Desmodium Legumes: A Climate Resilient Adaptation in Coffee Production

How desmodium cover crops can be used for weed management, soil fertility, and yield improvement in coffee and as fodder from African farmers.

The two main species are the “Greenleaf” (Desmodium intortum) and the “silver leaf” (Desmodium uncinatum) types that grow well in tropical conditions. Originating from Central America, desmodium is a creeping branched perennial plant adapted to warm climates favoring temperatures between 25- 30° C (77-86 °F), 30° South, and 30° North, with favorable altitudes being 300 – 2500 m (985-8202 feet) above sea level and annual rainfall ranging from 700 – 3000 mm (Heuzé et al., 2017). This perennial plant has deep roots, withstands moderate drought, and is shade tolerant which can be found in grazing pastures or farms 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 (Heuzé et al., 2017). With reducing land sizes associated with population growth and urbanization, land for the production of coffee is declining, and desmodium is being promoted as an intercrop with other crops, with scientific studies showing the immense benefits of nitrogen fixation.

Desmodium, when intercropped with maize, has a mechanism that leads the parasitic Striga weed seed to suffer from “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 (Midega et al., 2017). The relevance of legume fodder cover crops such as desmodium relates positively to their ability to reduce nitrogen leaching from the soil, thereby influencing the net greenhouse gas emissions while positively contributing to improved crop productivity (Abdalla et al.,2019).

Desmodium as fodder replacing commercial feeds for livestock farmers.

The current Kenyan livestock production practices rely heavily on commercial feeds, most of whose ingredients are grain-based, comprising maize, wheat, soya, and sunflower (Ayantunde et al., 2005). The global demand for grains has already resulted in elevated commercial fodder prices for livestock farmers beyond the point of commercial viability (Ayantunde et al., 2005). Additionally, in the face of increasing production costs, grains are almost getting out of reach of the many smallholder livestock farmers (Ayantunde et al., 2005). 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 (Heuzé et al., 2017). Additionally, desmodium has a lower neutral detergent fiber making its digestion faster, and this is attributed to lower energy loss and reduced methane emissions (Heuzé et al., 2017). Desmodium has been shown to have a potential yield of 17 tons per hectare (6.9 tons/acre) per year with 4 successive cuttings when rainfall is well distributed (Rose & Kearney, 2019). It has high levels of protein with its tannin content, giving it the advantage of bypassing protein resulting in higher productivity (Williams et al., (2015).

Desmodium Tannins in reducing livestock methane emission

IPCC emissions from agriculture aggregate the huge impact of livestock methane emissions associated with their natural digestive system in the feeding process (IPCC, 2022). The livestock feed type determines the overall methane emissions ranging from 120 – 320 liters per full-grown cow per day (Anantasook et al., 2015; Chen et al., 2021). Legume fodder has been evaluated in the livestock digestive system concerning the internal processes involved in methane emissions from livestock (Williams et al., (2015). Legume fodder crops that have high tannin content have been seen to have lower methane emissions. This happens since the bypass protein contained in them is bonded in the rumen without breakdown and passes to the small intestines, where it is absorbed by the animal resulting in lower methane emissions (Tolera & Sundstøl, 2000; Yanza et al., 2021). The desmodium content of the condensed tannins has been positively correlated with the mitigation of methane and ammonia production in continuous cultures of mixed ruminal microorganisms (Williams et al., (2015).

Many studies on desmodium have shown that it has great potential to control weeds due to its creeping habit when introduced in crop production systems and in the supply of the required proteins for dairy animals while reducing the carbon footprint (Baloyi et al., 2009). Most of the current livestock feed production practices have been associated with intensive industrial and agricultural practices relying heavily on synthetic fertilizers (Boadi & Wittenberg, 2012; Beauchemin, 2009). The high carbon footprint associated with long-distance transportation, when factored in, could significantly increase the overall carbon footprint of intensive livestock production systems that rely heavily on commercial feeds (Benchaar et al., 2001). Therefore we wanted to find out the ability of desmodium to control weeds, support coffee production and provide livestock fodder.

