Aliomar Gabriel da Silva

Nutrientes na fitomassa de capim-marandu em função de fontes e doses de nitrogênio

Em pastagens manejadas intensivamente, que recebem altas doses de nutrientes, e necessario conhecer sua extracao para auxiliar as recomendacoes de adubacao. Este trabalho teve a finalidade de avaliar os nutrientes extraidos pela fitomassa de capim-marandu (Brachiaria brizantha (Hochst ex. A. Rich.) Stapf cv. Marandu) submetido a fontes e doses de N e seu efeito na recuperacao aparente do N, em experimento conduzido em Latossolo Vermelho Distrofico tipico, sob condicoes tropicais. Foram aplicadas tres doses de N: 50, 100 e 200 kg ha-1 corte-1, nas formas de ureia e de nitrato de amonio (NA), apos quatro cortes consecutivos na estacao chuvosa, alem da testemunha. Houve aumento na extracao dos nutrientes com doses crescentes de N, com valores elevados para K e N. As extracoes dos macronutrientes foram maiores para K seguidas de N, Ca, Mg, P e S e dos micronutrientes na seguinte ordem decrescente: Fe, Mn, Zn e Cu. A recuperacao media do N, pela forragem, de todas as doses da ureia foi de 84% da obtida com o NA, para o qual variou entre 38 e 51%. Em capim-marandu com producoes elevadas de forragem, a extracao de K e grande e a recuperacao media de N da ureia e inferior a media do nitrato de amonio.

Adubação nitrogenada em capim-coastcross: efeitos na extração de nutrientes e recuperação aparente do nitrogênio

Foi conduzido experimento em Latossolo Vermelho Distrofico tipico, em Sao Carlos, SP, para avaliar o efeito de doses e fontes de nitrogenio (N), no teor, extracao dos nutrientes e na recuperacao do N aplicado em capim-coastcross (Cynodon dactylon cv. Coastcross). Foram aplicadas sobre a superficie do solo cinco doses de N (0, 25, 50, 100 e 200 kg ha-1corte-1), na forma de ureia ou de nitrato de amonio, em cinco periodos consecutivos, durante a estacao chuvosa. Foram determinados os teores e calculada a extracao de nutrientes e a recuperacao do N. Houve aumento na extracao dos nutrientes com o aumento da producao de forragem, com elevados valores principalmente para N e K. Para altas producoes de forragem (tratamento 500 kg ha-1 ano-1de N) e para as duas fontes de nitrogenio as extracoes dos macronutrientes foram maiores para K e N, seguidas de Ca, S, P e Mg e dos micronutrientes Fe, Mn, Zn e Cu. A recuperacao media de N da ureia foi de 68% do N obtido do nitrato de amonio, que variou, em media, de 68 a 75%.

Efeito de fontes e doses de nitrogênio na produção e qualidade da forragem de capim-coastcross

Forage production and quality of coastcross grown on a dark red latosol (Hapludox) were evaluated in 1998-1999 and 1999-2000, from November to April, in Sao Carlos, Sao Paulo state, Brazil, under a tropical altitude climate. The experimental design was a randomized block design, in a split-plot arrangement, with four replications. In the main plots were allocated ten treatments, organized in a 2 ´ 5-factorial scheme (two nitrogen sources: urea and ammonium nitrate, and five N levels: 0, 25, 50, 100, and 200 kg N/ha/cutting, in five consecutive cuttings - repeated measures). Data were analyzed by MIXED procedure of SAS, using a repeated measure model. Nitrogen fertilization increased DM yield, CP concentration, in vitro DM digestibility, and nitrate concentration, and reduced DM and NDF concentrations in the forage. In the first year, N doses associated with 80% of the maximum forage yield were 88 and 78 kg/ha, corresponding to average dry matter yields of 2,769 and 3,202 kg N/ha/cutting, respectively, for urea and ammonium nitrate. In the second year, N doses which produced 80% of the maximum forage yield were 91and 116 kg/ha, respectively, for urea and ammonium nitrate, corresponding to average DM yields of 2,312 and 3,073 kg ha/cutting, respectively.

