Add time:09/28/2019         Source:infona.pl

The conventional 1 M NH4O Ac-exchangeable potassium (K+) soil test is inadequate in soils where nonexchangeable K+ contributes significantly to crop nutrition. Studies were conducted (i) to compare the abilities of the 1 M NH4O Ac method with a modified NaBPh4 method to estimate critical soil K+ levels, (ii) to estimate the contribution of nonexchangeable K= to plant-available K+, (iii) to compare the abilities of the 1 M NH4O Ac method and the modified NaBPh4 method to estimate plant dry matter yield and plant-available K+, and (iv) to compare the abilities of both methods to measure soil K+ balance. Winter wheat (Triticum aestivum L. Abe) was grown in eleven Midwestern soils in a greenhouse using consecutive 28-d defoliation and regrowth cycles. Soils also were incubated for 6 mo with five K+ rates (0-809 mg K+ kg-1). Ammonium acetate- and NaBPh4-extractable K+ (5-min extraction period) were determined in soil samples taken after every three defoliation cycles and after incubation. Critical soil K+ levels could not be determined by either method alone but could be predicted by including cation-exchange capacity (CEC) and illitic K+ content in regression models. Nonexchangeable K+ represented a significant portion of plant-available K+. Plant-available K+ and dry matter (DM) yield were well related to NH4O Ac-extractable K+ only in soils with low nonexchangeable K+ contribution (r2 = 0.889 and 0.915, respectively), but they were well related to NaBPh4-extractable K+ in all soils (r2 = 0.984 and 0.874, respectively. Slopes for NH4O Ac-extractable K+, illitic K+, and clay content, but for NaBPh4-extractable K+ slopes were near unity. These studies suggest that the modified NaBPh4 method may be a superior K+ soil test compared to the NH4O Ac method. Illite content and CEC data may help in developing better soil K+ management guidelines.

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