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T.K. Hartz, A. Baameur and D.B. Holt

A study was conducted to determine the feasibility of fieldscale CO2 enrichment of vegetable crops grown under tunnel culture. Cucumber, squash and tomato were grown under polyethylene tunnels in a manner similar to commercial practices in southern California. The buried drip irrigation system was used to uniformly deliver an enriched CO2 air stream independent of irrigation. CO2 concentration in the tunnel atmosphere was maintained between 700-1000 ppm during daylight hours. Enrichment began two weeks after planting and continued for four weeks. At the end of the treatment phase, enrichment had significantly increased plant dry weights. This growth advantage continued through harvest, with enriched plots yielding 20%, 30% and 32% more fruit of squash, cucumber and tomato, respectively. As performed in this study, the expense of CO2 enrichment represented less than a 10% increase in total pre-harvest costs. Industrial bottled CO2 was used in this study; since bottled CO2 is captured as a byproduct of industrial processes, this usage represents a recycling of CO2 that would otherwise be vented directly to the atmosphere.

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T.K. Hartz, A. Baameur and D.B. Holt

The feasibility of field-scale CO2 enrichment of vegetable crops grown under tunnel culture was studied with cucumber (Cucumis saivus L. cv. Dasher II), summer squash (Cucurbita pepo L. cv. Gold Bar), and tomato (Lycopersicon escukntum Mill. cv. Bingo) grown under polyethylene tunnels. The drip irrigation system was used to uniformly deliver a CO2-enriched air stream independent of irrigation. Carbon dioxide was maintained between 700 and 1000 μl·liter-1 during daylight hours. Enrichment began immediately after crop establishment and continued for ≈4 weeks. At the end of the treatment phase, enrichment had significantly increased plant dry weight in the 2 years of tests. This growth advantage continued through harvest, with enriched cucumber, squash, and tomato plots yielding 30%, 20%, and 32% more fruit, respectively, in 1989. In 1990, cucumber and squash yields were increased 20%, and 16%, respectively. As performed, the expense of CO2 enrichment represented less than a 10% increase in total preharvest costs. A similar test was conducted on fall-planted strawberries (Fragaria × ananassa Duch. cvs. Irvine and Chandler). Carbon dioxide enrichment under tunnel culture modestly increased `Irvine' yields but did not affect `Chandler'.

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D.R. Pittenger, Donald R. Hodel, David A. Shaw and D.B. Holt

A previous field study had shown that Baccharis pilularis, `Twin Peaks', Drosanthemum hispidum, Vinca major, Gazania hybrid, Potentilla tabernaemontanii and Hedera helix, `Needlepoint', express no loss in relative aesthetic appearance when irrigated for one season at 50% of reference evapotranspiration (ETo), but three species did not perform acceptably at 25% of ETo. In this study these six species were grown in the field for 16 months under treatments of 50%, 40%, 30% and 20% of real-time ETo to more closely determine their minimum irrigation needs.

Analysis of seasonal plant performance ratings indicates that for Vinca, Gazania and Potentilla there is no significant increase in relative performance when irrigated at more than 30% of ETo. Baccharis, Drosanthemum and Hedera exhibited no significant improvement in performance when irrigated above 20% of ETo. A general decline in aesthetic appearance and performance was observed during the study in Gazania and Potentilla at all treatments, suggesting that their long-term minimum irrigation need may be more than 50% of ETo.