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Using less fertilizer aids corn for fuel - but what about corn for food?

By Martin Leggett - 28 Feb 2011 15:7:1 GMT
Using less fertilizer aids corn for fuel

Proving again that there's no such thing as a black-and-white story, when it comes to green issues, the journal Environmental Science and Technology has ostensibly great news, both for corn farmers and for the environment. Agricultural scientists at Houston's Rice University have discovered that being frugal can be fruitful, when it comes to the application of fertilizer for cellulosic bioethanol production.

This could benefit both the bottom line for farmers, as well as their planetary footprint. Less fertilizer means less nitrate run off, and also less greenhouse gas emissions. What is less clear-cut is the effect on food production of reducing fertilizer application. And that is a huge issue at a time of rising food prices.

The research conducted, by Morgan Gallagher and Carrie Masiello of Rice University, looked in particular at how the amount of nitrogen fertilizer affected the proportion of cellulose in corn plant residues. It is the cellulose in the residues left from harvesting that offers the potential for a new approach to producing bio-ethanol.

Most corn grown for fuel in the States uses the grain itself for producing ethanol. That is a problem, as it directly competes with grain grown for food. The switch to grain for fuels in the US is widely held to have indirectly contributed to global food price increases – pushing poorer sections of the developing world back towards hunger.

But ethanol can also be produced from the cellulose in the stems and leaves of corn, via processes of chemical hydrolysis, or microbe fermentation. These don't compete directly with food production, so using cellulose production matters.

What the team at Rice have found is that over-applying fertilizer may boost grain yields, but it also encourage the growth of woody lignin. This is at the expense of cellulose. So to maximize the cellulose production needed for residual biofuels, nitrogen fertilizer needs to be cut right back.

Masiello says ''There's really only a small amount of fertilizer needed if you're cropping strictly for cellulose''. That's good news for reducing nitrate run-off – and may also help to keep the carbon from plowed-in residues firmly locked in the soil - both big pluses environmentally.

But if, in a quest for increasing ethanol production, reduced inorganic fertilizer inputs cuts grain yields, that still seems likely to produce a negative effect on food prices. Switching from corn ethanol to cellulose ethanol may not take biofuels off of the green consumer's blacklist yet.