Few farmers would apply chemical fertilizer without doing a little preplanning and carefully metering it out. But that’s not always the case with manure. There is a temptation to just head to the nearest field and dump it, saving time and fuel. However, there is a logical and efficient way to use it. Here’s how to maximize its value.
According to Patrik Mooleki, a soil and nutrient management specialist with the Saskatchewan Ministry of Agriculture, planning a proper manure-spreading strategy starts long before the first bucket full is dumped into a spreader. “They (farmers) first need to know what kind of nutrients they have in the field where they are going to spread it,” says Mooleki. The only way to find that out is by soil sampling, just as you would before applying any fertilizer.
“Secondly, you need to know what kind of crop you’re going to grow and its nutrient requirements,” he continues. And finally, the manure needs to be tested to determine its fertilizer value. “You need to know what nutrients are there and in what quantity.” Only then can farmers develop a spreading plan that makes the best use of manure, reduces the annual chemical fertilizer bill and prevents contamination of nearby waterways.
TAKE A SAMPLE
When taking a sample of solid manure, Mooleki recommends mixing it up thoroughly, first. That will ensure you get a representative sample to send away. Labs that do soil testing will also be able to measure the nutrient content of manure. Once you have all the results on your desk, it’s time to do some calculating.
Keep in mind most of the nutrients present in fresh manure are in organic form. That is an especially important consideration when looking at nitrogen (N) amounts. “N will need time to mineralize to be available to plants,” says Mooleki. But information on how much is immediately plant available should be included in the lab report.
That data will determine the spreading rate. “(In solid cattle manure) phosphorus (P) is going to be the limiting factor,” says Mooleki. Average usable P concentrations in fresh, solid manure are much greater than N amounts. Research published by the Saskatchewan Ministry of Agriculture reveals solid cattle manure from feedlots in that province contains about 0.14 per cent P, that works out to about 2.8 pounds per imperial ton. Usable N amounts are typically only about one pound per imperial ton.
APPLY ACCORDING TO PHOSPHORUS CONTENT
Solid manure should only be spread at a rate that meets a crop’s P requirement. “That is how you make the decision on how much to apply per acre,” says Mooleki. Spreading it at a rate that applies enough N will deposit far too much P, which will contaminate runoff. Adding additional N from chemical fertilizer will get the amount up to what is required.
If you are spreading manure from livestock other than beef cattle, the nutrient profiles will be a little different, due to the different feeds and digestive processes Mooleki explains.
The next phase is getting the spreading rate right. A quick test and some simple math will put you in the ballpark. If you need 30 pounds of P per acre, using a figure of three pounds per ton (roughly the average value), means you have to spread 10 tons per acre.
CALIBRATE YOUR SPREADER
The easiest way to measure the rate of spreading in the field is to first determine how many tons your spreader holds. If you have access to a scale, weigh the spreader empty and again with a load on to find its capacity. Next, calculate the area covered when spreading one load (the width of the spread times the length of the run in square feet). To convert that to acres, divide by 43,560 (the number of square feet in an acre). With that data you can determine tons per acre.
If you don’t have a scale, you can use an alternate method. To do that, Mooleki recommends placing four pieces of plastic on the ground at various points along the spread path, each one covering about 100 square feet (10 feet by 10 feet). Hold them down with stones at the corners. Sampling in four places will compensate for uneven spreading patterns.
Gather up each piece of plastic with the manure that landed on it. Place them in separate five-gallon pails. Weigh each pail. Subtract the weight of the plastic sheet and bucket to get the weight of the manure (be sure to weigh the plastic and buckets ahead of time to find their empty weight).
Determine the average weight of manure captured on the plastic sheets to find the average spread rate. Multiply that by 435.6 to get pounds per acre. Divide by 2,000 to get tons per acre. If your spreader has a wide spread-pattern, you could use a larger sheet of plastic to collect a bigger sample for better accuracy. Just be sure to make the necessary changes to the pounds-per-acre calculation.
If you consistently use the same ground and PTO speed, you’ll get a pretty accurate assessment of the spreader’s application rate. Changing ground speed will allow you to increase or decrease the tons applied per acre until you get it right.
Combining accurate manure spreading with chemical fertilizer as required will put exactly the right blend of nutrients where they are needed. And it will eliminate green patches and lodging due to over fertilization. So using this process to develop a spreading plan will also help squeeze a little extra profit out of next year’s crop.