Struvite from manure safer in canola seed row

Manitoba Soil Science Society serves up a heaping helping of new research

Woman presenting at a podium with microphone.

There’s a whole lot of stinky goodness in hog manure, and researchers at the University of Manitoba have been working hard to make it more convenient for grain farmers to use.

Experimental extraction of struvite, or magnesium ammonium phosphate — the same greyish-white crystallized minerals that kidney stones are made of — has shown promise as a way to extract valuable nutrients from manure and put them in the seed row in a much more user-friendly powder or granular form.

At the recent Manitoba Soil Science Society annual conference, Yeukai Katanda of the University of Manitoba’s department of soil science, presented her findings from an experiment that looked at how struvite performed as compared to mono-ammonium phosphate fertilizer in terms of canola seedling toxicity.

Because struvite is less soluble than MAP, Katanda and her colleagues suspected that it could be placed alongside the seed in much higher quantities without killing the newly growing plants. Too much MAP in the seed row, even at levels that the growing crop requires, dissolves and leaves behind salts that can kill seedlings.

“We concluded that hog manure-derived struvite has potential to be applied at higher rates than those that are possible with MAP,” said Katanda. “Whereas MAP would induce some toxicity, struvite proved to be not as toxic.”

Manure and groundwater

Does repeated application of liquid hog manure on pastures pollute the groundwater?

Ainsley Hamm, a researcher from the university’s department of animal science, said that so far, based on her work done at a test site near La Broquerie, the answer is no.

To determine whether this was happening, Hamm identified the bacterial composition of pig slurry. Each month from May to September she looked for their presence in the soil and groundwater, which lay just four to 12 feet below the surface at the site.

After a spring application of slurry, samples showed that the concentration of one type of clostridium bacteria had increased, but by the end of the growing season, their numbers had tapered off.

“Unlike soil, in groundwater there were no significant treatment differences,” said Hamm.

Her team also looked for zoonotic pathogens such as E. coli, salmonella, and Yersinia bacteria, in the pig slurry, but could not find any. A single sequence was found in the cattle fecal samples, but since such bacteria make up around one per cent of the gut ecosystem, the researchers deemed it insignificant.

Coliform bacteria were found in the groundwater samples, but they were not necessarily of fecal origin and they couldn’t be traced back to the slurry or the cattle manure.

Testing of well water samples later the same fall found only a single genetic sequence out of 13,000 tested that could have come from the manure application.

“So overall, there is very little evidence that slurry bacteria are being transferred to the groundwater,” said Hamm.

From the Grainews website: The great pigs-on-pasture experiment

Compost and potatoes

Does a one-off shot of compost boost potato yields and help fend off early dying syndrome?

The statistics from research in Manitoba don’t really suggest that it can, said soil scientist Oscar Molina.

He and his fellow researchers tested single applications of separated, composted hog slurry solids on fields of Russet Burbank potatoes.

Varying amounts of compost were applied and incorporated into the soil to a depth of 15-20 cm, and levels of verticillium fungus were compared prior to application and before harvest.

“When we looked at disease, the reduction was not that big,” said Molina, who noted that plots where a soil fumigant was applied did show significantly less verticillium presence.

In terms of severity of early dying, the compost-applied plots showed a slight reduction of 10 to 30 per cent, however.

Forty tonnes of composted hog manure solids showed a 14 per cent yield increase over the control, which used typical production practices.

Despite the limited effect from a single dose, Molina suspects that repeatedly adding microbial-rich compost, or higher applications of up to 80 tonnes per acre, could over a longer period of time boost the population of beneficial micro-organisms populating the soil ecology and “create challenges” for the verticillium fungus that damages potato crops.

“It can survive in soil for 20-30 years, so it’s going to be there,” said Molina. “Even if you stop growing potatoes for 10 years and then start again, you will have it because it doesn’t just disappear.”

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