Leveraging Soil Microbes with Good Farming Practices for Higher Soil Carbon Sequestration (SCS) and Farm Productivity

Abstract

Plants reduce carbon dioxide content in atmosphere through photosynthetic absorption. Though they also add it by respiration, the amount absorbed is more than the amount added as evident from the growth of plants having more than 50% carbon. It makes agriculture as the net carbon sink. The movement of carbon dioxide from atmosphere to plants is under carbon cycle of the natural ecosystem. Though the ecosystem is resilient, human activities releasing carbon dioxide intensively can disturb it. Any farming activity releasing carbon dioxide from soil to atmosphere including injury to soil microbes, which are integral to ecosystem, can disrupt the ecosystem processes. Soil microbes playing key role in exchange of nutrients between soil and plants receive the photosynthetic food via roots. They repeatedly process it turning it into stable humus. This is “soil carbon sequestration (SCS).” These creatures can be leveraged with good farming practices that ensure their food and safety. Such a leverage can enhance soil health, farm output, and SCS reducing atmospheric carbon dioxide level which imply a perfect business case. However, as only informed farmers can do it, they need to be oriented to understand good farming practices and their benefits. This chapter aims at just that.

1. Introduction

IPCC Climate Change Report 2021 [1] reveals that the rising levels of greenhouse gases (GHG) in atmosphere, which are behind the climate change, are due to rising anthropogenic emissions. This is not a new revelation as similar inferences were recorded earlier also. The fact that burning of fossil fuel is the highest GHG emitter among all human activities is recorded in IPCC Report-2014 [2]. Thus, reducing fossil fuel burning reduces GHG emissions including carbon dioxide, the biggest constituent of GHG. But no significant reduction in fossil fuel burning could be achieved because fossil fuels are burnt to meet energy needs of the modern economy. However, it is imperative to reduce the emissions as well as to remove carbon dioxide from atmosphere to combat climate change. Agriculture can help the world in this regard. Agriculture, the occupation of growing plants, uses photosynthesis every day. The photosynthesis is a natural process as part of global carbon cycle that moves carbon from one pool to another pool while maintaining balance as necessary to sustain life. As photosynthetic absorption of carbon dioxide is more than respiratory discharge, plants thrive with growth of biomass that contains more than 50% carbon. Thus, agriculture/farming growing plants is a negative emission activity.

As farming activities are intertwined with natural processes, the same cannot be carried out in an industrial commodity production system. The status of agriculture as a negative emission activity may change if farming activities act against natural processes. Farmers are at liberty to align their activities with the natural processes or to ignore existence of the ecosystem with its natural processes. Since the farming activities aligned with natural processes need less effort from farmer and cause least harm to environment, they are considered as good farming practices while the opposite ones are bad practices. As a detailed discussion on the ecosystem and natural processes is covered in the next section, it is not elaborated here. Wisdom lies in aligning farming practices with the natural processes as it minimizes the farming effort and adverse impact on the environment while maximizing plant growth and yield.

IPCC Report on agricultural, forests, and other land uses (AFOLU) [3] recorded in 2014 that the agriculture’s contribution to GHG emissions is only non-CO₂ because of photosynthetic absorption of carbon dioxide while FOLU’s contribution includes almost all GHGs. With soil carbon sequestration as the main theme of this paper, discussion on the non-CO₂ emissions is beyond our scope. Also, since “FOLU” is not agriculture, emissions from “FOLU” are beyond the scope of this chapter. So, restricting our focus on agriculture alone, it is beyond dispute that agriculture with good farming practices is a negative emission sector that can give emission credits to needy sectors to offset their emissions.

Coming back to the process of growth of plants, photosynthesis turns carbon dioxide into food (simple sugar) called photosynthate which diffuses to all part of the plant. The photosynthate, when it reaches the roots is repeatedly processed by soil microbes that turn it into humus, highly stable carbon compound. This is called “soil carbon sequestration (SCS)” which is permanent transfer of carbon from atmosphere to soil for storage for long periods as part of a natural process. In fact, the transfer of carbon from the atmosphere to the plant by photosynthesis is first but temporary sequestration since biomass or timber or wood, or other produce of the plant is subsequently used which releases carbon dioxide to atmosphere. However, as the word “sequestration” signifies carbon transfer/storage on long term basis, temporary transfer from atmosphere to plant biomass is not called sequestration.

Here it may not be out of place to record appreciation of the tiny creatures living in the soil who carry out the miraculous feat of SCS as well as looking after wellbeing of the plant life. Being invisible and inaudible, they do not draw our attention, but the good farming practices help them to be at their best. When they perform well, soil health, farm productivity and SCS are optimum. So, it makes sense to leverage them through adoption of good farming practices.

