Seasonal and fertiliser effects on microbial phosphorus and nitrogen in soils under pasture

Abstract

Significant quantities of phosphorus (P) and nitrogen (N) are present in the soil microbes compared with pasture requirements for these nutrients. Seasonal and fertiliser effects on microbial P and N were investigated in a controlled environment (CE) experiment, two field trials and a glasshouse trial. In the CE experiment there was a basic seasonal pattern of storage of P and N by the microbial biomass over "winter" and release of these nutrients in "spring". Climatic variations affected this pattern in the field trials. Withholding fertiliser did not affect soil microbial P and N in the field trials, despite a decline in pasture production of up to 20%. Soil microbial P and N did decline in the glasshouse trial, in which a much larger drop in herbage production (X30%) was induced by nutrient deficiency. Keywords soil microbial biomass, microbial phosphorus, microbial nitrogen, seasonal effects, withholding fertiliser, plant nutrients