Understanding a Soil Test Randall H. Zondag Zondag.firstname.lastname@example.org lake.osu.edu Commercial Horticulture Educator OSU Extension –Lake County
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Healthy Plants • Friable soils • Proper nutrient balance • Proper soil pH – acid vs. alkaline • Proper root and crown spacing • Ample soil moisture • Proper soil temperature • Proper light levels • Pure air • Free of insects and diseases
Soil Properties: They are not independent – they interact to affect soil characteristics Biological Physical Chemical
Physical Properties Soil Texture, Consistency, & Structure Soil Compaction (Bulk Density) Soil Moisture Chemical Properties pH Cation Exchange Capacity (CEC) Mineral Nutrient Availability Biological Properties Microorganisms bacteria fungi (e.g. mycorrhizas) protozoa nematodes Macroorganisms arthropods earthworms nematodes Decomposition / Nutrient Recycling Aeration Aggregation (e.g. “microbial glue”) Soil Properties:
Soil Chemistry • Chemical bonding • pH • Nutrient Availability • Cation Exchange Capacity (CEC)
Nutrient Relationships “A crop’s yield is restricted by the lack of one single element even though there may be sufficient quantities of all other essential elements.” J. von Liebig
Fertilizers are designed to provide the elements necessary for plant growth. About 90% of the plant weight is made up of water. The remaining mass constitutes the plant dry weight, which is made up primarily of 17 elements that are required for plant growth. Let's define some terms. Essential nutrients are the 17 elements required for proper plant growth and development. They are C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Cl, Ni. Carbon (C), hydrogen (H), and oxygen (O)make up 90% of the plant dry weight. These elements are obtained from air or water and are not included in fertilizers.
Plant Nutrients • Nitrogen (N) – A constituent of protein and hence the promoter of growth. Also a constituent of enzymes which accelerate the metabolic process and control metabolism through their catalytic action and of other physiologically important materials. Directly involved in photosynthesis as a constituent of chlorophyll (leaf green). N is absorbed in the form of NH4 (ammonia), NO3 (nitrate) or CO (NH2)2 (urea). • Phosphorus (P) – A constituent of compounds essential for life, particularly in the conversion of energy. Activates organic substances. An important constituent of basic structures such as cell membranes and nucleic acids (carriers of the genetic code). • Potassium (K) – Not a structural element but very important from the point of view of plant physiology: improves the osmotic pressure or swelling of the cells and thus regulates the plant’s water retention. Enhances resistance to frost and drought and the absorption capacity of the roots. Stimulates the storage of carbohydrates in the reserve cells. Potassium is therefore extremely important if the plant’s generative phase is to proceed satisfactorily.
Plant Nutrients • Calcium (Ca) – Responsible for the structural and physiological stability of the plant tissue, i.e. for proper cell division, cell wall formation and cell extension. Some of the typical consequences of calcium deficiency are: collapse of plant tissue (e.g. bitter pit of apples, blossom end rot in tomatoes). • Magnesium (Mg) – As the central atom of chlorophyll (leaf green) of particular importance to the process of photosynthesis. Supports the assimilation of CO2 and the synthesis of protein. Helps to stabilize the cell membranes and activities a large number of enzymes. • Sulphur (S) – As a constituent of amino acids, sulphur promotes the synthesis of protein. Sulphur deficiency symptoms are thus similar to nitrogen deficiency symptoms. All the following nutrients, i.e. the trace elements, are in all cases constituents of enzymes and help to activate enzyme systems.
