Farmers use chemical fertilisers and pesticides to meet their requirements, but this destroys soil health and causes a reduction in soil biodiversity.
Agricultural land is an imperative component for the production of food, housing, and fibre for humanity. As well as providing self-employment, agriculture plays a dynamic role in the economics of developing countries. Many physiologists suggest that soil is a primary source of plant nutrients; moreover, soil quality is required for agricultural production, and quality increases with soil bacteria, fungi, and protest.
The moist biodiversity on this planet contains a microbial biosphere. In other words, microbes can be thought of as soil machinery that recycles nutrients. Soil microorganisms inside the soil system can increase soil quality or soil upkeep.
Soil microorganisms in the soil arrange the breakdown of organic materials such as animal remains and plant remains, as well as the construction of soil structure and the rate of biogeochemical cycling. As the human population grows at an alarming rate, the demand for agricultural land grows to meet the demands for food, fuel, and raw materials.
Farmers use chemical fertilisers and pesticides to meet their requirements, but this destroys soil health and causes a reduction in soil biodiversity. During the next 30 years, agricultural output demand will rise by up to 70%. In the future, people will become more conscious that sustainable agricultural practises are critical to fulfilling world agricultural demands. Because of its chemical and physical composition, soil varies around the world.
To increase soil fertility and plant growth soil contains millions of microbes. Soil physical or chemical properties determine the quantity and quality of organic matter in the soil, as well as pH, redox potential conditions, etc., as well as their function in the soil. All these factors greatly impact their structure and dynamic microscopic population.
By improving soil health and plant nutrition, microbes can play a significant role. Commonly, people believe that microbes are germ-causing agents in our ecosystem. With the assistance of these microorganisms, the degradation of organic material will be accomplished.
Furthermore, numerous bacterial species have been used to observe the mineralization process of organic pollutants in soil.
CURRENT CHALLENGES FACED BY THE AGRICULTURE SECTOR
In the 21st century, agriculture will face many challenges: how to feed the growing world population, how to help reduce the world’s still-high prevalence of rural poverty, and how to address growing concerns about natural resource management.
SOIL DEGRADATION
Few ecosystems around the world are immune to the effects of human activity, and one of the most ubiquitous influences is agricultural activity, which inevitably includes significant changes to the local environment and may have far-reaching consequences.
Conservation and enhancement of the quality of natural resources, particularly soil and water, are critical to guaranteeing food security for the world’s rising population. The ever-increasing salinity of these two primary resources, together with soil degradation, is the most significant constraint on our ability to practise sustainable agriculture and provide food security.
To keep productive lands from becoming salinized and to make use of existing salty land and water, it is important to rectify the hazardous situation using appropriate technologies.
Soil degradation is a process in which the loss of soil characteristics is caused by inappropriate usage, most commonly for agricultural, pastoral, industrial, or urban purposes.
It is a serious global ecological disaster that may be exacerbated by climate change. Soil degradation is one of the most serious risks to humanity, as it not only reduces an ecosystem’s productive capacity but also has an impact on the global climate.
According to a recent FAO/UNEP estimate, the normal rate of soil deterioration is around 8–9 m ha/year, having already damaged more than two billion hectares of land globally. It is predicted that desertification and soil erosion have reduced the production of some regions by half.
For example, in African countries, yield reductions owing to past soil erosion can range from 2 to 40%, with the continent as a whole losing 8.2% on average.
NUTRIENTS DEPLETION
Because of the expansion of land use for agricultural production without the effective application of external inputs, soil nutrient depletion is a major concern in emerging and least-developed countries.
The persistent absence of essential nutrient replacement for nutrient-depleted soils, as well as nutrient losses due to wind and water erosion, are not only increasing soil degradation but also threatening agricultural sustainability in these regions.
This is seen in the long-term reduction in crop yields in many countries in Africa. Many studies have been conducted to evaluate soil nutrient budgets for agroecosystems using a universal mass balance approach, but few have focused on individual crop productivity.
As a result, it is difficult to understand how the soil nutrient budget relates to either soil nutrient losses caused by natural events or nutrient deficiencies induced by insufficient crop harvest compensation. It is also difficult to assess the effects of nutrient deficiencies caused by humans on specific crop productivity.
ENVIRONMENTAL POLLUTION
Plants are vulnerable to a variety of biotic and abiotic environmental challenges. Despite all other environmental pressures, heavy metal stress is one of the most significant stresses affecting plant growth, development, and yield.
Heavy metal toxicity also influences plant physiological and biochemical responses. Heavy metals are metallic elements that have a relatively high density and are harmful even at extremely low concentrations. Heavy metals are a collection of metalloids and metals with atomic densities three or more times greater than those of water, or greater than 4 g/cm3.
As a result, when compared to the density of heavy metals, chemical characteristics are the most significant aspect.
Heavy metals include cadmium (Cd), chromium (Cr), lead (Pd), nickel (Ni), arsenic (As), cobalt (Co), iron (Fe), silver (Ag), zinc (Zn), and platinum (Pt). Heavy metal pollution in soil occurs in the environment as a result of both natural and anthropogenic activity.
The parent material is the primary source of contamination, and it is found in soil. Ingenious rocks make up 95% of the overall earth’s crust, whereas sedimentary rocks make up the remaining 5%. Overall, basaltic igneous rocks possess a high concentration of heavy metals such as Cd, Co, Ni, and Cu; nevertheless, shales are abundant in Cd, Cu, Pb, Mn, and Zn.
