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World soil day – Agroforestry can help to reverse the trend of global soil degradation

Published on December 5, 2018 | Author: Linus Karlsson
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Soils are the foundation of food production and essential for groundwater quality. Soils store carbon and currently hold more carbon than all aboveground vegetation, regulating emissions of greenhouse gases. Soils are also hosting an immense diversity of organisms that provide key ecosystems services. 

One third of the global soils are already degraded!

With population increase, economic development and an increasing demand of biofuels, additional pressure will be put on the world’s soils. But already today human pressure on soils is approaching a critical limit. Furthermore a significant part of the expected population growth will take place in regions with poor and unproductive soils, which will further compromise food security for vulnerable farmers.

In our publication Scaling up Agroforestry: Potential, Challenges and Barriers, we show that farmers practising agroforestry can conserve the soil while increasing yields primarily through four different mechanisms:

  1. Agroforestry increases nitrogen content in the soil

Many tree species planted in agroforestry systems capture nitrogen from the atmosphere and store it in the biomass. When the leaves are shed and decompose nitrogen is made available for crops. Trees can also improve nutrient cycling in the soil by using nutrients in deep soil layers and transport these to the soil surface. The effect of agroforestry on the soil phosphorus content is though limited. The improved cycling of nutrients that trees bring can provide some of the phosphorous requirements in an agroforestry system but not all to sustain high yields. Soil fertility where agroforestry is practiced could therefore often be improve by adding inorganic rock phosphate and improve recirculation of organic phosphorous.

  1. Agroforestry protects soils by reducing erosion

Erosion is a major problem in tropical regions and is mainly caused by heavy rainfall on unprotected land. Apart from reducing soil fertility, erosion causes eutrophication in aquatic environments where the soil ends up. Conservation strategies, such as hedgerows, intercropping and mulching, can reduce erosion with up to 90%. If these strategies are combined with soil conservation strategies, e.g. no-till and contour planting, erosion can be basically eliminated.

  1. Agroforestry helps to improve soil structure

The soil structure is formed by the distribution of macro-pores. These pores are created by formation of soil aggregates and voids. A good soil structure is essential for many ecosystem services such as groundwater formation and prevention of water logging and oxygen deficiency in the root zone. When trees are planted together with crops, more organic matter is added to the soil and the conditions for microorganisms and soil fauna are improved. This leads to an improved soil structure.

  1. Agroforestry creates good conditions for soil microflora and macrofauna

Below the soil surface there is an immense diversity of organisms that is essential for food production. The microflora, such us fungi and bacteria, decomposes organic material and make nutrients available for plants. The macrofauna, e.g. worms and beetles, is important for the soil structure and also helps the microflora to degrade organic matter. The abundance of soil organisms increase in the vicinity of trees which has been show to correlate with improved soil fertility.

Celebrate the Wold Soil Day by learning more about land restoration and how agroforestry can halt soil degradation and contribute to the SDGs: