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With crop fertilizer, there can be too much of a good thing

By Matt Reese

Consultant Joe Nester looks at a corn plot with 150 pounds of total N, a rate that, in many cases, is still meeting or exceeding the plants' nutrient needs.

Nitrogen is a critical nutrient in corn production and farmers, crop consultants, the Joyce Foundation, the Natural Resources Conservation Service and the Environmental Defense Fund (EDF) are teaming up to find out how much a productive corn crop really needs.
In the past, nitrogen applications have been based on the yield potential of the field.
In the past, when the N cost was very low, the safe bet was to add a little extra to make sure that it was not the limiting factor in corn production. High N cost and increasing awareness of the potential water quality impacts, however, have made that safe bet of the past not so safe anymore. But determining how much N is needed to maximize corn production while minimizing costs and environmental impact is not easy.
In the On-Farm Network of N research plots in part of the Lake Erie Watershed in northwest Ohio, crop consultant Joe Nester has been working extensively to target the ideal rate of the nutrient for the specifics of each unique situation in the field.
“We are getting good data now and we’re getting guys ratcheted into a finer N rate. As tight as the economics are in agriculture, you can’t spend money on N that you do not need,” Nester said. “We’re trying to get a target pretty close to what the crop is going to need for optimal yield. This isn’t something that you can say, ‘We’re going to raise 160 bushel corn and we need this much N.’ That is not the case at all. This can vary by farming operation, practice, soil condition, weather, drainage and a whole bunch of different things that come into play. But with this program, farmers are learning about what affects their N and they are making some adjustments in their application with the rate and the timing of their N.”
The soil and the plant can only handle so much N, the rest leaves the soil, often in the water. Nester is working to find out how much the N application rate can be reduced without hurting corn yields. The study includes N rate test plots in the fields, soil samples, aerial imagery, corn stalk nitrate tests and yield data. This is a tremendous logistical effort that is time consuming, but it provides a fairly complete picture of how much N is needed.
Nester is working with 90 farmers in his area and the On-Farm Network is also tied in to identical projects in several other watersheds around the country. The results have been surprising in that the most productive soils are often requiring the least amount of N.
“We’re finding that the highest yielding areas of the field top out at the lowest N rate and the lowest yielding areas of the field might need more N to reach an optimum yield — exactly opposite of what we thought before,” he said. “The reason is recoverability. In the good areas of the field, I may have three times the root system I have in the poor areas of the field so the plant can recover more N.”
While every field is different, there are some trends showing up.
“We don’t want to be short because we know the penalty, but we want to find that breaking point. By going down to 100 pounds, we usually do. Weather comes into play then. We’re never going to pin this down exactly, but the farmers are learning how much N they need for their different conditions,” Nester said. “In many cases that 100 is our break point. In the first year, we tried 50 pounds and that was always too low. We were always losing money there. In the last couple of years we are finding that N rates were often optimized between 100 and 150 pounds of N.”
These results are allowing farmers to reduce their N rates accordingly, which improves the profitability and environmental sustainability of their farms.
“We’re finding that farmers who participate in the program are reducing N use by 10% to 20% because they see that they can do this and be more profitable,” said Karen Chapman, Great Lakes regional director for EDF. “This is not an environmental program, this is an economic program. Reducing nitrogen offers an economic value to producers and they are contributing to improving water quality at the same time.”

For more about the On-Farm Network, visit http://www.isafarmnet.com/#.

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