Luciano de Almeida Corrêa

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.

Qualidade e valor nutritivo de silagens de capim-marandu (B. brizantha cv. Marandu) produzidas com aditivos ou forragem emurchecida

The objective of this experiment was to evaluate the quality and nutritive value of marandugrass silages. It was evaluated the followings treatments: T1- forage without treatment (control); T2 - 10% of pelleted citric pulp (CiP); T3 - enzymatic bacterial additive (EBA) (SIL-ALL-C4 of Alltech) applied at 5 g/L of water/t of forage; T4 - Coarse chopped forage wilted for 4 hours under the sun. The grass was harvested with 60 days of regrowth (24% DM). The intake and digestibility evaluations were realized in 16 crossbred steers with 200 kg of BW, which received silage plus 1.0 kg of concentrate/animal/day. The EBA did not affect silage composition, but CiP addition and wilting increased the DM silage concentration from 24% (control) to 31 and 48%, respectively. The CiP decreased the NDF and ADF concentration in 12.0 and 4.0 percentage units, respectively. The CiP and wilting decreased the pH values (4.17 and 4.58) and N-NH3 concentration (6.78 and 7.99% TN) of the silages, respectively. Wilting resulted in higher animal intake (111.8 g/DM/LW0,75) compared to control or EBA treatments. Addition of CiP resulted in similar DM intake compared to other silages. The treatments did not affect nutrient digestibility, and the mean digestibility values for DM, CP, TCHO, NDF, ADF and TDN were 67.0, 65.4, 68.8, 63.0, 62.5, and 65.6%, respectively. Proteolysis was not reduced by EBA while CiP or wilting decreased this process, stimulating intake. Addition of CiP, wilting and EBA did not improve the nutritive value of marandugrass silage harvested with 24% DM.

Pesos e relações de peso de bezerros filhos de vacas nelore e cruzadas canchim x nelore

The objective of this work was to study birth (BW) and weaning (WW) weights, and birth weight/cow weight at calving (BWR) and weaning weight/cow weight at calving (WWR) ratios of 1/2 Canchim + 1/2 Nellore and 1/2 Charolais + 1/4 Canchim + 1/4 Nellore calves out of straightbred Nellore and crossbred 1/2 Canchim + 1/2 Nellore cows, and sired by Canchim (5/8 Charolais + 3/8 Zebu) and Charolais bulls, respectively. Analyses of variance were carried out separately for each genetic group, by the least square method, with models that included the effects of year and month of birth of calf, sex of calf, age of cow and origin of cow (for the Nellore cows only). Year of birth affected all studied traits, except BW and BWR of the 1/2 Charolais calves, while month of birth had no effect on BW of those calves only. The heaviest calves at weaning were those born during the dry period (from July to September). The highest weight ratios were for the calves born from July to November. Sex of calf affected only the traits measured at weaning; male calves were heavier and showed higher weight ratio than the females. There was a tendency for increasing weights and decreasing weight ratios as the cows aged. Origin of the Nellore cow affected the traits of the 1/2 Canchim calves. The least square means obtained were equal to 31.6 ± .2 kg (BW), 195 ± 1 kg (WW), 71.0 ± .5 g/kg (BWR) and 437 ± 3 g/kg (WWR), for the 1/2 Canchim calves, and 36.1±.2 kg (BW), 246 ± 1 kg (WW), 72.4 ± .4 g/kg (BWR) and 492 ± 2 g/kg (WWR), for the 1/2 Charolais calves. These results suggest that straightbred Nellore and crossbred 1/2 Canchim + 1/2 Nellore cows may be considered of good productive efficiency, measured by the ratio weight of calf/weight of cow, when mated to Canchim and Charolais bulls, respectively.