Plant population, shading and thinning studies in wheat

Abstract

Three wheat experiments are described in which a range of plant populations were shaded during different periods of development; in two of the experiments plant thinning was also carried out at a number of growth stages. Shading during the period of ear development caused an appreciable decrease in grain yield by decreasing the number of grains per ear. Shading during the grain filling period also reduced grain yield, this being brought about by decreased grain size. Thus in contrast to the barley experiments reported earlier (Willey & Holhday, 1971), these particular results gave no indication of a potential surplus of carbohydrate for grain filling and an associated limited ear capacity. However, when plant thinning was carried out at anthesis to make more carbohydrate available for grain filling in the remaining ears, grain yield per ear did not increase. It is argued, therefore, that grain yield probably was determined at least partly by a limited ear capacity. Plant thinning at earlier stages showed how the development of competition during the ear development period progressively reduced the potential capacity of the ear; the greater competition of higher plant populations accelerated this reduction in ear potential.From an examination of the effects of plant population, it is suggested that the number of grains per ear is the component having greatest influence on the decline in grain yield at above-optimum populations. The possible importance of the number of grains per unit area as an indicator of ear capacity on an area basis, and as a determinant of grain yield per unit area, is emphasized. A close relationship between grain yield per unit area and number of grains per unit area is illustrated for a number of plant-population response curves, and it is suggested that the decrease in grain yield at high populations is probably determined by a decrease in the number of grains per unit area. Evidence is presented to substantiate the idea put forward in the barley paper that this decrease in the number of grains per unit area may be attributable more to a lower production of total dry matter by the high populations during the later stages of ear development, than to an unfavourable partitioning of such dry matter between the ear and the rest of the plant. INTRODUCTIONt o t h a t U 8 e d m t h e b a r l e v m t n a t a r a n 8 e o f plan* populations were shaded during different periods An earlier paper (Willey & Holliday, 1971) of development. In two of the experiments the reported the effects of plant population and shading range of plant populations was much greater than in some barley experiments. This paper deals with that used in the barley and a more detailed examinathree similar wheat experiments. The main purpose tion of the various development periods was underwas to examine the physiological factors deter-taken. Also, in these same two experiments, selected mining the relationship between plant population treatments were thinned at different stages of and grain yield, particularly the decrease in...

Response of Bread Wheat (Triticum aestivum L.) Varieties to Seeding Rates at Kulumsa, South Eastern Ethiopia

“…On the other hand, the lower number of tillers for variety Digelumight be attributed to the death of tillers due to low rainfall late in the growing season. This result was in agreement with Willey and Holliday (1971) where they indicated that high seeding rates generally increased number of spikes per square meter, although fewer and smaller kernels per spike can occur which results in little change in total grain yield. Kumar et al (1991) and Ahmad et al (1999) also confirmed the present result, where higher sowing rates increased the number of tillers mG 2 due to more plant population but number of tillers per seedling decreased with increased in seed rate.…”

Yield Formation in Mediterranean durum wheats under two contrasting water regimes based on path-coefficient analysis

“…wheat (Slafer & Rawson, 1994) and barley (Willey & Holliday, 1971). Moreover, the experimental decrease of competition for assimilates by removing tillers from the plant in spring wheat resulted in lower floret abortion (Mohamed & Marshall, 1979).…”

The effect of soil fertility on the contribution of main stem, tillers and kernel position to grain yield and grain protein content of wheat

“…The number of grains of the second tillers (T 2) was not significantly affected, although it increased by 13.3%. In field experiments, several authors (Puckridge & Donald, 1967;Willey & Holliday, 1971;Fischer, Aquilar, Mauver & Rivas, 1976) have reported that an increase in grain yield was positively correlated with an increase in grain number. Our results indicated that grain yield per ear was strongly associated with grain number per ear.…”

“…Kernel mass depends on the availability of plant assimilates during the stage of grain-filling, and this is closely related to the leaf area duration after anthesis (Spiertz, Ten Hag & Kupers, 1971;Thome, 1974;Annandale, Hammes & Nel, 1987). Puckridge and Donald (1967) and Willey and Holliday (1971) found that very high numbers of grains can only be achieved in dense crops, in which radiant energy for grain-filling will be limited and grain weight will decrease due to less reserve carbohydrate in ear-bearing shoots after anthesis. Briggs (1991) concluded that genotypic variation in kernel mass (or seed size) within wheat cultivars is common and will depend on the levels of environmental stress in a particular growing season, as well as on the specific plasticity of individual cultivars.…”