Emergence, growth and dominance in drilled and square-planted barley crops

Abstract

A barley crop (cv. Clipper) was grown at three densities and in two plant arrangements, square-planted and drilled. Studies were made of the emergence and growth of individual plants within permanent quadrats. Later-emerging seedlings gave rise to smaller plants at stem elongation and at the early grain stage, and they produced fewer grains than plants which had emerged earlier. On drilled plots, at the normal commercial sowing rate (the medium density treatment), the regression of grain number per plant on day of emergence was - 14.4% of the mean number of grains per plant, so that a delay of 3 days in emergence caused a reduction of 43 % in the number of grains formed. The regression of grain number on day of emergence in the medium density square-planted plots was - 8.3 %. It is suggested that the difference in the regression coefficients within the drilled and square-planted plots respectively was due to the different incidence of intra-plant and interplant competition in the two situations. Plants were regrouped into decile groups at stem elongation (day 70). Thereafter, larger plants achieved not only greater absolute increases in weight, but also greater relative growth rates; the large plants thereby further increased their percentage contribution to the crop. For all plant sizes within both planting arrangements and within each of the three densities, the number of grains per plant was linear on the weight of the plants. The ear number per plant was the principal feature of difference between large and small plants, followed by spikelets per ear. The significance of these phenomena in plant breeding and agronomy is discussed. Appendix 1 reports two methods for the non-destructive estimation of the yield of individual plants in a cereal crop.