Effect of zinc fertilization on yield and grain zinc concentration of rice under field conditions

Twenty-five field experiments were conducted on rice (Oryza sativa) as test crop across Uttar Pradesh, Punjab, Haryana and Himachal Pradesh during the two consecutive kharif seasons of 2015 and 2016. The effects of soil and foliar fertigation of zinc (Zn) on rice grain yield and grain Zn concentration were studied. Farmer's field under three different Zn application methods was designed with complete randomized block design in three replicates, as following treatments: (i) Farmers’ practices without Zn application or business as usual (control), (ii) Farmers’ practices with 50 kg ZnSO4.7H2O/ha soil Zn application before transplanting of rice crop and (iii) Farmers’ practices with foliar Zn application (0.5% (w/v) aqueous solution of ZnSO4.7H2O was realized two times (i. e. first at anthesis or heading and the second one at early milking stage of rice crop). Both Zn application methods increased rice grain yield across 25 sites. However, the effect of soil Zn fertilizer on grain yield was more effective than foliar Zn. Foliar Zn treatments on rice increased grain Zn concentration significantly over control across all locations. In particular rice crop, soil Zn application noticeably increased grain yield and slightly less content of grain Zn over foliar Zn application. However, foliar application of Zn at particular growth stages of rice was an important agronomic practice for the farmers to enhance grain yield and Zn concentration to alleviate ‘hidden hunger’. In conclusion, soil Zn application method increased rice yield and profitability as compared to farmers’ practices (control). Given the high effectiveness of foliar Zn application in increasing grain Zn concentration, it is recommended that farmers apply Zn to rice by foliar application for both grain yield and optimum grain Zn biofortification to combat Zn deficiency.