Impact of physical and melting mixing of zinc and urea on maize yield and fertilizer nitrogen and zinc use

Objectives This study examined the effects of combining zinc (Zn) and urea in different ways on dry matter and grain yield, quality, and utilization of nitrogen (N) and Zn by maize. The results will provide a scientific basis for the best combination of zinc and urea to develop new zinc-containing urea fertilizer.

Methods 0.5 and 5 parts of Zn sulfate heptahydrate were mixed into 99.5 and 95 parts of ¹⁵N-label urea (w/w) by physical (U+Zn) and fusion methods (UZn) to prepare four Zn-containing urea products: U+Zn0.5, U+Zn5, UZn0.5, and UZn5. A maize pot experiment was carried out with the four products, with pure urea, Zn SO₄·7H₂O, and blank (No N) as control. At maturity, maize shoots were harvested and divided into five parts (leaf, stem, bract, cob, and grain) to determine dry biomass, N contents,¹⁵N abundance, and Zn content. Soil samples in 0−30, 30−60, and 60−90 cm depth were collected for the determination of N, available Zn content, and ¹⁵N abundance.

Results Compared with the pure urea and U+Zn treatments, UZn0.5 and UZn5 (P<0.05) increased the maize grains per ear. There was no significant difference between UZn0.5 and UZn5. Further, UZn0.5 and UZn5 treatments increased total N and fertilizer N absorption of maize, increased Zn accumulation in the grains, with UZn0.5 increasing by 62.08% over the common urea. Compared with the physical mixture and common urea treatments, UZn0.5 (P<0.05) increased the residual nitrogen of fertilizer in 0−60 cm soil depth, and UZn0.5 (P<0.05) increased that in 0−30 cm soil depth than UZn5. In contrast, the physically mixed fertilizer did not significantly affect fertilizer residue other than in CK. Both physical and fusion mixtures of Zn and urea significantly decreased fertilizer N loss; however, the fusion mixture's effect was significantly higher than physical mixtures.

Conclusions Mixing Zn and urea by fusion showed a much better effect than physical mixture in increasing maize growth, grain yield, the absorption of fertilizer N and Zn, and Zn accumulation in grains. Compared with the physical mixture method, mixing Zn and urea by fusion increased the residual amount of fertilizer nitrogen and reduced the loss rate of fertilizer nitrogen. The fusion of 0.5% Zn into urea decreased fertilizer N loss and increased fertilizer N residue in soil compared with adding 5%.