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  • Author or Editor: A. Shrestha x
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Despite the worldwide importance of overhead, mechanized irrigation for crop production, the potential of this technology has been poorly studied in California. Field studies were conducted at Five Points, CA, in 2010 and 2012 to compare the effects of overhead irrigation (OH) and drip irrigation (DR) on transplanted tomato (Solanum lycopersicum) crop growth and yield. Similar amounts of water were applied to both systems in each year to match crop evapotranspiration demands. Crop growth measured by percent canopy coverage and aboveground biomass accumulation were similar between the OH and DR systems early in the growing season in both years but were lower in the OH system during the second half of each season. Tomato yield was 38% greater in 2012 than in 2010 and averaged over the 2 years, 48% higher in the DR than in the OH systems, respectively, due presumably to the higher soil water evaporation losses of the OH system relative to the DR system and also, we propose, to the ability of the drip system to very precisely apply in-season fertigations directly to the crop root zone while OH fertigations were applied at the soil surface and over a greater area. Soluble solids concentration of fruit in 2010 was 5.99% for the DR system and 6.65% for the OH system providing further evidence of water stress in the OH tomatoes. Production costs associated with transitioning from a subsurface drip tomato crop to a sprinkler or surface drip-irrigated crop such as onion (Allium cepa) or garlic (Allium sativum) could be $130 to $420 per acre lower with the OH system compared with the drip system, if yields were maintained. Because operation and labor costs of OH systems are typically lower than those of DR systems, further research on OH irrigation of tomato is warranted to address the shortcomings of OH management that this study has identified.

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Methyl bromide (MB) has been widely used in California cut-flower production for effective control of a broad range of soil pests, including plant pathogens and weeds. However, MB is an ozone-depleting substance, and its availability to growers is limited according to the Montreal Protocol guidelines. Steam has been suggested as a nonchemical option for preplant soil disinfestation. Five trials were conducted in protected greenhouse structure or open-field cut-flower nurseries in Monterey, San Luis Obispo, and Ventura counties to evaluate the effect of steam application, alone or in combination with solarization, on soilborne plant pathogen populations, weed densities, and crop growth. Several steam application methods were used including steam blanket, spike-hose, buried drip irrigation lines, or drain tile, and these varied among trials. Calla lily (Zantedeschia aethiopica) nursery trials initiated in 2007 and 2008 showed that steam alone or with solarization was similar to or more effective than MB:chloropicrin (MBPic), applied via drip lines, in controlling weeds and Verticillium dahliae at 6-inch depth. Trials conducted in Spring and Fall 2009 in an oriental hybrid lily (Lilium sp.) nursery showed that, 112 days after steam treatment (DAT) in the spring, the steam (spike-hose) treatment had fewer Fusarium oxysporum propagules than the MB treatment. Lily plant growth in the steam-treated plots was similar to MB-treated plots and taller than in control plots. In the fall trial, fewer lily plants emerged by 44 DAT in the untreated control than in steam- and MB-treated plots and steam was not as effective as MB in reducing Pythium populations. In the 2010 sunflower (Helianthus annuus) and bupleurum (Bupleurum griffithii) trial, all steam treatments reduced Pythium and Phytophthora cactorum survival compared with the untreated control plots, whereas weed densities were reduced only in the spike-hose steam-treated plots. These trial studies showed that steam appeared as effective as MB in suppressing pathogens and weeds and improving crop growth in cut-flower nurseries. However, additional information on fuel consumption, treatment time efficiency, and long-term effects of steam treatment on soil health are needed before steam can be recommended as a viable alternative to MB in California cut-flower nurseries.

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Methyl bromide has been used extensively in open-field perennial crop nurseries to ensure the production of plants that are free of soilborne pests and pathogens. California regulations require that nursery stock for farm planting be commercially clean with respect to economically important nematodes. Under the terms of the Montreal Protocol, the use of methyl bromide by developed countries was phased out 1 Jan. 2005. Although the perennial nursery industry in the United States largely continues to use methyl bromide under critical use exemptions and quarantine/preshipment criteria allowed under provisions of the Montreal Protocol, nursery growers need viable alternatives to this fumigant. Two fumigation trials in perennial crop field nurseries with sandy loam and clay loam soils, respectively, were conducted to compare the efficacy of fumigants applied through standard shank-injection equipment or as emulsifiable compounds applied through drip irrigation equipment. In the garden rose (Rosa multiflora) nursery trial, nematodes were detected at planting in the untreated control, no-tarpaulin 1,3-dichloropropene + chloropicrin, and chloropicrin alone several months after treatment. Nematodes included root-knot nematode (Meloidogyne spp.) and stunt nematode (Tylenchorhynchus semipenetrans). At harvest 2 years later, root-knot nematode was detected in rose roots from untreated plots and plots treated with untarped 1,3-dichloropropene + chloropicrin, metam sodium, and chloropicrin alone. In the nut tree (Prunus spp.) nursery field trial, shank-injected treatments typically provided better nematode control than the same chemicals applied via the drip lines, although weed control and marketable trees were similar among treatments.

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Traditional processing tomato (Solanum lycopersicum) production in California’s Central Valley relies heavily on tillage to produce high yields. However, recent research and farm innovation have produced a variety of conservation tillage (CT) management alternatives that cut costs, reduce soil disturbance, and produce fewer emissions. A 12-year study in Five Points, CA, demonstrated that CT methods reduced tractor passes by 40%, lowered tillage costs by ≈$80 per acre in 2011 dollars, and achieved comparable yields as standard tillage (ST) methods. As comparable yield performance and net profitability are further demonstrated, an array of CT systems will become increasingly attractive to producers and more common in Central Valley tomato growing areas.

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