Australian farmers are increasingly planting sunn hemp, a fast-growing legume with bright yellow flowers, as a natural way to reduce fertiliser costs while improving soil health. The crop is gaining attention as fertiliser prices continue to climb following disruptions to global supply chains and conflict in the Middle East, which have pushed the cost of urea to record levels.
Unlike traditional cash crops, sunn hemp is primarily grown as a cover crop. Instead of being harvested for sale, it is planted between main cropping seasons to restore soil quality. As a legume, it forms a natural partnership with soil bacteria that capture nitrogen from the atmosphere and convert it into nutrients that plants can use. This natural process reduces the need for synthetic nitrogen fertilisers such as urea.
Sugarcane grower Neil Maitland, near Cairns, has been using sunn hemp in his farming system for several years. He says the crop has helped reduce his nitrogen fertiliser use by around 25 per cent, saving more than $400 per hectare on fertiliser costs while maintaining productive crops. Although he still applies phosphorus and potash, the amount of expensive urea required has fallen significantly.
Researchers are also finding promising results. Scientists from the Queensland Department of Primary Industries (DPI) have been trialling sunn hemp in cotton-growing regions of Central Queensland. Their studies indicate the crop can generate nitrogen equivalent to approximately 220–320 kilograms of urea per hectare, offering substantial savings for growers.
Beyond fertiliser savings, sunn hemp is proving valuable in pest management. DPI trials have shown it can dramatically reduce populations of reniform nematodes, microscopic pests that attack cotton roots and reduce crop yields. Researchers observed nematode numbers fall from about 3,000 to just 100 per 100 grams of soil after sunn hemp was grown for around two and a half months.
Additional research is underway near Ingham, where agricultural specialists are testing mixed cover-crop systems. Early findings suggest combinations including sunn hemp, cowpea, lablab, and soybean may improve soil carbon, biodiversity, and nutrient cycling while reducing reliance on synthetic fertilisers.
While researchers continue studying whether sunn hemp may host certain crop diseases in cooler regions, its performance in tropical and subtropical Queensland has been encouraging. With fertiliser prices remaining high, more growers are expected to adopt cover crops as part of sustainable farming systems that improve soil health while lowering operating costs.
The growing popularity of sunn hemp highlights a broader shift in Australian agriculture toward practices that combine environmental sustainability with long-term economic benefits for farmers.
