Farmers usually apply phosphorus (P) and potassium (K) fertilizer and lime in the fall when there is more time and equipment available and soil compaction is less of a concern. This simplifies spring operations and streamlining planting. On soils with optimum fertility levels, field research has shown that 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.
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. This practice is particularly important in areas close to rivers, drainage
The two most commonly available dry P fertilizers, diammonium phosphate (DAP) 18-46-0 and
Fall P rates should be based on a reliable soil test and realistic yield goal. Michigan State University Extension P and K fertilizer recommendations utilize a build-up,
P and K content of fall-applied manure should be taken into consideration to determine if and when more synthetic fertilizer is required. On average, 80 percent of P and 100 percent of K in manure will be available in the first year of application. On short-term rented land having low to average test levels, it may not always be economically justified to apply P and K fertilizer at the buildup rates. If fertilizer prices are high and resources are tight, a short-term strategy would be to apply only the crop removal rates. This temporary approach will provide adequate nutrients for near optimum production at a lower cost.
The soil test should indicate the soil pH and if lime is needed to rectify the acidity. Fall offers the best opportunity to apply lime as it provides more time to neutralize soil acidity. Long-term experiments in Michigan have shown that
Source: George Silva, Michigan State University
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