Using scientific evidence to support the efficiency of desmodium

Increasing population and climate change continue to pose challenges to sustainable coffee production, from the need to increase incomes while adapting to the impacts of climate change. Most coffee farmers practice mixed crop-livestock production, and livestock fodder has been a major challenge among farmers, especially during dry weather. Intensive coffee production practices such as hand weeding have been seen to increase soil susceptibility erosion and lead to reduced yields. Our study focused on comparing the adoption of desmodium legume fodder cover crop as a weed control and climate-smart adaptation strategy while comparing it with hand weeding and herbicide usage in coffee production practices in Kenya. Using the completely randomized block design, we had three treatments of 9 x 9 meters (30×30 feet) blocks comprising hand weeding, herbicide usage, and adoption of desmodium legume fodder cover crop as the treatments. Our objective of the study was to compare the efficacy of weed control, coffee yields, and biomass yields among the treatments. Using ANOVA, there were considerably better coffee yields of 1.8 times better than herbicide treatment and 1.2 times better than hand weeding and biomass production from the desmodium legume fodder cover crop, indicating the advantage of adopting a cover crop. The reduction in the need for regular weeding and control of soil erosion could be among the major reasons that farmers should embrace the use of the desmodium legume cover crop as an advantage to climate-smart agriculture in times of climate change.

Study objectives and Study design

Our study at the University of Nairobi, Kabete coffee plantation aimed to compare the efficacy of different weed control methods, the impact on coffee yields, and desmodium biomass yields. The study comprised 3 treatments of hand weeding, herbicide treatment, and desmodium legume fodder cover crop intercropped with coffee. The experimental design adopted was the randomized complete block design for the treatments inside the coffee plantation with plots measuring 9 m x 9 m (30 x 30 ft) where already coffee bushes have been planted and have uniformity in growth. The coffee species named SL 14 have a spacing of 2.7 x 2.7 meters (8.9 x 8.9 ft) between bushes and rows.

Information regarding the setting up of the experiment and data collection

All the plots were hand weeded before any treatment was started for all the plots and the treatments were administered after 3 months, namely, hand weeding, herbicide treatment, and establishment of desmodium cover crop. The layout of the plot was on flat ground, and the treatments were replicated 3 times using the randomized complete block design to give an outcome of the following Block 1 (A, B, C), Block 2 (ACB), Block 3 (CBA),

Whereby

•  Desmodium legume cover crop between coffee
•  Manual weeding on the coffee rows as practiced by farmers
•  Herbicide (Glyphosate) weeding of the coffee rows

The study was carried out for 2 years between 2019 and 2020, and the data on weed diversity, the effectiveness of the treatment on weed control, and coffee yields were collected.

Data on weed diversity used the Shannon wiener weed diversity method where a rectangle of 1x 1 meter (3.3 x 3.3 ft) was used to uproot all the weeds and identify them, then dividing them into annuals, semi annuals, and perennials and thereafter evaluating which were the most dominant species.

Coffee harvesting was done periodically at the time of the harvest, whereby each bush yield was weighed differently while each treatment total was calculated independently. The coffee yields were based on the actual harvests per season per treatment and then divided over the number of bushes and yields compared.

Desmodium legume fodder biomass data were obtained by harvesting the entire plot area after every 4 months and assigning 1 square meter of the harvest, which was weighed and the weight of the biomass determined using the ‘t’t Mannetje (2000) biomass calculation method, then extrapolating per hectare.

Analyzing the data

Descriptive statistics were chosen for the evaluation of soil moisture content which was inputted into the Excel data sheet for all the corresponding recordings. The final data was then processed with GenStat 14.1 following the GenStat Procedure Library Release PL22.1.

All the individual emerged weeds at the stage of 20 cm were uprooted and grouped for identification for each subplot, with 1 m x 1 m (3.3 x 3.3 ft) frame assigned for each plot where weeds were present, especially for the hand-weeding section. The emerged uprooted weeds were then grouped into annual semi-annual, and perennials. The most common weeds that we observed with a population of more than 30 emerged plants attaining a height of 20 cm (7.9 inches) in the 1m x 1 m (3.3 x 3.3 ft) sampling subplots were Amaranthus spp (pigweed), Bidens pilosa (blackjack), Oxygonum sinuatum (Double Thorn), and Tagetes minuta (Mexican marigold) for the broad-leaved annual weeds. The perennial weeds observed with high occurrence frequency were Commelina benghalensis (Wondering Jew), Cynondon dactylon (Stargrass), Cyperus rotundus L. (Nut grass), Digitaria abyssinica (Couch grass) and Oxalis latifolia (Wood sorrel). The creeping habit of some of the perennial weeds makes them challenging once established. In contrast, the production of numerous seeds from the annuals makes their abundance a challenge to control, especially after the onset of the rainy season.

