Nitrogen and phosphorus are major plant nutrients necessary for crop production.
Proper nutrient management is essential to help keep adequate nutrients available to crops in the field and out of waterways.
Producers must select the relevant best management practices for their crops and land to both maximize nutrient efficiency and protect water quality.
Nutrient & Fertilizer Management Facts
- Nitrogen is the nutrient that most frequently limits irrigated crop production in Colorado.
- The nitrate (NO3– ) form of nitrogen fertilizer is extremely soluble and subject to runoff and leaching losses.
- Phosphorus in most Colorado soils is tightly held to soil particles and may contaminate surface water through soil erosion in runoff.
- Organic forms of phosphorus found in humus, manure, and crop residues tend to be more soluble.
General Nutrient Management BMPs
- Develop a yearly fertilizer plan for each field and crop.
- Test soil, plant tissues, and irrigation water.
- Analyze and credit nutrients from manure, compost, and biosolids.
- Establish realistic crop yield expectations.
- Keep fertilizer records.
- Utilize a crop consultant.
- Manage irrigation application to avoid nutrient runoff and heavy leaching.
- Practice soil conservation and erosion management.
- Establish buffer zones around waterways.
- Identify and closely manage crop areas subject to erosion, runoff, or leaching.
- Follow the 4R nutrient approach to fertilizer management:
- Right rate
- Right time
- Right place
- Right source
Fertilizer Application
Nitrogen BMPs
- Right rate: apply rates for adequate crop nutrition while avoiding over-fertilizing
- Utilize soil testing and a nutrient management plan to determine nitrogen application rates.
- Split nitrogen applications
- Avoid high rates of nitrogen in the fall or at planting time
- Meter nitrogen applied by irrigation with a properly calibrated device
- Right time: time application for maximum crop uptake
- Avoid fall nitrogen applications for spring-planted crops, in areas with high fall/winter precipitation, on soils subject to high leaching, and where pre-plant irrigation is necessary
- Wait until the crop is well-established before applying large amounts of nitrogen
- Right place: place nitrogen for efficient crop uptake and minimized loss
- Subsurface
- Banded
- Incorporate suface-applied or broadcast fertilizers
- Only apply nitrogen through irrigation systems where efficiency and uniformity is high
- Avoid nitrogen applied through ditch water unless tailwater recovery is used.
- Right source: utilize nitrogen sources that provide immediate or delayed crop-available nitrogen when needed
- Avoid large amounts of nitrate on soils with higher leaching potential.
- Utilize nitrification and urease inhibitors.
Phosphorus BMPs
- Right rate:
- Utilize soil testing and a nutrient management plan to determine phosphorus application rates.
- Credit all available phosphorus from manures and other organic residues
- Fertilize soils with ‘low’ to ‘medium’ phosphorus soil test values
- Avoid phosphorus fertilizer on soils testing “high” unless a banded starter is needed to compensate for low soil temperatures.
- Do not apply phosphorus fertilizer to soils testing “very high.”
- Consider variable rate application, particularly in large fields.
- Right place: place phosphorus in the root zone for efficient crop uptake and minimized loss
- Band application at planting
- Incorporate surface-applied or broadcast P fertilizer
Fertilizer Storage and Handling BMPs
- Follow all label directions.
- Minimize the amount of fertilizers stored on-site
- Store fertilizers in a dry and secure location with impermeable floors.
- Store, mix, load, and perform cleanup 100 ft. from any water source.
- Mix, load, and clean up at the application site whenever possible.
- Prepare or mix only the amount of fertilizer needed.
- Maintain wellheads to prevent direct contamination to groundwater.
- Inspect and maintain chemigation equipment to ensure proper function.
- Properly dispose of rinsate, containers, and leftover product.
- Maintain a readily accessible spill cleanup kit.
- Calibrate manure and fertilizer application equipment.
Resources
- Best Management Practices for Agricultural Nitrogen Management
- Best Management Practices for Agricultural Phosphorus Management
- Phosphorus Fertilizers for Organic Farming Systems
- Fertilizing Cool Season Grasses and Grass/legume Mixtures
- Fertilizing Corn
- Fertilizing Dry Beans
- Fertilizing Mountain Meadows
- Fertilizing Potatoes
- Fertilizing Spring-Seeded Small Grains
FAQ
What are best management practices (BMPs)?
Best management practices, or BMPs, are recommended structures, methods, and practices designed to protect water quality. BMPs can provide environmental, agronomic, and economic benefits.
The cost, economic return, ease of implementation, and overall effectiveness will vary from practice to practice. Recommended BMPs may include already widely accepted and utilized agricultural practices.
Every farm is unique and requires a particular combination of practices that meets the needs of the land and the producer.
How are the nitrogen and phosphorus cycles relevant to agriculture?
Nitrogen and phosphorus each naturally cycle through the environment through chemical and biological transformations into various forms. Crop growth is dependent on the forms of these nutrients that are available for uptake and use by plants. Understanding nutrient cycles can help maximize plant growth and crop yields while minimizing harmful losses to the environment.
What forms of nitrogen are available to plants?
Plants can use nitrogen in two forms:
- ammonium-nitrogen (NH4+ – N)
- nitrate-nitrogen (NO3– – N)
What is nitrogen mineralization?
The process that converts nitrogen into forms that are available to plants. Microbes decompose organic nitrogen from manure, organic matter and crop residues into ammonium (NH4+).
Rates of mineralization vary with soil temperature, moisture, and soil aeration.
What sources provide nitrogen to the soil?
- Organic matter: crop residue, manure, biosolids, compost
- Synthetic fertilizers
- Atmosphere: nitrogen fixation, lightning, nitrogen deposition
What are quick-release nitrogen fertilizers?
Synthetic nitrogen fertilizers containing ammonium, nitrate, or urea are considered to be “quick-release” fertilizers that rapidly become plant available.
What are slow-release and controlled-release nitrogen fertilizers?
These synthetic fertilizers are designed to delay the release of plant available nitrogen.
What is phosphorus mineralization?
The process that converts phosphorus into forms that are available to plants. Microbes break down organic phosphorus and release inorganic phosphates that are available to plants.
What forms of phosphorus are available to plants?
Plants use forms of phosphorus known as orthophosphates:
- H2PO4–
- HPO42-
What is an “agronomic rate” of nutrient application?
A nutrient application rate based upon current crop needs that takes into account already available residual soil nutrients as well as nutrients from all applied sources, such as commercial fertilizers, manure, and irrigation water.