Final Report for GW10-010
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.
Two field studies were conducted to understand the response of processing tomatoes to alternate furrow irrigation and the potential to decrease applied water without decreasing yields. The first study (2010) was conducted in a 4500-m2 (1-acre) field at Campbell Research and Development Station in Davis, California. This study evaluated two widely planted cultivars under careful irrigation management with all other practices similar to commercial processing tomato fields (details below). The second study was composed of four on-farm trials in adjacent fields with three different soil types (details below). Stakeholder involvement was constant all through the duration of the project, and their input was considered for structuring the experiments and field evaluations.
– 2010 research station experiment
This study focused on the response of leading processing tomato cultivars in the region to alternate furrow irrigation (AFI) and every furrow irrigation (EFI). Two highly productive and widely planted processing tomato (Solanum lycopersicum) cultivars were used: AB2 and CXD255. The field was divided in four irrigation strips of six beds (1.52-m wide) each (24 beds total) grouped in two blocks. Irrigation treatments were randomly assigned to each irrigation strip within a block. In each irrigation strip, six plots were randomly assigned to the two cultivars (three plots per cultivar per strip; 12 plots per cultivar and 24 plots total). Each plot was 9.1-m long, and planting density was a single row per bed with plant spacing of 36 cm. A complete randomized block design with a split block structure was set up to evaluate effects of AFI and EFI on tomato cultivars. The soil was mapped as a Reiff very fine sandy loam, a coarse-loamy, mixed, nonacid, thermic Mollic Xerofluvent.
The field was machine transplanted on May 18, 2010, and sprinkler irrigated the following day to assure good plant establishment. Soil moisture data and water inputs as rain, sprinkle and furrow irrigations were measured and total water applied estimated. Irrigation treatments were started with the first furrow irrigation (23 days after transplanting; DAP) and continued in average every nine days for a total of 10 irrigations. At each irrigation, the AFI strips received water on every other furrow, i.e., the ‘dry’ furrow was irrigated. The EFI strips had all furrows irrigated at each irrigation event. Irrigation was applied using gated pipes to control water flow and even moisture distribution into the beds and furrows. The irrigation was controlled by damming the furrows to control even distribution along the length of the furrow and produce no run-off. To represent normal irrigation practices, a well experienced furrow irrigator and the field manager were totally in charge of deciding about irrigation, and we only took measurements throughout the irrigations without providing input on the irrigation practice itself. Furrow inflow was measured for every furrow in all irrigations. Estimates of the total water applied were calculated based on the duration of each irrigation.
Measurements of crop development and plant performance were done all through the season until harvest. Canopy measurements were done every 12 days with an infrared digital camera (Dycam, Woodland Hills, CA) mounted on an inverted ‘L’-shaped pole to consistently cover a 3.6 m2 area. One picture for every plot was taken and processed with Briv32 Version 1.27 software to obtain percent canopy cover (Colla et al. 2000). Leaf gas exchange measurements were taken with a field portable open flow infra-red gas analyzer (IRGA; Model 6400, LI-COR Inc., Lincoln, NE, USA). Measurements were taken between 1000 and 1300 h with a 6 cm2 chamber, with the CO2 reference set at 400 ?mol m-2 s-1, and with saturating light using a LED source (PAR in: 2000 ?mol m-2 s-1). A total of six measurements were taken between 69 and 86 DAP (i.e., stage of maximum plant growth and fruit set) on mature fully expanded leaves from the top of the canopy.
Biomass evaluations were conducted at the beginning of fruit set (65 DAP) and at harvest (126 DAP). At 65 DAP, four plants at each plot were cut at the base of the stem, separated into shoots and fruits, dried at 60C and weighed (24 plots and 96 plants total). At 126 DAP, a 4-m bed section (?11 plants) were cut at the base of the stem and separated into shoot, green fruit, harvestable fruit and decay fruit. All biomass was weighed in the field and sub-samples taken, dried at 60C and weighed. Samples for ?13C from shoots at harvest were ground and analyzed in the Stable Isotope Facility at UC Davis. A machine harvest was conducted at 132 DAP with the two middle beds harvested (48 bed sections in 24 plots total). Standard fruit quality parameters for the processing tomato industry were evaluated from samples taken from this harvest: pH, soluble solids and fruit color.
