Climate Change Wreaking Havoc on Farms; Cover Crops Can Help

“Food and forage production will decline in regions experiencing increased frequency and duration of drought. Shifting precipitation patterns, when associated with high temperatures, will intensify wildfires that reduce forage on rangelands, accelerate the depletion of water supplies for irrigation, and expand the distribution and incidence of pests and diseases for crops and livestock.”

—National Climate Assessment

Declining crop yields. Crop loss due to drought, fire, and flood. Pest and disease outbreaks. Depleted groundwater supplies and degraded soil and water quality.

The National Climate Assessment (NCA) report released last week included all these evils and more in its grim forecast for American farmers. With our food supply at stake, it is a future we all share.

Tennessee farm, under 12 feet of floodwater. USDA Image by Lance Cheung

USDA Image by Lance Cheung

The NCA highlights the degradation of soil and water resources as one of the major threats climate change poses to agriculture.

“The degradation of critical soil and water resources will expand as extreme precipitation events increase across our agricultural landscape. Sustainable crop production is threatened by excessive runoff, leaching, and flooding, which results in soil erosion, degraded water quality in lakes and streams, and damage to rural community infrastructure. Management practices to restore soil structure and the hydrologic function of landscapes are essential for improving resilience to these challenges.”

—National Climate Assessment

Farmers in the US and across the world are already on the front lines of climate change, and undoubtedly have challenges ahead of them. But they also have the potential to be part of the climate change solution, and that solution is in the soil.

Restoring our soil is more than a helpful tool in our toolbox to fight climate change and water quality degradation—it is an essential task. The NCA highlights cover crops and crop rotations as a key practice to restore soil quality and help fight climate change.

Unfortunately, only a small percentage of our cropland is planted to cover crops—less than 3% according to the 2012 Census of Agriculture.

How Do Cover Crops Help Fight Climate Change?

If you know anything about cover crops, you probably know that they are great for improving soil health and water quality. Healthy soil stores more water, which makes farms more resilient to the impacts of extreme weather brought on by climate change. But did you know that cover crops can also help mitigate the greenhouse gas emissions that contribute to climate change?

NRDC asked consultant Noel Gurwick to research if and how cover crops can reduce greenhouse gas emissions. Dr. Gurwick’s 2016 analysis and literature review revealed the following ways cover crops impact greenhouse gas emissions from agriculture.

Increasing Soil Carbon Storage

Plants convert CO2 into organic matter through photosynthesis, so natural ecosystems like grasslands and forestland are incredibly important to mitigate climate change. Cover crops can also sequester carbon from the air and add it back to the soil. There’s enormous potential to fight climate change by improving soil health through cover crops—about 70% of cover crops greenhouse gas mitigation potential comes from soil carbon storage. But available research on soil carbon potential of cover crops varies widely in scientific literature, depending on the crops used, the length and location of the studies. Also, farms need to be continually managed for soil health to reach this potential; if farms are plowed up or converted to urban development, the soil carbon benefits will be lost. 

Reducing Nitrous Oxide Emissions from Groundwater and Surface Water

Crops depend on nitrogen, and so farmers add nitrogen fertilizer to soil to make sure they will have healthy crop. Unfortunately, if that nitrogen isn’t taken up by the crop, it can wash away into surface and groundwater or evaporate from the soil, where it can volatize and turn into nitrous oxide, a harmful greenhouse gas that can trap nearly 300 times more heat than CO2. Planting cover crops indirectly reduces nitrous oxide emissions because the crops themselves take up the nitrogen and add soil cover that reduces nitrogen runoff into water supplies. By reducing runoff into water supplies, cover crops reduce the likelihood of nitrogen turning into nitrous oxide.

It’s important that we also note cover crops’ impact on direct nitrous oxide emissions from the field. Soil microbes convert nitrogen in fertilizer (ammonia) to nitrate that goes into water (and can then evaporate as nitrous oxide) or nitrogen gas. Cover crops can take up nitrogen so that there is less nitrogen for soil microbes to convert, but cover crops also stimulate microbial activity in the root zone, meaning that more nitrogen is converted to emissions. If the balance isn’t just right, cover crops can increase these direct nitrous oxide emissions from the field, which might offset the benefits of indirect emissions reductions from the water. However, on balance, Dr. Gurwick’s research suggests the net benefits of cover crops outweigh this risk.  

Reducing Emissions from Fertilizer Production and Transport

It stands to reason that if cover crops are taking up more nitrogen and reducing loss of nitrogen from the field into water supplies, or even fixing their own nitrogen from the air, that farmers will need to apply less fertilizer on their crops after planting cover crops. If farmers continuously use cover crops for several years, they can naturally fix more and more nitrogen in their soil and scale back application of synthetic nitrogen fertilizer. This natural fixation reduces the embedded greenhouse gas emissions from fertilizer production and transport as well as direct and indirect nitrous emissions.

Solution: Support Farmers with Soil and Climate-Friendly Agricultural Policy

The NCA points to crop insurance as a key policy to help farms adjust to climate change. But relying on the crop insurance program as the sole risk management strategy in a changing climate may actually increase risk for farmers over time—not to mention the rising costs incurred by the program. Currently, the Federal Crop Insurance Program (FCIP) treats climate-friendly farming just the same as the status quo, and this is a huge missed opportunity. We recommend that the FCIP reward farmers who use climate-friendly techniques with better crop insurance premiums. As it is now, the FCIP encourages farmers to be overly reliant on their crop insurance policies, without making adjustments to improve their soil for the perils of a changing climate.

At NRDC, we advocate for changes to our crop insurance program that will make it more climate friendly in the long run. You can read our paper, Covering Crops, for a full list of recommended reforms that are not mentioned in the NCA report. Some of these were included in the Senate version of the Farm Bill, and we are keeping our fingers crossed that Congress includes these innovative healthy soil policies in the imminent final version of the farm bill (read my blog here for a list of the healthy soil policies NRDC supported in the Senate bill). There is too much at risk to let another four years go by without shifting to a more holistic risk management strategy for farmers.

It’s not just up to farmers to make the change to regenerative, climate-friendly agriculture techniques; we all have a stake in the future of our farms. That’s why it’s so important to create policies that will drive change toward regenerative agricultural systems. Let’s help farmers be part of the solution to climate change, instead of setting them up to be the victims.

PS: Don't forget to celebrate World Soil Day on December 5th! Stay tuned for more from my colleagues...

About the Authors

Lara Bryant

Deputy Director, Water & Agriculture; Nature Program
Blog Post

The Senate Agriculture Committee just marked up a Farm Bill today that includes some innovative new provisions to improves soil health on farms. While the overall bill has some problems and there is room for improvement, this bill does some good work on soil policy.

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