Keywords: Carbon dioxide, carbonated water, trellises, training, plastic covers, tomatillo, carbonic acid.
This study was conducted during the spring-summer cycle 1996 in Chapingo, Mexico. The following factors were studied: soil application of CO2 dissolved in water at concentrations of 0 (control), 300 and 1200 mg×liter-1; use of plastic mulches, which included transparent plastic, white-on-black plastic, and a control without plastic mulch; and a training system with and without (control) trellis. The results indicated that soil application of CO2 dissolved in water, especially the treatment with 1200 mg×liter-1, significantly increased the leaf area, weight of leaf and stem dry matter, and yield in the last harvest. However, initial and total yield, fruit weight, number and volume, branch length, total leaf acidity, percentage of CO2 in the soil and CO2 assimilation rate were not significantly affected, possibly because CO2 was not absorbed by the roots and neither was there additional formation of organic acids. Also, soil pH decreased slightly with 1200 mg×liter-1 of CO2. The use of plastic mulches, principally the transparent mulch, significantly modified the morphology of the plants: increase in stem diameter, number of leaves and flowers, plant height, branch length, leaf area, dry matter, fruit weight, initial and total (73.8 t×ha-1) weight, and soil temperatures. The highest total yield was obtained with white-on-black mulch (78.7 t×ha-1) and the lowest with the control (44.9 t×ha-1). Management on trellises produced a higher total yield (67.73 t×ha-1) than traditional management on the ground (63.87 t×ha-1), which modified the initial pattern of translocation of assimilates in the plant, increasing the dry matter in stems and leaves at the expense of initial fruit yield. The highest total yield was obtained with trellis training with white-on-black mulch and 1200 mg×liter-1 of CO2 (83.3 t×ha-1); this treatment had a benefit/cost ratio (B/C) of 0.52. The highest B/C ratio resulted from the treatment without trellises with white-on-black mulch and without CO2, producing 75.6 t×ha-1. The control treatment (without CO2, without mulch, and without trellis) yielded 42.8 t×ha-1 with a 0.55 B/C ratio.