Impact of zinc application methods on zinc concentration and zinc-use efficiency of popularly grown rice (Oryza sativa) cultivars

In the present investigation, 26 rice (Oryza sativa L.) cultivars viz., some locals, aromatics, high yielding varieties (HYVs) and hybrids were evaluated for yield efficiency, Zn content in grains and also Zn recovery efficiency in a strip plot design during the rainy (kharif) season for the consecutive 2 years (2009 and 2010) under varied Zn application practices. Rice cultivars differed significantly in their yield and native Zn contents as well as recovery of applied Zn allocation in grains, straw and roots. Grain and straw yields as well as harvest index of different cultivars showed wide variations both with and without Zn applications. On an average, grain yields of different rice cultivars increased by 29 and 22% with soil + foliar and only soil application of Zn, respectively. HYVs showed highest yield efficiency followed by hybrid, aromatic and local cultivars, irrespective of methods of Zn fertilization. The content of native Zn in whole rice grain was the highest in aromatics (27.8 mg/kg) followed by locals (26.3 mg/ kg), HYVs (23.0 mg/kg) and hybrids (22.0 mg/kg). Zinc content in whole grains increased significantly in all the cultivars with Zn-application and the magnitude of increase was higher when Zn was applied as soil + foliar application (118%) than soil application only (30%). Zinc concentration in milled grains increased to the extent of 29.5 and 119.5% upon soil application and soil + foliar application of Zn fertilizers. In rice bran and husk Zn concentration increased to the extent of 21 and 155% and 41 and 373% through soil and soil + foliar application, respectively. Zinc -use efficiency varied from 0.53 to 2.83% with a mean value of 0.90% upon soil application of 20 kg Zn as ZnSO4.7H(2)O and 1.89 to 4.80% with a mean value of 2.74% upon application of 20 kg Zn as ZnSO4.7H(2)O with two foliar spray @ 0.5% ZnSO4.7H(2)O solution i.e. soil + foliar applied Zn increased the Zn-use efficiency, on an average, three fold than with only soil applied Zn. Thus, soil + foliar application of Zn offers a useful means for enriching rice grain Zn concentrations irrespective of the cultivars tested and contributed towards enhanced Zn-use efficiency by rice.