Optimum range in leaves of potato grown under plastic mulches. IV. Bioindicators of micronutrients

For 3 years (1993 to 1995) Solanum tuberosum L. var. Spunta. was grown unde r different polyethylene [PE] mulches (25 mu thick, transparent PE, (T1); 2 5 mu-thick, white PE, (T2); 50) mu-thick coextruded black-and-white PE (T3) , and 25 mu-thick black PE, (T4). Controls were left uncovered (T-0). Fresh leaf material was analysed for the following biochemical indicators: ascor bic-acid oxidase, catalase, peroxidase, polyphenol oxidase and ribonuclease enzymes. We also determined ortho-di- and total phenols as physiological i ndicators. From yield and analytical data the optimum foliar nutrient range was obtained.