Impacts on Soil

1. Metals, 2. Wood-waste Breakdown Products, 3. Pesticides, 4. Fuels, 5. Nutrients, 6. Salts, 7. Carbon: Nitrogen (c:n) Ratio, 8. Plant Diseases

Text A.

Soils have an equilibrium C:N ratio of the order 12-15:1. The application of wastes with a higher C:N ratio (wood-waste has a C:N ratio of 300:1) will tie up free nitrogen in the soil. The continued application of such a waste will cause continued nitrogen fixation until a new soil equilibrium is attained. Soil with a high C: N ratio will have less nitrogen available for plant use.

Text B.

Most metals are relatively immobile and crop uptake is small. Application of wastes containing metals results in an unwanted accumulation in the topsoil. Crop yield reduction or even toxicity can occur for some crops at relatively low levels of metals. If waste containing metals is applied to soil, precautionary measures must be taken. Once buildup has occurred, and damage produced, it is too late to correct. Although levels in the soil may not harm plant growth, plant levels may be toxic to animals. Toxic effects of metals in livestock may be caused by the ingestion of plants or soil. Some types of manure contain high levels of metal, mainly copper and zinc. Waste oil and hydraulic fluids also contain high metal levels. Metals are generally more available in acid soils (soils with a low pH).

Text C.

The primary nutrients are nitrogen, phosphorus, and potassium. The secondary nutrients are sulphur, magnesium and calcium. The micro-nutrients are iron, magnesium, boron, chlorine, zinc, copper, and molybdenum. If applied in excess amounts to soil, these nutrients can reduce crop yields or become toxic to plants. Furthermore, when levels in the soil are not deleterious to plant growth, plant levels may be harmful to animals. The main sources of nutrients are manure and fertilizer.

Text D.

The accumulation of excess or unwanted pesticides on the farm increases the potential for soil and water contamination from pesticide storage. Pesticide losses may occur due to leaks in containers and/or unanticipated exposure to weather elements.

Improper handling of pesticides may lead to spills during mixing and loading. The specific characteristics of the pesticide used, particularly its persistence and solubility, strongly influence the potential for soil pollution from spills when handling pesticides.

Pesticide application can result in some amount of pesticide missing its target. When pesticide pollution of soil occurs, beneficial insects may be killed, crops may not grow, or the type of crop grown may be limited. Animals including birds may be harmed or killed by eating contaminated crops or soil, or suffer adverse effects such as weight loss and reproductive failure. They may also accumulate pesticides in their tissues making them unfit for consumption.

Text E.

Petroleum (gas, diesel, kerosene) and petroleum-based products (oils, greases, solvents) are complex organic compounds which contain metals and other potential contaminants. Some petroleum products are volatile which results in them being lost to the air; however, many others either firmly or loosely bind to soil particles. In either case, petroleum products restrict the growth of plants. Petroleum products that are loosely bound to soil can be either washed or leached into surface or groundwater. The sources of environmental concern are storage tank leaks and spillage during handling.

Text F.

Transfer of plant diseases is common in areas where nursery equipment moves either from field to field or nursery to nursery, or when plants are relocated between nurseries. Movement of machinery in turf operations may transfer diseases rapidly through a field. Often, bacteria, fungi or other organisms growing on the crop or in the soil are picked up by equipment. Plant disease organisms may also be transported from field to field by livestock. Contamination can also result from plant diseases being moved in manure. Plant disease infestations can result in significant losses in quality and/or growth. Severe soil contamination may reduce the range of plants that can be grown.

Text G.

The salt content of a manure depends on the feed constituents. Many manures contain between 10% and 13% salts (dry weight basis). High annual application rates of manure can increase soil salinity in areas of low precipitation. Salt sources include wood-waste from salt sorted logs, compost and fertilizer. Elevated salinity levels adversely affect many crops.

Text H.

Wood-waste (sawdust, shavings, chips, bark, etc.) may be a useful soil conditioner or mulch; however, if inappropriate rates are used, it may have a negative impact. When exposed to water, air and soil microbial activity, wood-waste breaks down and releases soluble compounds that can lead to the contamination of soil. Some of these compounds, particularly tannins, and resin acids, are toxic to some plant life. Wood-waste breakdown by-products are also acidic and will cause certain metals and nutrients to be released from the soil. Because the breakdown by-products are leachable, they can enter groundwater. High application rates of wood-waste to the soil surface or incorporated into the soil will cause nutrient imbalances or shifts in soil microbial populations. For example, a heavy application of sawdust that is incorporated into the soil will cause nitrogen deficiencies (see Carbon: Nitrogen Ratio in this subsection) and may cause the soil pH to drop.

Exercise 10. Read the texts above once again and find the right answer after each question given below:

1. What action will free nitrogen tie up in the soil?

a. – the application of pesticides

b. – the application of wood-waste such as sawdust, shavings, chips, bark, etc.

c. – the application of wastes with a higher C:N ratio

2. What are the common places of plant diseases transfer?

a. – places with high application rates of wood-waste incorporated into the soil

b. – places where nursery equipment moves either from field to field or nursery to nursery, or when plants are relocated between nurseries

c. – places with application of wastes containing metals

3. Why can the breakdown by-products enter ground water?

a. – because the breakdown by-products are leachable

b. – because the breakdown by-products are solid

c. – because the breakdown by-products are mixed with soil when they are used

4. How can pesticide pollution damage the environment?

a. – soil will have less nitrogen available for plant use

b. – beneficial insects may be killed, crops may not grow, or the type of crop grown may be limited

c. – pesticides that are loosely bound to soil can be either washed or leached into surface or groundwater

5. How can excess amounts of nutrients affect soil?

a. – excess amounts of nutrients can reduce crop yields or become toxic to plants

b. – excess amounts of nutrients can adversely effect plant growth and limit the range of plants

c. – excess amounts of nutrients can be harmful to animals

6. How may toxic effects of metals be caused in livestock?

a. – toxic effects of metals in livestock may be caused by excess amounts of primary nutrients

b. – toxic effects of metals in livestock may be caused by elevated salinity levels in soil

c. – toxic effects of metals in livestock may be caused by the ingestion of plants or soil.