People often ask how much livestock, and in particular, pigs, Manitoba can handle. 

 

Don Flaten has the answer. It’s 598,802,395 nursing and weaner pigs. Or 7,142,857 calves less than a year old. Or 2.5 billion broiler chicks.

 

However, he’s also quick to point out those numbers are meaningless, as they only take into account the phosphorus manure those critters put out, not the fact that there needs to be a base of breeding stock to produce them.

 

The University of Manitoba soil scientist crunched the numbers to illustrate his main point to his audience at Manitoba Ag Days. While phosphorus contamination does exist in some areas of Manitoba, and while the potential exists in other areas, the province as a whole does not have a problem with excess nutrients.

 

If the only factor to consider was the amount of nutrients that are taken up by crops, the province could have five to six times the number of animals it has today.

 

In fact, 73 per cent of the province’s soils are deficient, which makes it second only to Saskatchewan for having the highest rate of phosphorus deficient soils in North America.

 

Annual crops in this province remove, on average, 101,000 tonnes of phosphorus annually. The province’s farmers add about 114,000 of synthetic fertilizer and another 17,000 tonnes in the form of manure, leaving a relatively small surplus.

 

That said, Flaten noted using livestock manure as a fertilizer is fraught with management challenges, mainly because the livestock population isn’t even dispersed over the landscape.

 

As well, the ratio of available nitrogen to phosphorus in manure is typically less than one to one. Yet the removal ratio of nitrogen to phosphorus is around two to one.

 

“If you apply manure to meet the nitrogen-removal rate, you are over applying phosphorus,” Flaten said.

 

And it’s possible to get into trouble fairly quickly, depending on the type of manure being applied. For example, cattle manure contains relatively higher levels of phosphorus. So if a farmer applies manure to meet an 80-bushel yield goal, he or she needs 3,390 gallons of liquid hog manure or 21 tonnes of cattle manure per acre.

 

That equates with 72 pounds per acre of phosphorus from the hog manure and 134 pounds of phosphorus from the cattle manure. Based on crop removal rates, those applications create a surplus of 37 pounds per acre from hog manure and 90 pounds per acre for cattle.

 

The scenario is even worse when using manure on grazing land because cattle only remove about five pounds of phosphorus per year. In short, a farmer would only apply cattle manure once in 56 years in order to avoid excessive applications.

 

Flaten stressed that manure applications must be balanced with the farming system in use, and that nutrient management has to be addressed on a case-by-case, field-by-field basis.