Soil Function
The purpose of this entry is to briefly review soil function, introduce resources that identify soil, cover soil testing, interpret soil test results, share typical data for soils in Kittitas County, how to enrich them and prepare them for growing food and finally, soil conservation.
Soil provides nutrients, water and physical support for plants, air for plant roots and a medium for microorganisms. An idealized soil may contain 45% soil mineral particles, 5% organic matter, 25% air and 25% water. Individual particles of sand, silt and clay tend to cluster and bind together forming aggregates called peds. Aggregation is a function of biological activity (e.g. earthworm burrowing), root growth and organic matter, which acts as a natural glue that stabilizes and strengthens peds. The spaces between peds are called pores and depending on their size are either macro or micro. Macropores influence aeration and permeability, the rate at which water moves through the soil. Micropores influence available water capacity. Porosity is a function of texture, structure, compaction and organic matter. Soil that has a balance of macropores and micropores provides adequate permeability and water holding capacity for good plant growth.
Soils meter nutrients to plants. These nutrients come from weathering and organic matter decomposition. Plants can only take up nutrients dissolved in soil water. The surface of clay particles and organic matter are negatively charged and hold positively charged nutrients such as ammonium, potassium, calcium and magnesium in an available reserve to be released into soil solution to replace nutrients taken up by plant roots. Soil chemical properties are a function of soil origin, soil texture, drainage, soil weathering and organic matter.
There are a multitude of organisms that thrive in soil. Mycorrhizae, rhizobia bacteria and earthworms are key players in the complex soil food web. Mycorrhizae are fungus that infect plant roots and increases the plants ability to take up nutrients. Rhizobia bacteria convert atmospheric nitrogen into plant available forms. Earthworms mix large volumes of soil and create macropore channels. In every handful of healthy soil there are 6 billion soil organisms, as many as there are people on the planet.
Soil Identification
The Web Soil Survey (http://websoilsurvey.nrcs.usda.gov/app/) is an internet based free tool that can be used to broadly identify a soil and its characteristics. Keep in mind, if the area of interest is close to a boundary then it is wise to field check the area of interest by digging a profile or using a probe to examine the soil profile.
Useful information that can be gleaned from this resource includes:
- Depth to restrictive feature, a hardpan is an example of a restrictive features, it restricts rooting depth and permeability.
- Drainage class refers to the frequency and duration of wet periods; however alterations of the water regime by human activities, either through drainage or irrigation, are not generally considered. There are seven recognized drainage classes; they are excessively drained, somewhat excessively drained, well drained, moderately well drained, somewhat poorly drained, poorly drained, and very poorly drained.
- Depth to water table is the depth to the saturated zone, but again may be different as a result of irrigation and drainage projects. Evidence of this zone includes gray soil with mottles.
- Available water capacity refers to the quantity of water that the soil is capable of storing for use by plants. The capacity for water storage is given in inches of water per inches of soil. Available water capacity is a function of the organic matter content, soil porosity, soil texture, bulk density, and soil structure, with corrections for salinity and rock fragments.
- Finally, the typical profile is a description, primarily textural, of each typical soil layer.
With a soil sample from the area of interest, the soil textural triangle is a useful tool to verify soil texture. Sand is gritty, silt is smooth and clay can be formed into a long strong ribbon before breaking. For example, a loam falls out last, neither grittiness nor smoothness predominates. Another way of qualitatively assessing soil texture is to put soil samples of clay loam, silt loam, and sandy loam in separate clear jars with water, shaking them and comparing the amounts of sand silt and clay that drop out. The sand will settle out in a minute or two, silt in about an hour and clay several hours to a day.
Clay soils hold a lot of water, but are hard to dig, dry slowly in the spring and are prone to compaction. Sandy soils can be planted into earlier in the spring, but need more frequent watering. Coarse fragments are not harmful, but can be a nuisance and do not contribute to the productivity of a soil.
