Maize (Zea mays L.) Protein Nitrogen Response to Zinc Fertilization

A field experiment with zinc sulfate supplements was conducted in Moldova to study protein nitrogen of maize (Zea mays L.) during years 13 through 15 of systematic application of mineral fertilizers (No fertilizer control, P60, N60K60, N60P60K60, N90P60K60 and N60P90K60. Zinc treatments for three years were P60Zn10, N60P60K60Zn5, N90P60K60Zn5 and N60P90K60Zn10 on half of each long term treatment. The soil at the experiment site was carbonate chernozem, containing humus 4.3%, total nitrogen 0.29%, CaCO3 1.7%, plant available phosphorus and potassium average 0.88 and 34.5 mg/100g respectively, extractable cations Ca²⁺ and Mg²⁺ 31 and 2.9 meq/100g respectively, with pH_H2O value of 7.9 at the 0-20 cm soil depth. The results revealed that long term phosphorus application induced zinc deficiency in plants and stunted growth. Applied zinc increased its concentration in leaves from 27.7-29.5 (P60, N60P90K60) to 36.6-38.2 mg.kg^-1 (P60Zn10, N60P90K60Zn10) at 8-10 leaves stage averaged over three years.  These changes were positively reflected on plant growth and development, and maize protein metabolism. Although, there was not a large difference in  protein nitrogen concentration in maize leaves at 8-10 leaves stage, combined macro and microelements application increased protein nitrogen accumulation in leaves 112.7-229.1 and in stems 37.6-155.6 mg.plant^-1at physiological maize maturity. There were strong positive correlations between zinc concentration in leaves and yield of maize.  Hence, combined application of micro-and macroelements following systematic application of phosphorus fertilizers to carbonate chernosem soil is important to improve maize protein nitrogen content and accumulation on a long term basis in cropping system.