STUDIES IN RESPONSE TO NITROGEN

Regression equations have been calculated for the primary growth of a ryegrass sward as FM (fresh matter), DM, DOM and for uptake of N, K, P, Ca, Na and Mg after application of 59,118 or 177 kg fertilizer N/ha on 16 Apr. These have been used to predict changes in response with time, the responses in terms of time, the dates when specific yields of DM are attained, the different characteristics of herbages at specified yields of DM and the effects of changing harvesting interval on annual DM yield and uptake of minerals. DM and DOM show significant responses to 118 kg N/ha but no response to the next increment throughout the 57-day growth period. All other attrihutes, including FM, showed responses to 177 kg N/ha. Calculated response as days gained suggest that for short-interval grazing systems the use of even 118 kg N/ha is questionable. The reduction in annual DM production and the increase in N uptake when growth intervals are shortened are related to the form of their growth curves.