When the Pit Is Full and the Field Is Wet

There is a point every fall when manure management starts to feel less like agronomy and more like logistics, or, in a few years, panic. The crop is ready, or at least getting ready, to come out. The manure pit keeps getting fuller. The forecast has another chance of rain in it. You look across the field and wonder whether it is actually dry enough to get a tractor through without leaving tracks that will still be there next spring. And then you look at the pit again.

That is where we find ourselves this fall. It has been wet, harvest has been delayed, and some soils are already saturated or ponded. At the same time, we have a very strong El Niño developing. That gives us reason to expect a warmer-than-normal fall and winter, although it certainly does not mean every week will be warm or every forecast will bring rain. What it does mean is that we should probably be thinking about flexibility. Livestock do not stop producing manure because the field is too wet, and every day that goes by takes a little more of our storage cushion away and makes us wonder whether there will be enough suitable hours in the fall to get all the manure our farms generate on the ground.

Buying Time Instead of Emptying Storage

There is an important distinction between having to move some manure to make it to our fall application window and having to empty the pit. When storage starts getting full, our instinct is to find acres. If there aren't any acres ready, that can make the situation feel like a dead end. Instead, the first question might be: How much storage capacity do I actually need to create, and how much time do I need to buy?

If you need enough room for another two weeks of manure production, that is a different problem than needing enough capacity to make it through the winter. If you can create that space by moving part of the manure, there may be no reason to remove all of it. Yes, we need to think about biosecurity when moving manure from one storage to another, and I would not take manure from a swine finishing site and move it into an in-barn storage at a gestation or farrowing facility. But there are times when moving manure makes sense, even if it creates some extra work. The point isn't necessarily to empty the pit. The point is to buy enough time that we aren't forced to put manure on a field simply because the storage clock ran out.

Take the Windows When They Come

That also means that when a field does become fit, we should probably be willing to use it. When I heard state climatologist, Justin Glisan, talking about the possibility of a wetter fall than normal, my first thought wasn't that we should forget about 50-and-falling. It was that the waiting game may be particularly difficult this year. If the soil is fit, the environmental risk is low, and this may be the year to take the application opportunity when it comes available rather than assuming another one will be waiting for us a week later.

Can the Field Carry Equipment and Safely Receive Manure?

That doesn't mean every acre is an acceptable acre. With liquid manure, I think there are two questions that sometimes get lumped together: Will the soil carry the equipment, and can the soil safely receive the manure? Those aren't necessarily the same thing. While soil compaction is a concern, the more immediate question this fall may be can the soil receive any additional water. 

Liquid manure is mostly water. A manure that is 95% water and applied at 5,000 gallons per acre puts roughly 4,750 gallons of water on that acre. That matters when the soil is already struggling to handle the water it has. We need that water to infiltrate and be held where we put it if we want the nutrients to stay there, too. Putting manure on saturated soil isn't just a question of whether the tanker can get across the field; it is a question of whether the field has anywhere left to put the water.

If You Must Apply, Reduce the Risk

If we have to apply, make the problem smaller. Pick the fields that are less prone to runoff and nutrient loss. Stay away from the wettest and most vulnerable areas. Cut rates if that is what it takes to keep the application from becoming a runoff problem, and spread the manure over more acres if we can. Get a cover crop established where possible. A cover crop won't magically make manure nitrogen available to the next crop, but it can take up nitrogen that otherwise might move through the soil to the drainage system. We may not get all of that nitrogen back in the following crop, but keeping it in the field gives us a chance to get it back eventually instead of sending it downstream.

Balancing Storage Pressure and Nitrogen Management

And eventually we get back to nitrogen. I wrote recently about the importance waiting for 50°F and falling before applying fall manure or anhydrous ammonia. I still think that is a useful brake on premature application. But 50°F isn't a magic switch, and in a year like this the question becomes how much risk we are taking by waiting.

Why Nitrification Inhibitors May Be Worth the Investment

As soil temperatures get within roughly 10 degrees of 50°F and falling, nitrification inhibitors become a more practical tool because we are getting into a temperature range where their activity and persistence can help us hold ammonium longer. The soil may look cool right now, but historically we would expect to have more than a few weeks before we reach the point where 50°F and falling becomes the normal condition. If storage is becoming the limiting factor, that gives us another tool for managing the risk of getting manure on a little earlier.

Truthfully, even if it is 50 and falling, this is a year when I would lean toward an inhibitor. They aren't a magic pill, but our research has shown that when we have wet springs and more drainage, there can be a significant yield response to using an inhibitor with well-timed fall manure compared with manure without one. If this fall sets us up for more water moving through the soil profile, that is a pretty good situation in which to keep ammonium around a little longer.

There Is More Runway Than It Feels Like

The other thing I would keep in mind, we don't need to panic yet. We don't know exactly when the soil will freeze, and a strong El Niño changes the odds of the weather we get; it doesn't tell us exactly what October or November will look like. There are still going to be application opportunities. The mistake would be assuming that every acre has to be treated during the first opportunity. It can be hard to wait when you are watching the pit fill, but we probably have more runway than it feels like we have. As a point of reference, on average Iowa soil will first reach freezing temperatures around Thanksgiving, but typically don’t stay below freezing or frozen in Iowa until December 22 plus or minus a week (Figure 2). With a warm fall and wet soils that are holding more energy, we might expect a little later freeze this year.

Storage Creates Flexibility 

That gets back to something I wrote earlier this year: Weather Variability and Storage Capacity: Are You Designed for the Year You Actually Get? Storage isn't just a place to put manure until we can get it on the field. Storage gives us flexibility. There will be wet falls like this one when we wish we had more capacity, and there will be years when November turns cold early and we wish we had taken advantage of more opportunities in October. The value of storage is that it lets us respond to the year we actually get rather than forcing every year into the same manure-management calendar.

And creating that flexibility doesn't have to happen entirely in the fall. Spring is another application window. I don't think every acre of manure needs to move to spring, and there are certainly fields and systems where spring application isn't the best choice. But if we can take a few feet of manure out of storage in the spring, that may give us several more feet of flexibility the following fall. It is a relatively simple change in thinking: instead of asking how we can get every gallon applied in the fall, ask how we can strategically move some manure into other application windows so that we aren't making agronomic decisions under a storage deadline.

That same thinking applies to equipment that makes spring, sidedress or summer application more practical, alternative crop rotations that give us more opportunities for manure, edge-of-field practices that help manage nitrate, and technologies that recover nutrients from manure and turn them into a more flexible fertilizer product. None of those things will make a wet fall disappear. But each one gives us another option.

Bottom Line 

For now, I don't think the answer is to panic. If conditions are fit, we should be willing to put manure on the ground. If they aren't, we should be looking for ways to buy some time, move manure, create storage, choose lower-risk fields, reduce rates, establish cover crops and use the nitrogen-management tools we have available. And looking ahead, we should be thinking about how to create enough flexibility in our manure system that next year's weather doesn't force us to choose between a good agronomic decision and simply getting the pit emptied.