Chapter 4.32
4.32 - Sesbania rostrata as Green Manure for Smallholder Famers
Kaitlyn O’Donnell, University of Guelph, Canada
Figure 1. Sesbania rostrata (Taken by A, Rao (n.d.), retrieved from plantnet.org 2024)
Suggested citation for this chapter.
O’Donnell,K. (2022) Sesbania rostrata as Green Manure for Smallholder Famers . In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
Introduction
Sesbania rostrata (Figures 1 & 2) is a leguminous, woody perennial that can grow up to 3 m in height (ACIAR 2020). It is found in Asia where it is cultivated/naturalized and is native to many regions of Africa (Botswana, Central African Republic, Chad, Democratic Republic of the Congo, Ethiopia, Mali, Malawi, Mauritania, Namibia, Niger, Nigeria, Senegal, Sudan, Tanzania, Zimbabwe, Madagascar) (ACIAR 2020). This species has a critical photoperiod of 12-12.5 hours (World Agroforestry 2009) and excels in temperatures over 25 ºC (Rice Knowledge Bank, n.d.). Sesbania rostrata is tolerant to many climates – good in upland and lowland areas, and tolerant to salt, and able to grow in saline–alkaline soils with an optimal pH of 5.5 (ACIAR 2020). This plant can also live in soils with a pH as low as 4.3 but suffers from losses in nitrogen fixation capacity (ACIAR 2020). It is found in regions experiencing 600 – 1,000 mm of rainfall but 20 kg/ha of phosphorus fertilizer is suggested where the soil is not as fertile (ACIAR 2020). In this essay, I examine Sesbania rostrata as a green manure intercrop that provides essential nutrients to the soil.
Benefits of Green Manuring Practices
Many early civilizations, like the Roman Empire, used leguminous crops to improve soil fertility (Fageria, 2007). Inside legume roots, bacteria known as rhizobia convert gas in the atmosphere into usable nitrogen fertilizer for plants, a process called nitrogen fixation (Fageria, 2007). Thus, out of all plants used for green manuring, legumes are favoured because of their ability to fix atmospheric nitrogen (N) and replenish lost N in the soil. In fact, 40 % of the world’s fixed nitrogen comes from legume-rhizobia symbiosis (Fageria, 2007). Moreover, green manure adoption into a crop rotation interrupts cycles of disease, insect or weed infestations which improves the yield and quality of the food crop of interest (Crookstoon et al., 1991).
How Plant Sesbania rostrata is a Useful Green Manure for Small-Scale Farmers
S. rostrata is useful for fertilizing crops of interest as an intercrop. Research shows how this species can fix atmospheric nitrogen via nodules on the stem and roots, which has the capacity to outperform other leguminous intercrop species restricted to nodules only on the roots (Fageria 2007). This species has been observed to promote a higher yield of rice in India, Thailand, Nigeria, and Senegal (Fageria, 2007). Mature Sesbania rostrata can create enough biomass where the embedded nitrogen can provide 50-100 % of that required by rice itself (Simarmata et al., 2023). When 2 tons of Sesbania rostrata enriched manure was integrated into the soil per hectare, the rice yield increase was comparable to the use of 0.066 tons of nitrogen per hectare (Prayoga et al., 2020). And, with long-term use, this species integrated into the soil (5 tons/ha) could increase rice productivity by 9-11 % in comparison to when just chemical fertilizers were used (Naher et al., 2020).
Climate change is accentuating drought and rainfall events. These events leave soils infertile and nutrient deficient (Simarmata et al., 2023). The use of inorganic fertilizers is further contributing to these climate events by releasing greenhouse gases such as nitrous oxide, and disrupting aquatic systems by pumping nitrogen into waters, thus leading to eutrophication (Simarmata et al., 2023). To avoid crop loss and environmental damage, it is suggested that biofertilizers [natural fertilizers] could be used to maintain soil integrity through these adverse climate conditions (Simarmata et al., 2023). In the light of food uncertainty with climate change, food security will increase with the energy conserved by using green manure. More specifically, due to the ability of Sesbania rostrata to provide at least 50% of the nitrogen needed by rice, global energy will be conserved (Naher et al., 2020).