Soil moisture was sampled before planting, at mid-season and after harvest (-6, 65 and 132 DAP). Samples were taken from the furrow and on the bed (30 cm from the center) at three depths: 0-15, 15-30 and 30-75 cm. The furrow sampling started with the 15-30 cm depth because the 0-15 cm depth was accounted as the bed height. Soil sampling was always done on both sides of a bed to account for the alternate irrigation, and thus, one furrow being ‘drier’ than the other in AFI strips. A composite sample from both sides of a bed was taken from the field for gravimetric soil moisture (total of 70 composite samples in 24 plots). Soil deep coring was done to a 3-meter depth at -5 and 137 DAP to evaluate if AFI and EFI affect soil water depletion. Soil samples were taken from 0-30 cm, and then at 45-cm increments (total of seven depths).
– 2011 on-farm trials
In 2011, four on-farm trials were conducted in a grower’s fields that were managed under similar conditions as the 2010 study: furrow irrigated, single row tomatoes in 1.52-m wide beds. Meetings with growers were conducted to establish the collaboration and details on the trials. Fields were chosen based on different soil textures with same cultivar and close transplanting dates to minimize other environmental effects on crop response, e.g., temperature and precipitation.
The four on-farm trials were set up in adjacent fields of 26 ha each (65 acres). Two field trials were conducted on a Reiff very fine sandy loam soil because of the low water holding capacity and potential for water stress to affect yield. The other two trials were on a Yolo silt loam soil and a Sycamore silty clay loam soil.
All fields were machine transplanted between April 4 and 5, 2012 to cultivar Shasta at a density of 38-cm between plants in a single row on the bed center. All four trials had the same lay out and included 36 beds divided in three blocks of 12 beds each (two six-bed irrigation strips). Irrigation treatments were randomly assigned within each block. To account for water infiltration pattern along a furrow/bed, four plots were set up in each irrigation strip and spaced at 20 m from each other, with the first plot always starting at 20 m from the top of the field (irrigation ditch). Each plot was 10 m long and 6 beds wide.
Irrigation treatments were set up in each trial, and irrigation decisions were made by the grower and the irrigation foreman. As in the 2010 trial, irrigation was monitored for furrow inflow, duration of each irrigation and correct alternation of furrow in the AFI treatment. To maintain irrigation practices as normally done in commercial fields, no input was provided about the irrigation scheduling or management. Irrigation treatments were started with the first furrow irrigation at 29 DAP and continued in average every 12 days for a total of six irrigations.
Measurements of crop development and plant performance were done all through the season until harvest, similar to the 2010 trial (details above). Canopy measurements were done every two weeks in all fields. Leaf gas exchange measurements were taken four times in every field (24 plots per field and 16 days of measurements). Leaflet samples for ?13C and N content were collected three times during the season, starting at fruit set (69 DAP) and at 80 and 104 DAP. Biomass evaluations at harvest were done between 115 and 121 DAP for all fields, and it was coordinated with the grower such that evaluations were performed the closest to the commercial machine harvest. Two 2-m sections of the two middle beds in each plot were harvested (i.e., bed 3 and 4). Plants were counted, shoot and fruit separated, sorted and processed as described above. Two harvestable fruit samples (1.5 Kg each) were taken from each plot to conduct fruit quality parameters. Soil moisture was sampled twice during the growing season: 21-25 DAP and 113-119 DAP for all fields (24 plots per trial; 96 plots total). Sampling included also deep coring to 255 cm, but limited to two plots per strip at 21-25 DAP and 126-133 DAP (12 plots per field; 48 plots total). Soil sampling was similar to the 2010 trial (see above).
This project shows promising results on irrigation alternatives that can increase crop water use efficiency by decreasing the amount of total applied water to a processing tomato field without a yield decrease.