This chapter aims to empower farmers with fundamentals of ecosystem, natural processes, and good farming practices while nudging global community to support eco-farming as a climate solution. As switching over from current toxic farming to good farming practices aligned involves extra effort, investment, and loss of farmer’s income during transition period, there is a case to compensate them for rendering ecosystem services through good farming practices. But no financial support after three years of transition period is warranted since enhanced productivity is rewarding enough for farmers. However, concessional extension services for training them to update their knowledge/skills should be organized by the state on pattern of continuous professional development (CPD). It is expected that the global community would recognize the potential of good framing practices as a solution for climate change. This is the perspective that drives both farmers and the global community.

2. Agriculture in the context of ecosystems

2.1 Natural ecosystem and biogeochemical cycles

As farming activities are intertwined with natural processes of the ecosystem, farmers need to be conversant with the ecosystem and its natural processes that sustain life. The word “ecosystem” stands for a system of interconnected processes to achieve an objective in most efficient manner. The natural ecosystem is a life-sustaining environmental system operating in a geographical area that is composed of living (biotic) and non-living (abiotic) components interacting among themselves. Plants, animals, and other organisms are biotic components while land, air, water, sun, and weather are abiotic parts which interact among themselves as well as with adjacent ecosystems. The matter and energy are exchanged in all ecosystem interactions to sustain life. Life is sustained by the food that is initially produced from the inorganic matter (carbon dioxide) by photosynthesis. Subsequently, a food chain evolves where an organism is food of another organism. The organisms making own food from inorganic matter are called autotrophs. As the plants use sun’s energy to make food by photosynthesis, they are also called photoautotrophs. Autotrophs are the primary producers of food in the food chain. The organisms who cannot make their own food and eat primary producers are called heterotrophs or consumers. Herbivores (plant eaters) and carnivores (animal eaters) are also known as “primary” and “secondary” consumers, respectively. Thus, life sustains on web of life called food web/chain. Microbes decompose dead bodies back to inorganic elements which are reused by autotrophs in making organic matter. This is the circular economy of nature which has no waste product. The photosynthesis is part of carbon cycle which, in turn, is part of biogeochemical cycles that control transformation and flow of elements among components of the earth system [4]. A cycle moving a particular element is known by the name of that element. Thus, we have cycles such as carbon cycle, nitrogen cycle, oxygen cycle, etc. Carbon and nitrogen being major constituents, these cycles are discussed here in detail.

Carbon cycle moves carbon from one reservoir/pool to another or from one ecosystem to another. Sediments, oceans, biosphere, and atmosphere are main reservoirs of carbon. The biosphere includes life above ground and soil life below ground. Photosynthesis, respiration, and decomposition are the main processes moving carbon from/to organisms. Photosynthesis fixes atmospheric carbon to plant biomass and then to soil life. Part of this carbon is turned into humus which stays in soil for thousands of years making soil as the biggest reservoir of terrestrial carbon. Carbon in sedimentary rocks of earth’s crust is of the order of billions of billion tons while oceans store 38,000-billion-ton carbon at great depths. After earth’s crust and oceans, soil is the biggest carbon reservoir containing 1500 billion tons organic carbon and 1000 billion tons inorganic carbon. Atmosphere contains about 750 billion tons of carbon mainly as CO₂ while earth’s biosphere store about 560 billion tons of carbon. Terrestrial carbon stock in gigaton (GT) or peta-gram (Pg) is summarized in Table 1 below.

S. No.	C pool/reservoir	Value in GT	% Terrestrial carbon
0	Sedimentary rocks	10000,00,000	NA
1	Oceans	38,000	NA
2a	Soil (organic carbon)	1500	39.3
2b	Soil (inorganic carbon)	1000	26.3
3	Biosphere (life on earth)	560	14.7
4	Atmosphere	750	19.7
	Total	3810	100

Table 1.

Terrestrial carbon stock.

Source: FAO-2017 Soil Org Carbon-Hidden Potential and many other documents.

A pictorial view of the above figures in a pie chart is shown below (Figure 1) (Terrestrial Carbon Stock).

Figure 1.

Pictorial view of terrestrial carbon stock.

Earth’s carbon cycle moves carbon between various pools but the store of carbon in these pools remain unchanged due to dynamic balance between inflows and outflows. However, a disturbance of severe magnitude can disturb this balance. For instance, disturbance caused by human activities like too much fossil fuel burning or deforestation has caused an imbalance leading to high levels of carbon dioxide in atmosphere and consequent global warming/climate change. Though current concentration of CO₂ is a small figure of 0.04% (corresponding to about 410 ppm), the greenhouse effect caused by it is severe enough to result in global warming/climate change. As rise of CO₂ levels in atmosphere is on account of anthropogenic emissions, onus lies on humans to take the remedial measures.

