Very good agitation might be the most important step in utilizing liquid manure as a nutrient to grow a crop. If every gallon is homogeneous throughout the pump-out, we have a better opportunity to be successful year after year using manure as fertilizer.
Well-agitated manure is predictable. Its nutrient content can be spread consistently throughout the field at agronomic rates. A manure lagoon without an ability to be well agitated is only as valuable as the poorest gallon of wastewater it holds in terms of nutrient value. There is too big of a risk of under-application and missing crop production opportunity when the manure can’t be evenly applied in the field.
Because of this, over-application happens too often, and this not only limits the higher return a farm could make by utilizing a nutrient asset to a fuller potential, but it also puts the farm at risk of environmental consequences.
Turning a wastewater into a high-value fertilizer is simple – agitate until everything is even and in suspension, sample the nutrient and apply correctly.
Manure, naturally, has many nutrients, micronutrients, biologicals and organic materials that are excellent at building soil structure and growing a quality crop.
In western Iowa, Kelly Cunningham operates a dairy that utilizes liquid manure on all of its crop ground without supplementing any acres with commercial fertilizers.
On new ground on which he’s been the first to utilize manure-only nutrient application, he has brought the soil’s organic material up at least 0.5 percent. He thoroughly agitates his lagoons with agitation boats and direct-injects liquid manure using a dragline system. This 0.5 percent increase in organic material may not seem like a big deal, but the increased moisture retention is obvious, he says, especially in dry years.
Near Atwater, California, another dairy owner has been operating an agitation boat for the past year on his lagoons that have limited access points for stationary agitators.
After using strong agitation to move stored solids out of his lagoon last fall, he’s seeing improved crop results on the fields that received that nutrient. Compared to fields on his farm that went without manure, moisture retention between irrigation events is better, and his corn is visibly stronger in a side-by-side comparison.
This past year, before irrigation events, he has been aggressively agitating his final lagoon with an agitation boat to send enriched lagoon water to his crop. Previously, he was utilizing agitation before irrigation, but he didn’t have the ability to quickly bring his entire lagoon into suspension, as much of that lagoon is not accessible from the shore.
The change has been significant with better agitation, and he no longer worries about solids building up in his final cell.
Storage capacity is important in how the dairy utilizes water. Removing settled solids regularly from his final lagoon keeps his flush water clean, his barns clean and his herd healthy.
Liquid manure naturally stratifies in a lagoon, and it takes powerful, aggressive agitation to bring heavier solids into suspension, especially sand.
Traditionally, agitation units are placed along the edge of a pond or storage unit, and liquid is moved horizontally for agitation. These units will keep a zone of about 80 feet in suspension. Around the edges of this area of influence, liquid velocities slow and solids settle out of suspension in mounds.
Storing solids year after year places unnecessary stress on the farm. Sure, the nutrients aren’t being fully utilized, but each year storage capacity becomes less. It’s harder to manage water, and as the situation becomes more extreme, irrigation units start plugging, odor issues rise and herd health declines.
Then, the farm faces a lagoon clean-out. Handling years of stored nutrient in a single event can be expensive, messy and may require more land than what’s available for the high loads of phosphorous.
Pumps must have high flow to maintain high liquid velocities that keep solids in suspension. For adequate agitation, the pump must be able to access the center and all edges of the storage.
Especially for large-scale lagoons, mobile, remote-controlled, floating agitation units, such as an agitation boat, have the capabilities to easily move around to address all parts of the lagoon.
Floating pump units can agitate vertically through the lagoon profile, blasting top water directly down at settled solids to bring them into suspension. The goal with good agitation is to provide complete yearly clean-out and a homogeneous nutrient for land-application.
If the manure isn’t consistent and predictable, it’s not worth much; there is too big of a risk of nutrient under-application and missing the opportunity for full crop production.
If the dairy is growing much of its own feed, this can turn into a vicious cycle of too little fertilizer on the field, yielding too little nutrient for feed, lowering nutrient in the manure further and so on, requiring the dairy to import feed or fertilizer or both onto the farm to break the cycle.
Good, effective, energy-efficient agitation is the key to maximizing the nutrient value of liquid manure.
Agitation can be expensive. How can you decrease costs of agitation? Identify the total time agitation is needed for the pump-out. Will 40,000 gallons per hour be hauled to the field, or 160,000 gallons per hour be pumped to the field through a pipeline or dragline?
How many agitation units are required to bring the lagoon into suspension? What is their fuel cost hourly and how effective are they? Are your current methods and costs achieving your goals?
Very good agitation allows for consistent application throughout the field as a valuable fertilizer. The natural characteristics of manure allow for a slow release of nitrogen that continues to be available in subsequent years.
Building organic material, biological activity and soil structure often happens in the first several years of manure application, with noticeable and positive results. Water retention in the soil increases, leaching and run-off decrease, and when applied correctly, yields thrive.
By emptying lagoons annually or semiannually before a growing cycle, nutrients can be delivered to the fields regularly and predictably.
Unless there are large changes in feed, bedding practices, scale or manure treatment, the content of the manure should be similar during each pump-out event, and management is predictable. Avoiding build-up issues through good agitation can make the whole farm run better.
Continue to use manure as a nutrient and find ways to minimize handling costs for the best financial return. PD
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We need to know four things to calculate friction loss using the Hazen-Williams Equation (Figure 1):
This calculates to 462 feet of head. If we look at our pump performance curve for the Cornell 6NHTB-19 with a 375-horsepower engine, we see 462 feet of TDH will happen at 2,250 gallons per minute. (Figure 2)
