Soil microbiological and biochemical properties affected by plant growth and different long-term fertilisation

The purpose of this study was to measure the effects of plant growth on soil microbial biomass C (Cmic) and soil enzyme activities. In a pot experiment using spring barley and sugar beet, we investigated the response of Cmic, hot water extractable C and N fractions (Chwe, Nhwe), and enzyme activities involved in C, N and P cycling in a loess-derived Chernozem from Bad Lauchstädt (Central Germany). The study site has been receiving the same fertilisation treatments for 100 years. The soil originated from plots fertilised with 15 t ha−1 farmyard manure (FYM) year−1 + mineral fertiliser (NPK), or 15 t ha−1 FYM year−1, or NPK or from an unfertilised control. Pots were sampled monthly, and alkaline phosphatase- (AP), β-glucosidase- and protease-activities were analysed. At the beginning and the end of study, levels of Cmic, Chwe and Nhwe were also measured. All three enzyme activities and Cmic were significantly and positively correlated with Corg and Chwe. Results suggest that the enzyme activities measured originated mostly from microorganisms and that Chwe is an important C source for soil microorganisms. β-Glucosidase and AP activities were higher in summer months than at other times. In contrast, protease activity changed only slightly during the growing period.