All you need is your yield monitor files, your soil samples, and your state's crop nutrient removal figures to carefully manage both your crop yields and your input budgets. Here's how.
Yield monitors have dramatically increased our ability to improve nutrient management on each and every field. Historically, nutrient recommendations were based on yield goals chosen by farmers, which often meant that they were based on a farmer’s aspirational yield, rather than the actual needs and reasonable expectations of a field’s yield potential. In some cases, this led to massive over-applications of fertilizers which, beyond costing farmers a lot of money, has also had negative impacts on water systems across the country. Getting the right nutrients, in the right amount, to the right part of the field is the key cost-effective nutrient management, and one powerful tool in identifying those factors is your yield files.
Yield monitor data allows farmers to accurately replace the nutrients that have been removed from the soil by the previous crops by showing them exactly where nutrients were removed. Top yielding areas within a field remove more nutrients, so it’s generally safe to assume that in a field with big variations in yields, you’ll need to change your application rate within the field to make sure you get the nutrients to where they’ve been removed. If farmers aren’t careful to replenish these nutrients, field fertility will decline, decreasing the yield potential in the field every year.
Organizing your yield monitor data into zones can be a valuable way to determine the amount of nutrients that are removed from an area in a cropping year. These zones can be defined in multiple ways; by soil types, grids, aerial imagery, historic yield data, etc. The smaller your chosen zones are, the more accurately you’ll be able to apply replacement nutrients, within the limitations of equipment and time. If soil test data is available for the field and can be summarized for each zone, the rates can be adjusted so that excess applications will not waste the input and zones with low soil test values can have higher rates applied to increase yield potential and fertilizer efficiency.
More antiquated methods of determining applications, like the whole field yield goals previously discussed, tend to average out applications across fields, so that you often end up applying less than what is needed in high-yielding areas, possibly crippling your yield potential for the coming seasons, while over-applying and wasting fertilizer in low-yielding areas.
Crop nutrient removal numbers vary between states, and more information on crop nutrient removal numbers can be found at state agricultural extension service pages online. The USDA also has compiled a list of removal rates and has created tools to access the information (https://plants.usda.gov/npk/main). Using these defined removal factors, each zone in your field can be treated as an independent field and have its own recommendation calculated so that you can have more confidence that you’re getting nutrients exactly where they’re needed most.
The best way to check your nutrient application strategy on any zone in the field is to soil sample on a regular basis (most recommendations suggest a four year soil test rotation for all fields) and keep records of all inputs between sampling cycles. By using precision application methods to apply nutrients, you can use your crop nutrient removal numbers, your application totals, and your soil sample information to determine if your application strategy is really helping you replenish your soil’s nutrients, and ensure your soil reaches and maintains its peak fertility.