A scan of recent news reveals the wide-ranging impacts of too much or too little rain: intensifying drought in the Great Plains; the largest dead zone in the Gulf of Mexico ever recorded, driven in large part by a wet spring that flooded parts of the Midwestern Corn Belt; and historic summertime rain in the mid-Atlantic. Climate change promises to bring more of this rainfall variability, with devastating effects on farmers and communities. But a new report we released today contains good news: healthier soil on farms can help combat the impact of floods and droughts.
A major take-home from our report is that the soil – yes, the “dirt” under our feet – can help buffer farmers and downstream communities from these events, particularly when farmers use practices that keep their soil covered with living plants year-round. And this is good for rural and urban residents, taxpayers, and farmer’s bottom lines.
Practices that keep farmland covered year-round retain more water in soil and can increase resilience to
floods and drought. Image: USDA-SARE/Edwin Remsberg.
Farmers have the power to make their soils “spongier”
Farmers want water to stay in the soil for their crops to use, rather than running off downstream. To understand how farming practices can help with this, we asked a series of scientific questions. The first was: how does soil’s ability to absorb and hold water change in any given place if land is managed using different practices? And by that, I mean different from the norm in the Corn Belt today, which is dominated by one or two annual crops grown on millions of acres, often with soil left bare for months in between.
Practices we wanted to know more about included no-till cropping (in which soil is not plowed); planting of cover crops between cash crop seasons (when soil would otherwise be bare); use of ecological livestock grazing systems (which intentionally manage animal numbers and rotation through pastures); integration of crops and livestock; and use of perennial crops (crops such as alfalfa that have living roots in the soil year-round).
To answer the question, we performed a rigorous review of prior field studies (150 experiments in total on six continents) that used any of these practices and focused on properties of the soil that make it more sponge-like, including the infiltration rate (the rate that water enters the soil), its pore space (or porosity), and the water in the soil available to plants.
We found that:
- 70% of all the experiments we analyzed led to increases in these sponge-like soil properties, compared to more conventional practices.
- The largest and most consistent improvements came from those practices that keep roots in the soil throughout the year. So-called “continuous living cover” practices included cover crops, perennial crops, and improvements to grasslands through grazing management.
- Heavy rainfall events – more than one inch of rain per hour – could be significantly offset with some of these practices, particularly perennials. In more than half (53%) of the experiments that compared perennial crops to annual crops, water entering the soil not only increased, but did so at a rate higher than a one-inch per hour rain event. This is so critical as downpours grow more frequent across the U.S.
- Continuous living cover practices change the structure of soil, by a measurable amount. We found an 8-9% improvement in both pore space and plant available water.
The value of continuous roots in the soil is depicted in this diagram: roots can make the soil more porous to store more water, and crop cover helps reduce water losses from runoff and evaporation. When managed properly this can lead to more water available to crops.
Spongy soil can be a solution on farms…and in cities downstream
This was all very encouraging. But we also wanted understand how these farming practices could reduce runoff in flood events and increase water in the soil during drought events if they were adopted on a large scale, and how these benefits might increase or decrease given likely future climate scenarios.
Here, we also found quite encouraging results when we used a model to represent such a shift in a representative farming region, the state of Iowa. Our model predicted that shifting the most erodible or least profitable croplands in Iowa to include more cover crops and perennial crops resulted in:
- Up to 20% less runoff in historic flood events
- Flood frequency (the number of months reaching flood stage) reduced by approximately one-fifth in some regions
- Up to 16% more crop water use during droughts as severe as those experienced in 1988 and 2012
- In a hotter, wetter climate that is projected for Iowa, we found a similar magnitude of benefits: 7 or 11% more crop water use and runoff reductions of 11 or 15%
Farmers and cities know they need to adapt to a changing climate
Soil quality can affect city dwellers as well as farmers. Excess runoff from farms with bare soil can contribute to flooding in towns and cities downstream, with resulting damage to homes, businesses, and critical infrastructure. Cedar Rapids, IA, was inundated by flooding in June 2008. Image: USGS/Don Becker.
There are many approaches proposed for climate adaptation, from improved seed varieties to more efficient irrigation technologies to insurance for disasters. What our report looks at specifically is the multiple benefits of healthier soil, because we know that the solutions we describe have multiple benefits: for reducing water pollution, for cities downstream, and importantly for improving farmer’s bottom lines.
The importance of managing water in heavy rain events is also something I’ve heard farmers and researchers repeatedly address. Farmer Tom Frantzen describes for Practical Farmers of Iowa in a podcast interview (listen here at ~10 mins) the tremendous benefit of his hybrid rye crop. Because he planted the crop the prior fall and it was fully protecting his soil the following spring, he had no soil erosion at all during a damaging three-inch rain event, when many surrounding fields were bare.
A Nebraska farmer made news by sharing a video of himself wakeboarding on flooded fields this spring. Interestingly, heavy rains in April and May haven’t been enough to keep the Plains out of a lingering dry spell.
The media outlet No-Till Farmer reported in June that a soil scientist stuck in a heavy downpour watched water infiltrate down to eight feet into the soil profile while waiting out the storm, serving as a light-bulb moment for illustrating to him the true water value of soil health. That scientist now reports that on his own ranch, he and his wife are working to restore perennial cover for livestock grazing.
And we know that cities benefit as well.
“Healthy, spongier soils are a win-win for farmers and water utilities and benefit rural and urban communities alike,” said Tariq Baloch, Cedar Rapids water utility plant manager and participant in the Middle Cedar Partnership Project, which receives funding from a USDA grant program called the Regional Conservation Partnership Program (RCPP), which brings together landowners, utilities and farmers to reduce nutrient runoff into drinking water sources. “Investing in soil health means investing in soil productivity and reduced soil loss. Doing so will improve source water quality, reduce runoff that contributes to flooding and, ultimately, enhance the sustainability and prosperity of our communities.”
There is growing interest in the contribution of soils, and we hope that our analysis helps to quantify the benefits of this approach. Our report also addresses the ways that policy can help farmers make changes to protect their soil, and further posts will address this.