New ways worth exploring

Sugarcane grower Neil Maitland’s experiment with some left-over grains seed has produced some unexpected results. Mr Maitland thought he would use up some left-over sunn hemp (Crotalaria juncea L.) seed on his family-run property at Aloomba, south of Cairns.

Mr Maitland grows 83 hectares (205 acres) of sugarcane with about 15ha of fallow/rotation ground each year. He has been on the property for 45 years and normally always plants a break crop, usually a legume.

After planting a mixed species product in 2022, some sunn hemp seed remained, so he decided to run it out. Driven on by the humidity and high rainfall (Aloomba averages almost 2000mm per year), the crop was hugely impressive. Its vigorous growth rate, particularly in the tropics, sees a crop fully grown in 90 to 120 days.

Initial biomass trials at the Aloomba property found the early crop had put some 210kg/ha of nitrogen into the soil. Considering sugarcane in the area requires about 120kg/ha, Mr Maitland was impressed with the results. Mr Maitland then contacted DAF extension officer, Jack Robertson to help conduct various trials on the property.

Tests showed it boosted the organic carbon in the soil by 0.4 to 0.6 per cent. Generally, a higher organic carbon level means less additional (synthetic) nitrogen is needed. Needless to say, the Maitland farm has reduced its fertiliser input but maintained its yield. The farm produced a 144t/ha cane crop last year.

Mr Maitland said he was keen to find out how long the organic matter would continue to release nitrogen. His own experience had been that the woody stalk of the sunn hemp crop breaks down slowly, which could have beneficial impacts on the soil over a longer period of time. In fact, soil tests after harvesting the cane found the level of organic carbon did not diminish. The increase in organic matter caused Mr Maitland to notice a visible difference in how easily the soil was worked.

Mr Maitland said that it is difficult to produce a cash crop through summer in the wet tropics, so sunn hemp had been a great success, and even if the sunn hemp crop wasn’t harvested, it could be ploughed back in for numerous green manure benefits.

An additional result has been greater water penetration meaning less farm run-off and increased moisture holding capacity. All very good news for reef water quality and the environment as a whole.

The Maitlands have been ahead of the curve in terms of sustainable land practices switching to ‘high floatation’ tyres decades ago, to lessen compaction and they built trailers to suit their controlled traffic operation.  After their success with this cash crop, other Far North Queensland farmers are now exploring and experimenting with sunn hemp.

About sunn hemp

Sunn hemp is a native plant of Bangladesh, Bhutan and India. When the plant decomposes, the fixed nitrogen is mineralised and released into the soil and is available for subsequent crops. It is recommended for rotation with crops prone to root nematode infection such as potatoes and sugarcane due to its resistance and suppressive action against these pests.

Sunn hemp can be used as a livestock feed because it is high in protein. While the fibrous stalk makes it tricky to bale, it is suitable for fodder or silage production. The plant can also be used for fibre production in the manufacture of twine, cord, canvas, fishing nets, paper and pulp.

Biodiesel can be produced from the seed due to its oil content, while international work has been done on its pharmaceutical uses.

Mr Maitland has encouraged Sugar Research Australia (SRA) to explore the possibilities for the sugar industry and said more scientific evidence would help to drive adoption by other sugarcane growers.