The rapid mining of soil potassium (K) is the major yield limiting factor in cotton production in Pakistan and elsewhere. Potassium influences cotton yield and quality due to its versatile roles in the physiology and biochemistry of cotton. Interestingly, cotton requires K as much as nitrogen, during entire growth and development, to offer optimum yield. However, in many parts of the world, K fertilization is a very costly agricultural input. Hence, the farming community, especially in developing countries, seldom include K fertilization in crop production programs. Recent literature on K nutrition of cotton has witnessed that K requirement of cotton varies among genotypes. Modern, insect-resistant, high yielding cotton varieties require more K as against obsolete varieties. This monograph reports the comparative K requirement of Bt and non-Bt cotton genotypes and identifies cotton genotypes for their suitability to fit well under low and high K input sustainable agriculture systems. This book is a dependable compendium for the students, teachers and researchers working in the domains of K nutrition of cotton and nutrient-use-efficient genotypes.