Utilization of nitrogen (15N) from urea and green manures by rice as affected by nitrogen fertilizer rate.

The use of green manures (GMs) in combination with nitrogen (N) fertilizer application is a promising practice to improve N fertilizer management in agricultural production systems. The main objective of this study was to evaluate the N use efficiency (NUE) of rice plant, derived from GMs including sunn hemp (Crotalaria juncea L.), millet (Pennisetum glaucum L.) and urea in the greenhouse. The experimental treatments included two GMs (sunn hemp-15N and millet-15N), absence of N organic source (without GM residues in soil) and four N rates, as urea-15N (0, 28.6, 57.2 and 85.8 mg N kg-1). The results showed that both rice grain and straw biomass yields under sunn hemp were greater than that of millet or without the application of GM. The NUE of rice under sunn hemp was greater than that under millet (18.9 and 7.8% under sunn hemp and millet, respectively). The urea N application rates did not affect the fertilizer NUE by rice (53.7%) with or without GMs. The NUE of GMs by rice plants ranged from 14.1% and 16.8% for root and shoot, respectively. The study showed that green manures can play an important role in enhancing soil fertility and N supply to subsequent crops.

Nitrate and potassium concentration in fertigated soil cultivated with wine vines.

In the semiarid region of Brazil the use of irrigation systems for applying fertilizers in horticulture is the primary means for incorporating nutrients in the soil. However, this technique still requires its use in wine vines to be assessed. In view of this, this study aimed to assess nitrate and potassium concentrations in soil fertigated with nitrogen and potassium fertilizers in 3 wine grape growing cycles. A field experiment was conducted with ?Syrah? wine grapes, in Petrolina, Pernambuco, Brazil; it assessed five nitrogen doses (0, 15, 30, 60 and 120 kg ha-1) and five K2O doses (0, 15, 30, 60 and 120 kg ha-1) applied by drip irrigation system with two emitters per plant, with a flow rate of 4 L h-1. The experimental design used was the factorial split-plot, making up 13 combinations arranged in 4 randomized blocks. Soil solution samples were collected weekly with the aid of porous cup extractors for all treatments and at depths of 0.4 and 0.6 m by determining nitrate and potassium concentrations and electrical conductivity. Increased levels of both nutrients in the irrigation water increased the availability of nitrate and potassium in the soil solution. The highest nitrate and potassium concentrations were found in the second growing cycle at both depths studied.

Annual crop rotation of tropical pastures with no-till soil as affectedby lime surface application.

Soil acidity and low natural fertility are the main limiting factors for grain production in tropical regionssuch as the Brazilian Cerrado. The application of lime to the surface of no-till soil can improve plant nutrition, dry matter production, crop yields and revenue. The present study, conducted at the Lageado Experimental Farm in Botucatu, State of São Paulo, Brazil, is part of an ongoing research project initi-ated in 2002 to evaluate the long-term effects of the surface application of lime on the soil?s chemical attributes, nutrition and kernel/grain yield of peanut (Arachis hypogaea), white oat (Avena sativa L.) and maize (Zea mays L.) inter cropped with palisade grass (Urochloa brizantha cv. Marandu), as well as the forage dry matter yield of palisade grass in winter/spring, its crude protein concentration, estimated meat production, and revenue in a tropical region with a dry winter during four growing seasons. The experiment was designed in randomized blocks with four replications. The treatments consisted of four rates of lime application (0, 1000, 2000 and 4000 kg ha−1), performed in November 2004. The surface application of limestone to the studied tropical no-till soil was efficient in reducing soil acidity from the surface down to a depth of 0.60 m and resulted in greater availability of P and K at the soil surface. Ca and Mg availability in the soil also increased with the lime application rate, up to a depth of 0.60 m. Nutrient absorption was enhanced with liming, especially regarding the nutrient uptake of K, Ca and Mg by plants.Significant increases in the yield components and kernel/grain yields of peanut, white oat and maize were obtained through the surface application of limestone. The lime rates estimated to achieve the maximum grain yield, especially in white oat and maize, were very close to the rates necessary to increase the base saturation of a soil sample collected at a depth of 0?0.20 m to 70%, indicating that the surface liming of 2000 kg ha−1is effective for the studied tropical no-till soil. This lime rate also increases the forage dry matter yield, crude protein concentration and estimated meat production during winter/spring in the maize-palisade grass inter cropping, provides the highest total and mean net profit during the four growing seasons, and can improve the long-term sustainability of tropical agriculture in the Brazilian Cerrado.