- Author: Michael Cahn
- Contributor: David Chambers
- Contributor: Noe Cabrera
Growers will need to implement best management practices that reduce nitrate leaching losses on the Central Coast to comply with Agricultural Discharge Order 4.0. The use of drip irrigation has allowed many growers to be efficient with both water and nitrogen fertilizer. Fertigating through the drip system allows for spoon feeding nitrogen in amounts matching the pattern of crop N uptake, and to place fertilizer in the root zone. Tools like the soil nitrate quick test and the online irrigation and nutrient management platform, CropManage, can help farm managers accurately determine the right amount of fertilizer to apply to satisfy crop N requirements without jeopardizing production.
Once the right amount of fertilizer to apply has been determined, it is important that irrigators have the tools that they need to accurately inject the correct volume into the drip system. Fertigation trailers usually consist of a nurse tank that can hold a maximum volume of 500 to 1000 gallons of fertilizer and are equipped with a small gas or electric pump used to inject liquid fertilizer into the drip system. Often irrigators rely on markings on the side of the nurse tank to determine the volume of fertilizer that they are injecting. These markings are usually not accurately calibrated nor have fine enough graduations to precisely measure out fertilizer volume. Furthermore, tank markings can be hard to read, especially if the trailer is not level.
A flowmeter could increase the precision of metering fertilizer into a nurse tank or for measuring the volume of fertilizer injected into the drip system. Using a flowmeter for metering fertilizer would also facilitate tracking the volume of fertilizer applied to each crop by either noting the meter readings or by interfacing the flowmeter to a datalogger that can record the application volumes.
We evaluated the accuracy of three models of flowmeters designed for metering liquid fertilizer: 1. Banjo FM100 meter, 2. Dura-meter, and 3. Blue White F-1000 (Fig. 1). Each model relies on a different mechanism to monitor fertilizer volume. The Banjo meter measures flow using a magnetic sensor, while the Dura-meter uses a nutating disk, and the Blue white meter uses a small propeller. The accuracy of the flowmeters was tested using 25 gallons of either water, ammonium nitrate (20% N), or urea-ammonium nitrate (32% N). A testing manifold was set up in the UCCE Monterey greenhouse that pumped a calibrated volume of each fluid through the flowmeters using an electric diaphragm pump. Five or more test runs were made for each meter and fluid. The average volume measured and standard deviation from the mean volume was calculated.
All three models of flowmeters accurately measured water and fertilizer volumes (Table 1). Measurement errors were generally less than ±2% of the true volume. The Dura-meter which uses a nutating disk to measure volume was the most accurate flowmeter of the three models and had an overall average absolute error of -0.2 gallons per 25 gallons measured, and a coefficient of variation of ±0.3%. The Blue White meter, which uses a paddle wheel to measure volume, was least accurate and had an overall absolute error of 1 gallon per 25 gallons measured and a coefficient of variation of ±1.3%. The type of liquid metered affected the accuracy of the Banjo and Blue White meters more than the Dura-meter.
Table 1. Accuracy of flowmeter measurements of water and two types of liquid fertilizer (AN20 and UAN32).
Although the Dura-meter was most accurate of the three flowmeters, it did require an initial calibration before testing began. The other meters could not be manually calibrated. The nutating disk mechanism directly measures volume of a liquid which may explain why the Dura-meter was not affected by the density of the liquid tested. Both the paddle wheel and the magnetic sensor mechanisms used in the Blue-White and Banjo meters indirectly estimate flow rate. Another advantage of the Dura-meter was that it was the cheapest of the three meters when the tests were conducted. Another version of the Dura-meter can be used to turn off an injection pump when a specified volume of fertilizer has been injected. This version is available as part the auto batch system (Dura-ABS™). The Banjo meter is also available in a model (MFM100) the can output an electrical pulse proportional to flow rate so that volume of fertilizer injected can be recorded on a datalogger.
Conclusions
Three commercially available flowmeters were demonstrated to accurately measure fertilizer. Either of these meters could help irrigators more precisely apply the intended volume of fertilizer to a crop as well as verify and maintain records of the fertilizer volumes used to grow each crop. Depending on the practices of the growing operation it may be more efficient to install the meters on either the nurse tank trailer or the main fertilizer tank. If the nurse tank is used for injecting fertilizer at several fields during the day, then installing the meter on the trailer would be logical, but if the nurse tank is only filled for a single field at a time, the flowmeter could be installed on the main fertilizer tank.
