Potassium fertility status of several sonoran desert soils

There have been several recent reports of cotton lint yield response to potassium (K) fertilization from areas east and west of Arizona in the Cotton Belt. However, there is no documentation of the K status in southern Arizona within these Sonoran Desert soils. The physical, chemical, and mineralogical properties affecting the K status of 10 soils (six Entisols, three Aridisols, and one Mollisol) common to cultivated soils of the Sonoran Desert were studied to determine which soils might respond to K fertilization. The dominant clay minerals included mica, vermiculite, smectite, and palygorskite. All the soils contained some vermiculite but, none contained more than 5% vermiculite in the clay fraction. Mica was common in the clay fraction of the soils, except for the Superstition sand, which contained the lowest levels of exchangeable K (≤100 mg kg⁻¹) throughout the 1.2 m of the soil profile. A minimum of 210 mg K kg⁻¹was contained in the top 0.6 m of the soils. These levels of exchangeable K are much greater than levels of exchangeable K in other areas that have reported K deficiencies. In an attempt to quantify the K status of these soils, the K sufficiency level for the surface 0.3 m was calculated and compared with the exchangeable K level. Only the Superstition soil had a K deficit (−20 mg kg⁻¹) when compared with the exchangeable K. The other soils contained > 110 mg kg⁻¹more exchangeable K than the calculated sufficiency level. Additionally, the K desorption rates were calculated for the surface 0.3 m of each soil, and each had the capacity to desorb > 10 mg K kg⁻¹per typical irrigation event. With the exception of Superstition sand, none of these soils was determined to have exchangeable K levels or clay mineralogy that would indicate that fertilizer K would be required for crop production. Rotations that could potentially remove large amounts of K in consecutive years from any soil will require that exchangeable K levels be monitored by soil-testing procedures.