SUMMARYIncreasing plant density in maize from 8 to 32 plants/m2, without irrigation, had little effect on the time of ear primordia differentiation but delayed the time of silking (by up to 16 days), reduced the potential grain sites available for pollination and the number of grains pollinated, and increased grain abortion during the grain fill period. In cv LG11 sufficient fertile ears were retained to maintain grain yield throughout the wide range in density, whereas yield fell in Anjou 210 due to barrenness after silking, which was the major factor responsible for the intolerance of this variety to high density. However, in a variety such as Anjou 210, which has a tendency to barrenness under stress, the grain content of the end product would not be affected at the plant densities normally used for maize silage.
Work that has been reported from some African countries indicates a dependence of grain yield in maize on the duration of leaf area after flowering. This paper studies maize yield in south-east England and confirms work at a similar northern latitude in Canada which has shown that considerable remobilization of photosynthate from the stem to the ear takes place during the main ear fill period.A similar grain yield was obtained from two contrasting hybrids. In a short early hybrid, Kelvedon 75 A, there was a low peak leaf area index (5-3) but the net assimilation rate was high due possibly to efficient light interception by leaves that maintained an erect posture. Stem dry matter was also low and hence in this hybrid the high reproductive/vegetative ratio shows that there has been economy in the production of leaves and stem, especially as a 48 % stem loss occurred during the period of ear fill.In contrast, in a later hybrid, Anjou 210, the final shoot dry matter was 20 % higher as the peak leaf-area index of 7-7 gave slightly higher crop growth rates than K 75A. Although the remobilization of stem dry matter was similar in both hybrids it was notable that a different partition of dry matter in the ears of Anjou 210 gave a higher grain/rachis ratio.The factors influencing grain yield in the tem-matter may occur from the maize stem which goes perate cereals include the source of carbohydrates towards filling the ear from about 2-3 weeks after which fill the grain and also the storage capacity of silking. They suggest that dry matter continues to the flowering head. It has been shown that a large be stored in the stem during the first 3 weeks after proportion of the carbohydrates in the grain of silking due to an inadequate ear sink. Later, the these cereals is produced after flowering (Thorne, losses in. photosynthate from the stem may be due 1965; Lupton, 1968;Bingham, 1969), the pre-to the enlarged sink capacity of the ear or to a dominant source being the 'flag' leaf in the case of reduction in the production of photosynthate by wheat and photosynthesis by the ear itself in bar-the leaf canopy towards the end of the growing ley. A similar dependence on a supply of photo-season. synthate produced after flowering has been claimed The results to be described in this paper are for the maize crop by van Eijnatten (1963), Mueller concerned with the growth and partition of dry (1964) and Allison & Watson (1966), all of whose matter in three maize hybrids (Kelvedon 75A, work was carried out in Africa. Allison & Watson Kelvedon 33 and Anjou 210), grown at a range of (1966) suggest that ear photosynthesis is negligible seeding rates in south-east England (51° N, 1° E). as the surface area of the ears is only 2 % of that of the leaves. Also the illumination is low at the position at which the ear is held on the stem. More recently, a group of workers in Ontario, Canada Data has been taken from two experiments (Exps. (Daynard, Tanner & Hume, 1969) have produced 1, 2) for which the treatments, methods and the evidence that ...
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