Precision Agriculture Testing Manual For pH & Electrical Conductivity(EC) In Soil – Fertiliser – Water
pH
Good nutrition is essential to growing plants successfully. One of the first questions to consider to improve production is, “Have you tested your soil?” Soil pH is a measure of how acidic or “basic” (the opposite of acidic) your soil is. Soil pH is important since it affects the growth of plants and the severity of some diseases.
pH affects the ability of plant roots to absorb nutrients. Calcium, phosphorus, potassium and magnesium are likely to be unavailable to plants in acidic soils. Plants have difficulty absorbing copper, zinc, boron, manganese and iron in basic soils. By managing soil pH, you can create an ideal environment for plants and often discourage plant pests at the same time.
Measuring pH
pH is measured on a scale of 0-14. A soil or water pH reading below 7 is considered acidic, while a pH reading above 7 is basic. A pH reading of 7 is neutral, and is ideal for many plants and spray materials.
The pH scale is logarithmic, which means that a pH reading of 6 is 10 times more acidic than a reading of 7.
You can measure the pH of your soil, your spray tank water, or your irrigation/fertigation water.
Soil: Crops, ornamentals and turf need careful pH management to maintain their best quality and appearance. The wrong pH can lock nutrients in the soil, making them unavailable to plant roots. A pH that’s too high or low can make disease, insect and weed problems worse.
Spray tank water: If your spray tank water is too acidic (low pH) or too basic (high pH), the pesticides you mix in can be deactivated and may even burn your plants.
Irrigation/fertigation water: The pH of water you apply to your plants should match your desired soil pH. Otherwise it will gradually change the soil pH
pH levels
Acceptable pH varies by plant type. If you’re not sure what’s best for your plants, you can check a reference book or ask your seed or Ag Chemical dealer, Cooperative Extension agent, or private consultant.
Remember, when you adjust soil pH levels you can affect plant growth, nutrition and susceptibility to pests. When setting a pH goal for your soil, you will want to take all of these considerations into account.
Acidic fertilizers can be used to lower pH. Limestone is often used to raise pH. The type of limestone applied and your soil type can make a difference in how quickly and how much the pH will change
Testing Your Soil pH
1.) Sample — When taking samples, use a soil probe or trowel, a clean plastic bucket for collecting and mixing samples, and plastic bags or wax paper sacks to hold sub samples for testing. Make sure that you use clean tools. If the soil in your field is uniform, take 15 to 20 samples from random locations throughout the field and mix them together in the plastic bucket. If the soil is highly variable from one part of the field to the other, divide the field into several more uniform sections and take samples from each one. Write down where the samples were taken in a notebook.
Do not take samples from only one side of the field, only from the corners of the field, or from the same spot on each side of the field. Also, avoid taking soil samples near lime or manure piles, animal droppings, fresh fertilized rows, low spots, fences and roads.
When taking samples in turf and other shallow rooted crops, sample the top three inches of the soil. In ornamentals and other deep-rooted cultivated crops, sample the top six inches of soil — though you may test a shallower sample if it is taken shortly after tillage. In non-cultivated crops, soil samples should be six to eight inches deep. With deep-rooted non-legume crops such as corn, wheat and cotton, take a soil sample of seven inches to 24 inches in addition to the tillage sample.
2.) Mix — Place these samples in a clean plastic container.
3.) Measure — Remove a small amount (coffee measure) of 2 parts soil from your mix and add 1 part bottle drinking water. Do not pack soil in cup and always use a flat bottom measure cup to assure proper proportions.
4.) Shake and wait — Stir or shake the soil and water mixture vigorously. Then let sit for 1 to 2 minutes.
5.) Test — Turn on your pH meter, be sure you have calibrated your meter before running the test ( see owners manual ) remove the cap to expose the sensor, and dip the sensor completely in the solution. Record the reading displayed on the meter
Understand Your Soil Test: pH-Excess Lime-Lime Needs
The relationships among pH, soil type, and lime requirements are explained.
