolution of inorganic P. Following organic fertilization, the phnF gene was dominant factor to promote the mineralization of Or-P, because it encodes CP lyases that pyrolyzes the CP bounds in organophosphate esters. Overall, organic fertilization decreased P release risk in soil aggregates, especially for the micro-aggregates that showed a higher capacity to activate non-available P and immobilize endogenous P in farmland soil. These results provide a theoretical guidance for the source control of P pollution in agro-ecosystems.