Environmental concerns have led the fertilizer industry to adopt the 4R's of nutrient stewardship, which focuses on the "right" rate, placement, timing, and source of nutrients to maximize crop yield and minimize environmental impacts. The 4R's also fit a discussion on manure source nutrients, especially related to the in-crop application of manure. Rate, timing, and placement strategies of 4R Nutrient Stewardship are most relevant. Rate is critically important as we balance nitrogen and phosphorous available to the crop and potentially lost to downstream waters.
In the past ten years, a new manure application strategy of in-crop placement of manure has gained attention. The practice of in-crop liquid manure application for wheat and corn has several considerations. First, there are economic savings of replacing purchased fertilizer replacing purchase nitrogen. Second has been a noted corn yield increased over fertilizer N applications. The returns from these first two considerations make moving manure to more distant locations more feasible. The practice also opens another window for manure application for livestock producers.
The foundation of any manure application should include a soil test for the field targeted for application and a manure test to identify the nutrient content of the manure source to be applied. The nutrient value of manure-sourced nutrients in crop production depends on the nutrient form, weather conditions after application that affect nutrient cycling, and the application timing closer to crop need. The phosphorus nutrient form in manure is similar enough in soil reactivity and solubility to manufactured fertilizer that the manure sourced P can be considered a 1:1 substitute for fertilizer P. The only exception is when starter P nutrient is needed since the water solubility of the manure P is not as great as fertilizer P. Potassium is also a direct 1:1 substitute for fertilizer sourced nutrients. Nitrogen in manure is either in the organic or ammonium forms. Both N forms are subject to the same soil conversions, whether they are from manure or commercial fertilizer. Therefore, the ammonium content is directly equivalent to manufactured N fertilizer. The organic fraction will become available through mineralization.
"Rate" based manure nutrient strategies have included:
- A "Nitrogen Limited" rate of manure application where the N needs of the crop following manure application determines the application rate. N rate-based applications often result in phosphorus applications greater than crop P utilization, and soil test P levels are built beyond the agronomic need for many manure sources.
- "Phosphorus Limited" manure application rates match the manure application rate to the rotational P need of planned crops. This strategy avoids the continued building of soil test P levels with the "Nitrogen Limited" strategy. This "Phosphorus Limited" rate requires supplemental N for crops such as corn or wheat due to the lower manure application rate.
For in-crop application, the N content of the manure can often be matched to the N need of a corn or wheat crop and provide in many cases all of the phosphorous needs for a two-year crop rotation. For wheat, the manure application timing is at green-up of the winter wheat crop in the spring with a surface application. For the corn crop, the application occurs before V4 and is generally incorporated between the rows. This placement and timing allow the N in manure to substitute for manufactured fertilizer N. Manure from swine operations has the nutrient content that works best as a total manufactured fertilizer substitute. Dairy manure is often lower in N content, so additional N is required, especially for corn. Manures with low N content like dairy can be supplemented with fertilizer N before application or using a follow-up application. The manure analysis and crop needs should guide these decisions.
"Timing" the manure application close to the crop need limits the loss of N and maximizes the manure N content for meeting the need of the crop. Thus, manure has the potential to provide enough N to replace purchased N inputs fully.
"Placement" in relation to the soil surface will impact losses of manure N. Surface applied manures have the potential for volatilization losses which reduce the N available to the crop. Rainfall that does not result in a runoff event shortly after application can reduce volatilization losses. Incorporating the application can limit the volatilization losses and maximize the crop available N.
The phosphorus nutrient form in manure is similar enough in soil reactivity and solubility to manufactured fertilizer that the manure-sourced phosphorus can be considered a 1:1 substitute for fertilizer phosphorus. The only exception is when a starter phosphorus nutrient is needed because the water solubility of the manure phosphorus is not as great as fertilizer phosphorus. Potassium is also a direct 1:1 substitute for fertilizer-sourced nutrients.
Manure nitrogen is either organic or ammonium forms. Whether manure or fertilizer, ammonium undergoes the same soil N conversions to nitrate. The ammonium content of manure is directly equivalent to manufactured nitrogen fertilizer. The organic N fraction will become available through mineralization over several crop seasons.
