Dry Matter Partitioning and Harvest Index Differ in Rice Genotypes with Variable Rates of Phosphorus and Zinc Nutrition

Phosphorus (P) and zinc (Zn) deficiencies are the major problems that decrease crop productivity under rice-wheat cropping system. Field experiments were conducted to investigate impacts of P (0, 40, 80 and 120 kg/hm(2)) and Zn levels (0, 5, 10 and 15 kg/hm(2)) on dry matter (DM) accumulation and partitioning, and harvest index of three rice genotypes 'fine (Bamati-385) vs. coarse (F-Malakand and Pukhraj)' at various growth stages (tillering, heading and physiological maturity). The experiments were conducted at farmers' field at Batkhela in Northwestern Pakistan for two years in summer 2011 and 2012. The two year pooled data reveled that there were no differences in percent of DM partitioning into leaves and culms with application of different P and Zn levels, and genotypes at tillering. The highest P level (120 kg/hm(2)) partitioned more DM into panicles than leaves and culms at heading and physiological maturity stages. The highest Zn level (15 kg/hm(2)) accumulated more DM and partitioned more DM into panicles than leaves and culms at heading and physiological maturity stages. The hybrid rice (Pukhraj) produced and partitioned more DM into panicles than F-Malakand and Bamati-385 at heading and physiological maturity stages. Higher DM accumulation and greater amounts of partitioning into panicles at heading and physiological maturity stages was noticed with increase in P and Zn levels, and the increase was significantly higher in the coarse rice genotypes than fine. We concluded that the growing hybrid rice with application of 120 kg/hm(2) P + 15 kg/hm(2) Zn not only increases total DM accumulation and partitioned greater amounts into the reproductive plant parts (panicles) but also results in higher harvest index.