A pasture association comprising short-rotation ryegrass, red clover, and white clover was subjected to three different intensities of defoliation by cutting down to 1, 3, and 5 in.A t 4-day intervals over a period of 32 days, nleasurements were taken of herbage d r y matter yield, the leaf area per unit area of ground, and the percentage of light penetrating to a level 1 in. above the ground surface.Where pasture was defoliated to 1 in., light interception was almost complete (95 per cent. or. over) approximately 24 days a f t e r cutting, whereas pastures defoliated to 3 in. and 5 in. intercepted almost all the incident light 16 and 4 days a f t e r cutting respectively.A t these stages of growth the leaf area was approximately 5 sq. f t per sq. f t of ground and the herbage yield approximately 1450 lb dry matter per acre, regardless of treatment.The r a t e of pasture growth increased until complete light interception was approached, and thereafter a n almost constant maximum rate was sustained.Leaf efficiency (the rate of increase of herbage dry weight per unit area of leaf) was greatly influenced by intensity of defoliation. Efficiency was initially lower following severe defoliation than following less severe treatment. I t increased rapidly to a nlaxiniurn and thereafter declined gradually. Maximum efficiency in the 3 in. and 5 in. cutting treatments was attained when maximum growth yate was first reached. F o r pasture defoliated to 1 in., i t reached a maximum level during the phase of accele~ating growth.

Relationships between light interception and leaf area in the regrowth of pure stands of short-rota,tion ryegrass (Lolium perenne L. x L. multi$orum Lam.), perennial ryegrass (L. pere~me), timothy (Phleum prate?ase L.), white clover (Tr

An experiment is described in which the effects of frequent hard grazings at different times of the ye'ar on the productivity and species yields of a pasture of short-rotation ryegrass, cocksfoot, and red and white clover were determined over an eighteen-month period. Frequent hard grazings during the winter encouraged the growth of all sown species, and dry-matter (d.m.) yields were high for these pastures after a change to less-intensive grazing in later seasons. Frequent hard grazings during the spring reduced immediate d.m. yields markedly but because there were no detrimental effects on plant survival of any of 'fhe sown species except red clover, subsequent d.m. yields of these pastures were also relatively high when the management system reverted to the less-intensive system. Frequent hard grazings during the summer resulted in widespread death of all sown species except white clover. Subsequent d.m. yields obtained from these pastures were ,thus severely reduced. Frequent hard grazings during the autumn reduced immediate d.m. yields by approximately 20% but, it is suggested that because the lightshielding clover canopy was controlled, yields obtained from the sown grass species in fhe following seasons were high. The results highlight the importance of summer grazing management to ensure persistency of pasture species, the importance of intensive grazing in the late autumn to bring a'bout a rapid change in botani'cal composition from dominance of summer-growing species ,to dominance of winter-growing species, and the relatively high yields obtained by avoiding long spelling during the winter. The results are discussed in relation to existing pasture-management principles and productivity.

The growth curve of a pasture consisting of short-rotation ryegrass, red clover, and white clover was determined by measuring dry matter yields at intervals over a 9-week period in the spring of 1953. To determine the effects of temporary weather variations on growth, the experiment was replicated in time as well as space. The experimental technique is described. The curves of growth for ryegrass and total herbage were sigmoid. In the second phase of growth of approximately 6 weeks when rate of growth was constant, the daily increment in total herbage approached 150 1b dry matter per acre. Total herbage yields were separated into two parts to give a growth effect for a constant (mean) climate and an irregular weather effect. This latter separation showed agreement with fluctuations in temperature and rainfall. The results are discussed in terms of pasture management practices, and the possibilities of growth rate studies for future pasture experimentation are considered.

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An experiment is described in which the rapidity and extent of changes in the genotypic structure of a mixed perennial and Manawa ryegrass popul

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