Drip irrigation of tomato using carbonated water and mulch in Colorado

The effect of irrigation with carbonated water (CW) and without (C for control) was tested on mulched (1 mil black plastic) and unmulched tomato (Lycopersicon esculentum Mill.) 'Patio Prize' a fresh market "bush" type transplanted to the field in early June, 1988. The drip irrigation tubing was placed on the soil surface. Cumulative evapotranspiration was determined weekly using a neutron probe so that root profiles were completely recharged by two irrigations per week. A commercially available carbonator injected CO2 at about 276 kPa so that irrigation water pH was reduced from 6.4 to 4.5 for the CW treatments. Marketable fruit yield was increased (P<0.05) by the CW treatment in a mulched experiment; however, in an unmulched experiment, the increase was not evident. Above-ground plant profile enrichment (15 cm) by CW application was observed on the day of irrigation in the mulched plots (P<0.05) but not in the unmulched plots. Soil atmospheric enrichment by the CW treatments was observed in the mulched plots on the day of irrigation and a residual effect was noted 3 to 4 days after irrigation (P<0.05). Soil enrichment did not occur in the unmulched plots. The CW treatment increased the Zn uptake in the mulched treatments (P<0.05). The results suggest that mulch is necessary for response to carbonated irrigation water applied to the soil surface. Irrigation water as the sole system for CO2 delivery may not provide an optimum solution to the problem of CO2 enrichment in the open field. This is probably because CO2 application is associated with irrigation demand and thus, cannot be supplied on a continuous basis as in the greenhouse. This in turn results in pulsed application of CO2/HCO3 and short term soil pH reduction.