This green manuring practice will also decrease the need for pesticides and herbicides because of the ability for Sesbania rostrata to outcompete weeds and limit pathogens in the soil (Naher et al., 2020). In addition, microbial diversity is increased, ensuring healthy and fertile soil (Naher et al., 2020).
In addition, if a farmer is experiencing eroding soils, leguminous groundcover crops can provide soil stability (Fageria, 2007). For example, Sesbania as green manure showed the least amount of soil loss in comparison to maize and soybean under different tillage practices, where 1 kg of seeds were sown in a 35 m^2 plot (Sheikh et al., 2023). Moreover, the deep roots of this woody plant encourages the nutrients to penetrate deep within the soil (Choudhury and Kennedy, 2004). S. rostrata has more than one use to a small-scale farmer because the leaves can be collected and used as animal feed for sheep goats, and camels (ACIAR 2020). The nutritional value of Sesbania to animals includes 54.6% neutral detergent fiber (NDF) and 39.2 % acid detergent fiber (ADF) (ACIAR, 2020). ADF refers to the parts of the plant not easily digested, where NDF refers to the parts of the plant that the animal can easily use for energy (Crop Watch, 2023). Therefore, Sesbania rostrata provides a unique opportunity for the management of foraging since the balance of NDF provides energy while the ADF potentially prevents the plant from being overgrazed. The whole plant has a crude protein level of 24 % (ACIAR 2020) which promotes milk production (Mutsvangwa, 2017).
How to use as an intercrop and biofertilizer
It is cultivated/naturalized in Asia but is native to many regions of Africa as noted above (ACIAR 2020). It can be propagated from 30 cm-long cuttings by incorporating them into the soil or from seed (ACIAR, 2020). If propagating from seed, the hard seed coating must be removed for efficient growth by either: physically scraping off the seed coat, boiling in water for 3 seconds and/or by soaking them for 15 minutes in sulfuric acid and rinsing them with water afterwards (ACIAR, 2020). In the northern hemisphere, the seeds should be sown (20-40 kg/ha) between February and May for green manure purposes (ACIAR, 2020). To use it as a biofertilizer, at 45-60 days after planting, the plant should be incorporated into the soil. This can be done in several ways. Firstly, the farmer can chop the plant up into smaller pieces for easier ploughing. Another way is to have an animal-drawn wooden plank to run over the S. rostrata before ploughing (Rice Knowledge Bank, n.d.).
Critical Analysis – Drawbacks
Because Sesbania rostrata is a perennial woody tree, there are quite intensive labour requirements to incorporate its biomass into the soil. It is suggested that a hydrotiller is best suited for this type of ploughing (Rice Knowledge Bank, n.d.); however it may be difficult to access such equipment in remote locations in addition to financial constraints. Furthermore, seeds are not usually available in large quantities for purchase (UC Davis, 2021). The leaves are also seen to be a poor source of animal feed for cattle and carabao (ACIAR, 2020).
Additionally, green manuring cannot single-handedly provide enough nutrients to sustain crops, and therefore it is suggested to be used alongside chemical fertilizers (Fageria, 2007). This can be seen as a partial benefit to farmers as the can save money due to the lesser use of costly synthetic fertilizers. This green manuring technique can be seen as financially manageable since farmers can grow their own Sesbania rostrata (Simarmata et al., 2023). However, urea-nitrogen fertilizers are widely available and subsidized compared to green manuring practices in certain regions (Naher et al., 2020). As a complete replacement for urea, it can reduce rice crop yields (even though it still maintains soil fertility and the sustainability of the landscape) (Choudhury and Kennedy, 2004). Moreover, there is evidence pointing to impaired wheat growth when using poultry manure + vermicompost + Sesbania rostrata as a green manure (Hossain et al., 2020).
Practical Links & Resources to get Started
For additional information, especially about seeds, please consult the Sesbania Cover Crop Database (Sustainable Agriculture Research & Education Program at UC Davis): https://sarep.ucdavis.edu/covercrop/sesbania
To obtain seeds (Source: Echo Community):
- AgroForester, P.O. Box 428, Holualoa, HI 96725, USA, e-mail: seeds@agroforester.com
- Soil Productivity Research Laboratory, Private Bag 3757, Marondera, Zimbabwe.
