- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6400) Unit Title: HORTICULTURAL SOILS & PLANTING MEDIA ____________________________________________________________________________ (CLF6403) Topic: MANAGING HORTICULTURAL Time Year(s) SOILS 2 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (G-3) - List and discuss four advantages of soil improvement and conservation techniques. - Describe three management practices that result in productive growing media for horticulture. Special Materials and Equipment: References: Ball, Vic. (Ed.). (1985). BALL RED BOOK (14th ed.). Reston, VA: Reston Publishing Co. Cooper, Elmer L. (1990). AGRISCIENCE: FUNDAMENTALS AND APPLICATIONS Albany, NY: Delmar Publishers. Hartmann, H. T., Flocker, W. J., & Kofranek, A. M. (1981). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS. Englewood Cliffs, NJ: Prentice-Hall. Hausenbuiller, R. L. (1972). SOIL SCIENCE: PRINCIPLES AND PRACTICES. Dubuque, IA: Wm. C. Brown Company. Editors of Sunset Books and Sunset Magazine. (1984). LANDSCAPING ILLUSTRATED. Menlo Park, CA: Lane Publishing Co. Editors of Sunset Books and Sunset Magazine. (1988). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Evaluation: Unit Exam TOPIC PRESENTATION: MANAGING HORTICULTURAL SOILS REVIEW: Nothing is as important as the soil when producing an ornamental crop, or when maintaining healthy plants in the landscape. The condition of the soil has a direct and immediate effect on the well-being of plants. Correctly managing horticultural soils (or growing media where soilless mixes are in use) is the first step that must be taken to have success in horticulture. A. Managing Field Soils: Field soils can mean soils either literally "in the field" and used for producing ornamental plants and materials such as cut flowers, or it can mean soils that are part of a landscape or turf planting. They have different management considerations than those soils used in the greenhouse or nursery, or those used in container plantings. Following are some practices helpful in managing field soils: 1. Sampling and Testing: Before establishing a crop or a landscape, the area to be planted should be sampled and the soil tested. a. Nutrient status should be tested for, so the correct fertilizers and nutrients can be added as necessary. b. Textural analysis should be conducted to determine if amendments will be necessary to compensate for textural deficiencies. c. pH and EC tests should be conducted to determine if acid or alkaline conditions need to be corrected or if the soil is too salty. d. Testing and analysis should be done by a reliable laboratory, (although pH and EC tests are easy to conduct yourself if you have the right equipment). Most do-it-yourself soil testing kits are inadequate if there is a valuable horticultural crop or landscape at stake. e. Take representative samples of the soil, and handle samples in such a way that they are not contaminated. For detailed information on soil sampling, refer to (CLF333) Influence of Texture on Soil. f. As horticultural crops are harvested, nutrients are removed and not returned. Periodic testing will indicate whether or not certain nutrients need to be replaced by artificial means. 2. Amending: As testing or the appearance of plants indicate, the grower can use any number of available amendments to correct soil conditions and improve the soil. These fall basically into two categories: organic, that is, carbon-based materials deriving from things that were once living, such as peat moss and manure; and inorganic, materials that are basically mineral in nature. a. Inorganic amendments: These are used primarily to correct chemical problems in the soil such as pH imbalance and tilth. 1) Lime (calcium carbonate) can be incorporated to raise pH in acid soils, and will also add calcium as a nutrient. 2) Gypsum is used to counter high levels of sodium (Na+) in sodic soils and improve tilth and water movement in heavy clay soils. Gypsum helps displace the sodium, and thereby allows clay particles to clump together, forming larger, more beneficial soil aggregates. This improves soil structure and tilth. Calcium sulfate is another name for gypsum. 3) No vermiculite or perlite should be used in the field, both for cultural reasons and expense. 4) In general, sand should NOT be used as an amendment in the landscape or field. Sand compacts clays and silts to ruin soil structure. 5) In the case of golf course greens and athletic fields, pure sand is used to form a high quality sand base for turf grasses. The sand base drains quickly, holds up well structurally under heavy use and maintenance activity, and is easy to repair when damaged. Also, sand is used as a backfill on greens after aerating ("plugging") operations. b. Organic amendments: Because organic materials are constantly decomposing, they must constantly be replaced to maintain their effect in the soil. In nature this process occurs naturally as decomposing materials recycle naturally. In ornamental horticulture, where crops are removed and leaves and other debris are cleaned up and removed from the landscape, replacement of organic materials must sometimes be done artificially. 