Illinois Fertilizer & Chemical Association
Supply · Service · Stewardship

Two-Rate Nitrogen Trials

Hundreds of full-rate N trials like the one shown in the photo above have been used to develop the N rate calculator that generates Maximum Return to Nitrogen (MRTN) N rates using current corn and N fertilizer prices. Whether we use N rates in the MRTN range or amounts higher than that, canopy color almost never tells us whether that the amount of N was less than, about equal to, or more than the crop needed in that field, that year. A corn crop with 50 or 60 pounds more N than it needs looks just like one with less N, so those who use high rates have no way to know that the extra N did not pay for itself. Nitrogen deficiency symptoms rarely appear in productive soils unless the soil stays wet for a period of time, in which case symptoms are worse in lower-lying parts of the field.
We are initiating a program that we think will help improve the MRTN approach, by telling us how much, if any, yield we gain by using higher N rates, or lose by using more modest N rates. Where possible, we hope to use aerial imagery (drones) to monitor canopy color development and match it to yield differences. In fields where the higher N rate produces more yield, we hope to be able to use information from these comparisons to learn how to predict when that will happen, and to use more N in such fields.
Here's the plan for doing trials like this in the field:
  1. Each trial will have only two rates: One is the N rate already planned for the field, counting all sources of N: MAP/DAP, pre-plant N, N applied with herbicide, and sidedressed N. We’ll call this the field N rate (FNR). If the FRN is around the MRTN rate (180 lb N or less in central and northern Illinois and 200 lb N or less in southern Illinois for corn following soybean; 210 lb N or less for corn following corn), the comparison N rate (CNR) will be 50-60 lb more than the FNR. If the FNR is 225 lb N or more, the CNR will be 50-60 lb less than the FNR.
  2. The CNR is applied in a single strip through the field at a chosen location in the field, well away from the edges of the field. A second strip can be placed in another part of a large field, or the comparison can be done in several different fields.
  3. The CNR strip should be wide enough to allow yield data to be collected from two combine harvest passes, with each pass compared to a harvest pass at the FNR next to (on each side of) the CNR strip. For example, if the N applicator covers 40 ft. and the corn head is 8 rows (20 ft.) wide, one applicator pass is enough, although two passes might be better. Mark both sides of the CNR strip with flags, and with GPS if possible.
  4. Yields from the four passes (two at the CNR and two at the FNR) will be taken using a combine yield monitor, with each harvest pass labeled as a separate load if possible.
Please click below to fill out a field form to participate. Our goal is to have these comparisons in every county in Illinois. If you have any questions, please contact Dan Schaefer, (217-202-5173). If you are south of I-70, please contact John Pike, (618-727-1234).