Abstract
Under the rice-wheat cropping system (RWS), the continuous cropping of rice (Oryza sativaL.) and wheat (Triticum aestivumL.) deplete soil fertility, and reduce crop growth and total rice biomass. In RWS, both phosphorus (P) and zinc (Zn) deficiencies are considered important nutritional constraints for reducing rice crop growth rates (CGR) and total biomass/biological yield (BY). The objective of this experiment was to investigate the impact of phosphorus (0, 40, 80, 120 kg P ha(-1)) and zinc rates (0, 5, 10, 15 kg Zn ha(-1)) on CGR and BY of three rice genotypes [fine (Bamati-385) versus coarse (Fakhre-e-Malakand and Pukhraj)] in Northwestern Pakistan during summer 2011 (Y1) and 2012 (Y2). The results revealed that higher CGR at various growth stages and total BY was obtained with the integrated use of higher phosphorus (80 and 120 kg P ha(-1)) and zinc rates (10 and 15 kg Zn ha(-1)). The lower CGR and BY were recorded when P and Zn were not applied (control) or when P and Zn were applied alone. In the case of rice genotypes, the highest CGR and BY were recorded for the hybrid rice (Pukhraj) than the other two genotypes. The CGR was increased to the highest level at the heading stage as compared to tillering and physiological maturity. The increase in CGR had a positive impact on the total BY of rice cultivars. The increase in BY had a positive relationship with grain yield and grower's income. It was concluded from the study that the combined application of higher P and Zn rates to the coarse rice genotypes (Fakhre-e-Malakand and Pukhraj) could increase CGR, total BY, crop productivity and profitability.