Phosphorus is an essential nutrient and a vital component for healthy crop production. It’s estimated that globally, agriculture consumes 47 million tons of phosphate fertilizer each year costing over $41 billion each year.
For retailers and growers, phosphorus management comes down to the soil, and more specifically understanding how essential nutrients work together in the soil; how to conduct and analyze soil tests; and being aware of each crop’s nutrient needs to prepare and make informed fertilizer decisions. Retailers should have the knowledge and understanding to help their customers implement the best strategies to ensure crops are able to access the appropriate amount of phosphorus to achieve the maximum yield potential.
Nitrogen v. Phosphorus
Phosphorus is immobile in the soil, but the problem with this essential nutrient is that it often gets tied up in the soil making it unavailable to the plant. In contrast, nitrogen is very mobile in the soil, and can be lost through leaching or denitrification if not absorbed by the crop.
In the day-to-day management of phosphorus, retailer and growers should be most concerned about keeping phosphorus available for crop uptake. This process is very different for phosphorus versus nitrogen.
With nitrogen, growers feed the crop directly as it is a “leaky” nutrient that can “stray” away easily. Phosphorus, unlike nitrogen is much less prone to loss, and should be applied to the soil directly, near the plants roots, so the plant can take up the nutrient as it is growing. In most cases, any phosphorus loss is due to soil erosion or runoff from soils recently fertilized with surface applications of fertilizer, sometimes into surface tile inlets in tile-drained fields.
Plants need phosphorus to maximize their yield potential. Plants are able to use a combination of the phosphorus available in the soil and from fertilizer added to the soil to help address their needs. Increasing soil levels can be challenging because of the high levels of competition for phosphorus, since many nutrients already present in the soil are attracted to it and may lessen the amount that is available to the plants.
It’s important to think about all the soil conditions that affect phosphorus availability.
- Soil organic matter, for example, contains phosphorus. So if the soil has low amounts of organic matter then it won’t mineralize the organic phosphorus making it available to the plants.
- Soil pH is another factor that can affect phosphorus uptake
- Acidic soil contains high levels of iron and aluminum which can tie up phosphorus.
- Alkaline soil contains high levels of calcium and magnesium which can reduce phosphorus availability.
- Soils with a higher cation exchange capacity (CEC) and more clay content can hold more nutrients such as iron, aluminum, calcium and magnesium. However if these nutrients are present in large amounts, they can also tie up phosphorus so it’s unavailable for plant uptake.
Low Testing vs. Higher Testing Soils
Growers should conduct soil tests to determine their soil test levels for phosphorus, so they can determine how much phosphate fertilizer is needed to achieve their yield goals.
Soil tests are crucial to determine the critical soil test level, which growers need to maintain to achieve 95 percent maximum yield without any fertilizer input. Soil test levels help growers determine whether to maintain or increase a fertilizer program, based on the amount of nutrients needed and the amounts already present in the soil.
For phosphorus, higher soil test levels will likely achieve maximum yield, but with low soil test levels, yield can be severely limited if fertilizer is not applied at the appropriate amount. For many soils, it takes 10 to 20 pounds of phosphate per acre to increase soil test levels by one part per million. Industry experts have documented that only about one third of the phosphorus applied in the fall is available to the plant the following season. In low testing soils, this can be substantially greater – and a costly endeavor! Which is why having a strong fertilizer strategy to help maximize the potential yield is so important.
A strong starter fertilizer program is always the first recommendation to provide essential nutrients to the seedling and maximize the genetic potential; especially in cool, wet conditions and early in the season when the plant has a developing root system that struggles to pull nutrients from the soil.
Because phosphorus is so immobile in the soil, it tends to move less than one inch from where it is placed when applied. In addition, plant roots only access about one percent of the soil volume, so they have evolved to accelerate root growth in areas higher in phosphorus. This makes band application of phosphate fertilizer an excellent strategy in low testing soils. Banding can increase soil solution concentrations more than a hundred times, giving young seedlings a great head start in low testing soils, especially when planting early into cooler soils.
Phosphorus availability has always been an issue, but now they have the tools and technologies available to better manage phosphorus.
Climate FieldView™ can help growers quickly and holistically view their soil maps for all their fields. including field-by-field summaries of key soil properties such as texture, organic matter, pH and CEC. In addition, growers can upload their gridded soil sample data to ensure they are staying up to date on soil and fertility needs.
At the end of the day phosphorus management is not easy, but soil data can help lead the way to a successful and effective solution. Then growers can share their data with their agronomy partner to develop a plan for their fields on how to better manage phosphorus, which will help the grower maximize their yields and get a better return on their investment.