Application of microbiological knowledge in growing media based cultivation systems

Cropping systems with growing media offer a range of possibilities to control the microbiological quantity and quality in the root environment. Carbon is often limiting microbial activity in naturel ecosystems. However, in growing medium systems, little is known about the availability of carbon or of extracellular enzyme activities breaking down complex organic molecules. Here we studied how, in peat based growing medium, different fertilizers affected the easily available carbon as well as availability of nitrate and nitrite extracellular enzyme activities in a greenhouse experiment with tomato plants. The inputs of digestible carbon on a day-to-day basis in a first experiment were a) the growing medium (between 1000 and 1500 mg C m^-2 d^-1); the plant (between 100 and 500 mg C m^-2 d^-1); organic fertilisers (between 250 and 2000 mg C m^-2 d^-1). The digestible C input was thought to be directly related to microbial activity but still subject to influence of abiotic factors like temperature, water content, oxygen content and pH. Transient accumulation was found for ammonium and nitrite. In conclusion, it is possible to maintain a desirable level of microbiological activity (related to 1000-3000 mg C m^-2 d^-1) with technical measures including the choice of growing medium; plant species; the supply quantity, frequency and quality of organic fertilisers and organic additives; and the values of temperature, water content, oxygen content and pH.