- Author: Michael D Cahn
- Author: Richard Smith
Understanding the nutrient value of nitrate in irrigation water often leads to confusion. Laboratories commonly report nitrate concentration of water samples in parts per million of nitrate (PPM NO3). However, as shown in Table 1, the reported nitrate value must be multiplied by 0.225 to express it in equivalents of nitrogen (PPM NO3-N). This conversion is required because the nitrate molecule has three oxygen atoms for every nitrogen atom, meaning that the nitrate molecule is 22.5% N by weight.
Several more calculations must be made to determine the pounds of N contained in a volume of water. Factors for converting PPM NO3 or PPM NO3-N to lbs of N per acre-foot (or acre-inch) are presented in Table 2. For example, multiplying a water test of 45 PPM NO3 by 0.62 would determine that an acre-foot of water contained about 28 lbs of N. If the same water test was reported as PPM Nitrate-N it would be equivalent to about 10 PPM N and would be multiplied by 2.72 to convert to lbs of N per acre-foot of water.
How much of the nitrogen in irrigation water should be credited as fertilizer value to a crop is debatable, especially for shallow rooted vegetables such as leafy greens. It is unclear if leafy green crops can make use of nitrate in irrigation water when concentrations are less than 20 ppm NO3-N. The soil nitrate level that optimizes lettuce growth is considered to be in the range of 15 to 25 ppm NO3-N. But this concentration is expressed in terms of weight of nitrogen per weight of soil (mg of N/kg of soil). Since soil is about 20% to 25% water by weight, the nitrate concentration in the soil water of most commercial lettuce fields would range between 60 to 120 ppm NO3-N. Field monitoring of nitrate concentration in soil water using suction lysimeter tubes installed in the root zone of lettuce has confirmed that most commercial fields are in the range of 50 to 150 ppm NO3-N, which is substantially higher than the concentration of nitrate found in most irrigation water.
Applying a leaching fraction to minimize the build-up of salt in the soil would also affect how to credit the fertilizer value of nitrate in irrigation water. Much of the nitrogen contained in the extra water applied to leach salts would presumably percolate beyond the root zone and not be available to the crop. In the Salinas Valley, growers report that ground water with a high nitrate concentration often has high levels of sodium and chloride salts. These water sources are often from shallow wells, where both salt and nitrate have leached over time into the aquifer. In these circumstances where elevated levels of salts are associated with high nitrate concentrations, a greater leaching fraction may be required and therefore less of the nitrate can be credited to the crop.
Irrigation efficiency can also factor into estimating the fertilizer value of nitrate in irrigation water. Fields with irrigation systems that apply water with poor uniformity would have areas where water drains below the root zone and other areas where less than the desired volume of water is applied.
Considering the above concerns, perhaps the fairest way to value nitrate in irrigation water is to take credit for the water that the crop uses for evapotranspiration (ET). This would be equivalent to the volume of water that enters the plant roots or evaporates from the soil surface leaving salts including nitrate behind. Lettuce transpires 5 to 8 inches of water between germination and maturity in the lower Salinas Valley during the summer. Factoring in irrigation system uniformity also makes sense. If the irrigation system uniformity is 80%, one may assume that 20% of the N in the applied water would likely percolate below the root zone and would not be available to the crop. For a crop that has a seasonal ET of 7 inches and an irrigation uniformity of 80%, the following values (Table 3) would approximate the N contribution of irrigation water for the indicated range of nitrate concentrations. Most wells in the Salinas Valley with elevated concentrations of nitrate are less 20 PPM NO3-N; therefore, we would expect that for most wells with this range of nitrate concentration, the irrigation water would contribute 20 to 30 lbs of N/Acre to a lettuce crop.
Conclusions
Growers have long been advised to reduce their standard nitrogen fertilizer rate if their irrigation water is high in nitrates. Extension publications commonly suggest that one can credit the nitrogen in irrigation water by multiplying the concentration of nitrate by the volume of water applied to a crop. As can be seen from the above estimates, water containing less than 45 ppm NO3 generally does not contribute a significant amount of nitrogen to crop growth (< 15 lbs N/acre). However, if well waters contain more than that amount, irrigation water may contribute greater amounts of nitrogen for crop production. In the future, we hope to conduct field trials to verify these estimates of the fertilizer value of nitrate in irrigation water.
