Desmodium legume cover crop? Is it the solution to food insecurity in Africa?

The baking sun around the equator gets hotter across the African savannah inducing drying up of many species unable to withstand the heat. The areas that have even a greater impact are the areas that have been converted into land for crop production. Actual soil temperature measurements during hot September weather in Kenya give an indication of the comparisons ranging from 19°C in desmodium planted areas, 24.5 C° in areas where desmodium has been cut and 43.8 °C in areas where the ground is bare. This is a great comparison to make farmers understand the relationship between soil evaporation and leaf area transpiration which definitely impacts on yields. ?Desmodium acts as mulch while increasing rainwater infiltration and protecting the soil from soil erosion.

Parasitic weed challenges in maize production

The parasitic weed by the name of striga (Striga Harmonthica and Striga Asiatica), has been indicated as among the most dangerous weed in maize production due to its ability to reduce yields by up to 90 % in poor degraded soils and with more prevalence during dry periods. Climate change impacts many sub-Saharan countries experiencing striga challenges experience extended periods of dry weather. Many chemical control programs for Striga have not borne any significant fruits while soil degradation has been accelerated by the intensive land practices, which increases the vulnerability of the farmers and results in increasingly lower yields translating into food insecurity, poor nutrition, and higher poverty levels. Striga has the ability to produce more than 1 million seeds with dormancy periods of up to 20 years. Germination of the seeds is triggered by the volatile chemicals produced in the maize roots where the striga parasitic weed attaches relying solely on the maize plant as the source of nutrients and water. This exploitative relationship results in very poor yields and chemical and mechanical weed control methods have been unsuccessful.

Its nicknamed the “witchweed” since it results in farms with pink flowers attached to the maize whereby trying to uproot the parasitic weed results in uprooting the maize plant as well. The farmers are left puzzled by the fact that is only present when maize or sorghum is planted while other legumes and tubers remain unaffected. Without control, it is estimated that in East Africa, striga yield losses can translate to USD 48 million

Experiments conducted by ICIPE, with the “Push-Pull” companion cropping using desmodium, and has already proven the great advantage that farmers who have adopted desmodium are getting through the adoption of cover cropping. Desmodium has a high potential of biological nitrogen fixation of up to 125 kgs per hectare per year, high biomass potential (17 tons per hectare per year), controls soil erosion, controls other weeds, and is currently being applied in repelling the moths of the maize stem borer (Busseola Fusca) and the fall armyworm (Spodoptera Frungiperda), that lay their eggs on the maize plant which develop into voracious larvae that have currently reduced maize yields significantly.

The desmodium Species (Desmodium intortum “Greenleaf” and desmodium uncinatum- “silver leaf”)

Originating from Central America, desmodium is a creeping branched perennial plant adopted to warm climates favoring temperatures between 25- 30° C, 30° South, and 30° North with favorable altitudes being?300 – 2500 m above sea level and annual rainfall ranging from ?700 – 3000 mm. The plant can be found in grazing pastures or since its establishment in the early 70s in Kenya. Desmodium has been tested and proven advantageous in the fodder production systems among smallholder farmers who practice the cut and carry livestock systems. With reducing land for production, desmodium is being promoted as an intercrop with other crops with scientific studies showing the immense benefits of nitrogen fixation.

The great success that has been proven by ICIPE indicates that since the quantity and dormancy of striga weed seed help its survival, desmodium when intercropped with maize has a mechanism that leads to the striga parasitic weed seed “suicide germination” by giving chemical stimuli for the seed to germinate but with the inability to attach to the maize plant. This reduces the seed bank and eventually depletes the seeds that can attack the maize plants.

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Invasive pests challenge to maize production in Africa

The fall armyworm (Spodoptera Frungiperda) originally from the Americas, has become the most important maize pest in Africa. The moth lays eggs on several grass family species which develop into larvae that devour all the leafy parts of the plant, the stem, and even the maize ears. The problem is perpetuated by the continuous presence of host plants making the pest a perennial problem unlike in the USA, where the winter season leads to population reduction. Currently, in the hot warm tropics, more than 6 generations per year are likely to develop if there are sufficient host plants supporting their survival.

The ability of the desmodium to repel the moths and reduce their ability to lay eggs in the maize plants is a major success for farmers in the drive to reduce production costs and as well reduce the intensive use of pesticides thereby protecting biodiversity. The ability of desmodium to control other weeds from its perennial and creeping nature adds the advantage to the farmer of reduced weeding costs while at the same time increasing mulch that protects the soil from higher temperatures.

Desmodium as a fodder replacing commercial feeds for livestock farmers.

The current livestock production practices rely heavily on commercial feeds most of which ingredients are grain-based comprising maize, wheat, soy, and sunflower. The global demand for grains has already resulted in elevated commercial fodder prices for livestock farmers beyond the point of commercial viability. Additionally, in the face of increasing production costs, grains are almost getting out of reach of the livestock farmers. Desmodium fodder has been proven to be rich in minerals with estimates giving calcium 7.6 g/kg, cobalt 120.7 mg/kg, copper 17.9 mg/kg, iron 264 mg/kg magnesium 1.6 g/kg, manganese 91.4 mg/kg, Phosphorous 3.5 g/kg, potassium 17.8 g/kg, sodium 0.15 g/kg, and zinc 25.3 mg/kg. Additionally, desmodium has a lower neutral detergent fiber making its digestion faster and this is attributed to lower energy loss and reduced methane emissions. Desmodium has been shown to have a potential of 17 tons per hectare per year with 4 successive cuttings when rainfall is well distributed. It has high levels of protein with its tannin content giving it the advantage of bypass protein resulting in higher productivity.

Desmodium compound benefits.

In a summary, desmodium should be embraced for its five great reasons making farmers richer and protecting the environment. The reasons are biological nitrogen fixation reducing the need for intensive synthetic fertilizers usage; soil ecosystem services (nitrogen fixation, moisture loss control, soil erosion control, and increased biodiversity); control of weeds (parasitic striga and others non-parasitic); reduction of pest pressure (repelling the moths of the fall armyworm and maize stem borer) and providing high protein fodder for livestock reducing the competition for grains to serve as commercial livestock feeds.

In relation to climate change adaptation and mitigation, desmodium ticks all the boxes in that being a perennial with deep roots, it has a high level of carbon sequestration and reduces the intensive soil operations responsible for methane emissions, and has a high potential for biological nitrogen fixation. The high value of the protein fodder having condensed tannins and bypass protein serving as livestock feed results in reducing methane emissions from livestock.

Proposition

Desmodium should thus be scaled up in the cropping systems for the majority of the African farmers to achieve food security through decreased production costs, and reduced risk from parasitic weeds and invasive pests, while benefiting from the ecosystem services and provision of livestock fodder which has always remained a bottleneck in profitable livestock production.

Supporting studies

1.?????Optimization of ecosystem services for sustainable coffee production under changing climate - https://eajsti.org/index.php/EAJSTI/article/view/353

2.?????Evaluating Cover Crop Ecosystem Services for Buffering Coffee against Changing Climate - https://bit.ly/31rNDXh

3.?????Assessment of Ecosystem Services Knowledge, Attitudes, and Practices of Coffee Farmers Using Legume Cover Crops.”Ecosphere13 (4): e4046. https://doi.org/10.1002/ecs2.4046???