Modifying the planting density to change water utilization in various soil layers and regulate plant growth and yield formation of cotton

Planting density management can regulate cotton (Gossypium hirsutum L.) biomass accumulation and seed cotton yield formation, which are associated with water consumption. However, it is unclear whether modifying the planting density affects the water use in different soil layers and thus regulates the plant growth and yield formation of cotton. In a two-year field experiment in 2020–2021, cotton was grown at various plant densities (1.5, 3.3, 5.1, 6.9, 8.7, and 10.5 plants m−2), and the spatial profile of water consumption, plant height, the leaf area index (LAI), biomass accumulation, and seed cotton yield were evaluated. The results showed that increase in planting density leads to more water consumption in the middle and lower soil layers (40–80 and 80–120 cm), and improved water use efficiency (WUE) in each soil layer (0–40, 40–80, 80–120 and 0–120 cm). The difference in plant height was attributed to cumulative total water consumption (0–120 cm), and the variation in LAI was due to planting density and cumulative total water consumption. More aboveground biomass at higher planting density was mainly attributed to more water consumption of the middle and lower soil layers (40–80 and 80–120 cm). Additionally, excessively high planting density may lead to the premature senescence of root systems, as the correlation between the water consumption at 40–100 cm and belowground biomass was weaker under high planting density. Moreover, the WUE at 0–40 cm was proportional to the boll distribution on the lower part (1st-6th fruiting branches) of the plant and boll number per unit area, was inversely proportional to boll weight and harvest index (HI), and had parabolic relationship with seed cotton yield (y = −426.83 +244.50–3.48x2). Taken together, our data focused on the effects of water use in various soil layers induced by planting density on cotton growth and yield formation; moreover, these findings fill knowledge gaps within cotton science and provide a feasible direction for determining reasonable water management practices on the North Plain China.