Thinking about using foliar fertilizers in soybeans?
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EmailMany foliar fertilizer products are marketed to soybean producers that claim to increase yield, but which ones actually do?
Soybean farmers do a lot of thinking. I won’t say where they do their best thinking, but they do a lot of thinking about many different topics, especially about how to produce a better soybean crop and how to increase their profitability. One of my goals as the Michigan State University Extension soybean educator is to answer farmers’ questions using research-based, practical information. That is one of the reasons why the partnership between Michigan State University (MSU) Extension and Michigan Soybean Committee is so valuable—taking advantage of the intersection between university research (at MSU and nationwide) and “boots-on-the-ground” crop production.
I will be writing on many topics over the coming months and years related to soybean production and what farmers are thinking about, and frequently I will be working alongside Michigan State University Extension content-specific experts to share research findings to answer key questions. This article will focus on the question of whether using foliar-applied fertilizer products in soybeans can increase yield and profitability.
Crops like soybeans obtain the bulk of their nutrients by extracting them from the soil as they take up water. That is why most fertilizers are applied to the soil, whether with the planter in-furrow or as a 2x2 starter, broadcast or banded in the spring prior to planting, or the previous fall. Since soybeans are good nutrient scavengers, fertilizer applications can also be made successfully ahead of the previous crop depending on the soil type and nutrient applied. Extension bulletins like MSU’s E2904, “Nutrient Recommendations for Field Crops in Michigan,” and the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa are excellent resources for knowing how much of a given nutrient is required to grow a crop.
However, to a lesser extent, plants can also take in some nutrients through their leaves when liquid fertilizers are applied. Nutrients can be taken in through stomata (microscopic openings in the leaf surface where oxygen and carbon dioxide are exchanged and water vapor is released) and through micropores in the waxy cuticle (outer protective layer). If the stomata are closed or the cuticle is thickened under water stress to avoid water loss, nutrient uptake will be reduced.
Typically, micronutrients (manganese, boron, zinc, iron, etc.) are better suited to foliar feeding as they are required in smaller amounts (e.g., several pounds to under a pound) compared with macronutrients such as potassium or phosphorus (e.g., tens to hundreds of pounds) depending on the nutrient. Foliar feeding can also be useful for “rescue treatments” when deficiency symptoms appear during the growing season.
Numerous foliar fertilizer products have been trialed in the Michigan Soybean On-Farm Research program since 2011. Of the 132 site-years included in the studies, foliar fertilizers significantly increased soybean yield only 9% of the time. However, the yield increase at the responsive sites did not always provide enough revenue to pay for the cost of the product and application.
A summary of these results is included in Table 1, but to see more details about each study, the full annual reports are available on the Michigan Soybean Committee website. If you don’t see a report you are interested in reading, contact Eric Anderson for assistance. These results suggest that foliar fertilizers are more likely to be profitable when a low-cost product is combined with an existing sprayer pass.
We are committed to including new or successful foliar products in the Michigan Soybean On-Farm Research program. If you have been using a product that has consistently increased soybean yields or know of a product you think we should trial, reach out to Eric Anderson and we will consider it for the program the following season.
Table 1. Results of soybean on-farm research trials conducted 2011-2024 with different foliar fertilizer products.
|
Product |
Year |
Stage applied |
Rate (per ac) |
# Locations |
Average yield increase with product (bu/ac) |
Average income difference with product ($/ac) |
|
Conklin package (2-14-16-2S+Mn+B) |
2011 |
V3-4 |
2.25 gal |
2 |
-1.2 |
|
|
Nachurs foliar boron (10% B) |
2011 |
R1 |
32 oz |
4 |
0.5 |
|
|
K-Man (0.46 N, 0.91 P2O5, 2.48 K2O, 0.367 Ca, 0.137 Mg, 0.046 Zn, 0.6 Mn, 0.065 Bo) |
2011 |
V2-3 fb 2-3 wks later |
3 gal |
2 |
2.3 |
|
|
Nitrogen (28-0-0 or 21-0-0-26) |
2011 |
R3 |
21 lbs N |
2 |
0.3 |
|
|
Ndemand High End (26-0-0) |
2011-12 |
R2-4 |
1 gal |
18 |
0.6 |
5 † |
|
Borosol 10 (10% B) |
2012 |
R1 |
32 oz |
1 |
-2.0 |
-43 |
|
Ndemand High End (30-0-0) |
2012 |
R3 |
1 gal |
2 |
0.8 |
0 |
|
Mn sulfate monohydrate |
2013 |
V1-V3 |
3.2 lbs |
3 |
0.1 |
-9 |
|
Solubor (20.5% B) |
2013 |
R1 |
1.2 lbs |
2 |
0.1 |
-8 |
|
Potassium thiosulfate |
2014 |
R1 |
1 gal |
4 |
1.0 |
-2 |
|
Various (prescription-based) |
2016-17, 2022-23 |
V4 or R1 or R2-3 |
varied |
27 |
0.3 |
-17 ‡ |
|
MAX-IN Sulfur (0-0-19-13S) |
2018-19 |
R1 (2018) or R3 (2019) |
1 qt (2018) or 2 qts (2019) |
9 |
0.0 |
-12 |
|
Ndemand 88 (10-8-8-2S + 0.25B, 0.06 Cu, 0.25Mn, 0.25Zn) |
2020-21 |
V4-R1 |
1 qt |
17 |
0.8 |
6 |
|
eNhance (7-0-0-8.7S + trace Zn, Mn) |
2022-23 |
|
|
18 |
-0.2 |
-8 |
|
Architech (10-5-5 + trace B, Cu, Mn, Mb, Zn) |
2023-24 |
V4-R1 |
1 qt |
14 |
-0.3 |
-15 |
† Income difference calculated from 2012 data only.
‡ Income difference calculated from 2022-23 only.
As mentioned previously, foliar fertilizers are most commonly used to remedy micronutrient deficiencies—manganese (Mn) deficiencies in particular are common on the higher pH soils of Michigan. Manganese deficiency symptoms manifest as interveinal chlorosis (yellow/white leaf tissue between veins that remain green) on new growth. Applications of Mn will not easily increase soil test levels due to Mn fixation, so if deficiency symptoms occur, foliar applications are the most effective means of getting the nutrient into the plants.
However, if Mn deficiency symptoms appear, it is likely they will reappear again if soil Mn concentrations are not remedied when Mn-sensitive crops are grown. Dry soil conditions can also induce Mn deficiencies, which may dissipate quickly once rainfall returns. Michigan State University Extension recommends applying 1–2 pounds of actual Mn when deficiency symptoms appear, scouting new growth seven to 10 days later, and making a second application if needed.
Numerous university research studies across the country have shown that foliar fertilizer applications in soybeans rarely produce a consistent yield increase. For example, in 2019–2020 a group of soybean specialists from 16 states tested six foliar fertilizer products and found that yield was not consistently improved, grain composition was not altered, and profitability was equal or lower when the products were applied compared with the non-treated control. When trying a new product, MSU Extension recommends leaving at least one non-treated check strip (three or four would be better) long enough to measure with a yield monitor or weigh wagon to see whether the product paid for itself.