Accurate soil tests can be an excellent management tool. Misuse of soil tests leads to increased production costs, yield losses, or both. The elements required by plants for proper growth have been determined by experimentation. Experience has shown that soils differ greatly in their capacity to supply these elements. The amount of each element supplied by a soil depends on several factors. Two important ones are: (1) the type of material from which the soil was formed, and (2) the treatment the soil has received since being placed under cultivation. Not all of a particular element in a soil is available to a plant. Thus, the soil test must be able to predict whether a soil contains sufficient amounts of available nutrient elements for a specific crop.
The acid and base levels of a soil solution are important because microorganisms and plants are responsive to their chemical environment. Three possible chemical reaction conditions for the soil solution are acidity, neutrality, and alkalinity. The reaction of the soil solution can be defined by an index using the concentration of hydrogen ions in the soil solution. This index is called the pH. A pH of 7 is neutral, pHs less than 7 are acid, and pHs greater than 7 denote a basic (alkaline) condition. Soil pH can be an indicator of the kind of nutrient problems to expect in a soil. Obviously the pH is not a “cure-all” analysis, but may indicate a possible problem, which may then be investigated with additional analysis. In mineral soils, pH is a general indicator of soil nutrient availability, presence of free lime (calcium carbonate), presence of excess sodium, and excess hydrogen. Almost all soils are mineral soils; thus, soil pH is a good indicator for possible nutrient problems. For example, sulfur is available from pH 5.5 to 8.5; boron, copper, and zinc are most readily available from pH 5 to 7; and iron and manganese are abundant below pH 5, but moderately available from pH 5 to 7. Iron chlorosis frequently occurs at pH above 7.7.
Factors influencing pH
Initially, factors such as parent material, rainfall, and type of vegetation were dominant in determining the pH of soils. Under cultivation, however, organic acids from plant roots, repeated use of acid-forming fertilizers, plant removal, and replacement of calcium and magnesium by hydrogen eventually lowers the pH of topsoil. Most of the nitrogen and phosphorus fertilizers used today are acid forming. For example, about 1.5 pounds of lime is required to neutralize the effect of applying 1 pound of anhydrous ammonia to the soil. Some irrigation water in contains substantial quantities of calcium and magnesium bicarbonates (lime) which help neutralize the acidifying effects. Thus, soils (without free lime) under production become increasingly acid unless lime is artificially applied or is present in the irrigation water. This means farmers need to frequently check soil pH to determine whether they are maintaining a proper soil acidity level.
Large Area pH Adjustment Tables
The table below offers a field method of estimating the amount of lime needed in your specific soil condition. It uses pH, texture and organic matter content of the soil to serves as a general guide.
| Average amount of powdered limestone (CaCO3) in pounds per acre for soils of average organic content to bring pH to 7.0 | ||||
|---|---|---|---|---|
| PH Test Result Show Soil @ | Sandy Soil | Sandy Loam | Loam | Silt & Clay Loams |
| 4.0 | 2500 | 5000 | 6500 | 9000 |
| 4.5 | 2000 | 4000 | 5200 | 7200 |
| 5.0 | 1500 | 3000 | 4000 | 5500 |
| 5.5 | 1100 | 2000 | 2800 | 3800 |
| 6.0 | 700 | 1000 | 1500 | 2000 |
| 6.5 | 300 | 500 | 800 | 1000 |
| 7.0 | 0 | 0 | 0 | 0 |
| 7.5 | 0 | 0 | 0 | 0 |
| 8.0 | 0 | 0 | 0 | 0 |
| Average amount of powdered limestone (CaCO3) in pounds per acre for soils of average organic content to bring pH to 5.5 | ||||
|---|---|---|---|---|
| PH Test Result show Soil @ | Sandy Soil | Sandy Loam | Loam | Silt & Clay Loams |
| 4.0 | 1200 | 2000 | 2700 | 3700 |
| 4.5 | 700 | 1000 | 1500 | 2000 |
| 5.0 | 350 | 500 | 750 | 1000 |
| 5.5 | 0 | 0 | 0 | 0 |
| 6.0 | 0 | 0 | 0 | 0 |
| 6.5 | 0 | 0 | 0 | 0 |
| 7.0 7.5 8.0 | See next page for procedures to lower soil pH | |||
Acidifying soils or lowering their pH: This is done mainly to increase solubility of iron and manganese for plants that can not get adequate supplies from high pH soils. e.g. azaleas, rhododendron, pin oak trees, some red maple trees, etc. Common methods of lowering the pH include:
- Powdered sulfur (oxidizes slowly to sulfuric acid)
- Ferrous sulfate or aluminum sulfate
- Sulfuric acid (reacts rapidly and is expensive - must be handled with care)
- NH4 fertilizers: (NH4)2SO4,NH4NO3, NH3 (NH4)2SO4 produce acid as the NH4+ converts to NO3-and releases pH. Acidifying a soil with fertilizer is a slow, long term effect.