Irrigation water is only one of several possible sources of nitrogen for a crop. The soil organic matter, added organic amendments, and previous crop residues continuingly mineralize releasing nitrogen. Fertilizer N is also periodically applied through sidedress and fertigation applications or as a slow release product. The good news is that you can account for the N contribution from the nitrate in the applied irrigation water as well as these other sources by using the quick nitrate soil test. However, keep in mind that this test only shows what has happened, and will not estimate the contribution of N from these sources, including irrigation water, to predict future crop N needs.
Table 1. Conversion factors between NO3 and NO3-N
Conversion between nitrate (NO3) and nitrate-nitrogen (NO3-N):
|
To convert |
To |
Multiply by |
|
Nitrate (NO3) |
Nitrate-nitrogen (NO3-N) |
0.225 |
|
Nitrate-nitrogen (NO3-N) |
Nitrate (NO3) |
4.43 |
Table 2. Factors for converting between nitrate concentration in irrigation water and pounds of N per volume of water.
Nitrogen content of irrigation water*
|
Water content of |
Multiply by |
To determine |
|
PPM NO3 |
0.052 |
Pounds N/acre inch |
|
PPM NO3 |
0.62 |
Pounds N/acre foot |
|
PPM NO3-N |
0.23 |
Pounds N/acre inch |
|
PPM NO3-N |
2.72 |
Pounds N/acre foot |
* water analyses from most labs report NO3 in units of ppm, but it is very important to pay attention to which units the results are reported.
Table 3. Estimated fertilizer N value of nitrate in irrigation water for lettuce production.
|
Nitrate (NO3) concentration in irrigation water |
Nitrate (NO3-N) concentration in irrigation water |
lbs nitrogen/acre in seven inches of irrigation water taken up by lettuce* |
|
45 |
10 |
13 |
|
89 |
20 |
25 |
|
177 |
40 |
51 |
|
266 |
60 |
76 |
* multiplied by 0.8 to account for the irrigation system efficiency
- Author: Michael D Cahn
CropManage Workshop
Monterey County Agricultural Center Conference Room
1432 Abbott St, Salinas CA 93901
Wednesday, March 13th / Tuesday, April 2nd 2013
(9 am – 11 am)
We will offer two hands-on workshops to learn in depth about the features of CropManage, a new Web-tool that provides decision support on irrigation and N management of lettuce. Learn how to use CropManage for improving the efficiency of your farming operations or for adding value to your consulting services. Wi-Fi internet access is available at our conference room so you are welcomed to bring a laptop or tablet computer so that you can follow along as we tour through the features of the software. There should be sufficient time to answer questions as we cover the following topics:
- Purpose and main features of software
- Getting started with CropManage (login, setting up new ranches, adding new plantings, fertilizers).
- Using CropManage for decision support and record keeping (soil nitrate quick test, recommendations on N fertilizer and irrigation schedules, maintaining fertilizer and irrigation records).
- Additional features (advanced settings, exporting data, integrating flow meter data).
- Discussion of new features or changes needed.
To keep the group size manageable so that we can provide individual help, we would like to limit each workshop to 20 participants. Please RSVP in advance by sending an email to larriaga@ucdavis.edu with the subject heading “CropManage workshop” and let us know which workshop (March 13 or April 2) you will be attending and the number of participants in your group. We will email you a confirmation
Hope to see you soon,
Michael Cahn
- Author: Michael D Cahn
Dear CropManage users,
UC Cooperative Extension, Monterey County will host an annual Irrigation and Nutrient Meeting in Salinas on Tuesday, February 26, between 7:45 am and 1:45 pm. The meeting will be held at the Agricultural Center at 1432 Abbott St, Salinas CA.
This meeting will be an opportunity to learn more about CropManage as well as research on irrigation and nutrient management of vegetables (see agenda below). We will serve a pizza lunch after the morning session and host a mini-workshop highlighting CropManage between 12:45 and 1:45 pm.
We hope to see you there.
Michael Cahn and Richard Smith
University of California Cooperative Extension, Monterey County
2013 Irrigation and Nutrient Management Meeting
Agricultural Center 1432 Abbott Street, Salinas, CA
Tuesday, February 26
7:45 a.m. to 1:45 p.m.
