Chapter 5 Summary

Download PDF Print Page Citation Share Link

Last Updated on May 5, 2015, by eNotes Editorial. Word Count: 941

There exists a reciprocal and symbiotic relationship between the earth’s soil and earth’s life forms. The decay of all forms of matter continually contributes to soil production. Simultaneously, living organisms use the soil and the substance therein to perpetuate their lives. Moreover, a typical acre of soil contains thousands of pounds of life forms such as bacteria, fungi, and algae. These organisms are largely responsible for generating the decay of “animal and plant residues” in the soil. They are also credited with modifying nitrogen for absorption by plants and for the oxidation and reduction processes in minerals that are used by plants.

Illustration of PDF document

Download Silent Spring Study Guide

Subscribe Now

Often, soil contains incredible numbers of mites and “wingless insects” known as springtails. Each year, these tiny organisms digest tons of discarded plant foliage and mix the decomposed matter back into the soil. Other creatures also make enormous, but largely unnoticed, contributions to healthy soil production. One primary example is the earthworm. These underappreciated inhabitants of the soil are responsible for transporting tons of soil over the ground. In addition, their active and energetic routine of burrowing in and out of soil serves other beneficial purposes. The industry of the earthworm aerates the soil, aiding plant roots in soil penetration and supporting soil drainage systems. Finally, the tiny earthworm enriches the soil with excretory wastes from its digestive tract. Consequently, the earthworm serves as an ideal illustration of the reciprocal relationship between the organisms whose lives are sustained by the soil and their beneficial contributions to healthy soil production.

Concerns have arisen regarding the effects of chemicals on these soil-dependent organisms. Sterilants, insecticides, and fungicides are used to destroy specific populations that inhabit the soil. They also contaminate the soil and expose a variety of soil-inhabiting creatures to poisons. Despite the growing concern,

this critically important subject of the ecology of the soil has been largely neglected even by scientists.

The impact of insecticides on the soil has yielded inconsistent results. It seems that the extent of the damage to the soil varies by soil type. Therefore, one type of soil could be negatively affected to a greater extent than another would. Nonetheless, there are measurable and irrefutable damages that can result from the introduction of pesticides into the earth’s soil. For instance, the process of nitrification can be inhibited by the herbicide 2,4-D. Nitrification is important because it provides plants with the nitrogen they require for life. Other chemicals such as “lindane, heptachlor, and benzene hexachloride (BHC)” can potentially interrupt the nitrification process in as little as two weeks. Sometimes the chemicals prevent bacteria or other organisms from successfully performing functions that are essential to plant life. As a result, some soil populations are eradicated while others experience a population explosion. The exploding populations now have the potential to increase so quickly that they become harmful pests.

Because the chemicals used in pesticides take decades or longer to break down, once chemicals have been introduced into the soil, they remain long after their intended task has been accomplished. Aldrin has been shown to remain in soil for four years after use, toxaphene has been discovered after ten years, BHC remains present for eleven years, heptachlor has been found after nine years, and chlordane has been identified twelve years following its initial application. Still, the persistent presence of these chemicals is not the only startling concern.

Time has proven that insecticides remain lethal agents long after they are introduced to the soil; they do not simply perform a function and dissipate. In fact, many chemical insecticides and pesticides intensify their effect over time. To illustrate, consider the permanent contamination of soil that has resulted from the use of arsenic as an insecticide. Most applications of arsenic to tobacco crops ended during the 1940s. However, the tobacco plants continue to absorb the chemical from the soil, and the plants evidence an ever-increasing contamination of the poison. Likewise, there is evidence that arsenic residues are present in “the soil of a large proportion of the land planted to tobacco.”

The degree to which chemicals are absorbed within plant tissues varies depending on the soil type, the chemical concentration, and the nature of both the chemical and the plant tissue. The absorption of too much chemical contamination by plants can result in an unmarketable and inedible crop. A large manufacturer of baby food products suffered from this problem. Because the manufacturer insisted on purchasing only crops grown in nontoxic soil, it was forced to reject an entire supply of sweet potatoes that contained residues of BHC. To safely prepare the baby food, it spent considerably more to purchase noncontaminated potatoes. Peanut growers often face similar problems. Because peanuts are often paired with cotton in crop rotations, soil that has been contaminated with HBC often contaminates the peanuts, producing “a telltale musty odor and taste.” There are no processing treatment techniques that can successfully mediate or remedy the contamination.

Chemicals in the soil can retard the proper growth and development of some plants, thereby destroying entire crops. In 1955, on the advice of agricultural experts, hops growers in Washington and Idaho treated their crops with the insecticide heptachlor, hoping to prevent an infestation of the destructive strawberry root weevil. Although the farmers were pleased by the successful annihilation of this pest, they were dismayed by the unforeseen consequences of the insecticide. A year following treatment, the vines of the hops plants were wilting and dying in the fields. Four years later, heptachlor was still present and still destroying vines four; it rendered the soil useless for hops production. The farmers turned to the legal system to seek compensation for their losses.

Unlock This Study Guide Now

Start your 48-hour free trial and unlock all the summaries, Q&A, and analyses you need to get better grades now.

  • 30,000+ book summaries
  • 20% study tools discount
  • Ad-free content
  • PDF downloads
  • 300,000+ answers
  • 5-star customer support
Start your 48-hour free trial
Previous

Chapter 4 Summary

Next

Chapter 6 Summary