Not all forms of nitrogen are created equal. A pound of nitrogen in one form will produce a completely different crop response than a pound of nitrogen in a different form. This is why organic growers often describe requiring only a fraction of the N requirement to produce a bushel of a given crop when compared with mainstream N applications.
The ultimate ideal is for plants to absorb amino acids and proteins directly from the soil microbial population and in the form of microbial metabolites. These forms of nitrogen contribute a lot of energy to plants, much more than. That represented by the N they contain.
The second most efficient form of N for most crops to absorb is urea, or amine nitrogen.
The third most efficient form of N for crops to absorb is ammonium.
The least efficient form of N for crops to absorb is nitrate. Plants must use a significant amount of their photosynthetic energy to convert nitrate to amino acids and proteins. When a corn crop absorbs 80% of it’s N requirement, it requires 16% of it’s total photosynthetic energy just for nitrate conversion (Marschner) A plant also requires three times more water to convert nitrate to amino acids as compared to ammonium. These are just the beginning items on a long list of reasons why you want plants to absorb only minimal amounts of nitrate, and obtain the majority of their nitrogen from other forms, preferably directly from the microbial population.
Ultimately the goal is to develop soil microbial populations that can deliver 100% of a crops nitrogen requirement every year. This is a very realistic and achievable goal. Only if you stop killing them with synthetic N applications in the first place, of course.
While on the pathway to reducing N applications, the first step is to make certain that any applied N is rapidly consumed by the soil bacterial population, and converted to microbial proteins and amino acids. These microbial forms of N are not leachable and are available to plants even when there is less water in the soil profile.
To convert applied N, either liquid 32-0-0, liquid 28-0-0, or liquid urea 21-0-0 (the most efficient of the liquid N sources) we simply need to provide the food sources and stimulants for biology to rapidly consume the applied nitrogen.
Here is a recipe we use on a lot of acres, very effectively:
1. 3% of the total solution (either weight/weight or volume/volume) should be humic acid. We use HumaCarb.
2. Add ATS, ammonium thiosulfate 12-0-0-26S to produce a 10:1 nitrogen to sulfur ratio in the final solution.
3. Add a carbohydrate source, we use Rejuvenate at 3% of the total solution
4. Add molybdenum, needed for the nitrate reductase enzyme. We use Rebound Molybdenum at a pint or a quart per acre.
It isn’t realistic to make universal recommendations, given the wide variability in soils, crops, and management practices, but we commonly observe that growers reduce nitrogen application rates by 30%-40% or more in the first year and produce the same or higher yields as compared with controls when using this combination. Use sap analysis to diagnose precisely whether the crop has adequate N, we don’t live in a world where we have to guess and be uneasy. Many times, we use this approach, and growers are amazed that their crops constantly show they have abundant, even surplus nitrogen. This is a start down the path to producing all your own N in the soil profile. We walk around in 78% N, the only reason we buy any is because we have destroyed the capacity of our soils to produce it’s own.
The same solution can be used for dry N applications if you can get it applied to the dry product.
Nitrogen management is a big topic, look for more thoughts on this in the future.