Nutrient Management Recommendations for High-Yield Soybeans

Mike Staton, MSU Extension Soybean Educator

Soybean yields and net income can be reduced when essential nutrients are not available at the time, or in the quantities required by the crop. However, net income is also reduced when applied nutrients fail to produce yield increases large enough to offset their costs. The following research-based nutrient management recommendations will maximize soybean income.

Soil pH:

While soybeans can tolerate a wide range of soil pH levels (6.0 to 7.0), the ideal pH for soybean production is between 6.3 and 6.5 to maximize biological nitrogen fixation and nutrient availability. Soil pH levels above 6.5 have been shown to reduce manganese availability and increase soybean cyst nematode populations. Variable rate lime application based on grid sampling or management group sampling is highly recommended.

Starter Fertilizer (2x2 and In-furrow):

Starter fertilizers (2x2 and in-furrow) have produced mixed results in on-farm trials. In-furrow fertilizer increased soybean yields in two of 11 trials and decreased yields at one location. Starter fertilizer placed in a 2x2 band increased soybean yields in eight of 26 trials and decreased yields at two sites. Eleven of the 2x2 starter fertilizer trials were conducted in 2021 and 2022. Only two of these were profitable and the average net income for all eleven trials was in the red by more than $30.00 per acre. The potential for a positive yield response from starter fertilizer increases when phosphorus and potassium soil test levels are below the critical levels for these nutrients and/or cool or dry soil conditions occur after planting.

Foliar Fertilization:

Foliar fertilization has produced mixed results in hundreds of university trials conducted across the U.S. and is rarely profitable. Due to producer interest, 156 on-farm foliar fertilizer trials have been conducted in Michigan since 2009. Fifteen of the trials (10 percent) were profitable. Due to the low probability of a profitable response, foliar fertilization of soybeans is not recommended unless manganese deficiency symptoms are visible.

Nitrogen:

Biological nitrogen fixation conducted by wellnodulated soybeans combined with nitrogen mineralized from soil organic matter provides sufficient nitrogen for optimum soybean production in most cases. Therefore, nitrogen fertilizer applications to soybeans are rarely profitable and are not recommended. Research results from five on-farm trials support this. Three trials conducted in 2011 and 2012 showed that late-season nitrogen applications on irrigated, coarse-textured soils did not increase soybean yields. In 2016, three nitrogen rates (0, 40 and 100 pounds of N per acre) applied as anhydrous ammonia were compared at one site. The 100 pounds per acre rate yielded 2.5 bushels per acre less than the 0 pounds per acre rate and the yields from the 40 pounds per acre rate and the 0 pounds per acre rate were not significantly different. In another trial conducted in 2016, six gallons per acre of 28% UAN banded two inches beside the row at planting failed to increase soybean yields.

Phosphorus:

Soybean yield responses to applied phosphorus (P) using any application method have not been consistently demonstrated and are not expected when soil test P levels exceed 20 ppm reported as Mehlich III. However, maintenance levels of P fertilizer are required to keep P soil test levels between 20 and 40 ppm. Soybeans remove 0.8 pounds of P 2 0 5 per bushel per acre so a 60 bushel per acre soybean crop removes 48 pounds per acre of P 2 0 5 . The maintenance application can be applied biannually in corn-soybean rotations produced on mineral soils if the fertilizer is applied prior to planting corn, the pH is below 7.4 and the application rate accounts for the P removed by both crops.

Potassium:

Soybean producers can make important potash allocation decisions by comparing their K soil test levels to the values listed in Table 1. If your K soil test levels are at least 10 ppm above the critical level, eliminating potash applications should not adversely affect 2023 soybean yields or drop K soil test levels below the critical level.

However, if your soil test levels are less than 10 ppm above the critical levels, a maintenance level K application is warranted. The K levels reported in

Table 1 are Mehlich III values. If your soil test report lists K levels as ammonium acetate values, multiply by 1.14 to convert to Mehlich III.

Maintenance levels of K fertilizer should be applied when necessary to keep the K soil test level above the critical level. Soybeans remove 1.15 pounds of K 2 O per bushel per acre. Therefore, the maintenance application rate for a 60 bushel per acre soybean crop is 70 lbs. of K 2 O or 117 pounds of 0-0-60 per acre. The maintenance application can be applied biannually in corn-soybean rotations produced on mineral soils under the following conditions:

• The fertilizer is applied prior to planting corn

• The application rate accounts for the K removed by both crops

• The CEC is 5 meq/100g or higher When applying K fertilizer prior to planting soybeans, spring applications (two weeks prior to planting) are recommended over fall applications