into weather-sensitive crop models that can help design crop varieties to match climate conditions, as well as determine optimal management of crops in specific climate conditions, either in the present or in the future. Biotechnology innovations that will increase the water-use efficiency of both food and biofuel crops will be of great value, as the introduction of biofuels will in some regions lead to an increased demand for water that will also increase the value of drought-tolerant varieties of crops.

Finally, biotechnology research and development can be important in improving lignocellulosic, microbial, and bioconversion as well as thermochemical conversion technologies. Although the cost of cellulolytic enzymes, which are used to break down these forms of biomass into biofuels, has decreased in recent years, sugar release from biomass still remains an expensive and slow step, perhaps the most critical in the overall process. Intensive research and development has produced a reduction in the cost of such enzymes by a factor of 10 to 30, down to 20 to 30 cents per gallon of ethanol produced. Although this decrease in price is an important advance, it is estimated that the enzyme cost will have to be further reduced to a level comparable to that of current approaches that produce ethanol from the starch in corn kernels at a cost of 3 to 4 cents per gallon of ethanol (Stephanopoulos, 2007).

REFERENCES

Fipps, G., and L.L.New. 1991. Water for Agriculture: Improving the Efficiency of Center Pivot Irrigation with LEPA. Report prepared for UNESCO Inaugural International Seminar on Efficient Water Use, Mexico, October 21, 1991. Available online at (http://www.unesco.org.uy/phi/libros/efficient_water/wfipps.html). Accessed on July 13, 2007.

Payero, J.O., C.D.Yonts, S.Irmak, and D.Tarkalson. 2005. Advantages and Disadvantages of Subsurface Drip Irrigation. University of Nebraska-Lincoln Extension Publication EC776. Lincoln, NE: University of Nebraska-Lincoln. Available online at (http://www.ianrpubs.unl.edu/epublic/live/ec776/build/ec776.pdf). Accessed on July 13, 2007

Scharf, P., E.Souza, and K.Sudduth. 2001. Spectral Radiometer to Control Variable-rate N Applications for Corn. Proposal prepared for University of Missouri and U.S. Department of Agriculture (USDA) Agricultural Research Service. Columbia, MO: University of Missouri, Columbia. Available online at (http://aes.missouri.edu/pfcs/research/prop501.pdf). Accessed on July 13, 2007.

Stephanopoulos, G. 2007. Challenges in engineering microbes for biofuels production. Science 315:801–804. Available online at (http://www.sciencemag.org/cgi/content/full/315/5813/801). Accessed on July 13, 2007.

Troyer, F.A. 2006. Adaptedness and heterosis in corn and mule hybrids. Crop Science 39:528– 543.

U.S. Department of Agriculture, Economic Research Service (USDA/ERS). 2004. Irrigation and Water Use: Glossary for Irrigation Systems and Land Treatment Practices. Available online at (http://www.ers.usda.gov/Briefing/WaterUse/glossary.htm). Accessed on July 13, 2007.



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