The energy farming nursery at the Rabgayling Tibetan Settlement is currently growing over 8,000 Pongamia pinnata seedlings. Tending to a nursery of this size requires lots of attention to ensure that the seedlings get the right amount of water, sunlight, and nutrients.
During the summer, temperatures in South India reach as high as 110ºF. Mature Pongamia pinnata trees can withstand high temperatures, but seedlings need extra protection. A shade net was built to cover the nursery during this very hot part of the year.
To encourage higher seed yields from the Pongamia pinnata trees, energy farming utilizes a technique known as grafting. When a seedling’s stem is about pencil-thick, a notch is cut into the top of the seedling, and a branch from a mature high-yielding Pongamia pinnata tree is attached to the seedling. From that point forward, the seedling is pruned to ensure that all future growth comes from this added branch. The branch, like its parent tree, will produce a high volume of seeds for maximum biofuel extraction. This technique also encourages earlier fruit bearing—normally a Pongamia pinnata tree won’t produce seeds until the seventh year, but a grafted tree produces in the fourth year.
The nursery is organized by seedling size. After the larger seedlings have been grafted and pruned, they are planted with the other Pongamia pinnata trees in the fields. Continued pruning ensures that the plants are well balanced and helps maximize the fruit-bearing external branches. As seedlings are taken out of the nursery, new seeds are planted to replace them. In this way, a constant stream of growth is maintained from seed to establishment.