Getting the Most from Your 2004 Nitrogen Dollars in the Corn Belt
By Harold Reetz, Tom Bruulsema, and Scott Murrell1
High natural gas prices are forcing nitrogen (N) fertilizer prices upward. Natural gas is used as a feedstock – a source of both energy and of the hydrogen to combine with N from the air to form ammonia (NH3) in the production of anhydrous ammonia. Each ton of ammonia requires 25 to 34 million btu of natural gas, plus additional energy for handling and shipping. The increase in prices is causing many farmers to re-evaluate their N plans for 2003, and may lead them to adjust rates or consider changing to a crop that uses less N. The information here is presented to help with those decisions.
Since all other N fertilizers…urea, urea-ammonium nitrate (UAN) solutions, and ammonium nitrate…are produced from NH3, prices for these products may increase as well. Some N products are imported from other countries where gas prices have not increased as much, so their relative increases in price may be less.
Phosphorus (P) and potassium (K) applications may also be evaluated. Usually P and K management are planned for a long-term, so any deviations from that plan should be made cautiously. It is important that P and K be maintained at optimum levels in order to get most efficient use of the N that is applied…a consideration that is even more critical with the higher N price.
Dealing with Higher N Prices
Data collected from 50 Illinois environments where corn followed soybeans and from 28 environments where corn followed corn provided N response curves that form the basis for Illinois N recommendations (Figure 1). The optimum N rate is that place on these curves where the last pound of N was just paid for by the yield increase from that N.
Figure 1. Nitrogen response curves for corn in Illinois.
Figure 2 illustrates the impact of increased N price on the optimum N rate for corn priced at $2.30/bu. Based on the Illinois response curves in Figure 1, this analysis includes a $0.22/bu charge for handling and drying costs. Note that the N price impact on optimum N rate is slightly greater for corn following corn. However, even substantial changes in N price do not markedly change the optimum rate.
Figure 2. Optimum N rate for corn after corn and corn after soybeans at varying N price. Based on University of Illinois N response studies, using corn @ $2.30/bu less $0.22/bu for handling and drying costs.
Table 1 is based on the same data used in Figure 2, for corn priced at $2.30/bu. These data suggest a reduction of about 6 to 10 lb of N/A for each 5-cent increase in the price of N per pound, which is equivalent to an increase of $82.00/ton of ammonia. In both rotations, adjusting the N rate downward to accommodate a 5-cent increase in the cost of a pound of N will result in a yield decrease of only about one bushel per acre.
Table 1. Effect of changing N price on rate of N needed to attain economic optimum yield and the effect on yield of changing the N rate.1
1Since the locations used in the continuous corn studies were not all the same as those used for the corn-soybean studies, the data in this table cannot be used to determine the N reduction appropriate for corn after soybeans.
This does not mean that profit will not change as N costs increase: a price move from $246/ton (15 cents/lb) of ammonia to $492/ton (30 cents/lb) would mean a reduction in N rate from 177 to 157 lb/A for corn following soybean, but the cost of N per acre would rise from $27 to $47, or by $20/A, and the yield would drop by 2 bu/A, for a loss in income of $4.16, totaling a drop in net revenue of $24/A. For corn following corn, the comparable figures would be an increase in N cost from $26 to $44/A, and a decrease in yield of about 1 bushel, for a decrease in income per acre to N of about $22/A. So, increasing N price does reduce profit, but reducing N rate may be the wrong reaction to take.
Balance N with Adequate Phosphorus (P) and Potassium (K)
The 2001 report, Summary of Soil Test Levels in North America, PPI/PPIC/FAR Special Publication 2001-1, indicated a serious depletion of P and K levels. These two other primary nutrients must be at optimum levels to maximize efficiency in N utilization by the crop. It is poor management to lose N because P or K levels are not adequate. Nitrogen and P boost each other’s uptake, particularly in starter fertilizer programs. High P levels in the plant help the transfer of energy necessary to assimilate the N into organic compounds, like amino acids, proteins and enzymes that are critical for plant growth. Phosphorus is essential to all energy conversion processes in plants.
Adequate K supports efficient N utilization, because K helps regulate the enzymes that assimilate N into critical biochemical compounds. Potassium is also critical to maintaining the water relations in crops, and adequate K helps reduce negative impacts of drought and other stresses. Figure 3 shows the impact K level can have on corn yield response to N. Increasing the soil test K level reduced the amount of N required to reach optimum yield, and the optimum yield was higher with less N when K was adequate.
