Dragline systems are the fastest and most efficient way to move liquid manure, and the field injection of manure also retains nutrients longer, providing more favorable conditions for farmers. Custom applicators know that high-quality work is what ensures job security in the future. The most cost-effective and beneficial dragline operation begins with proper agitation.
Effective manure agitation is the key to an even application of nutrients for the greatest benefit of crops. Consistency in your slurry provides an even mixture of nutrients across the field, and the breakdown of suspended solids allows you to clear the whole lagoon. Clearing out the manure storage helps farmers regain capacity in their lagoons, lengthening the time between pump-outs.
To get the right consistency in lagoon effluent, proper agitation relies on efficiency and pressure. You are trying to force a stream of liquid vertically through many feet of lazy liquid to where the solids rest. If you create mass flow without pressure, you mix the water well but never reach the solids. Lagoon agitation should take place primarily under the surface to reach the solids at the bottom, as well as to minimize odor release increased by surface agitation.
Tools for agitation
Lagoon pumps are the most common option for lagoon agitation, and they allow you to keep your banks clean. The lagoon stick extends deep into a manure lagoon to agitate the liquid before force-feeding your main pump. The breakdown of solids allows the liquid manure to flow faster and farther through the hose when pumping it out to the fields.
A lagoon pump is a great option for a small lagoon, but with larger dairies, it can struggle to reach the center of the manure storage. This drawback in reach led to the development of the second-most common lagoon agitator: agitation boats.
Providing an increased zone of influence, an agitation boat (Figure 1) can break up the solids found in the middle that a force-feed lagoon stick may not reach. Agitation boats may also have an autosteer system that can set the optimal path to cover the entire manure lagoon without direct oversight.
Necessary time to agitate
After breaking up solids, they will only remain in suspension for a limited time before settling again. Certain types of bedding, such as sand, can sink faster than others, but all solids will eventually sink again.
The necessary time to agitate varies between a day and a week prior to pumping out, depending on the presence of surface crust. Solids should still be in suspension throughout the entire pump-out and application process.
Application for nutrient consistency
Compared to swine, the nutrient content of dairy manure is moderate. The agitation of manure before application can provide consistency in your nutrients to maximize fertilizer value. If a lagoon is not well-agitated, phosphorus, potassium and nitrogen can accumulate in the solids left at the bottom of storage.
Although this buildup is not considered a gross nutrient loss, it is a short-term loss for the current year. Relative to phosphorus and potassium, nitrogen faces even more potential loss pathways.
Dairy manure holds two different types of nitrogen, typically found close to a 1:1 ratio. The first type of nitrogen is organic nitrogen, which produces a slow release of plant-available forms of nitrogen. During the first year after injection, approximately 35% of organic nitrogen is released, with around 12% in year two and about 5% in year three. The second type of nitrogen found in dairy manure, called ammoniacal, is comparable to commercial fertilizer, as it is readily available during the first crop season after application but is at risk of major loss due to volatilization. When surface-applied to fields, ammoniacal nitrogen will release into the atmosphere, costing the farmer valuable nutrients. Injection of well-agitated slurry can conserve the nutrients at risk of volatilization by increasing its contact with the soil.
With the roughly 50/50 mix of the two types of nitrogen in the ground, you get readily available nitrogen as well as a slow release of nitrogen for future soil viability. Well-agitated manure injection is not only beneficial in the first year but continues to provide value year after year. Injection is becoming the most important part of good manure application, as it not only minimizes potential nutrient loss but also minimizes runoff and environmental impact. Injection is a good way to satisfy both issues while increasing efficiency. It is also considered a best management practice for the industry, as it retains about 97% of nutrients compared to other application methods.
Ideally, your manure injection should still be within reach of the crop’s root, typically around 4 inches to 8 inches deep. The aggressive tillage ensures your manure – and the valuable nutrients – stay in place until crops are planted and can take hold. Application rates are dependent on the crop to be planted, and the maximum rate allowed is determined by your state regulations. The higher the rate, the larger the trench you need to make to hold that liquid. With that information in hand, you can plan for the type of dragline equipment you will use for injection at this job site.
Planning for application
Proper calibration of draghose equipment requires the measurement of tractor speed, spread width and flow rate through the hose. Most draghose systems incorporate the use of flow meters to present an accurate measurement of flow rates while in the field. Using your desired application rate, you can use the formulas from Figure 2 to find the necessary toolbar width, ground speed or flow rate for a job.
In addition to planning for the injector type and application rates, the planning process should include booster pump placement and hose layout. Plan where you will need to cross roadways and what sensitive obstacles, such as creeks or culverts, will need a booster pump. The last booster in your line should be only half a mile away from the applicator for best flows (Figure 3). If all your boosters are in place, the only thing stopping you from achieving higher flow rates is your hose size.
Keep in mind that pressure loss decreases as you increase hose diameter. Inversely, pressure loss increases as you increase the flow rate. As you increase your gallons per minute, your hose should increase in diameter as well to prevent pressure loss. When moving to a larger hose, you have a choice to make: Go the same distance and get more gallons, or keep the same rate for a longer distance traveled with fewer booster pumps. The decision will come down to your specific job and the job site of your operation.
With proper agitation, a consistent effluent is not only easier to pump out and apply; it is also the best way to get a consistent mix of vital nutrients. Agitation below the surface breaks up the solids and minimizes odor release, making neighbors happier. Reducing runoff after application can also improve relations with neighbors, as manure injection significantly lessens the environmental impact. Of course, the farmer also benefits from maximized fertilizer value and an emptied lagoon. Weighing the immense benefits with the increased efficiency, manure injection dragline operations become a win-win-win scenario for farmers, the community and custom applicators alike.
