Microbial biomass, organic matter mineralization and nitrogen in soils from long‐term experimental grassland plots (Palace Leas meadow hay plots, UK)

Abstract

The Palace Leas meadow hay plots have received different annual manure and fertilizer applications since 1897 and represent the second oldest permanent grassland experiment in the world. Although the soil properties have diverged as a result of the experimental treatments since 1897, the soil organic carbon (SOC) contents of the plots have remained largely unchanged between the 1980s and 2006. In this study we have determined the effects of contrasting manure and fertilizer treatments on the total N contents of the soil, the recalcitrance of soil organic matter, the contributions made from different depths to the overall C mineralization, and the distribution of soil microbial biomass in the soil profiles. Relative to the control plot, which has received no manure or fertilizer additions since 1897, the two plots that have received manure or P plus K contain significantly more N, which in the case of the P plus K plot is consistent with abundant Trifolium spp. in the sward. The plot that has received farmyard manure (FYM) contained 11% more N than the control. The two plots that received large inputs of (NH4)2SO4 and which have consequently become highly acidic (around pH 4) contain 15–27% less N than the control despite the N addition and the accumulation of SOC in these plots. The plot that has only received P has also apparently lost total N (20%) relative to the control. The rates of C mineralization of the microbial biomass were closely related to total SOC contents but have been positively influenced by the increased N in the P plus K plot. Values for soil N, C mineralization rate and microbial C are reported because such data from sites that have been under known long‐term known land‐use are extremely rare and because there is increasing realization of the potential importance of soil data, especially biological characteristics, for monitoring environmental changes.