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In-soil fertilisation leads to less phosphorous loss

A study shows that in-soil placement of fertiliser results in less phosphorous loss from snowmelt runoff.

Water that runs off a field can take some of the valuable fertiliser with it. In Canada this water can take 2 forms: rainfall runoff or snow melt. It’s the latter type of water – snow melt – that causes the most runoff losses in the Canadian prairies.

“Right place, right rate” calculation

Knowing how each form of runoff affects fertiliser will impact a farmer’s “right place, right rate” calculation. Rainfall runoff and snow melt runoff may result in different fertiliser management recommendations. So, Jeff Schoenau from the University of Saskatchewan and his team focused on runoff from snowmelt, reports ScienceDaily.

“This work contributed to finding better practices for phosphorous fertilisation,” Schoenau explains. “These will help growers in the northern prairies make better use of their fertiliser. By applying the fertiliser in the right place at the right rate, growers can greatly lower the phosphorous loss from snowmelt runoff.”

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For the “right place” part of the fertiliser, they studied applying fertiliser to the top of the soil and leaving it there versus in-soil placement. The in-soil placement can involve placing the fertiliser in the furrow with the seed or next to it in a separate furrow. It can also refer to broadcasting fertiliser onto the soil followed by mixing it into the soil rather than leaving it on the surface.

Less phosphorus loss

Different amounts, or rates, of these two forms – on-top-of-soil and in-soil – were applied. The results showed that the in-soil placement resulted in less phosphorous loss from snowmelt runoff.

“In the case of phosphorous fertilisation practices, in-soil placement is helpful because it can help roots better access and take up phosphorous,” he says. “Also, having the phosphorous placed in the soil rather than on the surface reduces its interaction with runoff from snowmelt in early spring.”

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Fertiliser is being placed in the row whilst planting potatos, using a so-called Ferti-Flow system. - Photo: Frank Uijlenbroek
Fertiliser is being placed in the row whilst planting potatos, using a so-called Ferti-Flow system. - Photo: Frank Uijlenbroek

Too much phosphorous can cause harm

Phosphorous is often applied to fields as fertiliser. It can come in different forms, and end up in different forms depending on the chemistry of the soil. When applied, it undergoes transformation in the soil through reaction with minerals and organic matter. Ideally, it will end up in a form that the plants can use. However, too much of a good thing can be bad because it can run off and cause harm to nearby rivers and lakes.

Jeff Schoenau, University of Saskatchewan:

Benefits can be realised by getting the phosphorous fertiliser into the soil where the roots are rather than leaving it on the surface

“In our research we were able to employ some novel techniques to help us find the nature and origin of some of these forms in soil and water,” he says. “Our main message here is that benefits can be realised by getting the phosphorous fertiliser into the soil where the roots are rather than leaving it on the surface.”

Runoff from snow different than runoff from summer rains

Schoenau explains that runoff from snow is different than runoff from summer rains. The force of rainfall can loosen pieces of the soil containing phosphorous. Snowmelt runoff moves the element differently, mostly in its dissolved form from the soil and pieces of plants on the surface.

“In order to encourage growers to follow the best practices, it’s important to document and understand why and how a specific practice like the one we tested works,” he says. “I am both a scientist and farmer on the prairies interested in furthering the environmental and economic sustainability of our modern cropping systems.”

Also read: Installing phosphorous-filtering technology at the farm level

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