Microbial Solutions for Soil Fertility and Nutrient Cycling

What are the roles of microbes in the soil?

Microorganisms, like bacteria and fungi, break down organic matter, recycle nutrients and enhance the soil structure and soil fertility. They play a crucial role in maintaining the soil’s health and fertility [1-3].

1. Nutrient Cycling

Microbes in the soil act as nature’s recyclers. They take part in every chemical reaction in soil and make nutrients available for plants uptake. They break down organic matter from dead plants and animals, transforming it into valuable nutrients such as carbon, nitrogen, phosphorous, potassium and ammonium as well as carbon dioxide that plants can absorb and are major requirements for plant growth [4-6]. 

2. Nitrogen Fixation

One of the important nutrients required for plant growth is nitrogen, which is often limited in supply. Some remarkable bacteria, like Rhizobium and Bradyrhizobium, can form a special relationship with leguminous plants [6]. They create nitrogen-fixing nodules on the plant’s roots, converting atmospheric nitrogen into a usable form for the plant [7]. The plant, in return, provides the microbes with nutrients [7], this reduces the need for nitrogen fertilizers and their environmental impact.

3. Mycorrhizal Fungi

Mycorrhizal fungi have a symbiotic relationship with root of plants. They form a network of thread-like structures called hyphae that expand beyond the root’s reach, enhancing the plant’s access to water and essential nutrients, particularly phosphorus and micronutrients [8]. This partnership boosts plant health and growth by improving nutrient uptake.

4. Organic Matter Decomposition

Soil microbes break down dead plant material into simpler organic compounds in a process called decomposition. This process allows plants to absorb nutrients that return to the soil, enriching them with organic matter and mineral nutrients. [9]. Studies have shown that about 90% of the nitrogen (N) and phosphorus (P) that are absorbed by plants, and 60% of other mineral elements, come from nutrients recycling during the decomposition process [10]. Nutrients like carbon, nitrogen, and phosphorus are released back into the soil through this process, this enriches its nutrient content [10]. Additionally, the humus formed during decomposition improves the soil structure and helps in retaining water in the soil, too.

5. Biological Control of Soil Pathogens

Certain soil microorganisms act as natural antagonists of harmful pathogens in the soil. Bacteria and fungi like Pseudomonas spp., Bacillus spp., Streptomyces spp., and Trichoderma are known for their ability to produce antibiotics or enzymes that help inhibit the growth of pathogens in the soil [11, 12]. Using these organisms to control the growth of pathogens is known as the biological control method, it can reduce the need for chemical pesticides, which in turn promotes an environmentally friendly pest management practice [11].

Practical Applications and Strategies

1. Organic Farming Practices

Organic farming prioritizes the preservation and enhancement of soil microbial diversity. Crop rotation, cover cropping, and reduced tillage are examples of organic farming that maintain healthy soil ecosystems [13]. Synthetic pesticides and fertilizers that can harm soil microorganisms are avoided [14].

2. Biofertilizers and Bioinoculants

Biofertilizers contain beneficial microorganisms like nitrogen-fixing bacteria and mycorrhizal fungi [15]. These fertilizers enhance nutrient availability and reduce the need for synthetic fertilizers [15]. Bioinoculants are beneficial soil amendments leveraging beneficial microbes to foster plant growth and development [16]. These formulations contain either dormant or live cells of highly efficient microorganisms, including strains proficient in nitrogen fixation, hydrogen cyanide production, and siderophore synthesis. Several plant growth-promoting microbial strains Azospirillum, Rhizobium, Bacillus, Pseudomonas, mycorrhiza, Trichoderma, and yeast, have been identified as bioinoculants [17, 18]. 

The tables below provide some examples of biofertilizers and bioinoculants and microorganisms involved in each.

Table 1: Some common types of biofertilizers 

Table 2: Some common types of  bioinoculants

3. Reduced Chemical Inputs

Minimizing the use of synthetic fertilizers and pesticides helps maintain a balanced soil microbial community. Integrated pest management (IPM) approaches prioritize biological control methods over chemical treatments, reducing harm to beneficial soil microorganisms [28].

4. Soil Restoration

Reforestation and land rehabilitation projects are efforts used to restore degraded soil. These efforts focus on rebuilding soil microbial communities that are essential for long-term soil health and ecosystem sustainability.

The richness and wellbeing of the soil are mostly dependent on soil microorganisms crucial in nutrient recycling, breaking down organic matter and inhibiting the growth of other microbes that are harmful to the soil. Utilising the potential of these soil microbes is vital for a more sustainable agriculture. Organic farming, application of biofertilizers and bioinoculants are approaches that can nurture these soil microbes, enhance soil fertility, and reduce the dependence on artificial inputs, ultimately fostering a more sustainable and robust agricultural system.

If you want to read more, please visit the section Soil and Water Conservation.

 References

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