7:45 Registration and Refreshments
8:00 Salt water intrusion update Tamara Voss, Groundwater Hydrologist, Monterey County Water Resources Agency
8:30 Evaluating efficiency of irrigation systems Tom Lockhart, Staff Research Associate, UC Cooperative Extension, Monterey County
9:00 Introduction to CropManage: an online irrigation and nutrient management tool Mike Cahn, Irrigation and Water Resources Farm Advisor, Monterey County
9:30 ET-based irrigation scheduling of cool season vegetables Lee Johnson, Senior Research Scientist, CSUMB/NASA
10:00 Break
10:30 Strategies to remove nitrate and phosphate from tile and surface waters Tim Hartz, Vegetable Crops Specialist, UC Davis
11:00 Fertilizer technology evaluations and nitrogen uptake by vegetables Richard Smith, Vegetable Crops Farm Advisor, Monterey County
11:30 Soil and plant nutrition of potassium for vegetables Stuart Pettygrove, Extension Soils Specialist, UC Davis
12:00 Conclusion and Pizza Lunch
Afternoon Session:
12:45 Mini-workshop on CropManage and the quick nitrate soil test for improving nitrogen and water management of vegetables
Mike Cahn, Barry Farrara, and Richard Smith
1:45 Conclusion
* Sponsors: University of California Cooperative Extension; Resource Conservation District (RCD);
* Certified Crop Advisor Credits have been requested
* For more information call Richard Smith 759-7357 or Michael Cahn 759-7377
- Author: Michael D Cahn
Why online software? To help growers quickly make decisions on water and fertilizer management we developed CropManage to be fast, convenient, and easy to use. Our vision is that CropManage should be accessible from anywhere you work at anytime. You can use it in your truck from a smart phone, in the office from your desk top computer, or from home with your laptop or tablet computer. To achieve this flexibility we designed CropManage as an online application. Because the software is hosted on the internet you do not need to sync devices to update records, and multiple users can view and interact with the data. You are also free from the hassles of periodically updating the software on your computer.
Why use a database? CropManage can only provide accurate decision support on water and fertilizer management using specific information about your fields. This data includes properties of the soil, planting information, and characteristics of the irrigation system. To keep CropManage simple to use, data needed for future calculations are stored in a database. When you want an irrigation or fertilizer recommendation for any of your fields additional inputs of data are minimal because most of the required information is already loaded in the software. Because CropManage retains your data, you have access to your soil test, fertilizer, and irrigation records at anytime whether you are in the field or at the office. You can also export all of your data to your computer that can be viewed with a spreadsheet program such as Excel.
How do we keep your data private? Perhaps the biggest concern of an online tool is the security of the data. The University of California has a long-standing practice of keeping grower information confidential to the fullest extent possible under UC policy and California statute. We take this commitment seriously because we want to assure continued cooperation between growers and UC researchers.
We designed CropManage to maintain the privacy of all grower data. User access to ranch data is determined by a “virtual” ranch manager, who designates which users can view and edit data. This feature allows the grower to determine who can and cannot view and edit data. The “virtual” ranch manager can change user access and privileges at any time.
Another privacy concern is that your data will be available to other entities. Many commercial websites do collect data about their users which they may use for internal purposes or sell to outside entities. To the fullest extent allowable under UC policy and California statute your information will not be sold, exchanged, transferred, or given to any non-UC entity for any reason whatsoever, individually or in aggregate. However, it is possible that we may have to release your information if required by law.
As with all UC research projects, we will not analyze your data unless granted permission by the grower.
How do we protect your personal information? A minimal amount of personal information is needed to set up a login for access to CropManage (email address and name). Nevertheless, we implement a variety of security measures to maintain the safety of your personal information when you enter, submit, or access your personal information.
We use a secure server. All supplied sensitive information is transmitted via Secure Socket Layer (SSL) technology and then encrypted into our database to be only accessed by you, or UC personnel authorized with special access rights to our systems for development purposes.
All data is regularly backed up onto other servers so that any hardware failures will not cause a loss of information.
After deleting your account, your information will be removed completely, and unavailable to any entity including UC ANR.
Do we use cookies? We use cookies to help remember and process the data for your login information. No cookies are used to collect information related to your farming practices.
Can a user remain completely anonymous? Some users of this software may prefer to remain completely anonymous. The data cannot be traced back to a specific user or farm if names are changed and no spatial data are entered. CropManage uses longitude and latitude coordinates when Spatial CIMIS is selected for the source of evapotranspiration data.
In order to ensure your full privacy, these 3 steps can be taken:
- Use an anonymous email address when registering for this system.
- Do not enter your farm coordinates into the system. Choose the appropriate CIMIS stations manually.
