Potato (Solanum tuberosum L.) `Spunta' plants were grown with the root zone covered by different types of polyethylene plastic mulches. The plastic mulches used were transparent, white, co-extruded black and white, and black. As a control, plants were grown without plastic mulch. The parameters analyzed were soil temperature, root concentration of K and Ca, and enzymatic activities of ATPase and pyruvate kinase (PK), measured as basal and in the presence of K+ and Ca2+. The physical characteristics of the plastic mulches directly influenced soil and root temperatures in potato plants. In addition, the concentration of cations in the roots (particularly Ca2+) and basal ATPase activity were affected by soil temperature, whereas basal PK was not affected by soil temperature. The use of co-extruded black and white plastic mulch improved the nutritional status of Ca in the roots of potato plants. Finally, the basal ATPase and PK activities in the presence of K+ and Ca2+ were related with the root levels of these cations.
During three consecutive years of field experiments, three crop-covering treatments [noncovered (C), perforated polyethylene (PO, 500 holes/m2), and a nonwoven polypropylene (AO) sheet] were used to create different environmental conditions for growth of `Nagaoka 50' chinese cabbage [Brassica rapa L. (Pekinensis Group)]. The PO and AO treatments reduced solar irradiance and increased air and root temperatures compared to C plants. Plants were sampled five times each year from transplanting to harvest, and fresh and dry weights, yield at harvest, leaf pH, citric and ascorbic acid concentrations, and cell-wall fractions were determined. The PO floating row cover was the most beneficial for yield and chemical composition of chinese cabbage of the early spring crop in southern Spain, where environmental conditions during an unfavorable season can injure sensitive crops.