Long-term cropping on potassium release and fixation behaviors

Abstract

Twenty paired surface samples (20 cultivated and 20 adjoining virgin soils) from sugar beet growing areas located in the north-west of Iran were used to study potassium (K) release and fixation behaviors of the soils as affected by continuous cropping. Potassium release was determined by successive extractions with 0.5 mM citric acid over a period of 2160 h. Potassium fixation was determined by adding several rates of K varying from 0–600 mg kg−1. Long-term cropping influenced K release from the non-exchangeable fraction of the soil. The cumulative amounts of K released ranged form 423–2472 mg kg−1 with a mean of 1663 mg kg−1 for the cultivated soils and from 849–2387 mg kg−1 with a mean of 1810 mg kg−1 for the adjoining virgin lands. Parabolic diffusion model provided a best description of the K. Continuous cropping significantly increased (p ≤ 0.01) the fixation capacity for K in all the soil types. The percentage of K fixation of applied K was found to be 41 to 102% in low-K soil types and nil to 41% in K-rich soil types indicating that continuous cultivation, mostly without K or with little quantity of K, resulted in a considerable K depletion.