- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7500) Unit Title: SOIL TILLAGE, LAND PREPARATION AND CONSERVATION ____________________________________________________________________________ (CLF7505) Topic: EROSION Time Taught in Year(s) 2 hours 3 and 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (I-9) - Identify four types of soil water erosion and describe four conservation practices which are used to minimize each. (I-10) - Discuss affects of wind erosion and list management procedures used to control it. Special Materials and Equipment: None References: Brady. THE NATURE AND PROPERTIES OF SOILS. Pages 5334-568. Donahue. SOILS. Pages 421-448. Hartman, Hudson. PLANT SCIENCE. Pages 213 to 216. Evaluation: Quiz by instructor TOPIC PRESENTATION: EROSION A. Erosion of the soil is a natural process influenced by climate, topography, and the nature of the soil itself. 1. Erosion is more or less gradual and in equilibrium with the soil forming processes where permanent and undisturbed plant cover exists. 2. Erosion is accelerated in the absence of plant cover. 3. No other soil phenomenon is more destructive worldwide than is soil erosion. 4. The U.S. government has spent billion of dollars since 1935 on voluntary soil and water conservation, but erosion still is not adequately controlled. 5. Erosion is serious in all climates since both wind and water are involved. B. Erosion by water is divided into four categories. Specifically: splash, sheet, rill and gully. 1. Raindrop splash erosion in particularly destructive to soils of fine sands and silt. a. Raindrop splash exerts three influences: 1) it detaches soil, 2) it destroys granulation, and 3) it may cause an appreciable movement of soil. b. Raindrops fall at approximately 30 ft./sec, beating the soil into flowing mud, which splashes as high as two feet and for a horizontal distance up to five feet. 2. Sheet erosion refers to the quite uniform removal of soil from the surface of an area in thin layers. a. For sheet erosion to occur there must be a smooth soil surface, which seldom exists. b. Many times sheet erosion will go unnoticed by farmers because it is slow (but persistent). 3. Rill erosion is the formation of a multitude of very shallow trenches by the movement of water (concentrated flow). a. None of these trenches may grow appreciably in size or depth, and so the surface soil is removed rather uniformly from the field. b. Sheet and rill erosion work hand in hand and sometimes the combined process is also called sheet erosion and can be distinguished from gully erosion. 4. Gully erosion is the process whereby water accumulates in narrow channels and, over a relatively short period, removes the soil from this narrow area to considerable depths. a. The resultant gullies range in size from 1 to 2 feet to as much as 75 to 100 feet. b. Gullies attract immediate attention and give the impression of soil destruction and land neglect. C. Several factors are important to consider when controlling erosion: 1. The amount of plant cover on the soil. 2. The intensity, duration, and distribution of rainfall. 3. The topography of the land (slope gradient and length). 4. The soil's physical properties. 5. The practices used for erosion control. D. The most suitable method(s) of preventing erosion will depend on soil type, topography, climate and the specific cropping and livestock system being used. E. Practices that have proven successful for controlling erosion are listed below. 1. In some areas grass (sod) waterways have proven successful. a. These are strips of land of varying widths which are permanently seeded to grass sod. b. They control water runoff from sloping land and conduct the runoff water to drainage outlets. c. These waterways are used with contours and terraces that drain into them. 2. Another practice is to till the land on the contour (contour tillage) instead of up and down the hill. a. The fields are plowed and the crop rows are planted and cultivated around the slope. (At the same elevation from one end of the row to the other.) b. Rows are curved following the contour of the land. c. Best results are obtained when this practice is combined with strip cropping or terracing. 3. Strip cropping is a practical means of reducing erosion. a. This is a practice of growing crops that require different types of tillage, such as row and sod, in alternate strips along contours. b. The width of the strips is determined by the steepness of slope, amount of precipitation, and the erodibility of the soil. c. This practice is used to conserve both soil and water. 4. A terrace is a raised, more or less level strip of land usually constructed on a contour and designed to make the land suitable for tillage and prevent erosion. (They appear as steps on a hillside.) a. They are used on long gentle slopes to decrease runoff and increase water Infiltration. b. Water is directed to follow the gentler slopes of the terraces rather than the steeper natural slope. c. Terraces are costly to construct and require yearly maintenance. d. They are feasible where usable land is in short supply or valuable crops can be grown. F. Wind, like water, erodes land by removing topsoil. 1. As with water erosion, the best protection against wind erosion is to provide vegetative cover for the land during the periods of high winds. 2. Wind erosion is increased when the soil is dry, poorly aggregated, bare, smooth, and the winds are strong. 3. Soil blowing may be expected during periods when land is being prepared for planting, before a crop has reached large enough size to protect the soil, or when land is being fallowed. 4. Some factors that influence wind erosion can be controlled by the landowner. a. Wetting soil by irrigation will reduce wind erosion. b. Keeping the soil surface rough is helpful. c. The planting of windbreaks at right angles to the prevailing wind will help reduce the effects of winds. d. The use of vegetative cover is the most important control. G. The loss of soil due to water and wind is a natural problem. a. Erosion clogs rivers with silt, complicates droughts and floods, and increases energy inputs. b. The important consideration is that each unit of land is managed according to its needs. 1) Land not suitable for agriculture should be left for wildlife and recreation. 2) Forest land should be used to produce trees. 3) Grasslands and range should be used for grazing livestock. 4) Crop land should be saved for crop production. c. The success of conservation programs used on the farm will depend on the judgement used in selecting a land use pattern that is within the capability of the land. 7/25/90 sg #%&C