Depletion of Soil Potassium under Exhaustive Cropping in Inceptisol and Alfisol

Abstract

Pot-culture studies of intensive cropping without potassium (K) application, taking three successive crops of rice on Sonakhali (Inceptisol) and Ranibundh (Alfisol) soils, revealed that all the forms of soil K declined after the third crop compared to the corresponding initial soil status. A similar trend was also found for nonexchangeable K extracted sequentially and termed as Step K and CR-K (constant rate K). The CR-K contents showed little variations with cropping. Except for the potential buffering capacity of the soil for K at equilibrium (PBC^K ₀) values, all the quantity/intensity (Q/I) parameters, namely activity ratio of potassium (AR^K _e), labile K (–ΔK₀), specifically held K (K_X), and total labile pool of K (K_L) values, decreased in both the soils as they were subjected to repeated cropping. The PBC^K ₀ values changed to a smaller extent in both the soils. In both soils, the threshold levels for release of intermediate K in terms of activity ratio, exchangeable K, and K concentration in soil solution decreased after the third cropping as compared to the initial status. The dry-matter weight of rice, K concentration, and K uptake decreased with the cropping sequence. The difference in values of each parameter between initial status and the third crop was much wider in Inceptisol than in Alfisol.

Keywords:

• Constant rate K
• exhaustive cropping
• nonexchangeable K
• rice
• Step K
• threshold value