154 Pak. j . life soc. Sci. (2013), 11( 2): 154-164 E-ISSN: 2221-7630;P-ISSN: 1727- 4915 Pakistan Journal of Life and Social Sciences www.pjlss.edu.pk RESEARCH ARTICLE Effect of Supplemental Foliar-Applied Potassium on Cotton ( Gossypium hirsutum L.) Yield and Lint Quality under Drought Stress Rashid Ahmad 1 , Raja Ghulam Muhammad Hur, Ejaz Ahmad Waraich, Muhammad Yasin Ashraf 2 and Mumtaz Hussain 3 1 Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan 2 Crop Stress Management Group, Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan 3 Department of Botany, University of Agriculture, Faisalabad, Pakistan ARTICLE INFO ABSTRACT Received: Accepted: Online: Oct 06, 2012 Nov 06, 2012 Jul 24, 2013 A study to determine the effect of supplemental foliar-applied potassium on cotton (Gossypium hirsutum L.) yield and lint quality under drought stress was conducted using six cotton varieties, three drought tolerant (CIM-496, CIM-473 and FH-1200) and three drought sensitive (CIM-534, CIM-554 and FH-945) and two levels of supplemental foliar- applied potassium (0 and 1 %). The experiment was conducted in lysimeter for consecutive two years with four water levels i.e. well watered (100% FC), medium watered (80% FC), low watered (60% FC) and soil stored moisture (40% FC). Results indicated that tolerant cotton variety maintained higher yield and lint quality at all drought stress levels. Supplemental foliar application (1%) of potassium significantly improved the drought tolerance potential and yield in all cotton varieties. However, cotton variety CIM-473 ranked first in fiber strength and fiber length whereas fiber micronaire was higher in cotton variety CIM-496. The variety FH-1200 with the foliar application (1%) of potassium produced the highest cotton yield. Foliar application of 1% potassium as supplementary source under drought stress conditions was found helpful in improving yield and quality of cotton. Keywords Cotton Foliar potassium application Lint quality Yield *Corresponding Author: uaf_rashid@yahoo.com INTRODUCTION Crop production in water-limited environments depends upon the intensity and the pattern of drought, which vary from year to year (Soriano et al., 2004). Drought stress affects plant growth and development by inhibiting cell expansion resulting in reduced biomass production (Ashraf et al., 1994), disturbing different metabolic activities of plants (Khan et al., 1999; Lawlor and Cornic, 2002) by altering nutrient balance (Kidambi et al., 1990) and inhibiting enzyme activities (Ashraf et al., 1995). Cotton, though relatively a drought tolerant crop is still affected by drought like other crops and water stress has marked adverse effects on morphological, biochemical, physiological and yield attributes of cotton (Patil et al., 2011). Cotton yield and quality is negatively affected by potassium deficiency (Cassman et al., 1990). Cotton requires 3 to 5 kg potassium per day per hectare during boll fill and on an average mature cotton crop is estimated to require a total of 110 to 250 kg potash per hectare (Halevy, 1976). Potassium plays an important role in photosynthesis, water relations, balance between cations, translocation of carbohydrates and resistance against insects and diseases (Brar and Tiwari 2004). Potassium contributes for water relations of plants making them survive under water deficit conditions as it is the major osmoticum in plants. It accumulates in cell and enhances water uptake so maintains the cell turgor required for growth and development (De La Guardia and Benloch, 1980) and stomatal opening (Fischer and Hsiao, 1968). Mullins and Burmester (1991) stated that the duration of active growth, eventual size of plants, and the amount of potassium taken up and removed ranges from 1 to 1.5 kg per acre per day from the soil plant system by harvesting can affect potassium availability and total crop potassium demand. In general, higher boll loads and higher seed cotton yields requires and depletes more potassium from the soil system than with lower boll loads and yields. Soils in Pakistan are naturally high in potassium. Even then to maintain soil potassium at optimum levels, it is