Soil Testing
The soil survey can only take you so far. Soil testing can take you a step closer to knowing your soil and will account for past management. There are four local labs that do soil fertility testing. Their contact information is listed in the resources section. Before collecting a sample contact the lab to get instructions. Soiltest farm consultants offers basic lawn and garden sampling techniques at http://www.soiltestlab.com/forms/GardenReqForm.pdf
Interpreting Soil Test Results
Soiltest farm consultants offers a general soil test interpretation guide at http://www.soiltestlab.com/forms/soil-handout.pdf
General Kittitas County Soil Information
The soils in the Kittitas Valley are very diverse. At the base of the hills on the east side of the Kittitas Valley, the pH can be high at 8.0 or higher, the soluble salts can be high at 3 to 5 m.mho/cm, the organic matter can be modest at 1 to 2%, the available phosphorus can be modest at 8 ppm (parts per million), the available potassium can be modest at 80 ppm and nitrate, sulfate and boron can be all over the place. In the wet part of the Kittitas Valley, near the Yakima River, the pH can be low at 6.0, the soluble salts are usually not an issue at 1 m.mho/cm (although areas that are not well drained may be high in soluble salts), the organic matter can be high at 5 to 6%, the available phosphorus can be moderate at 10 to 20 ppm and the available potassium, nitrate, sulfate and boron can be all over the place.
Enriching Soil
The next step is to determine what to add to your garden soil and how much. This discussion is not comprehensive, it will cover improving soil fertility with regard to the primary nutrients, increasing soil organic matter and finally decreasing soil pH and soluble salts.
Nitrogen, phosphorus and potassium are the primary nutrients. Nitrogen is a key element in proteins, is a food source for soil organisms, and causes green growth. Phosphorus gives plants energy and is necessary for the growth of flowers and seeds. Potassium aids in protein synthesis and in the translocation of carbohydrates to build strong stems. Soil test results will likely include an interpretation guide, which will convey whether the soil tested has high, medium or low nutrient levels.
The following table displays general nitrogen, phosphate and potash recommendations for gardens with low, medium and high nutrient levels from three sources. The three sources are a 1982 Fertilizer Guide entitled “Home Vegetable Garden for Irrigated Central Washington”, a 2005 Fertilizer Recommendations Guide published by South Dakota State University and the 2006 edition of How to Grow More Vegetables by John Jeavons. In the absence of a soil test, use the recommendations for gardens with medium nutrient levels. I elected to use the numbers in the 1982 Fertilizer Guide for further calculation. Since most of us will not be working at the per acre level, I converted the numbers from lbs/acre to lbs/100 sq ft by dividing by 43,560, the number of square feet in an acre and multiplying the result by 100.
Table 1. N, P and K Recommendations for Gardens with Low, Medium and High Nutrient Levels
The next step is to determine how much fertilizer to add based on its analysis. These figures, 0.2 lbs of N per 100 sq ft, 0.4 lbs of phosphate per 100 sq ft and 0.2 lbs of potash per 100 sq ft can now be entered into the Organic Fertilizer Calculator. The Organic Fertilizer Calculator can be downloaded at http://smallfarms.oregonstate.edu/organic-fertilizer-calculator/register at no cost, but you have to register. A user guide accompanies the calculator. Things to know are that values can be entered into yellow cells (all other cells are locked), any units can be used without changing the formulas as long as units are kept consistent and PAN is the acronym for plant available nitrogen. One of the first things to do is select the “Nutrient provided” tab and enter the amounts needed in the “Total needed” row. Be sure to enter the nitrogen requirement under “Estimated PAN after full season” (column F) rather than under “Total N applied” (column C). Now as different amounts and combinations of fertilizers are entered above, the “Total needed” can be compared to the “Total applied”. If 10 lbs of NutriRich is entered, a slow release pelletized supplemented chicken manure, we learn that the N needed is met; we are short on the phosphate needed and a little over on the potash. It does not have to be perfect, just close. If the fertilizer is not listed and the analysis is known, go to the “Fertilizer analysis” tab and enter the analysis in an open row. The fertilizer manufacturer may need to be contacted to ascertain the % dry matter, a spreadsheet requirement to get “PAN after full season”.
