In the lean years, farmers focus our efforts on trimming costs where we can and maximizing profitability on what we can’t cut completely. In the good years, every once in a while, we have a situation where high input prices force us to do the same. This cost-conscious behavior is something we should be doing all the time, but we pay more attention to it some years more than others.  

Fertility is critical to a good crop, so we know not to ignore our crop fertility needs, but we don’t always think about ways we may be able to trim costs by better utilizing local nutrients. Manure has many benefits, including some related to soil health, but perhaps the most recognized benefit is that manure contains the nutrients our crops need. Manure isn’t always an inexpensive product, but it contains multiple nutrients that are highly valued when planning your fertility program. To find out exactly which nutrients are in your manure, and how much, you will need a lab analysis. If you are already using manure and don’t have an analysis, take a sample and send it to a lab, or ask for the analysis results from your manure supplier. A manure analysis is one cost that cannot be cut. The small analysis fee up front will save you money in the long run. After all, you wouldn’t use commercial fertilizer without knowing exactly what the nutrient make-up of it is, would you?

Commercial fertilizer and manure work together well, but only if you know how many nutrients you’re putting out in manure so that you can cut back some on commercial fertilizers and save that expense. Manures have both ammonium nitrogen and organic nitrogen. Ammonium nitrogen is usable by crops, but it can be lost to the atmosphere if manure is not incorporated into the soil. In years when fertilizer prices are high, considering incorporation or injection to capture the Ammonium nitrogen might be more worthwhile. Organic nitrogen is like a slow-release fertilizer; it becomes available over time with only about 40% of it available the first year and another 35% becoming available over the next 3 years. Depending on the type of manure you’re using and how you apply that manure, you may still need more nitrogen, but it is possible that other nutrients can be omitted from future applications.

Phosphorus (P₂O₅) is about 70% available and potassium (K2O) is 80% available the first year after manure is applied, with the remainder of both becoming available in the future. We’re often applying manure at rates that are more than sufficient for these nutrients though, so additional commercial fertilizer is not needed for several years. If you need help figuring out how much of your applied nutrients will be available for your crop next year, let me know, and I’d be glad to help you determine that or you can use our recently updated NebGuide, Determining Crop Available Nutrients from Manure.

Once you know what’s in your manure, how can you be sure of how much of those nutrients you are putting on your field? You need to know your application rate, of course. You would multiply your available nutrients by your application rate to know the total amount of nutrients applied. But how do I know my application rate for manure, you ask? The same way we know exactly how much commercial product we’re applying. We know how much manure we are applying because we calibrate the spreader. If you hire someone to do your application, you may not realize that they calibrate their spreaders too, but they’d have to. If they didn’t, they may run out of product before they’re done or have extra when they leave your farm.

Just like adjusting your combine to minimize loss out the back end or soybean shatter, you need to make sure your manure spreader is set to apply at the rate that you want if you want to maximize those nutrients you’re using. To know how much of that manure we are applying, we need to calibrate our manure spreaders. Just like every combine must be adjusted because they’re all slightly different, every spreader is different, and they run differently on different tractors. So, the very first step of every calibration is to note which piece of equipment you’re using and what you’re pulling that piece of equipment with.

There are a variety of ways of calibrating a manure spreader depending on the dryness of the product and equipment you have available. For the purposes of this article, I’m going to focus on surface application and the kind of calibration that requires the least amount of equipment – equipment that you likely have on hand or can access quickly. I’m happy to answer questions about other types of calibration; let me know and I can help you out.

For a liquid manure spreader that is spreading on top of the ground, start by placing a rain gauge along the center line of the applicator’s path and two more 10 feet on either side of the center line. Start the spreader with normal settings prior to reaching the rain gauges and continue past the gauges for a little distance, noting the settings of the spreader and tractor (RPM, gear, how far the gate is open, etc). Calculate the average amount of manure in the gauges to determine the rate in inches, then take that number and multiply it by 27,154 to convert from inches to gallons/acre (which should correspond to your manure analysis).

For a solid manure spreader, cut some plastic drop cloth or landscaping fabric into 3 pieces that are 5 feet by 4 feet 4 inches (22 square feet). The size of the sheet is important in minimizing the amount of math for this process. Lay the sheets in the path of the spreader (with typical Nebraska wind, make sure to hold down the sheets with large rocks or some kind of stakes). Start the spreader with normal settings prior to reaching the sheets and continue past the sheets for a little distance –noting all the settings of the applicator just like for the liquid spreader. Collect the tarps with manure on them (being careful not to lose any manure from the edges) and weigh the manure and sheets together in a bucket. We find that either a fish scale or shipping scale work well. Do this for all 3 sheets, then weigh the bucket and an empty sheet and subtract that number from each of your previous weights to get the weight of the manure on each sheet. Average the weights of the manure and you have your application rate (1 pound of manure on a sheet = 1 ton per acre). If you use any other size sheet, you’ll need to calculate the weight per area but by using the 22 square foot sheet, you have already factored that in.

Now you know your base settings. Repeat the process for different settings to determine the necessary tractor and spreader settings needed to apply the most appropriate rate for your field and the manure you’re using. Because manure is variable, I always recommend doing a calibration multiple times so that you know for certain that your application rate is correct. And, do it again if you change types of manure because different consistencies of manure will spread differently. Still have questions or need help? Contact me or any of the manure team.