Potassium Fixation and Release in Some Calcareous Soils under Orange Cultivation

Abstract

Arid and semiarid soils of southern Iran may fix a large content of applied potassium (K), but the fixed K may be gradually supplied to plants. Sixteen representative soils under orange cultivation (Citrus sinensis (L.) Osbeck) from arid and semiarid regions of southern Iran were selected and K fixation capacity of the soils were calculated. Then, the K-treated and control soil samples were extracted for K during 10 stages with 0.01 M CaCl2. Results indicated that the studied soils were able to fix 25 to 280 mg K kg–1. Mean contents of cumulative K released ranged 48–262 and 8–512 mg kg–1 for the control and K-treated soils, respectively, with significant difference (p < 0.05). The control soils released 42–69% (mean of 57%) of K during the first three stages of extraction, and this was significantly (p < 0.05) lower than that for the K-treated soils (55–86% with mean of 69%). No significant difference was found between the control and K-treated soils in K release during 4 to 10 stages of extraction. The fixation of added K is occurred in more available sites (wedge zone) of clay minerals and the fixed K may be released easily during the K extraction experiment. Thus, the availability of the fixed K (originated from chemical fertilizers) is considerably more than the native non-exchangeable K ions due to its fixation in the mineral edges. Generally, calcareous soils in arid environments had a high proportion of K-bearing minerals and able to fix added K fertilizers, but the fixed K may be released easily during the plant growth season and it should be considered as a benefit process.