Curt / Jim,

A few years ago, here in Ontario, we accumulated all of the N research that had been done for the last 40 years, and ran some serious statistical (pronounced sadistical) analysis on it. For whatever reason, we had one of the most extensive databases in North America across a range of soil types and previous crops and some really interesting trends jumped out of it. Since then, we have overhauled our Corn N recommendations after they were subjected to confirming trials for several years.

First, the traditional recommendation of 1.1-1.25 lbs per bushel of expected yield was done in the days of 100-120 bu yields where a greater percentage of the N was used to build the "factory" before the grain output could be produced. Second, most of our research was done in continuous corn rotations. Third, the trials were conducted primarilly on sandy loam soils (just happened that research farms get plunked down on some nice uniform, forgiving stuff). The significance of these conditions will be come evident...

Factors Affecting your decision...

1. Expected yield - new genetics with higher grain to stalk ratios require about 0.9 pounds per bushel, especially at yield levels of 160+

2. Price Ratio - of N to corn. This is a minor player, but a player no less. As N gets expensive relative to corn, then you use a little less of it. Despite the fact that N seems expensive, it is actually cheaper than the last few years, relatively.

3. Previous Crop - Corn on Corn was a zero adjustment, corn on soybeans was -20%. Soybeans don't produce net nitrogen, they just leave less residue to suck N up and hold it away from the next crop.

4. Soil Texture - believe it or not - HERE - a silt or silt loam is the best soil for N sequestering and ready release (just like water, by the way). the closer you got to a clay or sand, or even a sandy clay, nitrogen applications had to be adjusted up by 15% vs. SiltLoam.

5. Timing - Preplant vs. Side-dressed: Side-dress allows another 10% reduction in application rate. This holds across soil types (assume lighter soils will have some leaching, heavier will have dinitrification), and it even holds with the Silt Loams.

The other thing that the confirmation trials revealed was that in years where the actual yield was greater than normal, the very same ideal growing conditions also mineralized organic matter faster than normal, and the soil was able to supplement the extra N in the abnormal year. Ergo, the need for extra applied insurance 'N' in case we have that great year is generally false.

An example: I have a yield average (not goal) of 180 bu on a field.

Base - 180 bu x 0.9 = 162 lbs/ ac.

Price Ratio - difficult to explain, but for now let's assume it is neutral = 0

Previous Crop - Soybeans (-20%)  162 - 20% = 129.6 lbs/ac

Soil Texture - I'm on a Silt Loam - zero adjustment, but any other soil type towards sand or clay add 15% = 129.6 lbs

Timing - We side-dress - subtract 10% = 116.6

To sumarize - it recommends 116 lbs of N for 180 bu of corn. We have done it often enough that we know it is correct - HERE.

Suggestions for Plot:

0  40  80  120  160  200 lbs of N

We do at least one of these per year. We band 30 lbs with the planter, and then side-dress with NH3. Generally, when we graph the results and fit a curve, max yield is obtained between 80 and 120 (we don't even drop a 160 or 200 anymore). Our MERN (Maximum Economical Rate of N) is a little earlier on the curve, and usually occurs well before the 100 lb line...

Luke   aka Ken SWOnt