Input of dry matter by roots and shoots of summer cover crops

Abstract

The advantages of using cover crops or green manures are already well known, but little is known about the contribution of the root system of these plants in the stock of organic matter in the soil. The aim of this study was to evaluate the dry matter, carbon and nitrogen supply by above ground parts and roots (down to 1.0 m deep) of cover crop plants (Jack-bean - Canavalia ensiformis; velvet bean - Stizolobium niveum Kuntze; Crotalaria juncea L.; and millet - Pennisetum americanum), in sequence of corn - turnip - oat plus vetch. Trenches were dug and roots samplings were collected at seven depths (0-0.10; 0.10-0.20; 0.20-0.30; 0.30-0.40; 0.40-0, 60; 0.60-0.80; and 0.80-1.00 m). The experimental design was randomized blocks and the results were submitted to ANOVA and Tukey test. Despite millet presented the highest dry mass input (3.58 Mg ha-1) from above ground part (AGP), its C contribution from root system (RS) was lower than C. juncea, because AGP/RS millet relation was 1.46 while this value for C. juncea was 0.75. Among the evaluated green manures, the roots of C. juncea contribute the most carbon (1.40 Mg ha-1) than the others, while the roots of velvet bean contribute the largest amount of nitrogen (72.38 kg ha-1) to the soil.