The Elbert Files: Save our soil
Many of the environmental problems associated with farming, including flooded fields and polluted waterways, can be traced to land management, soil expert Doug Peterson told a group recently at Plymouth Church in Des Moines.
Land management practices of the past 50 years produced unintended consequences, he said, including changes in the ability of soil to hold water and store nutrients.
Much of what Peterson, a soil specialist with the U.S. Department of Agriculture’s Natural Resources Conservation Service, told the group at Plymouth Church is common knowledge among Iowa farmers, although some of it is relatively new knowledge.
For most of the city folk at Plymouth, though, it was new information. And some of it was surprisingly counterintuitive.
Peterson began his talk with two trays of soil. One tray, he explained, was from a field that was regularly tilled. The other was from a no-till field, which meant the land had not been plowed for at least three years.
The soils appeared identical until Peterson took a fist-sized clump of each and placed them in side by side beakers of water in a soil stability test.
“Watch,” he said.
The tilled soil began to disintegrate immediately and drift to the bottom. After several minutes, most of the clump had dissolved and settled to the bottom.
Meanwhile, the no-till clump remained in one piece.
Peterson did a second infiltration experiment, placing gravel-sized clumps of each soil type on wire grates.
When he poured water over the wire grates, it easily drained through the no-till soil.
But the tilled soil quickly disintegrated into a muddy mixture that clogged the grate, forcing water to pool atop the mixture, much like rain does on low areas of farm fields.
During the late 1990s, scientists discovered substances, which Peterson described as “biotic glues from fungi and exudates from plant roots and slime from burrowing earthworms that help bind the soil together.”
Tilling, he explained, breaks apart the glue, leaving unstable soil that is more easily eroded by water and wind.
The counterintuitive part is that in no-till fields nature’s “glue” allows the soil to remain intact and more porous, so water can infiltrate. As a result, no-till soil will hold significantly more water than soil degraded by annual plowing.
A common assumption throughout history was that breaking up soil with plows allowed water to flow more easily and deeper into the ground, promoting plant growth and creating underground storage.
That was true at one time, Peterson said. But not today.
Most soils today are so degraded that any tillage further inhibits their ability to retain water.
When it rains, he explained, tilled soil, like the sample placed on the wire grate, dissolves and reforms in impenetrable cakes. The result is an increase in standing water in fields and increased runoff that causes more downstream flooding.
The soil expert also talked about the “huge cost” that Iowa’s two crops – corn and soybeans – extract from the soil and the “need to do something besides traditional corn and soybean rotation.”
Peterson explained the purpose of cover crops, which consume excess nitrates. And he expressed concern about how slowly knowledge of cover-crop benefits is spreading.
He said soil problems cannot be fixed with traditional conservation practices, which are too expensive.
But, he added, a combination of no-till and cover crops, when properly applied, could go a long way toward fixing the problem.
Farmers are just beginning to understand how soil really works, said Matt Russell, an Iowa farmer who introduced Peterson.
“The next 20 years, there is going to be as big a transformation in agriculture as from the 1930s to the 1950s,” predicted Russell, executive director of Iowa Interfaith Power and Light, a faith-based conservation group.