December 27, 2021
My previous column addressed the first steps you need to take to deal with and relieve some of the pressure from high fertilizer prices. Now it is time to key in on a change that livestock farms, especially those that produce a lot of manure, can make to reduce or completely offset their fertilizer while supporting high crop yields.
The first step is to recognize that manure is your major source of nutrients.
Calculations I made several years ago showed that for many farms, especially in New York state, more fertilizer arrives on the grain truck than arrives on the fertilizer truck. This is especially true for farms with low-forage diets — less than 60% — that import a lot of feed.
Even with a daily spread of manure, there are steps you can take to maximize the reuse of those nutrients.
Breaking down nutrients
Manure has 20 to 30 pounds of nitrogen per 1,000 gallons — with half as volatile ammonia and half as organic nitrogen. About 35% of the organic N is available by decay the next year. Thus, you potentially have 10 to 15 pounds of ammonia N, plus 3.5 to 5.25 pounds of organic matter N per 1,000 gallons.
If you spread manure daily or surface-spread without immediate incorporation, you lose the 10-15 pounds of ammonia, but keep the organic N unless it physically washes off the field to nearby waterways. This is especially true if you spread on snow-covered ground.
On an 8,000-gallon-per-acre manure application, this means you are throwing away $80 to $120 per acre of ammonia nitrogen by not incorporating or injecting it. Instead of having 108-162 pounds of nitrogen, you only have 26-42 pounds of N. In other words, you threw away 75% of the nitrogen and now must buy expensive fertilizer to make up for it.
Spreading without immediate incorporation means you must apply much more manure to meet your nitrogen needs. This greatly overfertilizes the phosphorus and potassium, wasting this valuable fertilizer.
Phosphorus is 8 to 10 pounds per 1,000 gallons of manure and is not lost by volatilization. Leaving manure on the surface over winter allows a significant amount to move into streams during spring runoff.
Leaving a field bare without a living cover allows more highly available dissolved phosphorus to also move off the field and into water. Research has found that this occurs often when manure is spread on bare ground in fall and winter. All this will accelerate the non-uniform phosphorus level on your farm.
Unless you grid sample or have a variable-rate fertilizer applicator on your planter, you are stuck with fertilizing for the lowest-testing part of your field to minimize yield loss. This is money lost as medium- and high-testing areas get fertilizer that has no economic return to pay for it.
Potassium is also 20 to 30 pounds per 1,000 gallons. At 8,000 gallons per acre, it is equal to 240 to 400 pounds per acre of 0-0-60 fertilizer. Potassium will attach to soil particles, so it is less likely to leave. But spreading on frozen or snow-covered ground can also allow this valuable fertilizer to leave the farm, too.
Manure has a big range of fertilizer content and makeup. Agitation can have an effect on this, too. There is no substitute for manure sampling at the beginning, middle and end of emptying the storage.
The first step of management is knowing the data you are working with.
If manure has equivalent 30-10-30 fertilizer per 1,000 gallons, that is equal to $59.20 per 1,000 gallons in purchased fertilizer. If you’re looking at spreading 8,000 gallons per acre, then you are applying $473 per acre. This is a big number considering the high price of fertilizer.
If your commercial fertilizer applicator went out and randomly drove around the field and spread fertilizer wherever, you would rightly be mad. Why do that to yourself?
The biggest opportunity to offset fertilizer is the use of manure injectors. The number and types are increasing each year as more farmers realize the economic and environmental benefits of this technology. By simply putting the manure into the soil instead of on top, you can dramatically reduce or even eliminate the loss over winter from runoff.
More importantly, nitrogen is not volatilizing along with your money. The ammonia interacts with the soil exchange and stays there until the soil is warm in spring. With the use of an ammonia inhibitor compound, it can be held for six to eight weeks after the soil warms before converting to nitrate.
Our research in the Delaware, N.Y., watershed found that injecting manure into winter forage or cool-season grasses in November through freeze-up could meet all the needs of that crop the next spring. As soon as it turns warm, the ammonia converts to nitrate and is quickly taken up by the roots of the rapidly growing grasses or winter triticale. With enough manure injected, you can meet all the fertilizer needs of the crop without any of it running off into the streams or the air.
This environmentally sound late application leaves more room in your storage in case spring application is delayed. With these high fertilizer prices, it doesn’t take long to pay for an injector system. The only complaint I have heard is that the farmer runs out of manure too soon.
For grass fields and winter forage, you can still inject if you do not have manure storage. Simply take your daily spread tanker with rolling injectors on the back out to the field and start injecting. When the tank is empty, stop, lift the injectors and start there the next day with the next load until you have the field covered.
We do not suggest knife injectors because of the higher horsepower and the tendency to bring up more stones. We suggest running a roller after the field is fertilized to push down any sod or stone that was left lifted. Go through with the narrower setting.
The downside to daily manure spreading are days when the soil is too wet for traffic. Injecting or surface-applying can do long-term damage to your yields in this situation.
By keeping axle loads under 8 tons per acre, you can avoid yield-robbing deep compaction. Keep tire pressure at 15 pounds per square inch to spread the weight over more area and to avoid surface compaction.
If you inject into grass sods or well-established winter forage, the roots will cushion the impact and spread the weight out more. As the roots grow, they exert tremendous side pressure to push the compaction out. Think of tree roots lifting a concrete sidewalk.
For spring application, Quirine Ketterings, manager of the nutrient management spear program at Cornell, has taken injection a step further by injecting on 30-inch rows and then planting the corn no-till or strip till directly over those rows. As soon as the corn seed puts its roots out, they are immediately into the NPK of the manure.
The farmer she worked with was able to get maximum yield on just manure, and Ketterings has found no root burn.
Another clear advantage is that you can inject right next to non-farm neighbors, and there is no residual smell.
Kilcer is a certified crop adviser in Kinderhook, N.Y.
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