Corn cobs suitable for bioenergy production

When energy officials proposed using crop residues to produce cellulosic ethanol, concerned scientists took to the fields to learn more about how these residues protect soil from erosion and enhance soil quality. Agricultural Research Service soil scientist Brian Wienhold led the research, focusing on a single component of the residue - the corn cob.

“We didn’t have data on how postharvest cob residues might protect soil quality,” said Wienhold. “But corn cobs make up 20% of residue by weight, which means that the average US production of corn could provide 40 to 50 million tons of cobs for feedstock every year.”

Wienhold, with the ARS Agroecosystem Management Research Unit, led studies that compared run-off rates and sediment loss from no-till corn fields where postharvest crop residues were either removed or retained. The scientists also removed cobs from half of the test plots that were protected by the residues.

After the test plots were established, the scientists generated two simulated rainfall events. The first occurred when the fields were dry and the next occurred 24 hours later when the soils were almost completely saturated.

During the first event, on plots where residue was removed, run-off began around 200 seconds after the ‘rain’ began, whereas run-off in the residue-protected plots didn’t start until after around 240 seconds. Run-off from the residue-free plots contained 30% more sediment than run-off from all the residue-protected plots. The presence or absence of cobs on the residue-protected plots did not affect sediment loss rates.

Wienhold’s team concluded that even though cob residues did slightly delay the onset of run-off, sediment loss rates were not significantly affected by the presence or absence of the cobs. The results indicated that the cobs could be removed from other residue and used for bioenergy feedstock without significantly interfering with the role of crop residues in protecting soils.

In a related study, Wienhold examined how the removal of cob residues affected soil nutrient levels. He placed litter bags containing cob pieces on the surface of no-till fields or buried them 0 to 10 cm deep in the soil. Every two months, he tested cob samples from the bags for levels of carbon, nitrogen, phosphorus, potassium, sulfur, calcium, manganese, iron, magnesium, copper and zinc. Over the course of a year, his sampling indicated that cobs were a source of soil potassium, but that they weren’t a significant source of any other plant nutrients.

Wienhold believes his findings demonstrate that harvesting cobs for biofuel production would not result in any notable loss of soil quality. This means that Nebraska’s York County - where average corn production results in around 0.2 million tons of cobs - could potentially provide enough cob feedstock every year to keep two 40-million-litre ethanol plants in business.

Results from this work have been published in Agronomy Journal.

Credit: USDA/ARS.