- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7500) Unit Title: SOIL TILLAGE, LAND PREPARATION AND CONSERVATION ____________________________________________________________________________ (CLF7501) Topic: SOIL TILLAGE, LAND Time Taught in Year(s) PREPARATION & CONSERVATION 4 hours 3 and 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (I-1) - List and discuss four advantages of cultivation. (I-2) - Identify four methods of land preparation and seeding. (I-3) - List four objectives of tillage operations necessary for good crop production. (I-4) - Explain the order and purpose of each tillage operation necessary to prepare a good seedbed. (I-5) - Explain the effect of depth of planting on seed emergence. Special Materials and Equipment: Dealers brochures with various tillage and seeding equipment, equipment company catalogs. An area of ground or at least a planter box to experiment with planting depths and tilling methods. References: Forth, H.D. FUNDAMENTALS OF SOIL SCIENCE. Pages 53-58. Donahue. SOILS. Page 75-85. Deere and Company. FUNDAMENTALS OF MACHINE OPERATION, TILLAGE. Evaluation: Quiz by instructor TOPIC PRESENTATION: SOIL TILLAGE, LAND PREPARATION, AND CONSERVATION A. Crop productivity is determined, to a large extent, by the way the soil is managed. 1. Good land management is a combination of tillage, cropping systems, and soil treatments that compliment each other. 2. Tillage is the mechanical handling of soil to provide a favorable environment for plant growth. 3. Unfavorable soil moisture content will result in poor tillage and can damage soil structure. B. There are several soil terms which we often relate to tillage. 1. Hardpans are hardened layers of soil, in the lower A horizon or in the upper B horizon caused by the cementing of soil particles. a. These layers often cause problems of water penetration and lack of drainage. b. When they are located close enough to the surface to be reached with chisels or subsoilers they can be broken up and thus improve the water penetration and drainage. 2. Crusts are surface layers of soils, ranging in thickness from a few to several centimeters. They are harder, more compact and brittle when dry, when compared to the soil located underneath them. a. These crusts slow water penetration and aeration. b. Crusts can be a barrier to seedling emergence of small seeded crops. c. They can be easily broken by most cultivation tools, or can be softened by irrigation to allow seedling emergence. 3. Crop residues are the portion of crop plants remaining after harvest. a. Included in crop residues would be leaves, stems, stubble, straw, chaff and the roots of plants. b. These residues add to the organic matter content of soil. C. Cultivation is the tillage between seedling emergence and crop harvest. 1. There are several advantages of cultivation. a. Probably the main reason for cultivation is weed control. b. It can also temporarily improve water infiltration, soil aeration, conservation of soil moisture, loosen compacted soils and often help in insect control. 2. The deleterious effects of tillage, however, also must be considered. a. Some of the harmful effects of tillage are the loss of organic matter, the destruction of plant roots during cultivation, the baring of the soil surface which can increase soil erosion and the deterioration of aggregation. b. Compaction is another problem. 1) This problem is accentuated on some soils and some crops by the size and design of modern equipment. 2) A compacted layer (plow pan) can also result from plowing at the same depth for many years. 3) Compacted layers can be formed at lower depths by the use of heavy equipment on moist, fine-textured soils. D. The major objectives of tillage are to improve soil tilth, provide weed control and manage crop residues. 1. Management of crop residues can be achieved by chopping and/or cutting and mixing the crop residues into the soil profile. This has value in terms of organic matter and also lessens interference with subsequent operations such as planting. 2. Tillage for weed control is effective and removes weeds that would otherwise compete for water, nutrients and space. 3. Tillage to improve soil tilth is important in order to provide a uniform seedbed for planting depth control and to provide soil density for optimum soil moisture capacity. E. Other objectives of tillage can include: 1. Soil aeration to improve the oxygen supply. 2. Moisture management a. Keeping the soil loose and open in situation of excess soil moisture. b. Keeping the soil surface firm in order to reduce evaporation in situation of low soil moisture. c. Eliminating high and low spots in irrigated fields. 3. Insect control can be achieved in some instances by burying crop residues to eliminate an over-wintering host site for some insects. 4. Temperature improvement can be achieved by having a dry soil condition in the spring months. This may allow for earlier planting. 5. To prepare for irrigation, beds, furrows and ditches should be created to bring in and take away irrigation waters. 6. Erosion control a. Crop residues left on the field surface tend to decrease soil erosion. b. A roughened soil surface tends to decrease soil erosion. F. Tillage is done for several different purposes and with a variety of equipment. 1. The plow may be used as the first step in preparing the seedbed. It inverts the soil and covers crop residues, but often leaves the soil in lumps that must be broken into smaller size. 2. Disks are used to reduce clod size by fracturing them with shearing and pressure. Sometimes the disk can substitute for the plow, especially when the soil is in good tilth. 3. The harrow function is to further reduce the size of the soil clods left after discing. It smooths and levels the soil and destroys small weeds. 4. A lister is a small plow with a double moldboard that produces a ridged furrow. The lister is often followed by a drill for planting and covering the seed. G. An understanding of the fundamentals of soil science and experience with specific cropping systems is paramount for continued productivity and soil conservation. H. Good seedbed preparation is essential for successful field and garden sowing. 1. A seedbed should have a loose, but fine physical texture that gives close contact between the soil particles and the seed. 2. This will allow soil moisture to be supplied continually to the seed. 3. It will allow adequate aeration without drying too rapidly. 4. The subsoil should be permeable to air and water, thereby providing adequate drainage. 5. Depth of planting is critical in that it will determine the rate of emergence and the density of the stand. a. If the seed is planted too shallow it may dry too rapidly. b. If it is planted too deep, emergence of the seedling will be delayed, or, in extreme causes the seedling may not be able to emerge. c. Depth of planting is determined by the kind and size of the seed, the condition of the seedbed, and the environment at planting time. d. A rule of thumb is to plant seeds to a depth of "four times its average diameter." e. Remember that the proper environment for seed germination requires available moisture, proper temperature, a supply of oxygen and (sometimes) light. __________________________________________________________ ACTIVITY: 1. Have the students view pictures of tillage and seeding equipment. Test their skills by having them name each piece of equipment. a. Distinguish between a moldboard plow and a disk plow. b. Distinguish between a disk plow and a disk harrow. c. Distinguish between a spiketooth harrow and a springtooth harrow. d. Distinguish between a chisel and a subsoiler. 2. Have students prepare a seedbed for a local crop. Be sure that it is moist, friable, allowing air to circulate and be free of large clods. Several variations can be tied for comparison: a. Soil too wet; b. leaves large clods; c. soil is not firm; d. contains too much organic matter. 3. Have students run experiments trying different planting depths of various seeds. A planter box with a glass side works well for this. __________________________________________________________ 6/21/90 sg #%&C