Many different analyses for soil samples are conducted at the KSU Soil Testing Lab. The most common analyses requested include tests for pH, phosphorus (P), potassium (K), nitrate (NO 3 ), and organic matter. However, other analyses are performed on a daily basis including: calcium (Ca), magnesium (Mg), sodium (Na), cation exchange capacity (CEC), iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), ammonium (NH 4 ), sulfate (SO 4 ), chloride (Cl), aluminum (Al), texture, soluble salts, and salt alkali.
Samples that come into the lab are dried in an oven overnight and ground with a pulverizing-type grinder the next morning. The bulk of analysis will be completed after grinding or the following day. Once the data is complete and has been reviewed, sample information sheets are printed and mailed to the producer.
Samples are kept on storage shelves for a time so samples may be available for additional analysis at the producer’s request.
The various tests available from the soil testing laboratory are described below. Read the description of each test and mark on the information sheet which tests you desire on your samples.
This test is recommended where crops grow normally, but you desire to know the amount of lime, if any, and the kind and amount of fertilizer needed for optimum plant growth. The test includes determinations for pH, lime requirement on those samples with a pH of 6.4 or less, available phosphorus and exchangeable potassium. On a majority of the soils in Kansas, this test will be adequate. The results of the general fertility test may be supplemented by one or more of the tests listed below.
This test is recommended on areas that are suspected of having appreciable residual inorganic nitrogen (nitrates). Continuous heavy applications of commercial nitrogen fertilizer and/or heavy rates of manure may result in residual available nitrogen, especially where yields have not been proportional to the nitrogen applied. Under summer fallow conditions, appreciable quantities also may accumulate. Because nitrates are water soluble, movement of the nitrates down in the profile will occur when moisture penetrates into the soil.
Thus, sampling for the available nitrogen test should include subsoil samples to depths deeper than the tillage layer. A surface soil sample (0 to 6 inches) plus a subsoil sample (6 to 24 inches) should be taken. The samples must be air dried as soon as possible to stop microbial activity. This means spreading the sample on a clean sheet of paper or plastic to dry before sending the sample to the laboratory. Caution: Be sure the sample is not contaminated by fertilizer dust, manure, salt, etc. Samples should be dried within 24 hours.
This test is recommended on areas with high yield potential for corn or soybeans, which by erosion, terracing, or leveling for irrigation have had the topsoil removed. Sandy soils, low in organic matter, under high yield conditions also should be checked for zinc. Wheat, alfalfa, grain sorghum, and pastures are not likely to respond to zinc so this test is not recommended for these crops.
This test is recommended on the calcareous soils of the western part of the state to determine the likelihood of iron chlorosis on grain sorghum, soybeans, and corn. The test also can be beneficial for selection of shrubs, etc. around homes.
KCl Extractable Aluminum
Extremely acid soils (pH of 5 or less) may contain appreciable KCl extractable aluminum, which is very toxic to plant roots. This test is recommended for use where extremely low pH's are found and lime is not immediately available for spreading. The test results also are helpful in diagnosing problems of poor plant growth.
The majority of the sulfur in the soil is in the organic fraction and is microbially mineralized to the sulfate form for plant utilization. For interpretation of the sulfate-sulfur test, soil organic matter and texture also need to be known. Therefore, the organic matter test needs to be requested and texture reported on the information sheet. Sulfur deficiency is most likely to be found on low organic matter, very sandy soils. Samples should be to a depth of 24 inches.
Available Profile Chlorides
Wheat has been shown to respond to chloride application. Because the chloride ion is quite soluble and, therefore, mobile, soil samples to a depth of 24 inches is recommended. Chloride research with crops other than wheat is in progress, but no interpretation of profile chloride results are available for any crops other than wheat.
Organic matter in the soil is the storehouse of most of the nitrogen, sulfur, and several of the micronutrients. Organic matter results can be very meaningful to agronomists in better understanding the soil conditions on your farm. Organic matter levels can be useful in determining rates of herbicides. This test is not recommended on all samples, but only in cases where the additional information is desired.
You Will Need:
- Auger or spade
- Clean pail
- Sampling tube
- Soil Sample Information Sheet (PDF)
- Soil sample containers
Step 1Draw a map of the area to be sampled on the information sheet and divide your fields into uniform areas. Each area should have the same soil texture, color, slope, and previous fertilization and cropping history.
Step 2From each area, take a sample consisting of 20 to 30 cores or slices, mix thoroughly in a clean container, and then fill your soil container from this mixture. All row crops should be sampled to 6 to 8 inch depth and all permanent sod to 4 inches. If the available nitrogen, chloride, or sulphur tests are desired, a subsoil sample to 24 inches is necessary.
On fields that have been reduced-tilled no-tilled for several years, a split sample from the top 6 or 8 inches (i.e. 0 to 3 inches and 3 to 6 inches) is encouraged to assess pH and nutrient stratification near the surface. Caution: For the zinc test collect soil samples in a plastic container to avoid contamination from galvanized buckets or material made of rubber.