Effect of fertilizer nitrogen rate and timing on herbage production and nitrogen use efficiency for first‐cut silage

Abstract

AbstractEight field‐plot experiments were carried out on established grassland swards between 1984 and 1988 to examine the effects of date and rate of application of calcium ammonium nitrate (CAN) on herbage dry matter (DM) yield and apparent efficiency of nitrogen (N) use at first‐cut silage.CAN application significantly increased (P <0 ·001) the mean yields of herbage and N uptakes by herbage in all experiments. Herbage yields were similar (P > 0·05) with N rates of 100 kg ha−1, 125 kg ha−1 or 150 kg ha−1 in five experiments but in the other three there were increases above 100 kg ha−1. Date of N application had a significant effect on DM yield in three experiments; this effect was inconsistent for both single and split dressings. Lower production was associated with reduced uptake of N, a trend that primarily reflected lower DM yields and not wide herbage N content variation.It is concluded that selection of the date on which to apply fertilizer N in early spring to obtain optimum herbage yields at first‐cut silage often required little precision. The use of fertilizer N rates >100 kg ha−1 should be questioned where there are likely to be appreciable quantities of available N derived from non‐fertilizer sources.