TWIN FALLS — The key to building soil health is fairly simple.
“If you have more carbon entering the soil than leaving, your kids will probably farm your land,” soil-health specialist Jay Fuhrer said at a recent soil-health workshop in Twin Falls. “If you have more carbon leaving then entering, they probably won’t.”
Carbon is essentially the fuel that runs the nutrient cycle. As microbes in the soil break down plant material (carbon), essential nutrients are released that plants can then use to grow. Carbon can be measured by the amount of organic matter in the soil.
“You need to recognize where the carbon is and where it’s going,” Fuhrer said.
Fuhrer began his career as a district conservationist with the U.S. Department of Agriculture’s Natural Resources Conservation Service in Burleigh County, N.D., in the 1980s. Much of his efforts focused on building waterways to handle water running off fields. The more waterways he helped farmers build, the more waterways the area seemed to need.
Eventually Fuhrer began to wonder why water kept running off fields instead of soaking in. He began to recommend no-till or direct seed technology. Gradually, growers began to quietly experiment with cover crop mixes.
“All no-till did was minimize carbon loss but cover crops bring carbon in,” he said.
Once cover crops were introduced into farming systems in his area, water started soaking into fields rather than running off.
Fuhrer asked if anyone had have ever dug up a plant in the summer, cleaned off the root tips and tasted them. If so, you have tasted sugar. A sugar-like substance oozes from the root tips and acts as a glue that holds soil aggregates together and allows water to infiltrate. If there’s nothing in the soil for bacteria and fungi to eat, they will eat the glue holding the soil together.
Soil aggregates also help reduce soil erosion but the aggregates are fragile and short lived.
“Nature is a continual feed system,” Fuhrer said.
In his position as the soil health specialist for the North Dakota NRCS, Fuhrer recommends cover crop mixes based on both grower goals and what condition their soil is in.
Soil microbes need a mix of carbon and nitrogen to break organic matter into plant nutrients. Soil has a carbon to nitrogen ratio of 10:1 but an ideal microbe diet is 24 to 1. Peas — a nitrogen-fixing legume — have a ratio of 29 to 1 while wheat straw is closer to 80 to 1.
If the ratio is too low, the cover crop will deteriorate quickly and the soil microbes will get hungry quickly. But a ratio that is too high may mean a grower is still looking at crop residue two years after harvest.
When he’s working with a grower who has not used cover crops previously or has little soil biological activity, Fuhrer tends to use cover crop mixes with a lower carbon to nitrogen ratio.
He is also a proponent of livestock grazing, although he says grazing is not a requirement for building soil carbon. Fuhrer likes to graze off half the available forage and let the animals trample the other half to put green material on the soil surface where microbes can easily feast. He has seen soil organic matter climb more quickly in grazed fields compared to ungrazed ones.
“Anytime you can integrate livestock, the more positive the impact will be,” he said. “But it’s not a deal breaker if you can’t graze.”
North Dakota growers are starting to plant “green” — in other words, into a living cover crop. They seed cereal rye following corn harvest. The rye may not even come up in the fall, but will in the spring. Growers seed soybeans directly into that cover crop and terminate it later.
If it’s a wet spring, growers terminate the crop later than during a dry spring. Driving planting equipment over a living crop reduces compaction issues.
“We want a mycorrhizal handshake between the cereal rye and the soybean,” Fuhrer said. Keeping a living root in the soil for as much of the year as possible helps accomplish that and helps preserve the “glue” that is holding soil aggregates together.
“Which is better for your soil in the long term,” he asked, “pulling iron or pushing carbon?”
“We want a mycorrhizal handshake between the cereal rye and the soybean.” Jay Fuhrer, North Dakota soil-health specialist