LETHBRIDGE – It took 10,000 years to build prairie soils so restoring lost nutrients and organic matter will not happen overnight.
The Prairies have distinct soil areas from the brown zone with low organic matter, to the richer dark brown types, to grey-wooded soils in the northern regions, said agrologist John Harapiak.
“The kind of cover that grew in that area has the biggest impact on what that soil is all about,” said Harapiak at a legume grazing conference in Lethbridge Nov. 28.
Prairie soils developed on glacial till and lakes after the ice ages.
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There is a strong clay zone to the soil in a band from Drumheller, Alta. to Kindersley, Sask., into southern Manitoba. It is associated with glacial lakes that left clays from sediment.
Farmers often create pastures in poor soil zones but then battle high salt contents where plants struggle to grow.
Soil contains pores full of air or water necessary for plant roots to grow. The amount of water held in the soil is a major issue for prairie agriculture.
On the southern Prairies where water is normally in short supply, the moisture often evaporates before plants can use it.
“In the brown soil zone your crop could really need a foot more water to satisfy its needs,” he said.
In the northern, grey-wooded zone there is less evaporation, so crops survive on less rain.
Clay soils are more finely textured than sandy soils. Rain more readily runs off clay because pores are tighter.
“When a crop dies from lack of water, there is still quite a bit of water in that soil, but it is held so tightly the crop can’t get it,” Harapiak said.
“When you get to Drumheller, Regina and Moose Jaw, one good general rain that lasts four or five days in June or July, they are guaranteed they are going to have a crop. Those soils will meter out that water slowly and those crops will survive,” he said.
Prairie soils also range in acidity level. Most legumes work best in a pH of 6.5 to 7.5 to form nitrogen-containing root nodules. Alsike clover can grow down to six, but 5.5 hinders growth in most crops. Blueberries will grow well on low pH soils often found in the Maritimes or in grey-wooded soils.
For most prairie crops, nitrogen is also a limiting factor.
Alfalfa, known as a soil building crop, can produce up to 300 pounds of nitrogen per acre, but the plant needs nitrogen to maintain itself.
Nitrogen can be delivered in chemical form or in manure. Manure fertilizes the soil and adds organic matter but its quality is variable. It should be analyzed for nutrient content and applied at the correct rates.
Half the nitrogen in manure is organic and half is mineral. Nature requires time to convert organic nitrogen to an inorganic form that plants can use.
The highest levels of potash, nitrogen and phosphorus per pound are in chicken manure, but it can be too rich and burn the soil.
Liquid hog manure can be injected into the soil. If it is incorporated within 24 hours, there is a one to four percent loss of nitrogen. Solid manure from a feedlot is bulky, high in moisture and low in nutrients because the nitrogen volatilizes.
Manure is also rich in phosphorus.
“If you apply your manure to satisfy your crops’ requirements, you are going to apply more phosphorus than you need,” Harapiak said.
The organic matter from adding manure or other soil amendments improves water holding capacity.
With four to five percent organic matter, soil can hold 165 to 195 lb. of water whereas 1.5 to two percent organic matter only holds 35 to 45 lb. of water.
