- Malheur Experiment Station
In order for onions to be properly nourished, fertilizer must be precisely applied to the soil. If fertilizer is applied in excess, or lacks needed nutrients, the onions will not flourish. One way to ensure accurate fertilization is to complete soil tests. Soil test results show nutrients residing in the soil that are plentiful, sufficient, or deficient. Armed with this information, growers are able to know what type and amount of fertilizers to apply to their land.
A soil sample is a combination of soil gathered from a variety of places within the testing area. The soil is extracted up to 12 inches deep by using a soil probe and combined with all other samples from the same area. By mixing soil from different parts of one field or lawn, the results will better show the makeup of all soil, not just a small portion. Soil testing laboratories usually provide bags for transportation to prevent contamination. Once the soil arrives at the lab, it is tested for nutrient, micronutrient, and lime levels.
Generally, soil tests are completed once a year, either in the fall before planting or in the spring. Soil tests completed in the spring measure levels of nitrogen amongst other nutrients (Feibert, 2013). Soil tests completed in the fall measure all nutrient levels but nitrogen; nitrogen is not included because it has not been applied yet (doing so before planting onions causes nitrogen leaching). Soil tests can also analyze the amount of lime present in the soil and determine if more should be added. For additional information, please see Soil Testing.
In addition to traditional soil testing, growers can utilize soil solution tests for growing season needs. Soil solution testing should be completed once a week for best results.
Each of these methods can increase productivity, size, and yield of onions, while helping growers engage in economically and environmentally sustainable practices. By knowing exactly what the soil does and does not need, farmers can apply fertilizer where and when the onions need it. Applying fertilizer properly not only saves money but conserves environmental health.
Soil test reports are made up of two charts: one concerning crop response to fertilization and the other detailing recommended micronutrient application rates. For aid in understanding results, please visit Understanding the Soil Test Report.