Sunn hemp a Natural Boost for Soil Fertility
Sunn hemp originated in India where it has been grown since the dawn of agriculture. It has been utilized as a green manure, livestock feed, and as a non-wood fiber crop. It has also been grown in Brazil and Bangladesh as a soil-improving crop.
Research with sunn hemp has been conducted in the United States since the 1930s, where it was reported to be excellent in improving soil conditions (Cook and White, 1996).
In Africa soil degradation is increasingly threatening farm profitability and there is urgent need for embracing green manuring through which farmers can take a low-cost yet powerful step toward rebuilding soil health and ensuring better yields.
Locally a number of farmers have embraced the growing of sunn hemp for green manuring purposes. The crop provides excellent biomass within a short growth and is known for its vigorous growth and ability to suppress weeds, further reducing the dependence on chemical weed control.
A Marondera farmer Berin Stockil who planted a huge hectarage of this legume plant told Mudhumeni Mukuru that the plant has numerous benefits and increases the soil richness which cuts down more on the amount of fertilisers that one has to purchase for the next farming season
“When you apply it to the soil your soil will turn darker and it helps the soil to have enough humus to contain moisture especially when you are faced with a dry spell.
“We planted down the crop in February and by the time we get to September all the debris will have decomposed and it’s a foundation for farming principle”.
He added that most farmers do not rest their soils and also have no knowledge of how to improve them to give better yields.
“We haven’t given our soils a rest for many years so the only way to do so is by putting in these crops .
“We have done this for about thirty years but other communities especially in rural areas have never done it meaning that their soils are depleted of all the humus, the soils are very hard and have very low pH’s”.
For farmers who would want to plant this crop timely sowing is important, as green manure crops should be incorporated back into the soil before they start flowering—generally within 40 to 50 days of sowing—for maximum benefit.
This practice is particularly beneficial for small and marginal farmers who often struggle with the high cost of inputs.
Beyond soil health, green manuring plays an important role in sustainable agriculture by reducing chemical residue, promoting biodiversity, and improving the long-term productivity of farmland.
It also contributes positively to climate resilience by enriching the soil with carbon and improving its water-holding capacity.
In conclusion research has proved that Sunn hemp can be used as a cover crop, can improve soil properties, reduce soil erosion, conserve soil water, and recycle plant nutrients.
‘Tropic Sun’ is also resistant to root-knot nematodes.
Other potential uses for sunn hemp are forage, paper fiber, and as alternative fuel crop.









