The 32 combinations of applying or not applying nitrogenous fertilizer on five dates, with 6-week intervals between dates, during one treatment year were compared in three field experiments with Italian ryegrass (Lolium mvltiflorum). Phosphorus (P)and potassium (K) were applied at a uniform, high rate to all plots. All plots were harvested, by cutting, five times during the treatment year and once in May of the subsequent year.
Dry-matter yields and dry-matter yield responses to N were lower at the September and October harvests than at the May, June and July harvests. Where no N was applied 6 weeks before a harvest, N applied 12 weeks before that harvest generally increased yields of dry matter, N, P and K. On the other hand, where N was applied 6 weeks before a harvest, N applied 12 weeks before that harvest tended not to increase dry-matter yield and tended to reduce P and K yields. Applying 420 kg N/ha/year compared with nil approximately trebled the amounts of dry matter, P and K harvested in the treatment year. At the May harvest in the subsequent year dry-matter yield was increased by N applied in the treatment year, for all five application dates, although the previous autumn there had been no positive residual effect of the early applications. Apparent recovery of N was low compared with that recorded with Italian ryegrass in Cambridge. The content of N, as well as P and K, in herbage in May was reduced by the application of N the previous year. In the 1972 experiment the proportion of ‘stem’ in the harvested produce was markedly increased by N application. The size of this effect may have been associated with the rather small amount of soil N available. Applied N increased the number of tillers in the sward, but this effect appeared to be rather short-lived. A major reason for the positive effect of applied N on dry-matter yield, including the positive residual effect, appeared to be the increase in leaf blade length and probably sheath length due to N.