1) A large number of organic amendments are available to incorporate into the soil at the time of planting. a) These include nitrified redwood sawdust, rice hulls, processed manures, sludge products, cocoa bean hulls, processed straw products, fir bark, and leaf mold. b) As these products decompose they add humus to the soil. Humus, the colloidal breakdown product of organic material, is highly desirable in soils as it considerably improves moisture retention and cation exchange capacity. c) Any time organic materials are incorporated into the soil, they should be sufficiently decomposed to prevent nitrogen "tie-up" by microorganisms. Amendments should be incorporated with enough nitrogen available to meet the needs of both the microorganisms and the plants. d) Organic amendments must be used in large enough quantities to have a significant effect. 2) It is difficult to incorporate organics once a crop is established. However it is often useful to mulch a crop to hold down weeds, conserve water, and reduce erosion. As this top dressing of organic material decomposes, humus and other organics are steadily added to the soil. 3) Vertical mulching of trees and shrubs adds organic matter and promotes aeration in the roots. 4) While most ornamental plantings are helped by adding organic matter, the opposite is true of established turf plantings. They must be de-thatched in order to remove excess organic matter. a) Turf may benefit from substantial soil amendment with organics only at the time of planting, but usually amending is not necessary if a good seed bed is prepared. b) The fast growth of turf, combined with repeated mowings and fertilizings, results in a massive development of roots, and over time a buildup of dead stems and leaves (thatch). c) This thatch must be removed periodically. Its natural decomposition does not keep pace with the buildup. d) If thatch is not removed the result will be an increase in turf diseases and insect problems, resulting in a decline in overall turf vigor. c. Soil can be "inoculated" with microorganisms such as mycorrhizal fungi to improve the cycling and transfer of nutrients in the soil. This is a costly procedure, and is usually justified only with high-value plants such as in nurseries. 2. Tilling: Tillage practices can improve or harm the soil, depending on how they are handled. Some points: a. Compaction of the soil is always detrimental to the root zone because it excludes air. 1) Avoid unnecessary or extra tillage or travel through a field, especially when the soil is wet. 2) Restrict machinery operation, if possible, to the areas away from the root zone of plants. b. Plowing and planting should occur across a slope rather than up and down a slope. This will discourage erosion and save valuable topsoil. c. Crop residues can be incorporated between croppings to boost soil organic matter. Nitrogen may need to be added at incorporation to support the breakdown of the residue. d. While not truly a tillage operation, aeration of turf plantings on an annual basis will help counter the effects of soil compaction due to recreational use and mowing operations. e. The repeated use of a rotary cultivator (which is very common in nursery settings) can lead to the development of a hardpan at the depth of the tines. Occasionally ripping or deep plowing the soil will help break up this hardpan. 3. Soil Sterilization: This is not often necessary, but for certain sensitive crops or for situations in which pathogens have built up in the soil, it is desirable to "clean up" the soil. Two methods can be used: a. Steam pasteurization in which the top layers of soil are covered with a tarpaulin and heated with steam to temperatures which kill the pathogens. The logistics of this are difficult on a large scale. b. Chemical fumigation. This is easier to accomplish on a large scale, with a fumigant such as methyl bromide applied under a large plastic tarp. The disadvantage of this method is that many desirable soil organisms are killed along with the pathogens. Also, methyl bromide is quite dangerous to use. 4. Irrigation: Irrigation practices can affect the soil in numerous ways. Some practices which help to conserve and improve soil follow: a. Be aware of the infiltration rate of the soil and irrigate at a rate the soil can absorb water. 1) This will reduce runoff, which in turn will reduce erosion of topsoil. 2) The use of detergent surfactants can improve water infiltration and penetration in some soils. b. Soil crusting occurs where the impact of sprinklers (or rainfall) is absorbed directly by the soil. 1) This can exclude the free passage of air and water. 2) Use mulches and alternative irrigation methods such as drip irrigation to reduce this problem c. Be aware of the quality of your irrigation water. Water high in sodium or other harmful salts needs to be managed carefully to avoid salt buildup in the soil. d. Soils that are high in salts or have fertilizer residue built up in them can be leached or "flushed" by a long continuous irrigation. e. Be sure to allow soils to "breathe" between irrigations. Keeping soils constantly at field capacity will kill plant roots and deny soil organisms the oxygen they require to keep the soil vital. B. Greenhouse and Container Soils: The grower has much more control over soils that are used in the greenhouse and in container culture because the soil is formulated by the grower from the beginning, using specifically chosen materials. Managing these soils becomes more a matter of handling them correctly than amending them further. 