Management studies in seed production of Tama Westerwolds ryegrass (Lolium multiflorum Lam.) including aspects of seed physiology : A dissertation submitted in partial fulfilment of Bachelor of Agricultural Science (Honours)

Abstract

The seed production of Tama Westerwolds Ryegrass (Lolium multiflorum Lam.) was investigated under 2 different management systems on a commercial scale during 1979. One system involved grazing with ewes over lambing with 25 kg nitrogen per hectare applied in July, September and October. The crop was shut up for grass seed in mid-September and harvested in December.The second block was ungrazed, had 15 kg nitrogen per hectare applied in September, and was also harvested in December. The distribution of 14c-assimilate during seed fill was examined in selected plants within this trial. The source of 14c was 14c-urea applied to the lamina of either the flag or penultimate leaf. · A pot experiment was also conducted in the winter of. 1980 to supplement field data by determining the effects of defoliation (both prior to and after stem elongation had begun) on seed yield components of individual tillers. In the field trial the grazing plus nitrogen significantly increased t he :number of fertile tillers at harvest from 580 ears per m2 (ungrazed) to 750. However, this was accompanied by a decrease of 2.0 spikelets and 0.8 grains per ear, both of which were significant. This management · system also increased the degree of lodging observed in the crop. Despite this, the final yields from commercial harvesting showed that the grazed block (1000 kg/ha) yielded far better than the ungrazed block (590 kg/ha). In the pot experiment, defoliation, once the stem apex had been raised 2.5 cm above the soil level, significantly reduced spikelet numbers per inflorescence and floret numbers per s pikelet. Thus reduced yields would be expected if defoliation occurs after stem elongation has begun. Studies of production by individual tillers showed that the main stem contributed more spikelets and florets than the first and second tillers, which in turn were more productive than later formed tillers. Of the recovered 14c-assimilate from the flag and penultimate leaves, 2-10 percent was found in the ear and there appeared to be equal contribution from both leaves. The main site of 14c-assimilate accumulation from the flag leaf was in the internodes (75-91 percent~ while the penultimate sheath ·had accumulated 68-80 percent of the 14C-assimilate from the associated lamina.