Comparison of old permanent grassland, Lolium perenne and Lolium multiflorum swards grown for silage 3. Effects of varying fertiliser nitrogen application rate
T. Keating et P. O'Kiely, Comparison of old permanent grassland, Lolium perenne and Lolium multiflorum swards grown for silage 3. Effects of varying fertiliser nitrogen application rate, IRISH J A F, 39(1), 2000, pp. 35-53
The aim was to identify modifications to the N-fertiliser regime that would
optimise the annual productivity of three grass swards managed within inte
nsive silage production systems. Replicate main plots within an old permane
nt grassland (OPG) sward of diverse botanical composition were unaltered or
were reseeded with Lolium perenne (LP) or Lolium multiflorum (LM). In the
first and second years after reseeding, plots located within three main plo
ts per sward were sub-divided into six sub-plots, and six annual rates of f
ertiliser N (0, 230, 330, 430, 530 and 630 kg N / ha) were randomly allocat
ed among the latter. There were four harvests each season of OPG and LP and
five of LM. Neither sward botanical composition or tiller density (P > 0.0
5) were altered by the rate of fertiliser N applied. In the absence of fert
iliser N input, mean annual dry matter (DM) yields were 7.3, 6.2 and 8.7 t/
ha, mean in vitro DM digestibilities were 721, 775 and 786 g/kg, mean crude
protein concentrations were 153, 153 and 132 g/kg DM and mean water-solubl
e carbohydrate (WSC) concentrations were 19, 29 and 33 g/l for the OPG, LP
and LM swards, respectively. Increasing rates of fertiliser N application g
enerally increased annual DM yield and crude protein concentration and redu
ced WSC concentration. Whereas they did not affect the mean digestibility o
f OPG or LP swards, they caused a reduction with the LM sward. Whereas appa
rent recovery of applied N in herbage decreased in the OPG sward with incre
asing fertiliser N input, this pattern did not occur with the ryegrass rese
eds. It was concluded that under the harvesting-interval system used, avera
ge annual inputs of approximately 360, 460 and 480 kg N/ha could be appropr
iate for OPG, LP and LM swards. Furthermore, ensilability and digestibility
characteristics should be better for ryegrass reseeds than the OPG sward.