Figure 3. Corn response to N and soil test K. Data from Johnson, et al., Ohio State University, 1997.
Without adequate P and K to balance N, photosynthesis and N assimilation are reduced, growth is reduced, maturity is delayed, and yield is reduced. Without adequate P and K, yield potential is never realized, regardless of the amount of N applied. Maintaining P and K fertility is critical to maximizing N response. This may be the best advice you could give your farmer customers this year.
Limited N Supplies
Because of the high gas prices, some of the manufacturing facilities were shut down, leading to a possibility of tight supplies of some N products in some areas. To get the most efficient use of applied N, or if the total amount of fertilizer N needed for all acres cannot be obtained, growers should consider each of the following suggestions in planning N programs.
Allocate fertilizer across all corn acres: Since the yield response to applied N is greatest for the first units of N applied, allocate the available supply across all fields as a percentage of the amount of product available. As shown above, reductions in application rates of 10% and often as much as 20% will have minimal impact on yield provided current levels are optimum. However, not applying any N fertilizer in the experiments reported in Table 1 resulted in yields of 106 and 83 bu/A, respectively, for the corn-soybean and continuous corn rotations.
Take credit for homegrown N: Corn yield is almost always better for corn following another crop, especially a legume, and the N requirement is less for corn following a legume than for corn following corn or grass. Reduce the N application for corn following soybean. Many studies have shown that corn following a good stand of alfalfa needs no additional fertilizer N. At the very least, reduce N application by 100 lb/A for corn following alfalfa.
Use alternative N sources: Utilize livestock manure, whether your own or from a neighbor, as a N source.
By-product fertilizers, such as urea or ammonium sulfate solutions, may be available from industries. Liquid urea should be incorporated to avoid volatilization loss.
Change crop rotation: In the unlikely event that you are not able to get enough N, consider shifting part of the acreage to a legume such as soybean. Soybean following soybean will yield about 10% (4 to 5 bu) less than soybean following corn. Growing second year soybeans will increase the potential for disease and nematode problems, so use care in selecting varieties.
Use proven crop production practices: N use efficiency will be optimized when soil pH is maintained above 6.0, and soil P and K tests are maintained at the optimum level for your soil type. Use proven practices to control weeds, insects and diseases. Plant adapted, high yielding varieties for your area.
When injecting anhydrous ammonia, make sure soil conditions will allow for good sealing to prevent volatilization.
Consider using a nitrification inhibitor with anhydrous ammonia.
If at all possible, inject urea or UAN into the soil. For surface application, incorporate within 2 to 3 days with a field cultivator or disc. A rotary hoe will not do as good a job, but is better than not incorporating.
If incorporation is not possible, apply urea or UAN within 1 to 2 days of anticipated rain or irrigation.
If surface applying, avoid applying urea or UAN when temperatures are high and/or soils are moist and the surface is drying rapidly. Significant N volatilization takes place during these conditions. Utilize a urease inhibitor if applying in conditions that favor volatilization.
Split apply N. Apply half to three-fourths of your N needs preplant, a small amount as a starter fertilizer, and the remainder sidedress. This maximizes the crop’s utilization of the N and reduces the chance for significant N loss from denitrification or volatilization.
Plan for a Good Year
All management decisions should be made in anticipation of a good production year. Following best management practices will support the most return from a good year, and will best protect from losses when problems arise. It is rarely possible to anticipate which specific problems will confront the crop in any given year.
Acknowledgements
Some of the information above was adapted from previous publications from 2001 when a similar spike in N prices occurred.
GETTING THE MOST FROM YOUR 2001 NITROGEN DOLLARS, 2001. R.G. Hoeft and E.D. Nafziger, Department of Crop Sciences, University of Illinois.
Maximize Efficiency of Nitrogen Fertilizer Programs This Spring, 2001. Kim Polizotto, PCS Sales.
1 Dr. Reetz is the Foundation for Agronomic Research (FAR) President, located at Monticello, Illinois; e-mail: hreetz@ppi-far.org.
Dr. Bruulsema is PPI/PPIC Eastern Canada/Northeast U.S. Director, located at Guelph, Ontario; e-mail: tbruulsema@ppi-far.org.
Dr. Murrell is PPI Northcentral Director, located at Woodbury, Minnesota; e-mail smurrell@ppi-far.org