Effects of plant residues on crop performance, N mineralisation and microbial activity including field CO2 and N2O fluxes in unfertilised crop rotations

The impacts of crop rotation and input of organic matter in the form of green manure crops, straw residues and incorporation of catch crops on crop yield, nitrogen uptake, microbial biomass and activity were studied in unfertilised crop rotations differing in input of plant residues, i.e., high-input rotations with a grass-clover crop and catch crops included and low-input cereal rotations without catch crops. The parameters studied included substrate induced respiration (SIR), hydrolysis of fluorescein diacetate (FDA), arylsulfatase activity (ASA), N mineralisation, N2O emission, and soil respiration. These parameters were measured in bare soil plots, to estimate the effects of previous years' crops and input of plant residues. In neighbouring plots crop performances were registered by measuring yields, above-ground biomass and nitrogen uptake during the growing season. Generally, all measured parameters were significantly higher in the high-input than in low-input rotations. Estimates of metabolic quotients indicated that the microbial communities in the low-input rotations were less efficient in utilising the C sources than those in the high-input rotations. Calculations of N2O emission factors indicate that the current IPCC methodology for estimating N2O emission from plant residues needs to be improved.