The effects of stocking rate and nitrogen fertilizer on the productivity of irrigated perennial pasture grazed by dairy cows. 1. Pasture production, utilization and composition

Abstract

The effects of stocking rate and nitrogen (N) fertilizer on the productivity of irrigated perennial pasture grazed by dairy cows was studied for 2 years at Kyabram, Victoria. There were ten treatments: five stocking rates ranging from 4.4 to 8.6 cows ha-l at both 0 and 224 kg N ha-1 year-1 . Although weeds did not invade the pasture, increases in stocking rate resulted in reduced daily pasture growth, and this was related to the level of residual pasture after grazing. Annual pasture production in both years declined by 0.394 t DM ha-1 for every additional cow per ha. The levels of the herbage minerals, N, P, K, Ca, Mg and Na were adequate from an animal health point of view at all stocking rates, at least in the short term. The response to N fertilizer declined from 17 to 3 kg DM kg-1 N applied, as stocking rate increased from 4.4 to 8.6 cows ha-1, and it appeared that this response was due mainly to an increase in the growth of the grasses. Apart from the stocking rate responses, which are specific to the Kyabram environment, a number of relations were found, which showed how residual pasture after grazing, pasture allocation and pasture utilization at a single grazing, influenced pasture intake. Providing allowances are made for pasture type and the level to which any particular pasture type can be grazed, these relations could be expected to give a reasonable assessment of pasture intake in other environments.