Rapid screening of plant growth provides additional phenological information for cotton (Gossypium hirsutum L.), which may then be linked to productivity analysis in breeding and agronomy. We tested automated measurements of plant height, ground cover fraction (GCF), normalized difference vegetation index (NDVI), and canopy temperature (Tc) using a ground‐based platform mounted on a research sprayer on four cotton cultivars (DP1212, DP1219, FM2484, and PHY499) grown under 10 different irrigation levels at Lubbock, TX. Measurements consistently identified all irrigation treatments throughout the season in 2012, a dry year, and the lower irrigation treatments in 2013, a wet year, as well as differences in growth habits among cultivars in both years. The coefficient of determination (r2) of each in‐season parameter had a positive correlation with lint yield during both years. Lint yield values were compared with in‐season measurements at each sampling date. All cultivars had higher correlations between in‐season measurements and lint yield in 2012 than in 2013 because of the increased rainfall in 2013. In 2012, canopy temperature had highest correlation with lint yield, followed by plant height, GCF, and NDVI. In 2013, GCF, NDVI, and plant height all had higher correlations than Tc with lint yield. All the methods showed value in determining growth and yield, but selection of methods for screening may require adaptations based on the growth environment of the study.

The production of fruit on upland cotton (Gossypium hirsutum L.) varies with environment, cultivar, and management practices, including irrigation. Yield increase in response to irrigation is a combination of additional boll production on the plant and differences in the size of individual bolls. Previous research on this subject is incomplete. The purpose of this research was to compare the effects of irrigation on boll distribution and boll size in four cotton cultivars in West Texas. Boll distribution and boll mass in response to 10 daily irrigation levels (0–6.5 mm d−1) were compared among four cultivars with varying maturities [‘Deltapine 1212 B2RF’ (DP1212), ‘Deltapine 1219 B2RF’ (DP1219), ‘FiberMax 2484 B2F’ (FM2484), and ‘FiberMax 2011 GT’ (FM2011)] from 2011 to 2013 in Lubbock, TX. Boll production and retention followed cultivar‐specific patterns in all 3 yr. Two cultivars (DP1212 and FM2011) produced fruit primarily at the bottom and middle of the plant, one had increased production high on the plant (DP1219), and one produced fruit almost exclusively in the middle of the plant (FM2484). Both boll number and boll mass contributed to lint yield, with boll number being the major determinant (on average, 90%) of lint yield, whereas boll mass accounted for 10% of lint yield on average. The contribution of boll number and boll size to yield varied among cultivars and did not appear to be wholly maturity‐related. Research studies focused on boll number should be aware that boll distribution does not account for all of the variation in yield.

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Temporal remote sensing measurements of plant growth may give breeders a better understanding of crop growth habits, yield, fiber quality, and maturity in cotton (Gossypium hirsutum L.) genotypes. The objective of this research was to derive a spectral index maturity scoring method based on the normalized difference red edge (NDRE) index. Seasonal NDRE measurements were collected from 2015 to 2017. A growth inflection point (GIP) was generated based on a quadratic fit of the NDRE growth curves for nine commercial cotton cultivars under three irrigation treatments. This GIP was the number of heat units associated with the inflection point of the NDRE values during the season. It was compared with manual measurements of crop maturity, including nodes above white flower (NAWF), percentage open boll (POB), and end‐of‐season plant mapping indices. Each year had environmental conditions that changed growth habits and maturity of the cultivars. Cultivar and irrigation affected maturity in all 3 yr. The GIP correlated with each maturity assessment, with the highest correlations found with NAWF (r2 from 0.38 to 0.88) by irrigation. In most cases, the relationship between NAWF and GIP was not cultivar specific, suggesting that GIP may be used across multiple cotton genotypes within multiple growing environments. The GIP method provides a method to more rapidly and objectively evaluate maturity characteristics of cotton cultivars, as well as the effects of management on these characteristics.

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