Soil contains more microbes in a teaspoon than the human in the whole earth. Soil microbes contain beneficial, as well as harmful effects on the soil and also on the growth of plants.
Soil microbes & their benefits:
The most abundant biota in the soil is microbes. Microbes present in the soil performs different sort of functions in soil that involves recycling of organic matter. Organic matter helps in the fertility of the soil, also maintains the plant health and primary production of the ecosystem.
Beneficial microorganisms are those that develop a symbiotic association with roots of plants, helps in nutrients mineralization and availability. Plant growth hormones and antagonists of a plant pest, parasites or diseases (biocontrol agent) are also being produced by the microbes of the soil.
The main driving forces in the soil processes are fungi, bacteria, and protozoa. They perform different sorts of beneficial functions in soil, which helps plants in growing in that soil. Some other soil microorganisms include nematodes, arthropods, and earthworms. ( Nihorimbere et al., 2011).
Various beneficial functions are performed by the soil microbes;-
- They decompose the organic matter
- Faster soil aggregate stability
- Carbon, nitrogen and phosphorous are being recycled and regulated by microbes.
- They fix nitrogen so that the plant could utilize
- They increase the available plant root area for growing plants for up taking nutrients
- Degrades pesticides, reduces their chemical hazardous.
- Help in controlling the plant disease
- Helps in the process of nitrification of atmospheric nitrogen
- Promote mineralization of organic Sulphur
- They help in the process of mineralization of organic Phosphorus
- Fixation of Atmospheric Nitrogen
Different soil beneficial microbes are briefly explained below
1. Plant Growth Promoting Rhizobacteria (PGPR)
PGPR can colonize the plants’ roots directly or indirectly
2. Beneficial soil microbes(BSMs)
Soil is naturally occurring physical covering of the earth and represents the interface of three material states: solids, liquids, and gases
According to an estimate one gram of soil may contain 1010-1011 bacteria, 6000-50000 bacterial species and up to 200m fungal hyphae (Blackwell. 2011) and most of them are considered as beneficial for the for soil and also for the growth of plants, decomposition of O.M, nutrients uptake and also help in the growth of plants (Nihorimbere et al., 2011).
Soil becomes healthy if the BSMs are present in the soil
3. Plant growth-promoting fungi (PGFP)
Soil possesses a wide range of friendly fungi that affect plants at their different growing stages. According to an estimate, there may be up to 1.5 million fungal species in the ecosystem, but only 5-10% are briefly explained in nature.
80% of terrestrial plants show the mycorrhizal symbiotic association (Gaur and Kaushik, 2011; Marcel et al., 2015).
Recently the relation of mycorrhiza with PGPR has been tested for improvement of crop productivity under the harsh and stressful environment. Thus, mycorrhizal fungi help plants in up taking the soil nutrients and also saves them from biotic and abiotic stresses.
Role of BSMs in Sustainable Agriculture
- Bio-Fertilizer
Bio-fertilizer contains living organisms, they colonize the rhizosphere of the plants increases the availability of primary nutrients. They are used in the agriculture field in place of the conventional application of fertilizers.
They help in minimizing environmental pollution and cut down on the use of agricultural chemicals which are hazardous for plants as well as for the environment.
- Biopesticides
40% of the total yield of the whole globe is destroyed before it is harvested due to pest attack and 20% is destroyed by post-harvest proceedings. To overcome these challenges we use chemicals that are harmful to plants and also have the aftershocks on human health.
Microorganisms also help in different other environmental systems;-
- Used as bioherbicides
- Bioremediation
- Biodegradation
- Also helps in stress management
The use of BSMs in stable agriculture and environment management offers several benefits. Their use in the form of bio-fertilizers and biopesticides is becoming famous day by day and providing substantial help and support to the agroecosystems.
Their ability to survive in severe environmental conditions makes them efficient candidates in various sorts of stress management, whereas their catabolic diversity can be used in discarding recalcitrant pollutants. Our understanding of the BSMs’ response in agroecosystems is increasing, and their potentially significant effects on environmental restoration are also strengthening and collectively helping to obtain the goal.
Soil Microbes as a Foe
On one hand, microorganisms are beneficial for plants and environment at the same time some are pathogenic and causing severe earth borne diseases in the soil.
- De-nitrification
- Development of plant disease
- Formation of toxic compounds aid
- Competition for nutrients
De-nitrification
The biological reduction nitrates into gaseous nitrogen are known as de-nitrification. Denitrifying bacteria that live in the soil under an anaerobic condition that converts available nitrogen to unavailable form.
NO3 NO2 →N2 or N2o
Development of plant disease
Soil microorganisms destroy the plants and crops which are of good economic source for man. For instance, the blight disease of rice, apple, and pear are caused by bacteria. Fungi mostly affect crop plants.
Formation of toxic compounds
Due to improper decomposition of organic matter toxic substances such as methane, hydrogen sulfide are formed in anaerobic conditions.
Competition for nutrients
Nutrients such as carbon, hydrogen, oxygen, nitrogen, phosphorus are also used by microorganisms along with the plants. So competition for the uptake of nutrients is high between plants and microorganisms. Especially, at the time of decomposition of organic matter microbes uptake more nutrients, plants get insufficient nutrients for their growth.
Conclusion
Microbes present in the soil have benefits for plants and soil at different stages which are of vital importance for plants, crops and for soil to provide nutrients to the growing plants.
Different microbes present different functions ranging from decomposition, ammonification to nitrogen fixation.
Similarly, on the other hand, some microbes are impacting badly on plants’ growth and soil fertility & productivity. Some microbes bind the nutrients with soil essential for plant growth which results in stunted growth of plant crops.
Authors: 1Zohaib Afzal,2Faheem Shoukat
1Department of Soil Science, MNS- University of Agriculture, Multan, Punjab, Pakistan.
2Department of Entomology, MNS- University of Agriculture, Multan, Punjab, Pakistan.