Abstract:
The effects of suboptimal plant density and non-uniformity in plant spacing on grain yield of raingrown sunflower were examined using regression analysis. This involved quantifying the parabolic relationship between grain weight per plant and area per plant. A term for uniformity was added, based on the proximity of neighbouring plants within the row. Multiple regression accounted for 50% of the total variation amongst the 1071 plants analysed. The 3 constants in the regression were considered to indicate the yield potential of the crop, the proportion of space available per plant not utilised at low density, and the proportion of the most scarce resource denied to the individual plant at high density relative to an equivalent plant at even spacing. This technique permitted quantification of the levels of unevenness, and of the percentage yield reductions attributable to suboptimal plant density and to non-uniformity in plant spacing. Reductions in grain yield per unit area were mainly due to a lack of plants at low densities, and to unevenness at high densities. A technique is proposed for surveying crop establishment, and for estimating the percentage yield reductions attributable to the effects of plant density and uniformity in plant spacing over a range of crops. Further experimentation is warranted, to determine whether the percentage yield reductions found for this crop are generally applicable.