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

Authors: SAPKOTA, BALA - Texas A&M University; Adams, Curtis; KELLY, BRENDAN - Texas Tech University; RAJAN, NITHYA - Texas A&M University; ALE, SRINIVASULU - Texas A&M Agrilife

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2022
Publication Date: 11/16/2022
Citation: Sapkota, B.R., Adams, C.B., Kelly, B., Rajan, N., Ale, S. 2022. Plant population density in cotton: Addressing knowledge gaps in stand uniformity and lint quality under dryland and irrigated conditions. Field Crops Research. 290. Article 108762. https://doi.org/10.1016/j.fcr.2022.108762.
DOI: https://doi.org/10.1016/j.fcr.2022.108762

Interpretive Summary: Gaps remain in our knowledge of the relationship between plant population density and yield in cotton. Few cotton plant population studies have been conducted in relatively low-yielding dryland conditions, fewer have considered the impact of uneven crop stands (common in the field due to planting equipment errors and seed/plant death), and population studies that report fiber quality measurements by Advanced Fiber Information System (AFIS) testing are lacking (rather than just the standard High-Volume Instrument (HVI) measurements). We addressed these issues by conducting a two-year study in North Texas, USA that included different plant population densities and stand uniformities at two irrigation levels. The results showed that lint yield was largely unaffected by plant population density, reinforcing the results of previous studies. Unexpectedly, there was also little effect of stand uniformity on any measured variable. Fiber quality was likewise minimally affected by plant population density or stand uniformity. 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. The risk of yield loss is greater when overall plant density decreases below this level, especially in higher-yielding conditions. Before terminating a cotton crop because of stand quality issues, an assessment of overall population should be made and the economic tradeoffs of replanting or replacing must be considered.

Technical 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 are lacking that include Advanced Fiber Information System (AFIS) testing. To address this, a study was conducted in North Texas with combinations of two irrigation (0 and 90% ET replacement), five population (15,000, 30,000, 60,000, 90,000, and 120,000 plants ha-1), and two plant uniformity (even and uneven plant-to-plant spacing) treatments. 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 and stand uniformity in 2020, whereas an interaction between irrigation and plant population occurred in 2021. Lint yield was reduced by an average of 14% at 15,000 plants ha-1 relative to 30,000 plants ha-1 and greater only in irrigated conditions in 2021. There was no apparent or consistent effect of stand uniformity on any response variable. Poor stand quality is often the basis for terminating and replanting troubled cotton crops, but results suggest this is not justified with stand loss in the range tested here. The risk of yield loss is clearly greater when overall plant density decreases below about 30,000 plants ha-1, especially in higher-yielding conditions, but the economic tradeoffs of replanting must be considered. Yield compensation for low plant density and uneven stands was primarily by increased boll number per plant and secondarily by increased boll size. Fiber quality parameters 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.