2.1.1 Nitrogen cycle

Like carbon cycle, nitrogen cycle is also a sub cycle of biogeochemical cycles that moves nitrogen. But nitrogen is huge 78% of air as against 0.04% carbon dioxide, though it is inert and not usable. The nitrogen cycle moves and converts the inert atmospheric nitrogen gas into other active forms through processes of nitrogen fixation, nitrification, and denitrification. Organic nitrogen existing in tissues of organisms moves on consumption of food from food to the food consumer. The atmospheric nitrogen is inorganic which is made available to plants by the process of nitrogen fixation (NF) converting the inert nitrogen into reactive forms like ammonia (NH₃). Nitrogen fixation occurs naturally by lightning. Another natural process, called biological nitrogen fixation (BNF) mediated by the symbiotic bacteria converts atmospheric nitrogen into ammonia (NH₃) and later into ammonium (NH₄). The symbiotic bacteria carrying out BNF are known as diazotrophs. The Azotobacter and Rhizobium are well known examples of diazotrophs. Lastly, the nitrogen fixation is also done by humans as industrial production of nitrogen fertilizers. Under nitrogen cycle, nitrogen fixation is followed by the process of nitrification which converts ammonia/ammonium into nitrites and nitrates. Nitrification, mediated by bacteria in soil makes nitrogen nutrients available in soil for feeding the plants and completes transfer of nitrogen from atmosphere into plants. It is analogous to photosynthesis in carbon cycle which transfers carbon from atmosphere to plants. On consumption of plant-produces, atmospheric nitrogen enters bodies of animals/humans who consumed the plant-produces. When plants/animals die, the decomposed dead bodies release organic nitrogen back to soil as ammonium which is nitrified to nitrates to feed plants. In nitrogen cycle, nitrification is followed by denitrification process mediated by a set of bacteria that convert nitrates into gaseous nitrogen. Denitrification completes the nitrogen cycle.

Nature controls nitrification and denitrification processes to maintain balance between the two types of nitrogen to sustain life on the planet. But, like carbon cycle, the nitrogen cycle has also been disturbed by human activities like combustion of fuels and use of synthetic nitrogen fertilizers. These activities increase proportion of reactive nitrogen as compared to inert nitrogen unbalancing the cycle. Increasing use of synthetic nitrogen fertilizers deliver reactive nitrogen directly to the soil ecosystem without natural nitrification processes. Hence the cumulative amount of reactive nitrogen in the form of NH₃ and NO_x is unduly increased which, in turn, increases deposits on land that impacts radiation balance of the earth. In addition, the very process of manufacturing nitrogen fertilizers impacts GHG emissions which is compounded by their application. Hence caution is necessary in this matter.

2.1.2 Carbon and nitrogen linkage

The biogeochemical cycles of carbon and nitrogen are tightly coupled with each other due to metabolic needs of the organisms for these two elements. In other words, ratio of carbon and nitrogen is fixed in an organism though different organisms may have different C:N ratio. Thus C:N ratio is the inviolable parameter that links carbon with nitrogen for the organisms. So is the case with inorganic substances like fertilizers as well as with different soil ecosystems. So, the C:N ratio characterizes an organism or substance or soil. The carbon-nitrogen (C:N) ratio plays an important role in evaluating suitability of a fertilizer/manure for a particular soil and crop. As nutrient exchange in rhizosphere is mostly through soil microbes, it is important that any soil amendment or fertilizer to be used should be compatible with C:N ratio of the soil microbes. Generally C:N ratio of soil microorganisms is about 8:1, the C:N ration of fertilizer should be good enough to meet this metabolic need along with energy need. As energy need is met from carbon and it is double of metabolic need. Thus, the fertilizer should have a C:N ratio of 24:1 out of which 16:1 will be for energy needs and 8:1 will be for metabolic needs. Foods or fertilizers with less than 24:1 ratio fall short of microbe’s carbon needs and cause release of nitrogen from the fertilizer in soil raising the C:N ratio to around 24:1. Similarly, with foods/fertilizers with higher C:N ratio, microbes feeling short of nitrogen draw nitrogen from soil causing “N” deficit in soil called immobilization, which is made up on death of some microbes, called mineralization. It can also cause release carbon from soil bring down the C:N ratio to about 24:1. Synthetic fertilizers have high C:N ratio and, therefore, are of low quality while composts/manures having low C:N ratio are of high quality. The low C:N ratio food/residue is favorite of microbes who decompose it fast. The C:N ratio of crop plants is considered while deciding crop rotation. Thus, legume cover crop of low C:N ratio can be followed by wheat crop of high C:N ratio. The C:N ratio also plays a vital role in carbon sequestration in humus having C:N ratio of 10:1 as carbon cannot be sequestered unless adequate nitrogen is available in the carbonic substance being sequestered. In fact, performance of microbial function is also gauged from microbial carbon use efficiency (CUE) which is the ratio of carbon assimilated relative to the carbon lost as carbon dioxide.

