Nitrogen and sulphur on yield and water use efficiency of signalgrass from a degrading area

Nitrogen is indispensable for pasture establishment, maintenance and production recovery, and its effect is apparently dependent on sulphur supply. It was hypothesized that increasing nitrogen supply requires higher sulphur rates to recover signalgrass (Brachiaria decumbens Stapf), and that fertilization increases the water use efficiency by plants. The leaf area, dry matter yield, water consumption, and water use efficiency of the grass were evaluated under the application of nitrogen and sulphur rates. Cylinders of 15 cm diameter and 20 cm depth were used to collect signalgrass + undisturbed soil from an Entisol with degrading pasture. The experiment was carried out in a greenhouse, in Piracicaba, Sao Paulo State, Brazil, from November 2003 through March 2004. Five rates of nitrogen (0, 100; 200; 300 and 400 mg dm(-3)) and sulphur (0; 10; 20; 30 and 40 mg dm(-3)) were tested by the response-surface methodology based on a modified central composite design of a 52 fractional factorial scheme. Three harvests were performed in 30 day intervals. The interaction between nitrogen and sulphur rates was significant for the first harvest only, with exception of leaf area for which this interaction was significant for the second harvest as well. The effects of nitrogen were significant in the second and third harvest only. The concomitant supply of nitrogen and sulphur to signalgrass increased leaf area, forage yield, water consumption and use efficiency.