What is it:
The in-crop application of manure opens another window for manure application beyond non-cropping portions of the year. It places the nutrients where the growing crop can immediately use them. By offsetting purchased nitrogen in a corn or wheat enterprise budget, the cost of transportation and the manure application can be covered by the savings.
Figures 27a. Surface application of manure through a dragline to topdress wheat in the spring. Credit: Glen Arnold, OSU Extension.
Where is it used:
An economic return from an in-crop application system is best for a nitrogen-requiring crop such as wheat or corn. The practice can be used with any liquid manure storage system. Liquid manure is common with dairy and swine production, but some beef feedlots in the state have liquid handling systems. Tankers with proper tire alignments can make applications where fields are close to the manure storage. Direct pump systems using dragline hose will reduce soil compaction concerns compared to using a manure tanker. If fields are more distant, systems involving booster pumps or frack tanks can transport manure several miles from the storage unit.
Figures 27b. Sidedressing corn with a dragline hose using a coulter-till injector system. Credit: Glen Arnold, OSU Extension.
Why install it:
Most fields near well-established livestock operations have adequate phosphorus and potassium soil levels from years of manure application. Crops removed from these fields were fed to the livestock then livestock manure was applied. Historically, manure may have been applied at high rates, often combined with commercial phosphorus fertilizer, resulting in very high phosphorus soil test readings. In these fields, further manure application that increases soil test phosphorus levels should not occur.
Figure 28. Dragline hose application made to V2. Credit: Glen Arnold,
Figure 29. Tanker application to corn. Credit: Greg LaBarge, OSU Extension.
Applying livestock manure to growing crops can replace purchased nitrogen when side-dressing corn and top-dressing wheat. If the growing season is dry, the moisture from the manure can also spur crop growth.
The manure application between cuttings of forage crops is another window of manure applications to a growing crop. The forage crop can use the manure nutrients to jump-start regrowth.
The manure application to growing crops can also extend the manure application season by providing more available days for manure application. As a result, commercial manure applicators can have more days to generate income, and livestock producers can save money on purchased nitrogen.
Some livestock operations use center pivots to apply liquid manure containing low amounts of nutrients. This system can provide more available days for manure or wastewater application throughout the crop’s growing season.
What do I need to know about it:
Water quality experiments have not been done for this practice. Logically benefits should occur due to reduced nutrient applications. Manure nutrients substitute for fertilizer nutrients, especially with nitrogen. If the crop's need for N matches actual application rates, less residual nitrate-N would be expected at the end of the growing season in the soil profile. This residual soil nitrate is likely lost through the tile before the following summer's annual crop. If the application also balances the P needs of a two-year rotation, thus reducing excessive P application, there would appear to be an environmental benefit over other application timings.
Manure used for nutrient applications should have a manure test pulled. Test results are generally stable. Thus a 3-year history of manure test from a barn will give a good representation of nutrient levels. If changes in feeding programs, size of animals in the facility, or water content of the manure occur, a new test should be used.
Nitrogen is generally distributed throughout the depth of a pit. Phosphorus is associated with the solids, so will be in higher concentration in the bottom of the pit.
Swine Manure Recommendations
- The vast majority of N is in ammonium form (95%), with a small amount in organic N (5%).
- Lower N content manures from nursery units or gestation/sow units may need to have added 28% to provide adequate N for the crop but avoid excessive phosphorus rates.
- Finishing unit manure generally will meet N needs of corn or wheat plus a two-year rotation. Typically, 5,000 to 6,000 gallons will provide 180 to 200 units of N.
Dairy Manure Recommendations
- Due to handling, storage, and bedding, the nutrient content of dairy manure will need to be evaluated. In general, dairy manure is less concentrated than swine manure for both N and P. Thus, higher gallons per acre rates are used.
- Lower nitrogen content manure from nursery units or gestation/sow units might require 28 percent urea ammonium nitrate (UAN) or other nitrogen sources to be added to provide adequate nitrogen. Use the manure test to avoid excessive phosphorus rates.
- As dairy farms have moved from sawdust (organic) bedding to sand bedding, the nitrogen content of dairy manure has risen, while the phosphorus content has dropped.
