The Cornbelt is just about to celebrate its golden wedding anniversary with nitrogen, and the love affair has not waned. When nitrogen application came into widespread use about 1960, corn yields substantially increased, but like any marriage, farmers are still trying to figure out what makes their nitrogen partner tick, and fertility researchers at Land Grant Universities are still fully employed trying to help out. What have the marriage counselors found out? Will this marriage last? Has this relationship been faithful?

The quick answer is a recommendation to plan on nitrogen application for a long time to come. There are a lot of years left in this marriage. But the issues at hand focus on the wide variability of yield despite steady nitrogen application and will any of those new nitrogen technologies provide any help by increasing yields?

The issue of yield variability is addressed by University of Illinois researchers who looked at the success of the new philosophy of using the price of corn and the price of nitrogen to dictate the amount to be applied, since many farmers were applying more nitrogen than can be economically justified. Their research over 10 years looked at both c-c and c-s rotations to help find the actual crop need for nitrogen. Even using the optimum N rate, yield differences varied from 5 to 78 bushels for corn following beans, and from 12 to 85 bushels for corn following corn.

The researchers found some geographical differences in their data and reported, “The relationship between economically optimal N rates (EONR) values and the yield at EONR among individual sites from this experiment was surprisingly strong in southern Illinois,” where soils are generally lighter than in the balance of the state, and in central Illinois research plots. However, there were no such relationships found in northern Illinois where soils are similar to central Illinois. And they concluded, “Because the variability over years is due mostly to weather and not to soils or other predictable factors, it will remain difficult to predict N needs even if such a relationship holds up; as we saw in 2008, yields can be much higher than normal in a given year, regardless of how the crop is managed.”

Controlling nitrogen costs were difficult in the last season, causing many farmers to look at alternative methods of getting nitrogen to their corn. University of Illinois fertility researchers evaluated 9 different urea products, finding they require a higher level of management to prevent N loss and lower nitrogen use efficiency (NUE). Part of the reason is the 50% efficiency level that corn has in using nitrogen, allowing the rest to volatilize, leach, denitrify, and otherwise become unavailable for use. The alternatives, tested on both conventional and no-till, included:

1) Liquid urea-ammonium nitrate (UAN) sidedress injected,
2) Urea surface broadcast,
3) UAN surface broadcast,
4) Urea + agrotain© (Agrotain International) surface broadcast,
5) UAN + agrotain surface broadcast,
6) UAN + agrotainplus© (agrotain plus a nitrification inhibitor, Agrotain Intl.) surface broadcast,
7) UAN + 10% v/v CaTs© (calcium thiosulfate, Tessenderlo Kerley) surface broadcast,
8) SuperU© (urea with agrotain and a nitrification inhibitor, Agrotain Intl.) surface broadcast,
9) ESN©® (a polymer coated urea, Agrium US, Inc.) surface broadcast.

The researchers reported the tillage fields had significant responses to increasing N rates, economic optimum N rates, yields, and nitrogen use efficiencies; they could evaluate each product based on pounds of nitrogen per bushel of yield. Generally, the dry urea had a lower efficiency than the liquid urea in conventional tillage. In the no-till fields the urea (only) had a poor efficiency, but the other dry products had a significantly lower efficiency than the urea or the liquid products. And they concluded, “It appears that many of the N sources in this study may provide significant improvements in N use efficiency, especially during wet years. These differences appear to more important with no-till than with conventional tillage systems.”

Summary:
A series of research projects, designed to help increase the efficiency of nitrogen application on corn, appears to point to weather being a determining factor, both for impacting yield response to nitrogen, and for enhancing the availability of various urea products across tillage systems.