Factors influencing the yield and feeding value of pasture grown for conservation

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Abstract
The growth of ryegrass/clover pasture was monitored for 10 weeks after 3 closing dates in spring. The pasture was closed (a) before the start of stem elongation (Treatment 1; 30 September 1980, 28 September 1981); (b) when the developing meristems were just below defoliation height (Treatment 2; 21 October 1980, 19 October 1981); and (c) when 65–70% of apical meristems were removed (Treatment 3; 12 November 1980, 9 November 1981). Within each treatment, increasing dry matter (DM) yield was accompanied by a decrease in digestibility and crude protein content of the sward during the growth period. Compared with Treatment 1, Treatment 2 did not show a significant decrease in DM production, but the sward which developed under Treatment 2 contained more stem material, and was 3–12 percentage units lower in digestibility throughout the growth period. The digestible dry matter (DDM) yield was reduced by 15–40% with respect to Treatment 1 when the treatments were compared at the same digestibility. At 70% digestibility, Treatment 2 yielded an average of 4.8 t DM/ha per year over both years, compared with a consistent 6.3 t DM/ha per year for Treatment 1. The removal of apical meristems from Treatment 3 at closing produced a more vegetative sward with lower DM and DDM production than Treatments 1 and 2. The production of vegetative leaves in Treatment 3 resulted in a similar digestibility between Treatments 1 and 3 over most of the 1980–81 growth period. However, in 1981–82 the presence of late flowering Cynosurus cris‐tatus in the Treatment 3 sward resulted in the production of herbage containing more stem material in the early part of the growth period, and as a consequence, digestibility was reduced. In both years, after about 40 days growth, the completion of floral development in Treatment 3 prevented any subsequent fall in digestibility. The results indicate that early closing and cutting are essential to obtain conserved crops of high quality.

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