SUMMARYSimulating the accumulation of dead leaf sheaths in perennial ryegrass by masking the tiller bases increased leaf and sheath length and tiller weight but decreased tiller production. Exposure of previously masked tiller bases or stripping back the subtending leaf and sheath to expose the tiller bud in its axil stimulated tiller production. A photomorphogenic effect is postulated which controls the partitioning of dry matter between the growth of new leaf and sheath tissue on existing tillers, and the development of new tillers from tiller buds.
The infectivity of ten commercial mycorrhizal inoculants was examined in nursery conditions. Corn plants were grown in a soil-based medium and in two different soilless substrates, a potting mix prepared with redwood bark, pine sawdust, calcined clay and sand, and the commercial Sunshine #5 mix, mainly composed of Canadian sphagnum peat moss. The percentage of mycorrhizal colonization obtained with the different mycorrhizal inoculants ranged from 0 to 50%. This variation might reflect the presence or absence of viable propagules, the difference in the recommended rates applied as well as the difference in the content and type of infective propagules of each product. However, the infectivity of each mycorrhizal inoculant was also influenced by the growing media. Two products promoted higher values of mycorrhizal colonization in the Sunshine mix, three in the nursery mix and one in the soil-based medium. Mycorrhizal colonization did not enhance plant growth. Only the plants inoculated with the products that did not promote mycorrhizal colonization increased their growth relative to the non-inoculated controls, suggesting the presence of other growth promoters in the inoculum products. Based on these results, nurseries should conduct preliminary tests to determine which inoculants will perform in their potting mixes to assure the best fit of inoculum with their particular conditions.
An examination was made of the effects of different spring treatments on the growth of white clover in a ryegrass/white clover sward. Plots were either cut once (in February, March or April) or twice (in February and April) or left uncut. Nitrogen was applied to half of the plots in each instance. The clover was sampled at intervals of approximately 3 weeks from February to June to determine numbers of leaves and growing points and weights of plant parts. Rates of leaf appearance were also observed and estimates were made of total herbage mass from ground-level cuts.Percentages of white clover in the herbage were higher in unfertilized than in fertilized plots and in defoliated than in undefoliated plots. The percentage increases that followed defoliation were usually maintained into later regrowth, showing that clover content was not automatically reduced as herbage mass increased. Increases in growing points were recorded after the beginning of April in defoliated unfertilized plots but not in undefoliated fertilized plots or in plots fertilized and defoliated twice during the spring period, in which numbers fell substantially.Inverse relationships were found between rates of leaf appearance, or the number of green leaves retained per stolon, and herbage mass, whereas heights of clover and grass leaves and Correspondence: Alison Davies. [nstilule of Grassland and Environmenlal Research, Welsh Plant Breeding Station, Aberystwyth, Dyfed SY23 3EB, UK.the percentage of dry matter allocated to petiole rather than leaf in the clover increased with increasing herbage mass.We suggest that the observed differences between spring treatments in clover percentage result primarily from their differential effects on the formation and death of tillers and growing points in the early stages of regrowth.
In a study of growth rates and developmental morphology of simulated swards of two contrasting white clover varieties, Katrina and Kent, it was found tbat both varieties continued to produce dry matter throughout the winter at Aberystwyth. The gross crop growth rate in the coldest periods was about 7 kg ba~'d"'. The rates of formation and loss of new leaves were approximately equal so that there was no net increase in weight until the latter part of March. This initial net weight increase in both varieties was observed in the same harvest interval, the most important factor being the difference in weight between the new leaf plus petiole unit and the weight of the unit which it replaced. The weight of laminae and petioles throughout the experiment was somewhat higher in Katrina which has come to be regarded as the 'earlier' variety.The prospects for improving spring production in white clover by variety improvement are discussed.tntroduction The potential usefulness of white clover (Trifolium repens) m agricultural practice in the UK is restricted by the unreliability of the clover contribution in the sward and by the difficulty of maintaining a good clover percentage without sacrificing potential spring production of grass.Correspondence: Ms A. Davies, Welsh Planl Breeding Station, Plas Gogerddan. Aberysiwyih. Dyfcd SY23 3EB. UK.
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