The influence of different cover crop residues quantities on soil structural stability

Cover crops are widely known for their capacity to improve the soil biological properties and soil structural stability. Nevertheless, the cover crop residues quantity necessary to improve these soil properties is not yet really known. A 30-day incubation experiment was conducted to explore the effect of oilseed rape (Brassica napus) residues (ORR) as a cover crop on the soil aggregate stability of sandy loam soil. The fresh ORR was mixed with the soil at different rates starting from 1.0 to 6.0 g C kg^-1 of soil. The experiment consisted of five treatments: bulk soil (I), soil mixed with ORR at a rate of 1 g C kg^-1 of soil (II), soil mixed with ORR at a rate of 2 g C kg^-1 of soil (III), soil mixed with ORR at a rate of 4 g C kg^-1 of soil (IV), soil mixed with ORR at a rate of 6 g C kg^-1 of soil (V). During 30 days of incubation the soil moisture, soil water stable aggregates, and microbial substrate induced respiration rates were measured. The aggregate stability significantly increased after 30 days only in the treatment with 1 g C kg^-1 of soil. In turn, the ORR applied at a rate of 6 g C kg^-1 of soil significantly decreased the soil aggregate stability. The higher the ORR addition rate the lower was the soil basal respiration and substrate induced respiration. The general conclusion was that the higher quantity of ORR increased the soil moisture which subsequently created unfavorable conditions for the soil microbial activity and led to soil aggregate stability degradation. However, this conclusion must be validated in a field study where the soil moisture and temperature conditions are much more variable compared to our incubation experiment.