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Jeffrey P. Mitchell, Anil Shrestha, Karen Klonsky, Tom A. Turini and Kurt J. Hembree

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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Karen Mitchell, Elizabeth French, Janna Beckerman, Anjali Iyer-Pascuzzi, Jeff Volenec and Kevin Gibson

Soil incorporation of biochar appears to increase plant growth in some environments. However, the effect of biochar on root system architecture (RSA) or on weeds is not well understood. Our objective was to examine the effect of biochar on the growth and RSA of large crabgrass (Digitaria sanguinalis L. Scop.), a common and problematic weed. Plants were grown in rhizoboxes filled with field soil ± either a low-nutrient biochar (LNB) or a high-nutrient biochar (HNB). Rhizoboxes were either filled uniformly with field soil ± biochar (solid) or with + biochar and − biochar-amended field soil so that each occupied half of the rhizobox (split). Large crabgrass biomass and RSA were affected by biochar type in the solid design rhizoboxes and large crabgrass roots proliferated in biochar-amended soil in the split rhizoboxes, regardless of biochar type. This study provides evidence that plant roots can detect and grow toward biochar and suggests that the addition of biochar to soils may increase the ability of large crabgrass to spread vegetatively.

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Jeffrey P. Mitchell, William R. Horwath, Karen K. Klonsky, Randal J. Southard, Rich DeMoura, Daniel S. Munk and Kurt J. Hembree

Eliminating tillage passes is a means to reduce production costs and dust emissions in California's San Joaquin Valley tomato production region. Inserting winter cover crops between summer crops may be a way to add organic matter to the soil and thereby improve soil quality. From 1999, we evaluated conservation tillage (CT) and cover cropping (CC) in a tomato/cotton rotation in Five Points, Calif. During the course of the study, tillage operations were reduced an average of 50% in the CT system relative to the standard tillage (ST) approach. Yields in the CT no cover crop (NO) system matched or exceeded yields in the STNO system in each year. Tomato yields in the CTCC and STCC systems were comparable to the STNO except in the first year, when stand establishment and early season vigor were problems. Weed management and machine harvest efficiency in high surface residue systems are issues requiring additional work in order to make CT adoption more widespread.

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Jeffrey P. Mitchell, Karen M. Klonsky, Eugene M. Miyao, Brenna J. Aegerter, Anil Shrestha, Daniel S. Munk, Kurt Hembree, Nicholaus M. Madden and Thomas A. Turini

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.