1. Preparation of Soil Mixes: Some simple steps taken at the time a soil is formulated and mixed will improve chances for success: a. When mixing soil components make sure the various materials are mixed uniformly. This is especially true for components such as fertilizers, which are active in small quantities. A uniform mix will yield a uniform crop. __________________________________________________________ ACTIVITY: 1. Have students mix a batch of medium to be used in the greenhouse for containerizing new transplants. Students will need square-point shovels and a flat, clean surface on which to mix the growing medium. 2. The ingredients for the mix should include three (3) four-cubic-foot bales of compressed peat moss (these will expand to approximately six cubic feet upon lofting); one standard sack of perlite (approximately 5 cubic feet); five pounds of ground dolomitic limestone (i.e., agricultural lime); and four pounds of a pelleted, slow-release fertilizer, such as 14-14-14 "Osmocote." 3. The ingredients should be piled up all at one time, and the pile should be turned at least three times. Have students pay special attention to the center of the pile and material around the edges. 4. If desired, pass the mix through a shredder and a screen to assure uniformity of the growing medium. __________________________________________________________ b. Soil pasteurization is probably the single most important operation performed on soil used in the nursery or greenhouse. By freeing plants of competition from pathogenic organisms and weeds, they are able to grow to their genetic potential. This is critical for a grower trying to produce a quality, uniform crop for the market. Important points regarding soil pasteurization include: 1) Soil pasteurization is preferable to soil sterilization: a) In soil sterilization, soil is heated to a very high temperature for a period of time sufficient to kill all of the organisms in the soil, including beneficial bacteria. High heats will also adversely affect some soil components, especially if there are clays present. b) In soil pasteurization, soil is heated to approximately 140 degrees Fahrenheit (60 degrees Centigrade) for a period of 30 minutes. This kills harmful fungi, weed seeds, nematodes, and insects without harming soil bacteria which are so important for nutrient cycling. 2) The most common method of soil pasteurization is with steam heat. Steam can be applied by many methods, depending on the needs and resources of the grower. a) Soil being prepared for use in containers can be pasteurized by the batch, in trailers or soil bins specially set up for steaming. b) In the greenhouse bench, steam can be brought to the soil by the use of perforated pipes. Tarps are used to contain the steam so that the critical temperatures can be attained. 3) Electric soil pasteurization units can be used for small quantities of soil (i.e., less than a cubic yard). Soil heated by this means generates a bad odor. 4) Fumigation with methyl bromide or other soil fumigants can be convenient, and requires little specialized equipment, but there are some disadvantages: a) Methyl bromide is harmful to beneficial organisms in the soil. b) Fumigants are dangerous to people, and fumigated soil requires aeration after treatment. c) Some plant species are sensitive to the residual toxicity of methyl bromide. c. At the time of soil preparation, the medium should be tested. 1) pH and electrical conductivity should be tested. This is particularly important if the materials or the supplier are new, or if the recipe for the mix is a new one. 2) Nutrients can be tested, especially if fertilizers for the crop have been added to the mix ahead of time. If nutrients will be supplied with irrigation, there is less point in testing nutrients at this time. 2. Storage: The effort of soil preparation and pasteurization will go to waste if soil is not stored correctly. a. Storage facilities should be clean, and constructed in such a way that they can be easily emptied and sanitized if necessary. b. Use up all the soil in a bin before adding a fresh batch. Keeping soil moving, rather than letting it sit in a facility for long periods of time will minimize the growth of pathogenic organisms. c. Storage facilities should be kept dry. Soil pathogens thrive with moisture. 3. Handling Nursery Soils: Again, sanitation is the main concern. a. Make sure that the tools and equipment used to handle soil have not been exposed to field soil or other sources of soil pathogens. b. Don't leave soils exposed in the open for long periods of time where they can pick up weed seeds and other pests. c. Also, avoid any operations which unnecessarily compact soils. 4. Recycling Soil Mixes: Occasionally, leftover soil accumulates in a nursery operation. This soil can be recycled and used, but care must be taken: a. Check that the soil to be recycled is free of undecomposed organic matter (i.e., dead plants). These will support disease organisms. b. Be absolutely sure to pasteurize any soils to be recycled. c. Handle these soils separately and test for pH, salinity, and nutrients. You don't know "where it's been"! C. Benefits: There are many advantages to managing soils correctly, resulting in their improvement and conservation. 1. Air and water exchange capacity of the soil improves, resulting in superior plant respiration and nourishment. 2. Organic materials are maintained or accumulate, resulting in better soil moisture and nutrient availability to plants. 3. Valuable topsoil is conserved as erosion is discouraged. 4. The activity of soil pathogens is limited. 5. Plants can grow to their genetic potential and develop into uniform crops of good quality. 6. Use of fertilizers and other inputs such as pesticides can be minimized if soils are managed optimally. 12/14/90 MH/sg #%&C