To illustrate the meaning of a fertilizer analysis, NutriRich, which has an analysis of 4-3-3, contains 4% nitrogen, 3% phosphorus expressed as units of phosphate and 4% potassium expressed as units of potash and expressed as percentages of total fertilizer weight. This calculator can also be used to compare costs.
All of the fertilizers listed in the Organic Fertilizer Calculator are considered organic. There is a difference between organic fertilizers and processed fertilizers (aka inorganic fertilizers or synthetic fertilizers). Organic fertilizers require little or no processing, use recycled materials that would otherwise be discarded as waste, have a low analysis or often the analysis is unknown. They are usually slow release (e.g. many months) and are usually a source of organic matter. Processed fertilizers require industrial processing, can create waste, have a high analysis, are usually fast release (e.g. days or weeks), have a known analysis and have no organic matter. Further, the raw material for processed nitrogen is nitrogen gas from the atmosphere and requires a substantial amount of fossil fuels to manufacture. Processed phosphorus fertilizers come from phosphate rock treated with acid. The most common raw material for potassium fertilizers is sylvinite, a deep salt deposit, treated to remove the sodium salts to make it suitable for use as a fertilizer.
There are several points to consider when using fertilizer. First, the best time to apply fertilizer is so the nutrients in the fertilizer are available when the plants need the nutrients. For example, NutriRich, a slow release fertilizer, is spread after harvest, in September, so the nutrients will be available to the crops planted the following spring. Second, it is easy to apply too much processed fertilizer, which can harm crops and the environment. Too much manure can also be applied. Excessive amounts of fertilizer act as salt. Finally, as a general rule, in the absence of a soil test, in eastern Washington, usually only nitrogen is needed.
For the most part, all of the fertilizers listed in the Organic Fertilizer Calculator, will have to be imported. Importing fertilizers is not sustainable and should be a temporary fix to raise the soil fertility to a satisfactory level in a short period of time. Once that has been accomplished, the only sustainable way to maintain the fertility of your soil is by growing the crops that will replenish it. I hadn’t really wrapped my mind around this concept until recently, now I realize crop rotation, managing crop residues and composting are essential. Crop residues and compost are so essential, in part because they, with manure, are “the” sources of organic matter.
“If you follow practices that build and maintain good levels of soil organic matter, you will find it easier to grow healthy and high-yielding crops. Plants can withstand droughty conditions better and won’t be as bothered by insects and diseases…Soil organic matter is that important….A study of soils in Michigan demonstrated potential crop-yield increases of about 12% for every 1% organic matter.”
-Better Soils for Better Crops
Although organic matter is only a small component of the soil, the importance of organic matter cannot be overstated. Organic matter has three parts, living organisms, fresh residues and well decomposed residues. As organic matter is decomposed, nutrients are converted into forms that plants can use. The soils ability to retain these nutrients also increases with organic matter decomposition. The well decomposed residue is called humus. Humus is very stable, complex and serves special functions. It functions to hold on to some essential nutrients, storing them for slow release to plants. It can surround certain potentially harmful chemicals and prevent them from causing damage to plants. It also improves water retention by enhancing aggregation and by holding onto and releasing water. The best method to improve soil structure is to add organic matter, but how much?
It is stated in Better Soils for Better Crops, “There are few accepted guidelines for adequate organic matter content in particular agricultural soils”. An idealized soil may contain 5% organic matter. However, in a sandy soil 2% is very good and may be difficult to reach. In the Kittitas Valley, the organic matter can be modest at 1 to 2% on the east side and high at 5 to 6% by the Yakima River. The organic matter in soils farmed by one local farmer, who grows cover crops each winter and incorporates them into the soil the following spring, has been measured and ranges between 6% and 18%. Recommended application rates of compost and manure, reported by various sources, are listed in the following table. Keep in mind, manures may contain excess salt and vary widely in nutrient content and nutrient availability, depending on the type of animal that produced the manure and the age and handling of the manure; more is not always better.
