Effects of white clover and fertilizer nitrogen on herbage production and chemical composition and soil water

Abstract

SummaryEffects of seven levels of N application and three seeds mixtures were studied on two sites for 4 years. One seeds mixture comprised perennial ryegrass (Lolium perenne L.) and two comprised perennial ryegrass with white clover (Trifolium repens L.). One site (Trefloyne) was 24 m above sea level on deep soil and the other (Pwllpeiran) was 328 m above sea level on relatively shallow soil. The plots were cut seven times per year.White clover grew very strongly at Trefloyne in the first 2 years, fixing 350 kg N/ha/year where no N was applied; the clover declined very markedly during the 3rd year and there was very little in the sward in the 4th year; quite large quantities of clover were harvested in the 1st year even where 600 kg N/ha were applied. At Pwllpeiran the yields of clover were never high, but the clover persisted well where no N was applied. At Trefloyne the indirect contribution of the clover (in increasing the yield of grass) was greater in the first than in the second half of the year; clover was later than grass to grow strongly in the spring, but the extra grass growth compensated for this, so that the seasonal distribution of total herbage yield was similar on a grass-clover sward receiving no fertilizer N to that on a grass sward receiving six applications of N per year. At Pwllpeiran, on the other hand, the indirect contribution of the clover tended to be greater in the second than in the first half of the year where no N was applied.The olover was similar to grass in phosphorus and potassium content and higher than grass in calcium and nitrogen. The clover was higher in nitrate-N content than grass grown without clover, at low levels of applied N, and increased the nitrate-N content of the grass growing with it.Water consumption at Trefloyne was greatest on swards which contained olover and on the swards without clover which received at least 400 kg N/ha/year. The effect of clover on soil water was apparent particularly in the lower horizons of the soil.