Clover Nitrogen and Sward Productivity

Abstract

Under mowing conditions in the absence ofthe animal, ultra-simple swards based either on ryegrass or cocksfoot gave large increases in yield of dry matter and nitrogen from the inclusion of white clover in the seeds mixture. Raising the clover seed rate from 1 to 3 Ib./acre gave a further response in yield.As the swards aged, the continuing effect of increased clover seed rate was dependent on applied nitrogen.The rate of transference of nitrogen from clover to the soil depended upon the species of the associated grass, the clover seed rate, the age of the sward and the degree of reduction of the clover in the sward.Suppression of clover led to an increase in soil nitrogen, particularly with high seed rates of clover. Dry matter response to applied nitrogen (69 lb./acre/annum) was greater in cocksfoot than in ryegrass. Fertilizer nitrogen had little effect on the yield of nitrogen from the sward except where the high seed rate of clover had been used.

The Use of Nitrogen on Grass/White‐clover Swards*

“…The results obtained on the dry-matter yield response of mown swards to applied fertilizer nitrogen agree with those reported by other workers(l,2, 3, 4, 6,7,8,10,11,12,14). The consistent linear response of grass swards to 200 lb fertilizer nitrogen per acre is in direct contrast with the variable, often small, response from grass/clover swards.…”

“…In the poor year the grass/clover sward did respond well to applied nitrogen as the extent ofclover suppression was small. The grass yield of the grass/clover sward and the total quantity of nitrogen transferred from clover to grass were similar in good and bad years, and were unrelated to the bulk of clover present (6). In a poor year clover transferred more nitrogen per unit weight of clover foliage present than in a good year.…”

The Effect of Fertilizer Nitrogen and White Clover on Herbage Production

“…The effect of fertilizer N on N transfer could have been a result of increased underground transfer associated with clover suppression (7), but this is unlikely to have been the only reason since it occurred each year in Experiment 2 where the clover population was relatively stable. The effect was also unlikely to have been a result of differences in N recirculation by grazing animals as it has been noted on cut swards (5,7,10) well as on grazed swards (12), although it was greatest on the latter. Clover N transfer is estimated as the difference between grass N yield on the mixed and grass swards.…”

“…However, the response of mixed swards to applied N is variable and often small (4,7,8,9,10). In the majority of the reported work the herbage was cut and removed.…”

Gulle as a Grassland Fertilizer

“…This trial has again emphasized the value of the legume in sward output and the low apparent efiiciency of fertilizer nitrogen on a substratum containing much clover (1,6). In addition to it being difficult to alter the growth pattern of the young, clovery ley by fertilizer nitrogen, it would appear in this trial that total output was little affected by the way in which, over a season, the total nitrogen application was split up.…”