By JOHN PESEK, Guest columnist
Underfoot and out of mind seems to be the general attitude many have concerning soil, if they even give it a thought.
Soil naturally develops, over time, on terrestrial areas of the earth when the land surface is exposed to conditions that favor biological activity. In many cases, soils were formed thousands of years ago and then destroyed or covered by subsequent geological events.
The windblown loess-covered areas of western and southern Iowa are underlain by ancient soils once found at the surface. The latest glaciation in central and north central Iowa covered extensive forests, while the present soils in near northeastern Iowa were developed on geological material after ancient soils were stripped away by erosion. Evidence of such events is appears worldwide in the wake of every flood, landslide, earthquake or volcanic eruption.
Soils, wherever they occur, have been the ultimate source of plant products for food, clothing and shelter because they form the basis for green plant growth. Surface- and groundwaters are generated, for the most part, from precipitation falling on soil and bear the influence of the soil over which or through which they pass. Not only does soil influence quality of local water supplies, but its effect can be observed a thousand miles away, as in the hypoxic zone at the mouth of the Mississippi River. The air in soil pores is continually exchanged with the atmosphere, allowing soils to remove or add compounds in the air.
Humans have deliberately employed soil to meet their basic needs since agriculture and civilization emerged about 12,000 years ago. We have observed the demise of civilizations as a result of soil deterioration caused by human ignorance or neglect; they were not sustainable. Irrigated Mesopotamian fields declined in productivity due to salt accumulation for several centuries before they were abandoned to the desert from which they were acquired. Soil erosion was prominent in the decline of the Greek and Roman empires, and the denuding of the hills in Asia Minor led to erosion and the siltation of the harbor at Ephesus until it now lies several miles inland from the modern harbor.
There are some exceptions to this general rule. A prominent one is the Nile Valley where cultivation has continued for thousands of years with annually freshly renewed water and plant nutrients, however, some evidence indicates that massive human intrusion now may be having an undesirable effect. Some cultivated parts of China also have endured for thousands of years and apparently many of the rice paddies have been cultivated and remained productive through the millennia. One might argue that the nomadic peoples of central Asia, who once threatened Europe, have reached equilibrium with their environment as they follow a primitive form of agriculture.
Soil in Iowa, a history
We have used soils in Iowa for less than two centuries, and soil scientists have observed profound changes over that time period. Most of these changes are directly attributable to human activities, mostly to cultivation for food, feed and fiber production. In tandem with cultivation, our soils have been drained and streams straightened, both leading to loss of wetlands.
Some Iowa soils have eroded to the point where we now grow crops in what were formerly “subsoils.” In parts of western Iowa, almost all of the original organic matter has been lost from cultivated fields, along with much of the topsoil. Even in the relatively level landscape of north central and northwestern Iowa, we have lost more than half of the organic matter that had accumulated under prairie and wetland vegetation since the glaciers receded about 12,000 years ago. This loss is the result of cultivation that regularly stirs the soil and causes organic matter to oxidize at an accelerated rate.
I learned about the fragility of the soil when I was not even nine years old. A violent rain and hail storm devastated our crops, with major gullies forming on a sandy loam rise and much of the sediment deposited on a lower-lying field. We had put the land under cultivation only six years earlier, from its virgin state of short-grass prairie and brush. At the same time, our county had its first agricultural agent who helped my father establish lines for terraces. We built terraces with mule-power and brawn, and I spent much time on a scraper filling in those gullies.
Our family did not put any more land in cultivation until after it had been terraced to protect it from erosion and to conserve water. My affinity for soil was firmly entrenched from that time forward. I planned and built terraces in high school and college, and considered a career in soil conservation until military service altered my opportunities and plans.
The nature of agriculture in Iowa for the first century of statehood was one of numerous farms, almost all devoted to the production of both crops and animals. This kept some of the land under a dense plant cover of small grain and meadow grasses or legumes so it was not exposed to severe erosion for more than a year at a time. Thus, farming practices did not have a profound effect on water supplies, except that straightened streams encouraged streambed erosion and accelerated the accumulation of rain water causing flash floods.
The hay and grain produced was largely consumed by the animal enterprises on the farm, leaving the manure near at hand for distribution on crop land from which the feed had been taken. This system slowed the depletion of mineral plant nutrients, and replenished the organic nitrogen lost from soils by oxidization of organic matter.
Early impacts of conservation programs
Even this relatively mild system of farming did not prevent the depletion of some soils in the United States and Iowa. Steeper fields with more erodible soils were washed away, which encouraged serious flooding east of the Mississippi. This prompted Congress to appropriate funds to battle soil erosion in 1928. The Soil Erosion Service in the U.S. Department of the Interior was created in 1933. Later in the 1930s, the Soil Conservation Service (now the Soil and Water Conservation Service) was established, better to focus on the general objective of protecting the nation's soils.
One of the early experimental stations for study of soil conservation practices was along Iowa Highway 2 between Clarinda and Shenandoah. Pioneering work on soil and meteorological factors affecting the erosion of soils was conducted at this site from the mid-1930s.
Two world wars during the first century of Iowa statehood brought a heavy demand to increase food and fiber production to support the war effort of the United States and its allies, so more land was cultivated and exposed to erosion and depletion. Farmers also began to grow a new crop, soybean, for feed and oil. Like corn, it was cleanly cultivated with intense land preparation prior to its planting. To make matters worse, soybean plants left soils more susceptible to both wind and water erosion than did corn plants. Farmers began to grow more corn and soybean grain for use off their farms, accelerating nutrient depletion as well as increasing soil losses.
We have compensated for losses of nitrogen in soil organic matter and the more stable plant nutrients in soils by replacing them, in the absence of livestock manures, with synthetic nitrogen fertilizers, and by mining and processing phosphorus and potassium ores for use as fertilizers. This has led us to the point where the petroleum supplies for production of nitrogen fertilizer and for the mining of the ores is ever less available and more expensive, and its coal substitute is not looked upon favorably. The ore supplies are increasingly more difficult to locate, mine and transport, thus making fertilizer increasingly more expensive. The frightening aspect is that we're using these geologic resources to rectify our casual use of soil, all of which has occurred during the past 200 of the 12,000 years that agriculture has been practiced.
Our newest challenge
The most recent challenge imposed upon our soil is its cultivation for delivering vastly more fuel for mechanical power than ever was utilized in the animal-powered agriculture of only a century ago. Currently, plant materials for fuel are predominately from annual and formerly inter-tilled crops such as corn and soybeans. Part of the additional production may need to come from putting highly erosive soils into some type of permanent vegetation.
Experience has taught us that soil losses and accompanying losses of plant nutrients are severe on many soils without major efforts to retard water runoff and soil erosion on all but the least undulating topography. How best to produce more fuel without compromising our sustained ability to produce crops in the future will require ingenuity and a willingness to adopt new practices and different crops for fuel purposes than in the past.
Are we up to this challenge? Can we rebuild the integrity of our soils and adopt the practices needed to enter the age of renewable fuel production from agriculture? Can we develop a system that is sustainable? We will have to search for the answers; no less than civilization depends upon it.
John Pesek on Soil: Ubiquitous, underappreciated but indispensable | Leopold Center for Sustainable Agriculture
No comments:
Post a Comment