Articles, Blog

Marianna Soil Testing Lab Tour – U of A System Division of Agriculture


Hello! Thank you for coming on this virtual
tour of the Marianna Soil Test Laboratory. My name is Nathan Slaton and I’m the Director
of the Soil Test Program for the University of Arkansas System Division of Agriculture. Soil testing allows growers to evaluate soil
fertility and determine how much lime and fertilizer are needed to optimize plant production.
Each year, the Marianna Soil Testing Lab analyzes around 200,000 soil samples submitted by Arkansas
residents, including farmers, home gardeners, lawn enthusiasts, landscapers, and golf course
superintendents. Thanks to the Fertilizer Tonnage Fee Program, routine soil testing
is provided to Arkansas residents free of charge So please enjoy this virtual tour of the Marianna
Soil Test Laboratory. We hope that you will take advantage of our free soil testing services.
If you have any questions about having your soil tested, please contact your local County
Extension Agent. Soil testing services at the University of
Arkansas date back to at least 1945, when Dr. Robert Bartholomew accepted soil samples
from 10 farms from each county in Arkansas. With the assistance of his students, Dr. Bartholomew
performed chemical analyses on these samples, interpreted the results, and made lime and
fertilizer recommendations to farmers. Subsequent demand for these soil testing services quickly exceeded the capacity of Dr. Bartholomew’s lab. By 1953, up to 4,000 samples were received
for testing each month. That same year, a Fertilizer Tonnage Fee of twenty-five cents per ton was approved by the Arkansas State Legislature to support University soil testing services. With this funding, the Marianna Soil Testing Lab was constructed and began operating in 1954 originally only testing soil for the residents of 26 counties in eastern Arkansas but now handling all submitted soil samples. Over the years, soil testing procedures have
changed, but demand continues to grow. The University of Arkansas System Division of
Agriculture soil testing program is now one of the largest land grant soil testing programs
in the nation. In 1972, the 1 millionth overall sample was processed. The program tested its 2 millionth sample in 1992 its 3 millionth sample in 2005 and its 4 millionth overall sample in 2013. Today, fifty- to sixty- thousand samples are received each month during the peak soil testing season, and approximately 200,000 samples are tested annually. The development and adoption of grid soil
sampling and variable rate fertilizer application as tools of precision agriculture suggest
that demand for soil testing services will continue to increase. Looking to the future, the Marianna Soil Testing
Lab will continue to invest in technological enhancements, ensuring that the laboratory
and its services continue to be convenient and valuable resources for many years to come. Soil testing clients can currently submit
soil samples to any local County Extension office in Arkansas for direct shipment to
the Marianna Lab. Alternately, agricultural consultants may deliver large volumes of soil
samples directly to the Mariana Lab for processing. On any given day, the Marianna Lab may receive
as many as 10,000 samples—about 5 tons of soil! Workers unpack individual soil sample boxes from each shipment and tear off the tops, exposing the soil inside. Sample boxes are then arranged on trays in a specific order corresponding to the submitted paperwork. Keeping track of these samples throughout
the testing process is essential. In the stamping room, the trays of samples are double checked and cross-referenced again with the submitted paperwork. Stamps corresponding to each group
of samples are applied before proceeding to the next preparation phase. For every 11 soil samples received, the Marianna
Lab also tests a quality assurance sample. The quality assurance samples can be clearly
recognized during the preparation phase by one of three brightly colored boxes: yellow,
representing a standard check soil sample, red for a high standard solution, and blue
for a low standard solution, all with known chemical properties that can be used to check
instrument calibration. These quality assurance samples help ensure that the Lab’s analytical
results are consistent and accurate. The soil samples sent in for analysis may
arrive very dry, very wet, or anything in-between. To ensure that samples are sufficiently dry
and to destroy the viability of imported red fire ant eggs that may inadvertently be transported
with the soil samples, unpacked sample boxes are stacked on carts and placed in a large
oven set at 155 ºF for 48 to 72 hours. Once dry, the soil is processed through a
grinder to break the soil cores apart, homogenize the sample, and remove any stones, roots,
and debris that may be present. The homogenized soil is placed back in the original box before moving on to the analytical laboratory for testing. Routine soil analysis consists of two separate
tests: (1) The Mehlich-3 extraction, which estimates the availability of selected nutrients
like phosphorus, potassium, and zinc, to determine how much and what kind of fertilizers might
be needed, and (2) a Soil pH Analysis, which measures the soil’s acidity or alkalinity for the purposes of determining potential lime requirements. In the Lab’s prep area, lab technologists
measure precise scoops of the dried, ground soil samples for each of these tests. Two-gram
soil samples taken for the Mehlich-3 test are combined with 20 milliliters of the Mehlich-3
solution, which is a mixture of acetic acid and several other chemicals designed to extract
plant-essential nutrients from soil. This mixture is placed in a shaker for 5 minutes
to allow for a more complete extraction of available soil nutrients. Soil particulates
and solution are then separated by filtration. Filter papers catch the soil, allowing the
solution containing the extracted soil nutrients to be collected in test tubes for analysis. For the pH test, 40 milliliters of deionized
water is mixed with 20 grams of soil in a small cup. These sample cups are then lined up on trays and loaded into the pH instrument for analysis. It’s time for testing to begin. In the Instrument Room, test tubes of Mehlich-3
soil extracts are placed on a sampling tray. An auto-sampler withdraws a small amount of
solution from each sample and feeds the liquid into an inductively coupled argon plasma atomic
emission spectrophotometer, or ICAP for short. The liquid sample is sprayed into the ICAP
instrument’s plasma where the atoms of extracted nutrients become excited and emit photons
with unique, identifying wavelengths. The ICAP instrument’s sensors measure the wavelength
and intensity of these radiated photons and can then calculate the type and concentration
of nutrients in each soil sample. For the pH analysis, a pH meter moves along
rows of sample cups containing the soil-water mixture. The Marianna Lab’s pH meter has 12
pH electrodes so that 12 samples can be tested simultaneously. Spinning propellers blend
the soil and deionized water mixtures while the pH electrodes measure the soil pH. Once the Mehlich-3 and pH tests are complete,
test results are cross-referenced with the original paperwork and entered into a University
of Arkansas System Division of Agriculture soil analysis program. Depending on the test
results and what plants will be grown, this program generates lime and fertilizer recommendations
based on decades of soil fertility research. For samples submitted through the County Extension
Offices, a Soil Test Report is generated for each sample and transmitted back to clients.
Test results from large-scale grid-samples submitted by agricultural consultants are
compiled into a single data file for clients to use in third-party software programs. In addition to the free routine analysis,
the Marianna Lab also provides fee-based services for interested clients. For more information
or if you have any questions about soil testing, please contact your local County Extension
Agent or visit our website.

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