Effect of grassland management on N mineralization potential, microbial biomass and N yield in the following year.

Abstract

The effect of mowing or grazing and mineral fertilizer level on N mineralization potential and microbial biomass N (N flush) was studied in 1988 on a sandy soil and a sedimentary calcareous silty loam (loam) in the Netherlands. On the loam the residual effect of the treatments on N yield and herbage dry matter accumulation in the following year was also studied. The different management practices were started in 1985 on the sandy soil and in 1986 on the loam. The amount of microbial biomass N was larger under grazing than under mowing. The increase in the amount of microbial biomass N due to grazing was larger for the loam than for the sandy soil. The N-mineralization rate was higher under grazing than under mowing. The difference in N-mineralization rates between grazed and mown fields was 20-30 % in April for both soils, but increased considerably in the sandy soil during the growing season. It was estimated that the difference in N-mineralization between mown and grazed plots under field conditions was 110 and 40 kg N/ha per year in the sandy soil and the loam, respectively. Thus the optimum N fertilizer application rate should be considerably lower under grazing conditions than under mowing conditions, especially on sandy soil. Fertilizer level had no effect on the amount of microbial biomass and rates of N-mineralization. Both grazing compared to mowing and increasing N fertilizer levels above 550 kg N/ha per year affected the N yield and dry matter accumulation in the following year (= residual effects) on the loam. These effects were greater for N yield than for dry matter accumulation. The residual effect of previous fertilizer input was probably caused by the presence of different amounts of N in roots and stubble. The residual effect on N yield under grazing exceeded that under mowing by 28%. (Abstract retrieved from CAB Abstracts by CABI’s permission)