2.2 Agriculture as an ecosystem

As agriculture has biotic and abiotic components interacting within themselves to sustain life, it is an ecosystem. However, it is not a natural ecosystem as farm produces and residues are not allowed to be recycled but removed from the farm. Thus, agriculture is a mixed ecosystem where both nature and farmer operate simultaneously. Since growth of crop plants results in depletion of nutrients in the soil, farmer must replenish or recoup the nutrients. While biogeochemical cycles follow the laws of the nature, there is no law governing the farming activities. Farmers may or may not recognize existence of the natural ecosystem and treat soil as a natural resource to be preserved or treat as nutrient mine to be mined until all reserves are exhausted. Overexploitation or abuse of the natural resource of the soil is counterproductive and self-destructive. Orienting farmers to have an in-depth understanding of the natural ecosystem including soil ecosystem is, therefore, imperative. The cost involved for such orientation/training should be financed by the state as it is more in the interest of the community.

2.3 Soil as ecosystem

As reservoir of nutrients, soil is the natural resource for the terrestrial ecosystem sustaining life. Soil is an ecosystem also as it has both biotic and abiotic components interacting among themselves and with adjacent ecosystems of atmosphere, oceans, and biosphere (plants/animals) to sustain life. While inorganic/organic nutrients, air and water are major abiotic components, microorganisms with other creatures like worms are biotic components of the soil ecosystem that live on organic matter.

Soil comprising organic and inorganic matter is formed from rocks fragmented by streams, rain, wind, animals, microorganisms, and chemical actions over a long period of time. Though the organic matter content is a small fraction (within 10%) of the soil, it plays the main role in vegetation growth. In fact, soil without organic matter is lifeless dirt unable to support any vegetation. Soil organic matter (SOM), however, is not a homogeneous mass but a combination of live and dead plants/animals under different states of decomposition. As SOM contains 50–60% soil organic carbon (SOC), value of SOM can be used to determine the value of SOC and vice versa. The values of SOM and SOC are indicators of availability of nutrients in the soil as carbon is the major components of plants and other lifeforms.

Soil microbial community includes bacteria, fungi, protozoa, earthworms, insects, reptiles, and other small creatures. In fact, the microbes contributed to formation of the soil itself by etching away rocks with their acid attacks. Their metabolic wastes and dead bodies constitute nutrients for plants. Humus which contributes to stability of soil is made by soil microbes and mostly from necro mass or dead bodies of microbial population. In other words, soil microbes give their life to ensure soil health and fertility while working hard during their lifetime.

Bacteria and fungi are main microbes that play significant role in maintaining soil health. The Rhizobia, azobacter, and azospirillum are popular names of useful soil bacteria that help build soil structure and maintain soil health and fertility. Most bacteria and fungi have symbiotic relationship with plants. The symbiotic association of fungi with plants is called mycorrhiza while these fungi are called mycorrhizal fungi (MF). The host plant roots grow exudates outside main roots to attract MF to their roots resulting in much higher root biomass. The MF grow hyphae, the thread like structures on their body which extend to far distances forming mycelium network to mobilize nutrients and to work as communication network connecting plant and microbes. The MF are classified as under:

• Endomycorrhizal (which enter inside roots up to cell walls of roots)

• Ectomycorrhizal (which occupy space just around the roots)

Endomycorrhizal fungi include arbuscular mycorrhizae fungi (AMF) which develop unique “arbuscular” structures at hyphae to enclose plant roots. They produce “glomalin” protein which binds soil particles into aggregates stabilizing soil. Major part of the hyphae lies within intercellular spaces of roots of the host plant for exchanging nutrients while only a small part lies on the surface. Nutrient exchange is a fascinating process. On sensing nearby presence of AMF, the root creates a structure to let in the AMF’s hyphal tip up to cell wall and merge with it. A cavity is formed in the merged entity to receive payloads of nutrients from both sides under control of the plant cell membrane.

Ectomycorrhizal fungi form a mantle on the surface of the root. The root cells secrete sugars and other food ingredients into the intercellular spaces to feed the fungal hyphae. Effectively, the hyphae increase surface of the root many times resulting in higher absorption of nutrients. They orchestrate exchange of nutrients from humus/soil to plant. They secrete antimicrobial substances which protect roots from attack of pathogens. Symbiosis of these MF is generally plant specific.

2.4 Nutrients and their exchange

Carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, chlorine, iron, copper, boron, zinc, nickel, selenium, manganese, cobalt, molybdenum, silicon, and sodium are the well-known nutrients. Carbon which is the major building block of all living systems constitutes more than 50% of plant biomass while nitrogen is about 40% of plant biomass. The plants take “C” and “O” from atmosphere and “H” as water/moisture from atmosphere/soil. Since absorption of “CHO” require no human intervention, these are termed as “basic” while others are termed “non-basic.” Among non-basic nutrients, the N, P, K, S, Ca, and Mg are called macronutrients since they exist in major proportion in the plants and constitute structure of the plants. Other nutrients are micronutrients.

