Response of Rice (Oryza sativa) Genotypes Varying in K Use Efficiency to Various Levels of Potassium

Wide spread potassium (K) deficiency in soils of Pakistan is one of the major reasons for relatively low rice yield. The use of K-efficient genotypes to combat this issue is most viable and sustainable strategy. A pot experiment was conducted to study the response of rice genotypes to various levels of K. The air-dried soil was mixed with the N, P and Zn fertilizers (applied @ 130, 70 & 12.5 kg ha-1 as urea, diammonium phosphate and ZnSO4 [33%], respectively). Different K rates (0, 30, 60, 90 & 120 kg ha-1) were applied to three rice genotypes previously screened and categorized for their K use efficiency viz IR-6 (low K-use efficient), Super basmati (medium K-use efficient) and genotype 99509 (high K-use efficient). Significant improvement in grain yield and yield components was observed with K application albeit with different degree of efficacy. Low K-use efficient genotype (IR-6) responded poorly in terms of grain yield to application of K. High K-use efficient genotype (99509) remained unaffected, whilst medium K-use efficient genotype (Super basmati) behaved moderately. Optimum K rate for maximum rice grain yield was found as 60 kg ha-1 for all the three rice genotypes and application beyond 60 kg K ha-1 had no further positive impact on various growth and yield parameters. However, using the quadratic model, the optimum K rate for maximum rice grain yield was found 70 kg ha-1 for IR-6, while 62 kg ha-1 was found for genotype 99509 as well as Super basmati. The results implied that K-use efficient genotypes used the tissue K more efficiently. © 2010 Friends Science Publishers