ABSTRACT

Potassium (K) fertility requirements for cotton (Gossypium spp.) have been a matter of concern due to increasing interest and emphasis on fiber quality and numerous reports of X deficiencies in various cotton producing regions. To address this matter appropriately, a thorough understanding of the chemical, physical, and mineralogical composition of the soils in question is in order. Soil samples were collected from ten sites across southern Arizona that are representative of the common agricultural soils of the region. At all locations soils were sampled to a depth of 120 cm in 30 cm increments. All soils were characterized with respect to chemical composition by the following parameters: exchangeable K, total K, cation exchange capacity and particle size analysis. In addition to the chemical and physical characterizations, results of a K fertility field experiment conducted in 1991 on Upland (G. Hirsutum L.) cotton receiving both soil and foliar application of K are discussed. In this experiment, soil-applied K fertilizer at four rates (0 to 252 kg K₂O ha^-1) were broadcast and preplant incorporated before listing. The four foliar applications (5 kg K₂O ha^-1) were made in all combinations with soil-applied treatments over the first fruiting cycle (approximately 2 week intervals). There was no agronomic benefit resulting from K application in this study. With the exception of one soil, none of the chemically characterized soils contained less than 150 mg K kg^-1 of extractable K in the surface 90 cm of soil. All of the soils contained K-bearing mica and none of the soils contained any k-fixing vermiculite. From the initial chemical and mineralogical information and the 1991 Upland cotton field results, it is concluded that K fertilization is not likely for similar situations in Arizona. Further research is under way to quantify the K-fixing ability of each soil in this survey and additional field studies are also being conducted to evaluate K fertilization in with Upland and Pima (G. barbadense L.) cotton.