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.
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.
Comments
Does it take 15 years to restore soil which has been used by agribusiness for mono cropping with synthetic fertilizers?
Heather – four responses to your question.
1. In the particular case referenced above the increase of soil carbon reported (1.3%) is “over native carbon levels” (0.6%). So, this is actually additional carbon added to these soils as compared to what the carbon levels would be without agriculture (regardless of type of management).
2. Natural soil carbon building processes are extremely slow — you might say they occur on a geological time-scale. Management can increase this rate a fair amount [at least until a threshold is reached], but it is still a relatively slow process. The rates of sequestration observed on this particular farm are some of the fastest reported rates I’ve ever seen — and are a testament to the management strategy that Dale has developed.
3. The #1 criteria in determining the rate of sequestration is how much carbon is added by management. The fastest way to add carbon [artificially] is to bring it from somewhere else (ie. compost, manure, biochar, etc.). In the absence of an “amendment” approach, you have to “grow it on-site”. As mentioned above, Dale’s soils have some of the highest rates of sequestration I’ve ever seen for an annual cropping system where there was no use of an external amendment. He’s done it with a very intensive rotation of wheat and potatoes with a mustard cover crop.
4. We have established an experiment this year that artificially increase soil carbon (doubled it) using massive amounts of compost. This is a really expensive approach – and not viable in a commercial setting. Our goal, though, was to see if we could jump-start the process and begin to evaluate the benefits and value of soil carbon. There are some real down-sides to this approach, though, and we also want to better understand them. Look for results on this study in the future.
In terms of value, is the $50-$100 in carbon credits in 15 years vs $100 in one year on a per-acre basis? Or is it just a yardstick for comparison. For every $50-$100/15 yrs. from credits there could be $100/1 yr crop loss prevention?
Patrick – this is a fairly simplistic “yardstick” comparison. Let’s say that you store between 5-10 tons of carbon per acre over a 15 year period (a not-inconsequential amount to achieve). At $10 / ton as a credit you’d have $50-100 in totality over the 15 years.
The $100 worth of crop loss is not intended to be a prediction of the value of the carbon from increased water holding capacity — that would depend on crops and the variability of weather. However, it’s easy to see from the illustration how a single high-heat event occurring even once during the 15 year period would be worth as much as the “carbon credit” value.
Hi chad,
Have you looked at numbers with overwintering cover crops or just annual, spring grown mustard? In our soils, it’s not too hard to get up into the 4% OM range, especially with vetches and overwintering clovers, with rye, but then growers have the fuel and expense of incorporation, and they have to get planted while the cover crop can still make good growth before winter. Just wondering if your work is looking at west side cropping or focused on the Basin.
Anne,
I think Craig Cogger has some data for west-side conditions with variations in cover-crops. I’ll see if he will contribute some knowledge along these lines.
One of the important points you raise, though, is how valuable carbon additions are must be viewed in relation to initial conditions. A 4% soil is much, much, much more fertile than a 0.6% soil. How much more valuable is gaining an additional 0.7% in either situation? Does doubling in either case make the same contribution? Is there a threshold (e.g. 2%) at which most of the benefits are seen? At what point do you encounter diminishing returns? We really don’t have a lot of answers to these questions – and I suspect that it may boil down to very specific and localized conditions.
The one thing we know is that more is better …to a point.
In our organic vegetable systems experiment we compared two soil amendments (compost vs. broiler litter) and two cover cropping systems (fall rye-vetch vs. interseeded vetch) on an agricultural soil in western Washington. The compost supplied about 3-4X as much carbon as the broiler litter, and we observed increased soil organic matter, reduced bulk density, and increased infiltration rates in the soil receiving the compost. We made limited measurements on water holding capacity, and did not see differences. The fall-planted cover crop supplied more C than the interseeded crop (we’re still working up the numbers, but it is probably a factor of at least 3 or 4 as well), but we have not seen significant cover crop effects on soil physical properties. This indicates that the cover crop effects are harder to discern in soils that already have moderate to high levels of organic matter. There is no doubt that cover crops still provide benefits through N fixation, soil protection, and competition with weeds, but effects on physical properties appear small in our soils.
Hello Chad,
I can see that soil carbon really benefits growers in arid climates that need to maximize the water holding capacity of their soil. What have you heard from growers on the wet side of the state in terms of soil carbon (and in turn better soil structure) increasing soil infiltration rates? In theory that would be one of the benefits, but I would love to know if any growers are noticing this.
[…] Kruger blogged recently in “When soil carbon sequestration REALLY pays,” what will really drive farmers to build soil carbon is “adaptation and […]