Figure 1. Injection application of manure in wheat residue can be a valuable source for phosphorus.
With ground opening up for manure application after wheat harvest, this may be a good time to consider whether manure is a good fit for your wheat operation.
Take Home Messages
There are some situations when manure will work well in wheat rotations and others when it should be used with caution. Here are a few “Rules of Thumb” to follow.
- Soil and manure sampling is essential for manure use in all crops. (See these Nebraska Extension publications: Guidelines for Soil Sampling, G1740, and Manure Testing for Nutrient Content, G1450.)
- Manure before wheat:
- Use manure as a substitute for commercial phosphorus (P) fertilizer targeting those field with less than 25 ppm soil P levels (Bray test).
- High ammonium-nitrogen (N) manures (e.g., swine manure) injected into the soil can meet the N needs of wheat.
- High organic-N manures (e.g., beef open-lot manure) may require a spring top-dressing.
- Manure after wheat and before corn:
- High organic-N manures can be applied in late summer.
- Delay application of high ammonium manures (liquid swine) until late fall, possibly considering a nitrification inhibitor.
- To get the highest return from manure, plan first to use it in fields/crops requiring P and avoid building soil P levels beyond 50 ppm to protect the environmental.
Let’s discuss these points in more detail.
Manure Before Planting of Wheat
Manure applied ahead of fall wheat planting can be an excellent source of P for achieving optimum yields. Phosphorus increases tillering in the fall, resulting in increased number of heads and grain yield. Typically, optimum soil P levels (Bray test) are:
- wheat — 25 ppm,
- corn —15 ppm, and
- soybeans — 12 ppm
If field P levels have been maintained for corn and soybeans, manure can be an inexpensive way to raise soil P levels for wheat. Roughly, 18 lb of phosphate as P205 (or about 0.8 tons of beef feedlot manure — see table) would be needed per acre to raise soil P levels 1 ppm in the top 6 to 8 inches. To raise soil P level from 15 to 25 ppm would require about 8 tons of beef feedlot manure per acre.
University of Nebraska N recommendations for wheat (Fertilizing Winter Wheat, EC 143) consider price of N and wheat as well as residual soil nitrate levels. Applying 60-90 lb of N per acre would be typical for today’s wheat prices. Nitrogen demand is highest in April and May when growth and grain fill occur.
Table 1. Typical nutrient values for three types of manure.
To meet N needs, a manure high in ammonium-N (e.g., pig finisher manure, see Table 1) applied in late summer would be the preferred pre-plant option. Manure ammonium-N would be available to wheat similar to a commercial N pre-plant application. Typically, swine finisher manure that is directly injected at a rate of approximately 2,000 gallons per acre would meet wheat’s N requirements (Table 1). Injection is essential for conserving the ammonium-N.
Manures with N in the organic-N form (e.g., beef feedlot manure) will be less reliable at meeting wheat’s spring N requirements. Typically we assume that 25-35% of the organic N becomes available to a corn crop during the warm growing season. However, cool spring soil conditions may not convert organic N to plant-available N until it’s too late for the plant. If beef feedlot manure or broiler litter is used for a wheat fertility program, spring topdressing with a commercial fertilizer should be considered.
Manure After Wheat Harvest
July-harvested wheat followed by a spring-planted corn or grain sorghum provides a long window for manure application that can meet next year’s N and P requirements. For these conditions, a late summer application of manure high in organic-N would be acceptable. Most of that organic-N would be available for next year’s corn crop. However, a late summer application of manure high in ammonium-N presents a high risk of leaching N out of the root zone before the next crop. Application of high ammonium-N manures should be delayed until after November 1. Nitrification inhibitors may have some value for
mid-fall application of high ammonium-N manures, but are unlikely to be of value for late-summer manure application.
Figure 2. Manure’s most valuable nutrient is phosphorus. Manure’s nitrogen value is important but can be a smaller contributor. Selecting situations requiring P is generally your first choice for getting value from manure.
Summary
Manure can be a good fit with wheat in the circumstances discussed previously. Manure can deliver significant economic value based strictly on its nutrients (see Figure 1), especially in situations where supplemental phosphorus is needed. Additional value also comes from manure’s organic matter which improves soil quality and represents manure’s greatest advantage over commercial fertilizer (see
Finding Win/Win Opportunities for Manure). A little advanced planning will capture manure’s organic and nutrient value while preventing a bad experience for manure in wheat.