Absorção de cátions e ânions pelo capim-coastcross adubado com uréia e nitrato de amônio

Physiologic processes of plants are affected by uptake of cations and anions. The aim of this work was to determine the uptake of cations and anions when plants of coastcross grass received high doses of nitrogen. The experimental design was a randomized block, in a 2x5 factorial arrangement - two N sources: urea and ammonium nitrate and five N rates: 0, 25, 50, 100, and 200 kg ha-1 cutting-1 - with four replications. Treatments were applied after each of five consecutive cutting in the rainy season. Uptake of cations and anions by coastcross grass increased with increasing of N rates with both fertilizers, but was higher with ammonium nitrate. Increasing rates of N caused higher K+ uptake in relation to other cations, and in Cl- among the anions. Except for N, K+ uptake was greater than that of other nutrients, with a reduction on the relative content of Ca2+. High doses of N as urea or ammonium nitrate applied on coastcross grass favor absorption of cations and anions.

Lixiviação de nitrato em pastagem de coastcross adubada com nitrogênio

The goal of this work was to assess nitrate losses in the soil profile. Nitrate concentration was determined in the profile of a soil under coastcross pasture (Cynodon dactylon cv. Coastcross), in Sao Carlos, SP, Brazil, in the rainy season of two consecutive years. The soil was a dark red Latosol (Hapludox), affected by tropical altitude climate. Nitrogen doses of 125, 250, 500 and 1,000 kg ha-1 year-1, as urea or ammonium nitrate were broadcasted splited in five applications. Soil nitrate concentration was determined down to 160 cm depth. In 1999, nitrate level varied according to N sources, reaching higher figure in soil that had received 1,000 kg ha-1 year-1 of N. The highest NO3-N concentration occurred in soil layer down to 100 cm depth, in the plots treated with ammonium nitrate. In 2000, nitrate-N was measured weekly in the soil profile, in treatments with 500 and 1,000 kg ha-1 year-1. The greatest variations, from 0 to 81.2 mg kg-1 of NO3-N, occurred down to 40 cm depth. Results point to low danger of water table contamination in deep medium textured soils of intensively well managed tropical grass pasture, using N doses lower than the forage N cycling capacity and considering the potential soil N sources.

Determinação da composição mineral de subprodutos agroindustriais utilizados na alimentação animal, pela técnica de ativação neutrônica

O presente trabalho teve como objetivo analisar alguns subprodutos agroindustriais utilizados na alimentacao animal e identificar os principais minerais presentes. Amostras de farelos de algodao, arroz, canola, soja e trigo; farinhas de peixe, carne e penas + visceras; cascas de algodao, arroz, laranja; bagacos de tomate e de laranja foram coletadas em diferentes locais de producao. O metodo analitico empregado foi a analise por ativacao com neutrons seguida de espectrometria gama. Os niveis de minerais encontrados em todas as amostras, inclusive aqueles considerados toxicos, tais como As, Cd e Hg, nao excederam os limites maximos permitidos em dietas para animais domesticos. Os valores obtidos foram comparados com os comumente encontrados em forragens.

Multielemental Analysis of Agroindustrial By-Products Employed in Animal Feeding by INAA

Instrumental neutron activation analysis (INAA) with gamma-ray spectrometry was applied to determine As, Ca, Cd, Cl, Co, Cu, Cr, Fe, Hg, K, Mg, Mn, Mo, Na, Sb, Se and Zn in the Brazilian agroindustrial by-products. These materials are widely used in ruminant feeding. The results obtained were compared with requirement and maximum tolerable concentrations. The general conclusions from the data obtained were: (1) many by-products presented concentrations of some essential elements lower than the requirement concentrations, while in some concentrations of Cr, Fe, Mg and Se exceeded by a little the maximum tolerable concentrations, (2) the elements As, Cd, Hg and Sb, generally considered toxic, showed concentrations lower than maximum tolerable values.