RESUMO -Objetivou-se avaliar a produção de massa seca das folhas, a relação folha/colmo e alguns índices de crescimento do capim-xaraés submetido a doses de nitrogênio (N) e potássio (K). O experimento foi conduzido em casa-de-vegetação no período de novembro/2004 a fevereiro/2005. Adotou-se esquema fatorial 4 × 3, perfazendo 12 combinações, as quais foram distribuídas em delineamento experimental inteiramente casualizado, com quatro repetições, perfazendo um total 48 unidades experimentais. Foram utilizadas quatro doses de N (0, 75, 150 e 225 mg dm -3 ) e três doses de K (0, 50 e 100 mg dm -3 ). Verificou-se efeito das doses de N na produção de massa seca das folhas e na produção de massa seca total, em todos os cortes, com maior produção nas doses mais elevadas de N, ao passo que o K influenciou essas variáveis apenas no segundo corte. A relação folha/ colmo, a RAF, a AFE e a RPF somente foram significativas no terceiro corte da planta. Os efeitos das doses de foram decrescentes sobre essas variáveis, enquanto as doses de K agiram de modo antagônico às doses de N sobre a RAF e AFE.Palavras-chave: área foliar específica, nutrição mineral, razão de área foliar, razão de peso foliar Dry matter production, leaf/stem ratio and growth indexes of palisade grass (Brachiaria brizantha cv. Xaraés), cultivated with different rate combinations of nitrogen and potassiumABSTRACT -This work aimed to evaluate dry matter production, leaf/stem ratio and growth indexes of palisade grass cv. Xaraés grown under increasing nitrogen and potassium rates. The experiment was carried out in a greenhouse from November, 2004 until February, 2005. The experimental treatments consisted of a 4 × 3 factorial arrangement between nitrogen and potassium rates respectively. Nitrogen rates were 0, 75, 150, and 225 mg dm -3 , whereas potassium rates were 0; 50 and 100 mg dm -3 . The experiment design was completely randomized with four replications. It was verified a positive N fertilization effect both on leaf dry matter yield and total dry matter yield. Potassium influenced these same response variables only at the second harvest. The leaf/stem ratio, leaf area ratio (LAR), specific leaf area (SLA) and, leaf weight ratio (LWR) were affected by treatments only at the third harvest. Increasing N rates reduced these response variables (L/S, LAR, SLA, LWR) while potassium rates behaved in an antagonistic way on LAR and SLA.Key Words: leaf area ratio, leaf weight ratio, mineral nutrition, specific leaf area IntroduçãoAs folhas constituem-se em órgãos das plantas responsáveis pela fotossíntese, além de serem a principal fonte de nutrientes para os ruminantes em sistemas de pastejo. Evidencia-se, dessa maneira, a necessidade de se investigarem os modelos morfofisiológicos que se tornam indispensáveis para a definição de estratégias de manejo de pastos.As porções verde da planta são as mais nutritivas da dieta e consumidas preferencialmente pelos animais (Wilson & t'Mannetje, 1978). Segundo esses autores, alta relação folha/colmo representa forragem com ...

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SUMMARYNitrogen fertilization is a major component of the cost of agricultural production, due to the high cost and low efficiency of fertilizers. In the case of urea, the low efficiency is mainly due to losses by volatilization, which are more pronounced in cultivation systems in which plant residues are left on the soil. The objective of this work was to compare the influence of urea coated with sulfur or boric acid and copper sulfate with conventional N fertilizers on N volatilization losses in sugar cane harvested after stubble burning. The sources urea, sulfurcoated urea, urea coated with boric acid and copper sulfate, as well as nitrate and ammonium sulfate, were tested at amounts containing N rates of 120 kg ha -1 N. The integration of new technologies in urea fertilization can reduce N losses by volatilization. These losses were most reduced when using nitrate and ammonium sulfate. The application of a readily acidified substance (boric acid) to urea was more efficient in reducing volatilization losses and nutrient removal by sugar cane than that of a substance with gradual acidification (elemental sulfur).

The use of a rapid and accurate method in diagnosis and classification of species and/or cultivars of forage has practical relevance, scientific and trade in various areas of study. Thus, leaf samples of fodder plant species Brachiaria were previously identified, collected and scanned to be treated by means of artificial vision to make the database and be used in subsequent classifications. Forage crops used were: Brachiaria decumbens cv. IPEAN; Brachiaria ruziziensis Germain & Evrard; Brachiaria Brizantha (Hochst. ex. A. Rich.) Stapf; Brachiaria arrecta (Hack.) Stent. and Brachiaria spp. The images were analyzed by the fractal descriptors method, where a set of measures are obtained from the values of the fractal dimension at different scales. Therefore such values are used as inputs for a state-of-the-art classifier, the Support Vector Machine, which finally discriminates the images according to the respective species.

In Brazilian agriculture, urea is the most commonly used nitrogen (N) source, in spite of having the disadvantage of losing considerable amounts of N by ammonia-N volatilization. The objectives of this study were to evaluate: N lossby ammonia volatilization from: [urea coated with copper sulfate and boric acid], [urea coated with zeolite], [urea+ammonium sulfate], [urea coated with copper sulfate and boric acid+ammonium sulfate], [common urea] and [ammonium nitrate]; and the effect of these N source son the maize yield in terms of amount and quality. The treatments were applied to the surface of a soil under no-tillage maize, in two growing seasons. The first season (2009/2010) was after a maize crop (maize straw left on the soil surface) and the second cycle (2012/2011) after a soybean crop. Due to the weather conditions during the experiments, the volatilization of ammonia-N was highest in the first four days after application of the N sources. Of all urea sources, under volatilization-favorable conditions, the loss of ammonia from urea coated with copper sulfate and boric acid was lowest, while under high rainfall, the losses from the different urea sources was similar, i.e., an adequate rainfall was favorablet o reduce volatilization. The ammonia volatilization losses were greatest in the first four days after application. Maize grain yield differed due to N application and in the treatments, but this was only observed with cultivation of maize crop residues in 2009/2010. The combination of ammonium+urea coated with copper sulfate and boric acid optimized grain yield compared to the other urea treatments. The crude protein concentration in maize was not influenced by the technologies of urea coating.