Animal production, economic results and lessons from nitrogen fertiliser use on dry hill country

Abstract

Over a 7 year period, two trials were conducted on dry, steep hill country near Waipawa, central Hawkes Bay to examine the effects of combinations of nitrogen (N) and phosphorus (P) fertilisers on sheep and cattle production. Four farmlets were established and balanced so that each contained similar proportions of predominantly north and south facing aspects, and easy (0-200) and steep (>200) slopes. For Trial 1 from 1995 to 1999, the 'Low P' farmlets had a soil Olsen P test of 9 ìg/ml, and the 'High P' farmlets had a test of 28 ìg/ml (paddock averages). One each of the Low P and of the High P farmlets received N overall in early to mid winter at 30 kg/ha applied in urea fertiliser. The trial was stocked with an initial ratio of about 65:35 sheep (5 year old Romneys) to cattle (18 month old Friesian/Angus). The stocking rate for each farmlet was individually set to fully utilise the expected pasture growth on each farmlet during winter. Standard costs and returns were used for the economic analysis in all years. High soil P status and use of N fertiliser were not economically worthwhile unless ewe numbers were maximised and spring pasture was fully utilised. This was achieved by having farmlets fully stocked with ewes during winter with cattle introduced in early spring to control additional pasture growth. This strategy was particularly successful in a drought year (1998) when N fertiliser allowed a significantly higher ewe stocking rate during winter. The farmlets receiving N fertiliser averaged $148/ha economic net margin compared with $117/ha from those without N fertiliser. In Trial 2, differential application of P (to easy slopes only) and N fertilisers (to steep slopes only) occurred in two of the farmlets. This provided higher economic returns than in Trial 1. The plus-N farmlets averaged $234/ha compared with $184/ha for those without N fertiliser. A major advantage of the differential fertiliser application approach is that the appropriate N or P fertiliser is applied only to areas that will provide the best responses from that type of fertiliser The success of intensified fertiliser use and stocking of dry hill country is dependent on maximising pasture use while reliable soil moisture and pasture growth conditions prevail i.e. early winter- early spring. Outside this period management options must be flexible enough to cope with drying conditions at any time. Keywords: animal production, economic net margin, hill pastures, nitrogen, phosphorus