- Author: Jeannette E. Warnert
UC Agriculture and Natural Resources will receive $865,000 to help farmers in the Colorado River basin and the Salinas Valley integrate digital tools and artificial intelligence into their growing systems. The funds are part of a $10 million Sustainable Agricultural Systems grant from the USDA's National Institute of Food and Agriculture to improve the sustainability of the nation's food supply.
The intensive agricultural industry of the Colorado River basin – which includes the Palo Verde, Coachella and Imperial valleys in California; the Yuma Valley and other areas, such as Wellton-Mohawk Valley in Arizona – produces vegetables in the winter that are shipped across the country. Salinas Valley farms produce vegetables in the summer for markets throughout the nation.
“Vegetables are an essential part of a healthful diet. With this grant, NIFA is recognizing the role that California, Arizona and Colorado play in growing nutritious food for Americans,” said Khaled Bali, UC Cooperative Extension irrigation specialist. “The sustainability of these production systems into the future, particularly in light of challenges like climate change, increased drought and limited access to surface and groundwater, will require sophisticated technology.”
U.S. agriculture industry professionals are world leaders in the use of technology, including automation, drip irrigation, sensors and drones. “What's new is how you can now integrate technology into making decisions,” said Bali, who is leading the digital agriculture education and outreach aspect of the grant.
Bali said new farming tools work like smart thermostats in homes, which have sensors throughout the house and learn family patterns to make conditions perfectly comfortable throughout the day and night.
On the farm, instead of applying the same amount of water and fertilizer over hundreds of acres, sensors, valves and digital management allow small sectors to get treatments based on soil type, size of plants, pest pressure, salinity and disease management.
“This project will lay the foundation for a long-term shift to highly automated mechanized farm management systems – with full implementation likely decades in the future,” Bali said. “The precise application of inputs in agriculture will save water, reduce the percolation of fertilizer below plant roots, reduce the need for manual labor in the industry, increase yields and decrease expenditures, enhancing the industry's economic viability.”
Field demonstrations, training sessions, videos and handouts will bridge the gap between ongoing farming practices and academic and industry state-of-the-art digital technology. These activities are expected to increase the productivity and competitiveness of major crop growers.
The new project will expand the usage of a smartphone and website app called CropManage, a system developed in 2011 by Michael Cahn, UC Cooperative Extension advisor in Monterey, Santa Cruz and San Benito counties. CropManage allows farmers in the Salinas Valley to input information about their crops and soil, and then automatically receive recommendations about irrigation and fertilization needs that take into account weather conditions reported by the California Irrigation Management Information System (CIMIS), a network of automated weather stations managed by the California Department of Water Resources.
Currently, CropManage makes about 2,000 recommendations to Salinas Valley farmers each month during the growing season. The new funding will allow for the expansion of CropManage to help farmers manage salinity.
“To minimize salt toxicity to the crop, farmers may need to apply water to leach salinity below the root zone. But we don't want to leach nitrates,” Cahn said. “We want to decouple these processes and do the leaching when there are lower nitrogen levels in the system. Determining timing and water amount is something we will build into CropManage.”
The grant will also provide funding for new training and outreach that will enable more farmers to use the CropManage app.
The overarching $10 million grant awarded to UC Riverside is led by professor Elia Scudiero, an expert in soil, plant and water relationships. He and a team of UC Riverside scientists will develop artificial intelligence data needed for smart farming systems with new statistical and algebraic models that find repeated and generalizable patterns.
Another key piece of the effort will be supplying the agriculture industry with the next generation of growers, managers and scientists. Funds from the NIFA grant will establish a Digital Agriculture Fellowship program to recruit more than 50 data, environmental or agricultural science students over the next five years to develop and learn the technology. Internships with key commercial partners are also a feature of the program.
