EFFECTS OF LIME AND NITROGEN-FERTILIZER ON 2 SWARD TYPES OVER A 10-YEAR PERIOD

Two long-term field experiments were conducted on a clay soil near Car rickfergus, County Antrim from 1983 to 1993. The main experiment teste d the effects of lime (0, 4, 8 and 12 t/ha applied in 1983), N (160 an d 320 kg N/ha per year as ammonium nitrate/calcium carbonate), sward t ype (permanent pasture and perennial ryegrass reseed) and initial soil pH (5.1 and 5.5) on the yield and composition of herbage for 10 years . The secondary experiment studied the interaction between lime (0, 4 and 8 t/ha applied in 1985) and N (80 and 160 kg N/ha per year) for 8 years. In both experiments the plots were fertilized three times each year for three cuts of herbage. In the main experiment, dry matter (DM ) yield and N offtake over all 10 years depended little on initial soi l pH. Over all cuts and years, DM yields of both sward types increased with lime. Responses peaked after 3 years and were largest with the f irst cut of the reseed at the lower rate of N fertilizer. Over the fir st 6 years after lime application, the average responses from the rese ed at the lower rate of N fertilizer to 4, 8 and 12 t/ha of lime were 1.02, 1.85 and 1.65 t DM/ha per year respectively at the first cut. At the higher rate of N fertilizer, the response in DM yield of the rese ed to lime averaged 0.91 t/ha at the first cut over the same period. I n the last 3 years of the experiment, lime had no effect on DM yield e ven though soil pH ranged from 5.0 to 6.3 A significant response in N offtake due to lime only occurred at the first cut. Responses at the f irst cut averaged over all treatments were 3.5, 6.5 and 6.6 kg N/ha pe r year for 4, 8 and 12 t/ha of lime respectively. In the secondary exp eriment, responses to lime were again mainly at the first cut. There w ere few lime x N interactions in either experiment. Liming increased N availability either by increasing mineralization of soil N or by impr oving the uptake of ammonium and nitrate by roots. The effects of soil pH and Ca supply on these two processes are difficult to separate. Al l rates of liming at both N rates were cost-effective for the reseed, but only the lower rates of liming at 160 kg N/ha per year were cost-e ffective on permanent pasture. Current recommendations for liming gras slands should continue, particularly for swards reseeded with perennia l ryegrass.