Nivaldo Guirado

Utilization of nitrogen from green manure and mineral fertilizer by sugarcane

Given their potential for biological nitrogen fixation, legumes used as green manure are an alternative source of nitrogen to crops, and can supplement or even replace mineral nitrogen fertilization. The utilization of nitrogen by sugarcane (Saccharum spp.) fertilized with sunn hemp (Crotalaria juncea L.) and ammonium sulphate (AS) was evaluated using the 15N tracer technique. Amounts of 195.8 kg and 70 kg N per hectare, respectively, of sunn hemp and AS were added in the following treatments: without green manure and without AS; without green manure, with AS -15N; with green manure-15N and with AS; with green manure-15N, without AS; with green manure and with AS-15N. Four samples from the leaves +3 were collected and 2 m of the sugar cane row were harvested to estimate crop yield. The results for N contents (g kg-1), isotopic abundance of N (atoms % 15N) in leaf +3 samples, and sugarcane productivity were used to calculate cumulative N, nitrogen in the plant derived from the fertilizer-Ndff (% and kg ha-1), as well as percent recovery of fertilizer N (R%). Sugarcane was analysed and pol and total recovered sugar calculated. The highest Ndff percentages were observed eight months after sugarcane planting for treatments containing green manure without mineral N, and green manure with mineral N, at 15.3 and 18.4%, respectively. The best nitrogen recovery was observed during harvest, 18 months after planting; the treatment containing mineral fertilizer showed 34.4% recovery, while the sum between mineral N plus green manure N showed 40.0%. Treatments containing green manure plus mineral N changed soil attributes, by increasing Ca and Mg contents, sum of bases, pH, and base saturation, and decreasing potential acidity. In the plant, those treatments increased Ca and K contents.

Crop rotation biomass and arbuscular mycorrhizal fungi effects on sugarcane yield

A cana-de-acucar (Saccharum spp.) vem sendo cultivada no Brasil para producao de acucar e agroenergia. Em seu sistema de producao, apos um ciclo de 4 a 8 anos, e possivel a rotacao com plantas de cobertura, antes do seu replantio, para melhoria do solo e geracao de renda. Estudou-se a caracterizacao e produtividade de biomassa de leguminosas (como adubos-verdes) e girassol (Helianthus annuus L.), a ocorrencia natural de micorrizas, o teor de acucar e a produtividade em colmos da cana-de-acucar IAC 87-3396 e a viabilidade economica desse sistema com cultivo apos as opcoes de rotacao, com quantificacao da produtividade durante tres cortes consecutivos. O amendoim (Arachis hypogaea L.) cv. IAC-Caiapo, girassol cv. IAC-Uruguai e mucuna-preta (Mucuna aterrimum Piper and Tracy) foram as culturas que apresentaram maior percentagem de colonizacao por fungos micorrizicos. O girassol foi a planta de cobertura que mais extraiu nutrientes do solo, seguido por amendoim (Arachis hipogaea L.) cv. IAC-Tatu e feijao-mungo (Vigna radiata L. Wilczek). A colonizacao por fungos micorrizicos mostrou correlacao positiva com a altura de plantas de cana no primeiro corte (p = 0,01 e R = 0,52), mas nao se correlacionou com a produtividade de colmos ou acucar. No primeiro corte, o girassol foi a cultura de rotacao que ocasionou o maior aumento de produtividade, da ordem de 46% em colmos e de 50% na quantidade de acucar, em comparacao com a testemunha. Com excecao dos amendoins, todas as culturas em rotacao aumentaram a renda liquida do sistema na media de tres cortes de cana-de-acucar.

Nitrogen supply to corn from sunn hemp and velvet bean green manures

Due to their nitrogen fixation potential, legumes represent an alternative for supplying nutrients, substituting or complementing mineral fertilization in cropping systems involving green manuring. The objective of this study was to evaluate the N balance in a soil-plant system involving green manures [sunn hemp (Crotalaria juncea L.) and velvet bean (Mucuna aterrima Piper & Tracy)], both labeled with 15N. They were incorporated into two soils of contrasting textural classes: a clayey Eutrudox and a sandy-clayey Paleudalf, both cultivated with corn. The research was carried out in a greenhouse, using pots containing 6 kg of air dried soil, to which the equivalent to 13 Mg ha-1 dry matter of above-ground mass plus 2.7 or 2.2 Mg ha-1 of velvet bean and sunn hemp roots were incorporated, respectively, with 15N labeling of either shoots or roots. One hundred days after emergence of the corn, the velvet bean residues provided higher accumulation of N in the soil, higher absorption by corn plants and accumulation in the shoot. The green manure decomposition was more intense in the medium-textured Paleudalf. The highest nitrogen losses were also observed in this soil.