Chapter 5.16

5.16 -The Climate Change Mitigation Opportunities of Mustard Leafy Greens for Smallholder Farmers

Sarah McGill, University of Guelph, Canada

Suggested citation for this chapter.

McGill,S. (2022) The Climate Change Mitigation Opportunities of Mustard Leafy Greens for Smallholder Farmers, In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Climate Change Implications for Smallholder Farms

Smallholder farmers, working on 10 hectares or less, account for around 80% of the farmland usage in Sub-Saharan Africa and Asia (FAO, 2013). The majority of smallholder farmers in these areas are subsistence farmers, producing only enough food to feed their families (FAO, 2013). The negative impacts of climate change can have drastic impacts on these farmers. Smallholder farmers are more susceptible to the impacts of climate change due to limited adaptive capacity and increased vulnerability, coupled with land degradation issues (Makate et al., 2017). Studies have shown that sustainable agriculture practices and increasing adaptability to climate variability can lessen the consequences that climate change can have on smallholder farmers (Makate et al., 2017).

Introduction to Mustard Leafy Green Crops

Crops of the Brassicaceae, or mustard family, that are commonly cultivated include garlic mustard (Alliaria petiolata), white mustard (Brassica alba), Ethiopian mustard (B. carinata), Asian or brown mustard (B. juncea), oilseed rape/canola (B. napus), black mustard (B. nigra), yellow mustard (Sinapis alba), rapeseed (B. rapa), white ball mustard (Calepina irregularis), ball mustard (Neslia paniculata), treacle mustard (Erysimum repandum), hedge mustard (Sisymbrium officinale), Asian hedge mustard (S. orientale), and smooth mustard (S. erysimoides) (Rahman et al., 2018). They are widely grown in Africa and India, where it is called “sarson da saag”. It is often grown as a leafy plant in Sub-Saharan Africa, and oilseed production in Africa is largely limited to Ethiopia (Ojiewo et al., 2013). The leafy tops are then harvested by farmers to be sold to local markets or for food consumption, typically boiled and eaten with other food or saved for periods of fasting (Ojiewo et al., 2013).

Growing Mustard Leafy Greens

Planting mustard greens is a relatively easy process that can be done using seeds or seedlings (Rhoades, 2020). Planting of mustard vegetable crops can be done at any time in the year, though they prefer cooler temperatures and will have higher harvest success outside of summer months. Mustard seeds are typically planted one to two weeks after heavy rainfall (Ojiewo et al., 2013). When planting with seeds, they just need to be barely under the soil and should be a minimum of half an inch apart (Rhoades, 2020).

Mustard crops are estimated to tolerate annual precipitation of 500 to 4200 mm, annual temperatures of 6 to 27°C, and soil pH of 4.3 to 8.3 (Shekhawat et al., 2012). In a laboratory study comparing drought tolerance of different Brassica species, oilseed rape was classified as the most drought tolerant of the species studied, with brown mustard also showing high tolerance to drought stress (Ashraf & Mehmood, 1990). Certain agronomic practices that can be applied to make mustard leafy green crops more drought tolerant include utilizing drip irrigation systems, plastic mulching, patty straw mulching, and rice husk mulching, allowing for the possibility of raising yields by 65% (Tiwari et al., 2003).

Mustard seeds can be dried and stored for long periods of time; heat drying before storage may be necessary to drop moisture levels below 9% but air temperature should not reach above 65 degrees Celsius during this process (Damian, 2014). Dried seeds can be stored for up to three years, best stored in an air-tight container, away from sunlight, and in a cool, dry location (Sukprakam et al., 2006). Prepared mustard leafy greens can be stored for up to six months in a refrigerator or cool, dry place. Washing seeds in chlorinated water prior to cooling can slow the decay rate of seeds (Kitinoja & Kader, 2002). Seeds can be obtained from the World Vegetable Centre (AVRDC), with over one hundred mustard seeds available, representing different species and varieties. Some accession numbers for mustard crops on the AVRDC are B01121, B01002, and B01019 for Asian or brown mustard, B01090, B01092, and B01010 for rapeseed. Mustard crop seeds can also be obtained from distributors across India, such as National Seeds Corporation Limited, and Seeds for Africa in Africa.

Nutritional Benefits

Mustard leafy green crops are argued to be some of the most nutritious leafy green vegetables available in the winter seasons (Usha et al., 2020). Mustard green crops provide a significant amount of iron, vitamin A, and folate (USDA, 2020). Per 100 grams of mustard greens, there are approximately 1.46 milligrams of iron, 10,500 international units of vitamin A, and 187 micrograms of folate (USDA, 2020). They are also commonly used as important oilseed crops around the world, providing health plant-derived polyunsaturated fatty oil (Rahman et al., 2018). The dietary intake of fats for African meals tends to be low and mustard oilseed crops may be a possible solution (FAO, 1997). Oilseed production provides a rich source of fat, protein, and fibre, as well as a moderate source of vitamins such as vitamin B (FAO, 1997). Mustard seeds contain 25-47% fatty oil depending on growing conditions, and 25-45% protein (Ojiewo et al., 2013). Oilseed production from these mustard crops can also be used to produce cooking oil, which effectively reduces cooking time and, therefore, firewood requirements.

