Soil Testing After A Dry Growing Season

University of Illinois assistant professor Fabián Fernández said that many farmers are asking questions about adding nutrients to the soil in preparation for next year’s crop. The fact that grain yields and nutrient removal levels are lower than normal due to the drought and that some fields have been baled or harvested for silage complicates the interpretation of soil test results for phosphorus (P), potassium (K), and pH.

In Illinois, P and K removal rates, which are calculated by multiplying seed yield by seed nutrient concentration, are used to estimate appropriate fertilization rates. Historically, farmers based their calculations on the average yield for the field. Now many producers use yield monitors to estimate removal rates for different parts of a field and then use variable-rate applications.

Some farmers collect seed samples for analysis to calculate nutrient concentrations and removal rates for different parts of the field. Others use the standard removal rates published in the Illinois Agronomy Handbook. Fernández noted that the removal rates in the Handbook are at the upper end of the range of removal rates of current hybrids and varieties.

Whether a seed sample is taken to represent the inherent or drought-induced variability of the field or a removal rate value from the table is used, obtaining a good yield estimate is very important.

“While drought, soil fertility status, and yield level could affect the nutrient concentration of grain, our research has shown that yield is the most important factor impacting P and K removal rates,” Fernández explained. “Even though seed P and K concentrations varied widely, we have observed a positive linear relationship between yield level and P and K removal for both corn and soybean.”

Soil testing for P, K, and pH is used to determine the need for fertilization or limestone applications. Farmers are asking if the drought will affect how they should interpret this fall’s soil test results.

“This is a two-fold issue,” Fernández explained. “One is procedural: obtaining an appropriate sampling depth. The other relates to natural processes: leaching of nutrients out of plant materials and equilibration of nutrients in the soil.”

At the procedural level, it is difficult to control the sampling depth when the soil is dry. Moreover, if the soil surface is dry and crumbly, the top portion of the core may be lost during sampling. Conservation tillage systems such as no-till, and even chisel-plow, do not mix the soil, so nutrients tend to become stratified with higher concentrations in the soil surface. Tests using a sample less than 7 inches deep will overestimate fertility while those using a sample deeper than 7 inches or one that lost a portion of the top will underestimate fertility.

One of the main issues related to natural processes is that P and K cycling from the crop to the soil is an important mechanism of soil nutrient replenishment.

Corn and soybean return approximately one-fourth to one-third of the total P taken up, and about two-thirds of the total K taken up, to the soil. K cycling has the greatest impact on fall soil sampling because this nutrient remains in an inorganic form in plant tissues and readily leaches out of the plant with precipitation once the crop reaches maturity.

“We should not be as concerned about P because P is in organic form in plant tissues and those materials need to be decomposed before P is released back to the soil,” Fernández advised.

Fernández warns that this year it is not safe to assume that lower removal rates and lower yields will result in greater P and K levels in the soil because drought limits the equilibration of nutrients in the soil. During the season, plants have extracted P and K from the more easily available nutrient pools. Because of the lack of moisture, the soil has, to a large extent, not been able to replenish those pools from less available nutrient pools.

