Relationship between different forms of potassium with physical and chemical properties calcareous soils of southeast of Iran

Potassium occurs in soils in various forms. The behavior of potassium in soil can be difficult due to its interaction with the intrinsic properties of the soil. Although most soils contain large quantities of potassium, but most soils are not able to provide proper amounts for plant nutrition, so that the equilibrium reactions occurring between different forms of potassium have a profound effect on potassium nutrition. This research was carried out with the aim of investigating the relationship between different forms of potassium (soluble, exchangeable, non- exchangeable and construction) with physical and chemical properties of soils in citrus areas of Iranshahr and Khash towns in Sistan and Baluchestan province.

First, according to previous studies, 30 samples of soils in Iranshahr and Khash towns with different characteristics. Then samplings were taken from depths of 0 to 30 cm. Physical and chemical properties of soil and various forms of potassium (soluble, exchangeable, non- exchangeable and construction) with total potassium were measured and relationship between different forms of potassium with each other and physical and chemical properties of soil were investigated.

Soils were in general light in texture, non-saline and calcareous. Organic carbon values in soils ranged from 0.6 to 1.6 percent, cation exchange capacity ranged from 7.0 to 10.5 centimoles per kilogram, and the pH ranged from 7.0 to 7.4. The amounts of different forms of potassium in the city of Iranshahr, potassium soluble ranged from 1.4 to 20.4, exchangeable from 122 to 315, non- exchangeable from 177 to 388, construction from 5709 to 13987 and a total 8420 to 14200 mg kg-1 soil. In Khash city, potassium soluble ranged from 5.7 to 14.3, exchangeable from 129 to 273, non- exchangeable from 293 to 493, construction from 5412 to 14085 and a total 9892 to 13850 mg kg-1 soil. Correlation test showed that there was a significant positive correlation between soluble potassium and sand (r= 0.5*) and negative correlation with silt (r= -0.5*). There was a significant positive correlation between exchangeable potassium and organic matter (r= 0.7*), significant positive correlation with clay (r= 0.5*) and significant positive correlation with cation exchange capacity (r= 0.7*). Between non- exchangeable potassium and calcium carbonate there was a significant negative correlation (r= -0.8*). Significant positive relationships among various fractions of soil K indicated existence of a dynamic equilibrium between different forms of K.

The amount of potassium available in the plant (soluble, exchangeable, non- exchangeable potassium) is good in citrus growing areas in Sistan and Balouchestan province of Iranshahr and Khash, and therefore does not require potassium fertilizers in these two regions