- Author: Michael D Cahn
- Shared by: Mark Bolda
Growers follow a number of strategies for managing nitrogen during the early season. Some apply almost half of the seasonal nitrogen required by strawberry as preplant fertilizer before transplanting while others skip preplant fertilizer or use a reduced rate (Fig. 1). Others use controlled release fertilizers while some growers opt for conventional fertilizer products. These decisions are based on grower experience, cultivar, soil type, and anticipated weather conditions. The following are a few concepts on early season N management for strawberry to consider as we enter a new season.
On the central coast the N needs of strawberry are quite modest for the first few months after transplanting. This is because growth rates are low until March when average temperature and day length begin to increase. For most varieties, strawberries will take up 20 to 30 lbs of N/acre during this period. However, new transplants have a very limited root system and need nitrogen to jump start root and shoot growth. A rule of thumb is to have 10 to 15 ppm mineral N (nitrate + ammonium) in the upper foot during the early season, which is equivalent to 35 to 60 lbs N/acre, depending on the soil texture. Usually most of the soil mineral N is in the nitrate form. Checking the soil at least monthly during the early season can help determine if supplemental fertilizer is needed, which can be applied through the drip system.
The decision to use preplant fertilizer may depend on several factors such as anticipated rainfall, soil texture, previous crop, and initial soil nitrate concentration. When following vegetables, the concentration of soil nitrate can be high (20 to 30 ppm NO3-N) and can supply a large portion of the early crop N needs if not leached out by irrigation and rainfall. In contrast, the level of soil nitrate maybe low when planting after a strawberry crop (< 5 ppm NO3-N), and the transplants may need some fertilizer nitrogen to simulate root and shoot growth.
Soil type and anticipated rainfall should also be considered in deciding whether to use preplant fertilizer. Even with plastic mulch, a strawberry crop planted on a sandy soil could lose much of the soil nitrate during heavy rain events. On the other hand, preplant fertilizer may increase salinity near the root system, especially if it is banded near the plant row and rainfall is light during the winter (Fig. 2). Controlled released fertilizers are more expensive than conventional fertilizers but can be a good option if soil nitrate is low at transplanting and the release rate of the fertilizer matches the N uptake rate of the crop.
Also consider the nitrogen contribution of other sources of N to the crop. High nitrate irrigation water can supply much of the N needs of the crop in early season, especially during a dry year when the crop is frequently irrigated. Recycled water can also contain a significant amount of nitrogen as both nitrate-N and ammonium-N. More information on how to credit the N in irrigation water can be found in the Salinas Valley Blog. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7744 Added organic amendments and soil organic matter can also play a role in supplying N, depending on soil temperatures during the winter.
Because there can be several factors that affect soil nitrate levels during the early season, we recommend evaluating the soil nitrate concentration at least once per month and making adjustments by fertigating as needed. This approach provides flexibility so that the reliance on preplant fertilizer can be less without risking crop yield loss. The soil nitrate quick test is an accurate and easy tool to use that can allow growers to monitor soil nitrate. More information on using the soil nitrate test can be found on the Salinas Agriculture Blog. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4406
In summary, multiple approaches to N management can work for strawberry because the N demand is low during the early season, and the combination of residual soil nitrate, N mineralization from soil and amendments, and nitrate in the irrigation water can often supply much of the N that the crop needs to become established.
This article first appeared in the Strawberries and Caneberries blog.
- Author: Aliasghar Montazar
- Author: Michael D Cahn
- Author: Alexander Putman
Spinach is a fast-maturing, cool-season vegetable crop. In California, most conventional and organic spinach fields are irrigated by sprinkler irrigation. However, sprinkler irrigation could contribute to the speed and severity of downy mildew epidemics, as the most important disease in spinach, within a field when other conditions such as temperature are favorable.
Although fungicides are available for the control of downy mildew in conventional production systems, products with similar efficacy are not available for organic spinach. Adapting drip irrigation for high-density spinach plantings may be a possible solution to reduce yield losses from downy mildew and enhance resource-use efficiency in organic spinach production.
