David Green, Executive Director, The U.S. Sustainability Alliance, explains how the soil holds the answer to feeding the world
“The answer lies in the soil” was the 1950’s mantra of a panellist on the long-running BBC radio show, Gardeners’ Question Time. The saying became part of UK folklore, trotted out at will in response to almost any question.
Fast forward to 2021 and the global focus is very much on the soil being the answer to feeding the world.
Increasing urbanisation, erosion, nutrient imbalance, intensive farming and climate change are placing huge demands on the availability and health of the world’s earth.
In many croplands across the world, even the ‘black gold’ earth of the American Midwest, the layer of fertile topsoil is thinning, which is making it more difficult to grow crops for food.
That is why conserving (and building) the fertility of our soils is perhaps the biggest challenge for today’s agriculture.
Farming operations such as ploughing or tilling the soil to bury and kill weeds and provide a smooth seeding bed have been practised for millennia, since early farmers used an ard to break up the soil.
Crop yields may have improved since then, mainly from less weed pressure, but tilling also leads to the loss of vital soil bacteria and fungi and the release of glomalin, a carbon-based “glue” that binds soil particles, into the atmosphere.
Farmers across the world and particularly in developed countries are changing cropping practices to improve their soil by increasing organic matter, reducing tillage and minimising chemical inputs.
Increasing organic matter and feeding the world
Soil experts agree that the fundamental basis for soil fertility is to build and maintain the level of humus (decomposed organic matter) content.
To do so requires a wide variety of methods, including manure (animal and human), nitrogen-fixing plants, crop rotation, cover crops and old crop residues.
Organic matter improves soil structure, which means better root penetration, water absorption, more water infiltration following rains and increased water-holding capacity.
Rachel Stroer, President of the Land Institute, an agricultural research organisation based in Salina, Kansas, pointed out in a BBC Follow the Food broadcast, “Why Soil Is Disappearing From Farms”, that any time you till the soil, it destroys the natural ecosystem that exists in it … loosens it and serves as a welcome mat for weeds.
That is one of the benefits of no-till farming, particularly where herbicide-tolerant genetically engineered (GE) crops are used: the soil is not disturbed nor is it compacted through the use of heavy tillage equipment.
With GE crops, farmers can be confident of weed control and, as such, can leave old crop residue on the ground after harvest.
This residue not only provides shade during the summer heat, thus preserving moisture, it also eventually breaks down into much-needed organic matter, and to that extent helps to build topsoil.
An unheralded advantage of not tilling soil is that earthworm populations are virtually undisturbed.
Earthworms help to break down old crop residues and their burrows provide welcome channels for rain and moisture.
Farmers also are turning to cover crops (planted when a cash crop is not growing) to help keep the soil covered in winter and early spring.
This reduces erosion, helping with weed control and increasing the time when living roots are present for soil organisms to feed on.
For the Arkansas rice farmer Adam Chappell, cover crops helped save his farm from Palmer amaranth, an invasive and difficult-to-combat weed. Chemical treatment was becoming less and less effective, he told a USA Rice podcast.
In 2010, he began incorporating multiple grass and legume cover crops into his corn, soybean and rice production, and over the years he has noticed marked differences in cover crop ground planted with multiple grass and legume species, not only in weed control but in soil health.
Little did that Gardeners’ Question Time panellist know that his oft-quoted quip “the answer lies in the soil” has become the mainstay of how we will feed a growing world by 2050.