Processing tomato production in California is one of the state’s agricultural success stories accounting for 96% of U.S. production in recent years [U.S. Department of Agriculture (USDA), 2014]. Since the advent of recordkeeping and the shift of production from the eastern United States throughout the 20th century (Geisseler and Horwath, 2013), processing tomato yields in California have increased 742% due in part to technological advances achieved in harvesting equipment, irrigation management, and variety development (Hanson and May, 2006; Mitchell et al., 2012).
Current production techniques throughout California’s Central Valley (CV), where most tomato production occurs, rely increasingly on the use of transplants for stand establishment (Hartz et al., 2008), permanent subsurface drip tape for irrigation (Mitchell et al., 2012), and numerous intercrop tillage operations that are routinely performed for residue, and salinity management, and also to mix herbicide residues throughout the soil so they do not accumulate in certain zones of semi or permanent bed production systems (Mitchell et al., 2009, 2012). Advantages from DR include higher yields than with surface or sprinkler irrigation and thus account for the widespread and growing use of DR for tomatoes in the CV (Hanson and May, 2006). However, the main disadvantage of DR is its initial capital cost (Hanson and May, 2006) as well as ongoing costs associated with maintenance. In recent years, there is also a growing trend of coupling subsurface DR with 80-inch beds to increase land-use efficiency and this has resulted in further yield increases.
Much is known about optimal irrigation for high yields and soluble solids’ content of processing tomato (Hanson and May, 2005, 2006; Phene et al., 1985). The basic equation is now widely used by CV tomato farmers for irrigation scheduling is ETc = Kc × ETo, where ETc is the projected evapotranspiration of the tomato crop, Kc is a corresponding growth-stage-dependent crop coefficient, and ETo is reference evapotranspiration for a given production region (Hanson and May, 2005, 2006). Extensive work by Hanson and May (2006) determined the relationship between irrigation crop coefficients and canopy coverage and suggested using a crop coefficient of 0.19 for canopy coverage less than 10%, an average midgrowth stage crop coefficient between 0.99 and 1.08, with a late-crop growth reduction or irrigation cutback to improve crop quality. An advantage of DR relative to the former industry standard furrow irrigation has been the ability to precisely apply small amounts of water more frequently to maintain these ETc targets.
Overhead irrigation, including both center pivot and linear move systems, is a technology that is important for a wide range of crops and regions throughout the United States and many parts of the world but is currently not widely used in California. In this article, we use the term OH to denote both center pivot and linear move systems. Though pivots tend to cost less than linear systems to install, the operation and irrigation management for these two OH systems are similar. In recent years, Nebraska and California are the top two U.S. states in total irrigated acres, with 8.6 million and 8.0 million acres, respectively. Nebraska has an estimated 75,000 pivots in operation, but there are fewer than 350 in California (Johnson et al., 2011; USDA, 2007). Overhead irrigation may have a number of advantages that could conceivably be important for CV tomato farmers in terms of reducing production costs as a potentially cheaper production system alternative to DR, and also for maintaining fruit yields and quality under the State’s increasingly water-short conditions (Pelter and Sorensen, 2003). However, research-based information is needed to compare these systems in terms of their overall production costs and water-use efficiency. To date, there were a few commercial attempts in the CV to use OH for tomato production in the 1990s and another more recent effort in 2009. However, for a number of reasons including inability of the OH system to keep up with ETc demands in the 1990s instances and logistical issues related to water availability to the field in the 2009 attempt, these efforts were not economically successful and have been abandoned.
In many regions where OH technologies are used, they are commonly coupled with reduced tillage planting techniques in large part to further lower productions costs, but also because with OH customary planting, beds and furrows are no longer necessary as they are in surface irrigation systems. Because no studies in the CV have been published on the use of OH, there is a need to compare the performance and profitability of this practice with local standard subsurface DR minimum tillage (MT) production practices, to evaluate the potential for using pivot irrigation for an economically important crop such as tomato, and to provide best management guidance to farmers who may seek to use it. Therefore, the objective of this study was to compare crop growth and yield of tomato under DR and OH using MT.
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