LSU AgCenter researchers Dr. Jim Wang and Dr. Brenda Tubana are working on a project to calibrate the results of more sophisticated soil testing methods and the accompanying fertilizer recommendations to the variety of soils in the state. Their work includes plant/soil analyses in the lab and field tests at the LSU AgCenter’s Central Research Station.

Fertilizer recommendations for Louisiana crops are being improved with the adoption of new soil testing methods by the LSU AgCenter’s soils lab, according to Dr. Jim Wang.

Wang, a soil chemist, said the new, multi-element method is an improvement over older practices of testing for each soil nutrient individually. The challenge, though, is to calibrate the results from the new tests with the state’s soils.

"Louisiana has so many different soils and so many different crops. It took a long time to move from the older tests to the new method," Wang said. "We have to redesign tests for major soils and major crops."

To make the transition, Wang began by using a statistical method to adapt a new database of information accumulated in prior years.

"We want to validate the design and new calibration to be able to make the best recommendations based on these new testing methods," he said.

To help with the project, Wang is working with Dr. Brenda Tubana, whose area of expertise is soil fertility.

Tubana has been gathering samples of different soil types and testing them to develop comparisons with results from older data used to develop initial fertilizer recommendations that are now decades old.

For instance, Wang said, tests for phosphorus have shown that on acid soils, 30 parts per million is the "critical level" for corn production. Phosphorus levels below that reduce the soil’s yield potential.

Acidic soils – those that have a low pH – can be improved with the application of agricultural lime. "Liming can promote potassium availability," Wang said.

Wang said growers can approach fertilizer use in two ways. The "sufficiency philosophy" says fertilizer should be applied only in the amount necessary to meet the plants’ requirements for the current season while the "maintenance/buildup" idea, which currently is being evaluated, provides soil fertility levels that can support various levels of production according to the variables that occur during any particular year.

"This approach, along with the soil test, will give producers a choice," Wang said.

For the current year, Wang and Tubana are using statistics to calibrate the old fertilizer recommendations with the new testing methods, and they’re improving a soil-nutrient index system that will give growers nutrient level ratings so they can assess the fertility of their soils.

"We want to include yield potential along with soil tests in determining crop fertilizer requirements," Tubana said.

In addition to field studies, Tubana has gathered large samples of major soil types in Louisiana and used them in greenhouse research. Each soil type has been put in pots planted with corn to evaluate plant response to fertility levels in the soils.

The researchers hope to move to fertilizer recommendations based more on new research than on statistical relationships with the old database.

In addition to Wang and Tubana, other scientists contributing to this research include Dr. Rick Mascagni, Dr. Don Boquet, Dr. Ernie Clawson, Dr. Dustin Harrell and Dr. J Stevens.–Rick Bogren

(This article was published in the 2008 edition of the Louisiana Soybean & Grain Research & Promotion Board Report.)