Testing soils helps determine fertilizer needs

Soil surveys, produced by the USDA Natural Resources Conservation Service, are accurate to tens of acres or more depending on the intensity of land use. Besides knowing soil type and its range of characteristics to determine what actual nutrients or fertilizers are needed in a yard or garden for healthy plants means doing some site-specific soil testing.

Soil should be tested about once every three to five years prior to planting. This is an easy way to learn about what fertilizers are needed and how much can be added. The types of lab tests that are run on a standard soil sample often include organic matter, pH (acidity or alkalinity), nitrogen, phosphorus, potassium, sulfur, and micro nutrients like calcium, boron, magnesium, zinc, iron, manganese, and sodium.

Sample bags with instructions for collecting soils are provided by testing firms performing lab analyses on the samples and should be picked up ahead of time. Samples should be taken from the area to be planted.

Avoid lanes or paths, corners or edges, areas between beds, wet or areas previously used for confining animals (such as chickens, horses, cows or other livestock), compost, rock, or weed heaps, or manure piles. Take samples from the 0-12-inch zone from several areas in the yard or garden or deeper depending on the rooting depths of preferred plants.

Sample soils using clean shovels, trowels or augers and thoroughly mix materials in a clean bucket. Soil collected for testing should be devoid of undecomposed organic matter (manure, leaves, or grass, roots) and rock (of any size) that can contaminate a sample. Fill out the appropriate paperwork at the soil testing firm to determine costs.

Grant and Adams Counties soils often test low for nitrogen and sulfur, which are both soluble in water. This means these nutrients can leach away rather quickly with typical watering practices (or quicker with overwatering).

Some of the trace elements (micro nutrients) like boron, zinc, and copper are also important to plant health. Many of our soils are on the alkaline side of the pH scale. If pH gets much above 8 gardeners should consider adding sulfur to bring the pH closer to 7, which is considered neutral and the optimum level for growing just about anything.

More about soil testing next week. For answers to gardening questions, contact the Master Gardeners at the WSU Grant-Adams Extension office at 754-2011, ext. 4313 or email your gardening questions to ga.mgvolunteers@wsu.edu. Visit our web page at grant-adams.wsu.edu.