Table 2. Recommended Application Rates of Compost and Manure
The C:N ratio is probably the greatest single factor determining the rate of decomposition and mineralization of organic matter. If we are looking for the organic matter to provide short term nutrient availability, then we have to select organic matter that has a low C:N ratio or realize that if adding organic matter that has a high C:N ratio then, nitrogen immobilization may occur unless nitrogen is supplemented. The carbon to nitrogen ratio, reported by various sources, of some organic matters is listed in the following table.
Table 3 C:N Ratio of Some Organic Matters
According to the Organic Fertilizer Calculator User Guide, microorganisms that consume organic matter have a C:N ratio that ranges from about 10:1 to 15:1. If the C:N ratio in the organic material is below about 15:1, the material provides more nitrogen than the microorganisms need to develop and reproduce, so they excrete mineral forms of nitrogen that are easily taken up by plants. If the C:N ratio is higher than about 20:1, the microorganisms supplement the protein in their food source with mineral nitrogen in the soil solution, thus immobilizing the nitrogen that plants otherwise would use. However, we may be safe using a higher threshold. According to, the Better Soils for Better Crops publication, residues with a C:N ratio in the mid 20s to low 30s, will not have much effect on short-term nitrogen immobilization or release. What can be inferred is that addition of organic matter with a low C:N ratio must be used sparingly to prevent over fertilization and organic matter with a C:N ratio greater than 33:1, will likely result in immobilization where nitrogen is scavenged from the soil by microorganisms.Compost can be made. The key to composting is to supply a balance of air, water, energy materials and bulking agents. Energy materials are high in moisture, have low porosity and are high in nitrogen. They include fresh crop residue, grass clippings, fresh chicken or rabbit manure, fruit and vegetable waste and garden trimmings. Bulking agents are low in moisture, have high porosity and are low in nitrogen. They include grass hay, wheat straw and corn stalks. There are also materials characterized as balanced, which have low to medium moisture, medium porosity and medium nitrogen. They include ground-up tree and shrub trimmings, horse manure and bedding, deciduous leaves and legume hay and do not have to be mixed with other materials to become compost. The first recipe, from The Oregon-Washington Master Gardener Handbook, is one part energy source and two parts bulking agent, by volume. It is stated, in this source, that this mixture usually gives a reasonable mix for rapid composting, which leads me to think that this next recipe, from How to Grow More Vegetables, would yield faster composting. The recipe is 45% mature (dry) material, 45% immature (green) vegetation, including kitchen wastes, and 10% soil, by volume. It is stated, in this source, adding soil to the compost pile enables the pile to hold moisture better facilitating decomposition, contains microbes enabling decomposition and will reduce nutrient leaching.
Composting tips in The Oregon-Washington Master Gardener Handbook include mixing the pile thoroughly instead of layering it, if all the materials are on hand when you build the pile. And that smaller piece size will increase decomposition. Tips in How to Grow More Vegetables include using at least 3 different types of material of three different textures and locating the pile under the shade of a deciduous tree (excluding walnut trees), but a minimum of 6 feet from the trunk of the tree. Finally, although a pile of about one cubic yard (3’ by 3’ by 3’) may be adequate for year round composting in cold winter areas, bigger is probably better in our area. It is suggested in How to Grow More Vegetables, in colder climates, a minimum compost pile size of two cubic yards (4’ by 4’ by 4’) is needed to properly insulate the heat of the composting process.
Crop residues from cover crops are essential to building soil organic matter, additionally cover crops are valuable in that they capture and recycle nutrients that would otherwise be lost by leaching during the winter, protect the soil surface from rainfall impact, reduce runoff and erosion, suppress weeds, can supply nitrogen and can be a food source. The earlier cover crops are planted the more benefits they provide. Research in western Washington showed that cereal rye planted in September captured three times as much nitrogen as cereal rye planted in October. Winter cover crops can be planted as early as August 1. They make some growth before frost kills them or stops their growth. When harvesting very late season crops, cover crop seed can be sown between the rows a month or less before expected harvest. This technique lets the cover crop get a good start without interfering with vegetable growth. Cover crop residue can either be tilled or dug into the soil before they flower or cut before it blooms and composted. Cover crops may also be harvested for food. After flowering, plants become woody and decline in quality, but that material can be used as the bulking agent in compost piles.
