Response of wheat grain Zn concentration to foliar sprayed Zn in main wheat production regions of China

【Objectives】 Wheat grain zinc (Zn) concentration is generally low in China, and foliar application of Zn fertilizers is an important approach of increasing the grain Zn concentration. Therefore, researches and knowledge on response of wheat grain Zn concentration to foliar Zn application are of great importance for reasonable application of Zn and improving wheat grain Zn nutrition in China.【Methods】 Thirty field trials were conducted to study effects of the foliar Zn application on the wheat grain Zn concentrations, their differences between acid and alkaline soil regions, and the relation of grain Zn concentrations to main soil properties and the wheat shoot Zn concentration before the jointing stage in 14 provinces in major wheat production areas of China.【Results】 Results from the thirty field trials show that the foliar Zn application has no effect on grain yields, biomass amounts and harvest indies of wheat, but significantly increases the grain Zn concentrations by an average of 5.2 mg/kg (17.5%), with a 5.3 mg/kg (16.4%) increase in acid soil regions and a 5.2 mg/kg(18.4%) increase in alkaline soil regions. There are no significant differences between Zn uptakes and distribution of wheat in the acid and alkaline soil regions. Compared with the control, the foliar Zn application increases Zn uptakes of wheat grains, glumes, and stems by 19.4%, 28.7% and 99.2%, and up to 255.5, 26.0 and 117.5 g/hm2 respectively. The Zn harvest index of wheat under the foliar Zn application is 64.1%, 12.2% lower than the control. The grain Zn recovery rates and grain Zn biofortification indices are nearly the same in the acid and alkaline regions, with averages of 3.0% and 3.8 mg/kg respectively. A significant positive correlation (P0.05) is found between soil DTPA-Zn and the grain Zn concentration, with the grain Zn concentration increased by 4.0 mg/kg for each 1.0 mg/kg increase of DTPA-Zn, while a significant negative correlation (P0.001) is found between top 0-20 cm soil pH and the grain Zn concentration, with the grain Zn concentration decreased by 3.8 mg/kg for one unit topsoil pH rise. The grain Zn concentration is also significantly (P0.001) correlated with the shoot Zn concentration before the jointing stage, with each 1.0 mg/kg increase of the shoot Zn concentration resulting in 0.4 mg/kg grain Zn concentration increase. There is no significant correlation between topsoil organic matter contents and grain Zn concentrations. 【Conclusions】 Apart from the foliar Zn application, regulation of soil pH, increase of soil available Zn and promotion of wheat Zn uptake at the early growth stages are also important for increasing wheat grain Zn level in China.