By TIM THORNBERRY
Kentucky Correspondent

LEXINGTON, Ky. — As the state makes its move to the forefront of alternative fuel research, finding just the right biomass including crop residues has become a debatable topic, especially when it comes to conservation.

Ironically the use of alternative fuels may indeed contribute to the “greening of America,” but the use of crop leftovers such as corn stover and wheat stubble may cause conservation problems, not to mention a loss of money.

John Grove, a University of Kentucky (UK) College of Agriculture associate professor for soil nutrient management, released the first-year findings of a study looking at the short-term effects of various amounts of crop residue left in the field.

The study found, for instance, that leaving normal amounts of corn stover yielded nine more bushels of corn per acre than a field with no stover. That equates to a loss of $36 an acre with corn at its current price of $4 a bushel.

“The nine bushel per acre difference is due to improved water use efficiency,” Grove said. “The stover was able to help the soil retain some of its water during the last year’s drought.”

The study also found that residue left retains nutrients in the soil, alleviating the need for additional fertilizer and although the cost of fertilizer is coming down, farmers are faced with paying higher prices because of suppliers building up their stocks at elevated prices last summer.

“Producers need to realize that corn stover is a lot more than just carbon,” Grove said. “It also contains nutrients, such as nitrogen, potassium and phosphorus that the soil will retain and cycle for the next crop. When you remove stover, you change the soil’s fertility status.”

No-till and organic enthusiasts have blasted the use of crop residues for energy purposes citing the damage removing the residue can do to the soil. Ann Kennedy, a USDA-Agricultural Research Service soil scientist at Washington State University, wrote in a report that in a particular area in Washington state, more than half of the organic material in the soil there has been lost over the last 100 years of use.

“Organic matter provides nutrients crops need; it holds water and contributes to aggregation,” she said.

The report also noted that “soil is made up principally of mineral particles, organic matter and microorganisms that break down residue into organic matter. The percentage of organic matter in a given soil varies naturally from region to region, depending on climate, soil disturbance, moisture and vegetation.

“With that said, Kennedy added that, “A lot of people think residue is part of organic matter, but that is not correct. Organic matter is well-decomposed plant material and microbes. It is black and rich and gives soil its dark color.”

She also reported that tillage may mix the soil and residue too well, causing overfeeding of the microbes. which will consume the incorporated residue too quickly and release most of it into the air as carbon dioxide.

“It is like going to an all-you-can-eat restaurant every day and eating too much,” she said. “You cannot adequately metabolize all the food you ate. Cultivated soil is like a ‘pig-out’ for microbes.”
Grove suggested producers regularly evaluate crop residue values because they can change according to the dryness of the growing season and the price of fertilizer nutrients. He also noted that because of their benefits to the soil and subsequent crops, residue should not be removed every year.

Another suggestion is in the event farmers do remove residues, they should plant a winter cereal crop in the fall and consider “applying either compost, poultry litter or other animal waste to the field in the spring to make up for the organic matter and nutrients that were lost as a result of residue removal.”