Manure may not be the most romantic area of expertise in the realm of agricultural research, but it is vitally important both as a valuable fertilizer and as a potential future soil problem, says Lethbridge Research and Development Centre research scientist Xiying Hao, who has spent the last 30 years researching the subject.
“I look at manure in terms of land management and soil health,” she says. “Because this is a semi-arid area, and very dry, a long-term problem (from manure) is salt … In terms of manure most areas already have more than their land can handle in southern Alberta. They are actually trying to ship it out elsewhere, or find other uses for it like bio-fuel. Too much manure can cause salinity problems.
“Nowadays, we put in a lot of salt (into feed) for safety, not because the cattle actually need that much salt.”
Hao published a groundbreaking paper on this subject 20 years ago, which is still standard reference in the field of soil science in southern Alberta. Her findings at the time found 60 to 80 per cent of salt in cattle feed ends up in the manure, and ultimately in the thin topsoil of the region, which will continue to slowly turn the ground more arid and saline as the decades progress.
“One thing feedlots and producers should consider is limiting the amount of salt in the cattle’s diet,” she says. “You should also maybe be checking your salinity level in the soil regularly, and making sure you are not using too much manure.”
Hao is also in charge of the Lethbridge Research and Development Centre’s long-term plot study program, which has been active since 1973. She says her research there, and future modelling based on the findings of the past 45 years, paints a vivid picture of the effects of modern agriculture on the health of the soil.
“We have started to look through these long-term studies how long it will take for soil to return to its original state pre-agriculture,” she explains. “The prediction right now is for soil returning to the pre-manure state of salinity will take almost 200 years. And for phosphorous maybe another 100-200 years on top of that. Carbon is very fast to return to its original level, maybe 10 years.
“Basically, what you will observe as this continues is decreased yield, and salt exacerbates the problem, making it even worse. By continuing to apply too much manure, you will depress the yield. I see it in my samples, but the farmers don’t see it.”
One area of optimism Hao has discovered in her more recent studies is the levels of the greenhouse gas nitrous oxide emanating from the cattle manure itself are negligible.
“The problem of nitrogen in manure management has been vastly overstated,” she states, citing the mass of evidence she has collected from broad-based soil sampling and testing in the region. “In Canada we don’t have much data on rangeland, and how much greenhouse gas emissions are associated with that. My recent tests show you rarely find greenhouse gas in rangeland soil, and even in cropland soil there has been this emission factor calculated at one per cent nitrogen in soils, but you almost never find that. What you see is more like 0.3 per cent.
“Farm operations emit very low levels of nitrous oxide. For livestock, the main (greenhouse gas) issue is entero-methane, (within the cattle), not the manure produced.”
Hao loves what she does, and hopes her research can help farmers make better decisions on how to manage their manure and feed regimes by keeping the long-term interests of the soil in mind.
“As soil researchers we tie into all the sciences here,” she says. “We tie into the crop side of things and we tie into the animal side of things. Soil is the foundation for all life.”