Effects of Foliar Application of Zinc Fertilizer on Grain Yield and Zinc Content of Rice Grain cv. Sazandegi

IntroductionRice (Oryza sativa L.) is one of the major staples feeding more than half of the world population. It is grown in more than 100 countries, predominantly in Asia and provides 21% of energy and 15% of protein requirements of human populations globally. Zinc deficiency is one of the important abiotic factors limiting rice productivity worldwide and also a widespread nutritional disorder affecting human health. Chakeralhossein et al., (2009) evaluated the effects of rate, sources and application methods of zinc fertilizer on quantity and quality of rice and reported that, application of zinc fertilizer significantly increased yield and grain Zn content. The greatest yield enhancement (56.9%) was obtained in 3 g L-1 ZnSO4 along with application of 40 kg ha-1 ZnSO4 as soil application methods. In slightly alkaline sandy clay soil with sufficient Zn under flooded conditions, soil and plant Zn concentration were increased 1.8 times with foliar spray of 0.5 %w/v ZnSO4 which was applied at panicle initiation compared to soil application of ZnSO4 at the same stage. In a field experiment during two years in Egypt, the effects of Zn, Fe and Mn as single or combined application in soil and foliar spray to the rice growth and yield were evaluated. The results showed that the single or combine application of Zn, Fe and Mn significantly improved rice growth and yield. According to Zn deficiency is a widespread nutritional disorder affecting human health in many countries, especially where people rely on cereal-based food, the aim of this study was to investigate the effect of foliar application of nano-ZnO and zinc sulfate on yield and grain zinc content of rice.
Materials and MethodsA field experiment was conducted as randomized complete block design with three replications at the Isfahan Agricultural Research Center during 2013-2014. Treatments were consisted of six zinc foliar application levels: 150 and 300 mg L-1 nano-ZnO, 3 and 6 g L-1 ZnSO4, distilled water as the first control (Control 1) and no spray as the second control (Control 2). Rice plants were foliar sprayed until runoff using a hand-sprayer, at the tillering and grain milk stages. Nano-zinc oxide had a purity of greater than 99%, average particle diameter of 10-30 nm and specific surface area of > 30 m2 g-1. Also zinc sulfate was used with purity of 99%.
Results and DiscussionThe results showed that Fe, Mn and Zn concentrations of plant shoot at tillering and grain milk stages, and also grain yield and grain zinc content were significantly affected by zinc foliar application. Foliar application of nano-zinc oxide and zinc sulfate increased zinc concentration of plant shoot at tillering and grain milk stages. The highest shoot zinc concentration of 28.8 and 37.8 mg kg-1 were obtained in 6 mg L-1 zinc sulfate at tillering and grain milk stages, respectively. While the lowest shoot zinc concentration (24.2 and 30.5 mg kg-1) were observed in the first control treatment at tillering stage and in the second control treatment at grain milk stage, respectively. At tillering stage, foliar application of 3 and 6 mg L-1 zinc sulfate and 300 mg L-1 nano-zinc oxide increased shoot zinc concentration, whereas there was no significant difference between 150 mg L-1 nano-zinc oxide and two controls treatments. At grain milk stage, all zinc foliar application treatments increased shoot zinc concentration compared to the control treatments. The maximum grain zinc content (37.8 mg kg-1) was obtained with 6 g L-1 zinc sulfate which was 16.6 and 19.5% higher than first and second control treatments, respectively. Zinc foliar application significantly increased grain yield. Foliar application of nano-zinc oxide and zinc sulfate significantly improved grain yield compared to the control treatments. The highest grain yield was obtained in 6 g L-1 zinc sulfate fallowed by 150 mg L-1 nano zinc oxide, 3 g L-1 zinc sulfate and 300 mg L-1 nano-zinc oxide, respectively. Also, there were no significant difference between first and second controls. Zinc is a structural part of carbonic anhydrase, alcohol dehydrogenase, Cu/Zn-superoxide dismutase and RNA polymerase and serves as a cofactor for all 6 classes of enzymes (oxidoreductases, transferases, hydrolases, lyases, isomerase and ligases) and auxin synthesis in plants is also controlled by Zn. Adequate zinc in plants increases the synthesis of enzymes and hormones, metabolism of essential elements and stimulates plant growth and yield.
ConclusionsAccording to rice consumption per capita in Iran is 40 kg (110 g day-1) and the average daily human zinc requirement is 10-15 mg, zinc biofortification of rice and improving zinc of rice grain to 35 mg kg-1 will provide about one third of people’s daily zinc requirement (3.5 mg).