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Soybean Foliar Fertilizer Application (07/08/21)

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Producers are always interested in increasing soybean yield but of course there should be a return on investment. Agronomists often receive questions about foliar fertilization in soybean. Based on these requests, a large national research project was set up. Six foliar fertilizer products were applied and compared with an untreated control, in a randomized complete block design, with at least 4 replicates. This experiment was conducted at 20 sites throughout the US during the 2019 season, and 26 sites during the 2020 growing season (Figure 1), for a total of 46 site years. Data from North Dakota, South Dakota, and Minnesota were included in this experiment. The sites were fields without known nutrient deficiencies and represent average soybean growing conditions. Products were applied at soybean growth stage R3, aligning with commonly used fungicide and insecticide application timings. Nutrients applied per acre for each product are listed in Table 1.

 

         Table 1. Nutrients applied in pounds per acre.

         Table 1. Nutrients applied in pounds per acre.

 

There was a significant difference in yield among sites (Figure 1), but no significant difference in yield among treatments (Figure 2) and there was no treatment by site interaction.

Overall results show that prophylactic foliar fertilization decreased the profitability of soybean production (no increase in yield but a cost for application and the product). Foliar fertilizer products, similar to those tested, are not recommended for use by North Dakota soybean producers in the absence of symptoms of nutrient deficiency.

For information about soybean fertility recommendations see publication Soybean Soil Fertility SF1164 . For additional information about in-season application of foliar sprays of N, P, and K see link.

Figure 1. Map of sites in 2020 with their average yield (bu/acre). and Figure 2. Average soybean yield per acre for each treatment across 46 environments in the USA, during the 2019 and 2020 growing seasons.

 

Hans Kandel

Extension Agronomist Broadleaf Crops