When drainage is added, what happens to soil carbon?
Written by Jonathan Eisenthal
For farmers looking to boost productivity, tile drainage is a great investment. In the last decade, the trend of adding drainage is gaining speed in northwest Minnesota. But how does drainage affect the carbon cycle in the soil?
Drainage carries away some soil carbon, but it can also boost organic matter by making the soil more productive, according to Anna Cates, an assistant professor at the University of Minnesota’s College of Food, Agricultural and Natural Resource Sciences (CFANS).
In collaboration with Lindsay Pease, a CFANS assistant professor and Extension specialist, Cates is taking a closer look at how newly installed tile impacts the soil carbon sequestration balance and how long it takes for the system to rebound and rebuild in comparison to undrained fields. The research is funded in part by the Minnesota Corn Innovation Grant Program.
On a 60-acre plot at Extension’s Northwest Outreach and Research Center in Crookston, Cates and Pease will conduct the research, dividing the land into four sections, two drained and two undrained.
Carbon exists in the soil in a number of forms, according to Cates. One is in microbes that live in the soil. The biomass of microbes will be measured because that material is more likely to be soluble in water, making it easier to move through the soil profile. Carbon is also found in the mineral particles, but that material is less susceptible to drainage.
In order to get the full picture of the carbon cycle, the research will examine the air, water and soil.
“We’re trying to get that big picture of what is happening,” said Pease. “We’re looking at the carbon and nitrogen, hand in hand, to look at how when you add subsurface drainage, you change the moisture of the soil, then how is that changing the cycling of the nutrients? And potentially, how does that impact soil fertility later on?”
A more precise picture of mineralization will help farmers better calculate fertility needs for their crop in land that has just been drained.
“There’s a whole food web down there,” said Cates, who directs the Minnesota Office of Soil Health at the University of Minnesota. “When you feed any carbon to that web you get a number of benefits. When you build up soil organic matter with plants decomposing and all kinds of other organisms living there, then you get a fertility benefit. That’s something the farmers notice right off the bat. Everybody knows that high organic matter soil is more fertile than a low organic matter soil. But you also get a structure benefit.”
Cates said the organic matter helps hold soil particles together, providing soil aggregation allowing for water infiltration and holding capacity.
“The ability of the soil to have both small pores to hold moisture for a long time, and large pores to let water through rapidly—that really comes down to the soil’s ability to build aggregates, and soil organic matter is critical for building aggregates.”
