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Save money by saving soils: Leave a little on the top

It’s well-known that the topsoil is where producers make their money. Having good quality topsoil could be the difference between making it to the next growing season or not. The one aspect of farming that producers do or do not do that can have the biggest impact on the health of their soil is the tillage practices they use. Research on how the soil organic matter can assist producers and producers can improve organic matter through specific tillage practices has been a focus for researchers at North Dakota State University (NDSU) for years.

Posted 5/16/19

By Melissa Anderson

Chris Augustin, a soil health specialist for NDSU Extension, explained the science behind the building and destroying of organic matter and how this creates quality soil for crops to grow. While organic matter makes up only about 5 percent of soil composition, it is responsible for the majority of plant growth, providing valuable nutrients and holding water.

“Most of our soils in North Dakota are probably at barring erosion; we are at this organic matter in equilibrium. We have organic matter that’s giving us a lot of benefits physically and chemically within the soil, but it isn’t giving us the free fertilizer,” Augustin explained.

There are five different types of organic matter, with the most common being humus. Humus is a very stable organic matter that typically cannot be identified. This is the “dead” dirt. Active organic matter is the fresh residue that feeds the soil microbes. Passive organic matter, while not biologically active, greatly influences soil chemical and physical properties.

One chemical property that is highly sought after within agricultural soils is nitrogen. Soil organic matter has a huge impact on nitrogen. Potassium and phosphorus can be built up easily in soil through the use of fertilizer. Nitrogen cannot be built up easily through the use of fertilizer, Augustin explained, because nitrogen is easily lost. Upwards of 30 percent of nitrogen applied never makes it into the plant. This makes proper soil management practices very important as a way to save producers stress and money while also improving yields.

“We can build our soil nitrogen by increasing soil organic matter, “ Augustin explained.

By working to increase the soil organic matter over a number of years through good management practices, producers can increase nitrogen levels. A study cited by Augustin found that just 1 percent of organic matter contained 1,000 pounds of nitrogen. To bump up soil organic matter, producers need to reduce tillage as it reduces organic matter and also introduces greater amounts of oxygen in the soil which speeds up biological activity.

“Soil management doesn’t happen overnight,” Augustin quipped.

NDSU Soil Physicist Aaron Daigh explained that soil can best be thought of as a network of pipes where everything that impacts the soil- like water retention, heat conductivity, and everything in between that lives in the soil- is impacted by utilized tillage practices. Nature already has a way of organizing those “pipes” such as roots and earthworm tunnels that creates an optimum way for soil to function with water, heat, and nutrient flows.

“When we go in and do a lot of aggressive tillage, we disrupt that. We might get a little more heating that might dry it out for that moment that we want it to, but it might have consequences on soil health after that. You are kind of just adjusting the thermostat or water flow first thing in the morning and not worrying about how everyone in the office is doing in the evening,” Daigh said.

Over the past several years, Daigh, along with other soil researchers, has been studying the impact that different types of tillage can have on soil water retention and heat conductivity. The tillage types included no-till, vertical till, strip till, and chisel plow with field cultivation in the spring.

Cavalier County growers do mostly chisel plowing in the fall and cultivating in the spring. This is a more conventional practice, but there are producers starting to look at other forms of tillage that do less harm to soil health. According to the study conducted by Daigh and his fellow researchers, the move to other tillage practices will not only benefit soil health but also the producer’s bottom line.

Part of the study was comparing the cost of different tillage practices. The conventional chisel plow/cultivation on average would be $10 to $20 more in cost per acre than strip till, vertical till, or no-tillage.

“A lot of time we think about which management practice might be helping us yield more. That’s one way to look at it, but it’s also how much more do you need to yield to cover the cost of one management practice over another,” Daigh said.

The example that Daigh used to explain this was if it costs $25 more per acre to chisel plow versus strip till, whatever the grain market prices are at the time, that’s how many more bushels a producer would need to get out of their chisel plowed field just to pay for it before breaking even.

With chisel plowing being more expensive, a question raised may be how many times will that practice result in a higher yield when compared to other practices. Daigh found that only 12 percent of the time will chisel plowing actually produce more than the other tillage options that are out there.

“One out of eight fields will chisel plow yield higher for us. It starts adding up over time how many more bushels over that time will have price come out in your favor,” Daigh said.

Cavalier County, which has some of the most difficult fields to manage with high water table issues along with salinity and sodicity issues coupled with short, cool growing seasons, can find beneficial information from the tillage practices study. While no-till would provide the best benefit to limiting water uptake through capillary action, the soil will be cooler as a result of the heavy residue or organic matter on the surface. However, the no-till or minimal tilling utilized with vertical till also does not disrupt the sub-soil as much as the more aggressive chisel plowing which causes the soil to be warm but also dries it out.

“When it dries up, the deeper water wants to rise back up and replace it, and whatever is in that water will come along with it. If you know that you’ve got salts in a field, a little bit cooler soil might be okay if you can get better germination on that field,” Daigh said.

Over the course of the study, Diagh and fellow researchers found that chisel plowing increased soil temperature but did not hold water as well as the other tillage practices. Strip till had an in-between result with the bare areas being warmer but also drier than the areas with residual organic matter.

The tillage practices of vertical till and no-till, which leaves the most residual organic matter on the surface, held water longer but was also cooler in comparison to other practices. Vertical till, on average, held nearly as much water as the undisturbed areas of strip till and was of a similar temperature and had the added benefit of a noticeable amount of residual organic matter.

“The higher amount of cover you have, the more protection of losing your soil and organic matter you have,” Daigh said.

Vertical till will have between 60 to 80 percent more residue cover for soil. Having that cover on the surface of the soil protects it but also allows for the leaching of carbon out of the residue to occur and provide needed nutrients without having microbes within the soil use it up too quickly. The healthier soil, as a result of the thinner residue cover of vertical till with its benefits of erosion protection, water retention, and a nutrient source for microbes, will provide the organic matter needed for higher yields and a healthier bottom line for producers.