Response of white clover cultivars to fertiliser nitrogen

摘要

Fifteen white clover (Trifolium repensL.) cultivars were grown with perennial ryegrass to determine their tolerance to fertiliser nitrogen (N) application. There were four N treatments (0, 25, 100, and 225 kg N/ha per year) and the trial was mob-stocked by sheep 8 times a year for 3 years. N applied at 25 kg N/ha per year had no significant effect on either clover or total sward yield. However, 225 kg N/ha per year depressed clover yield by 38 and clover proportion in the sward by 45 but increased total sward yield by 27. There was no significant cultivar #xD7; N interaction for clover yield or proportion of clover in the sward. However, there was a significant difference among cultivars for N tolerance ratio in spring, calculated as N225divided by the mean of N0and N25of clover yield. Cultivars with the highest N tolerance ratio were Huia, Kopu, Bianca, and Crau; those with the lowest were Menna, Aran, Katrina, and N-line. Spring N tolerance ratio was not correlated with spring yield or any of the stolon characters measured. There were no significant cultivar #xD7; N interactions for stolon characters measured, including stolon length per unit area, stolon dry weight per unit area, and stolon growing point density. Similarly, there were no significant differences among cultivars for N tolerance ratio for any of the stolon characters measured. Total sward yield was significantly related to clover yield when N was applied at 25 kg N/ha per year. There were large differences among cultivars for clover yield, total sward yield, and proportion of clover in the sward. Cultivars with highest clover yields were Crau, G.23, Demand, Olwen, and Aran; lowest clover yields were from Menna, N-line, Kersey, Katrina, and Tahora. Total yields of swards containing Crau were significantly higher than that of most other cultivars. There was a significant cultivar #xD7; season interaction for clover yield and proportion of clover in the sward. G.23 had the highest proportion of clover in the cool autumn-winter period whereas Crau was highest in the warmer summer-autumn period. High summer clover contents were obtained for Aran, Olwen, and Demand, and high winter clover contents for Kopu.