Chemical Composition of Corn Sap As Influenced by Mineral Fertilizers Applied to Carbonate Chernozem Soil.

A field experiment was conducted in Moldova to evaluate the effect of zinc sulfate on the chemical composition of corn sap following systematic application of mineral fertilizers to carbonate chernozem soil. Long term phosphorus application induced zinc deficiency in corn, which affected the development of the leaves and was manifested as plant chlorosis. The combined application of zinc sulfate, nitrogen, phosphorus, and potassium restored plant growth and development, increased plant biomass, and positively affected the chemical composition of corn sap. A positive response was observed between zinc sulfate application rates containing macro elements and the measured corn sap volume, which increased by 88 % (N60P90K60Zn10) at the 8-10 leaves plant stage compared to without zinc application (N60P90K60). Zinc sulfate decreased the concentration of nitrate nitrogen (NO3-N) from 147.7 (N60P90K60) to 126.3 mg/L (N60P90K60Zn10) and increased the ammonium nitrogen (NH4-N) from 25.3 to 36.9 mg/L in corn sap at the 8-10 leaves stage. Translocations of NH4-N and NO3-N in the corn sap from the root system to the upper stalk and leaves were 2.8 and 1.6 times higher, respectively, in plants receiving zinc fertilization at that stage. Free amino acids (lysine, histidine, arginine, serine, glycine, alanine, valine, isoleucine, tyrosine, and phenylalanine) concentrations in corn sap following combined phosphorus and zinc applications (P60Zn10) were at the same level as in the control. However, free amino acid levels in corn sap at the 8-10 leaves stage were higher following both phosphorus and zinc applications compared to applications of phosphorus only without zinc (P60). Zinc sulfate decreased inorganic phosphorus from 188 (N60P90K60) to 143.7 mg/L (N60P90K60Zn10) and increased organic phosphorus from 57 to 80.7 mg/L in sap at the 8-10 leaves stage. Translocation of inorganic and organic phosphorus from roots to above-ground corn plants was 1.5 and 2.8 times higher in zinc fertilized plants at the 8-10 leaves stage. There was not a large difference in potassium concentrations in corn  sap, however, its translocation from the root system to upper parts of the plants was 1.8 times higher with zinc fertilization at that stage. Hence, in a phosphorus induced zinc deficient environment, zinc promote nutrient uptake and increases biosynthetic processes in the corn root system.