Legume Trees Found to be Sustainable Source of Nitrogen

Kelly MarshallEducation, Fertilizer, livestock, Nitrogen, Nutrient Management

nitrogenSilvopastoral systems refer to the combination of putting crops and livestock in the same location for the benefit of both, and that is just what Jose Dubeux Jr. hopes to accomplish.  Dubeux, an assistant professor of Agronomy at North Florida Research & Education Center, spent a lot of time on his grandparents’ farm in Brazil as a child.  Now he’s looking for solutions that affect tropical soil, specifically keeping enough nitrogen in the soil to grow forage for livestock.

Economic and environmental factors discourage many farmers from using industrial fertilizers. So Dubeux is exploring an alternative fertilizing method – tree legumes. Legumes naturally replace nitrogen in soil. Dubeux and his team wanted to know if tree legumes would be effective in a silvopastoral system. They needed to measure how much nitrogen the decomposing tree legume leaves and branches would put into the soil.

The researchers planted two types of legume trees in a Pernambuco state, Brazil, pasture. They gathered and bagged leaves from each of the two types of trees. They also gathered branches from the two types of trees, sorted by branch circumference. The team placed the bags of leaves and bags of branches in enclosed areas in the pasture and covered with cuttings. This simulated typical conditions around the trees. As the bags’ contents decomposed, researchers periodically weighed the bags and did a chemical analysis of their contents. Finally, researchers compared data from the beginning and end of the experiment.

“One of the most exciting and surprising things we found was that tree legumes could contribute significant nitrogen amounts to these systems,” Dubeux explains. “We could actually measure how much of the nitrogen deposited by the leaves and branches would be available for the grass.”

Of course, growing trees isn’t a practice that will pay off overnight.  The waiting can be worth the effort, though, says Dubeux.   “When you sum the lumber value with the livestock production, you can double the gross income for the producer.”

Silvopastoral system are also good news for the environment.  “Nitrogen fertilizer is produced using natural gas and has a high carbon footprint, increasing the effects of global warming.” Tree legumes, on the other hand, are a more sustainable source of nitrogen.

You can read more about the research in Crop Science.