Irrigated plot trials in cotton: Quantifying end effects and the influence of plot size upon intergenotypic competition

Individual rows of irrigated, multi-row plots in a cotton breeding trial were harvested, and seed cotton yields were measured. Intergenotypic competition had occurred between the neighbouring long sides of the oblong plots. A further trial was conducted to measure competition in three- and four-row plots and to establish which system gave the least biased genotype means for lint yield (kg/ha). However, competition in this experiment was minimal and both systems gave comparable results. The effect of bare ground at the end of plots was investigated. When bare ground, as compared to a discarded border, was present during their growing season, then end plants, for seven out of eight genotypes, were larger and plot yields were inflated. These results provided no conclusive evidence that current practices for field trials with cotton should be changed.