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Environmental Horticulture (Gardening)

Test Your Soil

The amount of fertilizer, lime, and other amendments recommended for soil improvement should allow optimum growth without undue risk of polluting the natural run-off. It is important not to apply more than is recommended, and if time of year or season of application is a part of the recommendation, these guidelines should also be closely followed. This will assure greatest plant response with the least chance of plant damage or drainage water pollution. Fertilizer, lime, and other amendments washed off by heavy rains contribute to stream pollution.

The purpose of a soil test is to supply you with enough information to make a wise fertilizer and soil amendment choice. A soil test will provide information on pH, available phosphorus, potassium, calcium, and magnesium and soluble salts. The results of the soil test are mailed to you with recommendations as to what kind of fertilizer or amendment should be applied for economical growth of the desired crop or specific plant. A soil test need not be performed more often than every three to four years. Submit your sample in the fall, prior to planting or tilling, so that needed lime or other soil amendments can be changing the pH over the winter. Fertilizers should be incorporated the next spring.

Soil test kits are available for checking soil at home are usually available from state government departments of agriculture and from horticulture or agriculture departments of universities. For best results, carefully follow the instructions given for the soil test. Private companies also do soil testing; these give detailed reports and recommendations in many cases, but may be expensive ($30 is not unusual).

The accuracy of the test is a reflection of the soil sample taken. Be sure your sample is representative of the area to be treated. Sample the soil from 10 random areas to the depth at which you till the garden. Avoid sampling unusual areas such as those near gravel roads, manure or compost spots, brush piles, or under eaves. Place the samples in a clean pail or container and mix the soil thoroughly, then transfer one cup of mixed soil to a container. The results will be mailed to you with recommendations for correcting any deficiencies or other problems that may exist.

Soils range greatly in their properties and in their suitability for different uses. Many of the differences in the soils relate to the geologic parent materials and the local topography.

The main soil types are sand, clay, silt, and loam. Sandy soil feels very coarse and grainy. Water drains through it very quickly. As a result, sandy soil dries out rapidly.

Clay soil is very thick, like putty. It holds water like a sponge. Clay soil does not dry out as fast as sandy soils, but when it does dry out, it becomes hard and very solid, making it quite difficult to break the soil surface with a shovel.

Silty soil is between sandy and clay soil. It holds water well but does not dry into a hard, solid mass.

Loam is the ideal mixture of sand, clay, and silt. Through the addition of organic amendments, loam can become the perfect soil for your vegetable garden.