Micro Nutrients • Iron (Fe) – Through its part in complex enzyme reactions iron plays an important role in the formation of chlorophyll and protein. • Zinc (Zn) – Similar to magnesium and manganese in its physiological activity. • Copper (Cu) – Participates in the production of carbohydrates and protein via photosynthesis. Seventy percent of the copper in a plant is in the chlorophyll • Boron (B) – Promotes the formation of protein which is required in order to sustain meristem activity (meristem = embryonic tissue). Being part of the cell walls it promotes the transport of carbohydrate through the cell membranes. • Manganese (Mn) – Extremely important to photosynthesis, or more precisely the Hill Reaction, i.e. the splitting of the water molecule. Plays an important part in the CO2 assimilation and the metabolism of N. • Zinc (Zn) – Similar to magnesium and manganese in its physiological activity. • Molybdenum (Mo) – Essential for the activation of nitrate reductase (the conversion of nitrate into nitrite). There is a higher Mo requirement when NO3 is supplied as a feed than with NH4. Molybdenum is the key to nitrogen fixing, particularly in legumes • Chlorine Cl- • Nickel -Ni
What Do Soil Tell Us • pH • Buffered index, buffered pH , LTI • Nutrient quantities – pounds per acre or ppm (parts per million) • Soluble salts levels • CEC • Organic Matter levels • Micro nutrient levels • Base Saturation numbers
Soil Test Results: Ideal Values pH Phosphorus P lb/A* Potassium K lb/A* Calcium Ca lb/A* Base Saturation Magnesium Mg lb/A* Cation ExchangeCapacity (CEC) meq/100g % Ca % Mg % K 7 – 10 or higher 5.5 – 6.5 50 – 100 800 plus 150 – 250 40 % - 80% 10% - 40% 3% - 5% 250 – 400 Soil Chemistry: Soil Test * To convert lb/A (pounds per acre) to ppm (parts per million), divide by 2: 100 lb/A = 50 ppm
Soil Testing – the only way to determine levels of available elements present Proper levels 5.5–6.5 50-100 250-400 800+ 150-200 7+ pH P K Ca Mg CEC
Acceptable Levels From Standard Soil Test • Test Parameter Acceptable Range • Ph 5.8 to 6.5 (ideal 6.2) Lime Test Index 68 to 70 Phosphorus (P) lb/acre 50 to 75 Potassium (K) lb/acre 300 to 350 • Calcium (Ca) lb/acre 2000 + Magnesium (Mg) lb/acre 150 to 200 • Cation Exchange Capacity - Course Textures (sands)1 to 5 Cation Exchange Capacity - Medium Textures (silts)5 to 20 Cation Exchange Capacity - Fine Textures (clays)20 to 30 plus • Base Saturation, % Ca 60 to 70 Base Saturation, % Mg 10 to 15 Base Saturation, % K 1 to 5
Cation Exchange Capacity • The CEC is the abbreviation for the cation exchange capacity of the soil. Any element with a positive charge is called a cation and in this case, it refers to the the basic cations, calcium (Ca+2), magnesium (Mg+2), potassium (K+1) and sodium (Na+1) and the acidic cations, hydrogen (H+1) and aluminum (Al+3). The amount of these positively charged cations a soil can hold is described as the CEC and is expressed in milliequivalents per 100 grams (meq/100g) of soil. The larger this number, the more cations the soil can hold.
Riding the CEC Bus: Soil Chemistry: CEC H+: hydrogen K+: potassium Mg++: magnesium Ca++: calcium The Passengers: Na+: Sodium Al+++: Aluminum Fe++ or +++: Iron NH4+: Ammonium
Potassium K K+ Hydrogen H H+ Sodium Na Na+ Calcium Ca Ca++ Magnesium Mg Mg++ Aluminum Al Al+++ Copper Cu Cu Nitrate N NO3- Chloride Cl Cl- Sulphate S SO4-- Phosphate P H2PO4- Chemical Symbol Chemical Symbol Ionic Form Ionic Form Cation Anion Soil Chemistry Common Soil Cations & Anions:
What is pH? • The measurement of acidity (H+) or alkalinity (OH) in the soil . • Affects nutrient availability • Determines what plants will grow well in some sites .
Soil pH .There is a correct soil pH range for all plants. When the soil pH is either below or above this range, nutrient uptake is reduced and plant performance is hurt. Therefore apply only the recommended amounts of lime (to increase the soil pH) or sulfur (to lower the soil pH). Split applications into no more than 50 lb./1000 sq. Ft. (5lb./100 sq. Ft.) Spring & fall.
14 - Lye 13 - Hair remover 12 - Household ammonia (10.5 – 11.9) 11 - Soap solutions, Milk of Magnesia 10 - Chlorine bleach - Baking soda, detergents 9 8 7 - Milk 6 - Black coffee 5 4 - Orange juice - Vinegar 3 - Lemon juice (2.0 – 3.0) 2 - Stomach acid (1.0 – 3.0) 1 - Battery acid 0 Soil Chemistry: pH pH
NEUTRAL 1 2 3 4 5 6 7 8 9 10 11 12 13 0 14 MOST DESIRABLE MOST AGRICULTURAL SOILS Soil Chemistry: pH
NEUTRAL 1 2 3 4 5 6 7 8 9 10 11 12 13 0 14 Nitrogen Phos. Potassium (K) Iron (Fe) Soil Chemistry: pH
NEUTRAL 1 2 3 4 5 6 7 8 9 10 11 12 13 0 14 MOST AGRICULTURAL SOILS Soil Chemistry: pH Blueberry: 4.5 - 5.0 Azalea: 4.5 - 5.5 White Pine: 4.5 - 6.0 Tomato: 5.5 - 7.5 Black Walnut: 6.2 - 7.5 Pin Oak: above 7.5 = Chlorosis
Buffered pH or Lime Test Index (LTI) • The amount of Calcium (Ca) or Magnesium (Mg) that is found on soil particles that will control the rate at which pH changes. • Numbers usually between 60 and 70 or 6.0 to 7.0 . The higher the number the more difficult it will be to drop pH ,but it will be very easy to raise the pH. • Determine lime or sulfur application .