- Echo also has free samples available for some farmers: https://www.echocommunity.org/en/resources/4cf334e5-9f93-4a3c-ae7a-3c4cdadd7c26
YouTube video
- Intercrop example and demonstration: https://youtu.be/z7N3ElPr1I0?si=pzVKmThtgOaSu7Xg
References
1. ACIAR (2020) Sesbania rostrata. Australian Centre for International Agricultural Research. Tropicalforages.info. Retrieved March 19, 2024, from https://www.tropicalforages.info/pdf/sesbania_rostrata.pdf
2. Choudhury, A. T. M. A., & Kennedy, I. R. (2004). Prospects and potentials for systems of biological nitrogen fixation in sustainable rice production. Biology and Fertility of Soils, 39(4), 219–227. https://doi.org/10.1007/s00374-003-0706-2
3. Crop Watch. (2023). Pasture and forage minute: Understanding ADF and NDF, hay quality. https://cropwatch.unl.edu/2023/pasture-and-forage-minute-understanding-adf-and-ndf-hay-quality-after-calving#:~:text=ADF%2C%20on%20the%20other%20hand,is%20available%20to%20the%20animal
4. ECHOcommunity (n.d.) Sesbania rostrata: A Green Manure Production System for Rice. ECHOcommunity. https://www.echocommunity.org/en/resources/4cf334e5-9f93-4a3c-ae7a-3c4cdadd7c26
5. Fageria, N. K. (2007). Green manuring in crop production. Journal of Plant Nutrition, 30(5), 691-719.
6. Hossain, M. A., Hasan, M. M., Hossain, M. B., & Islam, S. M. (2021). Effects of probiotic and organic fertilizers as soil amendments on the growth and yield of wheat. Applied Biological Research, 23(2), 157–164.
7. iNaturalist (n.d.). Sesbania rostrata. https://www.inaturalist.org/taxa/501103-Sesbania-rostrata
8. IRRI (n.d.) Sesbania - IRRI Rice Knowledge Bank. http://www.knowledgebank.irri.org/training/fact-sheets/nutrient-management/item/sesbania
9. Mutsvangwa, T. & Department of Animal and Poultry Science, University of Saskatchewan. (2017). The true value of feeding canola meal. In WCDS Advances in Dairy Technology (Vol. 29, pp. 109–221). https://wcds.ualberta.ca/wcds/wp-content/uploads/sites/57/2018/05/p-109-124-Mutsvangwa.pdf
10. Naher, U. A., Choudhury, A. T., Biswas, J. C., Panhwar, Q. A., & Kennedy, I. R. (2020). Prospects of using leguminous green manuring crop Sesbania rostrata for supplementing fertilizer nitrogen in rice production and control of environmental pollution. Journal of Plant Nutrition, 43(2), 285-296.
11. Prayoga, M. K., Yuwariah, Y., Simarmata, T., Setiawati, M. R., Stoeber, S., & Adinata, K. (2020). Is Green Manure (Azolla pinnata and Sesbania rostrata) a Climate-Resilient Strategy for Rice Farming? In Climate change management (Berlin. Print) (pp. 911 924). https://doi.org/10.1007/978-3-030-37425-9_46
12. Rao, A. (n.d.). Sesbania rostrata Bremek. & Oberm. (World flora). PlantNet. https://identify.plantnet.org/k-world-flora/species/Sesbania%20rostrata%20Bremek.%20&%20Oberm./data
13. Sheikh, A., Hassan, J., Ijaz, S. S., Zaman, A., Alam, T., Ali, S., ... & Khan, J. (2023). Exploring Optimum Management Practices in Rainfed Areas to Reduce Soil erosion and Nutrient Losses. Malaysian Journal of Soil Science, 27, 164-178.
14. Simarmata, T., Prayoga, M. K., Setiawati, M. R., Adinata, K., & Stӧber, S. (2023). Environmentally friendly bioameliorant to increase soil fertility and rice (Oryza sativa) production. Open Agriculture, 8(1), 20220185
15. World Agroforestry (n.d.) Agroforestree Species profile. https://apps.worldagroforestry.org/treedb2/speciesprofile.php?Spid=18097