Environmental concerns have led the fertilizer industry to adopt the 4R’s of nutrient stewardship which focus on the “right” rate, placement, timing and source of nutrients to maximize crop yield and minimize environmental impacts. The 4R’s fit a discussion on manure source nutrients especially as it relates to in-crop application of manure. The rate, timing and placement strategies of 4R Nutrient Stewardship especially affects the quantity of manure source N available for the crop.
In the past 10 years, a new manure application strategy of in-crop placement of manure has gained attention. The practice of in-crop application of liquid manure for wheat and corn has grown due the economic savings of replacing purchased fertilizer needed through better availability of manure sourced nutrients.
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 is dependent upon the manure nutrient form, weather conditions after application that affect nutrient cycling plus timing of application in relation 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 nutrient. Nitrogen in manure is in either an organic or ammonium form and subject to the same conversions in soil as either of these forms from commercial fertilizer. 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 rate of application. For many manure sources this resulted in phosphorus applications in excess of crop P utilization and soil test built beyond agronomic need.
- "Phosphorus Limited" manure application rates match the manure application rate to the rotational P need of planned crops. This avoided continued building of soil test P levels where P levels built under 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 and often timing that does not match crop use.
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 most or 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 prior to V3 and is generally incorporated between the rows. The placement and timing allows the N content of the manure to substitute for manufactured fertilizer N and a two-year crop rotation balance of P is applied. Manure from swine operations have 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. Manure N content might need to be supplemented with purchased N prior to application or in a follow up application depending on manure analysis and crop need.
“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. Manure has the potential to provide enough N to fully replace purchased N inputs.
“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. Incorporation with application can limit the volatilization losses and maximize available N to the crop.
The in-crop application of manure opens another window for manure application beyond non-cropping portions of the year plus places the nutrients where the growing crop can immediately use them. By offsetting purchased N in the corn or wheat enterprise budget, the cost of transportation and application of manure can be covered by the savings.
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 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.
Nitrogen in manure is in either an organic or ammonium form and is subject to the same conversions in soil as either of these forms from commercial fertilizer. The ammonium content is directly equivalent to manufactured nitrogen fertilizer. The organic fraction will become available through mineralization over several crop seasons.
The in-crop application of manure opens another window for manure application beyond noncropping portions of the year, and 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 application of the manure 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.
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 most common with dairy and swine production, but some beef feedlots in the state have liquid handling systems. Where fields are close to the manure storage, direct pumping systems can be used. Using a drag hose system will reduce soil compaction concerns compared to using a manure tanker. If fields are more distant, there are systems involving the use of booster pumps or frack tanks, where manure can be transported 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.
Most fields near well-established livestock operations have adequate soil levels of phosphorus and potassium from years of manure application. Crops removed from these fields were fed to the livestock and the livestock manure was then applied to the fields. Historically, manure may have been
applied as high rates, often in combination 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 sidedressing corn and topdressing wheat. If the growing season is dry, the moisture from the manure can also spur crop growth.
The application of manure 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 application of manure to growing crops can also extend the manure application season by providing more available days for manure application. Commercial manure applicators can have more days to generate income and livestock producers can save money on purchased nitrogen.
Center pivots are used by some livestock operations to apply liquid manure containing low amounts of nutrients. Again, this system can provide more available days for manure or wastewater application over the course of the crop’s growing season.
Water quality benefit experiments have not been conducted for this practice, but logically benefits should occur with careful attention to the nutrient content of the manure. Commercial fertilizer can be substituted for the manure sourced nutrient. If the crop's need for N is more closely matched to actual application rates it would be expected that is less residual nitrate-N would be in the soil profile at the end of the growing season subject to loss through tile. 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.
Water quality benefit experiments have not been conducted for this practice, but they are planned in Ohio. Logically, benefits should occur since the goal is to reduce commercial fertilizer use through maximizing
crop-available nutrients from the manure. Commercial fertilizer might still be needed to fill gaps where manure nutrient application does not meet crop needs. If the crop’s need for nitrogen is more closely matched to actual application rates, it would be expected that less residual nitrate-N would be in the soil profile at the end of the growing season, subject to loss through tile. If the application also balances the phosphorus needs of a two-year rotation, thus reducing excessive phosphorus 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 are generally fairly stable so a 3-year history will give a good representation of nutrient levels. If changes in feeding, size of animal in facility or water content occur, then a new test history should be developed.
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
- 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. Generally, 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 and higher gallon per acre rates will be used.
- Lower nitrogen content manure from nursery units or gestation/sow units might require 28 percent urea ammonium nitrate (UAN) or other nitrate source to be added to provide adequate nitrogen for the crop, but 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 will cause crop injury. Applications in corn can be made through the V3 growth stage if a dragline is used. If a tanker is used, application will depend upon the clearance of the equipment used. Wheat applications can be made up to GS 6 or prior to stem elongation.
- For dragline use, ground conditions should provide support to the hose. Better situations tend to be stale seed beds, spring-worked fields settled by rain, or where an existing cover was present.
- Smaller diameter hose (4 inches) has been used to minimize injury and reduce the horsepower needed to pull the hose.
- Transport logistics can be favorable for hauling manure greater distances when the nitrogen can be used to offset commercial fertilizer purchases.
The Commercial application industry has developed technology that provides cost effective infrastructure to move manure greater distances. Infrastructure includes specialized application equipment, transportation equipment including frack tanks, semi’s and other specialized equipment making the complex logistics of moving manure greater distances possible.
- Commercial application costs vary depending upon system of application plus use of labor and equipment provided by the livestock operation.
- Draghose pumped from storage directly to field costs average $0.06 to 1 cent per gallon with a range of 3-4 miles.
- Manure hauled on wheels which may include equipment, fuel, labor and infield application by draghose 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 type of manure and size of operation.
Crops need the macro-nutrients nitrogen, phosphorus and potassium to produce maximum yields. Through grain and residue removal (silage, straw, baling cornstalks, baling soybean stubble) macro-nutrients are removed from farm fields.
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 the form of milk, meat, or other animal products. Some additional nutrients are often brought to the farm as protein for animal diets, feedstuffs for properly balancing animal rations, or as the complete feed for the animals (most contract swine operations have their 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, it 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 a sidedress nitrogen or to wheat as top-dress nitrogen the famer 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 sidedress nitrogen needed also supplied the phosphorus and potassium needed for a 2-year corn-soybean rotation. Thus, a farmer could sidedress corn with liquid livestock manure and provide the nutrients needed 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 so fewer gallons were needed to meet the nitrogen needs of the crop and less phosphorus was applied. This could allow manure to be applied to a field in a situation where the farmer wanted to run a deficit in phosphorus to draw down soil phosphorus levels.
When applying manure nutrients to capture the 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.
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.