Economics | Forage | Horticulture | Livestock | Soils | Wildlife

How do I figure the actual cost per pound of nitrogen fertilizer?
Assuming the fertilizer value is based solely on nitrogen (N), take the dollars per ton and divide by the pounds of N in that ton. Fertilizer analysis is given on a percent basis so 82-0-0 (anhydrous ammonia) has 1640 lbs of N per ton, 46-0-0 (urea) has 920 lbs of N per ton, 34-0-0 (ammonium nitrate) has 680 lbs N per ton, 32-0-0 (UAN liquid) has 640 lbs per ton, etc.

For example:
• $500 per ton 82-0-0 is 500 divided by 1640, which equals $0.30 per pound of actual N;
• $460 per ton 46-0-0 is 460 divided by 920, which equals $0.50 per pound of actual N;
• $440 per ton 34-0-0 is 440 divided by 680, which equals $0.64 per pound of actual N; and
• $300 per ton 32-0-0 is 300 divided by 640, which equals $0.46.

What can I plant this summer for a hay crop?
Summer annual grasses such as sudan, sorghum sudan and forage sorghum are commonly planted in the Noble Foundation service area. Other options include pearl millet, foxtail millet, and soybeans.
Each species has its own advantages and disadvantages. Foxtail millet is the fastest maturing, often making a crop in just 60 days. However, it has less production potential than the others and it cannot be fed to horses. Pearl millet does well on sandy soils and is very efficient with nitrogen fertilizer. Sudan and sorghum sudan hybrids may be the most productive and yield multiple cuttings but also require the most nitrogen fertilizer. The advantage to soybeans is that they are a legume and can produce their own nitrogen.
Whichever you use, be sure to review variety test information for your area such as http://www.noble.org/Ag/Soils/NFEvaluates or your local land grant university. Also be sure to consider if it is cheaper to plant a hay crop each summer or use that money to apply more fertilizer to perennial pastures such as bermudagrass.

What fertilizer should I apply?
While that may seem like a simple question, it really is not. The fact is, we cannot answer that question with any amount of accuracy without a good soil test. While all plants require fertilizer nutrients, particularly nitrogen-phosphorus-potassium (NPK), the amount required depends on the plant and the soil in which it grows. The best answer to this question is obtained by having a recommendation made from a good soil test. In the absence of a soil test, any fertilizer recommendation is merely a guess. For more information see, "Do I need to soil sample, and why?"

What do the numbers on fertilizers mean?
The numbers on a fertilizer tag are the percent by weight of each nutrient and are always listed as nitrogen-phosphorus-potassium (N-P₂O₅-K₂O) in that order. N-P₂O₅-K₂O are more often presented as simply N-P-K, but the former is more technically correct. Sometimes there may be additional numbers at the end for sulfur and other nutrients. Therefore, 34-0-0 is 34 percent N, 46-0-0 is 46 percent N, 18-46-0 is 18 percent N and 46 percent P₂O₅ phosphate ion, 0-0-60 is 60 percent K₂O potash, 13-13-13 is 13 percent N, 13 percent P₂O₅ and 13 percent K₂O, and 10-20-10-5S is 10 percent N, 20 percent P₂O₅, 10 percent K₂O and 5 percent sulfur. So, from the examples above, a 50-pound bag of fertilizer may have 5 pounds of N, 23 pounds of N or something in between. Remember, we are working in percentages. Likewise, a ton of fertilizer may have varying pounds of N, P and K, depending on its analysis. This means that 100 pounds per acre of fertilizer is very vague. What is important to know is the pounds of actual nutrients. Again, these are always listed as nitrogen-phosphorus-potassium (N-P₂O₅-K₂O), in that order, and are listed as a percent by weight. To figure pounds of actual nutrients, take the pounds of fertilizer product and multiply by the percent of each nutrient on the tag – this gives you the pounds of actual nutrients.

What's the difference between 34-0-0 (ammonium nitrate) and 46-0-0 (urea)?
Ammonium nitrate is 34 percent actual nitrogen (N) by weight. In every 100 pounds of ammonium nitrate, there are 34 pounds of actual N or 680 pounds of actual N per ton. It provides both the ammonium and nitrate ion form of N, which provides a quick green-up. Its agronomic properties are excellent.

Urea is 46 percent actual N by weight. In every 100 pounds of urea, there are 46 pounds of actual N or 920 pounds of actual N per ton. It must be converted into the ammonia form and then to the ammonium form before it can be used by plants.
Both are dry N fertilizer sources. Both usually cost about the same price per ton. However, since there is more actual N per ton of urea, it is almost always the cheaper source on a pound of actual N basis.