– Applied water, crop water use efficiency and yield
Alternate furrow irrigation (AFI) decreased the total amount of water applied in the 2010 and 2011 trials. In 2010, AFI received 25% less applied water than every furrow irrigation (EFI) for the entire season (AFI: 31.6 “±” (+/-) 1.2 cm; EFI: 42.4 “±” (+/-) 1.3 cm; mean “±” (+/-) standard error). In 2011, all on-farm trials followed a similar pattern with at least a 28% reduction in applied water and an average decrease in 38% (AFI: 31.4 “±” (+/-) 1.6 and EFI: 51.3 “±” (+/-) 3.5 cm). Soil texture showed trends of more water applied on soils with higher clay content (e.g., AFI: 38.3 “±” (+/-) 1.0 cm and EFI: 66.6 “±” (+/-) 1.7 cm) than in sandy soils (e.g., AFI: 27.0 “±” (+/-) 0.5 cm and EFI: 38.0 “±” (+/-); 1.0 cm). Previous SARE projects have shown reductions in water applied in other crops: irrigation at wider bed intervals in corn under conservation tillage with decrease in total water applied (FW00-012 Hines et al.); and reductions of irrigation to 75% ETc in asparagus without decrease in yields (SW02-013 Drost et al.). These projects show the existing potential to make furrow irrigation more efficient without a yield decrease.
Yields of AFI were no different than EFI in 2010 and 2011. In 2010, yields of AFI were 111 “±” (+/-) 4 t ha-1 and EFI were 115 “±” (+/-) 3 t ha-1. There were no yield differences found in the cultivar*irrigation interaction, which suggests that possible cultivar trait differences did not affect crop productivity under AFI treatment. In the 2011 on-farm trials, the average yield for all fields was AFI: 84 “±” (+/-) 3 t ha-1 and EFI: 86 “±” (+/-); 3 t ha-1. Yields fluctuated among fields with the highest yield in the Sycamore soil trial (AFI: 116 “±” (+/-) 3 t ha-1 and EFI: 111 “±” (+/-) 3 t ha-1) and the lowest in one of the Reiff soil trials (AFI: 65 “±” (+/-) 3 t ha-1 and EFI: 73 “±” (+/-) 3 t ha-1). Regardless of these yield differences among fields, the 2011 trials show that AFI could become an irrigation alternative especially in dry years when water availability for agriculture decreases. The differences in applied water without a decrease in yields between AFI and EFI resulted in higher agronomic water use efficiency (yield/ applied water; WUEa). For instance, in 2010 the WUEa of AFI was 3.5 “±” (+/-) 0.1 Mg-yield cm-H2O-1 and EFI was 2.7 “±” (+/-) 0.1 Mg-yield cm-H2O-1, which was a 29% increase.
– Soil moisture
Soil moisture differed between AFI and EFI at different soil depths and positions relative to the bed center. In the 2010 trial, soil moisture differences between irrigations were present at 65 DAP in the bed at 0-15 cm depth (AFI: 17.4 “±” (+/-) 0.6 % and EFI: 20.8 “±” (+/-) 0.5 %) and 15-30 cm depth (AFI: 18.0 “±” (+/-) 0.3 % and EFI: 20.3 “±” (+/-) 0.5 %), and in the furrow at the 15-30 cm depth (AFI: 16.2 “±” (+/-) 0.7 % and EFI: 20.9 “±” (+/-) 0.3 %). No differences were observed in the 30-75 cm depth of the bed or furrow, but soil moisture decreased with time (i.e., before planting to harvest) from 24.5% to 17.8% in the bed and from 22.8% to 17.2% in the furrow. This data suggests that cultivars under AFI were able to utilize water deeper in the soil profile at the same rate as in EFI even though moisture differences were observed in the top 30 cm. Reducing the amount of applied water per irrigation and the total ‘wet’ surface area in a field could reduce soil evaporation especially before canopy closure, and thus, contribute to greater WUEa. Further analysis of the 2011 on-farm trial dataset could support the idea that increasing water use efficiency in processing tomatoes depends on cultivar capacity to perform well under an AFI pattern that wets only one side of the bed at each irrigation. Keeping lower water availability in the top 30 cm of a bed could reduce total water loss through soil evaporation without affecting yields.
