Composition of phosphorus species and phosphatase activities in a paddy soil treated with manure at varying rates

Rice paddy soils can act as natural bioreactors for retaining excess nutrients from manure. A paddy soil after receiving swine manure at four rates (0 [CK], 26 [M-1], 39 [M-2], 52 [M-3] kg P ha(-1)) for nine years was selected to determine the effects of long-term manure amendment on the composition of P species and phosphatase activities in the paddy soils. Long-term manure amendment at up to the M2 rate enhanced the P composition (mainly as orthophosphate and/or myo-IHP) but only in the plough layer (20-cm layer) of the paddysoil. Moreover, higher rates were not significantly beneficial for enhancement. The activities of alkaline-phosphomonoesterases, phosphodiesterases, and pyrophosphatases increased with the increase in manure amendment rate, whereas no significant difference in neutral phosphomonoesterase activity was found between M-2 and M-1 or M-3 treatments. The results suggest that P availability in paddy soils would be best maintained by mid-level swine manure amendment. (C) 2016 Elsevier B.V. All rights reserved.