Target Maximum Economic Corn Production And Get Environmental Sustainability As A Bonus!

OMAFRA and the University of Guelph staff, in partnership with OSCIA members, have been involved in a series of projects sponsored by the Ontario Greenhouse Gas Mitigation in Agriculture Program, funded by Agriculture and Agri-Food Canada.

The results of this research are encouraging, both agronomically and environmentally.

Maximum Economic Rate of Nitrogen (MERN)

First we must understand the concept of MERN. Targeting maximum crop yield does not maximize economic return since the cost of achieving maximum yield is often greater then the value gained. MERN takes into account the cost of nitrogen (N) and the price of corn in relation to the yield potential of a field. MERN is a single target nitrogen rate. Determining MERN requires rate response trials in corn fields. Estimating MERN requires research, on-farm trials and experience over several seasons. In any given season, the true MERN can not be determined until the end of the season when N rate strips are harvested and the MERN is calculated. But we can do a pretty good job of predicting MERN. Tools to assist with this include N-rate trials, historical yields, and the Ontario Nitrogen Calculator which can be found at the new Growing Ontario Corn GoCornNet website.

We need to understand that not fertilizing to MERN is costing us money. Over-fertilizing increases costs without an economical increase in yield. Conversely, under-fertilizing prevents maximizing the economic yield potential of the field. Both under- and over-fertilizing has an economic cost.

Research Trials

In these research trials, manure was applied as uniformly as possible. Cooperators were free to manage the application as they normally would in terms of application timing, rate and methods of application and incorporation. In the spring, 4 rates of commercial fertilizer were applied at side-dress time, at rates of 0, 50, 100 and 150 lbs of actual N per acre. Soil nitrate levels in the plots were sampled in early spring, at pre-sidedress nitrogen test time in June, and at physiological maturity. We also assessed stalk nitrate levels at harvest, and recorded crop yields and standability. Yields from the commercial rates of nitrogen were used to calculate individual field MERN's.

Figure 1 plots the fall soil nitrate levels from all the fields against the N rates above and below MERN. The dots to the left of the vertical axis were where N rates applied were below the MERN. To the right, rates of N applied were greater then the MERN.

Figure 1. End of season soil mineral N in the surface 30cm in relation to the amount of fertilizer nitrogen applied. A negative value indicates that fertilizer N rate applied was less than the fertilizer N rate required to economically optimize yield, and visa versa.

No Environmental Advantage to Under-Fertilizing

When the N application rate was above the MERN, the fall soil nitrate levels increased with increasing N application rates above MERN. However, the soil N levels were constant at all N application rates that were at or below MERN. Although applying nitrogen levels below MERN have an economic cost, under-fertilizing the corn crop did not reduce the level of soil N concentration in the fall. This suggests that there is no environmental advantage to under-fertilizing a corn crop, even though this has been proposed as a method to reduce nitrogen losses to the environment. The data indicates that applying nitrogen to MERN has the same impact on soil N levels in fall as does applying rates of up to 150 kg/ha below MERN.

Other Advantages of MERN

Applying N to MERN has other advantages above and beyond straight economics. Since economic yield is maximized at MERN, more stover per unit N is returned for building soil structure and holding moisture. More carbon is returned to the soil, which helps to reduce greenhouse gas emissions, and less fuel and time is used per unit of yield.

Therefore we need to determine how to consistently target MERN and capture all the advantages associated with correctly predicting the MERN consistently from year to year.

Related Links:

• Growing Ontario Corn Ontario Nitrogen Calculator

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