Biotech Fertilizer?
Research in molecular biology has put highly desirable and widely adopted traits for herbicide and insect resistance into crop plants. It is expected that the science will soon impact the rate of progress in yield improvement, and that genetically modified plants may show increased stress tolerance and nutrient use efficiency. Such improvements beg the question - what is the likelihood of being able to replace nitrogen fertilizer altogether?
Plants of the legume family have always been able to metabolically acquire a portion of nitrogen requirement. A complex symbiosis with rhizobial bacteria lets them make the ammonium they need for protein synthesis directly from the nitrogen gas abundant in the air. They fix nitrogen using the nitrogenase enzyme of the bacteria. It costs the plant something for energy, but perennial species like alfalfa are efficient enough at it that they rarely respond to nitrogen fertilizer. Transferring the trait to non-legume crops would be a major challenge. The most important grain crops of the world - the cereals such as corn, wheat, and rice - are all non-legumes. They take most, if not all, of their N from the soil. They generally do not produce high yields without N fertilizer.
Research on the genetic control of the legume symbiosis has led to identification of the plant genes that trigger the formation of nitrogen-fixing nodules. A breakthrough was reported in the summer of 2006. Dr. Giles Oldroyd, a scientist working at the John Innes Centre in Britain, said: “The fact that we can induce the formation of nodules in the plant in the absence of the bacteria is an important first step in transferring this process to non-legumes. However, we still have a lot of work before we can generate nodulation in non-legumes.”
Considering that both the plant and the bacteria need to take many more steps after nodulation in order to begin the process of effectively taking nitrogen from the air, it is clear that the science behind the transfer of the process to non-legumes is in its infancy. The genome of the rhizobial bacteria that fix nitrogen in alfalfa was published in 2001. At least 100 scientific studies since then have cited the article - which shows that the research is active.
The Brazilian Agricultural Research Corporation announced in December 2006 that it has finished mapping and sequencing the genome of another bacterium that works as a natural fertilizer. Gluconacetobacter diazotrophicus is found in sugarcane, sweet potatoes, and pineapples. As an endophyte - living between the cells of the roots of its host - its association is not as intimate as that of the rhizobia that invade the root cells of a legume to form nodules. However, this organism is responsible for the low nitrogen requirements of sugarcane and contributes to the high energy efficiency of the Brazilian ethanol industry. (Farm & Rancher Guide, 4/2/07).
