Effect of date of application and form of nitrogen on herbage production in spring

Field plot experiments were carried out for 3 years at four sites to study the effect of date of application of ammonium nitrate/calcium carbonate (CAN) and urea (U) on perennial ryegrass production in spring. Fertilizer (70 kg N/ha) was applied at weekly intervals for 10 weeks from 1 February. Herbage was cut on the same day at all sites. 3-4 weeks after the last N application. CAN and U at 50 kg N/ha were immediately re-applied and a second cut of herbage was taken after 4-5 weeks. From meteorological data, the dates after 1 February when soil temperature at 100 mm depth increased to 5.5 o C and the dates when cumulative average daily air temperatures 0 o C from 1 January reached 200 o C were calculated for each site and year. (…)