Agriculture’s Role in Nutrient Loss

Storing Water on the Land Isn't Just About Flood Control, It's About Capitalizing on Available Nutrients as well

Checking the news feeds across my conservation agriculture news, common thread are noticed. Increased nutrient loads at Lake Erie, Chesapeake Bay, the ever-present "dead zone" of the Gulf of Mexico and calls for more action on the state of LakeWinnipeg. The human contributions are relatively constant, albeit constantly increasing, so when things go south, the blame gets placed on agriculture.

Superficially, it all seems very logical. When you look outside of the urban areas, the watersheds are predominantly agricultural areas that are controlled by farming practices. If those landowners are in the business of draining, fertilizing and spreading manure on those lands, everyone is quick to assume that farming is the prime culprit.

Fortunately in Manitoba we have the ongoing research projects contained within the Tobacco Creek Model Watershed that paint a slightly different picture. What researchers from AAFC, Environment Canada, MAFRD and several universities have found is that the edge-of-field run-off is generally quite low in nutrient loads. Have researchers in other jurisdictions taken the time to actually track where in the watershed these nutrients are originating? Not likely.

Researchers from the University of Manitoba are in the process of using DNA fingerprinting techniques on the sediments east of the escarpment to determine where the loadings begin. Work is ongoing, but preliminary results would suggest that a lot of our nutrient loading occurs as the result of stream bank erosion.

Stream banks by their very nature are ideal areas for plant growth. They have ready access to abundant water, and since the creek itself drowns out tree growth, lots of sunlight as well. As the topography of these riparian areas does not lend itself to mechanical harvesting, most of the plant growth is left to winterkill and decompose at the edge of the creek over the coming months. In spring run-off and rainfall events, this nutrient-rich material is on the surface that erodes away first and makes its way downstream to Lake Winnipeg.

Further research on the South Tobacco Creek conducted by AAFC tells us that while Beneficial Management Practices (BMPs) have been very effective at lowering nitrogen and sediment loadings, they have been less effective at lowering phosphate contributions. In many situations of reduced-tillage systems and vegetated buffer zones, dissolved phosphates from decomposing plant matter have actually increased in the resulting run-off waters.

All of this takes us back to the best solutions to deal with the resulting problems. Adjacent to Lake Erie and Chesapeake Bay, there are more calls for increased controls on the farm use of fertilizers. Unlike urban fertilizer use, agriculture does not use nutrients for cosmetic purposes. If we reduce usage, there will be a corresponding drop in food production. If the edge-of-field run-off is already low on nutrient escape, will this approach work? Not likely.

We know that the agricultural contribution at LakeWinnipegis about 18 per cent of the total annual nutrient loading. (This is based on total loadings and total basin area. Yes, I know there are different numbers for nutrient-specific loadings and province-specific areas, but I'm a big-picture sort of guy.) The nutrient value of those loadings is approximately $100M per year if those nutrients were in the form of commercial fertilizers. Unfortunately they are not. They are in the form of dirty water.

The Tobacco Creek Model Watershed has received funding under the LakeWinnipegBasin Stewardship fund to increase stored water on the land. The area has received 120 per cent of normal rainfall so unlike the flooding issues fromYorktontoPortage la Prairie,crop conditions have been close to ideal except for the hot, dry weather in late July and early August. Today, it would be easier to sell ice to Inuit than to convince these farmers that they need to store more water, but not everywhere has been so lucky.

Source: Manitoba Co-operater

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