October 18, 2017
By George Silva
Soil testing is a best practice recommended by Michigan State University Extension to achieve the desired agronomic, economic and environmental outcomes from fertilizer practices. Timing-wise, there are several advantages to soil test in the fall compared to spring:
• More time. There is more time available in the fall to collect soil samples and make fertilizer decisions compared to spring. Based on the soil analysis, fall allows additional time to think about upcoming management decisions.
Farmers usually apply phosphorus (P) and potassium (K) fertilizer in the fall when there is more time and equipment available and soil compaction is less of a concern. This simplifies spring operations and streamlines planting. On soils with optimum fertility levels, field research has shown fall applications of P and K would be equally effective compared to a spring application prior to corn and soybean planting. For winter wheat, all the P and K requirements are best applied at fall planting.
Also, dry fertilizers can be safely and quickly applied in the fall. Some tillage will help ensure nutrients are placed below the soil surface. This will help reduce stratification and lower the concentration of dissolved P in the runoff water.
• More favorable weather. Weather conditions typically are more favorable for collecting soil samples as compared to spring. Michigan’s unpredictable spring weather can force postponement or even abandonment of soil testing for that year.
• Best time for lime. Fall offers the best opportunity to apply lime as it provides more time to neutralize soil acidity. The soil test results should indicate the soil pH and if lime is needed to rectify excess acidity. Long-term experiments in Michigan have shown that liming will improve nutrient availability and generate a good return for investment.
• Fertilizer cheaper in fall. Based on the soil test results, fertilizer can be purchased prior to the end of the year. Fertilizer is often cheaper in the fall compared to spring, when demand is high. Buying fertilizer before the end of this year could potentially have favorable tax implications.
• Labs less busy in fall. Soil testing laboratories are less busy. Generally, soil testing laboratories as busier in the spring compared to fall, as a majority of farmers, gardeners and homeowners wait until spring to soil test. Therefore, the turnaround time in spring is much longer. A longer wait for soil testing results may force delays in fertilizer timing.
There are several good quality labs available to Michigan farmers, Visit the MSU Soil and Plant Nutrient Laboratory for details on submission, interpretation, fee schedule and more. MSU Extension educators are available to assist people in learning more about utilizing the soil test data to their best advantage.
Silva is a Michigan State University Extension educator.
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