| Population level had a pronounced effect on days to heading. Treatments
of the low seeding rates were slower to head than were their counterparts
at the higher seeding rates. Cultivars headed earlier in narrow row spacings
than in their wide-row equivalents. Moreover, cultivar x seeding rate interaction
was significant for days to heading. Similar results were obtained by FINLAY
et al. (1971). The decreasing leaf area, particularly the flag-leaf
area and the competition for light at increasing population levels causes
the plants to enter earlier in their generative phase. Harvest index was clearly influenced by row spacing and seeding rate. Cultivar x seeding rate and row spacing x seeding rate interactions were also significant. At high population levels plants compete for nutrients and for light, hence the tillering is reduced to the extent that much part of the crop comprises of main tillers. As the side tillers share a little in the final yield, but some of the tillers remain headless in wider spacing, resulting in reduced harvest index of low population levels. GENC (1978), also reported a reduction in harvest index with increasing tillers per plant. One of the reasons of the increasing yield with increasing densities upto optimum is the control of weeds with narrow rows. In wide rows weeds develop quickly and vigorously consuming water and nutrients otherwise available to the crop under cultivation. BURNSIDE et al. (1964) reported reduced weed growth in narrow rows. They obtained a highly significant negative correlation between grain yield and weed growth (r=0.30**). Today, therefore, the best control of weeds could be achieved by reducing the distance between rows. Chemical weed control affects the micro-organisms present in the soil, causes genetic variations in the crop and increases the cost of production. With increasing seed rates, the number of fertile tillers per unit area increased resulting in yield increases upto an optimum after which despite of increase in seeding rate and fertile tillers, yield decreased most probably because of acute reductions in leaf area and the reduced seed number per spike and the seed weight at above optimum densities. The number of grains per ear is the chief variable accounting for the decline in grain yield in above optimum population (WILLEY & HOLLIDAY 1971). Precise recommendations for any situation are not possible, but the implications are that the optimal plant density depends on the amount of nitrogen available to the crop and possibly on other growth factors. Nevertheless, more yield trials of a similar nature are needed before a positive recommendation can be made. The most important agronomic characters are the maximum yield, early heading and a high harvest index. This experiment has shown that differences in population density can have marked effects on the growth of the plants, nevertheless, narrow row spacing with optimum plant densities appear most suitable for optimizing these characters. |
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