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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #81770
Title: POTASSIUM CONSIDERATIONS FOR SOUTHERN IDAHO SOILS

Author
item Westermann, Dale
item TINDALL, TERRY - UNIV. IDAHO (TWIN FALLS)

Submitted to: Western Nutrient Management Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Several crops are starting to respond to potassium fertilization on western irrigated soils. We conducted this study to identify the relationships between soil potassium factions so we could increase our ability to develop and make reliable potassium fertilizer recommendations. We found that the potassium extracted by sodium bicarbonate estimated the potassium in the soil solution and on the exchange complex, and that it was linearly related to the potassium diffusion rate. This indicates that the sodium bicarbonate extractable potassium is an excellent indicator of potassium availability to plants in these soils. Using only these laboratory relationships, we were also able to calculate potassium fertilizer recommendation rates that supported those found in a previous field study. Growers, consultants, and fertilizer field men can be confident in soil test potassium concentrations and recommendations developed using this extractant.

Technical Abstract: Understanding the new equilibrium established among the various soil K fractions after a K application is needed to enhance the ability to develop and make reliable K fertilizer recommendations. The objective of this study was to determine the magnitude of selected K fractions, and their inter-relationships to each other and to a standard soil test K method on soil samples taken from fields in the Pacific Northwest. Potassium extracted by 0.5M NaHCO3 was linearly related to soil solution K concentration but not to the slow-release K fraction. The slow-release K tion was over 1500 ppm on native soils and declined to less than 500 ppm in cropped soils. Solution K concentrations were also linearly related to an estimate of the K diffusion rate. Potassium fertilization rates calculated on a mass-balance basis were similar to those derived from a previous field study. Potassium fixation was estimated to be as high as 27% of K applied at a relatively low soil test potassium concentration (25 ppm K). These data indicate that the K extracted by 0.5M NaHCO3 is a reliable estimate of the available K fractions in these soils, including the K diffusion rate. In addition, the high K fertilization rates identified under field studies were confirmed by consideration of the K dynamics between K fractions in the laboratory.