Re-thinking the long-term value of manure

(Chase Chambers/RealAgriculture)

Research is valuable on both sides of the border — and we can learn a lot from each other through trials that have already been conducted.

One of these ongoing trials taking place south of the border is looking at the legacy of manure, in southern Idaho.

Southern Idaho happens to have a lot in common with Southern Alberta, as the area also grows plenty of sugar beets, potatoes, and has a fair amount of irrigation acres.

Dr. David Tarkalson, research soil scientist at the United States Department of Agriculture (USDA), based in Idaho, says current thinking around nitrogen availability under manured situations is three to four years of release for subsequent crops.

But research conducted in Idaho says manure applications actually have a much longer impact than originally indicated, in some cases, up to 13 years. The reason for that hinges on water availability — which, in irrigated areas, can be more controlled.

“When you’re irrigating, you’re able to meet the full crop demand. So water is no longer limiting,” Tarkalson explains. “So then you’ve got to start focusing on your other nutrients that can be limiting the production.” In the case of soil nutrients, it’s looking at the microbiome. The microbiome is a super complex system, and one science is really just starting to understand.

What’s fascinating is that the original study wasn’t actually meant to look at manure applications, but after years of soil testing the same plots and areas, the USDA started to recognize that the manure may actually be staying in the soil for much longer than originally thought, he says.

Tarkalson says now work needs to focus on the effect of that manure on the native microbiome, how it’s changing, and how the changed microbiome impacts crop production.

When it comes to making the most of manure, soil testing is best done in the spring to match soil and crop needs to fertility additions. How, when, and where to apply manure is still a complicated question, as the best time for manuring land doesn’t always line up with the most convenient time for farmers to apply it.

Check out the full conversation between Tarkalson and RealAgriculture’s Kara Oosterhuis, filmed at Farming Smarter’s Field Day at Lethbridge, Alta., earlier this month:

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