By Chad Kruger
Source: WSU CSANR Perspectives on Sustainability
The dog days of summer have arrived in Eastern Washington – with daily temps reaching the high 90s every day. This is the second extended stretch of heat in the region this year.
One of the critical concerns of high temperature days during the growing season is that irrigation and precipitation rates can’t keep up with the rates of evapotranspiration (ET = evaporation + water used by the crop) leading to reductions in yields or, depending on timing, reductions in crop quality as our fragile soils dry out. During these really hot stretches, as you travel through the Columbia Basin you’ll notice that irrigation systems are running 24/7 on growing crops to minimize the heat-induced losses. The map below from the WSU Ag Weather Net shows that much of the central part of Washington experiences ET rates ranging from 11-15 inches of moisture.
Accumulated Evapotranspiration (in) for Jul-01 to Jul-31-2013 – WSU Ag Weather Net
While there is a lot of discussion about the potential of financial incentives such as carbon credits to encourage the adoption of soil carbon sequestration by farmers, I think that in the long-run it is more likely that farmers will make the decision to sequester carbon on the basis of the “agronomic value of carbon”.
For instance, Dale Gies, a potato and wheat farmer from Moses Lake, who has focused on building soil organic matter (i.e., carbon) for the past 15+ years in an effort to improve soil quality, productivity, disease resistance and water holding capacity, has doubled his soil carbon from 0.6% to 1.3%. That doubling of soil carbon has increased his soil water holding capacity by approximately 30% — making it possible for his soils to hold enough water to “weather” the hot days when ET exceeds irrigation rates. While the value of that carbon for carbon credits or incentives might have only amounted to $50-100 over the past 15 years, the value of avoided crop loss could be equivalent to more than $100 per year!
For a dryland wheat producer, the concern may not be extreme heat affecting the yield of a growing crop (the wheat is usually drying down for harvest when summer gets really hot), but rather how much moisture the soil has retained when it’s time to plant the next crop – usually at the end of summer/early fall. Every extra bit of soil carbon holding more water makes the germination and establishment of next year’s crop more successful.