Managing Nitrogen Efficiently
in Nebraska Crop Production

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Two warm winters in a row decreased demand for natural gas until this season, when extremely low temperatures and increased use of natural gas to generate power drove the demand sky-high and more than doubled the price over last year. Natural gas producers are increasing production, but supplies will likely remain tight through this winter, according to the American Gas Association.

Natural gas accounts for 70 percent to 80 percent of the cost of producing anhydrous ammonia fertilizer, the most common nitrogen fertilizer for corn. The rapid price increase enticed some anhydrous ammonia manufacturers to shut down their plants and simply sell natural gas for a quick profit. That means anhydrous ammonia supplies also may be short. Farmers who need anhydrous ammonia for this year's corn crop will find prices around $400 per ton or 25 cents per pound of nitrogen, compared to $245 per ton or 15 cents per pound a year ago. For a farmer applying 150 pounds of nitrogen per acre, those prices translate into production costs $15 per acre higher than last year.

"The goal this year is to reduce input costs without sacrificing yield," Shapiro said.

Yield goals are a factor in calculating the amount of nitrogen to apply. The NU Institute of Agriculture and Natural Resources specialist recommends a conservative approach.

"Based on the price of nitrogen and the price of corn, it is best to use an average yield goal that is 5 percent greater than the five-year average," he said. "If the corn is under irrigation and there is less potential variability in yield, there is less justification in raising the yield goal at all."

Sticking to the university's recommended nitrogen application rates also can cut costs.

"When nitrogen prices are this high, it doesn't pay to add extra fertilizer," Shapiro said. "The probability of an increase in yield doesn't justify the increased input cost."

In calculating the amount of fertilizer needed, farmers should factor in the amount of nitrogen already available in soil and irrigation water as well as residual nitrogen from manure applied as fertilizer and legumes grown previously on the field.

"Take as many credits as you can, then put out commercial fertilizer to make up the balance," Shapiro said. "Any free nitrogen you can get will save you money this year."

Last year's dry conditions may have increased the amount of nitrogen available in the soil, so deep soil testing -- down to at least 2 feet -- is a good idea.

"Last year, farmers may have put out nitrogen for 150 bushels of corn, and they only got 100 bushels because of the dry weather. Some of that nitrogen could still be there," Shapiro said. "Also, normal soil processes release nitrogen, but the process doesn't work when it's dry. It is likely that spring rains will trigger additional nitrogen release."

Other careful cutbacks can help reduce fertilizer costs. Shapiro recommends site-specific soil sampling to determine which growing areas need phosphorus and potash and applying these fertilizers only to those areas. Also, farmers who normally apply starter fertilizers to help plants pop up early might consider holding off this year.

"Any way that you can save a few bucks will be helpful," Shapiro says. "However, if you have a soil fertility deficiency that needs attention, fix it."

If, once the nitrogen credits are added up, farmers can't afford or can't find enough commercial nitrogen fertilizer for their corn, there is still hope. Applying 60 percent to 70 percent of the crop's nitrogen needs early, then applying the rest after the corn emerges in the spring, is a reasonable alternative.

"A spinner-spreader used when corn plants are small works well with urea fertilizers," Shapiro said. "Then you have to cultivate the urea into the soil, wait for rain or irrigate it in to avoid any losses."

Waiting until spring to complete nitrogen application also may bring a welcome price break, said Don Johnson, chair of the agronomy education committee of the Nebraska Fertilizer and Ag-Chemical Institute Inc.

"In the late spring or early summer, the natural gas markets should stabilize to some extent and anhydrous ammonia plants should be running again, so we should see a better supply and better prices," he said. "Also, when prices fluctuate like this, we tend to see more imports of fertilizers, like urea, from other countries. Added competition from imports generally brings prices down."

Shapiro said careful decision making can ease the burden of high input costs combined with low corn prices.

"This is the time to fine-tune your farm management skills," he said. "Follow the university recommended nitrogen application rates, stick to reasonable yield goals, and keep looking for less expensive alternatives."

The recent rise in natural gas prices is driving up fertilizer costs. The price of anhydrous ammonia, the most common nitrogen fertilizer for corn, doubled in the last year. Higher fertilizer costs combined with low corn prices puts farmers in a challenging situation this year.

"We can't lower the price of anhydrous ammonia, but we can help you manage your input costs," said Charles Shapiro, a soils specialist at NU's Haskell Agricultural Lab near Concord, Neb. "We have an extensive database of nitrogen field research and demonstrations where various nitrogen rates have been applied to corn and the yields have been measured. These studies can help farmers make smart decisions on nitrogen application."

Through 20 years of on-farm testing, NU Institute of Agriculture and Natural Resources scientists have developed a specific method for determining optimum nitrogen rates for corn. There always is some yield variation, but the data is fairly consistent throughout Nebraska.

"What we have found is that when we use the NU recommendations, which account for a variety of nitrogen sources such as soil and irrigation water nitrates, previous legume credit and manure use, we get corn yields that are within 3 bushels of the maximum," Shapiro said. "We have also found that when you apply 50 pounds less than the NU recommended nitrogen rate, you lose about 6 bushels of corn per acre."

The NU recommendations put producers very close to maximum yields, but at nitrogen rates that are 30 to 50 pounds per acre less than what many farmers apply. At today's prices, the savings on 50 pounds of nitrogen easily could add up to more than $10 per acre.

