Relação entre qualidade e liberação de N por plantas do semiárido usadas como adubo verde

Abstract

R ESU M OO uso de plantas como adubo verde pode ser uma alternativa para melhorar a fertilidade do solo porém a liberação de nutrientes desses adubos para o solo irá depender dos teores de lignina, polifenóis (PP) e N no material vegetal utilizado. Tais teores foram determinados em 24 espécies vegetais encontradas em propriedades rurais do semiárido e relacionados com a mineralização de N, quando incorporados ao solo. Os materiais apresentaram grande variação nos teores os quais, por sua vez, sinalizaram baixa correlação com as proporções do N mineralizado depois da incorporação. Utilizando os teores e suas relações, realizou-se análise de componentes principais agrupando os materiais de acordo com suas similaridades, visando verificar a existência de relações entre a formação dos grupos referidos e o N mineralizado após incubação dos materiais orgânicos. Quatro grupos foram formados; no entanto, pouca informação útil foi gerada no sentido de tentar predizer a mineralização de N com base na qualidade dos materiais testados. O comportamento da lignina não foi bem definido na formação dos grupos e não apresentou relação clara com a mineralização do N devido, talvez, ao curto prazo de avaliação da metodologia adotada (28 dias). Todos os materiais que apresentaram relação PP/N menor que 0,5, mineralizaram N enquanto que os apresentaram a mesma relação acima de 5, imobilizaram N. Palavras-chave: nitrogênio, polifenóis, lignina, mineralização, imobilizaçãoRelationship between biomass quality and N mineralization in plant species used as green manure in semi-arid Brazil A B ST R A C T The use of plants as green manure may be an alternative to improve soil fertility in the region, but the release of nutrients to the soil will depend on the concentrations of lignin, polyphenols (PP), and nitrogen of the green manures used. These variables were analyzed for 24 plant species commonly found in farms of the semi-arid region of NE Brazil, and the relationship between plant biomass quality and N release after incorporation into the soil was evaluated. There was a large variation in the concentration of lignin, PP and N of the green manures tested but these variables presented a low correlation with N mineralization after incorporation to the soil. In order to try to identify patterns among the different manures regarding quality and N release, these were grouped using Principal Component Analysis techniques, but very little meaningful patterns were observed to help predict N release based on the quality of the materials. The lignin content of the materials played an important role to form different groups, but may be the short time of the incubations (28 days) did not allow for the development of the correlation between lignin content and N release. In general, it was observed that all materials that presented a PP/N ratio lower than 0.5 mineralized N, while those that presented values of this ratio above 5 caused N immobilization.

Nitrogen symbiotically fixed by cowpea and gliricidia in traditional and agroforestry systems under semiarid conditions

“…N concentrations of leaf samples were determined in 0.25 g of the material digested with sulfuric acid using the standard Kjeldahl procedure (Silva, 2009). N concentration of the larger branches (1.51%) was equal to that determined by Alves et al (2011) for these plants in the same location. The N concentration of cowpea grains (4.40%) was similar to that found by Arora & Das (1976).…”

Organic Nitrogen in Agricultural Systems

“…N input by organic fertilizers occurs predominantly through mineralization of organic N, although some mineral N fractions may be released [107,119]. The organic N mineralization rate is regulated by N fractions and C/N ratio of the decomposing waste, as well as by environmental temperature and humidity [120,121]. Under favorable conditions, high N content organic fertilizers mineralize quickly similarly to synthetic fertilizers, while those with low N content and high C/N ratio mineralize slowly [122].…”

Production, chemical composition and nutrient accumulation of winter cereal managed under integrated crop livestock

“…There is also in SILP, the pasture management and animal stocking, due to resulting in different quantities of produced mass and recycled nutrients, which can contribute with different amounts of C (SOUZA et al, 2008). However, this variation is due, in part, to the fact of the materials come from different species (ALVES et al, 2011), which despite belonging to the same family, accumulate different amounts of nutrients.…”