Long-term cover crops in paddy field increase enzyme activity and carbon stock and enable the system fertilization

The use of cover crops and the adoption of no-tillage are essential conservation practices to increase carbon and nitrogen stocks and increase soil microbial activity. However, in lowland areas cultivated with irrigated rice, there is a large gap on the effects of no-tillage with long-term cover crops on soil attributes, crop responses and the effect of the system fertilization. The aim of this work was to evaluate the long-term adoption of cover crops on soil microbial activity, soil carbon stock and on the response of irrigated rice to system fertilization. Treatments consisted of fallow-conventional, fallow-no tillage, Annual Ryegrass, Oat, Ornithphus micranthus and Lotus cornicultaus. In the sub-plots, system and conventional fertilization per crop were compared. The experiment was conducted in southern Brazil in an Entisol and started in the 1996/97 crop season. Cover crops associated with the use of no-tillage increases basal respiration (+ 31%) of the soil, β-glucosidase activity (+ 259%), and soil carbon and nitrogen stocks. Urease activity increased by an average of 41% in no-tillage under cover crops compared to the conventional system under fallow, with the exception of ryegrass. System fertilization promoted higher dry matter production (+ 130%) in grasses and a lower increase (+ 23%) in winter legumes. The use of long-term cover crops promoted higher rice productivity (+ 9%). In this way, the association of cover crops and no-tillage increases carbon and nitrogen stocks, the biological activity of the soil and makes possible the system fertilization in lowlands, with positive effects on productivity.