Has anyone considered the fact that most of the water does not actually stay in the plant but passes through it, evaporating off the leafs. After harvest, the distillation process releases more water vapour. It would seem then that most of the water “used” will ultimately be released and will stay in the local environment. Although it may be difficult to recapture it in arid regions

Dicoll3000@Yahoo.com.

Only water that falls naturally, requires no energy or ’subtracting’ from rivers or aquafers.

There are many ethanol plants around me. Practically no acres are irrigated. That reduces the water requirement back to the 3-6 gallons the plant uses.

Even in irrigated areas of the West, 1/2 to 3/4 of the water ‘used’ to grow corn falls naturally from the sky.

I believe in worst case, this water ‘use’ is off by 1/2, and for much of the corn growing area of the USA, it is off by 95%. Natural rain should not be counted as a ‘use’ as it is not pumped but natural, and mostly continues on it’s natural course as it passes through the corn field - used to grow weeds, grass, or corn it’s all the same as it goes on to aquifers or rivers.

National corn yield is 153 bu/a, in the parts of Minnesota with many ethanol plants corn yield approches 200 bu/a. Corn weights 56 lbs/bu, and ethanol plants are getting about 2.9 gallons/bu.

No need to desalinate or pump any water other than that used in processing for most corn growing areas?

Paul

1. The first mistake was using a value of 70 lb/bu of corn. Corn weighs 56 lb/bu.

2. The calculation used the smallest value reported for corn water use (17.2 inches to produce 168 bu/a corn) to get the value of 300 m3/T. These data are from only one year of data, and did not include soil water extraction as part of the water use (only rainfall and irrigation were used to get the 17.2 inches). So it wasn’t really total water use. What should have done is use the first equation given in the article:

yield in bu/acre = 10.4 x (water use in inches - 9.1)

Had that been done, a value of 24.5 inches of water needed to produce 160 bu/a corn would have been obtained, which equates to 563 m3/T.

Using the proper values in the energy analysis shows that growing corn for ethanol production and using some of the ethanol to power the desalinization process would still leave an excess of ethanol produced (74% of the ethanol produced would be used for desalinization, 26% would be left to put into the market).

In any case, 300 m3 of water/Ton of corn produced is probably too low, and a more realistic number is about 560 m3/T for 160 bu/a corn. The value decreases to about 520 m3/T for 200 bu/a corn. The value continues to go down as yields go up because the amount of water needed to grow the plant to the point where it can start producing grain doesn’t change (about 9 inches), and becomes a smaller fraction of the total water used to produce the final grain yield.

The linear relationship shown above and used to generate these values changes from location to location, with slight changes in the slope of the relationship, and some more significant changes in the offset. For example, using a water/yield relationship generated in Nebraska, we would need about 25.8 inches of water to grow 200 bu/a corn, which would lead to a value of 473 m3 water/Ton of corn (vs 520 m3/Ton using the Colorado relationship shown above). Water use efficiency of corn grain production generally improves as we move east and north of Colorado.

But as you can see, the previously posted analysis using 300 m3/Ton was incorrect and too optimistic.

David Nielsen
Research Agronomist
USDA-ARS
Akron, CO

United Nation’s Intergovernmental Panel on Climate Change scientists noted that rice production is perhaps a bigger source of global warming than carbon dioxide emissions of all industrial and power plants.

Story at Agnet and written at ABS-CBN.

So many factors!