ABSTRACT Decomposition processes and mineralization are essential to determine the time to deploy and manage species in consortia or rotations. The aim of this article was study the dynamics of biomass decomposition and release of macronutrients of plant residues of Fabacea. The species used were: jack bean (Canavalia ensiformis), pigeon pea (Cajanus cajan), dwarf mucuna (Mucuna deeringiana) and sunn hemp (Crotalaria juncea). The experiment was conducted in the field in a randomized block design, 4 x 5 factorial, four species of green manure and five times (0, 30, 60, 90, and 120 days). In the results, sunn hemp and pigeon pea had lower decomposition and release of C, N, K, and Mg. All species, K and P showed similar half-lives (t1/2). For N, sunn hemp presented the lowest coefficient of mineralization (k), 0.0040 g g-1 dia-1, associated with highest t1/2 (173.3 days), already, jack bean showed the highest k (0.0122 g g-1 dia-1) associated with the lowest t1/2 (56.8 days). In edaphoclimatic conditions, use of the jack bean and the dwarf mucuna is recommended for supply of nutrients in shorter periods of time for subsequent crops. However, sunn hemp and pigeon pea are recommended for greater persistence of mulch on the soil.

A adubação verde é reconhecida como alternativa viável para melhorar a ciclagem de nutrientes em solos agrícolas. O objetivo deste trabalho foi avaliar a produção de fitomassa e o acúmulo de nutrientes na parte aérea de adubos verdes de verão: feijão-de-porco [Canavalia ensiformis (L.) DC.], guandu-anão (Cajanus cajanvar var. Flavus DC.), mucuna-anã [Mucuna deeringiana (Bort) Merr] e crotalária (Crotalaria juncea L.), sob efeito da adubação nitrogenada e, ou, da inoculação com bactérias fixadoras de N. Utilizou-se o arranjo de parcelas subdivididas, sendo as parcelas constituídas pelas quatro fabáceas e, as subparcelas, por um fatorial 2(2,) cujos fatores e níveis foram: adubação nitrogenada (com e sem) e inoculação com bactérias diazotróficas (com e sem). O delineamento experimental adotado foi o de blocos casualizados, com quatro repetições. Nas condições edafoclimáticas deste ensaio, a crotalária é o adubo verde que apresenta os maiores valores de produção de fitomassa aérea (12,4 Mg ha-1) e acumulação de nutrientes, enquanto a mucuna-anã é a menos eficiente na produção de fitomassa aérea (3,9 Mg ha-1) e acúmulo de nutrientes. Os resultados mostram que não há efeito de adubação nitrogenada, ou de inoculação com bactérias fixadoras de N, na produção de fitomassa aérea ou acúmulo de nutrientes, com exceção da inoculação na ausência de adubação nitrogenada, que resultou (p<0,05) em maior acumulação de P, na crotalária, e maior acumulação de Zn e Mn, na mucuna-anã. Conclui-se que a adubação nitrogenada ou a inoculação com bactérias fixadoras de N2, para o cultivo das fabáceas, são práticas de baixa eficiência nas condições edafoclimáticas estudadas.

Green manuring is recognized as a viable alternative to improve nutrient cycling in soils. The aim of this study was to evaluate the phytomass production and nutrient accumulation in shoots of the summer green manures jack bean [Canavalia ensiformis (L.) DC.], dwarf pigeon pea (Cajanus cajanvar var. Flavus DC.), dwarf mucuna [Mucuna deeringiana (Bort) Merr] and sunn hemp (Crotalaria juncea L.), under nitrogen fertilization and/or inoculation with N-fixing bacteria. A split plot design was arranged with the four Fabaceae species as main plots and nitrogen fertilization (with and without) and inoculation with diazotrophic bacteria (with and without) as the subplots, in a 2² factorial. The experiment was arranged as a randomized complete block design with four replications. In the conditions of this trial, the sunn hemp had the highest production of shoot phytomass (12.4 Mg ha-1) and nutrient accumulation, while the dwarf mucuna had the lowest production of shoot phytomass (3.9 Mg ha-1) and nutrient accumulation. The results showed no effect of nitrogen fertilization or inoculation with N-fixing bacteria on the production of shoot phytomass and nutrient accumulation, except for inoculation without nitrogen fertilization, resulting in greater P accumulation (p <0.05) in the sunn hemp and greater Zn and Mn accumulation in the dwarf mucuna. These findings indicate that N fertilization or inoculation with N2-fixing bacteria for Fabaceae are low efficiency practices in the edaphoclimatic conditions of this study.