How can I better understand my soil report?
REPORT TERMS (as per order on our soil report)
Most soil test readings on our soil report are given a rating of:
- very low (VL).
- low (L).
- medium (M).
- high (H).
- very high (VH).
The purpose of these readings is to provide a guideline for determining optimum nutrient levels for crop growth. Upon request, results can be delivered in spreadsheet format, without guide levels. Optimum levels may vary slightly from those shown on the Soil Analysis Report, however, the best value is dependent on many factors such as crop, yield potential and soil types.
The soil pH measures active soil acidity or alkalinity. A pH of 6.9 or less is acid. Soils with a pH of 7.0 are neutral, values higher than 7.0 are alkaline. Under normal conditions the most desirable pH range for mineral soil is 6.0 to 7.0.
Electrical Conductivity (soluble salts) Millimhos/cm (mmhos/cm)
Electrical conductivity measurements are often used to measure the amount of soluble salts in the soil. Conductivity is generally expressed in mmhos/cm. The conductivity increases with increasing soluble salts. The soil is considered saline when the conductivity reading of the saturation reaches 2 mmhos/cm.
If the level of salinity is less than 1.0 mmhos/cm the effect on the crop is negligible. Readings greater than 1.0 mmhos/cm may affect salt-sensitive plants. A level greater than 2.0 mmhos/cm may require planting salt tolerant plants. An excessive concentration of various salts may develop naturally or be the result of poor irrigation water, excessive fertilization, or contamination from various chemicals or industrial wastes. One effect of high soil salt concentration is to produce water stress in a crop which may cause the plant to wilt or even die.
Results for the major and minor elements are reported in parts per million (ppm) on an elemental basis. An acre of mineral soil 6 to 7 inches deep weighs approximately 2 million pounds. Therefore, to convert parts per million readings to pounds per acre, multiply by 2.
Meq/100g (milliequivalents per 100 grams)Soil cations, such as calcium, magnesium, potassium and hydrogen can be expressed in terms of their relative ability to displace other cations. The unit of measure meq/100g serves this purpose. For example, one milliequivalent of potassium is able to displace exactly one milliequivalent of magnesium. The cation exchange capacity of a soil, as well as the total amounts of individual cations, may be expressed by using these units.
Organic Matter and ENR (Estimated Nitrogen Release)
Percent organic matter is a measurement of the amount of plant and animal residue in the soil. The color of the soil is usually closely related to its organic matter content, with darker soils being higher in organic matter. The organic matter serves as a reserve for many essential nutrients, especially nitrogen. Bacterial activity releases some of this reserve nitrogen, making it available to the plant. The ENR is an estimate of the amount of nitrogen that will be released over the season. In addition to organic matter level, ENR may be influenced by seasonal variations in weather conditions as well as physical soil conditions.
Two types of phosphorus tests may be reported. The P1 (weak Bray) test measures phosphorus which is readily available to the plants. The optimum level will vary with crop yield and soil conditions, but for most field crops, 20 to 30 ppm is adequate. Higher levels may be needed for especially high yields as well as for certain vegetable crops. The P2 (strong Bray) test measures readily available phosphorus plus a part of the active reserve phosphorus in soil. A level of 40 to 60 ppm is desirable for good yields of most crops.
The bicarbonate P(sodium bicarbonate) test measures the amount of readily available phosphorus in basic soils (pH >7.4) In basic soils the phosphorus exists mostly as alkaline earth phosphates (eg. calcium phosphate). The extraction by dilute sodium bicarbonate correlates with what the crops can extract from these soils. The weak and strong Bray extractions are acidic (low pH). These extracting solutions are neutralized by the presence of free lime in higher pH soils, thus giving lower phosphorus test levels.The relationship between P1 and P2 can help evaluate the phosphorus fixing ability of the soil. A wide ratio (greater than 1 to 3) may be the result of high soil pH, free calcium, high clay content or use of highly insoluble phosphate fertilizer. A narrow ratio (less than 1 to 2) means either the soil does not have a fixing ability for phosphorus or that a highly soluble source of phosphorus has been added recently.