The experimental results

Weed data was collected when the weeds had reached the 20 cm stage for each subplot, where the 1m x 1m square frame was used to uproot all the weeds, which was followed by grouping for the weeds. This was done on the plots which had weeds. The uprooted weeds, after grouping, were then classified as either annuals, semi-annuals, or perennials with naming using the east African weed catalog for each species.

Weed diversity comparing the most dominant weed species identified as Amaranthus spp (pigweed) at 25 %, Bidens pilosa (blackjack) at 20 %, Oxygonum sinuatum (Double Thorn) 15 %, and Tagetes minuta (Mexican marigold) at 10 % for the broad-leaved annual weeds. Commelina benghalensis (Wondering Jew) 10 %, Cynondon dactylon (Stargrass) 5 %, Cyperus rotundus L. (Nut grass) 5 %, Digitaria abyssinica (Couch grass) 5 % and Oxalis latifolia (Wood sorrel) 3 % were among the most dominant perennial weeds identified.

The coffee yields were tabulated among the different treatments and compared to show if there was any significant difference in yields between the bushes and the different treatments. The coffee yields comparison indicated that where the desmodium cover crop had been established, the coffee yields were 1.8 times higher than herbicide treatment and 1.2 times higher than the hand weeding. The coffee berries maturation was more elaborate in the areas where the desmodium legume fodder cover crop was established and with less immature fruit abortions observed.

The desmodium legume fodder cover after establishment completely covered the soil and eliminated any opportunistic weeds from emerging. In the long-term, this could be attributed to the weed seed bank reduction, resulting in fewer weeds emerging. The desmodium legume fodder biomass was harvested every 4 months. A 1 x 1 m (3.3 x 3.3 ft) quadrant was used to extrapolate the yields per hectare using the method (‘t’t Mannetje, 2000) of measuring the biomass of grassland vegetation. This method indicated the great potential of harvesting desmodium in the spaces between coffee bushes showing the actual yields of 15 tons per hectare (6 tons/acre) that would be expected to be harvested per year with a lifespan of more than 7 years.

All the benefits when introducing desmodium to your coffee plantation

The ideal tropical conditions of warm weather, especially during the rainy seasons, make the growth of weeds to be a significant concern for coffee production since CRF (2003) studies indicated possibilities of yield losses amounting to more than 50% could be attributable to weed challenges (Daramola, 2020). The weeds identified by the CRF (2003) study indicated that among the most troublesome weeds are Amaranthus spp (pigweed), Bidens pilosa (blackjack), Commelina benghalensis (Wondering Jew), Cynondon dactylon (Stargrass), Cyperus rotundus L. (Nut grass), Digitaria abbisinica (Couch grass), Oxalis latifolia (Wood sorrel), Pennisetum clandestinum (Kikuyu grass) and Tagetes minuta.

Our study was able to correlate with the previous studies since the most dominant weed species, as identified according to their regularity of occurrence, closely corresponded to the previous studies (CRF, 2003). The weeds were emerging rapidly in areas where hand weeding had been done and could be attributed to the weed seed bank in the soil. Once the soils are turned, the seeds exposed to the sun derive the desired conditions to favor their germination. During the duration of our study, there was a need for hand weeding at least 4 times per year which could be attributed to a considerable cost for farmers in the coffee production process. The process of hand weeding loosened the soil predisposing it to agents of erosion, especially during heavy rain storms (Gachene et al., 1997; Gao et al., 2016).

