Effect of zinc-enriched urea on productivity, zinc uptake and efficiency of an aromatic rice-wheat cropping system

Zinc deficiency is prevalent worldwide and is a barrier in achieving yield targets in crops. It is also now recognized as a leading risk factor for disease in humans in developing countries. Generally, soil application of 5-17 kg Zn ha(-1) y(-1) (25-85 kg zinc sulphate heptahydrate ha(-1) y(-1)) or more is recommended for rice. However, in the developing rice-growing countries of Asia, zinc sulphate of desired quality is not readily available and is also quite expensive, and the farmers generally fail to apply Zn, resulting in crop yield loss in rice. Availability of zinc-enriched urea (ZEU) makes possible not only the availability of quality zinc, but also assures its application. Therefore, field experiments were conducted for two consecutive years at the research farm of Indian Agricultural Research Institute, New Delhi, India, during rainy (rice) and winter (wheat) seasons of 2004-2006 on a sandy clay-loam soil to study the effect of various concentrations of zinc enrichment of urea on productivity, zinc concentrations, its uptake and use indices of aromatic rice-wheat cropping system. Eight treatments comprising prilled urea (PU) and 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5% zinc-enriched urea, replicated three times, were compared in a randomized block design. The enrichment of PU was done through zinc oxide containing 80% zinc. The results of this study revealed that the zinc-enriched urea (ZEU) had a significant effect on growth, yield attributes and yields of aromatic rice. Highest values for all these attributes and yields were recorded at the highest enrichment (3.5%) of the PU with zinc. The highest zinc concentration and uptake in rice grain and straw were also significantly higher with the highest level (3.5%) of zinc enrichment. The highest total zinc uptake recorded was 1,168 and 1,353 g ha(-1), during 2004 and 2005, respectively, with 3.5% ZEU. However, a major increase in grain yield of rice was recorded up to 1.0% zinc enrichment. The residual effect of zinc-enriched urea on succeeding wheat yield and zinc uptake was significant only at a higher level of zinc-enriched urea and only in the second year of study. Overall, 1.0% zinc-enriched urea recorded significantly higher productivity and zinc uptake over PU in the rice-wheat cropping system and is recommended for Delhi and adjoining areas. The recommendation is also made keeping in view the fact that with increased levels of zinc enrichment of urea, the partial factor productivity, agronomic efficiency, apparent recovery and physiological efficiency of applied zinc in a rice-wheat system decreased significantly. Considering all the economic parameters (benefit, benefit:cost ratio, IR gained IR-1 invested in zinc), 1.0% ZEU proved the most economic source for aromatic rice-wheat cropping system and therefore is recommended for rice-wheat cropping system in Delhi and adjoining areas of north India.