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Effect of Soil Salinity on K Critical Level for Cotton and its Response to Sources and Rates of KFertilizers
P. KESHAVARZ, M. NORIHOSEINI AND M. J. MALAKOUTI Ph.D. Student in Soil Science, Tarbiat Modarres Univ; and Scientific Staff member, and Research Specialist at Khorasan Agr. & Natural Resource Research Center; Director General, Soil and Water Research Institute and Professor TarbiatModarres Univ, Tehran, Iran, respectively.

In addition to reducing water availability and producing toxic ion effects in saline condition, high concentrations of Na+ and Cl- ions will normally upset or inhibit the cotton plant nutrition. Therefore, soil test interpretation in measuring nutrient availability and recommending fertilizer levels may be different in saline and non-saline soils.In order to estimate K critical level, 15 different main cotton fields under saline conditions and 10 fields under non-saline conditions were selected in Khorasan province in 2001-2002. Then, a field experiment with a completely randomized block design with two-potassium rates of 0 (K0) and 200(K1) kg/ha K2SO4 and three replications were carried out to estimate the critical level of K. Secondly,to determine the effects of sources and rates of K on the yield of cotton balls, completely randomized block factorial experiment was conducted with two sources of K [K2SO4 (SOP) and KCl (MOP)] and five rates of K [0, 50, 100, 150 and 200 kg/ha K2O] at two locations, namely with saline (EC = 17 dS/m, Kava= 200 mg/kg) and non-saline conditions (EC = 2.1 dS/m, Kava=180 mg/kg). The results showedthat, the use of K increases cotton balls yield significantly (13% and 6% for saline and non-saline soils, respectively). The K critical levels estimated by Mitscherlich-Bray equation were 244 and 213 mg/kg in saline and non-saline soils, respectively, while by Cate-Nelson graphical method the figures were 240 and 210 mg/kg in saline and non-saline soils, respectively. Also, the type of fertilizersused had a significant effect on the cotton yield. The maximum yield of cotton balls in saline condition was obtained using SOP (25% yield increase in comparison with MOP) and in nonsaline condition by MOP (10% yield increase in comparison with SOP). The relation between the potassium application and the yield of cotton balls (response curve) showed that maximum yield was obtained with the use of125 and 100kg/ha K2O under saline and nonsaline conditions, respectively. With respect to the positive effects of K in saline soils, the application of K fertilizer is highly recommended under those conditions.

KEY WORD: Soil salinity; Potassium; Critical level; K-fertilizer; Cotton yield.

IPI regional workshop on Potassium and Fertigation development in West Asia and North Africa; Rabat,Morocco, 24-28 November, 2004

1. Introduction
Irrigation with saline waters for agricultural purposes has produced favorable results (Rhoades, 1987). Nevertheless, the final outcome of such a practice on crop nutrition of mineral elements and on soil fertility is not well recognized. Soil salinity affects the yields of agricultural crops in various ways including a reduced level of plantavailable water, increased amounts of toxicity levels for certain toxic ions, reduced activity levels for the essential nutrients, high ratios of Na+/ Ca++, Na+/K+, Mg++/ Ca2+, Cl-/NO3- in plant tissues, nutritional problems, and reduction in crop yields and qualities as the most pronounced effects (Feigin, 1985, Grattan and Grieve, 1992). Potassium (K) is the main cation of plant, and as such it makes amajor contribution to reducing the osmotic potential in root cells to facilitate turgor pressure-driven solute transport processes and to sustain the overall water balance of plant (Marschner, 1995). Therefore, existence of sufficient amount of K for the plant life is necessary, especially in the saline conditions. There is a low concentration of K in the soil solution. The element is readily...
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