For part three in our series on prepping harvested and fallow ground for next year, we look at fall fertility applications. For this topic, we’ll discuss what nutrients can be applied in the fall and application timing. We’ll also explore the value each nutrient provides in plant health and growth processes.
Where to Start
It’s important to wait until your soil sample results arrive before you apply fall fertilizer to recoup nutrient losses from this year’s crop. As we discussed last week, look at the results as a whole to understand how each nutrient, your soil type and pH levels work for the plant and how these elements can affect yield. First and foremost, look at the cation exchange capacity (CEC) and pH levels of your soil.
CEC directly affects the required amount and frequency of fertilizer applications, especially when it comes to nitrogen — a common fall-applied nutrient in the northern Corn Belt. The higher the CEC level, the less nitrogen will leach because the soil has a higher percentage of clay particles and organic matter content. CEC and organic matter also naturally carry nitrogen. Consider that roughly every one percent of CEC gives you 10 pounds per acre of nitrogen. Soil organic matter provides between 20 to 80 percent of the CEC in the mineralized soil, and the rest comes from sand, silt and clay in the soil. Organic matter can release 20 to 30 pounds of nitrogen per acre each year for every one percent of CEC. Knowing these levels is important before you apply nitrogen.
Soil pH directly affects the nutrients available to your crops. Without a neutral soil pH, any fall fertilizers you apply may not be absorbed by soil particles. The ideal pH range in your soil falls between 6.5 and 7.5. If results are above or below this range, the nutrient uptake process may be compromised come spring as key nutrients such as phosphorus and potassium will form less soluble compounds.
The Top Seven for Fall
While a number of nutrients aid in the growth of corn and soybeans, not all should be applied in fall. Some require more time to be broken down by bacteria in the soil to transition into a plant-usable form come spring, so fall applications are timely. Here are the top seven fertilizer applications that could benefit your fields this fall.
If you have lower pH levels, you likely have acidic soil. For highly acidic soils, liming — the practice of adding calcitic or dolomitic limestone to the soil — can elevate pH levels. Liming applies high amounts of calcium and magnesium back into the soil, allowing it to lower acidity and improve fertility for your future crop. Liming is often recommended a month or two before fall fertility applications to allow time for the lime to dissolve and increase the pH level. The most cost-effective and common formulation is the dry (granular) form.
If growers are considering a lime application, they may benefit from adding gypsum to the mix. Gypsum can be added to lime to help elevate calcium and magnesium levels in the soil.
Spreading manure is a great source for many key nutrients, including potassium and phosphorus. Applying manure via knife injection helps get the appropriate nutrients into the ground so that they don’t leach. It also ensures less volatization of ammonia.
Phosphorus is important for the storage and distribution of energy throughout the plant and is necessary for seed production and overall plant strength and vitality. About 0.4 pounds per bushel for corn to 0.8 pounds per bushel for soybeans of phosphorus is removed every year with crops. For example, a 240 bushel per acre cornfield may take out 96 pounds of phosphorus per acre.
Potassium helps with the movement of nutrients, proteins and water in the plant and, according to Penn State Extension, helps improve the crop’s resistance to diseases and insects. Roughly 0.30 pounds per bushel for corn to 1.50 pounds per bushel for soybeans of potassium is removed every year with crops. For a 65 bushel/acre soybean field, this would equate to 97.5 pounds of potassium per acre removed from your field.
Nitrogen will play an important role in next year’s crop because it’s critical for photosynthesis, providing energy to the plant, enhancing the nutrient uptake process and, ultimately, helping the plant grow and produce top-end yields. While it may be too warm to apply nitrogen in the southern regions this fall (the nutrient needs soil temperatures 50 degrees Fahrenheit or slightly lower to avoid denitrification or leaching), northern regions can benefit from a fall application. University extension services may have soil temperature history charts that can help you determine the approximate date range that soil temperatures in your area may fall below the 50 degrees mark.
It’s important to remember that some farmers may not need nitrogen on their soybean fields every year because nitrogen occurs naturally in the soil or can be added through inoculants to their seed. For corn, however, annual nitrogen applications are necessary and should range anywhere from .7 to 1.2 pounds per bushel. Soybeans need approximately 3.8 pounds per bushel of nitrogen.
Next year’s crop will also benefit from a fall sulfur application, as it helps regulate photosynthesis and nitrogen fixation. Our experts recommend using ammonium sulfate or ammonium thiosulfate at one pound for every five to 10 pounds of nitrogen. If you’re experiencing high-pH soils, ranging above a pH of 8, these are considered very alkaline soils and could be brought down with an application of elemental sulfur. We recommend adding this to your lighter soils and in smaller amounts.
For more guidance on how to prep your fields for next season (before winter arrives), contact your local Stine agronomist.