Yield response to management practice is location dependent.
Crop monitoring is key to manage for potential yield-limiting factors.
A foliar-applied fungicide at R3 was the management practice that provided the most consistent response across all locations.
Graph 1. Historical U.S average soybean grain yield
Source: USDA-NASS1The U.S. average soybean grain yield has continued to increase over the decades. In 1960, the average soybean grain yield was 24 bu/A and in 2020, it was 51 bu/A (Graph 1). Advancements in soybean genetics is the primary factor for the historical yield increases, however, improvements in crop management have also contributed to increasing soybean yields. Enhanced fertility, foliar protection, earlier planting, biologicals and precision agriculture are just some of the management practices farmers can consider when growing soybeans.
Justus von Liebig famously popularized the law of the minimum which states that plant growth and yield is dictated not by total resources available, but rather by the scarcest resource or limiting factor. For instance, to apply this concept to agriculture, applying more of 1 nutrient will not increase yield if another nutrient is deficient and impeding plant growth. The law of the minimum applies to not only soil nutrients, but also water availability, pest control, solar radiation and many other factors that contribute to crop growth and yield.
Increasing soybean yields requires a systematic approach to management. Getting the plant off to a strong start sets up high yield potential early in the growing season and sustaining plant health through crop maturity helps maintain that yield potential.
Agronomic Research Scientist Brad Bernhard explains the soybean management trial the agronomy research team is conducting with fertility and foliar fungicide treatments.Management Approach
Golden Harvest® Agronomy in Action research trials were implemented at 9 locations across the Midwest to evaluate the effect of different management practices on soybean grain yield. The trials were designed as an additive or “stair-step” approach, starting with the farmer’s normal fertility program planted at 140K seeds/A as the standard. Each management factor listed below is an addition to the previous factor. The list and order of the management practices included:
Farmer Standard
Farmer’s normal fertility program with no additional
inputs planted at 140K seeds/A
+ Fertility
Planter-applied 2x2x2 placement of 14 N, 44 P2O5, 57
K2O, and 3 S (lbs. of nutrient/A)
+ Fungicide
Foliar application of Miravis® Neo fungicide (13.7 oz/A) at R3
+ Insecticide
Foliar application of Endigo® ZC insecticide (3.8 oz/A) at R3
+ Biological
Foliar application of YieldOn (1.5 pt/A) at R3
+ Nitrogen
Broadcast Agrotain®–coated urea (90 lbs. of N/A) at R3
+ Foliar Micros
Foliar application of MAX–IN Ultra ZMB (2 qt./A) at R3
+ Population
180K seeds/A
2 varieties were grown at each location. Either GH2041X and GH2329X, GH2788X and GH3088X, or GH3475X and GH3546X Golden Harvest soybean varieties were planted depending on the geography. There was no interaction between management factor and variety at any location, so all results are averaged across locations.
Yield Response to Management Practices
The average soybean yield at all locations was 70+ bu/A except for Bridgewater, SD, which experienced drought conditions throughout most of the growing season. Not surprisingly, yield responses to each management practice varied across locations. The management factor providing the largest yield response at each location is highlighted in orange in Table 1. On average across all locations, management practices had a significant effect on grain yield (Table 1).
Table 1. Change in yield with the addition of each factor to the previous management system. Orange highlights the management practice that provided the largest positive yield response for each given location. Application of a foliar fungicide provided the most consistent yield response of all inputs, ranging from 2.0 to 5.9 bu/A, depending on the location. Averaged across locations, foliar fungicide applications at R3 significantly increased yield by 3.7 bu/A. Increases in yield from foliar fungicide applications appear to be due to an increased number of seeds produced (Table 2). None of the other management practices resulted in an increase in seed number as seen with fungicide applications. Although fungicide did not increase seed weight, it likely helped maintain it.
Figure 1. Bean leaf beetle feeding at Clinton, IL Response to other management practices was much less consistent but significantly improved yields when specific yield-limiting factors such as insect pressure or soil nutrient deficiencies were present at a given location. For instance, the sandy loam soil with 1.7% organic matter and a cation exchange capacity of 7.0 meq/100g at the Geneseo, IL, site likely made P2O5 and K2O applied through the planter more available to plants, resulting in a 5.1 bu/A increase in yield over the farmer’s standard fertility program. Small amounts of sulfur (S) applied likely also contributed to the fertilizer response, as Geneseo had lower soil S levels. Japanese beetle and late-season bean leaf beetle feeding likely resulted in the 2.5 bu/A R3 insecticide application response at Clinton, IL (Figure 1).
Figure 2. Leaf burning from broadcast urea at the R3 growth stage at Clinton, IL Smaller and less consistent responses from foliar-applied micronutrients and biologicals were observed although not correlated with any specific yield-limiting factor. Increasing soybean seeding rates did not show a yield response when averaged across locations, and it was 1 of 2 management practices that never returned the largest yield improvement for a specific location. Broadcasting Agrotain-coated urea at R3 resulted in leaf burning at most locations and likely reduced yields in some cases (Figure 2).
Manage for the Location
The results from this study demonstrate that management practices need to be adjusted depending on the location. Locations with low soil fertility levels or soils that do not have the ability to hold available nutrients should benefit from fertilizer applied near the seed or from foliar-applied micronutrient. Insecticide should be applied when insect thresholds are met to reduce crop damage. A fungicide application was the management practice that provided the most consistent yield response across all locations. Continued crop monitoring is the key to identifying potential yield-limiting factors and to making management decisions to mitigate yield loss.
References:
1 USDA - National Agricultural Statistical Service (USDA-NASS). 2021. Soybeans. Grain Yield. United States, 1960 to date. USDA-NASS, Washington, DC.
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