The following table is a work in progress. It lists the cover crops that may work in the Kittitas Valley. The table includes summer cover crops and crops that have the benefit of producing food and compost material. Food crops include amaranth, canola, cereal rye, chickpea, corn, fava bean, lentil, millet, quinoa, barley, wheat, oats and sunflowers. Summer cover crops include buckwheat and corn. Cover crops that provide nitrogen include alfalfa, Austrian winter pea, common vetch, crimson clover, fava bean, hairy vetch, red clover and white clover. Species that break up hard pans include cereal rye. The main reason to grow cover crops is to increase soil organic matter, so choosing crops with large root systems is effective. It is estimated that one cereal rye plant in good soil grows 3 miles of hairs a day, 387 miles of roots a season and 6,603 miles of root hairs each season. Note: Soon cover crops will be added to the Organic Fertilizer Calculator.
Table 4. Cover Crops (work in progress)
Peat, ground bark and wood chips are also examples of organic matter, but they carry baggage. Ground bark and wood chips have such a high C:N ratio, nitrogen immobilization may occur, depending on how they are used. They should not be used in annual beds or vegetable gardens and should not be mixed into the soil. Wood chips are and excellent landscape mulch. The summer 2007 issue of the Master Gardener magazine, which can be accessed at http://www.mastergardeneronline.com/preview/index.php?issue=0707, extols the benefits of using them.
Concerns regarding the use of peat are discussed in the winter 2007 issue of the Master Gardener magazine, which can be accessed at http://www.mastergardeneronline.com/preview/index.php?issue=0107. The following is excerpted from it,
Hundred of years pass for sphagnum moss, the wetland plant that covers the
surface of peat lands, to die, decompose, and accumulate, mixing with native
soil to create sphagnum peat moss.
During this process, these specialized wildly diversified wetland perform critical ecological functions, such as:
Storing carbon, which helps regulate global climate.
Providing habitat for innumerable life forms, including rare, specialist, and endangered plants and animals.
Purifying and collecting water.
Research shows that mining seriously compromises the ecological functions of peat lands even years after restoration…. Changes include:
Release of carbon dioxide into the atmosphere, which exacerbates global climate changes.
Changes in water pH and nutrient levels, which results in repopulation by different vascular plants and animals.
Release of heavy metals, such as arsenic, into water.
Hydrologic changes, such as drying and flooding.
Peat is a common additive to potting mixes. The spring 2007 issue of the Master Gardener magazine, which can be accessed at http://www.mastergardeneronline.com/preview/index.php?issue=0407, discusses choosing the right mix of ingredients and quality.
Two challenges that a gardener may face in the Kittitas Valley are high soil pH and high soil salinity. Vegetables like to grow in pHs between 6 and 7.5. Elemental sulfur lowers soil pH. If you suspect your garden soil has a high pH, in the absence of a soil test, adding about 50 lb. of sulfur per 1,000 sq. ft. is recommended (Oregon-Washington Master Gardener Handbook). To decrease soil salinity, salts can be leached from the soil by applying irrigation in excess of the water holding capacity of the soil. Three inches of excess water removes about half of the soluble salts in a soil and five inches of water removes about 90 percent (The Oregon-Washington Master Gardener Handbook).
Preparing Soil
One method we used to prepare our garden soil was the deep soil preparation described by John Jeavons in How to Grow More Vegetable. There are 4 basic types of deep soil preparation initial double-dig, ongoing double-dig, complete texturizing double-dig and the U-bar dig. Because the soil we inherited was so poor we elected to do the complete texturizing, which was developed to improve soil texture more rapidly and is used one time only in place of the initial double-dig. It involves, defining the dimensions of the bed, getting the soil to the right moisture content so it can be easily dug, loosening the soil with a spading fork and removing the existing vegetation, spreading a ½” to 1” layer of compost over the area, defining the first trench (e.g. 48” wide by 12” long by 12” deep) and removing the soil from it, spreading compost in the trench, loosening the soil 12” deeper with a spading fork, standing on a digging board (e.g. 5/8” by 48” plywood), defining the second trench, loosening and moving the soil from it to the first trench, spreading compost in the trench and loosening the soil 12” deeper with the spading fork, raking after every 3 to 4 trenches to level the soil, repeating these steps until the last trench is filled out with some of the soil removed from the first trench. Due to the expansion of the soil volume with air, all of the soil removed from the first trench is not needed to fill out the last trench. Finally the fertilizers are sifted, using the spading fork, into the upper 2 to 4 inches of the soil, the bed is tamped with the digging board if there is excess air and the bed is planted.
