Achieving a final soybean stand of at least 100,000 plants/A is important to maximize grain yield potential.
In-furrow starter fertilizer applications consistently reduced final soybean stand.
The potential risk of seedling injury and stand loss with in-furrow starter applications warrants the use of alternative methods of fertilizer placement in soybeans.
Compared to corn, applying in-furrow starter fertilizer on soybeans is a less studied and less common practice among growers. Farmers should take caution when applying fertilizer in close proximity to germinating soybean seeds because they are more sensitive to excessive concentrations of fertilizer salts than corn seeds are.
What is In-furrow Starter Fertilizer?
Applying in-furrow starter fertilizer is the practice of placing fertilizer directly on or near the seed in-furrow at planting. This practice has been shown to have both an agronomic and economical benefit.1,2
Soybean Response to Starter Fertilizer
Positive responses are more common in cooler climates with limited early season root growth. Soybeans in these climates can struggle to accumulate nutrients. Salt injury occurs when the concentration of ions in the soil is greater than the concentration of ions within the plant cells. The high osmotic pressure created by the in-furrow starter fertilizer salts causes water to move out of the plant cells and into the soil. As water moves out of the plant cells, the tissue desiccates and becomes blackened or “burned,” eventually leading to death of the plant tissue.
Nitrogen and Potassium Fertilizer vs. Phosphorus Fertilizer
Generally, nitrogen- and potassium-containing fertilizers have a higher salt index than phosphorus-containing sources. Due to the potential for salt injury when applying fertilizers near the seed, many fertilizers labeled as “seed-safe” will use potassium acetate as the potassium source, which has a roughly 60% lower salt index than potassium chloride.
Soil Conditions
Soil conditions play a large role in the risk of seedling injury due to in-furrow fertilizer applications. Moist soils help dilute fertilizer salts and diffuse away the band, reducing the osmotic pressure. Dry soils do little to diffuse the high concentration of salts near the seed.
Soils with low cation exchange capacity (CEC), such as coarse-textured soils with low organic matter, react less to the fertilizer compared to high CEC soils. As a result, the high concentration of fertilizer salts in the soil solution remains. Therefore, the potential for fertilizer burn is greater in sandy, low organic matter soils, particularly in dry springs.
Agronomy in Action Trials
The Golden Harvest® Agronomy in Action research team implemented 8 trials across the Midwest in 2020 (Figure 1). These trials evaluated the effects of:
The soil types at these sites were either loam, silt loam or silty clay loam with organic matter ranging from 1.9 to 4.0% and CEC from 16.9 to 22.2 meq/100g (Table 1). All locations received a minimum of 0.5’ of precipitation within 2 weeks following planting.
5 targeted seeding rates were planted with and without in-furrow starter fertilizer across 2 different relative maturity varieties at each location. The fertilizer source was a combination of NACHURS playmaKer® (2-6-16) applied at 2 gal/A and NACHURS CropMax® (2-0-2-0.1B-0.15Cu-0.3Fe-1.5Mn-0.0005Mo-4Zn) applied at 1 pt/A. Either GH2041X and GH2552X, GH2788X and GH3088X or GH3934X and GH4307X varieties were planted, depending on the geography.
In-Furrow Fertilizer Trial Results
There was not a significant interaction between targeted seeding rate or in-furrow starter application and location on final soybean stand or grain yield. On average, final soybean stands were 12-29% lower than the targeted seeding rate. Higher targeted seeding rates resulted in a greater percentage of undeveloped seeds (Table 2). When in-furrow starter fertilizer was applied, final soybean stands were an additional 3% lower on average across all targeted seeding rates. This suggests that there was salt injury from applying the in-furrow starter fertilizer.
Similar to previous studies conducted by the Golden Harvest Agronomy in Action research team, yield potential was maximized with a final soybean stand around 100,000-120,000 plants/A (Table 2). A final soybean stand below 100,000 plants/A significantly reduced grain yield.
Overall, there was no effect of in-furrow starter applications on grain yield (Table 2).
Effect of Variety on Grain Yield
Varieties had similar responses to in-furrow starter fertilizer applications and targeted seeding rates, suggesting the selected variety should not impact the targeted seeding rate or decision to apply in-furrow starter fertilizer. In general, varieties GH2552X, GH2788X and GH3934X had a greater final stand compared to GH2041X, GH3088X and GH4307X at their respective locations. However:
Grain yield responses to variety were inconsistent, with only 4 locations having a significant response.
Earlier maturity varieties yielded higher in 3 of the 4 responsive locations.
Targeted seeding rate or in-furrow starter by variety interaction was inconsistent across all 8 locations.
Use Caution when Applying In-Furrow Fertilizer
Soybean fertility is still critical to attaining high yield potential. Applying fertilizer in a band near a growing plant has benefits such as:
Reduction of nutrient tie-up
Utilization of more nutrients
Increased grain yield potential and beneficial effects on the environment
Reduced nutrient loss through leaching or runoff
However, to reduce risk of injury, caution must be used when applying fertilizer in-furrow to soybeans. This study demonstrates the inherent risk of salt injury and losing final soybean stand when applying starter fertilizer in-furrow. Fertility on soybeans is still critical to attaining high yield potential, and alternative applications methods can be used to reduce the potential risk of injury from fertilizer. These results align closely with previous work looking at the effect of in-furrow starter fertilizer on final plant stand and grain yield.3
Using starter fertilizer out of furrow in a band placed 2” to the side and 2” below the seed is a safe alternative to an in-furrow application while still achieving the benefits of nutrients applied in a band near a growing plant.
For more information on fertilizer’s influence on soybeans, contact your local Golden Harvest Seed Advisor.
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References:
- Kaiser, D. E., J.A. Coulter and J.A. Vetsch. 2016. Corn hybrid response to in‐furrow starter fertilizer as affected by planting date. Agronomy Journal. 108(6): 2493-2501.
- Kaiser, D. E., A.P. Mallarino, and M. Bermudez. 2005. Corn grain yield, early growth, and early nutrient uptake as affected by broadcast and in‐furrow starter fertilization. Agronomy Journal. 97(2): 620-626.
- Rehm, G. W. and J. Lamb. 2010. Soybean response to fluid fertilizers placed near the seed at planting. Soil Science Society of America Journal. 74(6): 2223-2229.