Early effects of surface liming on soil P biochemistry and dynamics in extensive grassland

Liming effects on soil phosphorus (P) availability via biological P cycling are not clear. We conducted an 18-month field experiment on a long-term (60 years +) permanent fertilized grassland in a relatively dry environment. The aim was to examine the impact of liming on P biochemical processes and dynamics. Lime was applied at the beginning of the experiment to produce a soil pH range of 5.4-7.0, with no fertilizer P treatments. Soil sampling was conducted throughout the experimentation period at 0-75 mm. All soils were analysed for moisture content, pH, Olsen P, resin P, exchangeable aluminium (Al), microbial biomass P (MBP) and enzyme activities. At the final sampling, the soil samples were analysed for total C, total N and anaerobic mineralizable N (AMN). A sequential P fractionation was conducted for 0-30 mm depth samples. Liming effects on soil pH and P processes were limited to the surface 30 mm only, where labile inorganic P (P-i) fraction increased by 42% at pH 7.0 compared to pH 5.4, while labile and moderately labile organic P (P-o) decreased by 33% and 25%, respectively. Strong positive relationships were found between microbial P and: soil pH, labile P-i, total C and AMN. Absolute activities of acid and alkaline phosphomonoesterases were not affected by liming. However, their specific activity decreased by 47% and 28%, respectively at pH 7.0 compared to pH 5.4. Absolute enzyme activity of phosphodiesterase correlated strongly and positively with labile P-i. Our findings demonstrate that liming enhances plant P availability under field conditions in long-term fertilized extensive grassland. However, the effects are limited to near-surface depths in the soil.