Nitrogen fertiliser effects on white clover in dairy pastures

Abstract

Effects of high N fertiliser rates on white clover content in the sward and clover plant morphology were monitored over two years (June1993-June 1995) at the DRC, Hamilton. The clover study was part of a farmlet trial aimed at increasing milksolids (MS) production to 1750 kg MS/ha using urea (0, 200 or 400 kg N/ha/yr) to increase pasture production at low (3.2 cows/ha) or high (4.5 cows/ha) stocking rates. On low stocked farmlets clover contents declined to 10.6% (200 kg N/ ha/yr) and 2.2% (400 kg N/ha/yr) by June 1995 compared with 16.8% under no N. Decreased clover content was a result of increased competition from N-boosted ryegrass. At the high stocking rate, N application resulted in clover contents of 14.9% (200 kg N/ha/yr) and 6.8% (400 kg N/ha/yr) compared with 15.4% under no N. Pasture utilisation was better on these farmlets, suggesting the improved utilisation and control of additional feed, particularly during spring, was responsible for the higher clover content. Measurements of clover plant density supported the clover content observations. By June 1995 there were 438, 227 and 26 plants/m2 under 0, 200 and 400 kg N/ha/yr respectively. High N rates also affected clover plant morphology; plants developed fewer axillary buds and stolons, and had lower stolon dry weights under 400 kg N/ha/yr. Keywords: clover content, dairying, morphology, nitrogen, plant density, Trifolium repens, white clover