Fall Fertilizer Application Benefits To Incoming Soybean Crop
JOE BUNCK
EVEREST, KAN.
Farmers using a corn-soybean rotation have historically relied on residual fertility to fulfill the nutrient needs for the following season’s soybean crop. These days, farmers planning for a high soybean yield target realize it might pay to apply fall fertilizer.
Increased yield potential in corn has coincided with more soil nutrients being utilized and removed by that crop. Meanwhile, soybean yields have accelerated, making an investment in yield potential worthwhile. For high soybean yield targets (greater than 85 bu/acre for example), soil testing can help determine if residual field fertility is adequate to support soybean yield expectations.
Operating at low soil test levels of soil nutrients like phosphorus (P) and potassium (K) may reduce yield potential for the next growing season. If soil tests show nutrient availability to be above the critical levels, applications are not necessary for the next crop. If fertilizer is needed, a fall application has some practical benefits.
Fall is an optimum application time to apply P and lime. To neutralize soil acidity, lime must dissolve in the soil, and a fall application provides ample opportunity before the next growing season. Lime should be applied and incorporated a month or more before adding fertilizers because it can interfere with the availability of other nutrients, especially P. Fall is a good time to apply P and K because there is generally a lower risk for runoff.
In Kansas, farmers should evaluate next season’s soybean fields for nutrient deficiencies, particularly K, and weed escapes in the current corn crop. Monitoring for stalk lodging and grain loss during harvest can provide insight regarding next year’s risk for volunteer corn.
Few studies are available that demonstrate whether fall or spring is the best time to fertilize for soybeans. Testing this management technique on your own farm might be the best way to find an answer. Until then, if the weather is good and time allows, fall fertilizer applications are a viable option.
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JOE BUNCK: Channel Technical Agronomist