The first port of call this morning was to the NRCS, where I met with Jay Fuhrer. His job title is “District Conservationist”, and he is well known for hosting curious farmers from around the world. For some reason Burleigh County, which encompasses some of Bismarck, has a concentration of farmers and researchers who are interested in soil health.
There is that term again, so I ask Jay how he defines it. The answer is the same as I read last night in the USDA papers, and not terribly satisfying. I can’t help but be a little skeptical when people are telling you to do something that they can neither define nor measure. Maybe I am too cynical?
I ask Jay whether he thinks SOM correlates with soil health, and the answer is no, the system is too complicated for that. Having thought about this subject a bit more today, it occurs to me that there is a bit of a problem with the literature. The common method for measuring SOM is to perform the “loss on ignition” test. This involves the following steps, or a variation thereof:
- Heat soil to 105C for 90 minutes
- Weigh soil
- Heat to 500C for 2 hours
- Weigh soil. The carbon will have burnt off, and so the difference in weight is considered to be approximately the weight of the organic matter that was present.
Now if we consider the following USDA quote, there is a bit of a problem.
“it takes at least 10 pounds of residue to decompose to 1 pound of organic material”
If you test a soil sample with 10 pounds of residue and 1 pound of organic material in it, the result will show 11 pounds of organic matter, or something close to that anyway. This begs the question, how do you measure true SOM (sometimes called humus), and what is the USDA actually referring to when it talks about the value of SOM? Further investigation needed.
A name I am hearing a lot at the moment is Rick Haney, a scientist for the USDA, based in Texas. He has apparently developed a test which measures several factors and combines them into an overall soil health score. I wonder how well the test results correlate with real world productivity, that is the real key in my opinion. It sounds like I should have planned a visit down there, but it is probably not doable now.
At this point I was whisked off by another USDA employee, Darrell Oswald. He moonlights as a farmer (sorry, rancher) too, and we drove up to his farm (sorry, ranch) near the town of Wing, population 2oo.
Darrell grew up on the ranch, being told by his dad that he should really get a proper job when he left school. It was hard work running their 200 cows, and making hay to feed in the winter. After he took over from his dad, he met Ken Miller, another rancher who also works for the USDA. Ken is in to holistic management, and intensive rotation grazing. Darrell described him to me as “one of the top 10 graziers in the world”.
The traditional ranching method around here, and probably the rest of the country too, is to leave a group of cattle in one field for the entire year, and then use the rest of the land to make hay. This worked fine on Darrell’s ranch, but they had to rent in extra land, and then feed hay for 6 months a year.
Following advice from Ken, the first thing Darrell did was split the 4 existing paddocks into about 25, and then combine the 4 main groups of cattle into 1 large herd. This meant that instead of being grazed all year round, each paddock only had around 10 days with cattle on it, and 345 resting (if you think these numbers don’t add up, remember the winter period has no grazing).
Within a few years, the grazing season had extended from 6 to 8 months, and they no longer needed to rent land for hay production. Before you ask, they do not buy in any forage either. This seems like an excellent result to me, as the main cost of keeping cattle is incurred over winter. It is also a pretty low intensity grazing system, with the cows moved on average only every 4-5 days. Darrell thinks that if he was a full time rancher, and could move cattle at least every day, then he may be able to double his herd in size without taking on more land. I hope he tries one day.
He does still make some hay, and one field I saw had been in production since the 1970s. By 2006 the fertility was so low that it was difficult to get anything meaningful from it. Since then it has had several years of all-year cover cropping with plants like oats, peas, millet, turnips and clover. In 2011 he considered the fertility to have been built to a point where maize could be grown. This crop was partly fertilised with nitrogen at three different rates, 90lb/ac, 30 and 0. There was no difference between the three treatments.
Unfortunately we did not have a spade to hand, but I dug around with my fingers. The top inch of the field was pure compost, like you can buy at the garden centre. I have literally never seen anything like it, hopefully the photo above illustrates the point. As a rough estimate, if we assume it is half as dense as normal soil, then that inch would weigh about 185t/ha. I think a normal compost application on farm land in the UK is 10-20t/ha? OK, so the field was out of production for several years, but the time has not been wasted.
We went to a couple of other farms that afternoon, and took a look at some fields that were in the process of transitioning from tillage systems to continuous no-till. The picture above is the best example of a tillage pan I have ever seen (not a huge data set). The pea roots had gone down about 4 inches, hit a sudden density change, and turned 90 degrees to grow sideways. I suppose the normal cure would be more tillage – time to get off the hamster wheel perhaps?