JWSS - Journal of Water and Soil Science

Despite the great importance of potassium applied as a fertilizer in the orange orchards, no information is currently available regarding the rate of potassium release from rhizosphere and the bulk soils of such trees. The objectives of this study were to investigate the weathering of micaceous minerals and their non-exchangeable K release and also, to examine the status of different forms of K in the rhizosphere and bulk soils of orange orchards with different ages in Darab, Fars Province. Samples were, accordingly, taken from the rhizosphere and bulk soils of orange orchards with the ages of 5, 10 and 20 years; also, virgin soils (control) were obtained from three soil depths including 0–30, 30–60, and 60–100 cm. Water soluble, exchangeable and nonexchangeable K, and the clay mineralogy of the soils were determined. The results demonstrated that the concentration of soluble and exchangeable K in the cultivated soils was less than that in the control soil and that the concentration of nonexchangeable K in the soils of 20-year-old orchards was less, than that in other soils. Soluble and exchangeable K values decreased with depth in all soils. Clay mineralogy investigation also showed that the quantity of illite decreased and that of smectite and illite-smectite increased as the age of orange trees was raised. With increasing the age of orange trees and root development, more potassium could be taken up from soil and more changes occurred in the soil minerals. In order to avoid a very high decline in the reserved K in the soils under orange trees, particularly in the orchards with older trees, K fertilization has to be taken more seriously based on the soil testing results.

Droughts are natural events and could lead to declining surface water quality of regional basin. Understanding the complex impacts of drought may help authorities to monitor changes in different regional basin and to make appropriate decision on development of a river basin management plan. In this study 20 years annual precipitation time series from 1994-2013 from 7 synoptic weather stations located in the Halil-Rood basin were analysed using both Standard Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) and then dry (-1.35 to -1.75) and wet years (1/7 to 2.45) were determined by model simulation studies. Several climate based drought indices and remotely sensed based drought indices were used for monitoring and evaluating of drought. The impact of drought on the water quality parameters in the study area was evaluated. Results showed that there was significant relationship between most of the examined water quality parameters (Ca²⁺, Mg²⁺, HCO^3-, SO4²⁺, Na⁺, total dissolved solids TDS, SAR) and drought, however there was no significant relationship between water pH and drought. The study indicated that focus on the drought indices might be helpful as a tool in improving surface water resources management under drought condition and may promote sustainable water resources utilization and management in the study area. Also, dividing the Halil-Rood basin into several homogeneous regions is recommended for future studies to prepare a better ground for studying the effect of drought on the quality of water at a regional scale.