Soil is where plants receive their nutrients and water. Soil that does not contain sufficient nutrients will not likely be a suitable home for all but the hardiest plants. Accurate soil testing often requires laboratory equipment. Fortunately, most gardeners and farmers have access to local soil testing services. However, in order for the soil test to be accurate, the soil must be collected correctly.
Soil testing involves checking soil to see if there are any nutrients that are readily available in the soil for plants, such as phosphorus, potassium, calcium, magnesium, sodium, sulfur, manganese, copper and zinc. Soil tests also test the soil’s pH level and humic matter, according to the North Carolina Department of Agriculture (NCDA). After collecting the soil, it can be taken to the local university cooperative extension office for testing.
Soil sampling should occur before any major landscaping is performed, such as planting a new garden, laying sod or adding flowers. Soil should be tested early because lime and fertilizer take time to seep into soil and distribute evenly. Testing soil late will not give the farmer or gardener enough time to add adequate lime or fertilizer. Soil sampling is most frequently performed before fall so that lime can be added soon enough for the soil to be ready in the spring, according to the NCDA. Soil sampling early ensures that the laboratory will have enough time to test the soil. While soil testing takes as little as one week, it can take a month to get your results, depending on the laboratory's workload.
Soil samples should be taken at a depth of 4 to 6 inches. However, if the gardener plans to fertilize deeper than 6 inches, the soil sample should be taken that deep, according to the NCDA. Several samples must be taken from different locations in the garden area and these samples must be mixed together in order to give the testers a wide range of the nutrient content of the soil. The samples should be put in a laboratory bag or box.
Soil tests are performed in order to determine if fertilizer needs to be added to soil. Adding too little fertilizer can cause the plant to grow deficiently and adding too much fertilizer wastes money, interferes with the plant’s absorption of nutrients and also causes environmental problems when the fertilizer runs off into water sources. Soil tests also help gardeners and farmers know how much lime should be added to the soil, according to the NCDA. The testing laboratory will provide recommendations on what to do with the soil, according to Organic Gardening.
Soil samples are collected with spades, garden trowels, shovels and soil probes. Tools that contain copper or zinc should not be used because they will contaminate the samples and lead to inaccurate tests. Samples should be mixed in a clean, plastic bucket before storing it in the laboratory bag or box, according to the NCDA.