Currently, drip irrigation is not used for producing spinach in California, and there is a lack of information on the viability of this technology and optimal practices for irrigating spinach with drips. We initiated a study funded by the California Leafy Greens Research Board to evaluate the viability of drip irrigation for organic spinach production in California. The project was particularly aimed at understanding the system design to successfully produce spinach, and to conduct a preliminary assessment on the impact of drip irrigation on the management of spinach downy mildew.
So far, the experiment has been conducted over two crop seasons at the University of California Desert Research and Extension Center located in the low desert of California. Various combinations of dripline spacings and installation depths were assessed and compared with sprinkler irrigation as control treatment. Comprehensive data collection was carried out to fully understand the differences between the irrigation treatments.
Statistical analysis indicated very strong evidence for an overall effect of the irrigation system on spinach fresh yields, while the number of drip lines in bed had a significant impact on the shoot biomass yield. The developed canopy crop curves revealed that the leaf density of drip irrigation treatments was slightly behind (1–4 days, depending on the irrigation treatment and crop season) that of the sprinkler irrigation treatment in time.
The results also demonstrated an overall effect of irrigation treatment on downy mildew, in which downy mildew incidence was lower (approximately 5 times lower) in plots irrigated by drip following emergence when compared to the sprinkler. The likely mechanism causing this effect was a reduction under drip irrigation of leaf wetness, which is critical for infection and sporulation by the downy mildew pathogen.
The probe output of the leaf wetness sensors for a period of 12-day showed that sprinkler-irrigated crop canopies remained wet 24.3% times longer than the crop canopy irrigated by drip system. The preliminary findings: drip irrigation has the potential to be used to produce organic spinach, conserve water, enhance the efficiency of water use, and manage downy mildew, but further work is required to optimize system design, irrigation and nitrogen management practices, as well as strategies to maintain productivity and economic viability of utilizing drip irrigation for spinach. Assessing drip irrigation for the entire crop season, including germination, could be another research interest since spinach is a short-season crop and combining the sprinkler for crop germination and drip for such a short period might cause some practical issues. We will continue investigating these issues through this ongoing project in the next two years.
For more information about the results of this project so far, you may view the recently published research article in MDPI, Research Advances in Adopting Drip Irrigation for California Organic Spinach: Preliminary Findings
This article was also published in the August-September 2019 issue of Organic Farmer magazine.
- Author: Richard Smith
- Author: Michael D Cahn
During the past two years acreage of season-long drip in lettuce has increased rapidly in the Salinas and adjacent valleys. Using drip for the entire crop cycle allows growers to germinate seeded crops with buried tape (Photo 1), and eliminates labor needed for installing and removing sprinklers. The rapid expansion of this irrigation practice is due to 1) reliable thin-walled single-use drip tape which assures high application uniformity for less cost than thick walled tape; 2) Better injection equipment that can uniformly place drip tape 2-3 inches below the soil surface allowing cultivation without damaging the tape (Photo 2), and 3) development of tape removal equipment that saves labor and efficiently bundles the tape for recycling (Photo 3). The use of drip for germinating lettuce often can improve the uniformity of stands and save water by eliminating common problems associated with using sprinklers such as emergence patterns caused by wind and crusting of the soil surface. Drip germination works best on light to medium textured soil types such as sandy loams, gravelly sandy loams, loams, and silt loams (e.g. along the river and on the eastside of the Salinas Valley).
Unlike sprinklers which infiltrate water at the soil surface, water applied by buried drip wicks upward keeping herbicides and fertilizers sprayed on the bed tops close to the soil surface. The upward movement of moisture from buried drip tape and subsequent evaporation of water from the bed top yields a net accumulation of salts (including nitrate) near the soil surface (Photo 4). This upward movement of applied materials benefits the preemergent herbicide, Kerb, which is often pushed too deep in the soil by sprinkler applied water at germination. The amount of wetting of the soil surface provided by drip germination is sufficient to set Kerb and keep it in the zone where weed seeds germinate which improves its effectiveness (for more information on this subject go to:https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30847).
