Mulch

Seaweed mulch for fertilizer” by Rob n Rae Cornelius CC BY-NC-SA 2.0 via Flickr

Mulch is a layer of debris, usually organic carbon-rich material applied to the surface of the soil. Its main purpose is to conserve soil moisture, improve soil fertility through organic matter and increased microbiology, reduce weed growth, and to enhance the visual appearance of a garden. Organic mulches (such as wood chips, straw, leaves, grass clippings, and seaweed) decompose over time and add organic matter to the soil (Bogunović & Filipović, 2023).

In sustainable agriculture practices like permaculture, conservation agriculture and agroforestry plants that improve soil are sometimes considered “living mulches” (Farooq & Siddique, 2015; Feary, 2011). 

Increased organic matter in soil improves soil structure and microbial activity, therefore increasing fertility, water infiltration and retention. Keeping soil covered (as it would be in a natural environment) reduces erosion caused by wind and water, and provides an insulating layer to moderate temperature fluctuations in both hot and cooler climates  (Bogunović & Filipović, 2023). All these factors can influence the health of soil, and therefore plant growth.

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Name of NbS

Mulch

Type of NbS

  • Combination
  • Ecosystem restoration
  • Ecosystem Protection

Location

  • Urban
  • Peri-urban
  • Rural

Mulch can be used anywhere where appropriate to cover and improve soil, usually in gardens or agricultural settings.

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Conservation agriculture entails no tillage, crop residue retention as mulch, and crop rotations.” Photo by Christian Thierfelder CC BY-NC-SA 2.0 via Flickr

Relationship to Indigenous knowledge

Mulch as an intentional technique might be considered a recent occurrence related to modern agricultural practices that can afford high-energy imported materials. However, there are examples of mulch use in prehistoric Indigenous communities in Te Moananui Oceania to improve soils for agricultural purposes (Kuhlken, 2002; Ladefoged et al., 2010). More recently, mulching occurs in Indigenous agriculture and agricultural practices, where organic material is recycled to improve the often poor fertility of soils in many parts of Te Moananui Oceania (Thaman et al., 2006). 

Climate change benefits
  • Changes in rainfall
  • Desertification
  • Drought
  • Increased pests or spread of weeds
  • Increased temperatures
  • Loss of other ecosystem services
  • Reduced soil quality
  • Reduced water quality
  • Wildfire

Use of mulch can provide several benefits in the context of climate change (Bogunović & Filipović, 2023). These include halting and reversing land degradation, by improving soil structure and organic matter, mulch can prevent the process of desertification. 

In the context of drought, mulch conserves water content of the soil by reducing evaporation and regulating soil temperature. In post-fire land restoration, mulch can stabilise degraded soil and improve the recovery of vegetation (Wittenberg & Shtober-Zisu, 2023). By decreasing the impact of rainfall and the overland flow of water on the soil, mulch can prevent run-off that causes erosion and water-quality issues. 

Mulching is a form of nutrient cycling also, returning biomass to the soil increases soil organic matter and carbon levels, improves soil structure and boosts soil microbe activity, all of which improve soil quality (Bogunović & Filipović, 2023). Overall mulch supports ecosystem and agricultural resilience against climate change.

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Societal / socio-cultural benefits
  • Climate change adapatation
  • Food security and quality

Mulch aids climate change adaptation by improving agricultural outcomes. By moderating soil moisture and temperature, through reduced evaporation, increased infiltration and the insulating effect of mulch on the soil surface, the increasingly extreme climatic conditions occurring through climate change can be adapted to (Bogunović & Filipović, 2023; Manu et al., 2018). This adaption improves the resilience of food-growing agriculture. Alongside adaption, mulch improves food quality by contributing to increased soil fertility and therefore agricultural productivity. 

Outside of these benefits, mulch has aesthetic value in ornamental gardens, such as those in public urban landscapes.

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Ecological and biodiversity benefits
  • Decomposition
  • Disturbance prevention
  • Nutrient cycling
  • Soil building

As the organic material (like wood chips, straw, leaves, and seaweed) used for mulches break down, they increase soil organic matter, which is a key determinant of overall soil health (Bogunović & Filipović, 2023). The slow decomposition of mulch provides a continuous supply of nutrients to both soil microorganisms and plants. These processes create closed nutrient cycles for growers in Te Moananui Oceania. The ability of mulch to mitigate soil erosion reduces runoff and the loss of precious fertile soils (Thaman et al., 2006; Wittenberg & Shtober-Zisu, 2023).

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Technical requirements

Material characteristics are important when selecting a material for mulch, as not all mulches contain the same nutrients. A key consideration is the carbon-to-nitrogen ratio of a mulch material, as high carbon mulch materials may immobilise nitrogen in the soil, affecting plant growth and health. The use of mulch can vary depending on environmental conditions, especially considering the desired outcome. In an arid climate mulch will be crucial for conserving soil moisture, and in a wet climate, mulch might be instead important for weed control. Overall, mulches can be used in several ways depending on specific environmental circumstances.

Issues and Barriers

In some parts of Te Moananui Oceania, especially in small island nations, organic material suitable for mulching may be limited (Feary, 2011). Geographic isolation also means that imported mulches are unlikely to be viable. Decomposition rates can be high in warm, humid conditions, meaning mulch must be maintained more frequently. Additionally, traditional farming methods that do not employ mulch may mean that some people are hesitant to adopt new practices in Te Moananui Oceania (Thaman et al., 2006).

Opportunities

Te Moananui Oceania faces significant challenges relating to soil, especially erosion, salination, and loss of organic matter. The key opportunity provided by mulch is soil health and organic matter being improved with mulching practices. As the effects of climate change increase in severity and variability, making agriculture more resilient provides the people of Te Moananui Oceania with greater food security. Mulch as a nature-based solution aligns well with sustainable land management and indeed Indigenous land management practices.

Financial case

Mulch can increase agricultural productivity, through better nutrient cycling, enhanced soil fertility and therefore potentially improved yields. Mulch can also reduce the need for other costly inputs like fertilisers and irrigation in conventional agriculture. By suppressing weed growth, labour costs and the need for other management measures are reduced. Mulch improves long-term soil health and productivity outcomes, preventing land degradation. All of these factors have financial implications, especially for agriculture and food security.

References
  • Bogunović, I., & Filipović, V. (2023). Mulch as a nature-based solution to halt and reverse land degradation in agricultural areas. Current Opinion in Environmental Science & Health, 34, 100488. https://doi.org/10.1016/j.coesh.2023.100488
  • Farooq, M., & Siddique, K.H.M. (2015). Conservation Agriculture: Concepts, Brief History, and Impacts on Agricultural Systems. In M. Farooq & K. H. M. Siddique (Eds.), Conservation Agriculture (pp. 3–17). Springer International Publishing. https://doi.org/10.1007/978-3-319-11620-4_1
  • Feary, A. (2011). Restoring the Soils of Nauru: Plants as Tools for Ecological Recovery [Open Access Te Herenga Waka-Victoria University of Wellington]. https://doi.org/10.26686/wgtn.16992997
  • Kuhlken, R. (2002). Intensive Agricultural Landscapes of Oceania. Journal of Cultural Geography, 19(2), 161–195. https://doi.org/10.1080/08873630209478292
  • Ladefoged, T.N., Stevenson, C.M., Haoa, S., Mulrooney, M., Puleston, C., Vitousek, P.M., & Chadwick, O. A. (2010). Soil nutrient analysis of Rapa Nui gardening. Archaeology in Oceania, 45(2), 80–85. https://doi.org/10.1002/j.1834-4453.2010.tb00082.x
  • Manu, V., Whitbread, A., & Blair, G. (2018). Effects of vegetative mulches on growth of indigenous crops in the Kingdom of Tonga. Soil Use and Management, 34(1), 147–153. https://doi.org/10.1111/sum.12398
  • Thaman, R.R., Elevitch, C.R., & Kennedy, J. (2006). Urban and homegarden agroforestry in the Pacific islands: Current status and future prospects. In Tropical Homegardens (Vol. 3, pp. 25–41). Springer Dordrecht. https://doi.org/10.1007/978-1-4020-4948-4_3
  • Wittenberg, L., & Shtober-Zisu, N. (2023). Restoring fire-affected soils: The potential of nature-based solutions. Current Opinion in Environmental Science & Health, 36, 100520. https://doi.org/10.1016/j.coesh.2023.100520