Fluid Fertilizers

Are there differences in plant use between liquid and dry fertilizers?
      No. Properly applied, fluid fertilizers are no more or less efficient than dry fertilizers. Most fluid fertilizers contain the same basic ingredients as dry fertilizers. The only difference is that fluid fertilizers are dissolved in water, and dry fertilizers are not.
      Efficiency of fluid fertilizers is determined by the way they are applied. Proper application methods are discussed below.

What are the major types of fluid fertilizers, and what are the differences between them?
      The major types of fluid fertilizers are suspension fertilizers and solution fertilizers. Solution fertilizers are dissolved completely in water. Suspension fertilizers are partially dissolved in water, but some of the nutrients, particularly potash, are suspended in the water in the same way mud is suspended in water. Suspension agents are used in suspension fertilizers (typically a clay material) to keep the fertilizer material from settling out.
      You may store true solution fertilizers as long as the temperature stays above freezing. You should apply suspension fertilizers on the same day the dealer blends them.

What are some common grades of solution fertilizers, and of what are they composed?
      The two most common grades of solution fertilizer are urea-ammonium nitrate solutions (UAN). Basically urea and ammonium nitrate are dissolved in water. Because of the urea content, to avoid volatilization losses of nitrogen (N) to the atmosphere, you must follow the same constraints in managing UAN as you do for dry urea. Avoid surface applications in hot, dry weather. When used in reduced tillage, larger droplets help slow losses by volatilization.
      Thirty-two percent UAN (32-0-0) weighs 11.06 lb per gallon and will salt out at 32°F (the solids separate from the liquid).
      Twenty-eight percent (28-0-0-5) contains 5 percent sulfur in addition to the N. You can use it where you expect a response to sulfur, such as on sandy textured, low organic matter soils. It is manufactured by adding ammonium thiosulfate to UAN. It weighs 11.1 lb/gal and has a salting out temperature of about 0°F.
      Other common solution fertilizers are based on dissolving ammonium polyphosphate in water. These grades (10-34-0 and 11-37-0) are often applied as starter fertilizers in row crop production. Weights and salting out temperatures are available from vendors.
      Other grades of solution fertilizers are available. Mentioning or not mentioning a product in this publication does not mean we endorse any particular product.
      All solution fertilizers are low in potash because no more than 11% potash will go into solution, and 9% is more practical to manufacture. Most fluid fertilizers containing greater than 9% potash are suspension fertilizers.

What are suspension fertilizers? Why can they contain more potash than solution fertilizers?
      Suspension fertilizers are products in which the fertilizer is not held in a true solution but is held in a suspension, much like mud in water. Suspending agents, such as attapulgite clay, are used to prevent the fertilizer material from settling out.
      You can blend more potash into a suspension fertilizer because it does not actually have to go into solution to remain dispersed in the liquid. Suspensions will settle out if you don't use them soon after blending, so you should use suspension fertilizers the same day they are blended.
      Some contact herbicides, such as paraquat, are deactivated by binding to negatively charged clays. If the application contains paraquat, you must use suspending agents without negative charges. These suspending agents (for example, xanthum gum products) are usually more expensive than the clays otherwise used in formulating fertilizers.

What are some common grades of suspension fertilizers?
      Almost any grade of suspension fertilizer can be blended, so there is no standard analysis.

