Growing jack beans, farmers get a double shot in high protein food for their families and a doubling of the yield of their other crops as the bean restores health to rapidly degrading soils by cooling the soil, providing a soil erosion stopper, and adding green manure.
Every year African soils lose up to 60kg of nutrients per hectare which has degraded more than three-quarters of our cultivated land affecting 485 million people.
Cover crops fix this by cutting the nutrients lost in soils by half and slicing soil erosion down by 90 per cent.
In its Green Manure/ Cover Crops handbook for small farms, FAO advises farmers to plant jack beans because their big leaves reduce soil erosion which washes away the soil’s top layer with all the best nutrients, and also shade soils lowering their temperature.
In just 60 days, jack beans cover up to 85 per cent of the ground they are planted in and produce 2.46–7 tons of dry matter an acre. The beans can produce leaves for eleven months or the entire year. Its big leaves and dense vegetation reduce soil erosion by preventing raindrops from landing directly on the soil and reducing the speed water moves on the surface of the soil carrying away its topsoil.
On the foot of Mt. Meru in Tanzania, a region synonymous with soil erosion because of the strong rains it receives, international nonprofit ECHO highlighted farmers planting jack beans with their coffee and bananas which almost entirely got rid of soil erosion on their farms.
This good plant cover of Jack beans has the knock-on effect of reducing the amount of water the soil loses, increasing the amount of water it can hold, and eventually improving the yield farmers get.
The temperatures of bare soils during the hottest months, January and February, rise as high as 35 to 40°C during the day, and from July to August they average 30 to 35°C.
The FAO recommends farmers not to let their soil’s temperatures exceed 40ºC. This is because once soil temperatures hit 35ºC, the amount of water and the nutrients water carries from the roots of most plants becomes almost zero,
These high soil temperatures also make the small animals which improve your soil’s health ‘tired’ reducing the amount of activity they can do.
Soils with a good amount of water also have a higher number of better-quality earthworms and a higher number of small insects in them.
While in the soil Jack beans act as green manure with every hectare of the legume adding 187.04 to 229.6 kilograms of nitrogen to the soil. This is possible because Jack beans are legumes that have balls on their roots that house bacteria that inhale nitrogen from the air used by the plant to grow and are also shared with the nearest available crops.
Jack bean seeds should be harvested as they ripen for consumption because they do not grow uniformly. The seeds which have been promoted as a source of cheap and plentiful protein for farmer families in developing nations contain 29 per cent protein emerge four months after planting and continue popping out until the seventh month. They give 1,000 to 1,500 kg/ha of seed.
40 to 60 Jack bean seeds should be planted for every hectare at least two centimeters deep in the soil with the rows being 70cm apart.
The legume grows in areas with 650mm to 2,000mm of rain and can withstand drought, flooding, and being grown in salty water. Direct nitrogen application to the plant is not advised as this lowers its yield.
Photo: Shiela Chikulo/CIMMYT