Nitrogen and Italian ryegrass. 3. Growth up to 14 weeks: yields, proportions, digestibilities and nitrogen contents of crop fractions, and tiller populations
1976
The regrowth of Italian ryegrass following a cut in late April was studied at weekly intervals up to 14 weeks. There were four levels of applied N: 28, 84, 140 and 196 kg ha‐¹. The proportion of green leaf blade declined from 80% of DM yield after 2 or 3 weeks of regrowth to 5% after 13–14 weeks. About three‐quarters of the increase in DM yield of total herbage from week 3 to week 11 was attributable to increased yield of ‘stem’. The level of applied N had little effect on the proportion of crop fractions except during the period immediately before and after the begiiming of ear emergence when the higher rates of N increased the proportion of ‘stem’ and reduced that of green leaf. The most digestible crop fractions were green leaf, inflorescence and immature ‘stem’. D‐value of ‘stem’ declined by about 20 units from week 1 to week 14, while D‐value of green and dead leaf declined at about half this rate and there was little or no decline in D‐value of inflorescence. The N content of green leaf was consistently higher than that of the other fractions. The N content of ‘stem’declined markedly to around 0.5% by week 12. The N content of dead leaf and inflorescence was intermediate between that of green leaf and mature ‘stem’. The N content of all fractions was increased by applying more N. The tiller population increased during the flrst 3 weeks of regrowth and declined during the next 4. Applying more N increased both tiller population and weight per tiller.
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