Small Area pH Adjustment Tables
| Average amount of powdered limestone (CaCO3) in pounds per square yard for soils of average organic content to bring pH to 7.0 | ||||
|---|---|---|---|---|
| PH Test Result Show Soil @ | Sandy Soil | Sandy Loam | Loam | Silt & Clay Loams |
| 4.0 | ½ lb per sq yd | 1 lb per sq yd | 1.5 lb per sq yd | 2 lb per sq yd |
| 5.0 | ¼ lb per sq yd | ½ lb per sq yd | 1 lb per sq yd | 1.5 lb per sq yd |
| 6.0 | 1/8 lb per sq yd | ¼ lb per sq yd | ½ lb per sq yd | 1 lb per sq yd |
| 7.0 | 0 | 0 | 0 | 0 |
| 7.5 | 0 | 0 | 0 | 0 |
| 8.0 | 0 | 0 | 0 | 0 |
| Average amount of powdered limestone (CaCO3) in pounds per square yard for soils of average organic content to bring pH to 5.5 | ||||
|---|---|---|---|---|
| PH Test Result Show Soil @ 4.0 | Sandy Soil ¼ lb per sq yd | Sandy Loam ½ lb per sq yd | Loam 1 lb per sq yd | Silt & Clay Loams 1.5 lb per sq yd |
| 5.0 | 1/8 lb per sq yd | ¼ lb per sq yd | ½ lb per sq yd | 1 lb per sq yd |
| 6.0 | 0 | 0 | 0 | 0 |
| * See below the Average “alum” needed to acidify different alkaline soils in pounds per square yard | ||||
| 7.0 | ½ lb per sq yd | 1 lb per sq yd | 1 lb per sq yd | 1.5 lb per sq yd |
| 7.5 | 1 lb per sq yd | 1 lb per sq yd | 1.5 lb per sq yd | 2 lb per sq yd |
| 8.0 | 1.5 lb per sq yd | 1.5 lb per sq yd | 2 lb per sq yd | 2.5 lb per sq yd |
In small gardens it may be more convenient to apply the alum in solution; for example, if ½ pound per square yard was required, this amount could be dissolved in one gallon of water and applied.
In the table above the term “alum” is used in a general sense and the most economical form in which to apply such an acidifying chemical is as commercial aluminum sulphate. This may be broadcast over the soil at the rate indicated in the table but is preferably applied during a rainy spell so that crystals will dissolve promptly. As indicated above it is highly recommended to apply this in liquid form.