- Do not enter the name of your farm or fields.
Summary
We designed CropManage to be simple and convenient to use by taking advantage of cloud computing. All precautions are and will be taken to assure that private data remains private and protected from outside entities. UC will not redistribute your data to outside entities to the fullest extent allowable under UC policy and California statute. At any point, you can export your data to your own computer, and you retain the option to completely remove your data from the CropManage database by deleting your account. Finally, you can use CropManage anonymously by not providing data that would identify the users and farming operation.
- Author: Michael D Cahn
Cool season vegetable production requires significant inputs of water and nitrogen (N) fertilizer to maximize yield and quality. Proposed changes in water quality regulations on the Central Coast and higher fertilizer prices in recent years have prompted grower interest in increasing efficiency of nitrogen fertilizer use in lettuce. By improving water management and matching nitrogen applications to the uptake pattern of the crop, growers could potentially reduce fertilizer use and address water quality concerns.
Two tools available, the quick nitrate soil test and weather-based irrigation scheduling, have been shown to help lettuce producers better manage water and fertilizer nitrogen. Trials we conducted in commercial fields have demonstrated that soil nitrate concentrations greater than 20 ppm NO3-N, are sufficient to maximize crop production. In addition, we have shown that evapotranspiration data available from the California Irrigation Management and Information system (CIMIS), can be used to accurately estimate the appropriate volume of water to apply to meet crop needs and minimize potential leaching losses of nitrate-N.
Both the quick nitrate soil test and weather based irrigation scheduling require more management time for growers to implement in their farming operations. The quick nitrate soil test entails collecting a representative soil sample in the field, extracting the sample, and calculations to estimate the concentration of soil nitrate. Weather based irrigation scheduling requires calculating crop evapotranspiration (ET) from CIMIS reference ET data and a crop coefficient corresponding to the developmental stage of the lettuce crop. In addition, information on the soil type and irrigation system is needed to determine the optimal irrigation interval and run-time. With multiple fields and ranches to track throughout the season, customizing water and fertilizer for individual fields could become a significant cost for growers.
CropManage is an online database-driven tool that assists growers and farm managers in determining water and nitrogen fertilizer applications on a field-by-field basis. The software automates steps required to calculate crop water needs from CIMIS ET data, and estimates fertilizer N needs for lettuce using quick N test data and models of crop N uptake. The web application also helps growers track irrigation schedules and nitrogen fertilizer applications on multiple fields and allows users from the same farming operations to view and share data.
The software was developed by UC Cooperative Extension and is free to use, and can be accessed at: https://cropmanage.ucanr.edu/ The application can be accessed with a web browser using a smart phone, laptop, or tablet computer. The tool uses a secure login procedure so that only individuals with permission can view and/or edit water and nitrogen fertilizer records of a particular farming operation.
CropManage was designed to be as intuitive as possible for growers and farm managers to use. Once logged on, users can view a list of ranches/farms that they have permission to access. By following the hyperlink for an individual ranch, a user can view a list of all active plantings associated with the ranch. Each planting has a summary of the ranch name, lettuce type, planting configuration as well as soil type, field name and planting and harvest dates:
Tables summarizing soil nitrate tests, fertilizer applications, and irrigation schedule are shown for each planting:
Getting started with CropManage.
There are three steps to begin using CropManage:
- Obtain account username and password by following the “create new account link” at the bottom of the login page and completing the instructions. Read and accept UC privacy and data security policy to continue.
- Set up a new ranch in CropManage by selecting “new ranch” at the bottom of the ranch list page, or request to be assigned to an existing ranch/farm. All users are automatically assigned full access to a ranch named "UCCE Ranch" so that they can try out CropManage. To add a new ranch to CropManage, we recommend that you use the online form. One can also download the excel ranch template from the import/export options link. Fill in the required information and email the template to mdcahn@ucdavis.edu so that it can be uploaded into CropManage. For more details on setting up a new ranch, click here.
- Set up new plantings in fields within a ranch. Select “new planting” at the bottom of the current planting list and fill in or select required information.
If you have interest to learn more about using CropManage, please contact Michael Cahn (831) 759-7377 or Barry Farrara (831) 759-7365.
Note: CropManage is still in the development stage, so new features will be added in the upcoming months. Recommendations are currently specific for romaine and iceberg lettuce production. We plan to expand this tool to a wider group of cool season vegetables in the upcoming months as funding permits.