Table 1. Total mineral nitrogen (ammonium-N + nitrate-N) in the top 6 inches of soil. May 22 – prior to thinning; three subsequent sampling dates following application of 28-0-0-5 fertilizer by an autothinner
Since growers must report the total nitrogen applied to vegetables to the Regional Water Quality Control Board (RWQCB), the nitrogen remaining on the soil surface creates a problem. For instance, a typical application of 20 gallons of 14-0-0-5 contains 29 lbs of nitrogen/acre. This nitrogen is reported to the RWQCB but does not necessarily provide nitrogen for crop growth. More nitrogen would need to be added to keep up with the N demand of the crop. It would be advantageous to use materials in the autothinners that contain no or low amounts of nitrogen.
High levels of nitrogen on the surface also creates a challenge for collecting an accurate soil sample for determining plant-available nitrogen using the nitrate quick test or laboratory analysis. Photo 5 shows the results of three measurements: 1) high levels of nitrate-nitrogen found in the top 2 inches of soil (test strip on the left); 2) moderate amount of nitrate-nitrogen found in the 2 to12 inch layer (top 2 inches scraped off, test strip in the middle); and 3) high levels of nitrate-nitrogen found in the top 12 inches of soil (top 2-inches of soil is not scraped away, test strip on the right). We have always recommended scraping the dry surface soil away before collecting a soil core (see https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4406), however, the extremely high amounts of nitrate-nitrogen in the top 2 inches of drip irrigated fields that are autothinned with a nitrogen fertilizer makes this practices particularly critical in order to not over estimate the amount of plant-available nitrogen in the soil when making critical fertilizer application decisions.
Summary:
- Season-long use of buried drip keeps herbicides and soil applied fertilizers (from anti-crustants and automated thinners) close to the surface due to the water wicking upward.
- Surface applied fertilizers remain in the top 2 inches of soil and are not plant available for much of the season. Ideally, a zero or low nitrogen containing thinning chemical would avoid this issue.
- It is important to scrape away the top two inches of soil when collecting samples for nitrate testing in order to not over estimate the amount of plant-available nitrogen when making fertilizer application decisions.
This article was originally published in Salinas Valley Agriculture.
- Author: Michael D. Cahn
- Author: David Chambers
A tensiometer is a very useful tool for monitoring soil moisture status of vegetable and berry crops. Compared to other sensors that often require equipment such as dataloggers or a computer to collect readings, tensiometers can be easily read by irrigators in the field. Also, tensiometer readings are not affected by variations in soil texture, temperature, and salinity and they can operate without electricity (no batteries needed).
What is tension? Tensiometers measure soil moisture in units of negative pressure also known as tension. Tension is a measure of the force that plant roots need to exert to pull water from the soil pores. Large pores hold water with less force than small pores. As plants extract moisture from the soil, water is first taken up from the largest pores. As the soil dries roots need to exert more force to pull water from the smaller pores. Hence, high tension values mean that the soil is becoming dry.
How do tensiometers work? Tensiometers are filled with water (preferably distilled) that has been degassed by boiling. A key component of the tensiometer is a porous ceramic cup which allows water in the shaft of the tensiometer to freely pass into the soil without air bleeding though the small pores in the cup (Fig. 1). If the soil is not saturated, water will move from inside the cup into the unfilled soil pores. Because air cannot replace the space vacated by the exiting water, a vacuum develops in the shaft of the tensiometer that can be measured with an accurate gauge. Water will stop migrating from inside the tensiometer cup into the soil when the internal vacuum pressure of the tensiometer equals the soil tension, or the force needed to pull water from the soil pores. The vacuum gauge measures tension in units of kPa or cbars, which are equivalent (1 kPa = 1 cbar).
Interpretation of tension readings Because the tension value provides a sense of how much energy a plant would need to exert to suck water from the soil, tensiometer readings can be easily related to water stress in crops. At high tension values a plant experiences more water stress and growth slows. In addition, a tension reading has a similar meaning in terms of water stress whether the soil has a sandy, clay or loam texture.
