The effect of strategic fertilizer nitrogen and date of primary harvest on the productivity of a perennial ryegrass/white clover sward

Four management systems involving different dates for first harvest (simulated grazing, early silage, late silage and hay) and two fertilizer N rates in spring (0 and 80 kg ha ‐1 ) were imposed on a perennial ryegrass cv. Talbot/white clover cv. Blanca sward during 1981‐82. In each year, annual total herbage DM was increased by spring application of N but white clover production and content in the total herbage were reduced; however, white clover, which was depressed in the harvests immediately after N application, recovered during the season to amounts and contents in the total herbage similar to those given no spring N. Annual total herbage DM production increased as the date of primary harvest was delayed (935 to 1197 t ha ‐1 over two years) but mean organic matter digestibility values for the same period decreased (0‐769 to 0700). First‐harvest production made up substantial proportions of the annual production in the conservation systems. White clover, as shown by its production and the amount of stolon present, was tolerant of conservation systems, especially with no applied N. It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. The use of strategic spring N seems a viable option, but more knowledge of rates would be valuable since this experiment only compared 80 kg ha ‐1 with no applied N.