Natural mechanisms allow heavy metals from these rocks to infiltrate the soil environment, such as leaching, surface winds, and erosion, as well as terrestrial, meteoric, biogenic, and volcanic processes.
The processes of urbanisation and industry are the main anthropogenic sources of heavy metals entering the biosphere. Other anthropogenic activities, such as the use of chemical fertiliser, fossil fuel combustion, sewage irrigation, and municipal waste disposal, significantly contribute to the increasing concentration of heavy metals in agricultural soil.
Emphasise the potential of microbiology to provide sustainable solutions to these challenges
Sustainability in agriculture refers to the long-term preservation of soil productivity through the use of natural resources without harming the environment. The maintenance and protection of natural resources, particularly a diversified and functional microbial community in the soil, are critical to sustainable agriculture.
Environmentalists are beginning to adopt integrated soil management, which emphasises the management of ecosystem functioning through nutrient cycling, waste management, and soil microbial diversity. Microorganisms are the most diverse and numerous natural resources, but their small size causes them to be overlooked.
The estimated total number of microorganisms on Earth is 4-6×1030 cells. The total amount of carbon, nitrogen, and phosphorus added to the earth’s biomass is equivalent to that added by terrestrial plants. Microbes are microscopic little animals classified as bacteria, fungi, protozoa, microalgae, and viruses.
These organisms can be found in soil, air, water, space, glaciers, food, animal intestines, and a variety of other settings. Various microbial environments show a great diversity of biochemical and metabolic properties that have evolved in microbial populations as a result of genetic variation and natural selection.
Men harnessed microbial diversity to make fermented foods such as yoghurt, butter, bread, and cheese. Some soil bacteria release nitrogen that plants require for growth and emit chemicals that help maintain the crucial composition of the Earth’s atmosphere.
EFFECT OF MICROBES ON SOIL HEALTH
Through their metabolic activities, several microbial communities have an impact on plant physiology, nutritional, and physicochemical aspects of rhizospheric soils.
PGPR are crucial components of integrated farming because they help nourish crops by providing necessary nutrients. This PGPR aids in the fixation of atmospheric nitrogen, the solubilization and mobilisation of phosphorus, the translocation of minor elements such as Mo, Zn, Cu, and others to plants, the production of plant growth-promoting hormones such as IAA and GA, and the improvement of soil structure through the production of polysaccharides, all of which contribute to improved soil health and crop production.
They are said to promote nutritional intake of Ca, K, Fe, Cu, Mn, and Zn via proton pump ATPase. Many scientists have explored the role of PGPR in soil fertility maintenance. Inoculation of seeds with PGPR boosted soil-accessible P, microbial population, acid phosphatase, alkaline phosphatase, and dehydrogenase activity, and yielded much more than inoculated seeds.
DIVERSITY OF MICROORGANISMS IN SOIL HEALTH
Biological indicators can represent the general amount, kind, and activity of microorganisms as well as the diversity of living organisms in the soil, especially the microbial population. Soil microorganisms are crucial for long-term soil fertility and are regarded as sensitive indicators of the impact of management practises on soil health.
Healthy soil contains an abundant, active, and diverse microbial community, which is essential for many soil functions that influence soil productivity, such as nutrient cycling and organic matter decomposition, erosion control, and water regulation through the formation of water-stable aggregates and soil structure, as well as pest and disease control via predation, antagonism, and competition with hazardous organisms.
Although the nature of the microbial community influences the rate of agricultural residue composition and nutrient cycling. Fungi and bacteria are microorganisms that have the ability to break down crop residue and organic materials and mineralize (solubilize) nutrients in large quantities. This method is only carried out in areas where the soil is healthy and devoid of hazardous contaminants.
NEMATODES AND EARTHWORMS AS INDICATORS OF SOIL HEALTH
Because of the high concentration of microorganisms in the rhizosphere, there are more nematodes and protozoa that feed on bacteria and fungi, as well as more micro-arthropods that hunt on nematodes and protozoa.
Earthworms, which are rarely diversified, are the only biota that has been regarded as useful as biological markers because their cast is digested material expelled back into the soil. During the digestive process of the worm, the cast is enhanced with nutrients (N, P, K, and Ca) and microbes.
The fresh cast is a hotbed of microbial activity and nutrient cycling. Earthworms enrich the soil through increasing porosity, tilt, and root development. They also aid in the formation of soil structure and aggregate stabilization.
Earthworms also help improve soil temperature and aeration. Earthworms consume rhizospheric bacteria such as Azospirillum, Rhizobia, Pseudomonas, Bacillus, and Azotobacter, which increases their population.
As a result, those bacteria are used to convert unaccessible nutrients into available nutrients, make extra-enzymes used for plant growth stimulating hormones, and maintain soil fertility and health.
The presence of earthworms increases the number of microorganisms in the soil. As a result, the proliferation of soil microorganisms improves the pace of organic matter breakdown, which leads to improved soil health, increased nutrient uptake by plants, and increased crop yield.
Earthworms encourage the formation of beneficial decomposer bacteria in wastewater and operate as aerators, grinders, crushers, chemical degraders, and biological stimulators.
Saleem Sajjad from the Department of Soil and Environmental Sciences, College of Agriculture, University of Sargodha, Sargodha, Pakistan; Hafiz Muhammad Bilal from the Department of Horticulture, Auburn University, AL, USA; and Amanullah Baloch from the National Key Lab of Crop Genetic Improvement and the College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, China.