Acidifying most calcareous soils is not feasible because of the large amount of calcium magnesium carbonates they contain.
| Table Below gives pH Preferences to Various Crops, Turf Grass, Plants, Shrubs, Etc. | ||||||
|---|---|---|---|---|---|---|
| Common Name | Plant pH Preference | Common Name | Plant pH Preference | |||
| Abelia | 6.0 – 8.0 | Banana | 6.8 – 7.0 |
| Acacia | 6.0 – 8.0 | Baneberry | 6.0 – 8.0 |
| Acanthus, Soft | 6.0 – 7.0 | Barberry | 6.0 – 8.0 |
| Adder’s Tongue, Common | 6.0 – 7.0 | Barley | 6.0 – 7.0 |
| Ageratum, White | 6.0 – 7.0 | Bayberry | 5.0 – 6.0 |
| Ailanthus | 6.0 – 8.0 | Beach Plum | 6.0 – 8.0 |
| Alder | 5.5 – 6.5 | Bean | 6.0 – 7.5 |
| Alfalfa | 6.0 – 7.0 | Bean, Lima | 5.5 – 6.5 |
| Almond | 6.0 – 8.0 | Beauty Berry | 6.0 – 7.0 |
| Alpine Azalea | 4.0 – 5.0 | Bedstraw, Northern | 5.0 – 6.0 |
| Alsike Clover | 6.0 – 7.0 | Beech | 6.0 – 7.0 |
| Alumroot, Hairy | 5.0 – 6.0 | Bee Balm, Oswego | 6.0 - 7.0 |
| Alyssum | 6.0 – 8.0 | Beet | 5.8 – 7.0 |
| Amaryllis | 5.0 – 6.0 | Beet, Sugar | 6.0 – 7.0 |
| American Hophornbeam | 6.0 – 7.0 | Begonia | 6.0 – 8.0 |
| American Plum | 6.0 – 8.0 | Bellflower | 6.0 – 8.0 |
| Ampelopsis | 6.0 – 8.0 | Bent Grass, Carpet | 5.5 – 6.5 |
| Anemone | 6.0 – 8.0 | Bent Grass, Rhode Island | 5.0 – 6.5 |
| Apple | 5.5 – 6.5 | Birch, Sweet | 5.0 – 6.0 |
| Aralia | 6.0 – 8.0 | Bishop’s Cap, Lace | 5.0 – 6.0 |
| Arborvitae | 6.0 – 8.0 | Bitter Nightshade | 6.0 – 8.0 |
| Arbutus, Trailing | 4.0 – 5.0 | Bittersweet | 5.5 – 6.5 |
| Arethusa | 4.0 – 5.0 | Blackberry | 6.0 – 8.0 |
| Arnica | 5.0 – 6.0 | Blackcap, Common | 6.0 – 7.0 |
| Arrow Bamboo | 6.0 – 8.0 | Baddernut | 6.0 – 8.0 |
| Ash | 6.0 – 8.0 | Blazing Star | 5.0 – 6.0 |
| Asparagus | 6.0 – 7.0 | Bleeding Heart, Fringed | 5.0 – 6.0 |
| Aster | 6.0 – 8.0 | Bloodroot | 5.5 – 6.5 |
| Aster, Bigleaf | 5.0 – 6.0 | Bluebead | 4.0 – 5.0 |
| Aster, Seaside | 5.0 – 6.0 | Bluebell, Feather | 5.0 – 6.0 |
| Aster, Skydrop | 5.0 – 6.0 | Bluebell, Virginia | 6.0 – 8.0 |
| Aster, Stiff | 5.0 – 6.0 | Blueberry | 5.0 – 6.0 |
| Aster, Wave | 6.0 – 7.0 | Bluegrass, Kentucky | 6.0 – 7.0 |
| Astilbe | 6.0 – 8.0 | Bluets | 6.0 – 7.0 |
| Atamasco Lily | 5.0 – 6.0 | Bluets, Creeping | 5.0 – 6.0 |
