The Management Checklist provides a framework to disseminate practices and resources to Coalitions and their grower-members working to comply with the Irrigated Lands Regulatory Program (ILRP). Click on any item to learn more.
1 Learn About The Nitrogen Balance and Why It Matters
Due to complexity of the N cycle, the coalitions opted for a platform that is more robust than a simplified N balance. Monitoring and modeling results demonstrate clearly that over the long term, leaching is always less than the N balance due to other things that happen to N besides being removed with harvested crop material. The fate of N is driven by fertilization timing, form, or placement, and by irrigation management. Of course, the effects of management in any given location are also dependent on local climate, soil, and crop factors. Almost none of this is reflected in the simple equation A-R=N.
While the N balance is a helpful indicator of potentially leachable N, this value alone is not a predictor of N leached into groundwater because:
- there are several pathways that N in the rootzone can take (denitrification, volatilization, or soil storage as organic N in soil organic matter),
- crop rotational effects should be considered, and
- biological and chemical processes in the vadose zone (the area in between the crop root zone and the groundwater) can affect N movement and fate.
The amount of applied N affects the N balance differently for a single field, for groups of fields of a single crop type, and across different crop types.
- For a single field: When yield is constant, applying more N increases the N balance. If more N is applied to support a larger yield, some of the N applied may contribute to an increased N balance because N applications are rarely 100% efficient.
- Across different crop types: The relationship between N applied and N balance is much messier when aggregating data across different crops, because factors affecting recovery of applied N differ markedly among crops.
2 Keep Track of Your Compliance Requirements
The goal of the Irrigated Lands Regulatory Program (ILRP) is to restore and/or maintain the highest reasonable water quality while maintaining economic viability of agriculture in the Central Valley.
Learn about the ILRP Components
3 Apply Nitrogen Efficiently
Know your Crop Specific Requirements
Follow Crop Fertilization Guidelines, which were written by scientists from the University of California, Davis, with support from CDFA FREP. Fertilizer guidelines are available for 29 crops, including information on site specific adjustments. The adjustments document provides an overview of the considerations needed to account for N from non-fertilizer sources, and information on leaching, volatilization, and denitrification losses.
Select a crop in the drop down below to learn about their specific requirements.
- Almond Early-Season Sampling and In-Season Nitrogen Application Maximizes Productivity, Minimizes Loss from University of California, Division of Agriculture and Natural Resources. This article focuses on the rates of nitrogen application to almonds.
- Almond Nitrogen Model from University of California and California State University. This tool provides recommendations for making N and K fertilization decisions.
- Nutrient Management from Almond Board of California, Almond Sustainability Program. This training module covers nutrient management checklists related to the source, amount, timing, and place of fertilization.
- Nitrogen Best Management Practices from Almond Board of California. This document provides almond growers with guidance on nitrogen’s role in almond production and how to achieve efficiency and profitability nitrogen management.
Account for Sources of Non-Fertilizer N
Accounting for N in irrigation water, residual soil nitrate, and N mineralization from soil organic matter and crop residues can help with applying N efficiently.
- You can assume between 70-80% of N in irrigation water is available to the crop and is as readily available as N in chemical fertilizers, however the exact percentage is a function of irrigation application efficiency and should be customized to an individual irrigation system. By accounting for N in irrigation water, you can reduce rates of fertilizer N application.
- This calculator converts nitrate and ammonium found in irrigation water, as measured by a laboratory or other method, into pounds of N applied per acre. A fact sheet is available here (Español).
- Field trials show the fertilizer value of nitrogen in irrigation water from University of California, Division of Agriculture and Natural Resources. This article provides information on the utility of nitrate-N from irrigation water as an efficient fertilizer N source.
- Nitrate to Nitrogen Conversion and Estimating N Contribution from Irrigation Waters Containing Nitrate from University of California, Division of Agriculture and Natural. This 2012 blog post provides information to calculate the conversion between nitrate and nitrate-N.
- This N source is most significant in annual crop systems.
- Details on the Nitrate Quick Test from University of California, Division of Agriculture and Natural Resources.This 2011 blog post provides information about obtaining representative soil samples in order to conduct the nitrate quick test analysis.
