COTTON Relationships between Insufficient Potassium and Crop Maturity in Cotton

difficult to prove cause and effect for maturity differences being responsible for any variation in response Potassium deficiency in cotton (Gossypium hirsutum L.) depresses among genotypes to K. Theoretically, differences in root yield by decreasing late season growth and is reportedly more harmful to early maturing cotton genotypes. Research objectives were to detersystem size or effectiveness could be identified as genomine if the accelerated maturity caused by K deficiency was partially typic differences in response to different K fertility levcaused by earlier flowering and to further evaluate whether early els. Differences in cotton root surface areas have been maturity cotton genotypes are more susceptible to low K levels. Field linked to differences in K uptake and yield response to studies were conducted from 1995 to 1997 utilizing two okra-normal K fertility (Cassman et al., 1989; Brouder and Cassleaf-type near isoline pairs and two K fertilization rates (0 and 112 man, 1990). kg K ha 1). Okra leaf-type genotypes are earlier in maturity than Okra leaf-type cotton lines often are earlier in matutheir normal leaf-type counterparts. White bloom counts, dry matter rity and produce more flowers than their normal leafpartitioning, light interception, lint yield, yield components, and fiber type near isogenic counterparts (Heitholt et al., 1993; quality data were collected. Genotypes responded similarly to K rates Heitholt, 1995). By utilizing okra leaf and normal leaffor all of the parameters evaluated. Early season flowering rates briefly increased 11% when plants were grown without supplemental K. Latetype near isogenic pairs, one should be able to narrow season leaf area index (LAI) was 23% lower without supplemental K the genetic variation and provide a more direct comparicompared with plants fertilized with 112 kg K ha 1 in 2 of the 3 yr. son of whether earlier maturity leads to enhanced susThe increased LAI of the K-fertilized plants allowed them to intercept ceptibility to K deficiencies. The leaf-type genetic varia6% more of the late season sunlight than the 0 kg K ha 1 treatment. tion would still exist, but most of the other genetic Potassium fertilization increased yield 9% in 2 out of 3 yr, but low variation would be minimized. K had only minor effects on fiber quality. Early maturing okra-leaf Another characteristic commonly associated with cotcotton genotypes are not more susceptible to low K rates because of ton grown under low K conditions is that the crop can be their early maturity. The low K effect on crop maturity is due to a harvested earlier than comparable plants grown under premature termination of reproductive growth and a brief enhanceadequate soil K (Bennett et al., 1965; Gwathmey and ment of the early season flowering rate. Howard, 1998; Pettigrew, 1999). The prevailing assumption is that the crop runs out of K, causing an early termination of the reproductive growth and reducing O cotton (Gossypium hirsutum L.) yields are overall lint yields. While Kerby and Adams (1985) sugdependent on the availability of an adequate K gested that high soil K levels did not delay early boll supply throughout the growing season. Despite the conset, little if any research has addressed whether low siderable research conducted on cotton K fertility over K promotes earlier initiation of reproductive growth. the past 15 yr, questions and misconceptions still exist Earlier flowering and the resulting boll load may also concerning the effects that adequate and deficient K contribute to the earlier harvest observed with K-defilevels have on cotton growth and development, yield, cient plants. Other stresses have sometimes, but not and fiber quality. always, been able to accelerate the initiation of reproOne of the prevailing assumptions regarding K defiductive growth in cotton (Guinn and Mauney, 1984). ciency in cotton is that fast-fruiting, earlier maturing The plant hormone ethylene is often produced by plants genotypes are more susceptible to K deficiency than in response to various stresses (Lieberman, 1979). Artithe more full-season genotypes (Tupper et al., 1996; ficial products, such as ethephon [(2-chloroethyl)phosOosterhuis, 1999). Supposedly, the compaction of rephonic acid], that degrade into ethylene once inside the productive growth into a shorter time frame with high plant cells, have been reported to induce flowering in yielding, early maturing genotypes intensifies the K decertain plant species (de Wilde, 1971). mand and need during this period. This assumption perAn improved understanding of K nutrition in cotton sists even though one study found no differences in would help producers better manage their inputs for the response to K among cotton genotypes of varying optimal yield and fiber quality. Therefore, the objectives maturities (Pettigrew et al., 1996). The varying genetic of this research were: (i) to conduct a more direct test makeups of the genotypes used by Pettigrew et al. (1996) of whether the early maturing trait leads to an increased and in other studies complicate the issue and make it sensitivity to low K levels for cotton and (ii) to determine whether low K levels hasten crop maturity of cotUSDA-ARS, Crop Genetics and Production Research Unit, P.O. Box 345, 141 Experiment Station Road, Stoneville, MS 38776. Received ton through both an early initiation of flowering and an 2 Dec. 2002. *Corresponding author ([email protected]). early termination of reproductive growth. Published in Agron. J. 95:1323–1329 (2003).  American Society of Agronomy Abbreviations: DAP, days after planting; LAI, leaf area index; PPFD, photosynthetic photon flux density; SLW, specific leaf weight. 677 S. Segoe Rd., Madison, WI 53711 USA