Effects of combined foliar application of Zn with N, P, or K on Zn accumulation, distribution and translocation in wheat

Objectives Combined foliar application of Zn and macronutrients (N, P or K) has been thought an effective way to fortify Zn nutrition of human. In this study, the Zn accumulation, distribution and translocation within wheat plants were investigated to clarify mechanism of N, P, and K applications to enhance Zn concentration in wheat grains.

Methods Field experiment was conducted using wheat as materials from October 2010 to June 2014. A split plot design was used with soil N rates of 0, 120 and 240 kg/ hm² as the main plot factor, and the foliar application of distilled water (CK), ZnSO₄ 0.3% (Zn), ZnSO₄ 0.3% plus urea 1.7% (Zn + N), ZnSO₄ 0.3% plus KH₂PO₄ 0.2% (Zn + P + K) and ZnSO₄ 0.3% plus K₂SO₄ 0.5% (Zn + K) as subplot factors. By analyzing Zn concentrations in grain and vegetative tissues (leaves, glumes and stems) of wheat, the influences of combined foliar application of Zn with N, P and K on Zn distribution, and the relative contributions of Zn remobilization and post-anthesis shoot Zn uptake to grain Zn accumulation were evaluated.

Results Under the treatments of foliar applying Zn, Zn + N, Zn + P + K and Zn + K, the Zn concentrations were increased by 2.4–7.7 folds in the leaves, 2.0–4.7 folds in the glumes and 1.8–2.4 folds in grains, which were much greater than the increase in the stems (0.2–1.0 folds), compared with foliar distilled water application (CK). The increases of Zn distribution were significant in leaves and glumes. Compared with foliar Zn application alone, foliar Zn + N and Zn + K applications increased grain and leaf Zn concentrations, while foliar Zn + P + K application reduced grain and leaf Zn concentrations. Compared with foliar Zn application alone, the post-anthesis shoot Zn uptake and its mobilization to grain were increased by 12 and 14 g/hm² in foliar Zn + N application, and 44 and 32 g/hm² in foliar Zn + K application, but decreased by 37 and 18 g/hm² in foliar Zn + P + K application. Soil N application significantly increased the concentration and remobilization of Zn in all the wheat organs, but these increases were much lower than those of the foliar Zn treatments. The combined foliar application of Zn with N, P and K did not affect Zn distribution within wheat. The Zn recovery rates in foliar Zn + N and Zn + K applications were higher than that in foliar Zn application alone, while that in foliar Zn + P + K application was lower.

Conclusions The increased grain Zn concentrations in foliar Zn + N and Zn + K applications were resulted from increased post-anthsis Zn uptake and mobilization, while the decreased grain Zn concentrations in foliar Zn + P + K applications were resulted from decreased post-anthsis Zn uptake and mobilization.