| Avacado | 6.0 – 8.0 | Bogbean, Common | 5.0 – 6.0 |
| Bittersweet | 5.5 – 6.5 | Bog Rosemary | 4.0 – 5.0 |
| Blackberry | 6.0 – 8.0 | Bowman’s Root | 6.0 – 7.0 |
| Blackcap, Common | 6.0 – 7.0 | Box, common | 6.0 – 8.0 |
| Bracken | 5.0 – 6.0 | Daylily | 6.0 – 8.0 |
| Brake | 6.0 – 8.0 | Deutzia | 6.0 – 8.0 |
| Bristly Sarsparilla | 6.0 – 7.0 | Devils-Walking Stick | 6.0 – 7.0 |
| Broccoli | 6.0 – 7.0 | Dewberry, Swamp | 5.0 – 6.0 |
| Broomgrass | 6.0 – 8.0 | Dogbane, Spreading | 6.0 – 7.0 |
| Clubmoss, Shining | 5.0 – 6.0 | Dogwood | 6.0 – 8.0 |
| Coffee | 5.0 – 6.0 | Dogwood, Flowering | 6.0 – 7.0 |
| Coleus, Common | 6.0 – 8.0 | Douglas Fir | 6.0 – 7.0 |
| Colorado Spruce | 6.0 – 7.0 | Dropwart | 6.0 – 7.0 |
| Coltsfoot, Common | 6.0 – 8.0 | Dutchman’s Pipe | 6.0 – 8.0 |
| Columbine | 6.0 – 8.0 | Easterbells | 5.0 – 6.0 |
| Columbine, Colorado | 6.0 – 7.0 | Eggplant, Common | 6.0 – 7.0 |
| Columbine, Golden | 6.0 – 7.0 | Elaeagnus | 6.0 – 8.0 |
| Columbine, Hybrid Colorado | 6.0 – 7.0 | Elder | 6.0 – 8.0 |
| Coneflower | 6.0 – 8.0 | Elm | 6.0 – 8.0 |
| Convolvulus | 6.0 – 8.0 | English Ivy | 6.0 – 8.0 |
| Coreopsis | 5.5 – 6.5 | English Oak | 6.0 – 8.0 |
| Coreopsis, Hairy | 5.0 – 6.0 | Eucalyptus | 6.0 – 8.0 |
| Coreopsis, Rose | 5.0 – 6.0 | Eulalia | 6.0 – 7.0 |
| Coreopsis, Threadleaf | 5.0 – 6.0 | Euonymus | 6.0 – 8.0 |
| Coreopsis, Trefoil | 5.0 – 6.0 | European Mountain Ash | 6.0 – 8.0 |
| Corn, Indian | 6.0 – 7.0 | European Turkey Oak | 6.0 – 8.0 |
| Cosmos, Common | 6.0 – 8.0 | Evening Primrose | 6.0 – 8.0 |
| Cotoeneaster | 6.0 – 8.0 | Everlasting Pearl | 5.0 – 6.0 |
| Cotton, Upland | 5.5 – 6.5 | Fairy Bells | 5.0 – 6.0 |
| Cowpea, Common | 5.5 – 6.5 | False Indigo | 6.0 – 8.0 |
| Cranberry, Mountain | 5.0 – 6.0 | False Spirea | 6.0 – 8.0 |
| Cranesbill | 6.0 – 8.0 | Fairy Wand | 5.0 – 6.0 |
| Crinkleroot | 5.0 – 6.0 | Feather Fleece | 4.0 – 5.0 |
| Crocus | 6.0 – 8.0 | Fern, Asparagus | 6.0 – 8.0 |
| Crowberry | 4.0 – 5.0 | Fern, Bladder | 6.0 – 8.0 |
| Cuckooflower | 6.0 – 7.0 | Fern, Braun’s Holly | 6.0 – 8.0 |
| Cucumber | 6.0 – 8.0 | Fern, Crested | 6.0 – 7.0 |
| Cucumber Root | 5.0 – 6.0 | Fern, Christmas | 6.0 – 8.0 |
| Currant | 6.0 – 8.0 | Fern, Evergreen Wood | 6.0 – 7.0 |
