There are many variables for growers to consider when they’re implementing cover-crop mixes into their no-till rotation — including mix design, carbon-to-nitrogen (C:N) ratios, cash crop goals, termination strategies and biomass management.

“The goals will be different for everyone and will change from field to field, with changing conditions and with time,” says NRCS district conservationist Adam Daugherty.

Here are strategies for thinking through some of these important decisions that were shared by Daugherty at the National No-Tillage Conference last January.

Staying in Balance

It’s vitally important for no-tillers to understand the C:N ratio of crop residue and how they play a role in the soil. C:N ratios are especially important when ascertaining how long it will take for soil microbes to break down residue.

“The soil is a jungle ecosystem,” says Daugherty. “It has big and little critters. They all have to eat and they all play a role in cycling residue.”

The ideal C:N ratio to feed microbiology in the soil, so it can efficiently consume biomass and cycle nutrients, is 24:1. Higher C:N ratios will slow down the decomposition of biomass and lower C:N ratios will speed it up, Daugherty says.

Most annual cropping systems have a high C:N ratio: wheat straw is 80:1 and corn stover is 57:1, which means residue decomposes slowly and leaves more protective biomass on the soil surface. Plants with a lower C:N ratio (legume hay is 17:1) decompose residue faster and result in less cover being left on the soil surface.

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