BY NANCY COLE
MARIANNA - Escalating fertilizer prices and the growing popularity of precision agriculture have increased the demand for soil testing in Arkansas.
In 2007, the University of Arkansas Soil Testing and Research Laboratory in Marianna tested a record 115,000 samples, compared with just 56,000 in 1993.
So far this year, more than 51,000 samples have been tested, off somewhat from last year’s pace because heavy spring rains interfered with sample collection, said Doug Carroll, whomanages the laboratory.
Submissions to the laboratory tend to peak in March and April, with a smaller peak in October and November, Carroll said.
“This year we’re probably going to get a bigger peak in the fall,” as farmers try to catch up with their periodic sampling, he said.
A soil test is a chemical analysis that estimates a soil’s ability to supply plants with nutrients, said Morteza Mozaffari, a soil chemist who directs the Lee County facility. Based on that analysis and the crops a farmer plans to grow, the laboratory issues a fertilizer recommendation, Mozaffari said.
With too few nutrients, crops fail to reach their yield potential and farmers lose money on their investments in seed, fertilizer and other crop inputs. Beyond the sufficiency point, however, applying more fertilizers is a waste of money and time, and can have potentially negative environmental consequences.
“The example I like to give farmers is ‘ice cream is good, but none of us needs to eat five gallons of it,’” Mozaffari said.
The University of Arkansas began testing farm soils around the state in 1945 and opened the Marianna laboratory in 1954 to test samples from the eastern third of the state. In 1984, the laboratory began handling soil tests for the entire state, surpassing 3 million samples cumulatively by 2004, Mozaffari said.
Every sample is tested for a number of extractable nutrients - including phosphorus, potassium, calcium, magnesium, iron, zinc, manganese, boron and sulfur - and for pH, a measure of acidity or alkalinity that can affect the availability of some nutrients to plants.
Other soil tests, which can be conducted on request, measure: nitrate, a form of the macronutrient nitrogen; electroconductivity, a measure of salinity; organic matter, which affects the soil’s ability to retain moisture and nutrients; and soil texture, the proportion of clay, sand and silt particles.
Laboratory funding comes from a $1.20 per ton state levy paid by fertilizer buyers. The state Plant Board keeps 31 cents of the fee to support its fertilizer sampling and testing program. The remaining 89 cents go to the soil testing laboratory, which conducts most tests free of charge.
The demand for soil testing began to grow in about 1998,Carroll said, as more farmers began embracing the tools and techniques of precision agriculture.
Whereas farmers once took a single soil sample from a 100-acre field, many now take samples from every 2 1 /2-acre grid within a field, Carroll said. Using Global Positioning Systems, those farmers create fertility maps of their fields and use the information to operate variablerate fertilizer applicators.
The Marianna laboratory urges farmers to fertilize by soil type, not by the field, Mozaffari said.
“In a given field, you may have more than one soil type, particularly in the Mississippi River Delta,” he said.
Dow Brantley, who farms with his father, Laudies Brantley Jr., said soil variation is less of a problem on their farm near England in Lonoke County. Nonetheless, the Brantleys have relied on soil testing for about 15 years to maximize the value of the fertilizer they use, he said.
“For this year and the upcoming year, [soil testing] couldn’t be any more important, as expensive as things are,” Brantley said.
“Whereas in the past we would just put out a broad spectrum application across the farm, we’re going to be more site-specific just to control our costs,” he said.
Farmers are increasingly interested in alternative nutrient sources, such as poultrylitter and “biosolids” or treated wastewater sludge, as the prices of commercial fertilizers have doubled, if not tripled, Mozaffari said.
Strong demand and short supplies have pushed the price of urea, a popular source of nitrogen, to about $770 a ton, compared with $310 a ton in 2005, he said.
Potash and phosphate now cost about $1,000 a ton compared with $350-$400 a ton just a year ago, said Bob Stark, anagricultural economist at the University of Arkansas at Monticello.
“With the high fertilizer prices that we have, farmers want to know exactly how much fertilizer they need,” said Stark, who helps prepare annual soybean production budgets for the Cooperative Extension Service.
“Farmers already are looking ahead to 2009” because they are concerned about both the price and availability of fertilizers, he said.
