Why Soil Health Matters
Soil health can be determined by how well the soil can aid plant growth, the health of the plants and its ability to function in the ecosystem.
Soil microbes have a positive effect on plant biodiversity, in a very similar way to arbuscular mycorrhizae [29].
Elements for Good Soil Health
Soil Structure
Better soil structure is less prone to erosion and increases plant health and growth [37].
The types of soil are: Clay, Loam, Sand, Silt and Peat. This is determined by the size of the particles that make up the soil [37].
Understanding the soil type can help when managing growing crops. Biofertilisers and organic matter will help all with nutrient content.
Soil Chemistry
In general soil contains: 40 – 45% inorganic matter (rock), 5% organic matter, 25% water and 25% air [36].
Decomposition by soil microbes is responsible for the organic matter available to the plant roots in the soil. Utilising fungal and bacterial partners, the plants are able to obtain the nutrients they need.
Soils contain, carbon, oxygen, nitrogen, phosphorous, potassium, calcium, magnesium and sulphur [30].
Water Infiltration
The constitution of the soil will determine its ability to retain or leach water. Sand has larger particles, and therefore is not able to retain water or liquid feeds well. On the other end we have clay. This is great at water retention and needs less irrigation, but will hold water which can lead to rot. Compaction in clay also removes essential oxygen and air pockets in the soil [38].
One of the biggest problems with chemical fertilisers is the leaching affect. When chemicals are leached in to ground water, this is costly and complicated to remove.
Getting Nitrogen from the Soil
Nitrogen from the atmosphere is fixed in the soil by nitrogen fixing bacteria [44]. This method allows the nitrogen to be used by plants. Without these bacteria, the plants would not be able to access this nitrogen source [30].
Plants release volatile organic compounds in to the soil, these compounds attract both fungi and bacteria to the plant. This is the initiation stage of the symbiotic partnership [31].
Soil Health In Numbers
Soil Facing Erosion
The world’s population is set to exceed 9 billion people by the year 2050 [18]. Soil is being lost at a rate of 24 billion tonnes per year [37]!
With fewer and fewer people interested in large scale farming, this presents a huge problem for those left in business. Add to this the additional stress put on soils to produce more high quality foods, for the same price and we have a major problem on our hands.
Soil is a finite resource [19], and it is being degraded every year by increased urbanisation, soil acidification, soil erosion and contamination [17]. More and more inorganic fertilisers are being used to put back in to the soils what is being lost through harsh agricultural practises and mechanisation [17].
Arbuscular (plant specific) mycorrhiza provide an invaluable resource. Allowing plants to receive the nutrients they need for strong and healthy growth, increased yield, resistance to abiotic (environmental) and biotic (pest) factors [1].
Image Credit: Pexels
Causes of Soil Erosion
Agricultural Practices
Farmers have so much knowledge about their land, the soil and what it takes to keep soil health. The practices that have been used previously are not effective or sustainable. Farmers are looking for alternatives whilst needing to sustain their business and crop yields [21].
Soil can be saved through cover cropping and rotating of crops. These require moving away from tilling the ground after harvest, not planting over winter crops and moving away from a monoculture [38].
Topography
Land topography can impact soil erosion. In locations where the soil is on steep slopes or gradients, the soil can be washed down the slope. Wind can affect the soil on these gradients also [38]. This is especially a problem in arid environments.
On top of this the nutrients available to the soil are leached down the side of the slope and therefore the soil tends to have less nutrients. Degrading the quality of the soil and increasing the rate of erosion. The top soil on slopes tends to be shallow and therefore lacks the structure required for health plant growth [38] [19].
Pollution
An increasing problem is the amount of microplastics being found in soil. These include fibres from fabrics, domestic sewage, plastic beads from personal care products, landfill from urbanisation and industries, littering and illegal waste dumping [39]. The main affect from this pollution is soil toxicity and organisms consuming the plastics and transferring these and their toxins up the food chain [39].
Flood water is another massive problem, causing polluted soils. This is especially found in the developing world, but with increases in sea levels, this will be a domestic problem globally. Flood waters wash slurry and sewage on to land, rendering it unusable [40].
What can be done?
Fungi is plant specific, with 90% of plants forming symbiotic mycorrhizal associations [11]. Fungi used as biofertilisers have been found to increase plant yield by 50% [28]. Nutrient content was found to be twice that of non and inorganic fertilised plants [28]. Although there is limited evidence of biofertilisers being used on large scale farms [17].
The challenge is on land previously fertilised with inorganic fertiliser, as the higher nitrogen and phosphorus inhibits arbuscular mycorrhiza. But, not enough for it to be ineffective [28].
Choosing to work with the soil and allow the positive association of fungi and plant will help support healthy plants. Utilising the soils own microbes as pest control, fertiliser and herbicide will ensure the food you grow will be high yield and more nutritious [28]
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