Potassium Buffering Characteristics of Three Soils Low in Exchangeable Potassium

Abstract

Plant availability of soil K is controlled by dynamic interactions among its different pools. Misunderstanding of these dynamics leads to mismanagement of soil fertility. This study was conducted to evaluate buffering characteristics of low exchangeable‐K soils that showed different sugarcane ( Saccharum spp. L.) responses to K amendment. Three silt loams, Crowley (fine, smectitic, hyperthermic Typic Albaqualfs), Dundee (fine‐silty, mixed, active, thermic Typic Endoaqualfs), and Norwood (fine‐silty, mixed, superactive, hyperthermic Fluventic Eutrudepts), were evaluated by using a modified quantity/intensity (Q/I) approach, which allows partitioning of K changes in the soil–solution system into exchangeable and nonexchangeable pools. Total potential buffering capacity (PBC t ) was found to correlate significantly ( r = 0.97, P < 0.01) with the buffering capacity due to nonexchangeable K (PBC n ) rather with that due to exchangeable K (PBC e ). Impact factor (β), a measure of effect of added K on nonexchangeable K, was inversely correlated with a soil's conversion magnitude (α) of converting added K to exchangeable K ( r = 0.95, P < 0.01). Of the three soils, Dundee exhibited much smaller β values than Crowley and Norwood but the soil converted much of added K to exchangeable K (60–65%) throughout its surface and subsurface soils. Both Crowley and Norwood possessed higher PBC t as well as higher PBC n and PBC e than Dundee, but Crowley required relatively lower critical exchangeable K (EK r ) and solution K (CK r ) levels below which release of nonexchangeable K was initiated. The overall results indicated that the partitioned Q/I approach could be used to explicitly evaluate short‐term K dynamics in soil–solution systems. The nonexchangeable K buffering characteristics along with the differences between critical levels (EK r or CK r and EK 0 or CK 0 ) have important implications in assessing the likelihood of nonexchangeable K release and could be calibrated for soil fertility management.