The goal of double-digging is to loosen the upper 24” of the soil, without mixing it. The upper layer of soil, especially, should not be turned over during double-digging in order to minimize disturbance to natural soil layering and to soil organisms, about ¾ of the beneficial soil organisms inhabit the upper 6 inches of the soil.
The basic types of deep soil preparation differ in the following ways. Complete texturing differs from the initial double-dig in that compost is mixed into the upper 12 inches and another layer of compost is added before loosening the lower 12 inches. The ongoing double-dig differs from the initial double-dig in that that the compost is put on after the digging and sifted into the upper 2 to 4 inches with the fertilizers. Finally, the U-bar dig, which may be used as a substitute for the ongoing double-dig differs from the ongoing double-dig in that it does not prepare the soil as deeply, as limited by the 18” inch tines, but has the advantage of mixing the soil less.
Video demonstrations of double-digging can be viewed on YouTube at the addresses listed in the resources section or a comprehensive video demonstration is available for sale from Bountiful Gardens, the video is entitled “Dig It!”.
Soil Conservation
The lowest hanging fruit, enabling us to grow food in the soils we inherit, is soil conservation. It is the most cost-effective stewardship method to prevent soil loss, organic matter loss and soil compaction. Remember, regarding soil function, soil loss reduces the supply of nutrients and water. Soil compaction retards root growth and the circulation of air and water. And, organic matter loss accelerates erosion and may decrease water retention, structure, porosity, and resistance to compaction. These conditions are not easily reversed given the amount of time it takes for easily crumbled, humus and nutrient enriched soil to develop.
Conservation measures include using management practices that increase soil organic matter, minimizing bare soil by using mulches and cover crops and not working the soil when it is too wet or too dry or too much. Working excessively wet soil can destroy soil structure. Plowing wet soils with a tractor is especially damaging, as it creates a compaction layer that inhibits root growth, a rule of thumb is if it stays in a mud ball it is too wet. If it is powdery and clumped, it is too dry. If it crumbles freely, it is about right. If soil sticks to a shovel, or the turned surface is shiny and smooth when spading, it is still too wet. Clay soils are most easily compacted. Do not pulverize the soil. Over-tilling also destroys soil structure.
Soil is the medium in which so much of what we consume grows and it takes a long time for it to develop and no time to lose. In the US in 1995, approximately 1/28 of an inch of farmable soil was lost per acre due to wind and water erosion. Conversely, on the average, 1/500 of an inch of farmable soil is being built up naturally in the US each year. Thus the soil is being depleted 18 times faster than it is being built up in nature.
In conclusion, we have, in large part, inherited the soil we use to prosper today. Our challenge and that of future generations will not be growing vegetables, raising cattle or growing trees but will be building the soil on which they depend.
Resources
Local Labs that do soil fertility testing include:
Analytical Sciences Laboratory
Holm Research Center
University of Idaho
Moscow, ID 83844-2203
(208) 885-7081
NW Agricultural Consultants
2545 West Falls
Kennewick, WA 99336
(509) 783-7450
Soiltest farm consultants
2925 Driggs Drive
Moses Lake, WA 98837
1-800-764-1622
http://www.soiltestlab.com/
US Ag Analytical Services
1320 E Spokane Street
Pasco, WA 99301
(509) 547-3838
Andrews, N. and J. Foster. User Guide Organic Fertilizer Calculator, Oregon State University, 2007.