The herbicide treatment was able to control the weeds by killing them within 2 weeks, while the emergence of other weeds was somewhat delayed and grew more slowly than in areas where hand weeding had been done. In terms of efficacy, many of the weeds were killed, which could be why glyphosate is popular among farmers. However, there is an increasing challenge of weed resistance with the regular use of glyphosate in weed control (Bain et al., 2017). Nevertheless, soil protection was removed, and thus the bare ground was subject to soil erosion when heavy rains were received (Aktar et al., 2009). Glyphosate has also been implicated in the survival and population of honey bees needed in coffee pollination since it affects the larval development of honey bees (Alyokhin et al., 2020; Vázquez et al., 2018a). Other ecosystem worries are related to findings on the overall soil impact from glyphosate that has adverse effects associated with below-ground interactions between earthworms and symbiotic mycorrhizal fungi (Zaller et al., 2015).

The desmodium seedlings emerged and competed with the weeds in the first 2 months, and careful uprooting of the competing weeds was done. Within four months, desmodium could fully establish, covering the entire ground where weeds had no chance of germinating since the conditions favorable for germination had been impacted by the desmodium cover crop.

The ability of the desmodium to provide extensive coverage on the soil was able to remove the need for further weed control since only the desmodium was able to creep under the coffee bushes, which were periodically harvested every 4 months to serve as fodder for livestock (Tolera & Abebe, 2007). The ability of the desmodium legume fodder cover crop to suppress the growth of the weeds contributed to farmers’ savings (Alvarez et al., 2008). The provision of the soil cover provided a positive benefit of controlling soil erosion since when there were incidences of heavy rainfall, there was no soil erosion observed since runoff was controlled by the already established desmodium cover on the soil surface (Tadesse et al, 2016).

There has been a concern about the long-term coffee monoculture impact on the soil which is suspected to alter soil chemical properties and microbial communities (Zhao et al., 2018). There are added benefits of legume fodder cover crops in the influence of the soil microbial diversity, which has been found to mitigate a decline in perennial agriculture such as coffee (Vukicevich et al., 2016). Coffee has been indicated to be facing major climate change impacts, and its sustainability is a key concern; there is a need for adaptive measures that increase farmers’ resilience (Gomes et al., 2020; Wagner et al., 2021). The coffee yields that were found in the coffee with the desmodium legume cover crop could be attributable to the benefits of nitrogen fixation, whereby legumes can increase the soil nitrogen content from the atmospheric nitrogen fixation from their roots through a symbiotic relationship with nitrogen-fixing bacteria (Mendonça et al., 2017; Andrews et al., 2011; Didier Snoeck et al., 2000).

Mitigation of methane emissions has been a common subject of discussion. Including legume fodder in the livestock diet that is high in tannin content has shown positive results in reducing enteric livestock methane emissions (Animut et al., 2008; Kelln et al, 2021). Comparative studies on the potential methane production between C3 legumes and C4 grasses have shown that regular inclusion of legume fodder has positive benefits in the reduction of enteric methane emissions from livestock (Archimède et al., 2011).

The adoption of desmodium legume fodder cover in smallholder cropping regimes, therefore, fits the economies of scaling up climate-smart agriculture where the land equivalent ratio has an advantage and contributes positively to adaption to climate change (Bergtold et al., 2019; Blanco‐Canqui & Ruis, 2020). Harvesting cover crops for livestock production provides the extra advantages that considerably increase the ecosystem services from desmodium legume fodder cover crop (Blanco‐Canqui et al., .2020). The already bleak predictions on the impacts of climate change on coffee production (Bunn et al., 2015) require urgent attention, including boosting farmers’ incomes (Craparo et al., 2015: DaMatta et al., 2018). Desmodium fodder legume cover crop should thus be a suited candidate in the search for coffee farmers’ solution to increasing climate resilience (Bracken et al., 2021; Ires, 2021). Since the climate change relationship with coffee has to be considered in farmers’ adaptation and mitigation, it is important for policymakers to make considerable efforts to address the farmers’ challenges (Camargo, 2010; Kaye & Quemada, 2017).

Conclusion on Desmodium compound benefits

In summary, desmodium should be embraced for its five 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 other 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 carbon sequestration potential 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.

The value Proposition for African coffee farmers

Desmodium should thus be scaled up in the cropping systems for the majority of the African coffee 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.

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