Factors limiting soil microbial growth and activity in wheat-based cropping systems
Several soil biochemical processes related to soil fertility are microbially mediated. We know very well the factors limiting crop production but know little of the factors limiting the soil microbial community. The goal of this study is to clarify if N, P and C limit soil microbial growth and biochemical processes in the wheat and fallow phases of rotations receiving different N, P and crop residue-C inputs. Soil samples were collected July 28, 2003, and brought to the laboratory. Soils samples were treated with an N, C or P solution, with water only, or left untreated, and incubated for 48 hours. At the end of the incubation period, soil microbial biomass N was determined along with denitrification and nitrogenase activities. The results showed that the microbial activities and growth were limited by soil moisture at the date of sampling. Denitrification and nitrogenase activities were limited by N, P or C. The limiting nutrients varied with N, P and C inputs associated with the cropping system, regardless to soil moisture. The limitation of these elements to soil microbial activity was more frequently encountered under fallow.
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