- Soil Sampling Annual Crops from University of California Cooperative Extension Small Farms Program. This site provides basic information about sampling and soil testing to analyze soil nutrients.
- Soil Sampling in Orchards from California Department of Food and Agriculture in collaboration with University of California Davis. This article provides guidelines for soil sampling in orchards to optimize fertilization.
- A Guide to Collecting Soil Samples from Oregon State University Extension Service. This article provides information on collecting soil samples to assess the soil’s available nutrient-supplying capacity.
- Soil Analysis from University of California, Division of Agriculture and Natural Resources. This 2015 article provides information about soil sample analysis.
- SoilWeb Apps from The University of California Soil Resource Lab utilizes USDA-NRCS SoilWeb. Five different SoilWeb product apps are available, used for accessing the USDA-NRCS detailed soil survey data. Apps include SoilWeb (using an interactive Google Map), SoilWeb Earth (shows mapped areas in 3-D display), SEE – Soil Series Extent Explorer, Soil Properties App, and Soil Agricultural Groundwater Banking Index.
- This source may not be significant in low organic matter soils <2%, but can increase with crop residue or organic amendments.
- Cover crops
- Estimating Plant-available Nitrogen Release from Cover Crops from Oregon State University Extension Service. This 2012 extension publication compares plant-available nitrogen from several cover crops.
- It is important to consider that cover crops can be a source and a sink of nitrogen. Planting a deep-rooted, salt-tolerant cover crop can capture accumulated nitrate over the winter season.
- Organic amendments
- Organic production systems typically rely on amendments for N supply and soil nitrate can build up to significant levels at the beginning of the season, which are susceptible to loss with leaching and require particularly careful irrigation at the start of an organic crop season.
- Nitrogen Availability from High-Nitrogen-Containing Organic Fertilizers from University of California, Division of Agriculture and Natural Resources. This 2006 article evaluates the rate of net N mineralization from four organic fertilizers.
- Nitrogen Mineralization from Organic Amendments Calculator from Geisseler Lab, University of California, Davis. The calculations in this tool are based on an analysis of 113 datasets from the scientific literature. N mineralization rates are adjusted based on soil temperature data from local CIMIS weather stations. Soil moisture is assumed to be optimal near field capacity.
- Manure as a Fertilizer from University of California Cooperative Extension, Tulare County. This 1997 document helps determine how much manure is needed. It includes tables for various manures and their estimated N, P, K content.
4 Track How Nitrogen Is Removed
N is removed from a field through biomass that is either harvested or persists as permanent woody materials. The greater the value of N removed, the lower the balance of leachable N. When systems become more efficient, more of the applied N is captured by the crop, lowering the risk of N leaching.
These decision support tools can be used to estimate this value:
This calculator can be used to estimate N removed (R) and the ratio of N applied (A) to N removed (A/R). Results can be calculated from inputs for a single crop or for multiple crops. The conversion factors were developed by Dr. Daniel Geisseler based on best available information are continuously refined. Calculations may be completed online or offline.
This calculator reports potential nitrate leaching risk values calculated using literature data for N uptake (they are not recommendations). Weather conditions, management and variety selection all can affect N uptake and availability. It is therefore important to monitor the N status of the field during the season with soil or leaf analyses and to make adjustments to the fertilizer program.
5 Manage Water Carefully
Care for your water sources by protecting and maintaining existing well heads and properly caring for inactive wells.
- Wellhead protection practices are to help prevent the movement of contaminants into a well. Unprotected wellheads can transmit contaminants from the surface into groundwater. This one pager (Español) provides information about practices for wellhead protection and well maintenance.
- Improperly abandoned or maintained wells can transmit contaminants from the surface into groundwater and can also be a safety hazard. This one pager (Español) provides information about the destruction of abandoned wells and maintenance of inactive wells.
Trust that irrigation water nitrate-N is effective and reduce fertilizer rates accordingly.
- See Cahn, et al. 2017. More information on this subject is available in checklist #3: Apply nitrogen efficiently.