Abstract
ABSTRACT Plant growth regulator management has been a challenge for cotton growers, due to the increased weather instability and the adoption of early cultivars, in off-season crops. This study aimed at proposing a new method, called Crop Growth Rate, to define mepiquat chloride rates in cotton crops, as well as to compare it with traditional management practices. Except for micronaire, there was no difference in cotton growth parameters, neither in yield nor fiber quality, between the new method and the traditional one. The mepiquat chloride rates were, on average, 24 % higher and 43 % lower in late and early maturity cultivars, respectively, for the new method. The number of bolls in plants treated with mepiquat chloride was lower than in non-treated plants, for the IMA5672B2RF and IMA5675B2RF cultivars, but a higher average weight of bolls was observed for these genotypes. The new method is efficient in defining the plant growth regulator rate to avoid an excessive growth and results in less mepiquat chloride applied to early cycle cultivars, preserving lint yield and fiber quality.
Highlights
Cotton (Gossypium hirsutum L.) is grown in a wide range of environments
Plant growth regulator rates were higher under the Crop Growth Rate (CGR) method, when compared with the traditional growers practice (Table 3), except for the early cycle cultivar FM966
Since the CGR method takes into account the plant height and dry matter accumulated, the amount of plant growth regulators (PGR) applied was 70 % lower for the early cycle cultivar and 35-40 % for the other cultivars, as compared with the traditional method
Summary
Cotton (Gossypium hirsutum L.) is grown in a wide range of environments. Under a tropical environment, plants are exposed to excessive rain early in the season, combined with sunny and warm days, which usually result in rank growth and selfshading. Kerby et al (1986) observed a higher boll set at lower nodes and fewer at the top, if compared with non-treated plants, and Zhao et al (2017) reported an increase in lint yield, as a result of PGR application in early cotton growth stages This response was dependent of environmental conditions and cultivar. A close and significant (p < 0.05) correlation was found, with a coefficient of determination (R2) of 0.98, suggesting that the plant height measurement at field conditions may be a useful tool to estimate the plant dry weight Another experiment (Experiment 2) was conducted to determine the plant growth rate and PGR retention on plant leaves. In order to decrease growth rate, the amount of
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