Cover Cropping in Integrated Farming Systems

Well last week we had boots on the ground at the Big Soil Health Event in Cedar Falls, Iowa where agronomist David Kleinschmidt emphasized the importance of considering Carbon to Nitrogen ratios of cover crops and residues, particularly when making decisions about cover crop termination. Let’s dive in a little deeper.  

“If we start using cover crops, we have to understand that the microbial activity of that cover crop, or the soil is going to break down residues and so we’ve got to look at — if we’ve got respiration rates that are really low and we throw a lot of carbon out there, that baby soil can’t digest — it’s kind of like having a steak out there. So they can’t use it, they can’t digest it, it just goes onto the floor. So we need to feed lower carbon to nitrogen ratio plants or change when we terminate that cover crop and stuff like that to make sure that those ratios aren’t going to tie up the nutrients.”

“Now, when we get a higher Co2 respiration rate, then we can build those cover crops and allow them to mature longer and have a higher carbon to nitrogen ratio because they are going to break it down and mineralize it and feed it back to the soil and the plants quicker. I also use the analogy — it’s kind of like building a fire. So, when you’ve got low C02 respiration rates — think of that like building a fire with a small kindling and you throw on a 3-foot log onto that fire, what did we do, we just smothered it out. So if we have a bigger fire with bigger sticks on it, now we can throw on that 3-foot log and it’ll burn pretty good. So, that’s the higher carbon to nitrogen ratio. Now people will go out and apply nitrogen on a cereal rye cover crop in corn and say well I am giving that nitrogen to my corn crop. Well, the microbes in that soil were sitting there and saw all this carbon material but they didn’t have enough nitrogen. So the nitrogen we apply is kind of like pouring gasoline on the fire and you’re going to get a huge burst of energy but what’s going to happen is that outside that wood will just be charred . Because the microbes have all this carbon and want nitrogen and now they’ve got nitrogen to break down some of this carbon and it gets locked up and doesn’t get released to the next cash crop.”

Really great analogy there to talk about kindling on a fire to explain nutrients and cover crops in relation to termination decisions. 

Watch the full version of this episode of Conservation Ag Update.