EFFECT OF NITROGEN, PHOSPHORUS AND POTASSIUM FERTILIZATION ON HERBAGE YIELD AND QUALITY AND PLANT-PARASITIC NEMATODE POPULATIONS IN AN IRRIGATED RHODES GRASS (CHLORIS-GAYANA) PASTURE IN OMAN

Three fertiliser experiments with rhodes grass for hay production were carried out for more than a year under sprinkler irrigation in an arid environment. The objective was to examine the effects of different levels of major nutrients on dry matter yields and on plant parasitic nematodes. There were 5 N, 4 P and 5 K levels. The dry matter yield response to N was curvilinear with the highest rate of 840 kg/ha/yr N increasing yields from 13 to 53 t/ha/yr. No significant responses to P and K application were recorded. The harvest x N level interaction was non-significant, indicating similar trends in response to 5 N levels over 12 successive harvests. Although high rates of N and K reduced the nematode populations significantly, there was no correlation between these populations and the dry matter yield of pasture. Of the 3 nutrients applied, only N increased N and K concentrations in dry matter, and decreased P%. An application of 120 kg/ha/harvest N is suggested to obtain high dry matter yields in rhodes grass under a cutting regime.