By Chryseis Modderman
In the manure management world, we’re constantly telling you to incorporate your manure into the soil; get it under the soil surface as soon as possible after application or you could lose up to half of your total nitrogen. This advice directly contradicts soil health advice which advocates for minimum soil disturbance. Both recommendations are correct, and manure use and soil health are complements, not contradictions; so, what is a producer to do?
Why do we recommend manure incorporation?
We’re trying to minimize volatilization and nutrient stratification. Volatilization occurs when the ammonium form of nitrogen in manure converts to ammonia gas and is lost to the atmosphere. Volatilization is minimized when the manure is incorporated into the soil and not left on the surface. Most of this loss happens within the first 24 hours of application, and after four days we consider nearly all the ammonium form nitrogen to be gone. Remember, manure contains two forms of nitrogen: organic N (not immediately plant-available) and ammonium (is immediately plant-available). That means not all the manure’s nitrogen will be lost – the organic N will stick around – but the form that plants can immediately use will mostly be lost to the atmosphere. That organic N can eventually be used by plants after it is broken down by microbes, in a process called mineralization.
Nutrient stratification is the layering of nutrients in the soil. Without the soil mixing that tillage provides, nutrients tend to accumulate heavily in the first couple inches of the soil which stimulates root growth near the soil surface. In general, plant roots seek out and grow toward the components they need to live such as water and nutrients. And so, if soil water is not a limiting factor where the root would mine deeper to find moisture, root growth will tend to remain shallow. And a shallow root system may lead to root lodging from lack of a good, deep anchor. Another concern is nutrient pollution from runoff and erosion of the soil surface. Nutrient stratification is not just a manure challenge, it affects commercial fertilizer applications as well.
What should producers do?
There’s no easy answer here, and those with success in both manure management and soil health will understand that it’s a balancing act and it all boils down to what works for your operation. Fortunately, minimum tillage systems often already have factors working in their favor to minimize the consequences of volatilization and nutrient stratification. Many no-till fields have ample crop residue and remaining roots which helps hold surface-applied manure better than the bare soil of conventional tillage. Just as healthy soil improves rainfall infiltration, liquid manure applied to the surface will find its way into the soil easier than in fields with degraded soil structure due to excessive tillage. Also, even if nutrients are concentrated at the surface, runoff and erosion of those nutrients are less likely in systems with good soil structure and cover.
If an operation isn’t strictly no-till, minimum disturbance injection and tillage are options to get the best of both worlds as any small amount of incorporation will help retain ammonium, and even a small reduction in soil disturbance can improve soil health. Though keep in mind that soil type and moisture will impact how much soil is turned up and disturbed, even with minimum disturbance tools.
Remember that going no-till is not a black-and-white decision. Some operations choose to do both no-till and conventional till, sometimes within the same field, depending on the ammonium content of the manure, soil type and moisture, and proximity to sensitive features like tile intakes or streams. Every producer and operation must consider all factors and make the best decision for their manure management and soil health goals while balancing finance and environmental protection considerations.
Source : umn.edu