- Vegetables: tomatoes
- Production Systems: general crop production
Very promising results were obtained from the 2010 and 2011 trials on alternate furrow irrigation for increasing crop water use efficiency without a yield decrease. The collaboration between an industry leader, Campbell Research and Development, and the Jackson Lab at UC Davis was conducive to outreach to stakeholders involved in agricultural and environmental sustainability and tomato production. Trials evaluated yield and cultivar response to alternate furrow irrigation, i.e., one furrow of a bed receives water at each irrigation, to every furrow irrigation. Results suggest that higher water use efficiency (yield/water applied) is possible due to irrigation reductions of at least 25% in on-farm trials. Cultivars’ performance was mostly similar between irrigation treatments. Alternate furrow irrigation is a way to use less water without a decrease in yield or fruit quality and without investment in technology such as drip irrigation.
Alternative irrigation methods that use less water but produce high yields contribute to agricultural sustainability. This project focused on the promising partial root drying (PRD) technique to reduce water applied and increase crop water use efficiency (yield/water applied, WUE). The PRD technique lets half of the root system encounter areas with low soil moisture and has been shown to maintain the photosynthetic capacity of the crop, due to water availability on the other side of the plant (Loveys et al. 2004; Tahi et al. 2007). PRD is based on root signaling to shoots when the root system encounters areas of low soil moisture, resulting in stomatal regulation to reduce transpiration. Understanding crop responses and fine-tuning irrigation management must be done, however, to maintain photosynthetic rates and allocate biomass to reproductive structures, so that high crop yields are produced with less water. This project was a collaboration with growers, farm advisors and the industry to evaluate the potential of alternate furrow irrigation as a management practice in processing tomatoes to increase crop water use efficiency without a yield decrease.
As water demands from urban areas increase, and water availability may decrease as a result of climate change, agricultural activities need to adopt new practices to improve irrigation methods; especially in California, where agricultural water consumption is at least 75% of the water supply (Gleick et al. 2003). One approach to improve crop water economy is to efficiently manage irrigation to reduce total water applied, surface runoff and percolation below the rooting depth without a yield decrease. Furrow irrigation represents about 50% of all irrigated acreage in California, and it is the largest cost of field operations before harvest in processing tomato production (UCCE 2001). Thus, the furrow irrigation system is the focus, especially because it has a low WUE and generates high volumes of runoff water that contribute to erosion and potential nutrient and pesticide pollution (Sutton et al. 2007).
Alternate furrow irrigation is practiced by some tomato growers in California throughout the season but not always purposely used as a PRD technique (Gene Miyao, personal comm.). Under field comparisons, alternate furrow irrigated fields were shown to be statistically similar to drip irrigation for the amount of water applied and the yield of processing tomatoes (Hanson and May 2006). Thus, alternate furrow irrigation may better reduce water use and production costs of processing tomato and could have a broad impact on water conservation efforts, considering that California has an average area of 277,000 acres per year planted to tomatoes (USDA 2006).
The mechanisms that are involved in the PRD technique are fairly well-understood, but individual crop responses vary (Loveys et al. 2004; Tahi et al. 2007). PRD is already used in vineyards (Dry and Loveys 1999; Dry et al. 2001) and is increasingly being tested and used as means of reducing water use and increasing crop WUE in fruit trees (Loveys et al. 2004; Zegbe et al. 2007) and horticultural and row crops (Kang et al. 2001; Mingo et al. 2003). This management allows root growth and soil exploration and also stimulates plant physiological responses to drought stress-like conditions. Signaling between roots and shoot for the regulation of water use has been shown, for instance, through the increase of abscisic acid (ABA) concentration and/or pH of xylem sap, which can regulate stomatal conductance (Dodd et al. 2006; Mingo et al. 2003; Stoll et al. 2000). Slight reductions in stomatal conductance have been shown to not affect carbon assimilation while diminishing transpiration, thus increasing plant WUE (Tahi et al. 2007).
Some field studies show that yields under alternate furrow irrigation can be equal to conventional irrigation, while reduction in water consumption is about 35% in maize (Kang et al. 2000), 30% in potato (Shahnazari et al. 2007) and up to 50% in wine grapes (Stoll et al. 2000). For commercial production of greenhouse tomatoes, PRD treatment significantly decreased stomatal conductance, sap flow, leaf area and shoot biomass without affecting fruit biomass but increased quality with higher degree Brix (Kirda et al. 2007; Theobald et al. 2007). To achieve this gain in water reduction without affecting production, effective PRD management should be based on soil moisture utilization and crop morphological and physiological characteristics (Mingo et al. 2004).
Water use efficiency has inadvertently increased in the past 30 years during tomato breeding in California. Evapotranspiration rates (i.e., water loss via evaporation and plant use) have kept constant at an average of 648 mm, but yields have increased more than 50% since the 1970s to currently over 81 Mg/ha (Hanson and May 2006). A comparison of eight tomato cultivars released from 1936-2002 showed that phenological changes (early flowering and fruit set), smaller canopies and gains in photosynthetic rates may have contributed to this gain (Barrios-Masias and Jackson, unpublished data). These findings suggest that current tomato cultivars may further increase crop WUE in the short-term by improved irrigation management.
Objective 1. Conduct an on-farm case study to obtain data on a typical soil water budget and cultivar responses with alternate furrow irrigation.
Objective 2. Evaluate water use and physiological, phenological and morphological responses of different processing tomato cultivars to controlled full or alternate furrow irrigation regimes.
Objective 3. Increase understanding of PRD and alternate furrow irrigation management among growers as means of reducing total applied water, potential pollution and production costs.