Soils are our future: Natural systems agriculture

By Jerry Glover
The Land Institute

As our cultural identities become increasingly subsumed into technological identities focusing on what we can, or hope, to become, we have largely ceased considering the wellspring of our physical and chemical makeup. That wellspring - the Earth's soil - is a relatively thin and fragile but biologically active layer of the Earth's surface through which nearly all of the elements necessary for our bodily past, present and future must cycle. Soil is the elemental recycling center that provides our human DNA with a past and present. Without soil, human DNA has no future.

For those of us who inhabit the North American Great Plains and Midwest, the future depends on soils developed in prairie ecosystems that covered a large portion of the continent little more than a century ago. These prairie soils, some of the most inherently fertile soils in the world, are the product of near-miraculous management of nutrients, water and sunlight over long stretches of time.

Much of the effectiveness of the prairie system derives from its vegetative structure that consists primarily of mixtures of warm and cool season grasses, legumes and members of the sunflower family. These diverse, perennial plant assemblages evolved over tens of millennia, under the pressure of constant resource constraints, to capture and hold onto anything the system offered that could be used to fix carbon from the atmosphere, set seed and expand roots into the soil. The triumphant assemblages are those systems that waste little, produce much and save for the future.

Presence of plants

One key to the prairie's conservatism is the constant, living presence of plants. During the growing season the perennial cover of prairie vegetation shelters the soil from the erosive effects of wind and water while the thick layer of dead and decaying plant litter protects the soil during times of plant dormancy. Rainfall readily enters the undisturbed soil surface, is held in the soil profile and then quickly used by dense networks of roots.

The constant, living presence of roots in the soil efficiently transports nutrients and water upward and the products of photosynthesis downward. Some of these energy-rich products leak back into the surrounding soil where the living microbiological communities subsequently assist in their conversion to soil humus. Very little in the way of nutrients and water runs off the soil surface and very little makes its way through the soil beyond the reach of perennial roots. Most importantly, perennial roots hold tightly the fertile topsoil.

Diversity of species

Another important key to the prairie's success is the way in which different plant groups (e.g., cool and warm season grasses, legumes and sunflower family members) utilize resources. The plant groups complement one another in the use of resources across space and time. For example, cool season grasses grow rapidly early in the season using the available sunlight, nutrients and soil moisture. Later, warm season grasses put on growth, using resources that would be missed by cool season grasses, which shut down in the heat of the summer. Different root structures also use resources at different soil depths. Fibrous, widely spreading grass roots, for example, draw on near-surface resources while taproots of prairie sunflowers or legumes stretch deeper into the soil profile. Plant diversity ensures water and nutrients are used as fully as possible throughout the year and throughout the soil profile.

While perennial, diverse plant communities sponsor soil development, annual, uniform plant communities foster soil degradation. A century and half ago, when aggressive conversion of much of North America's grassland regions to annual cropping began, the conservatism inherent to the prairie system went largely unnoticed and unappreciated by the pioneer farmers living off the soil's stored reserves. Despite high yields, monocultures of annuals-like an undisciplined trust fund recipient-spend much and save little if anything.

Tillage exposed the rich soil humus to oxygen and biological activity, thereby releasing abundant nutrients to feed the annual crops but depleting the soil's reserves. The absence of protective cover rendered prairie soils vulnerable to erosion, destroying in a few decades what it took the prairie millennia to accumulate. Much of the rainfall ran unused across the surface or drained beyond the meager reach of annual root systems. Water flow through soil profiles under annual crops may be five times greater than through soil profiles supporting perennials, resulting in losses of as much as 45 percent of the annual precipitation through subsurface flow in annual cropping systems.

Even the great stored wealth of prairie soils failed to satisfy the exorbitant expenditures required by highly inefficient annual crops. Detailed research 150 years later has revealed the costs. Water lost from annual crop fields, carrying soil particles, nutrients and agrichemicals, eventually finds its way to rivers, lakes and seas. Agriculture, because of these losses, is responsible for approximately 70 percent of river contamination and is the principal cause of water quality problems in the United States. The National Water Quality Assessment (NWAQ) program found at least one pesticide in nearly every water and fish sample collected from streams and in over 50 percent of sampled wells in agricultural areas.

The 'dead zone'

The formation of an oxygen-depleted "dead zone" in the Gulf of Mexico-an area unable to support most marine organisms-is another example of the effects of the inefficiency of our annual cropping patterns. This zone continues to grow due to nitrogen enrichment that has been traced to agricultural lands drained by the Mississippi River. Five states with the greatest portion of the best farmland (Class I and II soils) in the nation, all located in the Upper Mississippi River basin, are leading contributors to this "dead zone." The annual corn and soybean crops grown in these regions simply cannot use the available resources efficiently enough to prevent the bleeding off of the prairie's former wealth and the additional commercial nutrients applied annually.

To reverse trends established by 150 years of annual cropping in the prairie region, researchers at The Land Institute in Salina, Kansas, are looking to the prairie's key components-perennialism and species diversity-to develop a truly sustainable grain production system. By breeding high yielding perennial grain crops that will be grown in mixtures, The Land Institute is working toward an agricultural system in which conservatism is a consequence of farming as it is in the prairie.

Plant breeders are working both with domesticated annuals and wild perennials to achieve this lofty goal of developing "domestic prairies." It is increasingly clear that as difficult as this goal might be to achieve, it is virtually impossible to devise truly sustainable farming systems based on monocultures of annual crops in the North American prairie region. Without rich prairie soils and a sound environment to support our descendants and DNA recipients, their future in this region will be limited if possible at all.

Jerry Glover is a soil scientist in charge of Natural Systems Agriculture projects at The Land Institute in Salina, Kansas. He can be reached at (785) 823-5376, or by e-mail, glover@landinstitute.org. He grew up on a farm in southeastern Colorado.