Optimum range in potato tubers grown under plastic mulches I. Macronutrients.

An experiment, conducted for three years with Solanum tuberosum L. var. Spu nta, consisted of covering the soil surface with different plastic polyethy lene [PE] sheets: transparent PE(25 mu thick, T1), white PE (25 mu, T2); co extruded black and white PE (50 mu, T3); black PE (25 mu, T4); no plastic c over (control, T0). In this research we determined optimum ranges of: (1) i onic balance and related parameters and ratios; (2) quality indices (pH, as corbic and citric acids); (3) physiological indices (alkaline index, Fe Ind ex and vegetative index) and (4) physiological ternary groups of soluble an d total macro and micronutrients. The dried tubers were analysed to determi ne: organic-, assimilated-, mineral- and total N, NH4+ and NO3-; total and inorganic P; total and inorganic Ca, Mg, K and Na, and sulphates. Frge was obtained.