Optimum range in leaves of potato grown under plastic mulches: IF. Bioindicators of macronutrients

For 3 years (1993 to 1995) Solanum tuberosum L. var. Spunta. was grown unde r different plastic mulches ([PE] sheets): (25 mu thick, transparent PE, (T 1), 25 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). F resh leaf material was analysed for the following biochemical indicators: n itrate reductase, pyruvate kinase, urease and foliar acid phosphatase activ ities. The following physiological indicators were also determined: foliar pigments (chlorophyll a, b, a+b, a/b, carotene, lycopene and anthocyanins), soluble aminoacids and proteins, and non-structural carbohydrates. From yi eld and analytical data the optimum foliar nutrient range was obtained.