Now Is the Time to Prepare for Fertilizer Applications

By Angie Rieck-Hinz

Just as taking good quality soil samples is important for making nutrient application recommendations, so is managing application rates and distribution of dry nutrients and lime. This also holds true for anhydrous ammonia applications and applications of solid and liquid manure but this article will focus on dry fertilizer application.

Under-application of dry fertilizer or lime that does not meet the required application rate recommendation can often cause a negative impact on crop yields. Over-application of nutrients can cause excess input costs. These misapplications can be caused by uneven distribution of nutrients. Often, we notice under-application in fields when we see “yellowish” repeating streaks in the field, usually in the spring. Distribution issues are more evident today  with more widespread adoption of aerial imagery with drones. This issue is more important with non-uniform application and under application of nitrogen (N) applications, than phosphorus (P), potassium (K) or lime, but all are crucial for crop production.  N and sulfur (S) streaks in fields are the most noticeable. You will rarely notice symptoms of over-application in the field.

What causes uneven distribution of dry products?

There are many factors that lead to uneven distribution of dry products, including poor adjustment of the application machine; fertilizer quality, including shape, size, density, and hardness; and improper swath width and lack of calibration.

What can the retailer/applicator do to mitigate these application and distribution issues.

These factors should be addressed by the retailer for each product, each year, and for major application rate changes and when product conditions change. One example of a change in product condition is when you get to the bottom of the pile and there is more product with a smaller size, or the shape has been changed as product is constantly scooped, pushed and loaded; in other words, there are more “fines”.  Fines can reduce the width of spread patterns.

1. Pattern calibration tests should be conducted for all types of application equipment, including spinner spreaders and pneumatic or air spreaders, so the applicator understands spread swath and particle distribution and adjustments to swath width can be made as needed.
2. Product quality should be analyzed. Particle density and hardness can greatly impact particle size as it comes off the spinners, which consequently impacts spread swath.
3. Don’t forget about the wind. Good fertilizer application depends on getting the right rate in the right place. Modifying direction or recalibrating the spreader can help to mitigate movement of particles by the wind. Not applying on windy days also makes sense.

What can farmers do to mitigate these application and distribution issues?

Farmers rarely apply dry fertilizers and rely on their agricultural service providers for such applications. In this case communication is key to alleviating future issues.

1. If you are seeing similar patterns of streaks or shorter crops in fields, or your yield monitor is indicating such patterns, consider asking your retailer to change the application pattern. Instead of applying north-south, perhaps change to east-west or vice versa.
2. Consider asking for products to be applied separately. Due to fertilizer particle size, shape and density, products applied with a spinner-spreader do not distribute evenly.  To achieve uniform distribution, it may be worth the effort to apply the products separately. 
3. Know your soil test numbers.  If your soil tests are in the optimum or higher categories, the impact of poor spread patterns for P and K may not be as crucial if soil test levels are low or very low and fertility can be yield-limiting. 

In summary, good fertilizer application and distribution is important to minimize yield loss in the field. Equipment calibration and product quality evaluation help to identify where adjustments can be made to maximize return on investment for your fertilizer dollars.