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 a nd phosphodiesterase activities of soils under long-term fertiliser managem ent (ca. 100 years) were measured to determine the effects of fertiliser in puts on the cycling and availability of P. Enzyme activities were compared with microbial biomass P, determined by fumigation-extraction, and with ext ractable P using NH4F-HCl. Experimental plots were divided into three group s: those receiving farm-yard manure (FYM), those receiving mineral P and th ose receiving no P amendment. Plots receiving FYM had the highest extractab le P values and the greatest enzyme activities. There was no obvious relati onship 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 h igh in all plots, including those where microbial biomass P levels were low . This supports the findings of previous studies suggesting that acid phosp homonoesterase activity in soils is primarily of root origin. All phosphata se enzyme activities were significantly correlated with extractable P in pl ots receiving mineral P. This relationship was negative for acid phosphomon oesterase activity (r(2)=-0.947), suggesting that acid phosphomonoesterase activity is suppressed by extractable P in managed grasslands receiving min eral P fertilisers.