– Canopy cover and total biomass
Crop development, measured as soil canopy cover, was not affected by the irrigation treatment in the year 2010 (e.g., at 94 DAP AFI: 85 “±” (+/-) 1 % and EFI: 86 “±” (+/-); 1 %) although differences between cultivars was observed especially early in the season (data not shown; http://ucanr.org/sites/Jackson_Lab/files/140049.pdf). In the on-farm field trials, canopy development was mostly similar between irrigation treatments when analyzed within trial (except at 23 DAP for two fields; data not shown). When data was analyzed with ‘trial’ as a factor, soil canopy cover was lower in the AFI treatment from 80 DAP until harvest (130 DAP; in average for all trials). The maximum soil canopy cover was achieved at 98 DAP (AFI: 78 “±” (+/-) 1 % and EFI: 83 “±” (+/-) 1 %; p= 0.04).
In 2010, shoot and fruit biomass at 65 DAP was similar between irrigation treatments and cultivars (e.g., shoot biomass was for AFI: 306 “±” (+/-) 8 g m-2 and EFI: 298 “±” (+/-) 12 g m-2), which is corroborated by the similar soil canopy cover data. Previous studies have also shown that canopy cover is highly correlated to shoot biomass in processing tomatoes (Barrios-Masias et al. unpublished data). Thus, during the on-farm trials in 2011, biomass sampling was only performed at harvest.
– Leaf gas exchange, 13C discrimination and N content
Photosynthetic rates (Pn), stomatal conductance (gs) and intrinsic water use efficiency (Pn/gs; WUEi), averaged across all dates, were not different between irrigation treatments in the 2010 trial. Mean photosynthetic rates were 29.8 “±” (+/-) 0.3 and 30.1 “±” (+/-) 0.3 µmol m-2 s-1 for AFI and EFI, respectively. Stomatal conductance was 1.15 “±” (+/-); 0.03 and 1.20 “±” (+/-) 0.3 mol m-2 s-1 for AFI and EFI, respectively. Shoot 13C discrimination values (an indirect measure of WUEi; ?13C) were not different and corroborated these results (AFI: 20.7 “±” (+/-) 0.1 and EFI: 20.8 “±” (+/-) 0.1). The cultivars used in the 2010 trial did not have different Pn or gs, but CXD-255 had higher WUEi than AB-2 (27.9.0 “±” (+/-) 0.5 and 25.0 “±” (+/-) 0.6 µmol-CO2 mol-H2O-1, respectively). This difference in WUEi at the leaf level suggests that processing tomato cultivars have the potential to adapt to new irrigation strategies even though some physiological differences in water use may exist among them.
Nevertheless, the ?13C data was not consistent with the spot-measured gas exchange data. The ?13C values are a more integrative measure of water use efficiency, and shoot samples for analysis were collected at harvest (126 DAP), which may show the overall performance of the cultivars towards water use and carbon assimilation in the entire season. Leaf gas exchange data processing from the 2011 on-farm trials is in progress and will contribute to understanding cultivar response to different soil textures and water availability. The 2011 data for the leaf ?13C values showed no difference between irrigation treatments when analyzed within trial. When data was analyzed with ‘trial’ as a factor, leaf ?13C values showed a slight difference between irrigation treatments at 80 and 104 DAP (e.g., at 104 DAP AFI: 20.55 “±” (+/-) 0.04 and EFI: 20.69 “±” (+/-) 0.05; p= 0.02).
Nitrogen content was not different in the 2010 shoot samples and in the 2011 leaflets sampled at 80 and 104 DAP. A very small difference in N content was observed between irrigation treatments at 69 DAP in the 2011 trials (AFI: 4.0 “±” (+/-) 0.0 % N and EFI: 4.1 “±” (+/-) 0.0 % N in leaflets). Nitrogen concentration in the leaves can affect the photosynthetic capacity of a leaf (Poorter and Evans 1998), and thus C assimilation and yields could be reduced as well. Alternate furrow irrigation did not affect N concentration in shoots (2010 trial) and in leaflets (2011 trials), especially at later stages of fruit filling.
– Fruit quality
Irrigation treatments did not affect fruit pH, soluble solids (°Brix) and color (a/b) (4.58 “±” (+/-) 0.02, 5.0 “±” (+/-) 0.1 and 2.19 “±” (+/-); 0.01, respectively), but differences were found between cultivars (data not shown; http://ucanr.org/sites/Jackson_Lab/files/140049.pdf). Fruit quality in processing tomato is important for the industry, and it is evaluated at the point of entry of the processing plant.
