Effect of Irrigation and Nitrogen on the Dry Matter and Crude Protein Yields of ‘Pangola’ Digitgrass1

Abstract

AbstractIn Trinidad, West Indies, a dairy industry is being developed on Piarco fine sand/fine sandy loam soil, classified as Aquoxic Tropudults. The soil is physically and chemically poor. The cattle obtain most of their food supply by grazing ‘Pangola’ digitgrass (Digitaria decumbens Stent.). There is an urgent need to increase grass production on this soil type. Inadequate water supply in the dry season limits grass production. Previous fertilizer trials with Pangola digitgrass on this soil type have indicated that N fertilizer is likely to give better yield response than P, K, or Ca. This trial was therefore conducted to determine the irrigation‐N management for wet and dry season production of Pangola digitgrass on this soil at adequate levels of P and K.The dry matter and crude protein yield responses of the grass to irrigation and N were studied in the field on established pastures. A split plot design was used with irrigation levels as the main plots and N levels as subplots. There were three levels of irrigation (irrigation back to field capacity at soil water deficits of 1.25, 2.50, and 3.50 cm per 30 cm of soil) and a control (no irrigation); and three levels of N, 224, 448, and 672 kg/ha.In the moderately dry year of 1972 in Trinidad, irrigation had little effect on the dry matter yields or the percentage or total crude protein of Pangola but in the severe dry season of 1973, dry matter yield was essentially doubled even when the soil was allowed to dry to a maximum water deficit of 3.75 cm per 30 cm.In the dry season of 1972, dry matter and crude protein yields increased with an increase in N fertilization from 224 kg to 672 kg N/ha/year but this was reversed in the wet season. The total annual dry matter production was best at 224 kg N/ha and irrigation back to field capacity at 1.25 cm deficit.The best irrigation‐N management for Pangola depended on the season of the year as well as on the severity of the dry season. In the moderately dry season, N substituted for irrigation and 672 kg/ha of N without irrigation was best. In a severe dry season, 224 kg N/ha/year and irrigation at the 1.25 or 2.50 cm deficit gave the best yields; and in the wet season, the management should be 224 kg N/ha and irrigation at the 1.25 cm deficit. The fertilizers were applied as split applications; N was applied after every 6‐week harvest and phosphate and potash, after every third harvest.