All nutrients existing in soil are compounds in the solution form. These are absorbed by the roots directly or indirectly. Most plants absorb nutrients indirectly via soil microbes. The area around the roots where nutrient exchange takes place is called rhizosphere. Though the plants are not mobile, they can acquire macro and micronutrients from distances by means of different mechanisms like changes in root structure and establishment of symbioses. Since deficiency of some nutrients in some soils is always a possibility, plants have evolved nutrient uptake strategies to cope with different situations and nutrient limitations. Changing the root structure is one such strategy adopted by plants to increase the overall surface area of the root and to increase nutrient acquisition to access new nutrient sources [5].

Nitrogen and phosphorus are among the elements most limiting to plant growth and productivity because these nutrients are often present in small quantities or not in bioavailable form. So, plants do form symbiotic relations with soil microorganisms like bacteria and fungi. Use of nitrogen fertilizers is harmful as excess nutrients turn into insoluble form and pollute ground water systems. Interaction of plants and symbiotic microorganisms is quite interesting. When the plant releases compounds called flavonoids into the soil, the bacteria are attracted to the roots. Then bacteria release compounds called nod factors that cause local changes in the structure of the root and root hairs to envelop the bacteria in a small pocket. Further details are skipped to avoid distraction from the main subject.

2.5 Replenishment of nutrients in soil

As growing plants absorb nutrients from soil, the nutrient reserves in soil get depleted which is made up by farmers by adding organic matter, farmyard manure, compost, or synthetic fertilizer. The synthetic fertilizers with inorganic nutrients do increase yield of crops but not without harmful effects.

Biofertilizers (BF) containing live microorganisms addressing the issue of harmful effects can replace or supplant the synthetic fertilizers. As they contain microorganisms of select bacteria, fungi, or algae, they restore nutrient cycles in soil just as the soil microbes do. As the nutrient replenishment in soil takes place as a natural process, no harmful effects are associated with the use of BF. Being natural, eco-friendly, renewable, and cost-effective the BF are considered as the most sustainable soil solutions [6]. Hence rest of this section covers an elaborate discussion on BF only.

The facts that atmospheric nitrogen can be used by plants through biological nitrogen fixation (BNF) by certain microorganisms and that insoluble soil nutrients can be converted into soluble form through activities of certain other microorganisms are used in formulating biofertilizers. Since most of the phosphorus and potassium nutrients exist in insoluble form, they are not available to plants. Use of certain specific microorganisms can make those nutrients water soluble and bioavailable to plants. Microorganisms that produce plant growth promoting compounds are also used in BF formulations. As microorganisms mainly belong to bacteria and fungi groups, BF are also classified as bacterial and fungal BF as described below.

2.5.1 Bacterial BFs

Bacterial BF include both nitrogen and phosphorus fertilizers as discussed below.

2.5.1.1 Nitrogen fixation

The nitrogen fixation process is operationalized by the nitrogenase enzyme which is present in diazotrophic microorganisms such as symbiotic and free-living nitrogen fixing bacteria. The nitrogen fixing process involves conversion of atmospheric nitrogen into ammonia (NH₃) which is bioavailable for plants. Such biological nitrogen fixation (BNF) can meet up to 50% of the demand of all plants though actual nitrogen fixation depends on the plant species and environmental factors. The nitrogen BFs contain nitrogen fixers like Rhizobia which are symbiotic with legumes. As symbiotic relation is between specific bacteria strain and specific crop, the specific strain suitable for a particular crop is selected. Free living bacteria like Azotobacter and Azospirillum which establish loose symbiotic relation with non-legume cereals are also used. As these bacteria also produce growth promoting compounds, these BF are also used as plant growth promoters (PGP).

2.5.1.2 Phosphorus solubilization

The phosphorus BFs contain phosphorus solubilizing microorganism (PSM) which solubilize solid phosphorus salts and mobilize them to roots for absorption. Phosphotika and Azotobacter are the main bacterial PSMs which have no crop specificity for symbiotic relations. Pseudomonas, Bacillus, Rhizobium, Enterobacter, Penicillium, and Aspergillus are main PSM genre. Bacillus, Rhizobium, and Pseudomonas are potassium solubilizing microbes. Combinations of bacteria and fungi are also used.

Cyanobacteria or Blue Green Algae (BGA) which are free-living nitrogen fixing bacteria have symbiotic relation with Azolla (aquatic fern) floating as green mat over water. These nitrogen fixers are also used in BF formulations for rice paddy crops and other similar crop plants.