Leave a Reply

Fertilizer Stories
FertilizerFall Fertility 2014: Forecasting Fertilizer Use
September 7, 2014
Great crops this year have tapped the soil, and fall work is definitely called for, but how challenging will that get? Read More
Aerial view of the West Fertilizer explosion site
FertilizerFertilizer Companies Blame City For West, TX, Explosion
August 6, 2014
El Dorado Chemical Co. and CF Industries contend the city failed to properly train the first responders and had insufficient protocols in place to battle the April 17, 2013, blaze at West Fertilizer Co. that triggered the explosion. Read More
FertilizerThe Fertilizer Institute: New President, Renewed Energy
February 3, 2014
Chris Jahn relishes the opportunity to lead the organization through the challenging times ahead. Read More
FertilizerA New Cycle For Fertilizer Demand
January 2, 2014
Changes in the corn market could have a major impact on the crop nutrients sector in 2014, say experts. Read More
Top 100 Articles
Growmark Group
CropLife 100GROWMARK In 2015: Back, To The Future
March 2, 2015
The nation’s third largest ag retail organization is simultaneously moving forward while remembering its past. Read More
CropLife 100Pinnacle Expands Sanders Brand In The South
February 27, 2015
Pinnacle has acquired Hopkins Seed and Chemical in Qulin, MO, which expands the company's Sanders brand to nine Southern states. Read More
CropLife 100Pinnacle Launches New Providence Agriculture Location In Indiana
February 27, 2015
Pinnacle Agriculture Holdings — ranked No. 6 on the CropLife 100 — has established a new retail location in New Castle, IN, which will operate as part of Pinnacle's Providence Agriculture brand. Read More
CropLife 100Cooperative CHS Returns $518 Million To Owners
February 23, 2015
The 2015 cash return to owners is based on CHS net income of $1.1 billion, the company's second highest on record. Read More
corn field
CropLife 100The Andersons’ Humic DG Now Available In Canada
February 13, 2015
The Andersons, Inc. Turf & Specialty Group has announced its Humic DG product is now available to customers in the Canadian turf, agriculture and horticulture markets. Read More
Farmer on tablet
CropLife 100Southern States Co-op: An Inside Look At Our Aerial Imagery Program
February 8, 2015
Now is as good a time as any to explore the basics of what a retail aerial imagery program looks like today. Read More
Latest News
Prairieland FS employees
Eric SfiligojWorkforce Worries
March 2, 2015
Finding good employees almost always ranks as the No. 1 or No. 2 problem for ag retailers in our annual CropLife 100 survey. Read More
Growmark Group
CropLife 100GROWMARK In 2015: Back, To The Future
March 2, 2015
The nation’s third largest ag retail organization is simultaneously moving forward while remembering its past. Read More
CropLife 100Pinnacle Expands Sanders Brand In The South
February 27, 2015
Pinnacle has acquired Hopkins Seed and Chemical in Qulin, MO, which expands the company's Sanders brand to nine Southern states. Read More
CropLife 100Pinnacle Launches New Providence Agriculture Location I…
February 27, 2015
Pinnacle Agriculture Holdings — ranked No. 6 on the CropLife 100 — has established a new retail location in New Castle, IN, which will operate as part of Pinnacle's Providence Agriculture brand. Read More
Management2,4-D Celebrates 70 Years; GROWMARK Uses Super Bowl Ad …
February 27, 2015
Jim Gray, executive director of the 2,4-D Research Task Force, lays out planned activities to mark the chemistry’s 70th anniversary. Read More
HerbicidesUniversity Of Arkansas Flag The Technology Program Adds…
February 27, 2015
Started in 2010, the Flag the Technology program provides a visual reference for applicators to distinguish between fields planted with different herbicide-tolerant trait technologies. Read More
Luckey Farmers, Inc.’s Berkey Farm Center
Industry NewsLuckey Farmers’ Berkey Branch Certified In 4R Nut…
February 26, 2015
The 4R Nutrient Stewardship Certification Program has announced Luckey Farmers Inc.’s Berkey Farm Center in northwest Ohio has been added to its growing list of nutrient service providers to achieve certified status. Read More
Crop InputsWinField Unveiling NutriVision Technology, Ascend Dry F…
February 24, 2015
New for 2015 are NutriVision Technology, a unique tool for monitoring in-season plant nutrient availability, and Ascend WSG plant growth regulator, a new dry formulation of Ascend plant growth regulator. Read More
FertilizerNew Formulation Of NutriSphere-N Protects High Volume U…
February 24, 2015
Verdesian Life Sciences is launching NutriSphere-N HVTM, a new polymer formulation of the proven NutriSphere-N Nitrogen Fertilizer Manager that protects high-volume applications of UAN. Read More
EquipmentIowa Ag Secretary Northey Names Hagie Water Quality Lea…
February 24, 2015
Iowa Secretary of Agriculture Bill Northey has named Hagie Mfg. as a recipient of the Secretary’s Water Quality Initiative (WQI) Leader Award. Read More
FungicidesEvito Fungicide Gives Canadian Wheat Growers New Diseas…
February 24, 2015
EVITO fungicide from Arysta LifeScience North America gives Canadian wheat and barley growers a new option for disease control. Read More
Eric SfiligojThe Commodity Classic Turns 20
February 23, 2015
Two decades in, this annual gathering of all things agriculture has become a must-see event. Read More
CropLife 100Cooperative CHS Returns $518 Million To Owners
February 23, 2015
The 2015 cash return to owners is based on CHS net income of $1.1 billion, the company's second highest on record. Read More
ManagementCropLife Retail Week: On The Road Edition
February 20, 2015
Editors Paul Schrimpf and Eric Sfiligoj discuss their recent trips to the National Farm Machinery Show in Louisville and the Read More
Crop InputsLand O’Lakes Acquires FLM+ Assets
February 19, 2015
FLM+ will become a wholly owned subsidiary of Land O'Lakes, Inc., and the company will retain its employee base after closing of the deal, which is scheduled for the second quarter of the year. Read More
Seed/BiotechUnited Suppliers, Stine Seed Form Marketing Alliance
February 19, 2015
The new alliance will greatly expand sales opportunities for Stine Seed with the United Supplier Seed Link Owners. Read More
Crop InputsVilsack To Deliver Commodity Classic Keynote Address
February 19, 2015
The secretary will deliver a keynote address to several thousand farmers and ag allies during the event's General Session, to be held Friday, February 27, in Phoenix, AZ. Read More
Crop InputsSoybean Storage Tips
February 19, 2015
On-farm storage of soybeans requires some special considerations compared to corn. Read More