| Cyclamen | 6.0 – 8.0 | Fern, Goldie’s | 6.0 – 8.0 |
| Cypress | 5.0 – 6.0 | Fern, Hartford | 4.0 – 5.0 |
| Daffodil | 6.0 – 6.5 | Fern, Hay Scented | 5.0 – 6.0 |
| Dahlia | 6.0 – 8.0 | Fern, Maidenhair | 6.0 – 8.0 |
| Dahoon | 5.0 – 6.0 | Fern, Male | 6.0 – 8.0 |
| Dalibarda | 5.0 – 6.0 | Fern, Marsh | 6.0 – 7.0 |
| Dandelion | 6.0 – 8.0 | Fern, Massachusetts | 4.0 – 5.0 |
| Daphne, Winter | 5.0 – 6.0 | Fern, Narrow-Leafed Chain | 4.0 – 5.0 |
| Daphne, February | 7.0 – 8.0 | Fern, New York | 6.0 – 7.0 |
| Fern, Sword | 6.0 – 8.0 | Grapes | 6.0 – 8.0 |
| Fern, Upland Lady | 5.0 – 6.0 | Grapefern, Broadleaf | 5.0 – 6.0 |
| Fern, Walking | 6.0 – 8.0 | Grapefern, Cutleaf | 5.0 – 6.0 |
| Fescue, Sheep | 5.0 – 6.0 | Grapefern, Triangle | 5.0 – 6.0 |
| Fir | 5.0 – 6.0 | Grapefruit* | 5.0 - 7.0 |
| Firethorn | 6.0 – 8.0 | Grass, Orchard | 6.0 – 8.0 |
| Flax | 6.0 – 7.0 | Grass, Carpet | 6.0 – 7.0 |
| Fleece Flower | 6.0 – 8.0 | Grass, Centipede | 6.0 – 7.0 |
| Flowering Quince | 6.0 – 8.0 | Grass, Velvet | 6.0 – 8.0 |
| Flytrap, Venus | 4.0 – 5.0 | Greenbrier, Coral | 5.0 – 6.0 |
| Forget-Me-Not | 6.0 – 8.0 | Greenbrier, Laurel | 5.0 – 6.0 |
| Forsythia | 6.0 – 8.0 | Ground Cedar | 5.0 – 6.0 |
| Fothergilla, Dwarf | 5.0 – 6.0 | Ground Pine | 5.0 – 6.0 |
| Foxglove | 6.0 – 8.0 | Groundsel | 6.0 – 8.0 |
| Foxtail, Meadow | 6.0 – 8.0 | Groundsel Bush | 7.0 – 8.0 |
| Franklinia | 5.0 – 6.0 | Gypsophila | 6.0 – 8.0 |
| Fringe Orchid, Green | 5.0 – 6.0 | Hackberry | 6.0 – 8.0 |
| Fringe Orchid, Large Purple | 5.0 – 6.0 | Hardhack | 5.0 – 6.0 |
| Fringe Orchid, Lesser Orange | 4.0 – 5.0 | Hartstongue | 6.0 – 8.0 |
| Fringe Orchid, White | 4.0 – 5.0 | Haw, Possum | 7.0 – 8.0 |
| Fringe Orchid, Yellow | 5.0 – 6.0 | Hawthorn | 7.0 – 8.0 |
| Fringe Tree, White | 5.0 – 6.0 | Hazelnut, Beaked | 6.0 – 7.0 |
| Fumitory, Rock | 5.0 – 6.0 | Heath | 5.0 – 6.0 |
| Fumitory, Climbing | 6.0 – 7.0 | Heather | 5.0 – 6.0 |
| Gaillardia | 6.0 – 8.0 | Heath Huckleberry | 5.0 – 6.0 |
| Galax | 4.0 – 5.0 | Heliotrope | 6.0 – 8.0 |
| Gardenia | 5.5 – 6.5 | Hemlock, Carolina | 5.0 – 6.0 |
| Gayfeather, Grassleaf | 5.0 – 6.0 | Hemlock, Common | 5.0 – 6.0 |
| Gentian | 6.0 – 8.0 | Hepatica | 6.0 |