This test measures available potassium. The optimum level will vary with crop, yield, soil type, soil physical condition, and other soil related factors. Generally, higher levels of potassium are needed in soils high in clay and organic matter; lower levels in soils which are sandy and low in organic matter. Optimum levels for light-colored, coarse textured soils may range from 100 to 150 ppm. Dark-colored, heavy textured soils may require potassium levels from 150 to 250 ppm.
Magnesium and Calcium
The levels of calcium and magnesium found in the soil are affected primarily by soil type, drainage, liming and cropping practices. These basic cations are closely related to soil pH. As the soil pH increases, the levels of calcium and/or magnesium usually increase. Calcium deficiencies are rare when the soil pH is adequate. Magnesium deficiencies are more common. Adequate magnesium levels normally range from 50 to 70 parts per million. The need for magnesium can be further determined from its base saturation, which should be above 10 percent.
Sodium is considered as it relates to the physical condition of the soil. Adverse physical and chemical conditions may develop in soil high in exchangeable sodium. These conditions may prevent the growth of plants. Reclamation of these soils involved the replacement of exchangeable sodium by calcium or magnesium and the removal of sodium by leaching.
Cation Exchange Capacity (CEC)
Ratios & Percentages (box at the bottom of each soil test report)
These percentages are also know as Percent base saturation, and refers to the proportion of the CEC occupied by a given cation (an ion with a positive charge such as calcium, magnesium or potassium) or combination of cations referred to as bases. The percentage saturation for each of the cations will usually be within the following ranges for optimum performance.
- Potassium: 2 to 5 %
- Magnesium: 10 -20%
- Calcium: 60 to 75%
NitrateThe soil test measures nitrate-nitrogen (NO3-N) which is water soluble and readily available for the plant. When considering nitrogen levels needed for optimum crop performance, this test will indicate the level of nitrate-nitrogen present. Depth tests determining NO3-N will give more detailed information for making nitrogen recommendations. It is important that other soil factors including organic matter content are taken into consideration when interpreting the nitrate-nitrogen soil test and predicting crop response. This test is not suited for high CEC soil, or high rainfall areas.
- Well-drained, low CEC soils
- Soils low in organic matter
- Low soil pH (below 6.0)
- Use of high-analysis, low-sulfur fertilizers
The 0.1 NHCl extraction is used to extract zinc. A test level of 3 to 6 ppm is normally adequate. If the DTPA extraction is requested, a level of 1.8 to 2.5 ppm should be adequate under normal conditions. Factors taken into consideration when interpreting the zinc test include available soil phosphorus, pH, crop and yield goal.
A test range of 20 to 30 ppm of extractable manganese is usually adequate when the 0.1 NHCl extraction is performed. A test range of 14 to 22 ppm is adequate when using the DTPA extraction. Soil pH is especially important in interpreting manganese test levels. In addition, soil organic matter, crop and yield goal must also be considered. Since manganese quickly reverts to insoluble (unavailable) forms shortly after application, row or band treatments and foliar applications are the recommended methods for applying manganese.
A level of 20 to 30 ppm of extractable iron is usually adequate for either the 0.1 N†HCl or the DTPA extraction. Soil pH is a very important factor in interpreting the iron soil test. In addition, crops vary a great deal in sensitivity to iron deficiency. Foliar applications provide the best results when correcting iron deficiencies.
A level of 1 to 1.8 ppm of copper should be sufficient for both extraction methods. The soil pH, organic matter level, high rates of nitrogen, and the crop to be grown are important factors that should be considered when interpreting copper tests.
Readily-available boron is extracted from the soil with hot water. Adequate levels range from 1 to 1.5 ppm. Factors to be taken into consideration when interpreting the boron test should include pH, organic matter and texture, as well as the crop to be grown.
For more information please contact us through:
Crop Nutrition Laboratory Services Ltd.
Off Limuru Road, Limuru, Kenya
Telephone +254 (0) 711094444, + 254 (0) 720 839 933