Six Secrets for Increasing Soybean Yields


Updated Six Secrets results shown at the 2016 webinar sponsored by the Illinois Soybean Association. (7.4 MB .pdf)


Based on the Six Secrets of Soybean Success results, we are now focusing on how specific management procedures interact to power yield and potentially identifying 'racehorse/offensive' and 'workhorse/defensive' varieties.


In 2016, we focused on the interactions of variety, fertility (N, P, S, and Zn), and foliar protection at three locations in Illinois (Yorkville, Champaign, and Harrisburg). Sorry, we don't have a fancy webpage with graphs and tables yet for 2016, but in the interest of time, you may download the .pdf of results here.


Summary from 2012- the beginning of the Six Secrets study

Management practices for soybean production have not kept up with genetic improvements for soybean yield, pest resistance, and stress tolerance. We believe that understanding the indivdual effects of six categorical yield factors may help us implement improved management practices for increased soybean yield. These factors are weather, fertility, variety, foliar crop protection (fungicides and insecticides), seed treatments, and row spacing; the so-called ‘Six Secrets of Soybean Success’.


With the support of the Illinois Soybean Association, Mosaic, Syngenta, BASF, and Monsanto we evaluated the Six Secrets concept at four locations across Illinois in 2012. A ‘standard’ management practice (a variety of typical maturity for the region with either untreated seed or a basic seed treatment) was compared to a ‘high tech’ management practice in which a full-season variety for the region was grown with additional N, P, S, and Zn fertility (MicroEssentials SZ), foliar protection from insects and fungal pathogens, and an advanced seed treatment package consisting of a fungicide, insecticide, and nematicide. All treatments were compared in 20-inch and 30-inch rows. Significant yield responses to the high tech package were detected in six of eight trials.


Averaged across six trials which included different variety comparisons and crop protection products, the ‘high tech’ package increased yield by 9.9 bushels/acre (P ≤ 0.05). Narrow row spacing increased yield at three of the four locations; Champaign, DeKalb, and Rushville with respective yield increases of 3.0, 6.5, and 1.6 bushels/acre. At the management responsive sites, banded fertility (N, P, S, and Zn) and full foliar protection (fungicide + insecticide) had the greatest individual effects on yield with respective contributions of 4.3 and 3.6 bushels/acre when averaged across the traditional and high tech systems. Switching from a variety of ‘normal’ maturity to a fuller season variety had a 3.2 bushel/acre effect on yield, and use of a seed treatment including a fungicide, insecticide, and nematicide contributed 2.6 bushels/acre. The results from 2012 highlight the importance of choosing a high yielding, locally-adapted soybean variety and managing it with fertilizer placement and a full suite of crop protection products.

Research approach

Five management factors (fertility, variety, foliar insecticide/fungicide, seed treatment, and row spacing) for high yield soybean production were evaluated in an effort to identify those with the greatest potential to increase soybean yields in an additive or synergistic manner. Although we cannot control the weather, multi-location trials conducted across multiple years will provide us the opportunity to understand soybean yield variability associated with environmental conditions, and allow us to determine how management inputs interact with weather. The management factors were evaluated in an omission plot design (Table 1).


This omission plot design contrasts a ‘standard’ farmer practice in which a soybean variety of appropriate maturity for the area is grown with no additional inputs to a ‘high tech’ management approach. The high tech approach includes improved N, P, S, and Zn fertility, a fuller season or ‘offensive’ soybean variety, protection from insect pests and fungal pathogens with foliar insecticides and fungicides, and an advanced seed treatment. One at a time, each factor is added at its high tech level to the standard management system, and at the same time, each factor is removed from the high tech system and replaced with its standard counterpart.

Table 1. Depiction of the soybean omission plot design. The omission plot design consists of 14 treatments. Two treatments, #1 (High Tech) and #8 (Standard), represent the high and low input management systems, respectively. Factors are removed from the high tech system (treatments 2 to 7), while factors are added to the standard system (treatments 9 to 14) to quantify the contribution of each factor to yield under both levels of management intensity. All treatments are evaluated in 20-inch and 30-inch row spacing. Varieties of appropriate maturity group are used at each location, while all other treatments are consistent across locations.
Soybean omission plot design

Response to narrow row spacing

The soybean omission plot management trials were planted in 20-inch and 30-inch rows and significant row spacing effects were detected at each location. Narrow rows increased yields at Champaign, DeKalb, and Rushville, while 30-inch rows were superior to 20-inch rows at Harrisburg (Table 2). The advantage of narrow rows increased from south to north suggesting that practices which promote early season canopy closure (Figure 1) may be of greater value in locations with a shorter growing season.


In general, there was no row spacing x treatment interaction, and the yields presented for the addition-omission treatments (fertility, variety, foliar crop protection, and seed treatment) are averaged across both levels of row spacing.

Table 2. Response to narrow row spacing (20-inch rows) relative to 30-inch row spacing. Values are averaged across the standard and high tech management systems. Two trials were located at Champaign and Rushville, while one trial was located at DeKalb and Harrisburg. Responses significant at P ≤ 0.05.
Soybean row spacing response
Narrow soybean rows promote canopy closure
Figure 1. Contrast between 30-inch rows (left) and 20-inch rows (right) at Champaign, IL in 2012. The same omission plot treatment (high tech management) is shown in both photos. Pictures taken approximately 65 days after planting.

Value of individual management inputs

Management responses of individual trials ranged from +7.5 to +12.0 bu/acre. The average increase from the full high tech package relative to the standard system was +9.9 bu/acre (P ≤ 0.05). Although the average increase from the full package was approximately 10 bu/acre, strictly evaluating this comparison does not indicate if each individual omission plot factor (fertility, variety, fungicide, insecticide, and seed treatment) contributed 2 bu/acre, or if some factors were of greater value.


The increases from adding individual management factors to the standard system as well as the yield decreases resulting from omitting individual factors from the high tech system are shown in Table 3. It is clear from this data that only implementing one management practice is insufficient to achieve the full 9.9 bu/acre increase from the combination of inputs that go into the high tech package.

Table 3. Increases in soybean yields resulting from adding one factor at at time to the standard system, and the decreases in soybean yield resulting from omitting a factor from the high tech management system. Yields are averaged across six trials and two levels of row spacing. All addition or omission treatments were significantly different from their respective control treatments (None or All) at P ≤ 0.05
Soybean management responses in 2012

Table 4. Summarized yield responses from individual practices that increased yield in 2012. Responses are averaged across standard and high tech management systems from the six responsive trials in 2012.
Summarized soybean management responses in 2012