For the determination of organic matter it is desirable to grind a representative sub sample and sieve it through 0. If the samples are meant for the analysis of micronutrients at-most care is needed in handling the sample to avoid contamination of iron, zinc and copper.
Brass sieves should be avoided and it is better to use stainless steel or polythene materials for collection, processing and storage of samples. Air-drying of soils must be avoided if the samples are to be analyzed for NO3-N and NH4-N as well as for bacterial count. Field moisture content must be estimated in un-dried sample or to be preserved in a sealed polythene bag immediately after collection. Estimate the moisture content of sample before every analysis to express the results on dry weight basis.
Plastic tray or bucket Points to be considered Collect the soil sample during fallow period. Reduce the bulk to about half to one kilogram by quartering or compartmentalization. Quartering is done by dividing the thoroughly mixed sample into four equal parts. The two opposite quarters are discarded and the remaining two quarters are remixed and the process repeated until the desired sample size is obtained.
Compartmentalization is done by uniformly spreading the soil over a clean hard surface and dividing into smaller compartments by drawing lines along and across the length and breadth. From each compartment a pinch of soil is collected. This process is repeated till the desired quantity of sample is obtained. Collect the sample in a clean cloth or polythene bag. Label the bag with information like name of the farmer, location of the farm, survey number, previous crop grown, present crop, crop to be grown in the next season, date of collection, name of the sampler etc.
Collection of soil samples from a profile After the profile has been exposed, clean one face of the pit carefully with a spade and note the succession and depth of each horizon. If you have a little hill with ponding frequent at the bottom and a cattle grazing on the top of the hill you would have a minimum of three management areas.
You should take soil samples depending on the size spaced across the land to try to capture the variability from each management area. Combine these subsamples from one management area into one sample bag to account for the range of characteristics in that site. An ice pack in an overnight package will do the trick for sending most samples, but an icepack in a cooler may be necessary.
Samples should be sent in a sealed and labelled plastic bag. You will also want to write down a note in your own records about where the samples came from, the depth, and the date sampled. Samples should be taken every 2 to 4 years or once in a crop rotation. Fields should be in the same crop each time when sampled to help reduce variability of test results.
Whatever method you decide to use, each sample should be a composite of a minimum of 10 to 15 cores. Additionally, it is ideal that a sample should not represent more than approximately 10 acres, unless available information suggests larger field areas have little variation, such as in soil type or yield potential. Multiple sampling areas per field help to determine if a uniform application rate or a variable or site-specific application rate for fertilizer, manure, or lime is more suitable.
Cores should be taken from a combination of locations--in the row, between the row, mid-way between the row and not just in one small radius within the sampling area. This is especially important if fertilizer or manure was banded.
Knowledge of the field history is important in choosing soil sample areas and understanding soil test results. Soil has a long memory, and past management can greatly influence what we see today.
For instance, around old feedlots it is not uncommon to see high phosphorus and potassium levels. When manure was hauled it wasn't commonly hauled to the corners of the field, but the area closest to the feedlot. Technology has advanced to allow farmers to better understand field history via the internet. Google Earth and other internet mapping services allow users to look at satellite imagery back several decades, but the Iowa State University Iowa Geographic Map Server allows users to search for historical aerial imagery as far back as the s.
This can allow incredible insight into prior uses of current farm fields and may help explain differences found in some soil test results. Aerial imagery from s compared to imagery from Note how one field today was treated as more than 10 fields in the s. Having a general plan of attack prior to heading out to the field is helpful; this plan would include a map of areas to sample, an idea of how many samples to take, and a plan for how to collect the samples.
Within each sample area, pull 10 to 15 cores to make a composite sample. This is particularly important for growers who mix their own media. Media testing during the growing season is an important tool for managing crop nutrition and soluble salts levels. To use this tool effectively, you must know how to take a media sample to send for analysis or for in-house testing, and be able to interpret media test results.
Determining the pH and fertility level through a soil test is the first step in planning a sound nutrient management program. Soil samples from soilless mixes are tested differently than samples from field soil.
There are three commonly used methods of testing soilless media using water as an extracting solution: dilution method, saturated media extract SME , and leachate Pour Thru. The values that represent each method of testing are different from each other. For example, 2. Likewise, values for specific nutrients are likely to differ with testing methods.
Always use the interpretative data for the specific soil testing method used to avoid incorrect interpretation of the results. See Table 2, Soluble salts levels determined by different methods of soilless media analysis. Many horticulture supply companies carry pH and EC testing equipment, usually in the form of pens or meters. Most pens and meters are temperature-compensating; however, the instructions that come with the equipment will help growers determine if any adjustments are necessary related to environmental conditions.
A buffer standardizing solution pH 4 or 7 should be purchased with pH meters or pens. A standard solution should also be purchased with EC pens and meters to assure that equipment is calibrated and working properly.
Most fertilizers except urea are salts and when placed in solution they conduct electricity. Thus, the electrical conductivity EC or soluble salts of a substrate solution is indicative of the amount of fertilizer available to plant roots.
In addition to carrying out a complete soil test, growers should routinely check the EC and pH of their growing media and irrigation water. These checks can be done onsite using portable testing meters, or samples can be sent to the University of Massachusetts soil test laboratory. Depending on the crop, and fertilizer practices, growing media should be tested at least monthly.
Sending the leachate solution collected from the Pour Thru method for laboratory analysis at least once during the growing season is a good idea, so that actual nutrient levels in the container can be determined and corrected if needed. The accuracy of EC and pH meters can also be checked by sending a leachate sample to the laboratory at least once during the growing season.
SME is currently "the" method of testing soilless greenhouse media and it is almost universally done by commercial and university labs, including the UMass Soil and Plant Tissue Testing Lab. In this test a paste is made using soil and water and then the liquid portion the extract is separated from the solid portion for pH, soluble salt, and nutrient analysis. Special skills and laboratory equipment are required to perform this test.
SME is probably not suitable for a grower to use unless the greenhouse operation is large enough to support a lab, a technically trained person is hired to carry out the tests, and there is a commitment to frequent testing and tracking of the results.
This method has been used for many years and has good interpretative data to back it up. In this test an air-dried sample of soil and water are mixed together in the volume ratio of 1 part soil to 2 parts water e. The liquid extract is then separated from the solids using laboratory grade filter paper or a common coffee filter. The extract is then ready for analysis. This is a very easy test to master and quite suitable for on-site greenhouse testing of pH and soluble salt using meters available from greenhouse suppliers.
The method is a very good choice for occasional pH and soluble salts testing by growers on-site. In addition to collecting a soil sample to test, growers can collect leachate from container grown plants using the Pour Thru method. One of the major advantages to leachate pour thru is that there is no media sampling or preparation.
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