Deep soil testing tracks nutrient movement
Going far below the surface for soil testing has been a trademark in eastern Manitoba for more than 10 years. Samples for nitrogen content are routinely collected at 1-ft. intervals to depths of 8-10 ft.
Two farm groups and a private consultant use hydraulic soil sampling machines to collect deep soil samples. The machines can be mounted on trucks, trailers, tractors, skid steers or ATVs.
Private Ag consultant Ron Tone, Tone Ag Consulting, St. Pierre, Manitoba, does soil sampling as part of his package for developing manure management plans, environmental audits and agronomic assessments on irrigation projects.
“We can go as deep as 40 ft.,” Tone says.
In practice, sampling to 10 ft. has been adequate. Clients for this deep sampling include a few large hog operations and potato growers.
“We like to look at 1-ft. increments down to 10 ft. or to the depth of the water table,” he says. “We charge about $100 Canadian per site to that depth and do a minimum of three sites on a field.” Lab fees are additional.
Tone finds more problems with high nitrogen values in heavy clay than on light soils. It's a function of the cropping practice rather than soil type, he says.
In Tone's area, the manure-treated clay soils are usually in an annual crop, whereas the light soils are usually in grass or other forage. Even at double the recommended rate on grassland, there has been no problem with nitrogen leaching.
“Compared to grass, annual crops don't appear to take up as much nitrogen,” he says.
A producer-based, deep nutrient testing program began in Manitoba in 1992, says John McGregor, Manitoba Agriculture extension specialist at Steinbach.
“The Southeast Soil Conservation Organization (SESCO) was trying to determine base levels for nitrates in the soil. There were concerns about nitrates moving down in the different soil types and to what levels.”
A 6-in. test with a hand probe had been an industry standard. Sometimes crops lodged after a soil-test recommendation had been followed.
SESCO introduced deeper sampling. Today, SESCO and a second group, South Interlake Land Management Association, use a Giddings Machine Company unit made in Ft. Collins, CO. A four-cylinder engine mounted on a trailer operates the 4-in. auger.
“Our testing showed nitrogen content in each 1-ft. level down to 6 ft. was fairly high — except for the top foot,” he recalls. Today, 2-ft. sampling is the recommended minimum and some growers use 4-ft. samples.
Some older livestock operations had a long history of applications close to the barn. “Deep sampling showed them it was time to spread it elsewhere,” McGregor says. “They were starting to lose the yield advantage.”
SESCO recently re-sampled sites where 9-ft. samples had led to management changes in the late 1990s.
“We saw they were drawing down the surplus nitrogen levels on those fields. The producers were saving money, because they basically had applied no fertilizer for four or five years on some of those fields,” he says.
Manitoba's hog industry went into a major expansion phase in the southeast around 1997. Manure application regulations became more stringent. Today, SESCO tests approximately 20 fields a year where manure has been applied.
“On the newer operations we're not seeing a buildup of nitrogen in the soil profile,” says McGregor. “With changes to environmental regulations that require manure management plans, we're seeing an attitude change. We're treating manure more like fertilizer, putting it on at rates that match crop production.”
A study of nutrient penetration under an outdoor hoop structure for hogs was presented in September 2004 by John Maltman, provincial swine specialist from Dugald, Manitoba, at the first annual Bedded Livestock Conference in Iowa. The deep sampling methods were used.
“We found that nitrogen and phosphorus were not moving down,” says Maltman. “Chlorides are, but that's only an indication that moisture is moving down. It showed we can continue to construct shelters this way, regardless of the soil type.”
Results from similar testing in Iowa and Australia were quite different. Both climates are warmer and rely heavily on sprinkler systems to cool hogs in the hoop structures. Iowa producers used corn stover for bedding, while Australian producers used cereal straw.
“The difference is bedding management,” says Maltman. “Cereal straw is very absorbent. By the time animals are out of the hoop structure, in our climate, the straw probably is 3 to 4 ft. thick. Most of the ammonia is tied up in the straw. The phosphorus, as we expected, is tied up in the top 18 in. of soil.”
As a result of deep soil testing efforts in eastern Manitoba, he says, protocols have been developed for fields when tests do show that nitrates are moving down.
“If nitrogen is a problem at 4 or 5 ft., we recommend that canola be grown on that field as often as the rotation will allow,” says Maltman. “At less than 4 ft., we recommend cereals. At more than 5 ft., we recommend a permanent cover with alfalfa, because alfalfa roots will pull nitrogen up from as much as 12 ft. down.”