SOIL ANALYSIS TERMS

SoilpHThesoilpH measures active soil acidity or alkalinity. A pH of 7.0 is neutral. Values lower than7.0 are acid; values higher are alkaline. Usually the most desirable pH range for mineral soils is 6.0 to 7.0 and for organic soils 5.0 to 5.5. ThesoilpH is the value that should be maintained in the pH range most desirable for the crop to be grown.Buffer pHThis is an index value used for determining the amount of lime to apply on acid soils to bring the pH to the desired pH for the crop to be grown. The lower the buffer pHreadingthe higher the lime requirement.PhosphorusThe phosphorustestmeasures that phosphorus that should be available to the plant. The optimumlevel will vary with crop, yield andsoilconditions, but for most field crops a medium to optimum rating is adequate. For soils with pH above 7.3 the sodium bicarbonatetestwill determine the available P.PotassiumThistestmeasures available potassium. The optimum level will vary with crop, yield,soiltype,soilphysical condition, and othersoilrelated factors. Generally higher levels of potassium are needed on soils high in clay and organic matter versus soils, which are sandy and low in organic matter. Optimum levels for light-colored, coarse-textured soilsmay range from 90 to 125 ppm (180to 250 lbs/ac). On dark-colored heavy-textured soilslevels ranging from 125 to 200 ppm (250 to 400 lbs/ac) may be required.CalciumPrimarilysoiltype, drainage, liming and croppingpractices affect the levels of calciumfound in thesoil. Calcium is closely related tosoilpH. Calcium deficiencies are rarewhensoilpH is adequate. The level for calcium will vary withsoiltype, but optimumranges are normally in the 65% to 75% cation saturation range.MagnesiumThe same factors, which affect calcium levels in thesoil, also influence magnesiumlevels except magnesium deficiencies are more common. Adequate magnesium levelsrange from 30 to 70 ppm (60 to 140 lbs/ac). The cation saturation for magnesium shouldbe 10 to 15%.SulphurThesoiltestmeasures sulfate-sulfur. This is a readily available form preferred by mostplants.Soiltestlevels should be maintained in the optimum range. It's important thatothersoilfactors, including organic matter content,soiltexture and drainage be takeninto consideration when interpreting sulfursoiltestand predicting crop response.BoronThe readily soluble boron is extracted from thesoil. Boron will most likely be deficient insandy soils, low in organic matter with adequate rainfall.SoilpH, organic matter leveland texture should be considered in interpreting the borontest, as well as the crop to begrown.CopperCopper is most likely to be deficient on low organic matter sandy soils, or organic soils. The crop to be grown,soiltexture, and organic matter should be considered when interpreting copper tests. A rating of medium to optimum should be maintained.IronSoilpH is a very important factor in interpreting iron tests. In addition, crops vary a great deal in sensitivity to iron deficiency. Normally a medium level would be adequate for most soils. If iron is needed it would be best applied foliar.ManganeseSoilpH is especially important in interpreting manganesetestlevels. In addition,soilorganic matter, crop and yield levels must be considered. Manganese will work best ifapplied foliar or banded in thesoil.ZincOther factors, which should be considered in interpreting the zinctest, include available phosphorus, pH, and crop and yield level. For crops that have a good response to zinc, thesoiltestlevel should be optimum.SodiumSodium is not an essential plant nutrient but is usually considered in light of its effect on the physical condition of thesoil. Soils high in exchangeable sodium may cause adverse physical and chemical conditions to develop in thesoil. These conditions may prevent the growthof plants. Reclamation of these soils involves the replacement of the exchangeable sodium by calcium and the removal by leaching.Soluble SaltsExcessive concentration of various salts may develop in soils. This may be a natural occurrenceor it may result from irrigation, excessive fertilization or contamination from various chemicals or industrial wastes. One effect of highsoilsalt concentration is to produce water stress in a crop to where plants may wilt or even die. The effect of salinity is negligible if thereadingis less than 1.0 mmhos/cm. Readings greater than 1.0 mmhos/cm may affect salt sensitive plants and readings greater than 2.0 mmhos/cm may requirethe planting of salt tolerant plants.Organic Matter and ENR (Estimated Nitrogen Release)Percent organic matter is a measurement of the amount of plant and animal residue in thesoil. The color of thesoilis usually closely related to itsorganic matter content, with darker soils being higher in organic matter. The organic matter serves as a reserve for many essential nutrients, especially nitrogen. During the growing season, a part of this reserve nitrogen is made available to the plant through bacterial activity. The ENR is an estimate of the amount of nitrogen (lbs/acre) that will be released over the season. In addition to organic matter level, this figure may be influenced by seasonal variation in weather conditions as well assoilphysical conditions.N03-N (Nitrate Nitrogen)Nitrate nitrogen is a measure of the nitrogen available to the plant in nitrate form. In high rainfall areas, sandysoiltypes and areas with warm winters, this measurement may be of limitedvalue except at planting or side dress time. In the areas with lower rainfall, the nitratetestmay be very beneficial.Cation Exchange Capacity (CEC)Cation exchange capacity measures thesoil'sability to hold nutrients such as calcium, magnesium, and potassium, as well as other positively charged ions such as sodium and hydrogen. The CEC of asoilis dependent upon the amounts and types of clay minerals and organic matter present. The common expression for CEC is in terms of milliequivalents per 100 grams (meq/100g) ofsoil. The CEC ofsoilcan range from less than 5 to 35 meq/100g for agricultural type soils. Soils with high CEC will generally have higher levels of clay and organic matter. For example, one would expectsoilwith a silty clay loam texture to have a considerably higher CEC than a sandy loamsoil. Although high CEC soils can hold more nutrients, it doesn't necessarily mean that theyare more productive. Much depends on goodsoilmanagement.Cation SaturationCation saturation refers to the proportion of the CEC occupied by a given cation (an ionwith a positive charge such as calcium, magnesium or potassium). The percentagesaturation for each ofthe cations will usually be within the following ranges:Calcium:40 to 80 percentMagnesium:10 to 40 percentPotassium:1 to 5 percent