Thomas looked out over his field after a long season, between less-than-ideal rainfall and some late winter storms he had still managed to eek out a decent yield for his Colorado corn field. Now was not the time to rest, however, as Thomas observed unsightly stalks of corn rising from the vestiges of his previous investment. In years past, he had always tilled the stalks below the soil’s surface to clean his fields in preparation for a new season, but a buzz was generating within his farming community to the benefit of maintaining residual. He thumbed the keys to his tractor passing the worn but familiar green and gold deer between his fingers as he weighed the risks of deviating from a program that had long been his status quo . Having done his research, he was still uncertain of the benefit, and full of concern for lingering pests and a disruptive spring planting, he gripped his keys into a loosely held fist, “maybe next year,” he muttered as he committed to what he knows.

Thomas is a representation of the struggle to face the unknown and build new practices, the risks that are taken when deviating from a plan that has been in place for generations. Too often practices like residual management that hold immense benefit are overlooked due to a lack of understanding and limited confidence to control conditions moving into the next planting season. Our goal is to share some of the benefits of maintaining crop residual and concepts behind degradation rates and how to exercise more control over a process that is typically temporally governed.

Carbon to nitrogen ratio of plant material

One of the primary contributing factors to degradation speed is the carbon to nitrogen ratio. Depending on the crop and the residual that is left behind, this ratio will shift. For example, soybean or peanut are going to leave rather low carbon to nitrogen residual (20-40), where corn will have a carbon to nitrogen ratio often between 50-70.

Using this logic, higher carbon substrates lack sufficient nitrogen for rapid degradation. All organic matter is broken down by soil microbes, and microbes require carbon and nitrogen in certain ratios to reproduce, if there is too much carbon and not enough nitrogen the ratio becomes imbalanced, and the rate of degradation slows.

Bacteria and fungi

Bacteria are the fastest group of degradative soil organisms; they quickly leverage nitrogen and simple sugars incorporating them into biomass. When looking into speeding up degradation, bacteria are typically the group that is considered. Adding more nitrogen to a high carbon residual is often an attractive proposal to help stimulate bacterial activity, however, it’s important to consider the role of fungi within the soil ecosystem before resorting to increased exogenous nitrogen usage.

Although fungi degrade material more slowly than bacteria, they have a much higher carbon to nitrogen ratio and are equipped with the tools needed to degrade complex lignin structures. Striking a balance between beneficial bacteria and fungi can go a long way towards more rapid residual degradation, selecting products that can stimulate fungal activity, like fish hydrolysate or kelp extract, also helps to boost in field activity.

Maintaining fungal biomass on residual also runs the benefit of a healthy soil microbiome leading into the next planting season. Inoculating soils with diverse microbial extracts, like from the TerraPod, helps to ensure the right saprophytic microbes are going to work on your residual from last season.

Efficient microbes within the ecosystem

In some fields, you may find fungal growth on some residual. It is worth taking note of the microorganisms that are working efficiently to break down your residual biomass. The affinity of a given microbe for the residual organic matter can be an effective tool to speeding up degradation. The microbe can be isolated, replicated, and reapplied after harvest to help spread the microbes to every corner of your fields. It is a highly customized solution that you know works because you found it in your very own fields!

Benefits of maintaining residual – soil armor

There are a lot of benefits to maintaining crop residues on the soil, for one they are sources of nutrients. Taking the residual off the fields is removing carbon, nitrogen, potassium, phosphorus, and other micronutrients from your system. Even tilling the residual beneath the soil can lead to rapid volatilization of the material, releasing most of the carbon and leaching valuable nutrition from the soil.

Residual helps to reduce erosion and compaction by forming a barrier over the top of the soil. The lack of direct sun on the soil surface can also help to hold water within the soil system and the increased carbon of the organic matter will help to fix nutrients in the biomass, making them more resistant to loss in the off season.

As the climate becomes less predictable, soils need to have elastic response mechanisms and higher resilience to perform at their optimum levels. Increasing the carbon content of the soil through residual management helps to build soil health and resilience over time. The long-term picture should always be considered when implementing different practices, and we need growers to start implementing novel processes to weigh the costs and benefits more effectively.

Terraforma works with a network of growers who are exploring these new frontiers, committed to finding better practices that build health and wealth over time.