Plant population density in cotton: Addressing knowledge gaps in stand uniformity and lint quality under dryland and irrigated conditions

Abstract

A recent literature review and data synthesis better defined the yield curve with plant population density in cotton (Gossypium hirsutum L.), but it also highlighted gaps in knowledge. Few cotton plant population studies have been conducted in relatively low-yielding dryland conditions; fewer have considered the impact of uneven crop stands, which are common in actual field conditions due to planting equipment errors and seed/plant mortality; and population reports that include fiber quality measurements by Advanced Fiber Information System (AFIS) testing are lacking (rather than just the standard High Volume Instrument (HVI) measurements). To address these issues, a study was conducted in North Texas, USA with treatment combinations of two irrigation levels (0% and 90% ET replacement), five plant population densities (15,000, 30,000, 60,000, 90,000, and 120,000 plants ha-1), and two stand uniformities (even and uneven plant-to-plant spacing within rows). Canopy development was tracked by unmanned aircraft system (UAS) measurements, late-season measurements were taken of boll density and size, and lint yield and quality measurements were collected at maturity. Lint yield was unaffected by plant population density in 2020 (i.e. 15,000–120,000 plants ha-1), whereas an interaction between irrigation and plant population occurred in 2021. Lint yield was reduced by 19% with 15,000 plants ha-1 relative to 120,000 plants ha-1 under only irrigated conditions in 2021. There was no substantial or consistent effect of stand uniformity on any response variable in either year. Poor stand quality is often the basis for terminating and replanting or replacing troubled cotton crops, but these results suggest this is not justified when overall population density is 30,000 plants ha-1 or greater, depending on production environment. The risk of yield loss is clearly greater when overall plant density decreases below this level, especially in higher-yielding conditions, but the economic tradeoffs of replanting or replacing the crop must be considered. In the cotton plant, yield compensation for low plant density and uneven stands occurred primarily by increased boll number per plant and secondarily by increased boll size. Fiber quality parameters as measured by HVI and AFIS were minimally and inconsistently affected by population density and stand uniformity, suggesting that population dynamics are not critical factors cotton producers must consider in optimizing the fiber quality of their product.