Tuesday, August 20, 2019

Manure Thoughts - beyond budgets

Last month we looked at manure budgets for different counties around the state, and I got a great question. In those counties where we see robust manure resources, what can be done to make sure they are using it, striving to be good stewards, and limit losses of nitrate from crop fields? I always view this question the same way; is there something we aren’t trusting about the manure alone to get the job done? In other words, what does the fertility program look like?
I think one common concern farmers have is how available is the nitrogen in manure. While the weather conditions in any particular growing season can vary, the more important factors are the species from which the manure comes from and the manure management system used. More information on estimating the nitrogen availability for Iowa conditions can be found in PMR 1003 – Using manure nutrients for crop production.
A second important area is the potential for loss of the nitrogen in manure, especially as related to application timing. Nitrogen in manure starts in either the organic or ammonium form, and while these generally aren’t susceptible to loss once they are in the soil, under warm conditions, they can be rapidly converted to nitrate, which makes manure application timing an important factor for estimating the amount of nitrogen in the soil and available to support crop production. Recent research has shown, in certain years, delaying manure application of liquid swine manure from early October until early November, could increase corn yields 30-60 bushels an acre, indicating if for some reason manure has to be applied earlier than intended, yield losses could occur. When farmers see this occurring, it can look like an availability issue, and cause loss of confidence in manure as a fertilizer course.
Finally, a third area of concern is uniformity of manure application and the consistency of manure. The precision age of agriculture has made farmers more aware of places in the field where yields are inconsistent. By its nature, manure has variability to it and while new technology, such as real-time nutrient measurement, may be able to help with this and correct this issue. Additionally, making sure those nutrients are applied at the correct rate and uniformly over the field is a critical component of using manure as a fertilizer, and trusting it will provide what you need, this needs to be done for both solid manure and liquid manure application equipment.

Figure 1. Image of manifold distribution evaluation