How Do We Affect pH? • Adding Lime to raise the pH . How much and what forms ? (dolomite, hydrated) • Sulfur to lower the pH ? How Much and what forms?(iron sulfate, aluminum sulfate , elemental sulfur, sulfur coated fertilizers).
Buffered pH or Lime Test Index (LTI) example • Two soils with a pH of 6.4. • One has a LTI of 65 • One has a LTI of 62 How much lime will it take to raise the ph to 7.0 ?
Mg2+ H+ H+ K+ H+ - - Mg2 - - OH- Ca2 - - - - - - Al3 H+ K K H Ca2+ - - - Ca2 H H+ - - - H+ K OH- - - Clay Particle OH- - Ca2 - Mg2 H+ - - H+ K - - - - - - - - H Al3+ H K H+ K Al3 H H Al3+ H+ Mg2 K+ OH- H+ OH- H+ Soil Chemistry: Buffer
Calcium • Other cations:Being a major cation, calcium availability is related to the soil CEC, and it is in competition with other major cations such as sodium (Na+), potassium (K+), magnesium (Mg++), Ammonium (NH4+), iron (Fe++), and aluminum (Al+++) for uptake by the crop. High K applications have been known to reduce the Ca uptake in apples, which are extremely susceptible to poor Ca uptake and translocation within the tree.
Calcium • Boron(B-):High soil or plant Calcium levels can inhibit B uptake and utilization. Calcium sprays and soil applications have been effectively used to help detoxify B over-applications. • Iron(Fe++) and Aluminum(Al+++):As the pH of a soil decreases, more of these elements become soluble and combine with Ca to for essentially insoluble compounds.
Calcium Sources • Liming Material Approx. % Ca*.Recommendation Rate • Calcitic Limestone 32 1,000 to 15,000lb./A • Dolomitic Limestone 22 1,000 to 15,000 lb./A • Hydrated Limestone 46 750 to 10,000 lb./A • Precipitated Lime 60 500 to 10,000 lb./A • Blast Furnace Slag 29 100 to 2,000 lb./A • Fertilizers Approx. % Ca. Recommended Rates ofProduct • Gypsum 22 500 to 1500 lb./A • CaCI 36 5-8 lb./A Foliar • Ca(NO3) 2 19 10-15 lb./A Foliar Ca-Chelates 3-5 0.25-3 gal/A Foliar
Gypsum • To remove excess sodium (Na) • To build soil calcium (Ca) levels when a pH change is not desired
Increasing Soil Calcium (Ca) Saturation • Lb. gypsum/acre = C.E.C. x (desired %Ca sat. - present %Ca sat) x 18
What Causes acidity in Soils? • H • Al • Fe
Approximate amount of ground sulfur needed to decrease the pH of the upper 7 inches of soil types to 6.5. Sulfur recommendations are based on using aground sulfur material containing 95% S. Sulfur to apply (lbs/1,000 square feet
Percent Base Saturation • Percent base saturation tells what percent of the exchange sites are occupied by the basic cations. If calcium has a base saturation value of 50% and magnesium has a base saturation value of 20% as shown above, then calcium occupies half of the total exchange sites (CEC) and magnesium occupies one-fifth of the total exchange sites (CEC). In this example, where the soil has a CEC of 5 meq/100g, 2.5 meq/100g of the CEC is occupied by calcium and 1 meq/100g of the CEC is occupied by magnesium. If all the exchangeable bases (Ca, Mg, K and Na) total 100%, then there is no exchangeable acidity.
Proponents of cation balancing consider base saturation ratios of about 65-75% Ca, 10-15% Mg, 2-5% K, 0.5-3% Na and 10-15% H optimal for soil, crop and livestock health. This guideline is sometimes called the Albrecht Formula, after soil scientist William Albrecht who researched and developed it. For sandy soils with low CEC, the formula is modified slightly, to about 60% Ca, 20% Mg and 6-8% K.