O. Primavesi

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%.

Metano entérico de bovinos leiteiros em condições tropicais brasileiras

The objective of this work was to quantify methane (CH4) emission using the sulfur hexafluoride (SF6) tracer technique, by dairy cattle on pasture in Brazilian tropical field conditions. Measurements were performed in the rainy season, with Holstein and Holstein x Zebu crossbred, from lactating and dry cows and heifers grazing fertilized Tobiata grass, and heifers grazing unfertilized Brachiaria grass. Methane and SF6 concentrations were determined by gas chromatograph. Methane emissions by lactating cows varied from 13.8 to 16.8 g/hour, by dry cows from 11.6 to 12.3 g/hour, by heifers grazing fertilized grass was 9.5 g/hour and by heifers grazing unfertilized grass varied from 7.6 to 8.3 g/hour or 66 to 72 kg/head/year. Methane emission per digestive dry matter intake (DMDI) varied from 42 to 69 g/kg DMDI for lactating cows, 46 to 56 g/kg for dry cows, 45 to 58 g/kg for heifers grazing fertilized grass and 58 to 62 g/kg for heifers in unfertilized grass pasture. The CH4 emission measured on dairy cattle feeding tropical grasses was higher than that observed for temperate climate conditions.

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.

Ruminal methane emission by dairy cattle in Southeast Brazil

Gases gerados durante o processo de fermantacao ruminal, metano em particular, representam nao so uma perda parcial de energia da alimentacao como tambem sao apontados como importantes fatores do efeito-estufa. Quantificaram-se as taxas de emissao de metano (CH4) ruminal por vacas em lactacao, vacas secas e novilhas com idade media de 24 meses, em pastejo sob condicoes tropicais do sudeste brasileiro, utilizando a tecnica do gas tracador hexafluoreto de enxofre (SF6). Foram utilizados quatro animais para cada categoria, distribuidos em quatro blocos. As medicoes foram realizadas em fevereiro e junho de 2002, com animais da raca Holandesa e Mestica Leiteira Holandes ¾ x Gir ¼ - Mesticas, mantidos em pastagem de capim-Tanzânia (Panicum maximum Jacq. cv. Tanzania) e capim-braquiaria (Brachiaria decumbens cv. Basilisk) adubadas, e tambem novilhas de ambas as racas em pastagens de capim-brachiaria sem adubacao, simulando as condicoes de producao extensiva. As concentracoes de CH4 e SF6 foram determinadas por cromatografia gasosa. Foram encontradas diferencas na emissao de metano (p < 0,05) entre os grupos geneticos. Animais da raca holandesa produziram mais metano (299,3 g dia-1) que as mesticas (264,2 g dia-1). Vacas secas e novilhas produzem menos metano (g dia-1) que vacas em lactacao. A media de emissao de metano (g dia-1) pelas vacas secas e novilhas foi de 268,8 e 222,6 g respectivamente e as vacas em lactacao 353,8 g. Os animais da raca holandesa, com maior potencial de producao de leite, perderam menos CH4 (p < 0,05) por unidade de materia seca ingerida (19,1 g kg-1) que as mesticas (22,0 g kg-1). A producao de metano pelas novilhas mantidas em pastagens adubadas (sistema intensivo) foi de 222,6 g dia-1, maior (p < 0,05) que os animais desta categoria em pastagens nao adubadas (179,2 g dia-1). A producao de metano variou em funcao da categoria de animal e pelo sistema de producao imposto aos animais.

Resposta da Aveia Branca à Adubação em Latossolo Vermelho-Amarelo em Dois Sistemas de Plantio

Two field experiments were carried out on a Red Yellow Latosol (Hapludox), at Sao Carlos, SP in order to determine the rates of N, P, and K to obtain maximum economic return per area of forage yield for the oat line UPF 87111 grown in two planting systems: conventional tillage and mulch-covered. The experimental design was a fractionated factorial type (1/2)4 3 , with two blocks. The treatments consisted of four rates of N and K 2 O (0, 70, 140, and 210 kg ha -1 ), using urea and potassium chloride, and four rates of P 2 O 5 (0, 60, 120 and 180 kg ha -1 ), using triple superphosphate. The N, P, and K rates for maximum profit were, in kg ha -1 for conventional tillage: N = 160, P 2 O 5 = 180, K 2 O = 180; and for mulch-covered: N = 200, P 2 O 5 = 120, K 2 O = 95 resulting in forage yields of, respectively, 7,398 and 8,111 kg ha -1 of dry matter. In both planting systems, the use of nitrogen resulted in higher forage yield per unit of applied fertilizer.

Methane emissions and estimates of ruminal fermentation parameters in beef cattle fed different dietary concentrate levels

Using sorghum silage, the effect of roughage/concentrate ratios was evaluated on nutrient intake, digestibility, ruminal parameters and methane production by beef cattle. Three treatments (0, 30 and 60% of concentrate in DM of the diet) were distributed in three Latin squares, with nine animals and three periods. Dry matter intake increased as the grain concentration in diet increased; pH showed opposite behavior. Methane emissions were lower for animals fed the diet exclusively with sorghum silage as compared with those fed 30% of concentrate, but was similar to that of animals receiving 60% of concentrate. Losses of ingested gross energy as methane were reduced by 33% when grain concentration was increased in the diet. Concentrations of propionic and butyric acids were greater in diets with grain concentrate; acetic acid concentration was not affected. Concentrate in diet increases available energy for the metabolism, measured by lower losses of ingested gross energy as ruminal methane.

Extração de nutrientes e eficiência nutricional de cultivares de aveia, em relação ao nitrogênio e à intensidades de corte

The objective of this experiment was to study the effect of nitrogen levels (0, 40, 80, 160, 320 kg ha-1 N) and forage cutting intensities (none, one and two cuts) on nutrient uptake and nutritional efficiency of oats (Avena byzantina / Avena sativa). The potential mineral uptake by forage and grains and their cycling through their straw, were also evaluated. This experiment was conducted on a Hapludox soil, in a split-plot design with complete randomized blocks and four replications, using the Sao Carlos and UPF 3 oat cultivars. Increasing levels of N affected both, the extraction of S and N in the first forage cut of Sao Carlos, influenced the K assimilation of both cultivars in the second cut, and S uptake, in both cultivars and cuts. In addition P uptake by straw of both cultivars, and Zn, Cu and Mn by Sao Carlos, were altered. The K concentration and extraction decreased from the first to the second cut. Potassium uptake was higher when oats were used as forage, at a level of 145 kg ha-1. Straw assimiliation of K was about 60 kg ha-1, which returned to the soil, while grain uptake was about 6 kg ha-1. Potassium, N, Fe and Mn were the nutrients of highest demand by both cultivars, which had similar nutritional efficiency and produced the same amount of forage dry matter. For grain production and use of nutrients, UPF 3 was more efficient than Sao Carlos.