PROJECT SUMMARY:
Potassium Fertility for Soybean Production in Virginia
Potassium deficiencies are common problems in Virginia soybean production. Traditional
potassium deficiencies persist in many areas of the state and include regions with sandy textured soils.
However, higher yields dictate great nutrient uptake and potassium deficiencies are becoming more
prevalent. The overall objective of this research project is to assist producers with management decisions
regarding potassium deficiencies and yield responses as they relate to full season and doublecrop
soybeans in no-tillage systems. Objectives include determination of appropriate potassium application
rates for common production systems throughout the Commonwealth and to disseminate research
information to farmers to integrate into their production systems. No-tillage soybeans will be planted
across Virginia with and without irrigation, full season and doublecrop, and in systems with and without
the straw removed from wheat/barley. The overall project design at each location is a factorial
arrangement of 5 potassium rates (0, 50, 100, 150 and 200 lbs/acre).
Budget: $45,394 for labor, travel, materials and supplies for field and laboratory analysis.
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VIRGINIA SOYBEAN BOARD
PROJECT PROPOSAL – 2013/2014
TITLE:
Potassium Fertility for Soybean Production in Virginia
DATE:
July 1, 2013 – June 30, 2014
ESTIMATED DURATION: Three years for sound scientific research and demonstration. Subject to
renewal on a yearly basis.
OBJECTIVE: The overall objective of this research project is to assist producers with management
decisions regarding potassium deficiencies and yield responses as they relate to high yielding soybeans.
More specifically, objectives include:
1. Determine if current potassium fertilizer rates are sufficient for our high yielding production
systems. We will investigate soybeans in the following no-tillage systems:
a. Full season
b. Double crop
i. With straw left on field and with straw removed
ii. With all potassium applied at wheat planting and with potassium split applied
between wheat planting and soybean planting.
c. Irrigation
2. Disseminate research information to farmers to integrate into their production systems.
JUSTIFICATION: Potassium fertility recommendations are dated and may need to be increased to
match current high-yielding crop production systems. Currently, many farmers are consistently harvesting
50 to 60 bu/acre of soybeans; which removes approximately 70 to 85 lbs K2O/acre in their soybean seed
(Table 1) (International Plant Nutrition Institute, 2013). Using current Virginia Cooperative Extension
(VCE) recommendations, a soil testing “High” would dictate 30 lbs K2O/acre for nutrient replacement for
full season soybeans (Figs. 1, 2, and 3). Any nutrient removal higher than this level would then be
“mining” the soil for the remainder of the nutrient. A similar question and problem persists for producers
utilizing a wheat-soybean double crop rotation. The VCE recommendation for potassium was made prior
to farmers consistently yielding 80+ bushels of wheat per acre. Establishing an accurate mass balance for
these wheat-soybean rotations, farmers harvesting straw, and those farmers consistently yielding high
with irrigated land is a necessity. Years of “mining” a soil for nutrients will eventually cause soil test to
drop, yield losses and large fertilizer bills within a single year if soil nutrient concentrations are not
maintained over time.
BACKGROUND: Generally, Virginia Tech and Virginia Cooperative Extension soil testing guidelines
are well established and tested due to many years of research (Maguire and Heckendorn, 2011). When
considering soil testing categories, soils testing “low” and “medium” will see significant yield reductions
if no fertilizer is applied. Soils testing “high” will not generally experience a yield reduction, but nutrients
will be mined from the soil. Fertilizer recommendations are currently in place with “high” testing soils to
replace crop removal to spread out costs and to supply fertility needs for future crops since soil testing is
not commonly done each year. Soils testing “very high” will not usually have positive crop reactions to
fertilizer and can be mined without yield reductions. However, many of these research experiments were
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conducted in fields producing significantly lower yields, with different varieties (non-glyphosate resistant
vs. glyphosate resistance for example), and using different management practices (conventional tillage vs.
no-tillage, etc.). New soil testing guidelines need to be conducted using modern production practices in
Virginia to verify soil testing guidelines.
