Row configuration and chemical topping affect fruit spatial distribution, yield and quality of machine-harvested cotton

An important strategy to arrest cotton plant development is chemical topping, which is commonly used in Xinjiang, a large cotton region in the north-west of China. Here, mechanical harvesting of cotton relies on certain row distances, but little is known about the relation between topping methods and different row spacing in their effect on cotton boll spatial distribution and yield. In this study, we aimed to reveal the interaction between two typical machine-laid cotton patterns and chemical topping and its effect on yield formation and quality, by quantifying spatial distribution patterns of cotton boll traits, to explain the causes of yield differences between treatments. A two-year field experiment was conducted from 2020 to 2021 in Xinjiang. The experiment included two topping treatments: chemical and traditional manual topping; and two typical row spacings for machine-harvesting: single rows (76 cm row distance) and double rows (10 cm + 66 cm). Chemical topping increased the boll fraction in the lower canopy, reduced the boll fraction in the upper canopy, and altered boll distribution through inhibiting horizontal growth of fruiting branches, which resulted in a greater inner boll fraction, and suppressed the occurrence of outer bolls. Chemical topping enhanced the contribution of middle canopy bolls to yield in single-row system. Our findings suggest that chemical topping can be an alternative in the face of labor shortages and rising costs, which in combination with proper spacing can improve machine harvesting efficiency, especially in large acreage areas.