by John Orlowski, Ph.D. – Research Agronomist, Growers
Are you wrestling to create a nutrient management plan that keeps nitrogen, phosphorus, potassium, and sulfur in the soil where they belong?
Creating a plan of defense to prevent nutrient loss can improve the sustainability of your farm and help you reap agronomic and economic benefits.
One technique we recommend to our farmers is variable-rate application. It ensures a crop receives only the nutrients it needs to reach maximum yield. It also limits the potential impact of excess fertilizer on waterways and other natural areas.
Here are the steps you can take to make sure nutrients stay in the field where they belong, so they’re available to help your crops grow.
Managing the 4 Most Important Crop Nutrients
Nutrient #1: Nitrogen
Nitrogen is the most important nutrient for crop production, but it’s also most susceptible to being lost before your crop can use it.
What you need to know:
- The vast majority of nitrogen exists as a gas in the atmosphere, making it unavailable to plants.
- Gaseous nitrogen must be fixed into a form that plants can use, either through the production of commercial fertilizer or symbiotic nitrogen fixation.
- Nitrogen exists in the soil in two forms, ammonium and nitrate.
How nitrogen is lost:
- Ammonium is positively charged, so it’s held by soil particles and not susceptible to leaching.
- As soils warm, ammonium is converted to nitrate, which is negatively charged and very susceptible to leaching.
- Denitrification, where nitrate is converted to gaseous nitrogen, can also cause nitrate loss.
How to prevent nitrogen loss:
- Match your nitrogen application with crop demand.
When crops are young and small, they have low nitrogen demand. As the temperatures rise, crops enter a rapid growth phase, and the demand for nitrogen dramatically increases.
Splitting the total amount of nitrogen fertilizer into multiple applications can ensure the crops use the nitrogen you applied.
For example, to match nitrogen availability with crop demand, apply a small amount of nitrogen in your starter fertilizer. Follow it up with multiple side-dress nitrogen applications.
Nutrient #2: Phosphorous
How phosphorus is lost:
- Phosphorus in the soil is negatively charged and can bind with positively charged ions in the soil.
- Leaching is usually not a major issue, except in sandy soils and soils with very high phosphorus levels.
- Soil erosion is a significant avenue for the off-farm movement of phosphorus.
How to prevent phosphorus loss:
Phosphorus is most readily available in the soil between pH 6 and 7, so proper variable rate lime application is necessary to ensure that phosphorus is available to the crop.
Management practices such as grassed waterways, reduced tillage systems, and cover crops can reduce erosion and keep phosphorus on the farm.
Nutrient #3: Potassium
How potassium is lost:
In soil, potassium is a positively charged ion and can leach in sandy soils and in areas that experience a lot of rainfall.
How to prevent potassium loss:
The majority of potassium used in crop production is surface-applied as a dry product, like potash. As a result, it’s important to incorporate the potassium into the soil where the crop can use it.
Nutrient #4: Sulfur
How sulfur is lost:
- Sulfur in the soil is negatively charged and therefore, susceptible to leaching.
- Susceptibility to leaching depends on soil texture, with sandier soils being more prone to leach sulfur compared to soils with more clay.
How to prevent sulfur loss:
- Farmers with sandier soils should be aware of the potential for leaching and avoid applying high amounts of sulfur in a single application.
- Using multiple sulfur applications that match crop uptake can help ensure sulfur is used to produce yield, not leave the farm.
- In the absence of sulfur fertilizer, the main source of sulfur for crop production is the breakdown of soil organic matter.
- Cropping practices that preserve or build soil organic matter can ensure adequate levels of sulfur in the soil, including reducing tillage, using cover crops, and applying compost and manure to the soil.
Make Loss Prevention Part of Your Nutrient Management Program
Now that you know why loss occurs and when it’s most likely to happen, you can build prevention and remediation into your nutrient management program. A reliable program can help you reduce input costs, prevent fertilizer overuse and waste, and increase the sustainability of your farm.
Not sure where to start? We can visit your farm, test your soil to determine nutrient levels, and create variable-rate prescriptions based on the data from your fields. Remember, the key is to only purchase what you need and only apply what you need.
Did You Know?
For the past 40 years or so, farmers in many areas of the country rarely practiced sulfur fertilization for field crop production. Instead, sulfur-containing exhaust from coal-fired power plants would mix and move with atmospheric currents. It would eventually fall back to earth with precipitation, providing“free” sulfur to many important crop-producing areas. However, a reduction in sulfur emissions has led to a drastic decrease in acid rain and the sulfur it provided. As successive cropping removes sulfur from the soil, the use of sulfur fertilizers is likely to increase in the future.