PROCEDURES: No-tillage soybeans will be planted in at least ten locations across Virginia on various
soil fertility levels (low, medium, high, and very high). Potassium will be tested by applying 5 potassium
rates (0, 50, 100, 150 and 200 lbs/acre) using Muriate of Potash (0-0-60) using granular fertilizer atplanting. Sites will include full season soybeans and soybeans in a double crop rotation with barley or
wheat with straw remaining and removed. All other production practices will be made according to
Virginia Cooperative Extension recommendations for no-tillage soybeans and based on Mehlich-1 soil
tests (Holshouser, 2001). Soybean leaf tissue will be collected to test for sufficiency ranges prior to
fertilizer application. Seed will be sampled at harvest. Leaf tissue and seed will be digested using nitric
acid and hydrogen peroxide and analyzed using inductively coupled atomic plasma spectroscopy (ICAP)
to evaluate % potassium. Plant biomass will be collected, weighed, and analyzed for % potassium; which
will allow investigation into total potassium uptake. Grain test weight and moisture will be reported for
each treatment. Yield will be collected using a plot combine and corrected to 13% moisture. The overall
project design at each location is a randomized complete block design. All data analysis will be conducted
in SAS at alpha = 0.05.
PERSONNEL AND FACILITIES:
Project Leaders: Mark S. Reiter
Assistant Professor, Soils and Nutrient Management
Eastern Shore Agricultural Research and Extension Center
Department of Crop and Soils Environmental Sciences
Virginia Polytechnic Institute and State University
33446 Research Drive
Painter, Virginia 23420
757-414-0724 ext. 16 (phone)
757-414-0730 (fax)
mreiter@vt.edu
David Holshouser
Associate Professor, Soybean
Tidewater Agricultural Research and Extension Center
Department of Crop and Soils Environmental Sciences
Virginia Polytechnic Institute and State University
6321 Holland Road
Suffolk, Virginia 23437
757-657-6450 (phone)
757-657-9333 (fax)
dholshouser@vt.edu
Facilities:
Crop & Soil Environmental Sciences Laboratory, Eastern Shore AREC and Tidewater
AREC. Both facilities contain equipment for drying and grinding of plant tissue,
instrumentation necessary for plant tissue digest (Eastern Shore), ICAP for potassium
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concentration determination (Eastern Shore), and extraction equipment necessary for
soil. Also, both facilities have a plot combine and necessary equipment for planting,
precision application of treatments, and agronomic production of soybeans.
OTHER COOPERATING ENTITIES: Farmers in various counties around Virginia for the use of their
commercial soybean production fields.
SOURCE OF OTHER FUNDS: No other sources of funding have been identified for this research.
BUDGET:
Graduate Student Salary
Graduate Student Fringes
Graduate Tuition
Hourly Wages
Hourly Fringes
Travel
Materials and Supplies
Total
$20,779
$1,766
$11,384
$6,000
$465
$2,000
$3,000
$45,394
The Virginia Soybean Board is paying for 100% of this research project.
WORKS CITED:
Holshouser, D.L. 2001. Virginia soybean production guide. Information Ser. 443. 111 p. Tidewater Agric.
Res. Extension Cntr., Virginia Cooperative Extension, Suffolk, VA.
International Plant Nutrition Institute. 2013. Estimates of Nutrient Uptake and Removal [Online].
Available at: http://www.ipni.net/article/IPNI-3296. Verified 1 Feb. 2013. International Plant
Nutrition Institute, Norcross, GA.
Maguire, R.O. and S.E. Heckendorn. 20011. Soil test recommendations for Virginia. Virginia
Cooperative Extension, Blacksburg, VA.
SUBMITTED BY:
Signature:
Printed Name: Mark S. Reiter
Title: Assistant Professor of Soils and Nutrient Management
Federal or State Government Program or Private Sector Company’s Name: VT Eastern Shore AREC
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Figure 1. Soil testing category determination for potassium.
Figure 2. Soil testing guidelines for full season soybeans.
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Figure 3. Soil testing guidelines for a wheat-soybean double crop system.
Table 1. Example potassium uptake and removal from common crop systems grown in Virginia.
Crop System
Low Yielding System
High Yielding System
(40 bu. Soybeans; 60 bu. Wheat)
(70 bu. Soybeans; 100 bu. Wheat)
Uptake
Removed
Uptake
Removed
----------------------pounds of potassium per acre---------------------Soybeans
144
56
252
90
Wheat-Soybeans
282
77
482
112
Wheat+Straw-Soybeans
282
194
482
320
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