Abstract:
Changes in dry matter yield and its components and plant survival were examined in hybrid pennisetum under different rates of nitrogen fertilization on irrigated and dryland areas throughout two growing seasons. The productivity of first, second and third year stands was studied. Production was markedly seasonal; almost half of the maximum annual yield of 11.4 t ha-1 came from six weeks regrowth in mid-summer. Summer production was restricted by drought and in 1975-76 by low temperatures and radiation. There was interaction between environmental conditions and responses to N. When conditions were favourable the dry weight and leaf area responses were linear. Under moisture stress, or low temperatures and radiation, plants responded only to intermediate levels of N because of suppressed leaf and tiller production. Protein concentration increased with N. Protein and digestibility were adequate for animal production except in mid-summer, when rapid plant development under irrigation and high N resulted in digestibility values of less than 60 per cent. Survival was high except when plants were cut just prior to winter, i.e. in April, or high rates of N fertilizer were applied. Production increased in the second year because of tiller multiplication; individual tiller weights decreased. Productivity was maintained into the third year.