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A new study from UBC Okanagan has uncovered a surprising new source of carbon dioxide emissions – irrigating valley orchards with lake water.

Melanie Jones, professor of biology and study lead author, says soil is a huge carbon storehouse.

During photosynthesis, plants remove CO2 from the atmosphere and convert it into plant tissue. At the same time, decomposition of dead plant tissue produces CO2 and releases it back into the atmosphere.

"Some of the CO2 that was removed from the atmosphere by plants can also be converted into soil organic matter by organisms, where it can remain in the soil for hundreds of years,” says Kirsten Hannam, an agroecologist with Agriculture and Agri-Food Canada, and a co-author on the study. “So major research efforts are underway to figure out how to increase soil organic matter content.”

Increasing the amount of organic matter in soil has the double benefit of sequestering greater atmospheric CO2 and improving the ability of the soil to grow crops.

Jones, Hannam and fellow UBC Okanagan soil scientist Andrew Midwood noted that some CO2 leaves the soil during irrigation.

Working in a drip-irrigated apple orchard, tests were repeated with different water supplies, using irrigation water or de-ionized water, and the results were remarkably different.

“It turns out that some of the CO2 released after irrigation comes from the natural salts, bicarbonates, dissolved in water from Okanagan Lake as it is applied to the soil,” says Midwood. “It’s a process we had not considered until we noticed some unusual results when we traced the source of the CO2.”

Hannam adds that irrigation is essential in the arid Okanagan.

"Along with causing the release of CO2, from bicarbonates in the water, irrigation is also promoting the removal of CO2 from the atmosphere by encouraging plant growth. It’s a balance and to understand the balance, you need to know all the component parts.”