Reliability of tensiometers The one Achilles' heal or weakness of the tensiometer is that if any air leaks into the instrument it will not retain a vacuum and the readings will be unreliable. There are several brands of commercial tensiometers available. Some are relatively inexpensive and simple to use, and others are more complex and can be interfaced with dataloggers to provide continuous readings throughout the day. Based on our experience, some of the most popular commercially available tensiometers often leak air and loses vacuum pressure, and in many cases the gauges do not provide accurate readings or are not durable. The loss of vacuum pressure means that the tensiometers need to be frequently refilled with degassed water. Also, irrigators may mistake a low reading to indicate that a crop has adequate moisture when in reality the soil may be dry.
A dependable tensiometer design We designed and tested a version of a tensiometer in 2018 that was simple to build and provided accurate readings for a material cost of less than $55 . The design improved the ability of the instrument to retain a vacuum at high tensions. Under moderately moist soil conditions the tensiometer usually required refilling with degassed water less than once per month. Even when the soil dried to tensions above the maximum range of the tensiometer (> 80 kPa), these tensiometers continued to hold a vacuum for about two weeks until all of the water in the shaft was depleted.
The following paragraphs describe the materials needed (Fig. 2) and procedures to build a tensiometer. The vendors of the materials are examples of ones that we use, but you may identify different or cheaper sources for these components. By carefully following these instructions, one should be able to build a dependable tensiometer that provides accurate tension readings.
Materials needed:
Ceramic cups
Vender: SoilMoisture Equipment Corporation, Santa Barbara CA (805-964-3525) Part Number 0655X01-B01M3, Dimensions: 0.875 inch OD x 2.75 inch length. Cost: $30.80 ea.
Epoxy (ceramic/plastic)
Vender: SoilMoisture Equipment Corporation, Santa Barbara CA (805-964-3525)
Part Number 0980V004, Description: 4 oz: epoxy and 4 oz hardener. Cost: $106 ea. Note that the epoxy/hardener is a sufficient volume to make several hundred tensiometers.
Vacuum gauge
Vender: Zoro.com/Grainger.com Part Number 4FMK3, Description: ¼ inch MNPT 2 inch diameter test vacuum gauge. Cost: $18.09 ea.
#1 size rubber stopper
Vender: Grainger.com Part Number 8DWU6, model RST1-S, Description: 24 mm neck, bottom diam. = 14 mm. Top diam. = 20 mm. Cost: $18.08 / 52 pieces
Schedule 40 PVC pipe (½ inch diameter) Vender: irrigation supply or hardware store
PVC “T”
Vender: irrigation supply or hardware store, Manufacturer: Spears Inc. Part number 402-072, Description: ½ inch slip x ¼ inch threaded reducing "T."
PVC glue (gray) and purple primer
Vender: irrigation supply or hardware store
Gas pipe thread sealant (white or blue paste type)
Vender: irrigation supply or hardware store
Painters masking tape
Vender: hardware store
Petroleum Jelly (Vasoline)
Vender: pharmacy
Tools needed:
- PVC saw or PVC cutting tool
- Aluminum Oxide grinding stone, Manufacturer: Forney Part Number: A11 60028 Description: 7/8 in [23 mm] diam. x 2 inch [50.8mm] length
- Power hand-held drill
- Miter box
- Pocket knife
Procedures
1. Cut PVC pipe sections in the following lengths
1 foot depth tensiometer: top shaft = 4 inches, bottom shaft = 17 inches
2 foot depth tensiometer: top shaft = 4inches, bottom shaft = 30 inches
It is advisable to cut the bottom shaft about 1-inch longer than indicated above and then carefully cut the lower end of the shaft using the miter box or electric miter saw to assure that it is cut at a 90-degree angle. The ceramic cup will fit crooked on the end of the shaft if the cut deviates from 90 degrees.
