The growth and performance of rain-grown cotton in a tropical upland environment: II. The relationship between yield and growth

Abstract

SUMMARYAn hypothesis, based on Mason's nutritional theory of boll shedding, was set up to relate the yield of cotton to crop growth in three agronomic experiments. It was postulated that bolls were set only if the demand for carbohydrates of the metabolic sink which they formed did not exceed the supply, both of which were estimated. Two components of the sink were recognized — the daily growth rate of a single boll, DGRB, and the number of bolls on the crop plants. The effects of genotype and environment on these components were analysed. Their product gave the size of the boll sink, CB, which was compared with the crop growth rate, C, to indicate respectively carbohydrate demand and supply. Three sets of evidence to support the hypothesis were considered: (i) when CB > C, the number of bolls, and hence the size of the sink, ceased to increase, and bolls started to shed heavily; (ii) a model to predict yield, based on the hypothesis, accounted for all non-random variation in yield between sowing dates and varieties; (iii) the correlation between yield and various crop attributes, recorded before picking, became strikingly closer between 110 and 130 days from sowing when CB > C, suggesting that yield was determined during that period of time. The network of relationships, studied in these papers in order to relate the yield of a cotton crop to its environment and genotype through their effect on its growth, indicates the form of a dynamic model to simulate growth and predict yields.