Corn needs nitrogen. A 20 ton/ac corn crop removes 180 pounds of nitrogen from the soil. That nitrogen comes from manure, decomposing soil organic matter, fertilizer and a small amount is deposited when it rains. A certain amount of nitrogen is lost when manure is applied (from ammonia volatilization), and other losses include leaching, denitrification, and fertilizer (urea) volatilization. In some cases, such as when the cover crop gets too mature, otherwise available nitrogen can become immobilized for more than a year. With all of these potential losses and other dynamics, how can one predict how much additional nitrogen fertilizer (if any) they will need to reach their corn yield potential?
By now, most of you have probably heard about the Adapt-N tool that Cornell developed several years ago; some may even be tired of hearing about it. This software is roughly analogous in concept to the ration-balancing software that your dairy nutritionist uses. In the same way that you don’t use your 2014 forage tests to develop your 2016 rations, the Adapt-N program will only give good information if you feed good and current information into it. The program needs data for each field including: expected yield, planting date, relative maturity of the hybrid you planted, plant population, manure test information, manure application dates, date of manure incorporation, soil organic matter, GPS location, etc. This allows the program to model nitrogen behavior in the soil, crop development, nitrogen demands, etc. It will even give you a ‘virtual pre-sidedress nitrate test (PSNT)’ that you can compare to a physical PSNT if you want to ‘ground-truth’ the program. It is a TREMENDOUS program. That said, no approach to N management is perfect.
- Guessing or just applying the same amount of N every year is a very bad idea.Some years you could run short and lose 30% of your yield. Other years you will over-apply and have environmental losses and a poor return on your investment.
- The PSNT can give good information, but between rocks that make sampling frustrating, trying to make hay, heat, labor, and other factors, it rarely gets done and often results in getting the recommendation too late. While the PSNT can yield a good recommendation and is certainly better than guessing, it is mostly blind to present and past weather conditions and often ends up over-recommending sidedress N.
The pieces of information that farmers often do not have and which often prevent them from being able to use Adapt-N are 1) a current soil test (to give us the organic matter number), and 2) current manure test reports/application rates. If you have those pieces of information for your farm, you are in a good position to try using this tremendous tool during the 2016 growing season.
What if I think the recommendation is wrong or scarily high or low?
Adapt-N WILL generate a recommendation, but we still need to use common sense. If the recommendation seems too high or too low, the reasons for that need to be investigated. An artificially low soil organic matter level will result in an extremely high N-recommendation and visa versa. I worked with a farmer last year whose soil test report indicated 1% soil organic matter. That is a very low number for Vermont, but I put it in. It yielded a MASSIVE N-recommendation. The farmer said, ‘I never put any sidedress N on and I always get 25-ton corn.’ Well, he was right. The corn field looked great except for some spots around the edges that were torched/stunted from N-deficiency; the stalk nitrate test also indicated that the plants had adequate amounts of nitrogen available to them. The places in the field that were clearly N-deficient were likely extremely sandy and represented low organic matter and high levels of leaching. The soil organic matter level in the field overall was probably significantly higher than 1%. It is a good tool, but it still needs to be informed by common sense and experience.
Two other virtues of the program compared with the PSNT: 1) you can get set up in Adapt-N now rather than late-June (as with the); and 2) it will email you nitrogen status updates on a regular basis, informing you of any major nitrogen loss events.
If you are interested in using this program for the 2016 growing season, get the aforementioned records together and contact me (firstname.lastname@example.org or 802-535-7922). I would be glad to show you how to run the program and help you get recommendations for several management zones (at least) on your farm. Agronomic Technologies (the company that owns the Adapt-N license) has given me quite a few acres ‘free’ to introduce the product to farmers, other acres can be covered for about $2.50/acre.