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Recycling of carbon (C) and nitrogen (N) from plants into soils is decisive for maintaining soil organic matter and soil fertility. Therefore, we quantified plant biomass and C and N in the shoots and roots from the topsoil layer for a wide range of annual crops grown under subtropical conditions. We grew 26 species, 13 main crops, and 13 cover crops, in the field in standard sowing arrangements. Root biomass was recovered from the 0.00-0.20 m soil layer at flowering, and shoot biomass was measured at flowering for all crops and at maturity only for the main crops. Root dry matter (DM) exhibited an average of 14.9 ± 5.7 % of the total shoot biomass at flowering, and the mean shoot DM to root DM ratio was 6.9 (2.8-15.0) for the 26 crops considered. Leguminous species had less root DM (0.5 to 1.0 Mg ha-1) than grass species (1.1 to 2.3 Mg ha-1). The shoot C to root C ratio varied consistently with DM, while the root N to shoot N ratio varied considerably among species. Proportionally more biomass, C, and N was allocated to the root systems of grasses (Poaceae species) than non-grass species (especially Fabaceae species). The findings of this study contribute to designing rotations to include species that promote cycling of N and have high potential for adding C to the soil through roots. In this sense, the use of intercropped grasses and legumes is a promising strategy, especially for cover crops.

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Cover crops have numerous benefits when used in a no-till system. Understanding the processes of decomposition and N release of summer cover crops (SCC) may help select species and management to be used in cropping systems. This study aimed to evaluate C and N loss of SCC shoots. Six SCCs were evaluated: velvet bean (Mucuna aterrima), pearl millet (Pennisetum americanum), dwarf pigeon pea (Cajanus cajan), sunn hemp (Crotalaria juncea), showy rattlebox (Crotalaria spectabilis), and jack bean (Canavalia ensiformis). The experiment was conducted for two years under no-till in soil classified as Typic Hapludalf (Argissolo). The C and N remaining of crop shoots were evaluated for 140 days using litter bags and the results were fitted with a simple nonlinear regression model. Elevated air temperature and rainfall volume accelerated C and N loss in the first year. Carbon and N loss was characterized by a rapid initial phase followed by a slower one. Jack bean had the highest C loss rates, while the lowest rates were found in pearl millet. Velvet bean and pearl millet had the lowest N loss rates in the first year, together with showy rattlebox in the second year. The rates of C (kC) and N (kN) loss were positively correlated with total N and water-soluble C and N in crop shoots. During the 35 days after cover crop termination, SCCs released 35 to 137 kg ha-1 N in 2010 and 5 to 66 kg ha-1 N in 2011. Velvet bean and showy rattlebox showed more gradual N release, which may favor the synchronization between N release and N uptake by the succeeding crop. The sunn hemp was the legume species that combined higher remaining residues on the soil surface, releasing less N but preventing soil erosion.

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RESUMOA elevada produção de resíduos sólidos orgânicos no Brasil aliada a falta de coleta e destino adequado podem resultar em problemas ambientais, neste cenário, alternativas de baixo custo e fácil implantação se mostram importantes, como por exemplo, a vermicompostagem. O objetivo do presente estudo foi compreender o efeito da vermicompostagem no tratamento de resíduos sólidos orgânicos alimentares, e caracterizar a composição química do vermicomposto e chorume oriundos de uma escola municipal na cidade de Três Passos, RS. O vermicomposto e o chorume foram analisados quimicamente após 90 dias da implantação da vermicompostagem. Dentre as análises químicas realizadas, o processo de vermicompostagem afetou o pH em água e a relação C/N dos resíduos orgânicos ao final de 90 dias. Após a estabilização do vermicomposto, o pH em água foi de 8,2 e relação C/N de 13,2, já o pH do chorume foi de 3,78 e 4,6 na C/N solúvel. Com base nos resultados obtidos, a vermicompostagem se mostra como uma alternativa ambiental viável, que alia a disposição adequada de resíduos sólidos orgânicos e ao possível aproveitamento agrícola, tanto do vermicomposto quanto do biofertilizante para culturas. Este estudo possibilitou a geração de dados científicos integrados as práticas de sensibilização ambiental com o envolvimento de estudantes na montagem e operação de uma vermicomposteira.Palavras-Chave: Restos de alimentos; Tratamentos de resíduos; Biofertilizante. ABSTRACTThe high production of organic solid wastes in Brazil together with the lack of adequate collection and destination can result in environmental problems, in this scenario, alternatives of low cost and easy implantation are important, such as vermicomposting. The objective of the present study was to understand the effect of vermicomposting on the treatment of solid organic food residues and characterize the chemical composition of vermicompost and slurry from a municipal school in the city of Três Passos, RS. The vermicompost and manure were analyzed chemically after 90 days of vermicomposting. Among the chemical analyzes performed, the vermicompost process affected the pH in water and the C/N ratio of the organic residues at the end of 90 days. After stabilizing the vermicompost, the pH in water was 8.2 and the C/N ratio was 13.2, and the pH of the manure was 3.78 and 4.6 in C/N soluble. Based on the results obtained, the vermicomposting is shown as a viable environmental alternative, which combines the adequate disposal of organic solid waste and the possible agricultural use of both vermicompost and biofertilizer for crops. This study allowed the generation of integrated scientific data on environmental awareness practices with the involvement of students in the assembly and operation of a vermicomposter.A quantidade de resíduos sólidos gerados em 2016 pelos brasileiros foi de 78,3 milhões de toneladas, sendo que 91% deste total foram recolhidos pela rede de coleta dos municípios, contudo, apenas 41,7 milhões de toneladas tiveram uma disposição final ambientalmente adequ...