The biggest problem with urea is that some of it, typically not more than 20 percent to 30 percent, can be lost to the atmosphere as ammonia gas. This occurs when it is applied to the surface of warm, moist soils in humid regions. Some ways to alleviate this problem are to incorporate urea with tillage or water, apply it when temperatures are cold or when rain is expected within two days, or apply it in a narrow band.

The biggest problem with ammonium nitrate is that it is a common ingredient in fertilizer/fuel oil explosives that have gained so much attention since the mid-1990s. This has made it much less available in the market due to security and documentation concerns.

Either source can work very well for crop or forage production – they just need to be managed and used properly.

Can I use urea-containing fertilizers without losing nitrogen to volatilization?
Yes. If the urea fertilizer is incorporated with tillage, rainfall or irrigation soon after application, there should be no nitrogen (N) lost to volatilization. Typically, we like to see incorporation occur within 48 hours after application. A urease inhibitor can also be added to urea fertilizers to give a much longer window – up to two weeks – for incorporation to occur. If water is the incorporating agent, it requires greater than 0.25 inches of rain or irrigation.
Also, if urea-containing fertilizers are used when temperatures are lower than 60 degrees F, then N losses are minimal because the enzyme that converts the urea to ammonia functions more slowly at colder temperatures.
For further reading, many articles can be found at www.noble.org/Ag/Research/Soils.htm.

Do I need to soil sample and why?
Yes, you need to soil sample, because it is the most accurate way to determine the nutrient-supplying ability of soil and the necessary amount of fertilizer and lime required to correct any deficiencies. Applying fertilizer without a soil test could result in over- or under-fertilization, which costs either in extra money spent or yield lost.

For further reading:
All I Want for Christmas is a Soil Sample from You...
Be Smart With Your Fertilizer Dollar
Soil Testing Makes Money

Should I fertilize or weed spray?
This question is really too complex to answer briefly, because details about the forage are necessary to determine the right answer. Some of these questions are: what type of grass is it, what condition is it in, what are the soil test results, what weeds are present, how is the forage used, are other factors more important than production and economics, like aesthetics, etc. There are some general rules, though. Generally, native grass does not respond economically to fertilizer. Generally, weed spray in native grass is also not economical and is addressing symptoms of larger problems. Generally, in introduced grasses, for every pound of weeds you control you get a pound of additional grass. However, there are always exceptions to these rules.

For further reading, see:
To Fertilize and Spray For Weed Control, Or Not To, That Is The Question
To Fertilize or Not to Fertilize???
Stretch Your Input Dollars
Tips for Coping With The High Cost Of Fertilizer

What can I do about fire ants?
The short answer is to learn to manage them. If you have them, you will probably never get rid of all of them. If you don't have them now, you probably will some day. The first step in management is to identify the problem. Red imported fire ants often build raised mounds of soil with no obvious entrance hole. When this mound is disturbed, the ants will swarm out. Identification is important because it is thought that some native ants may be enemies of fire ants, so don't assume all ants are bad and kill those that may be beneficial. Once you have determined the need to treat, the "Two-Step" process has proven to be most effective. With this method, insecticide bait is applied to a large area. The fire ant workers take this bait back to their mounds where others eat it and die. Several days after the bait is applied, contact insecticide is used on individual mounds to kill surviving ants. Before purchasing or using any insecticide, be sure to read the label and see if it was made for your intended use. For good control, use the insecticide exactly as the label says. Once you have fire ants under control, be vigilant against new invasions so they can be treated before populations have a chance to build. An excellent Web site with additional information is fireant.tamu.edu.

Additional information is also available at:
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2333/CR-7309web.pdf
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-3059/CR-7193web.pdf

When do I take a soil sample?
Any time is a good time to take a soil sample. However, spring is a good time to sample for summer crops and summer is a good time to sample for fall and winter crops. A sample taken 2 to 4 weeks before fertilizing for planting or plant growth allows time to get results back, but is also close enough to the time of use to take into account residual N. Samples should be retaken at least every 3 years and more often for high-value or high-input crops.

Where can I buy a soil probe and which one should I get?
There are many suppliers. Gemplers, Forestry Supply, Ben Meadows. Everyone has their opinion on which one is best. Some have foot pegs, some are long and some are short, some have removable handles and extensions that can be added. One personal favorite is the 19 inch JMC nickel plated. It is strong and short so you can get your weight over it.

Where do I send a soil sample, and what information do I need to send with it?
Fertilizer and lime recommendations vary greatly depending on local conditions and crops. Be sure to use a lab or consultant that understands the local conditions in your area. For assistance, contact your local county Extension office or the Noble Foundation. Wherever you send your soil sample, be sure to include this information with it: your name and contact information, name of field, intended crop, yield goal, what county the field is located in, if the crop is already established, etc.

For more information, see:
Soil Fertility Specialists Need Information to make Recommendations