Effect of long-term fertiliser use on acid and alkaline phosphomonoesterase and phosphodiesterase activities in managed grassland

Soil phosphatase activities play an important role in the mineralisation of soil phosphorus (P). In this study acid and alkaline phosphomonoesterase and phosphodiesterase activities of soils under long-term fertiliser management (ca. 100 years) were measured to determine the effects of fertiliser inputs on the cycling and availability of P. Enzyme activities were compared with microbial biomass P, determined by fumigation-extraction, and with extractable P using NH4F-HCl. Experimental plots were divided into three groups: those receiving farm-yard manure (FYM), those receiving mineral P and those receiving no P amendment. Plots receiving FYM had the highest extractable P values and the greatest enzyme activities. There was no obvious relationship between extractable P and microbial biomass P except in those plots where no P was added (r(2)=0.778), emphasising the importance of fertiliser management in P dynamics in soils. Acid phosphomonoesterase activity was high in all plots, including those where microbial biomass P levels were low. This supports the findings of previous studies suggesting that acid phosphomonoesterase activity in soils is primarily of root origin. All phosphatase enzyme activities were significantly correlated with extractable P in plots receiving mineral P. This relationship was negative for acid phosphomonoesterase activity (r(2)=-0.947), suggesting that acid phosphomonoesterase activity is suppressed by extractable P in managed grasslands receiving mineral P fertilisers.