Sunnhemp and millet as green manure for tropical maize production

Abstract

Commonly N release from legume residues is rapid in the tropics. Legume mixtures with grasses can result in slower nutrient release from residues, better matching the N requirements of the following crop. The objectives of this study were to evaluate the effects of the green manures sunnhemp (Crotalaria juncea) and millet (Pennisetum glaucum), alone or mixed, on the performance of a subsequent maize crop with and without the application of N-fertilizer. The experiment consisted of four randomized blocks, with split plots. The plot treatments consisted of previous cultivation of sunnhemp, millet, mixed sunnhemp+millet and weeds. The subplot treatments were 90 kg N ha -1 and absence of N-fertilizer. Substantial amounts of biological nitrogen fixation (BNF) nitrogen were present in above ground parts of sunnhemp alone (173 kg ha -1 ) and mixed with millet (89 kg ha -1 ). Decay rates showed that half of the N was released 15 and 22 days from sunnhemp and sunnhemp+millet residues, respectively. The difference was attributed to temporary immobilization due to the higher C/N ratio of sunnhemp+millet. The preceding sunnhemp+millet treatment resulted in a larger maize yield than sunnhemp alone, when no N-fertilizer was applied. This effect was not observed when N-fertilizer was added. This effect may be due to a more timely N release, compared to sunnhemp and millet alone, when available N is required for maize. Nitrogen budgets showed that 15% and 10% in maize grain N was recovered from BNF for sunnhemp alone and sunnhemp+millet respectively. The recovery of N-BNF by maize was 65% higher after sunnhemp+millet than after sunnhemp monocrop. Key words: N recovery, biological nitrogen fixation, decomposition rate, intercropping CROTALÁRIA E MILHETO COMO ADUBOS VERDES PARA A PRODUÇÃO DE MILHO NOS TRÓPICOSRESUMO: A liberação de nutrientes dos resíduos de leguminosas é rápida nos trópicos. A consorciação com gramíneas pode resultar em liberação de nutrientes desses resíduos mais lenta e adequada aos requerimentos de N da cultura subseqüente. Os objetivos do trabalho foram avaliar os efeitos dos adubos verdes crotalária (Crotalaria juncea) e milheto (Pennisetum glaucum), solteiros ou consorciados, sobre o desempenho do milho com ou sem a aplicação de N-fertilizante. O experimento foi instalado em quatro blocos casualizados em parcelas subdivididas. Os tratamentos da parcela consistiram do cultivo prévio de crotalária, milheto, crotalária+milheto e ervas. Os tratamentos da subparcela foram 90 kg N ha -1 e ausência de N-fertilizante. A parte aérea da crotalária solteira ou consorciada apresentou, respectivamente, 173 kg ha -1 e 89 kg ha -1 de FBN-N. Metade do N foi liberado em 15 e 22 dias, dos resíduos de crotalária solteira e crotalária+milheto respectivamente. Esta diferença foi provavelmente causada pela imobilização temporária devido à maior C/N da crotalária+milheto. Na ausência de N-fertilizante o cultivo prévio de crotalária+milheto resultou em maior produtividade do milho que a crotalária solteira. Esse resulta...

Crop rotation biomass and arbuscular mycorrhizal fungi effects on sugarcane yield

“…A large proportion of the N present in soybeans usually comes from BNF. Guimarães et al (2008) found that 96% of the N present in above ground parts of soybeans were derived from BNF, values which are in agreement with those obtained by Perin et al (2006) for sunn hemp. However, in the present study, only about 27% of the N present in the soybean residues were from BNF (Table 5), probably because of poor specific population of fixing bacteria for soybeans in the experimental site, which have been grown with sugarcane for long time.…”

“…There is an increasing utilization of sunflower as a crop rotation with sugarcane in Brazil, due to its use for silage, seed oil production, and to its potential as a feedstock for biodiesel (Porto et al, 2008) The amounts of N in the above-ground parts of sunn hemp (Table 4) were relatively low compared to those of Caceres and Alcarde (1995), who reported the extraction of up to 230 kg ha -1 of N, and to those of Ambrosano et al (2005), who found 196 kg ha -1 of N. However, the amounts of N returned to the soil are directly related to the nutrient concentration in the plant, which varies with the local potential for biological nitrogen fixation (BNF) and with the growth stage of the crop at the time of cutting, and with the biomass yield, which is affected by the weather, soil, and crop growing conditions. Perin et al (2006) found substantial amounts of N derived from BNF present in the above ground parts of sunn hemp (57.0%) grown isolated and 61.1% when intercropped with millet (50% seeded with each crop). The sunn hemp+ millet treatment grown before a maize crop resulted in higher grain yield than when sunn hemp alone was the preceding rotation.…”

“…This effect was not observed when N-fertilizer (90 kg N ha -1 ) was added. Intercropping legume and cereals is a promising biological strategy to increase and keep N into the production system under tropical conditions (Perin et al, 2006). A large proportion of the N present in soybeans usually comes from BNF.…”

Adubação nitrogenada para milho com o uso de plantas de cobertura e modos de aplicação de calcário

“…Portanto, após cultivos sucessivos de milho, caso a opção seja utilizar crotalária como adubo verde, verificou-se menor necessidade de N para elevar o teor de N na folha a valores considerados normais. Dados levantados por Perin et al (2006) demonstram que a crotalária em cultivo solteiro apresenta, em sua parte área, 173 kg ha -1 de N, sendo a metade liberada em 15 dias após o manejo. Silva et al (2006), em região de Cerrado, observaram acúmulo de 169 kg ha -1 de N pela crotalária contra 68,50 kg ha -1 acumulados pelo milheto, resultados que contribuíram para consolidar as respostas deste presente trabalho.…”

Crescimento inicial e absorção de nutrientes pelo algodoeiro cultivado sobre a palhada de Brachiaria ruziziensis

“…O cultivo de espécies de cobertura com alta relação C/N, tanto da parte aérea quanto das raízes, como é o caso das gramíneas forrageiras tropicais, pode alterar o desenvolvimento inicial das culturas subsequentes (Souza et al, 2006), devido também à imobilização temporária de N pela biomassa microbiana do solo (Perin et al, 2006) e pela competição por outros nutrientes. Olibone et al (2006) observaram que a soja cultivada sobre a palha de sorgo-guiné apresentou menor crescimento da parte aérea e da raiz, resultando em menor acúmulo de nutrientes na parte aérea.…”