The following is a reference guide to understanding the components of your AgSource Laboratories soil analysis. It provides a brief description of the essential nutrients along with the various ranges to allow you to effectively interpret your results.

SOIL pH

Wisconsin Application Guidelines for Field, Vegetable & Fruit Crops (15page PDF)

pH is a measure of the active hydrogen in soil. The presence or absence of hydrogen determines whether the soil is acidic or alkaline. The pH values of most soils range between 4.0 to 8.5, however, slightly acid conditions usually are the most productive (6.0 to 6.9).

Buffer index is determined to measure the total hydrogen (acidity) in the soil. As the index decreases the percentage of hydrogen increases, as Hydrogen increases the amount of limestone needed also increases. For this reason lime stone application guidelines are based off of the Buffer index measurement, not the soil pH.

Buffer Index is measured only when the soil pH is below 6.5.

This measures the amount of free limestone in the soil. This test is reported as: Very Low, Low, Medium, High, Very High. As the rating increases so the amount of free limestone. Changing the amount of excess carbonate in the soil is difficult and economically impossible to do. However, it can be important in herbicide selection as well as selection of fertilizer application techniques.

Soluble Salt is a measure of conductivity of soil solution or the salts which are soluble in water. Soils have a wide range of salt levels, but the relative critical level is 0.60 mmhos/cm. Values greater than this can cause damage on salt sensitive crops.

Generally high salt levels are associated with soils which have poor drainage conditions. The salts accumulate at the soil surface rather than leaching throughout the profile. If irrigation water contains a medium or high amount of salt the accumulation process increases.

Sodium provides information for use in reclaiming Saline-Alkali soils. Whenever the percent base saturation of sodium exceeds 5%, water infiltration rates can be reduced as well as impairing plant growth. Gypsum, Epsom salts and Elemental Sulfur are common amendments for aiding water infiltration rates.

CEC establishes the rate at which nutrients (cations) will be stored and released by a particular soil. The CEC value on the Harris report is an estimate, obtained by adding the values of the five major cations contained in agricultural soils (Potassium, Magnesium, Calcium, Sodium and Hydrogen). This CEC value can be used as an estimate of soil texture.

The above table holds true about 90% of the time, however, free calcium carbonate in the soil can over estimate the CEC value. If the excess carbonate values are high or very high, a particle size analysis would need to be analyzed to accurately determine soil texture.

The five major cations in soils are; Hydrogen (H), Potassium (K), Magnesium (Mg), Calcium (Ca), Sodium (Na). The actual percentage of each cation are reported on each of the Harris reporting options along the suggested percentage. By comparing the actual percent with the suggested percentage an idea of which kind of soil amendment (Lime, Gypsum, Sulfur) may or may not be needed. The suggested cation percentages listed on each report are:

Organic Matter is the result of the decay process of organic residues (plant and animal). Undecomposed organic residues (wheat straw, leaf litter or thatch) is not organic matter. In most agronomically productive soil the OM content ranges from 0.5 to 10.0%. The OM range for any specific soil is determined primarily by geographic and climatic conditions.

Organic matter acts as a storehouse for plant nutrients and improves physical structure of the soil. It has a very high capacity for holding cations as well soil water. Because of its active holding sites it is also an important factor for determining herbicide selection and adjusting application rates.

Nitrate-Nitrogen is the amount of available nitrogen present in the soil at the time it was analyzed in the laboratory. Because of it's solubility it can leach rapidly on various soil conditions. This mobility makes it difficult to predict how much nitrogen will be present through out the growing season. However, it can be a useful tool for determining nitrogen utilization efficiencies at the end of the growing season.

To convert ppm into pounds/acre use the following formula:

Sample depth (in inches) X .333 = conversion factor (CF)
CF X NO3 ppm = NO3 pounds/acre

Example:
Soil test = 7 ppm NO3
Sample collection depth = 0 to 8 inches

8 X .333 = 2.66
7 ppm X 2.66 = 19 pounds/acre Nitrate Nitrogen

Two types of phosphorus extractions are used for analysis, type is determine by the soil pH. If pH is < 7.2 a Bray I extraction is used, > than 7.2 an Olsen extraction is used. The interpretation of the two methods are different, the following table defines the two.

Potassium is a cation which is held on the soil's exchange sites. The form of potassium extracted is the readily available K. The following table provides a generalized interpretation for potassium. Soil textures have a great influence on it's availability. With sand textures high levels of K may be difficult to obtain because of it's ability to leach.

Below are the tables which gives a general interpretation for the above micro-nutrients.

Below are the interpretation tables for sulfur and boron. Both of these elements are soluble in water and subject to leaching.