- Author: Bradley Hanson
One of the largest weed issues affecting the California processing tomato industry is the parasitic plant, branched broomrape (Phelipanche ramosa; Orobanche ramosa)
- https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=50241
- https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=47701
- https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=43342
Last week, CDPR issued a positive decision on a 24c "Special Local Needs" label request to allow application of rimsulfuron (Matrix SG) via chemigation through subsurface drip irrigation systems. This newly-allowed use pattern should be helpful for suppression of broomrape in tomato.
The CDPR decision was posted here: https://www.cdpr.ca.gov/docs/registration/nod/nodmenu.htm and is in Report 2022-39 for the Week of September 30, 2022. I've also attached it to the bottom of this blog post.
Rimsulfuron is widely used in tomato in California both as PRE and early POST herbicide for control of many weeds. The 24c label simply adds a new application method that is targeted specifically at the broomrapes which are parasites that attached to the root of tomatoes and other host plants. The new use pattern puts the herbicide right in the rootzone of the tomato plant at the time when broomrape seeds are germinating and the seedlings just attaching to the host.
The protocol for this specific use is three applications of rimsulfuron; one at early bloom and two more at 10-15 d intervals thereafter. Each of the three applications should be 1.33 oz product (25% WDG) which equates to the yearly max allowed on the Section 3 label.
In our field trials, chemigated rimsulfuron provided significant reductions (about 4-fold) in broomrape clusters in a highly-infested field; however, no herbicide treatments were 100% effective for this A-listed quarantine pest. This may be of interest and utility to processing tomato growers who have light infestations or fields near infested fields that may be at some risk but should be combined with other sanitation practices.
One important note is that this SLN cannot be used with other rimsulfuron applications. The 4 oz product per year maximum is for all uses; so, if you apply rimsulfuron via chemigation for broomrape management, you cannot also use rimsulfuron for PRE or POST control of other weeds.
CDPR 24c decision rimsulfuron broomrape
- Author: Ben Faber
Chemicals are often injected through irrigation systems, hence the name chemigation. When applied to fertilizers, it is called fertigation. Surprisingly many growers still apply fertilizers by hand, however the predominant use of micro-irrigation systems in avocados readily lends itself to fertigation. This compatibility is due to the frequency of operation and the control the operator has over the system. If the uniformity of the system is high, applying fertilizers through the irrigation system can improve fertilizer distribution, allow for flexibility in fertilizer timing, reduce labor in spreading materials, allow for less fertilizer to be used and can lower costs relative to hand applications of fertilizers.
Chemigation can still cause environmental damage, particularly when the chemicals injected move readily with the irrigation water. Over-irrigation resulting in deep percolation can contaminate groundwater when a mobile chemical is injected. Contamination can occur if: 1) the irrigation water pumping plant shuts down while the injection equipment continues to operate, causing contamination of the water source or unnecessary amounts of fertilizer to be injected into the irrigation system, or 2) the injection equipment stops while the irrigation system continues to operate, causing the irrigation water to flow into the chemical supply tank and overflow onto the ground. To prevent these problems, backflow devices and check valves can be installed. Local regulations should be followed in selecting these devices.
Many different materials may be injected, including organic fertilizers, dry fertilizers and liquids. The major fertilizer injected is nitrogen, but potassium and micronutrients, as well as water treatments, such as urea-sulfuric acid are also injected. The important point to remember is that the materials must be soluble. Fertilizers delivered as a solution can be injected directly into the system, while those in a dry form must be mixed with water to form a solution.
Fertilizer material differs widely in water solubility, with solubility depending on the physical properties of the fertilizer as well as on irrigation water quality. Agricultural grade fertilizers and amendments are often coated to inhibit moisture absorption and to assist in material flow through machinery. These coatings and other foreign materials can cause clogging problems in the mixing tank, as well as the irrigation system. The foreign material exists in the tank as sediment or as a scum on the surface. To prevent problems, stock tanks should be agitated until the material is dissolved. To further prevent problems, the solution should be filtered between the stock tank and the injection point, and the injection point should be upstream of the irrigation system filters.
Irrigators wishing to inject chemicals have a variety of injection equipment from which to choose, including differential pressure or batch tanks, venturi devices and positive displacement pumps. The most expensive are displacement pumps that are powered by electricity or water. They put out precise amounts of material. Venturi and batch tanks are much less expensive and are relatively simple to operate. Their major drawback is that they require a pressure loss to force the material into the irrigation system. A 10 - 30 psi pressure differential is often required and in some places this differential is not possible. In that case a fractional-horsepower pump can be used to provide the pressure differential. Neither of these devices is as precise as the displacement pumps. However, fertigation does not require a fixed concentration of solution, only a known amount of applied material. And these pressure differential applicators do the job very well.