Ana Cândida 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%.

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.

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.

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.

Effect of the inherent variation in the mineral concentration of alfalfa cultivars on aphid populations

Plants have inherent variability of mineral content which affects their physiology and consequently the herbivorous insects feeding on them. Besides, insects need considerable amounts of potassium, phosphorus and magnesium in their diets, whereas little calcium, sodium and chloride are required. In this study, the inherent variation on mineral (Ca, S, Mg, N, P, K and also C:N ratio) concentrations and aphid (Acyrthosiphon spp., Therioaphis maculata, Aphis craccivora) populations on three alfalfa (Medicago sativa) cultivars (P3; Crioula, the most widely cultivated in Brazil, and CUF 101, an aphid-resistant) were studied between September/1997 and August/1998. A significant variation on mineral concentrations and aphid populations was observed among different sampling times and cultivars. The correlations between C:N ratio, Mg, N, P and S concentrations and aphid density variation suggest that the mineral status affects aphid population dynamics under field conditions.

Adubação de aveia em dois sistemas de plantio

The objective of this work was to determine the best 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 i.e conventional tillage and with a corn-residue mulch. The experiments were carried out in a Dark-Red Latosol (Hapludox). The experimental design was a incomplete (1/2)4 3 factorial, with two randomized blocks, with a total of 32 plots, without replication. The treatments comprised four rates of N and K2O (0, 70, 140, and 210 kg ha -1 ), using urea and potassium chloride, respectively, and four rates of P2O5 (0, 60, 120 and 180 kg ha -1 ), using triple superphosphate. The N, P, K rates for maximum profit were, in kg ha -1 for conventional tillage: N = 165, P2O5 = 50, K2O = 53; and for mulch-covered field: N = 210, P2O5 = 90, resulting in forage yields of, respectively, 6,641 and 7,322 kg ha -1 of dry matter. In both planting systems there was response only to N, and its use resulted in higher forage yield per unit of applied fertilizer.

Estudos sobre a nutrição mineral do maracujá amarelo: VI. efeito dos macronutrientes no desenvolvimento e composição mineral das plantas

O objetivo do presente trabalho foi o estudo do efeito da presenca e ausencia do macronutrientes no crescimento e composicao mineral da planta de maracuja e obter dados analiticos indicados do estado nutricional. As omissoes de nitrogenio, enxofre e calcio afetaram grandemente o desenvolvimento das plantas; a ausencia dos elementos fosforo, potassio e magnesio afetaram o crescimento, mas com menor intensidade. A analise do material revelou os seguintes teores dos nutrientes nas folhas do tratamento completo: N - 4,44%; P - 0,16%; K - 2,07%; Ca - 1,22%; Mg - 0,58%; S -1,18%. Determinou-se, para cada elemento, a parte da planta que melhor refletisse seu estado nutricional encontrando-se: folhas da haste madura - N, P, S, Mg; folhas da haste nova - calcio; gavinhas -potassio.