The BMP Challenge™ is a program that American Farmland Trust is running in Virginia’s Shenandoah Valley, in other Mid-Atlantic states, in New York, California and across the Midwest as a tool to help farmers implement BMPs, or Best Management Practices to achieve conservation goals, on their farmland. For farmers with fields in corn, nitrogen is one of the primary nutrients to help it grow, and farmers apply commercial forms of nitrogen fertilizer to provide the crop with added nutrients. The amount of nitrogen applied to the field is based on the farmer’s yield goal, or how many bushels of corn the farmer expects to grow per acre—one pound of nitrogen for one bushel of corn on average. But nitrogen’s availability to the plant is tricky, affected by temperature and the moisture in the soil. To ensure that the corn gets enough a farmer may apply extra nitrogen as insurance for reaching their yield goals.
When more nitrogen (or any other nutrient) is applied than what the plant can utilize for growth, the excess can leave the field as runoff and contaminate waterways. Farmers have no interest in wasting expensive fertilizer or sending nutrients into nearby waterways, but their harvest is their pay check for the whole year. The risk of being wrong is great. The role that the BMP Challenge™ plays is to allow the farmer to compare a new practice, designed to be more nitrogen efficient, to their standard practice with a guaranteed payment if they lose yield.
When a farmer agrees to participate in the BMP Challenge a crop advisor, like me, works with them to collect a detailed history on the enrolled field, outlining the history of corn grown and how much and what types of fertilizers have been applied to the ground. This allows us to establish how much nitrogen is already present in the soil and available for use by the newly planted crop. The crop advisor then asks what the farmer’s current yield goal is, so we can determine how much total nitrogen the corn will need by the end of the growing season.
Typically, farmers in the Shenandoah Valley apply fertilizer to corn twice; once at planting and again when they “sidedress” the balance when the corn is about knee high. This way fertilizer is available to the plant at every stage during the growing season. My job as a crop advisor is to help the farmer pinpoint exactly how much sidedress nitrogen is needed by using a Pre-Sidedress Nitrate Test, or PSNT.
The farmer and crop advisor collect soil samples 12 inches deep to measure the amount of nitrogen available to the plant just prior to the time when the young plants need the most fertilizer. The extra depth allows a more complete and accurate picture of how much nitrogen is available and helps guard against over fertilization. (Check out this video from the University of Wisconsin Extension for a look at PSNT in action.)
For the BMP Challenge™, We take soil samples from two different parts of the field. One is a strip through the middle of the field, or check strip, where the farmer was encouraged to sidedress the crop at whatever rate they would typically use based on their soil type and yield goal. In the remainder of the field the farmer agreed to only apply the amount of nitrogen recommended from the PSNT result. It is possible that the PSNT could be the same as what the farmer had already planned or it could even call for more nitrogen, but often, the PSNT indicates that the nitrogen sidedress can be reduced or even eliminated without causing a loss in yield.
At a time when commercial fertilizer can be a third of corn’s total cost of production, any savings a farmer can find will make a huge difference for their bottom line. Using a soil test to adjust nitrogen rates to the actual need can save money and improve water quality. But what if it’s wrong?
By using a side-by-side comparison within the same field it is possible for the farmer to prove to him or her self that the PSNT can be trusted. And by performing the test under the umbrella of the BMP Challenge™, the risk of trying this new practice is eliminated.
Next up… Half-way to Harvest – What’s the Score? -Ear Leaf Tissue Testing in the BMP fields