2.5.2 Fungal biofertilizers

Biofertilizers using fungi as main ingredients are called fungal BF. The fungi having symbiotic relationship with plant roots are known as mycorrhizal fungi (MF) which are commonly used in BF. Since MF are more efficient in the uptake of specific nutrients like P, Ca, Zn, S, N, B and are resistant against soil-borne pathogens, they are used to improve efficiency of nutrient exchange and to protect the plants against diseases. Fungal BF use fungi like Trichoderma, endoemycorrhiza, and ectomycorrhiza. As MF help in retaining moisture and increase resistance against root and soil pathogens, they are commonly used. Based on two types of MF, the fungal BF are also divided in two categories as described below.

2.5.2.1 Endomycorrhizae

These fungi, reaching up to the cellular surface of plant roots, enhance nutrient exchange and protect the plants from soil-borne diseases. Arbuscular mycorrhizal fungi (AMF) which are subgroup of endomycorrhizae are symbiotic with most trees and crops like wheat, maize, and soybean, etc. They stimulate natural processes of nutrient uptake and decomposition of organic residues while making growth hormones and antibiotics, etc. Thus, they enhance supply of nutrients while protecting plants against diseases. While AMF are in contact with the interior of root tissues, their hyphae and mycelial network outside the root zone explore far distances to mobilize phosphates and other nutrients. Due to their extraordinary abilities for mobilizing phosphorus, they are known as phosphate scavengers. In fact, they provide a comprehensive arrangement for long life of the plants with efficient acquisition of nutrient from soil, enhanced uptake of nutrients to plant tissues and improved soil structure/health.

2.5.2.2 Ectomycorrhizae

These fungi form a thick mantle structure within the intercellular spaces of roots, but not in touch with cellular surface of roots. Being symbiotic with big trees, they increase tolerance of trees to abiotic stress while reducing the level of toxins in the soil and shielding roots from biotic stress as well. They are used in BF formulations for mobilizing phosphorus, iron, zinc, boron, and other trace elements. There are many species/strains used in BF and it may not help in listing them here. Suffice it to state that Azospirillum, Pseudomonas, Aspergillus, Cladosporium, Macrophomina, Glomus, Trichoderma, and Penicillium are commonly used fungi of this group that activate nitrogen fixing, solubilization of phosphorus and potassium. Trichoderma fungi, ubiquitously present in roots and soil ecosystems, that thrive on decaying wood, soil, and organic matter are used as BF to harness soil nutrients and to increase the resistance of plants against diseases and abiotic stresses. It is an excellent fertilizer cum protector for potato, corn, and tomato etc. Other strains are not discussed here for want of space.

2.6 Farming practices (FPs)

Farming activities standardized over course of time are termed as farming practices (FPs). The standardization is partly universal and partly specific to culture, climate, crop, and farm size. Current FPs include use of machines to prepare soil and use of chemicals to restore soil fertility and to control weeds or pests/diseases. These FPs became mainstream about 50 years back when green revolution was launched as a drive against starvation. This transformed farming from a way of life to an intensive agriculture. With harmful effects of these FPs being noticed, alternative FPs are being explored.

As stated earlier, farming activities aligned with natural ecosystem processes are good FPs. The good FPs result in good growth of crops with less effort of farmers and no harm to environment. Bad FPs, being against natural processes, demand more farming efforts and harm the environment. The natural ecosystem encourages existence of healthy organisms and cleanses sick/dead bodies through decomposition by microbes. Any bad FP harming the environment is an invitation for pests/diseases.

Comparing crop yields under good and bad FPs is a blunder as crop yield is only one parameter of farm productivity. Yield happens to be the most visible parameter and so simple that even a school dropout can calculate its monetary value. With greed being an irresistible instinct in humans, farmers are focused on the yield alone. After all, they are also humans. The external costs of restoring soil and human health are too enormous to be ignored, though invisible. In fact, even visible costs of chemicals (increasing every year) can offset the gain in crop yield by bad FPs. While ban on the chemicals is not intended here, indiscriminate use of chemicals by uninformed farmers warrants community action to respond to promotional assault of toxic chemicals and harmful practices from industrial agriculture lobby and to protect uninformed farmers by equipping them with unbiased information on right FPs.

As paper titled “Soil C Sequestration as a Biological Negative Emission Strategy” published in 2019 [7] outlines following conventional practices as best management practices (BMP).

1. Improved crop rotations and cover cropping

2. Manure and compost addition

3. No-tilling or reduced tilling

4. Improved grazing land management

Increasing SOC is, thus, essence of optimizing both productivity and SCS. The Rodale Institute (RI), supporting regenerative agriculture (RA) claimed in its White Paper of Sep 2020 [8] that the RA practices can remove the atmospheric carbon dioxide levels at a rate higher than current anthropogenic emission rate. Some important RA practices listed below deserve a look.

