Tree seed oil could make fertilizer greener and last longer
Chepyala S, Vemuri PK, Nasam MK, Bathula J, Bodiga S
Soil Health
If you've ever wondered why lawn fertilizer needs reapplying so often or worried about runoff feeding algae in a nearby pond, this points to a seed oil that could keep nitrogen in the soil where roots can actually use it.
Pongamia trees produce seed oil that's long been used in soaps and biodiesel, and researchers found it contains a compound called karanjin that slows down the specific soil microbes responsible for turning fertilizer nitrogen into nitrate. That's useful because nitrate is the form that easily washes into waterways or escapes as a greenhouse gas, so a plant oil that keeps nitrogen locked in a more stable form could mean less fertilizer waste and less pollution. In tests, purified karanjin worked nearly as well as a widely used synthetic soil additive.
Key Findings
Crude pongam oil contained 3.24% karanjin and 0.45% pongamol, and both the oil and purified karanjin suppressed growth of ammonia- and nitrite-oxidizing soil bacteria in a dose-dependent way
Inhibitory strength ranked as synthetic DCD > karanjin > pongam oil > neem oil, with karanjin identified as the most effective plant-derived treatment via multivariate analysis
In urea-treated soil, pongam oil and karanjin increased ammonium retention while reducing nitrite and nitrate buildup, and also lowered microbial quorum-sensing activity, hinting at a possible added mechanism
chevron_right Technical Summary
Oil from the pongam tree's seeds, and a compound called karanjin found in it, can slow down soil bacteria that turn fertilizer into nitrate, which means less nitrogen washes away or turns into greenhouse gas. This plant-based option worked almost as well as a common synthetic nitrogen stabilizer, offering a greener way to make fertilizer use more efficient.
Abstract Preview
Original paper
Potential of pongam oil and karanjin as natural nitrification inhibitors: mechanistic effects on nitrifying microorganisms and soil nitrogen transformation.
Nitrification inhibitors delay the microbial oxidation of ammonium to nitrate, thereby improving nitrogen use efficiency and reducing nitrate losses and nitrous oxide emissions from fertilized soil...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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Pongamia pinnata is a species of tree in the pea family, Fabaceae, native to eastern and tropical Asia, Australia, and the Pacific islands. It is the sole species in genus Pongamia. It is often known by the synonym Millettia pinnata. Its common names include Indian beech, Karanja, and Pongame oiltree.