This bright yellow ATV was unloaded from the pickup and used to collect soil samples in our west quarter several weeks ago. We don’t have the results back yet, but the 2½ acre grid is the same as that used 3 years ago, so the maps can be compared to see differences. These conventional soil analyses are used to comply with the manure-management plan, to monitor long-term changes, and to adjust fertilizer inputs.
In addition to the standard NPK (nitrogen, phosphorous, and potassium) measurements, a conventional soil analysis gives us total organic carbon and that reflects overall soil health. Topsoil is a lot more than just a sponge to hold the chemicals used by plants. Topsoil is a complex living community of microorganisms and new types of observations are needed to more completely characterize biological soil health.
Earthworms are near the top of the soil food web. If there’s a healthy and diverse community of soil microbes, there will be lots of earthworms. So simply counting worms can give some idea of how healthy the soil is. But there are also more sophisticated laboratory measurements that can be used.
Last year I collected soil samples from four paddocks that had “rested” after grazing anywhere from a few days to several years. Biological analyses of these samples were done at a lab in Nebraska and the results support a common assertion by soil health proponents: the paddocks grazed many months earlier had better soil health indictors than those grazed most recently.
Cattle are an important part of healthy soil, however. Apparently the big “above-ground livestock” contributes to the vitality and diversity of the microscopic “below-ground livestock”. This fact has only recently been recognized and is incorporated in the concept of regenerative agriculture. In the most recent round of conservation practices encouraged by the Federal government, cover crops have been added to minimum tillage and crop rotation to encourage soil health. But, an important fourth component seems to be grazing animals. That provides some encouragement for diversified farming operations that include both row crops and grazing animals.
The whole idea of regenerative agriculture is laid out well in a recent book called Growing a Revolution: Bringing Our Soil Back to Life by David R. Montgomery. He’s a geologist who recently spoke at a soil health meeting here in Minnesota. The book does a good job of describing the excitement driving the economic interest in soil health, including examples from two farming operations in North and South Dakota.
Also, here’s a link to a brief report on the biological soil analyses done from the four paddocks on our farm. It has been shared with several people who are working to increase awareness of the importance of soil health. But, beware! There are charts here: https://retiredprofessorramblings.wordpress.com/2019/05/06/a-study-that-demonstrates-rotational-grazing-encourages-soil-health/
Very interesting. I would think one area of difficulty would be obtaining a single sample from a given paddock that was felt to be representative of the entire paddock. Would seem similar to some previous experience of taking coal samples (a subset of “soil”) when unit trains arrived at power plants from the coal mines — coal was not homogenous. Had to use statistical sampling to determine if coal supplier was meeting specifications.
Thanks, Jim~That’s exactly right. There’s a close analogy with sampling the coal trains and soil sampling. Conventional soil test procedures have evolved from a few “random” locations in a field to grids with cells of 1 acre. The biological soil analyses cost a lot more than the conventional analyses, so grid sampling will probably have to wait until technology brings down the price. In the meantime, some of the problem is reduced because the paddocks that are grazed rotationally are small—down to less than 10 acres. However, the coal train problem is really significant for the manure management programs. They sample liquid and solid manure periodically and compare the potential inputs to the nutrient needs in a gridded field. I’ll bet the variations in the manure composition are just as bad as in the coal! We should get together sometime and trade “war stories” about environmental science~ George