• No tilling or reduced tilling

• Biodiversity above and below ground

• Cover crops

• Retaining root and other residues of previous crop before planting new crop

• Using composts/manures for replenishment of nutrients

• Avoiding use of chemicals in farming

• Integrating livestock with farming

Conservation agriculture (CA) also emphasizes on non-disturbance of soil, permanent soil cover, and crop-diversity to balance economics with ecology in agriculture. Discussion on farming as well as soil management is incomplete without mentioning Dr. Rattan Lal, eminent soil scientist from Ohio State University. His paper on societal value of soil carbon [9] is simply transformative. Below is given a discussion on activities of soil preparation, fertility restoration, and farming management.

2.6.1 Soil preparation

All over the world tilling or ploughing is common farming practice for preparation of soil. The farmers generally point out that tilling is necessary for solarization, aeration, ridging for placing seeds, loosening of compact soil, and removing weeds. However, these reasons do not hold much water when scrutinized closely. So, tilling goes on more as a tradition than as a necessity. In fact, tilling adversely affects soil health, crop productivity, and environment. The soil erosion caused by intensive tilling is the first apparent and proven harmful effect of tilling. The second harm is that it exposes the SOM to atmosphere resulting in its decomposition without any productive use and decline in soil fertility. The fact that tilling injures/kills soil microbes is the third serious harm of tilling. The carbon dioxide released by tilling accelerates the dreaded climate change which is the fourth harm. It is also the last one because no living organisms would be left on the planet to be harmed further. So, digging/tilling soil means digging our own graves. Suitable alternatives to tilling need to be evolved to obviate serious consequences. Current no-till farming is far from ideal while organic no-till can be ideal solution only when it is affordable. In the meanwhile, farmers may counter adverse effects of tilling by good FPs.

2.6.2 Soil fertility restoration

Movement of nutrients from soil to the growing plants results in depletion of nutrients in soil. Replenishment of nutrients is done by farmers by adding organic matter, manure, or other fertilizers. As organic matter (OM) is the food for soil microbes who maintain soil’s wellbeing, adding OM to the soil supplies food to them besides supplying full suite of nutrients to the plants. The OM in soil helps in retaining moisture and formation of crumbly structure of soil that resists soil compaction. It is also helpful in improvement of soil aeration and water drainage. These and many other benefits show the importance of SOM and SOC. Ultimately, the SOM and SOC also improve soil carbon sequestration.

While harmful effects of synthetic fertilizers are beyond debate, total prohibition of such fertilizers may not make economic or ecological sense because deficiency of specific nutrients needs to be made up under all circumstances to avoid disappointment at the harvest time. Adding fertilizers without any evaluation of the needs of the soil results in utilization of a small part of the fertilizers by plants while the rest is turned into insoluble form degrading soil and lowering nutrient composition of the crops. The excess of nitrogenous fertilizers causes loss of carbon from soil to maintain the C:N ratio of the soil. Also, leakage of nitrous oxide gas into atmosphere and leaching of nitrates into water streams are additional serious problems.

Since microbes are most sensitive to chemicals, use of chemical fertilizers injures or kills them disrupting the ecosystem and harming the soil ecosystem. Hence, biofertilizers (BF) are gaining more traction from farmers, also as biofertilizers act naturally to reenergize and improve the soil health.

Biochar, a charred organic matter, made by burning biomass in absence of oxygen (pyrolysis) is also finding applications as soil amendment or organic fertilizer. Although low in nutrients, it can hold nutrients that might otherwise be lost to leaching or runoff. Being a stable form of carbon lasting for thousands of years in the soil, biochar also enhances SCS. In fact, it increases growth of soil microbes like MF by providing comfortable place for them to live safely and protect OM from exposure to the air and consequent decomposition of OM releasing carbon dioxide from soil.

2.6.3 Farming management

Farming management includes strategic management of entire farming enterprise including all components like inputs, soil, crops, and livestock. Thus, it is not a typical farming practice (FP). As you cannot manage what you don’t measure, defining metrics of performance and monitoring them is a good strategy. The first metric of farm productivity is defined in terms of value of farm produce and input costs. It involves maintaining periodical records of farm produce data and total costs. Total costs should include not only the cost of inputs but also the cost of labor (own family + hired) and external costs relating to environment and health of farmer/farm workers/consumers/public. Though it is too much of a non-farming task, its value is realized in the end. The top management should assimilate real value of good FPs and lay down guidelines for their adoption incentivizing good FPs. Monitoring of physical/chemical/biological tests of soil is also good strategy for sustainable soil management. Practices of mulching or cover crops are vital for soil health and fertility that lead to good crop growth. Replenishing nutrients is not the end of soil management unless food and safety needs of microbes in soil are fully met. As these tiny creatures do most of the farm work below ground while remaining out of sight, they deserve a better deal by ensuring their abundance and diversity of their community.

