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COTTON

Relationships between Insufficient Potassium and Crop Maturity in Cotton

USDA-ARS, Crop Genetics and Production Research Unit, P.O. Box 345, 141 Experiment Station Road, Stoneville, MS 38776

^* Corresponding author (bpettigrew{at}ars.usda.gov).

Received for publication December 2, 2002. Potassium deficiency in cotton (Gossypium hirsutum L.) depresses yield by decreasing late season growth and is reportedly more harmful to early maturing cotton genotypes. Research objectives were to determine if the accelerated maturity caused by K deficiency was partially caused by earlier flowering and to further evaluate whether early maturity cotton genotypes are more susceptible to low K levels. Field studies were conducted from 1995 to 1997 utilizing two okra-normal leaf-type near isoline pairs and two K fertilization rates (0 and 112 kg K ha^-1). Okra leaf-type genotypes are earlier in maturity than their normal leaf-type counterparts. White bloom counts, dry matter partitioning, light interception, lint yield, yield components, and fiber quality data were collected. Genotypes responded similarly to K rates for all of the parameters evaluated. Early season flowering rates briefly increased 11% when plants were grown without supplemental K. Late-season leaf area index (LAI) was 23% lower without supplemental K compared with plants fertilized with 112 kg K ha^-1 in 2 of the 3 yr. The increased LAI of the K-fertilized plants allowed them to intercept 6% more of the late season sunlight than the 0 kg K ha^-1 treatment. Potassium fertilization increased yield 9% in 2 out of 3 yr, but low K had only minor effects on fiber quality. Early maturing okra-leaf cotton genotypes are not more susceptible to low K rates because of their early maturity. The low K effect on crop maturity is due to a premature termination of reproductive growth and a brief enhancement of the early season flowering rate.

Abbreviations: DAP, days after planting • LAI, leaf area index • PPFD, photosynthetic photon flux density • SLW, specific leaf weight

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