Using a realistic yield goal also is part of the recommendations. Shapiro suggested using a five-year average plus 5 percent.

"Our research shows that many farmers use a yield goal higher than that, but fail to reach the yield goal 50 percent of the time," he said.

Shapiro noted that following the university's recommended nitrogen application rates and setting realistic yield goals may be particularly helpful this year.

"Many producers have been told that nitrogen fertilizer supplies may be short by 50 percent to 75 percent," he said. "Following our recommendations may show those farmers that 75 percent to 80 percent of their past nitrogen use per acre is actually closer to the amount proven to be the most profitable, especially at today's nitrogen prices."

When fertilizer prices fluctuate, nitrogen use can be increased or reduced accordingly. Shapiro's research shows that when corn is $2 per bushel and nitrogen is less than 13 cents per pound or $210 per ton of anhydrous ammonia, it is profitable to add 50 pounds of nitrogen to NU's recommended rate. However, when anhydrous ammonia prices rise above 22 cents per pound of nitrogen or $364 per ton, it is profitable to reduce the recommended rate by 50 pounds. This analysis doesn't include the application costs.

"Using data from 35 nitrogen demonstrations on sandy soils, average yields were 156 bushels per acre when the total nitrogen applied was 50 pounds less per acre than recommended," Shapiro said. "At the recommended rate, the yields were 162 bushels, and at 50 pounds more than recommended, the yields were 165 bushels. Other researchers have found similar results in other areas of the state."

Reports indicate anhydrous ammonia supplies are limited and the cost of nitrogen, if available, will be near the point where reducing nitrogen by 50 pounds per acre from the recommended rate will be profitable, Shapiro said. If prices continue to rise to 30 cents per pound of nitrogen, he suggested using 75 percent of the university's recommendation for nitrogen, then monitoring the crop and adding more nitrogen by side-dressing if nitrogen deficiency symptoms appear.

"While high fertilizer costs and low corn prices are discouraging to farmers, using NU's recommended nitrogen application rates can help reduce the negative impact," Shapiro said.

“Fortunately, one positive outcome of the warm and dry 2000 season appears to be an increased rate of soil mineralization,” explained Mick Reynolds, a University of Nebraska extension technologist at the South Central Research and Extension Center near Clay Center, Neb.

Mineralization is a term used to describe the conversion of organic forms of nutrients, which are not available to a plant, to inorganic forms that the plant can utilize. Because of this increased soil mineralization, more residual nitrogen is being found in soil samples. Increased nitrogen can translate into increased savings for the farmer through lower fertilizer inputs.

University of Nebraska Cooperative Extension technologists working on the Wellhead Area Protection Project (WAPP), an irrigation and nutrient management demonstration project funded by the Nebraska Department of Environmental Quality, the Upper Big Blue NRD and the Little Blue NRD, report they are finding increased soil residual nitrate-nitrogen in soil samples they have taken from demonstration fields. Increased soil residual nitrate-nitrogen rates are also being reported by area crop consultants and soil testing labs.

“Many of the fields are showing levels of residual nitrate-nitrogen twice as high as compared to last year,” said Reynolds. Some field soil samples “are even showing a four-fold increase over last year’s levels.” The increased nitrate-nitrogen residuals “provide an opportunity for farmers to significantly lower crop input costs,” explained Reynolds. Allowing a nitrogen credit for nitrate-nitrogen residuals stored in the soil reduces the amount of nitrogen required to meet the needs of the crop and helps farmers continue to protect our water resources.

So how can farmers make sure they get the nitrogen credit they deserve? The best way is by taking a representative soil sample of each field to determine the level of residual nitrate-nitrogen, explained Reynolds. For most soils, the depth of the soil sample should be three feet deep, unless crop-rooting depth is limited due to soil conditions such as coarse sand or a high water table, and then a minimum of two feet could be used. However, Reynolds warned that a three-foot sample was more accurate and the preferred depth to use.

Once the residual nitrate-nitrogen content of the field is known, a nitrogen credit can be determined to help offset the nitrogen input needed by the crop. With anhydrous ammonia costs nearing $325 per ton, substantial savings can result from allowing for the residual nitrate-nitrogen credit.

One example, taken from results at one of the WAPP demonstration sites, illustrates the potential savings that farmers may be able to realize. The residual nitrate-nitrogen credit, derived from a three-foot soil sampling, showed there was 100 pounds of N per acre in the soil available for crop use. Figuring anhydrous ammonia costs at $325 per ton gives the residual nitrate-nitrogen a value of $19.80 per acre. Following University of Nebraska soil sampling guidelines, the projected cost for nitrate-nitrogen soil lab analysis will be approximately $0.20 per acre. This results in a net value of $19.60 per acre. However, Reynolds reminded readers that the actual costs associated with collecting the sample were not included in this figure.

If a soil sample is not taken, a default value of 32.4 pounds per acre is assumed. Further savings can be achieved by taking into account nitrogen adjustments for soil organic matter, legume, manure and other organic wastes, as well as any irrigation water nitrogen credits that are available. “This year, farmers have even more reason to take the credit they deserve,” said Reynolds.

For more information on this issue, check out the following Cooperative Extension publications: