By Jasmine Thompson – 

Food security is increasingly being put under stress due to the rising population set to reach 9.8 billion by 2050 [1], with 2.37 billion people not having adequate access to food in 2020[2] this problem is certainly not going away. This leads to more land being converted into permanent field [3] and many farming practices either being changed or intensified to meet the rise in demand, like the increased use of slash and burn, which 7% of the global population now use [4]. Are et al., (2009) investigated to see the “effects of slash and burn on soil physical properties” [5].

Slash and burn in Madagascar. Image: Leonora Enking, CC BY-SA 2.0 Via Wikimedia commons

Slash and burn is a land clearing technique, where small scale farmers clear forests to establish pastures, to produce food and provide for their families [6]. Slash and Burn clears bush debris and helps to reduce weed infestation, which would normally ‘compete with crops for sunlight water and nutrients’ [5], which would reduce crop efficiency [5,6]. However, it can also leave the soil exposed to rainfall, causing nutrient loss, deforestation and soil erosion as the soil pores get clogged leading to more surface run off [5,4].

Slash and burn is used by 90% of farmers in South West Nigeria [5].  Nigeria is a rapidly growing country with a population of over 150 million which is expected to double by 2050 [7]. Are et al., (2009) investigated the effects of slash and burn on soil properties at 0-0.05m and 0.05–0.10 m in Southwest Nigeria [5]. They did this by slashing the bush vegetation on 2 sites using cutlasses and axes and left it to dry for 3 weeks before calculating the biomass weight and taking preburn soil and worm cast samples. They burned the area, and within 2 weeks took post burn samples and used soil cores to calculate water retention [5].

They found that the texture of the soil and worm casts where not affected but the macropores at 0.05 – 0.1m decreased by 17% and there was a decrease in infiltration due to ash deposits blocking the pores [5]. Soil erosion can alter soil nutrients affecting agricultural productivity and food security, as crop yields dramatically drop when erosion occurs at 0.1m-0.15m [8]. They also found using slash and burn as part of traditional farming practices with long fallow periods had little effect on crops sustainability as lost minerals were quickly replenished [5].

To conclude, if demographic pressures continue to put a strain on these farming practices, production may have to be intensified making it unsustainable due to effects on tillage and the soil may not be able to rejuvenate once degraded [5].  Therefore, to maintain crop efficiency and increase food security, slash and burn must not be intensified due to it having the potential to cause excess soil degradation [5].

References and further reading:

1 United Nations (2017) World population projected to reach 9.8 billion in 2050, and 11.2 billion in 2100. https://www.un.org/development/desa/en/news/population/world-population-prospects-2017.html [26.11.21]

2 Food and Agriculture organization of the United Nations (2021) The State of Food Security and Nutrition in the World. https://www.fao.org/3/cb4474en/cb4474en.pdf [26.11.21]

3 van Vilet, N., Adams, C., Vieira, I.C.G. and Mertz, O. (2013) “Slash and Burn” and “Shifting” Cultivation Systems in Forest Agriculture Frontiers from the Brazilian Amazon. Society & Nature resources 26, 1454-1467.

4 Stief, C. (2019) Slash and Burn Agriculture Explained. https://www.thoughtco.com/slash-and-burn-agriculture-p2-1435798 [29.11.21]

5 Are, K., Oluwatosin, G., Adeyolanu, O. and Oke, A. (2009) Slash and burn effect on soil quality of an Alfisol: Soil physical properties.  Soil & Tillage research, 103, 4-10.

6 Palm, C., Vost, S. and Sanchez, P. (2005) Slash-and-Burn Agriculture The Search for Alternatives. New York: Columbia University Press

7 Pate, M. and Schoppin, J. (2012) Africa’s Growing Giant – Population Dynamics in Nigeria. In: Growth, H. and Sousa-Poza, A. (eds.) Population Dynamics in Muslim Countries, Berlin: Springer, pp.211-224.

8 Zhang, L., Huang, Y., Rong, L., Duan, X., Zhang, R., Li, Y. and Guan, J. (2021) Effect of soil erosion depth on crop yield based on topsoil removal method: a meta‑analysis. Agronomy for sustainable development 41, 1-13.