Considered Yet How to Fertilize the 2007 Corn Crop?

No we didn’t miss a year! This may be the time to think about how you’re going to fertilize the 2007 corn crop. Nitrogen and fuel prices are hitting all time highs and commodity prices are low. We need to think about alternatives to applying all the nitrogen to corn as commercial fertilizer.

Underseeding Red Clover

While many corn producers do not have manure nitrogen, they do have other options for nitrogen, in particular red clover. In Ontario, the acres of winter wheat and spring cereals that are underseeded to red clover has steadily declined. This is due to concerns over potential interference with cereal harvest, effects on straw quality, cost of red clover establishment, and poor or inconsistent stands. The poor and inconsistent red clover stands that seem to be more prevalent than a decade ago are typically attributed to increasing wheat yields. However, many producers are growing high yielding wheat crops and also getting excellent red clover establishment. Other factors such as tillage systems, wheat varieties, nitrogen, fertility, and soil type also seem to influence red clover establishment. Research is underway to develop management systems to improve red clover stands.

Red clover stand variation may not be a major issue. Several previous studies indicate that red clover biomass and the amount of nitrogen available to the next crop are not strongly correlated above a minimum level of red clover growth.

The amount of nitrogen credit is more than you might think and can make a significant contribution to the following year’s corn crop nitrogen requirements. Previous recommendations have underestimated red clover’s contribution to corn nitrogen requirements.

Calculating Nitrogen Credits

Using the Ontario Corn Nitrogen Calculator on the Go Corn Website and estimating the nitrogen (N) requirements to grow 130 bu/ac of corn in a 2750 CHU zone across 3 different soil textures we get the numbers in Tables 1 and 2. Table 1a is the Maximum Economic Rate of Nitrogen (MERN) recommended assuming a nitrogen price of $0.42 per lb (2005 average estimate) and corn at $2.70/bu. Table 1b is the same, except that the nitrogen price is $0.34/lb, which is more similar to what we were paying in 2004. Next year’s nitrogen price is a mystery, although we are pretty sure of which direction it will be going.

The amount of nitrogen recommended across all soil types and crop rotations declines as the price of nitrogen increases (Table 1a vs. 1b). If the price of nitrogen continues to increase, the nitrogen rate will continue to decline, since the cost of the additional nitrogen is not captured by sufficient increase in crop yield. The crop price will also impact the nitrogen rate. Try different scenarios yourself by downloading the calculator from the website.

The Corn Nitrogen Calculator was developed by summarizing 40 years of nitrogen research and validated with 120 site-years of on-farm strip trial data from 2001-2004, providing a high level of confidence.

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Based on Expected Yield 130 bu/ac., Corn Price $2.70/bu., N Cost $0.34/ab., CHU 2750, N applied Preplant

Based on Expected Yield 130 bu/ac., Corn Price $2.70/bu., N Cost $0.34/ab., CHU 2750, N applied Preplant

Cost Benefits

The nitrogen contribution of red clover in all the soil types is significant. Comparing a previous crop of corn to that of winter wheat/red clover shows a 72 lb/ac N benefit to having a uniform stand of red clover in the system. Even compared to soybeans as the previous crop, red clover in the winter wheat gave a benefit of 47 lbs/ac of N. If corn was following wheat and required 104 lbs/ac of N compared to needing only 42 lbs/ac if red clover had been included, the cost savings was considerable. At $0.42/lb of N the fertilizer cost difference is $26.04/ac (104 - 42 lbs N/ac x $0.42/lb N). The cost of getting the red clover in would be about $10/ac for seed (6 – 8 lbs/ac x $1.25/lb) and possibly $5 - 8/ac for application. The net benefit of the red clover could be $8 - 16/ac. On 500 acres of corn, that would be a savings of $4,000 – 8,000.

All that is great, but we have to consider the costs and risks as well. The risk would be getting a uniform stand of red clover. There is also a cost associated with managing the red clover by tillage or herbicide. These costs depend on the changes that would be required in your system. If you fall plow, then no additional cost occurs. If you are a no-tiller and have to add another herbicide into the system, costs increase. The other negative is that although on average we expect 72 lbs/ac of nitrogen contribution to the next crop, poor spring conditions can lower that level or delay its availability.

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Weather Impacts On N Availability – The Good

The Long Term Crop Rotation Trial at Elora is summarized in Table 2. To profile extremes in spring weather and the impact on red clover nitrogen availability we use 1998 and 1996. In 1998, when the spring weather was good for crop growth and nitrogen mineralization (#1), the inclusion of red clover in the rotation previous to corn resulted in a high level of available nitrogen in the soil on June 1^st of the corn year. The nitrogen recommended from the PSNT and confirmed using MERN at the end of season, was 0 lbs N/ac (#2).

It is interesting that the nitrogen advantage from the red clover was equal to having two years of alfalfa in the rotation previous to the corn. This would suggest that the inclusion of red clover for a March to November period of a single year gave an equal benefit as a longer term forage rotation.

From Elora Long Term Rotation Study, U. of G

Weather Impacts On N Availability – The Bad

The risk of relying on nitrogen contribution from red clover occurs when the spring weather is poor, as experienced in 1996. The nitrogen available from the red clover was significantly lower than in 1998 (#3), and was not close to meeting the requirements. In this situation, 107 lbs/ac of additional nitrogen was recommended, and 110 lbs/ac (#4) was the actual MERN. The benefit from having red clover in the rotation, despite a uniform stand, was not much better than a narrow rotation of corn following soybeans or even continuous corn. The nitrogen in the red clover likely became available later in the season, but would have been of negligible value to the corn crop. Corn has its big nitrogen demand from late June to late July.

Keep in mind that the spring weather in 1996 was extreme. What this does suggest is that when incorporating organic sources of nutrients into the production system, more management has to occur. We should include a starter nitrogen program to ensure that early growth is not limited. When a cool backwards spring occurs, be prepared to conduct a PSNT test in June to ensure that sufficient nitrogen is available. If not, we need the ability to apply commercial nitrogen to overcome the organic source shortfall.

Other Benefits

Other benefits of red clover are more difficult to quantify but do make a positive contribution to the overall health and productivity of the crop rotation. These include addition of organic matter, improvements in soil structure and water holding capacity, and weed suppression.

Next issue we will explore some of the production techniques that may help create a vigorous, uniform stand of red clover when seeded into next springs wheat fields.

Related Links:

• Ontario Corn Nitrogen Calculator

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