EFFECTS OF NITROGEN FERTILIZER ON HERBAGE YIELDS AND SHEEP PRODUCTION ON IRRIGATED PASTURE, AND A COMPARISON OF METHODS OF YIELD ASSESSMENT

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Abstract
Nitrogen fertilizer was applied at various rates and times to an irrigated grass–legume pasture grazed by sheep at Lethbridge. Mean herbage yields were 4257, 5247, 5847, 6269, and 6446 lb D.M./acre where 0, 1, 2, 3, and 4 fifty-pound applications of N/acre were made annually.Sheep weight gains were 358, 406, 467, 504, and 530 lb/acre under these same fertilizer treatments. Early season applications gave the greatest response per unit of N. The effect on yield of a 50-lb/acre application was largely dissipated within 30–40 days. Daily gain, daily dry matter consumption by the sheep, and T.D.N. content of the herbage were similar under all fertilizing treatments.Three different techniques of harvesting herbage from ungrazed plots were compared with harvesting from caged areas within the grazed plots. The best estimate of cage yields was obtained with a technique in which herbage cut from the ungrazed plot was returned as a mulch to decompose. The standard clip-plot procedure with the herbage discarded did not give a good estimate of cage yields though the estimate was improved when cattle manure was applied each spring to replace part of the nutrients removed in the harvested herbage.

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