by Courtney Llewellyn
Regularly testing your soil to make sure it’s performing as best as it can is important, but so is testing the manure you spread as fertilizer. Mahmoud Sharara, waste management Extension specialist with North Carolina State University, shares the best management practices for sampling manure.
There’s a nutrient cycle on any animal operation, and the ultimate fate of manure is why it needs to be sampled, according to Sharara. The cycle starts with feed that different species eat, and those nutrients either leave the farm as finished animals (or animal products) or they remain on the farm as manure, which is then returned to fields to feed crops. Sampling manure ensures its proper management, which can in turn reduce fertilizer purchases, reduce manure nutrient losses (as it’s only applied when necessary) and result in better monitoring of manure treatment systems (be they compost piles or treatment lagoons).
Another reason to regularly test manure is government compliance. Regulations vary depending on what state you farm in, but in general labs will need to test samples of the manure to be applied to fields as close to the time of application as practical.
Sharara outlined the elements of proper manure sampling, if you’re doing it yourself: when to collect samples, where to collect them, how to properly collect them, what to do with your samples and what to do with your lab analysis.
As for the timing, Sharara said, “If you sample before [you spread manure], you’ll have a better idea of how much will need to be applied. You want to allow enough time to get results but not do it too early.” He noted that levels of nutrients can fluctuate based on the time of year. You also want to consider the turnaround time; at the NCSU lab, the timeframe is usually 10 to 14 days, but he said it’s safer to aim for three weeks to a month.
If you test samples after application, that can affect subsequent applications, which can cause violations if you’re already too close to nitrogen limits on fields, Sharara said. If the sampling is done during application, farmers will see the most accurate estimate of the nutrients in their fields. However, sampling during application provides a limited chance in which to adjust any issues that may arise.
It’s also recommended to sample more frequently (about once a month) during your application window. Sharara said to sample manure before hauling if you plan on applying anything from an agitated lagoon. Farmers should also consult previous years’ records to compare year-over-year analyses and detect trends. “Good recordkeeping can inform your next season and lead to multi-year analysis results to develop an operation-nutrient range,” he explained.
In addition to when, you also have to consider where the manure is being sampled. Is it coming from a lagoon, piles or windrows? When possible, it’s best to sample while it’s being hauled to assess the actual nutrients being moved.
The “how” is important as well. If you’re collecting samples yourself, you need the proper tools. For solids, that includes shovels, buckets, augers, sealable bags, gloves and a marker for labeling. With solids, collect multiple samples from different points inside the manure pile, getting different moisture levels and ages, and mix them in a large bucket to homogenize them. For liquids, you’ll need clean capped bottles, a telescopic arm, a sludge judge and a marker. It’s good to have a partner to assist you for safety, especially when working around liquids and lagoons.
Once the samples have been collected, either by you or a technician, the analysis results from the lab will break down the nutrients present in parts per million and will often include an estimate of nutrients in pounds/1,000 gallons.
“Manure sampling is critical to compliance and the sustainable operation of animal operations,” Sharara concluded. And proper sampling – along with thorough recordkeeping – will help farmers anticipate any issues in their nutrient systems.