By JORDAN STRICKLER
CAMBRIDGE, Mass. — Researchers at MIT could have just changed the landscape of planting. Scientists from the Massachusetts Institute of Technology have created a protective coating of silk which will not only provide a nitrogen fertilizer, possibly reducing the need for synthetic fertilizers in the future, but also help the plants grow successfully in soils that would be too salty for untreated seeds to develop normally.
The findings were published in the journal Proceedings of the National Academy of Sciences, in a paper by graduate students Augustine Zvinavashe and Hui Sun, postdoc Eugen Lim and professor of civil and environmental engineering Benedetto Marelli.
The work grew out of Marelli's previous research on using silk coatings as a way to extend the shelf life of seeds used as food crops. "When I was doing some research on that, I stumbled on biofertilizers that can be used to increase the amount of nutrients in the soil," Marelli said. "These fertilizers use microbes that live symbiotically with certain plants and convert nitrogen from the air into a form that can be readily taken up by the plants."
Seeds were treated with a bacteria which naturally produces a nitrogen fertilizer to help the germinating plants develop. The team hopes that this inexpensive process could open up avenues where land previously unfit for growers to plant, could now be used.
Marelli says that the new process will not only provide a natural fertilizer, but will avoid problems associated with other fertilizing approaches. "One of the big problems with nitrogen fertilizers is they have a big environmental impact, because they are very energetically demanding to produce."
While Marelli says that the nitrogen-fixing bacteria occurs naturally in soils around the globe, a downside is that they are hard to preserve outside of their natural soil environment. This could pose problems as different local varieties of the bacteria coating are found in different regions of the world. But, since silk can preserve biological material, Marelli and his team decided to try it out on nitrogen-fixing bacteria known as rhizobacteria.
"We came up with the idea to use them in our seed coating, and once the seed was in the soil, they would resuscitate," he says. Preliminary tests did not turn out well, however; the bacteria weren't preserved as well as hoped.
However, teammate Zvinavashe was able to work around this problem by adding trehalose to the recipe. Trehalose is a sugar which some organisms use to survive under low-water conditions. Soaking the silk, bacteria and trehalose in water provided an even coating of the seeds, resolving the issue.
Even if limited to legume crops, the method could still make a significant difference to regions with large areas of saline soil. "Based on the excitement we saw with our collaboration in Morocco," Marelli says, "this could be very impactful."
Marelli says that the researchers are now working on developing new coatings that could not only protect seeds from saline soil, but also make them more resistant to drought, using coatings that absorb water from the soil. Meanwhile, in 2020 they will begin test plantings out in open experimental fields in Morocco; their previous plantings have been done indoors under more controlled conditions.