Chalker-Scott, Linda. “Wood Chip Mulch: Landscape Boon or Bane?”. Master Gardener 1.3 (2007): 21-23. < http://www.mastergardeneronline.com/preview/index.php?issue=0707>
Dig It! Video DVD. < http://www.bountifulgardens.org/products.asp?dept=112>
Dodge, John c. and Darrell O Turner. . Fertilizer Guide: Home Vegetable Garden for Irrigated Central Washington. Puyallup, Washington, Washington State University Cooperative Extension, 1982.
Fertilizer Recommendations for Home Gardens and Landscaping compiled by soiltest farm consultants. Moses Lake, WA, soiltest farm consultants.
Forest Soil Productivity. 1992. http://nrs.fs.fed.us/fmg/nfmg/docs/mn/Soils.pdf
Gerwing, Jim and Ron Gelderman. Cooperative Extension Service, South Dakota State University and U.S. Department of Agriculture, Fertilizer Recommendations Guide, South Dakota, South Dakota State University. 2005.
Jeavons, John. How to Grow More Vegetables. Berkeley: Ten Speed Press, 2006.
Jeavons, John. “The Global Farm: The Challenge and the Solution”. Proceedings from the 2000 Soil, Food and People Conference Presented by Ecology Action at the University of California - Davis. Ed. Hugh Roberts. Willits: Ecology Action, 2001. 6-13
Magdoff, Fred and Harold Van Es. Building Soils for Better Crops:Sustainable Soil Management Third Edition. Sustainable Agriculture Research and Education (SARE) program. 2009 http://www.sare.org/publications/bsbc/bsbc.pdf
Munts, Pat. “Potting Mixes”. Master Gardener 1.2 (2007): 10-13. http://www.mastergardeneronline.com/preview/index.php?issue=0407
Nelson, Dan. Soiltest farm consultants. Telephone interview. 15 January 2010.
Oregon State University. Organic Fertilizer Calculator. http://smallfarms.oregonstate.edu/organic-fertilizer-calculator/register
Riskin, Cindy Shyev. "Too Popular Peat." Master Gardener 1.1 (2007): 18-19. http://www.mastergardeneronline.com/preview/index.php?issue=0107
Soiltest farm consultants offers Basic Lawn/Garden Sampling Techniques at http://www.soiltestlab.com/forms/GardenReqForm.pdf
Soiltest farm consultants offers a General Soil Test Interpretation Guide at http://www.soiltestlab.com/forms/soil-handout.pdf
Sustainable Gardening, The Oregon-Washington Master Gardener Handbook. Oregon State University, 2008.
Washington State University Fertilizer Guides & Summary http://grant-adams.wsu.edu/agriculture/General/fertilizerguides/Washington%20State%20Fertilizer%20Guides/Indexfertguide.html . Species specific papers with local, but dated crop nutrient requirement information are listed on the Washington State University Fertilizer Guides & Summary page.
Washington State University Master Gardener on-line Training. Washington State University, 2009. http://lms.wsu.edu/
Web Soil Survey. USDA Natural Resources Conservation Service. Jan. 2010. http://websoilsurvey.nrcs.usda.gov/app/
YouTube videos on double-digging http://www.youtube.com/watch?v=jx9pM9tPOWM, http://www.youtube.com/watch?v=_55121lPJNE&feature=PlayList&p=CE8F29A0D946E73C&playnext=1&playnext_from=PL&index=3,
http://www.youtube.com/watch?v=n1xcDrLjcKU&feature=PlayList&p=CE8F29A0D946E73C&playnext=1&playnext_from=PL&index=4
http://www.youtube.com/watch?v=xPivuNSm4Hc&feature=PlayList&p=CE8F29A0D946E73C&playnext=1&playnext_from=PL&index=5
Conversions: One 5 gallon bucket equals 0.67 cubic feet. There is 43,560 sq ft in an acre. If an application calls for 1 five gallon bucket of material, divide 0.67 by the number of sq ft of area to which the material is to be applied. The result is depth in feet, to convert to inches divide by 12. Assuming the upper 6 inches of soil weighs 2 million pounds, the weight of organic material in 6 inches of soil that contains 1% organic matter is 20,000 pounds.
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