Maize (Zea mays L.) Monosaccharides Content as Affected by Zinc Sulfate Following Systematic Application of Mineral Fertilizers to Carbonate Chernozem Soil Type

A three year field* experiment with zinc sulfate supplements was conducted in Moldova to study maize (Zea Mays L.) monosaccharides contents in years 13 through 15 years of systematic application of mineral fertilizers (no-fertilizer control, P60, N60K60, N60P60K60, N90P60K60, N60P90K60 kg ha^-1) to carbonate chernozem. Zinc treatments for 3 years were P60Zn10, N60P60K60Zn5, N90P60K60Zn5, and N60P90K60Zn10 on half of each long-term treatment. The soil at the experiment site was a chernozem, containing: humus 4.3%, total nitrogen 0.29%, CaCO3 1.7%, plant available phosphorus and potassium averaging 0.88 and 34.5 mg/100 g 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.  Long term phosphorus application induced zinc deficiency and decreased synthesis of carbohydrates and chlorophyll in maize. Zinc treatments compared to no zinc application significantly increased total monosaccharides in leaves (dry weight ranges 1.63-1.93% vs. 0.93-0.97%) and in stems (range 12.2-14.17% vs. 6.93-7.07% of at the 5-6 leaves stage. Chlorophyll concentrations (fresh weight ranges 14.07-17.73 mg% vs. 6.6-10.3 mg%) were significantly higher in plants supplied with zinc than those without zinc. Overall, zinc significantly increased leaf area 17.07 to 84.33 dm² per plant. Significant positive correlations were observed between monosaccharides in leaves or stems and chlorophyll content (r=.67 and r=.70 respectively), as well as between monosaccharides in leaves or stems and leaf area values (r=0.73 and r=.83). Hence, the use of zinc sulfate following systematic repeated application of phosphorous fertilizers to carbonate chernozem is essential to improving maize carbohydrates metabolism. *The results were obtained in Moldavian Scientific-Research Institute of Soil Science and Agricultural Chemistry, Chisinau, Moldova.