Cotton futures are more vulnerable to changes in oil prices that corn futures, despite not playing a major role in biofuels production, Societe Generale said.
Sure, corn is the "most directly affected agricultural commodity" in times of falling oil prices, SocGen said, examining the impact on ags of the tumble in oil futures to four-year lows this month, in the case of Brent crude.
Lower fuel prices, in cutting production costs, raise farmers' margins, and thus the appeal of raising production of corn and other crops.
"Initially, then, and perhaps into the next planting season, one can expect corn prices to fall in the face of increased plantings," SocGen analyst Christopher Narayanan said.
"In addition, lower transportation costs, owing to lower fuel costs, lowers the delivered price of corn in physical market, providing initial pressure on corn prices."
However, for corn, this impact is offset by the boost to consumption of ethanol, made in the US from the grain, as gasoline prices drop.
"Lower fuel prices tend to increase demand for gasoline… [which] in turn increases the amount of corn needed for ethanol production, and could create competition between livestock feeders and exporters," Mr Narayanan said.
"Therefore any increase in corn production from improving margins could eventually be offset by increases in demand for corn used in ethanol production on the back of higher gasoline demand."
On average, movements in oil prices will tend to take corn futures in the same direction, but by a modest 0.2% in values of the grain for every 1% in values of crude.
Thus a 15% drop in oil prices would "cause a 3% drop in corn prices", equivalent to some $0.11 a bushel.
In fact, crude values have dropped some 30% from June highs.
This is actually lower than the overall impact of oil values on prices of cotton – thanks to the relatively large cost of growing the fibre, and without any offsetting increase in demand from biofuel use.
"Cotton has the largest per-acre energy costs," compared with corn, soybeans and wheat, "as a large portion of the US cotton crop is irrigated," Mr Narayanan said.
Cotton will, in 2015, cost $529.56 per acre to grow, 46% more than corn, and quadruple that of wheat.
And of that sum, fuel accounts for $65.56 per acre for cotton, nearly twice as much as for corn, and triple the amount for wheat.
On SocGen's analysis, every 1% move in oil prices causes a 0.45% shift in cotton values, in the same direction.
"Thus a 15% drop in oil prices is expected to cause a 6.75% drop in cotton prices over the course of a 12-month period," equivalent to about 5 cents a pound.
The comments came as SocGen outlined the impact on other commodities of falling crude oil prices, whose decline has been spurred by an oversupply the bank term "not temporary in nature".
"We believe that we're in the middle of a very fundamental change in the oil markets – the type of change that only happens every decade or two," the bank said.
Factors contributing to the drop include a reduced reliance by the US on imported oil, thanks to its soaring shale gas usage, but a reluctance among producing countries, which have got used to high oil revenues, to implement the output cuts needed to prop up prices.
SocGen flagged a floor to oil prices at about $65 a barrel – the estimated breakeven cost for producing shale oil from the Bakken, Eagle Ford and the Permian regions.
"So if the market were down drive prices down to the point where it sees US output actually start to contract, we are potentially talking about Brent at $70 a barrel and World Texas Intermediate at $60-65 a barrel."