Soil has been overlooked because it’s underfoot, but he and other soil scientists around the world have been trying to bring it into the limelight, and highlight how better soil management can help reduce the water we use.
Just a spoonful of healthy soil rich in organic carbon will have billions of microbes that help plants thrive. These microorganisms need water, for which the soil forms a dark, rich organic matter called humus that emerges from decayed plant and animal matter — and humus acts as a sponge, helping the soil retain moisture.
Why Soil Gets Depleted
But our soil has been seriously depleted in many areas because we’ve been abusing it knowingly and unknowingly. This has reduced its ability to retain moisture and as a result we’ve been drawing heavily on fast-disappearing ground and surface water resources.
Soil depletion is caused by several factors, but overtilling of the land is a top reason, according to Rolfe. Growing only one crop without crop rotation and crop diversity, not putting in a cover crop during the winter and heavy use of fertilizers and pesticides are other reasons why soil gets depleted of its rich nutrients.
“China uses 400–500lb of fertilizer per acre, India uses 100lb per acre and the U.S uses 150–200lb per acre,” said Rattan Lal, a veteran soil scientist at Ohio State University, Columbus (OSU). [100lb is 45kg; 1 acre is 0.4 hectare.] “Sub-Saharan Africa uses only about 8lb per acre, but most are subsistence farmers. What we need is integrated nutrient management to help combat depletion in soil; fertilizer alone can’t compensate for it.”
Lal explained that healthy soils should have high soil organic carbon in the root zone, in the range of 1.5–2 percent. If the carbon is reduced, the soil’s ability to hold water is also reduced.
To keep the soil healthy, tilling and chemical inputs need to be reduced, and farmers are advised to put in cover crops in the off-season and to leave in root residue after harvesting, to feed the soil. The soil is akin to a machine in that a well-maintained, well-oiled machine runs better than one that is left idle until it’s needed. Soil is similar. It needs to have crops rotating throughout the year to feed it.
Conservation agriculture is the term applied to these practices, which help reduce soil disturbance and maximize sustainable, economically viable farming that improves yield and the soil’s ecosystem in the long run.
Know Your Soil, Help Save Water
“Knowing what soil you have is important. Once you know, you can manage it better in a drought,” Rolfe said, explaining that the NRCS maps all the soils across the U.S — something it’s been doing for 100 years – and this information is available online. There’s also asmartphone app that anyone can use to get an instant snapshot of the soil they’re standing over anywhere in the country.”
The payoff that healthy soil offers is huge — both in terms of water savings and climate change.
“If you increase soil organic matter by 1 percent, you can save 25,000 gallons [95,000 liters] of water per acre from being used, so you’re less dependent on other sources of water,” Rolfe said. “And the more you can store organic carbon in the soil, the less carbon dioxide is released, which also helps with climate and carbon sequestration.”
Current tillage practices are a legacy practice from the 1950s, but overtilling depletes the organic matter, which hurts the microorganisms and leads to the soil acting as a sieve instead of a sponge.
“We thought the best method was to go out and till,” Rolfe said. “We didn’t realize that we were hurting the soil ecosystem.”
Similarly, many farmers may not recognize the benefits of leaving in crop residue, which acts as a surface shade for the soil and helps soil microbes thrive.
Easier Said Than Done
“It’s not rocket science, right?” laughed Rolfe. “But it’s not easy to put into practice, because in California we have 300-plus crops compared to three or four in the Midwest, so there are barriers for farmers to change the way they do things.
Changing soil management practices is a risk that many may be reluctant to take, given the ramifications, he explained.
“I feel for the farmers because while it sounds simple, it’s not,” Rolfe said. “It’s like a diet – you think it’s simple going in but it’s not that easy to stick with it. It’s like a paradigm shift, you have to change your management systems and we’re used to doing things the way we’ve always done it.”
A big risk that worries growers is yields dropping while they transition to healthier soil practices. Transitions can take three to five years to happen, making it an economic risk. Nonbeneficial pests may increase during this period, and farmers may realize they need to invest in new equipment for minimum tillage and seeding, both of which can add to their financial burden.
Smart Agriculture
In May this year, secretary of agriculture Tom Vilsack released a roadmap for the U.S. Department of Agriculture’s “building blocks for climate smart agriculture and forestry” in which he lists soil health as a top priority.
Lal cited the example of an OSU experiment that proved soil health does impact water retention and crop production. When Ohio went through a bad drought back in 2012, OSU experimented by leaving in crop residue in one patch of the field and stripping residue from another patch.
They found that soil moisture was nearly one-third more in the patch with residue, because there was no surface runoff or evaporation, and what’s more, the soil temperature was cooler by 5–6 degrees Celsius. This led to a 60 percent hike in production.
“This is what we’re talking about — a cover crop can keep the soil cooler, more moist and what we call climate smart agriculture,” Lal pointed out.
Residue also helps feed earthworms, which then burrow channels up and down in the soil. These worm holes or biopores can be up to 2ft (60cm) deep, and plant roots will follow the holes, which leads them to deeper soil where there’s more water available.
One other advantage of soils with high carbon content and microbial activity is that it helps destroy plant diseases.
“The health of the soil, plants, animals, people and ecosystems are interdependent, interconnected and indivisible,” Lal said.