- Application windows are open from planting through the point where application equipment will cause crop injury. For example, applications in corn can be made through the V4 growth stage when a dragline is used. If a tanker is used, the application window will depend upon equipment clearance. Wheat applications can be made up to GS 6 or before stem elongation.
- For dragline use, ground conditions should provide support to the hose. Better ground conditions for application are stale seedbeds, spring-worked fields settled by rain, or when a cover crop existed.
- A smaller diameter hose (4 inches) will minimize injury and reduce the horsepower needed to pull the hose.
- Transport logistics can be favorable for hauling manure greater distances when the manure nitrogen offsets commercial fertilizer purchases.
The Commercial application industry has developed cost-effective infrastructure to move manure greater distances. Infrastructure includes specialized application equipment, transportation equipment, including fracking tanks, semi-trucks with tankers, and other specialized equipment making the logistics of moving manure greater distances possible.
- Commercial application costs vary depending upon the equipment used plus labor and transportation equipment provided by the livestock operation.
- Drag hose applications with manure pumped directly from storage to field have average costs of $0.06 to 1 cent per gallon when with a range of 3-4 miles.
- Manure hauled on wheels, including equipment, fuel, labor, and infield application by drag hose, is 3-5 cents per gallon and has a range of 10 miles.
- Self-equipped application has a cost structure that includes owned equipment and farm-sourced labor. Costs vary widely depending upon the type of manure and the size of the operation.
How does it work:
Crops need the macro-nutrients nitrogen, phosphorus, and potassium to produce maximum yields. However, macro-nutrients are removed from farm fields through grain and forage removal (hay, silage, straw, baling cornstalks, baling soybean stubble). The application of manure to farm fields, when properly planned, can be a closed-loop system. Crops are harvested, fed to livestock, and the livestock manure is returned to the field. Some of the nutrients leave the farm in milk, meat, or other animal products. Some additional nutrients are brought to the farm as protein for animal diets, feedstuffs for properly balancing animal rations, or complete animal feeds (most contract swine operations complete feed delivered).
The concentrations of macro-nutrients in animal manure can depend on the animal species, animal diet, and how the manure is stored and handled.
Liquid swine finishing manure, stored in a pit under the animals, is usually the highest in nitrogen. Most of this nitrogen is in the ammonium form and is readily available to a growing crop. When swine finishing manure is applied to corn as side-dress nitrogen or to wheat as top-dress nitrogen, the farmer can replace the commercial nitrogen typically purchased for these crops.
In Ohio State University research plots, applying swine finishing manure to emerged corn to supply the side-dress nitrogen needed also provides the phosphorus and potassium required for a 2-year corn-soybean rotation. Thus, a farmer could sidedress corn with liquid livestock manure and provide the necessary nutrients for the corn and soybean crops without increasing soil phosphorus levels.
In other research plots, the liquid livestock manure has been supplemented with 28% urea ammonium nitrate to increase the nitrogen content of the manure, resulting in fewer gallons of manure needed to meet the crop nitrogen needs, and less phosphorus was applied. This practice could allow manure to be used in fields where the farmer wants to draw down soil test phosphorus levels.
When applying manure nutrients to capture nitrogen, it is important to consider phosphorus levels in the soil. The repeated over-application of manure can increase soil phosphorus levels. As soil phosphorus levels increase beyond the maintenance level, the risk of phosphorus escaping from fields also increases.
Who do I contact in Ohio:
Questions, concerns or suggestions for website content on this practice.https://agbmps.osu.edu/submit/email-general-questions-comments-or-concerns
Videos depicting field applications under different conditions can be found at In Crop Applications. Other information is posted on the Ohio State Extension Environmental and
Manure Management Facebook page. Field trial results where manure was used in comparison to commercial fertilizer can be found at agcrops.osu.edu/on-farm-research. Also, manure handling
and application equipment in Ohio can be found through companies such as Homan Equipment, Bambauer Equipment, and Southwest Automation. Consult with OSU Extension or other agronomists for sampling criteria and current data to determine nitrogen-rate recommendations prior to making final nitrogen applications.