Soil: The Yield Limiting Factor We Take For Granted – DTN

    There’s a good reason the U.N General Assembly declared 2015 the International Year of Soils. It is agriculture’s fundamental resource.

    Over the next few days, I’ll be writing about soil health and how to assess it in a series of stories. It’s a complicated, but critical issue.

    As farmers we adopt practices such as conservation tillage, no-till, cover crops and crop rotation in attempts to limit and restore what we take from this precious resource. We utilize animal manures and put back additives such as gypsum and biologicals (humates, enzymes, and organisms) in an effort to promote good health. Yet, we seldom stop to measure and understand what we’re doing … or determine the next step and how it ties to yield goals..

    Over the past couple years, agronomists have begun to recognize that soil is more of a limiting factor in achieving high yields than most growers realize. It helps to think of soil as more than a medium to place seed, fertilizer or chemicals. It is a living entity.

    “Soil is alive, supporting various organisms while recycling carbon and nutrients and holding water. You can’t have (soil) health without life and you can’t have (soil) quality without health,” said Jill Clapperton, soil microbiologist and consultant with Rhizoterra in Spokane, Wash.

    “You have to remember that plants drive soil health. Their roots feed the soil and drive microbial activity. And soil nutrients are important to microbial metabolism,” said Clapperton.

    Put simply, a healthy soil has organic matter, structure and biological activity. Healthy soils allow rainwater to penetrate and that prevents excess runoff, sedimentation, erosion and flooding. Healthy soils store more water, support greater root and plant growth and ultimately promote increased productivity.


    The first step to good soil heal is good soil quality. “Soil health is defined as the productivity and functioning of the soil,” said Mike Kucera, USDA-NRCS resource conservationist, of Lincoln, Neb. “Key features that describe a healthy soil include nutrient cycling, water infiltration, physical structure, chemical balance and the biological diversity of the soil.”

    “Soil quality declines because of erosion, compaction, excessive tillage, organic matter loss, declines in biological activity, salinization and desertification,” explained Charles Shapiro, an Extension soil scientist with the University of Nebraska based at the Haskell Agricultural Laboratory near Concord, Neb.


    Measuring pH, electro conductivity, organic matter, nitrogen and phosphorus levels, bulk density, water infiltration and soil aggregate stability helps to assess soil quality. These chemical and physical characteristics need to be near ideal for microbial activity to flourish and nutrient and carbon cycling to occur.

    Measuring all these attributes takes time and effort, but knowledge of a soil’s strengths and limitations is necessary to remedy shortcomings.

    Think of soil as an engine. To measure the output (productivity) of an engine, we would put it on a dynamometer and measure horsepower. We then make repairs or changes to the engine to increase horsepower and efficiency.

    Over the next few articles, I’ll explain how to determine soil quality, measure its “horsepower” and make changes to improve it.

    For more information on the International Year of Soils go to:…

    Dan Davidson can be reached at

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