- First glue the top shaft and then the bottom shaft to the ½ PVC “T” using the PVC glue. Make sure that you do not glue the end of the bottom shaft that was trimmed to 90 degrees. In a well-ventilated location, apply PVC primer to both the end of the shaft and the inside of the “slip” end of the “T”. Then apply gray PVC glue to both sides, and push the parts together, and hold in place for about 30 seconds to 1 minute. Tip: slightly twist the parts by about 30 degrees immediately after gluing to assure that the parts are secure. Also cover the non-glued areas with painter's tape to prevent the outside from becoming covered with glue.
- Slightly bevel the inside of the lower end of the bottom shaft using the handheld drill and grinding stone (Fig. 3). Alternatively, one can use a knife to bevel the end. Whether using the drill or the knife to bevel the inside of the pipe, stop periodically and test fit the ceramic cup. This way you will not remove too much material, and will quickly get a feel for the appropriate amount to remove.
- Use epoxy to glue the ceramic cup to the lower end of the bottom shaft. Protect the ceramic cup during the gluing process by covering the outside with painter's tape (Fig. 4). Check that the ceramic cup fits snuggly into the PVC tube and is aligned straight. If using the epoxy from SoilMoisture equipment epoxy, mix up 1-part epoxy with 1-part hardener. Mix thoroughly. Only a small amount of epoxy is needed to coat the throat of the ceramic cup and the inside of the PVC tube, so it may be best to glue several tensiometers at the same time so that the epoxy is not wasted. One can usually glue no more than 20 to 40 cups at a time becaue the epoxy begins to cure after an hour. Approximately 20 ml of epoxy is needed for 20 tensiometers. The cure time is temperature dependent. Full cure is 8 hours at 77 °F. It is best to allow more time for curing. After gluing, painter's tape can be used to secure the cup to the shaft. Take care when securing the two with the tape to assure that the cup is aligned with the PVC shaft. Let the glue set for at least 24 hours with the tensiometer supported with the cup-end up in a vertical position. Tip: best if parts are glued at temperatures above 65 °F. More hardener may be needed at lower temperatures. Also, it is advisable to first test a small batch of epoxy to assure that the proportion of hardener to epoxy is enough for epoxy to set up hard.
- Coat the ¼ inch male threads of the gauge with pipe thread sealant and hand screw on the vacuum gauge. Tip: do not over tighten or the PVC “T” will crack!
- Fill the tensiometer fully with degassed distilled water. The water can be degassed by boiling it and allowing it to cool.
- Coat the lower end of the rubber stopper with a thin film of petroleum jelly and insert into the top end ofthetensiometer with a light twist to firmly seat the stopper (A loose stopper is the main cause for vacuum leaks).
Testing the tensiometer for air (vacuum) leaks:
After filling the tensiometer with water and sealing it with a rubber stopper, wrap a dry paper towel on the end of the ceramic cup and hold it tightly (Fig. 6). If the tensiometer is filled with degassed water, the tension should quickly increase to about 20 to 30 kPa as the towel absorbs water from the cup. If the gauge does not increase above 0, air is likely leaking into the tensiometer. Check the glue joints and assure that the stopper is tightly in place.
If the tension quickly increases to more than 20 kPa, then leave the tensiometer out in the sun to assure that the tension rises to above 70 to 80 kPa. This may take some time, minutes to hours, depending on the ambient temperature. If the tension does not increase to a high value, then check glue joints and the stopper. Also check that the gauge is securely threaded into the PVC “T.”
Installing tensiometers in the field:
Proper installation of a tensiometer in the field will achieve close contact between the ceramic cup and surrounding soil. Using a soil probe with a ½ inch diameter shaft, make a pilot hole to a depth a few inches shallower that the depth of installation (Fig. 7). Make a soil water slurry by thoroughly mixing soil with the water to a pancake batter-like consistency. Add some slurry into the hole and push the tensiometer to the desired depth (Fig. 8). The soil slurry assures that water can freely move between the ceramic cup and the surrounding soil and fills the voids between the hole and tensiometer shaft. Formation of air gaps between the ceramic cup and the soil will lessen the accuracy of tensiometer readings. After two days of equilibration, the tensiometer reading should accurately reflect the tension of the soil.