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Educational & Outreach Activities
• Barrios-Masias, F.H., Miyao, G., Jackson L.E. (in preparation) Alternate furrow irrigation can increase crop water use efficiency in processing tomato without a yield decrease.
• Barrios-Masias, F.H., Jackson L.E. (2011) Alternate furrow irrigation reduces water applied without yield reduction in California Processing tomatoes. Poster. ASA-CSSA-SSSA, Fundamental for Life: Soil, Crop, & Environmental Sciences. San Antonio, Texas, Oct. 16-19, 2011
• Barrios-Masias, F.H., Chetelat R.T., Jackson L.E. (2010) Effects of determinate growth and obscure veins on water use efficiency in California processing tomatoes. Poster. ASA-CSSA-SSSA, Green Revolution 2.0: Food+Energy and Environmental Security. Long Beach, California, Nov. 1-3, 2010
• March 2010: Several meetings were held with growers, cooperative extension, field managers, students and UC Davis professors. Purpose was to discuss irrigation management, present the AFI project and receive feedback.
• 05/22/10: Russell Ranch Field Day. Presented project to about 50 participants: growers, farm advisors, students and general public.
• 07/01/10: Field day at Campbell’s Research Station to give details about the AFI trial being conducted on site. Participants (20 total) were field managers, Campbell’s researchers and program directors.
• 09/17/10: Field day with representatives from NGOs working in sustainability (e.g., Sustainable Conservation) and the Tomato Growers Association.
• January-February 2011: Presentation of results to growers, farm advisors, Campbell’s researchers and field managers. Discussion for taking AFI to grower’s fields to conduct the 2011 on-farm trials.
• 06/02/11: Field day with collaborators to visit trials and discuss on-farm response of crop to AFI.
• 07/18/11: Field day with researchers, farm advisor, field managers, UC Davis students and researchers. Evaluation of potential yield and potential tradeoffs of AFI treatment vs. EFI.
The main outcome of this project is the evidence for processing tomato growers and other stakeholders that alternate furrow irrigation can reduce the volume of applied water by at least 25% without affecting yields and fruit quality. Thus, these results show that crop water use efficiency can be increased by adoption of new irrigation practices with no apparent risk to crop productivity. In addition, results show that AFI performs similarly to every furrow irrigation, even in lighter soils with low water holding capacity (e.g., Reiff very fine sandy loam) which could affect crop performance.
Irrigation reductions of 25% could help maintain agricultural land in production, especially in drought years when water deliveries are reduced and land may be put in fallow. With the results obtained in this project, it can be hypothesized that for every three hectares planted to tomato under AFI, one additional hectare could be planted. In the future, an irrigation reduction of one acre-feet (?30% of total applied water in a tomato field) across total tomato acreage (~277,000 acres = 123,660 ha) could save about $10 million per year based on a low estimate (?$35 per acre-feet) (CALFED 2000).
Farmer awareness is projected to increase in the coming years because other stakeholders (e.g., farm advisor, plant breeders, NGOs working in sustainability) have collaborated with us at different stages of this project and are aware of the results. The 2011 on-farm trials are an example of what could be possible to achieve under real farm situations. Growers’ interest on strategies to achieve higher water use efficiency is increasing, especially now that climate uncertainty is affecting projections on water availability for the next growing season. We expect to present our results at different growers’ meetings during this year and make the data available through online sources to make it more accessible to growers.
Areas needing additional study
This project shows the existing potential to reduced irrigation water in processing tomatoes under furrow irrigation. Additional research could address new management strategies for increasing water use efficiency in drip irrigated fields. Reducing irrigation volumes under drip would need a different approach than the partial root drying technique because the drip line is usually buried in the middle of the bed; and thus, wet/dry cycles cannot be applied to two different parts of the root system. Nevertheless, understanding of cultivar traits that can be beneficial under different irrigation management (i.e., furrow or drip) can also contribute to further increase crop water use efficiency in both irrigation systems: drip and furrow.