MISSISSIPPI STATE -- Sometimes good research just backs up what farmers already suspected.

Nine years of research at Mississippi State University's Delta Research and Extension Center in Stoneville revealed that using the tillage practice known as subsoiling in combination with irrigation does not improve cotton yields enough to cover the expense of these practices.

Everything done to a crop increases the cost of production and reduces the profits seen at sale. Producers weigh the expense of each management practice against the return they think they will get at harvest. Several years ago, Mississippi Agricultural and Forestry Experiment Station researchers put subsoiling and irrigation in the spotlight of science and economics, hoping to offer producers the information they need to make the best decisions.

Subsoiling came into widespread use in Mississippi in the 1970s. This form of tillage involves pulling a specially designed foot through the soil about 14 to 16 inches deep. Only the shank disturbs the top of the soil, but as it moves underground, the foot lifts and fractures the compacted soil above it, known as hardpan.

"This allows for better water and root penetration," said H.C. Pringle, MAFES associate agricultural engineer.

Pringle worked with MSU Extension Service agricultural economist Steve Martin to study the costs of using subsoil tillage in combination with irrigation in cotton production.

"This research started several years ago when one of our agricultural engineers asked if conditions where not conducive in the fall to do subsoiling, could we skip it for the year and just use irrigation. He wanted to know if yield would be lost under this scenario," Pringle said.

Subsoiling is best done in the fall when the ground is most dry and hard. If rains keep machinery out of the fields during this window, fields that are subsoiled in the spring may not benefit as much from the tillage.

For nine years, Pringle farmed cotton on his research plots in Stoneville, recording all the data, including environmental factors. He looked at cotton grown with and without irrigation on ground that was subsoiled or left undisturbed.

Martin ran the numbers to see what research indicated about cost.

"We found that the least expensive per pound of lint method for cotton production was to subsoil in the fall and not irrigate during the growing season," Martin said.

Returns were maximized with either the irrigated, non-subsoiled or the non-irrigated, subsoiled environments.

"Lower returns occurred in the irrigated, subsoiled environment due to the higher costs and lack of yield increase," Martin said.

He said most producers who don't have irrigation have been subsoiling for years. Those with irrigation have tended to use no-till or reduced tillage on their fields. Because of these common practices, Martin said the research results were not really a surprise.

"It has always been suspected that maybe you didn't need to use both practices, but it had never been quantified," Martin said. "We found that if you don't already have irrigation, you're just as well off by using subsoiling only. If you already have the investment in irrigation, you don't need to subsoil."

The full findings were published last year in the Journal of Cotton Science. More information is available online at http://journal.cotton.org.