The Effect of Time and Rate of N Application on the Productivity of Grass Swards in Two Environments

Six identical experiments (3 in Devon and 3 in Suffolk) investigated the effect of 200, 300 and 400 lb N/ac (224, 336 and 448 kg/ha), given in 1, 2, 4 or 8 equal applications, on the yield and seasonal production of perennial ryegrass swards cut every 25 days. Each rate of N Increased DM and N yields. Giving the N in 4 or 8 dressings gave higher DM, bnt rather lower N yields, than applying the N in 1 or 2 dressings. The effect on DM yield of splitting the N was most marked at 400 lb NJac (448 kgJha). Seasonal production was closely related to the time of N application and most uniform where N was given in 8 dressings. Differences between Devon and Suffolk were most evident where the N was given in 4 or 8 dressings and occurred in the second half of the season when the low rainfall in Suffolk apparently restricted N uptake and DM yield. The efficiency with which N taken up by the plant was used for DM production was affected by sunshine. It is concluded that rainfall and sunshine will limit the extent to which fertilizer N can he used to control herbage production.