Resilience to Climate Change Impacts

Mustard crops are beneficial to use as a rotation crop during winter months as they have been shown to amend soil and act as a biofumigant against soil-borne disease and pests, reduce erosion, balance nutrient losses, and generate income or a food source for farmers during these typically less profitable months (Hagos et al., 2020). Different species of Brassicaceae crops offer unique resiliency and adaptability qualities that can be strategically used to counteract consequences of climate change in poorer regions. For example, Ethiopian mustard (Brassica carinata A. Braun) has many agricultural benefits to offer smallholder farmers affected by climate change. Ethiopian mustard can withstand unfavourable environmental conditions and grow in areas with low to no other cropping areas (Hagos et al., 2020). The ability of Ethiopian mustard to produce high yields with relatively low production costs even under high biotic and abiotic stress makes it a considerable option to increase yields in semi-arid and arid climates of the world (Hagos et al., 2020). Ethiopian mustard is also very useful for crop rotations or intercropping with other food crops, such as wheat, chickpea, sorghum, and barley (Hagos et al., 2020). Ethiopian mustard has also been shown to have the most potential for phytoremediation, ranks with rapeseed for highest salinity tolerance, as well as having a high tolerance index for soils contaminated with nickel (Ni), lead (Pb), manganese (Mn) and cadmium (Cd) (Hagos et al., 2020). It has been shown that intercropping mustard greens can aid in pest management of crop fields due to its high concentration of glucosinolates, a natural biofumigant, that can be incorporated into the soil (Henderson et al., 2009). The use of these biofumigants has the potential to reduce the requirement of synthetic fumigants (Henderson et al., 2009). Mustard green crops have also been shown to be successful crops for weed control, improving crop yields through weed suppression (Al-Khatib et al., 1997). A study looking at green pea yields revealed that planting mustard green crops in advance to the green peas lead to 30% weed suppression and higher yields compared to green pea crops grown without mustard green crops (Al-Khatib et al., 1997).

Critical Analysis

Mustard greens can be profitable crops for smallholder farmers if markets are identified and necessary labour is available (Sanders, 2015). A study in Arkansas, United States, claimed an average yield of mustard crops to be between 250-300 boxes per acre (one box equals 24 one-pound bundles of greens), creating an estimated net income of approximately 1,000 - $1,500 USD per acre (Sanders, 2015). These estimations are largely dependent on having access to the labour required and to markets. Crops like Ethiopian mustard have lower yields on average than other commonly grown crops, but profit is still achieved due to high product prices (Everaarts et al., 2015). From a study looking at the profitability of crops grown in Tanzania, the average price of one kilogram of Ethiopian mustard was found to be 820 Tanzanian shillings, equal to 46 Canadian cents, significantly higher than the average crop product price of 541 Tanzanian shillings per kilogram (Everaarts et al., 2015). For mustard seed production, highest yields were found to occur under minimal tillage practices (i.e. no tillage: seeds sown along trench hoe) and optimally intercropped between maize and cowpea crops (Chan & Fantle-Lepczyk, 2015). This practice produced 945 kilograms of mustard seeds per hectare of farmland, accompanied with 27.4% profits (Chan & Fantle-Lepczyk, 2015). However, to achieve this optimal production strategy of mustard seed production, high labour efforts were required in order to sow and harvest the cowpea, maize, and mustard seed crops simultaneously, requiring around 440 days of labour per hectare of land (Chan & Fantle-Lepczyk, 2015). High monetary gains and valuable market prices for these crops are a prime driver for adoption of this method, if possible to do so (Chan & Fantle-Lepczyk, 2015).

Post-harvest economic gain from many species of mustard seeds can be achieved through the exporting of seeds for the creation of herbs, spices or mustard flour to be added to food. Yellow mustard seed, commonly used in North America to produce condiments, can be sold or consumed as a binding agent, protein extender, and spice to be used in prepared meals. Furthermore, mustard spices have higher antimicrobial, insecticidal, and nematicidal properties, commonly used in granaries to prevent insect invasions, or applied to crops for organic control of pests (Sastry, 2013).

It is also worth noting that while the glucosinolate fumigants present in mustard crops have been known to act as successful biocontrol agents of pests, the non-target implications of this biofumigant remains unclear (Henderson et al., 2009). It is possible that the biofumigants from mustard crops may result in interference with other biocontrol agents when used in conjunction to each other (Henderson et al., 2009).

Finally, mustard crops can be affected by aphid pests, white rust, downy mildew and stem rot disease, occurrences of cold spells, fog, and intermittent rains during crop growth increasing this possibility (Boomiraj et al., 2010). Fungicide treatments have been shown to be successful in the management of diseases for oilseed crops, improving yields by 0.5 t ha-1 in Scotland (Boomiraj et al., 2010).

Helpful resources to get started

Brassica Information Kit - http://era.daf.qld.gov.au/id/eprint/1965/4/brassica-grower4.pdf

Harvesting, Using and Preserving Wild Mustard (Youtube) - https://www.youtube.com/watch?v=mYDPP7Dslok&ab_channel=MagicalHoof

How to Grow and Harvest Mustard Seeds (Youtube) - https://www.youtube.com/watch?v=TZCRZVvlsGo&ab_channel=JohnSavesEnergy

Mustard Production Manual - https://saskmustard.com/production-manual/index.html

National Seeds Corporation Limited (India) - www.indiaseeds.com

Seeds for Africa - www.seedsforafrica.co.za

The Food and Agriculture Organization of the United Nations (FAO) - www.fao.org/home/en/ Family farming database - www.fao.org/family-farming/data-sources/en/

U.S. Department of Agriculture (USDA) Nutritional Database - https://fdc.nal.usda.gov/ USDA Food Surveys Research Group - www.ars.usda.gov/northeast-area/beltsville-md-bhnrc/beltsville-human-nutrition-research -center/food-surveys-research-group/

The World Vegetable Centre (AVRDC) - https://avrdc.org/ Leafy brassica improved seed lines - https://avrdc.org/seed/improved-lines/leafy-brassicas/ The AVRDC Vegetable Genetic Resources Information System (AVGRIS) - http://seed.worldveg.org/

References

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