How are fluid fertilizers applied?
      Fluid fertilizers are chiefly applied by broadcast spray, dribble, knife-in, or starter placement. Each method has advantages and disadvantages.
      Broadcast spray. Most suspension fertilizers are broadcast sprayed, but there are some situations where broadcast sprays are not advisable.
      Avoid broadcast sprays of UAN solutions whenever possible on hot, dry days unless the material will be cultivated in, irrigated in, or rain is imminent. A great deal of the applied N can be lost to the crop when the air temperature is above 70°. This loss can be lessened by rain occurring within 2-3 days.
      Nitrogen solutions are popular for grasses and small grains. However, you should avoid broadcast application to rapidly growing crops. Leaf burn may occur on small grains when you make combined broadleaf herbicides and N applications.
      Dribbling. Dribbling is applying fluid fertilizers in narrow bands in either large drops or small streams. Distance between bands depends on the individual situation.
      Concentrating the material in very small areas generally lessens potential nitrogen loss from the urea in UAN solutions. Less of the crop is touched by the material, so there is less potential for crop burn. Because the drops are larger than in broadcast sprays, they roll off the plant rather than staying and causing burn. Adoption of dribbling is limited because accurate application requires special equipment. Dribbling covers only small portions of the total field, so pesticides cannot be efficiently combined with the fertilizer when you use this method.
      Knifed-in. Using knife equipment allows precise placement of fertilizer material with respect to the plants. This is an excellent method of sidedressing crops because volatilization losses are lessened by placement within the soil, and there is no danger of crop burn from overhead sprays.
      The major disadvantage with subsurface application is the required specialized equipment. And, as with dribble application, pesticide application cannot be combined with the fertilizer because of the limited coverage area.
      Starter. Fluid fertilizers are often used as a starter or pop-up material, in particular on corn and grain sorghum. Starter refers to fertilizer applied in a band near the row at planting; popup is fertilizer applied directly with the seed. Applying N and P in localized zones promotes root proliferation near the placed fertilizer, but yield response depends on growing conditions and the effect of all management practices.
      Most solution fertilizers should be avoided as popup fertilizers, since ammonia is extremely toxic to emerging seedlings.
      Rates used in popup applications depend on the salt index of the fertilizer. You should not apply a salt index of greater than 5 in a popup application (directly with the seed). Salt index is determined by adding the amount of N to the amount of potash used. Phosphate does not contribute to the salt applied. An example is that if a 7-12-7 is used at a rate of 100 pounds per acre, 7 lbs of N and 7 lbs of K ₂O would give a total of 14 lbs of salt applied.
      Rates used in starter applications can be higher because distance from the seed is greater, but on sandy soils you should not use a salt index greater than 20 in a starter type application.

What are the problems associated with salt damage?
      Salt damage occurs when water is chemically removed from the seed by fertilizer salts in close proximity. In general, the problems caused by fertilizer salt damage are delayed emergence and reduced stands. A long dry period after planting will increase the chances of problems. In severe instances, replanting is required.

How do I calculate my fluid fertilizer application rate in gallons per acre if my recommendation is in pounds per acre?
      You must know the weight of the material. The fertilizer dealer can provide you with this information. Then, remember that 13-13-13 still means there are 13 pounds of N, 13 pounds of phosphate (P₂ O₅), and 13 pounds of potash (K₂O) per 100 pounds of material regardless if it is solid or liquid.
      Sample problem: A farmer wants to apply 120 pounds of N per acre using 32 percent solution. How many gallons does he apply?
      Procedure: 32 percent solution is 32-0-0, thus there are 32 pounds of N per 100 pounds of material.

1. Divide the desired amount of N by the percentage of N in the product: (120 lb N/0.32 percentage of material = 375 pounds of material necessary to apply 120 pounds of N per acre).
2. Then divide the amount of product needed by the weight per gallon of the product. 32-0-0 typically weighs 11.06 pounds per gallon: (375 lb material/11.06 pounds per gallon = 33.9 gallons per acre, or roughly 34 gallons per acre).

1. There is no agronomic difference in the efficiency of liquid and dry fertilizers if they are applied properly. Therefore, use the same rate of nutrients from either source.
2. The negative charged clay in most suspension fertilizers deactivates paraquat materials. Use other suspending agents, such as xanthum gum products if you are to apply these in the suspension fertilizer.
3. Do not broadcast spray a solution containing urea on hot, dry days to avoid N loss by volatilization unless you can incorporate by cultivation, irrigation, or rainfall within 2-3 days. Dribble or dry application is better in this instance.
4. Broadcast applications in reduced tillage should use droplets as large as possible.
5. Severe crop burn is possible with 32-0-0 applied broadcast spray on growing crops.
6. Pesticides can often be injected into most fluid fertilizers and save a trip over the field. Always perform a compatibility test with small amounts of the materials to determine if they can be mixed. ALWAYS READ THE LABEL ON ANY PESTICIDE TO DETERMINE IF IT IS LEGAL AND COMPATIBLE WITH FLUID FERTILIZERS.
7. Boron, sulfur, and other secondary and micronutrients can be custom mixed with fluid fertilizers if needed.

Publication 1466

Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director