Effect of zeolite on distribution of different soil potassium pools in Vertisols of Fars province

Due to the large surface area and high cation exchange capacity zeolite as an amendment of physicochemical soil characteristics can be secondary effects on the ability to use nutrients such as potassium and changing different forms of the element and thus the cycle. However, the addition of this compound to Vertisols mainly with high amounts in clay mineral with high capacity for k fixation such as smectite can affect the distribution of potassium. To investigate this, the effects of adding different amounts of the zeolite and wetting and drying treatment were studied on 6 Vertisols that were collected from different regions of Fars province.
Based on previous soil maps, aerial photos and topographic maps of Fars province`s Vertisols were selected and some soil profiles were dug in different climatic conditions. After description, six pedons were chosen as representative that almost all Vertisols studied in xeric moisture regimes in the northern and central parts of the province and all of them are in great groups Haploxererts and Calcixererts. Soils were located in the piedmont plain, plateau and lowland physiography. Experiment was a completely randomized 3×2×4×6 factorial arrangement on surface horizons after treatment of soils with zeolite (0, 1, 2.5 and 5%) and wetting and drying treatment. After 8 days, different forms of potassium consisting of soluble, exchangeable and non-exchangeable forms) were determined in the samples. Statistical analysis was done by using the software SPSS, Excel, SAS and comparison of means was carried out using the Duncan’s test.
The studied soils comprise ustic and xeric moisture regimes and mesic, thermic and hyperthemic temperature regimes. Although the mineralogical composition of the various soils were more or less the same, due to the different amounts of various clay minerals in different soils the amounts of different kinds of K was very different in soils. The results showed that zeolite application can increase the amounts of soluble and exchangeable potassium while it has no effect on non exchangeable potassium, which could be due to the high amount of potassium in zeolite and great tendency of zeolite to absorb potassium. Zeolite application with and without wetting and drying treatment has increased the amounts of soluble potassium in different soils. Maximum increase was observed in soil which has the lower amounts of smectites. Wetting and drying treatment caused significant reduction of soluble potassium in all samples. Exchangeable K has significantly increased by the addition of zeolite. Highest concentrations of exchangeable potassium were observed in soils with less amounts of smectite. Zeolite application has reduced non-exchangeable potassium in soils but had different effect on soil no. 4 and has increased the non-exchangeable potassium. This indicates potassium fixation in the soils which could be due to the high amounts of minerals capable to fix potassium. Wetting and drying treatment caused the reduction of soluble and non-exchangeable K and increase of exchangeable K.
The increase of soluble K as a result of zeolite application can enhance possibility of potassium leaching but on the other hand it is also able to prevent the leaching and fixation of K by retention of potassium in exchangeable sites. Considering the very low amount of available potassium in highly calcareous soils of Fars, which is the results of intensive agriculture and little or no K fertilization, zeolite application, may be able to improve the status of potassium in these soils.