Selection and rotation of crops are central to crop management. Ensuring ground cover and biodiversity are sound farming practices which should find a place in the farm management strategies. Mono cropping destroys biodiversity while poly culture and rotation of crops support the ecosystem. In fact, most of the problems of weeds, pests, and diseases can disappear by ensuring biodiversity. So, instead of using harmful chemicals as pesticides/herbicides, experimenting with preventive measures should be a strategy of farming management. As animals provide multiple benefits including higher soil fertility, it makes sense to integrate livestock with farming as a biodiversity measure also.

2.7 Microbial leverage

As soil microbes are central to soil fertility, plant growth, and carbon sequestration, it is prudent to ensure their abundance and diversity. Providing food and safety to them ensures their abundance. As organic matter is their food, ensuring organic content in soil ensures supply of food to them while avoiding physical injury to them with least disturbance to soil ensures their safety. They also need to be protected against chemical injury by avoiding use of chemicals as fertilizers/herbicides/pesticides. As symbiotic relation of the microbes and plants has specificity of plants, certain plants attract certain specific microbes. So, diversity among plants above ground results in diversity among microbes below ground. Thus, abundance of soil microbes is ensured by ensuring enough organic matter in soil while diversity of microbes is ensured by diversity of plants above ground. Once abundance and diversity of soil microbial population has been ensured, there is nothing more to be done by farmer. However, it is possible for farmers to support the microbial community by growing plants with thick root mass since microbes reside mostly in the root area. Direct inoculation of microbes can also add to the abundance. As microbes are at their best under good FPs, use of good FPs by farmers results in microbial leverage.

2.8 Potential of SCS as a climate solution

Global warming as an outcome of “blanket effect” of concentrated greenhouse gases (GHG) in atmosphere sets climate change in motion. Carbon dioxide, being major constituent of GHG, is the major causative factor behind climate change. Though warming effect of carbon dioxide starts long time after it enters atmosphere, it stays in atmosphere for thousands of years. So, carbon neutral or zero carbon emission commitments stopping further influx of carbon dioxide to atmosphere will not stop climate change immediately. Thus, removing a chunk of carbon dioxide from atmosphere is the only activity that can stop the climate change. Ecological agriculture or farming with good FPs is one such an activity that is also simple, inexpensive, and demonstrably proven all over the world.

Carbon dioxide removal (CDR) is being explored through emerging technologies but farming with good FPs is a non-technological option that can remove atmospheric carbon dioxide without any hassles. It leverages soil microbes with good FPs to enhance soil carbon sequestration (SCS). Potential of SCS is the amount of organic carbon that can arrive at the soil and stay there for ever. It depends on land area, type of soil, current storage state, and climate factors etc. The UN FAO publication on the re-carbonization of Global Soils [10] estimates that SCS potential of agricultural soils lies in the range of 1.44–3.45 GT carbon per year and that 25–75% of soil’s original carbon stock is already lost mostly due to bad farming practices which is recoverable through good farming practices. Considering middle figure in the range as estimated value, 2.5 GT C/y can be taken as SCS potential. A recent publication by FAO [11] on potential of SCS lays down methodology for precise estimation. The CGIAR Working Paper [12] indicates global potential of agricultural management practices as 5.5–6.0 GT CO₂eq/y.

As molecular weight of carbon dioxide is 44 and that of carbon is 12, factor for converting CO₂ weight to carbon weight is 0.27. Thus 6 GT CO₂/y potential is equivalent to 1.62 GT C/y potential. On cursory look at various estimates, the global SCS potential of agricultural soils can be rounded off to 2 GT/y.

It is worth repeating here that SCS decarbonizes atmosphere above ground and re-carbonizes soil at underground. It implies removal of carbon dioxide from atmosphere as a climate solution and enrichment of soil fertility for higher farm output. Thus, soil organic carbon (SOC) is the key both for SCS and farm produces. Farmers can keep their focus on SOC to maximize the crop yield while the global community can feel the better atmosphere with reduced carbon dioxide. From the estimates mentioned above, SCS potential can be safely taken as 2 GT C per year which is a significant figure.

3. Conclusion

The industrial agriculture has lured and trapped farmers with bait of high crop yield. Blinded by high yield, they are unable to discern the damage to soil caused by bad farming practices. Soils are so degraded by bad faring practices that they release carbon dioxide into atmosphere aggravating the climate change. Thus, agriculture has turned into a net carbon source though it has the potential to be net carbon sink with good farming practices. A big chunk of CO₂ is required to be removed from the atmosphere as stopping CO₂ emissions is not enough to halt the climate change. Agriculture being net carbon sink under good farming practices is one of the right climate solutions that re-carbonizes soil while decarbonizing atmosphere. It is like homecoming for the carbon from long exile at atmosphere.

A brief not on good or bad farming practices may not be out of place here. Farming is unlike an industrial commodity production system as farming activities are intertwined with natural processes of the ecosystem that sustains life on the planet. The current farming practices involving use of heavy mechanical equipment for soil preparation followed by use of chemicals as fertilizers to enhance soil fertility and as pesticides/herbicides to kill pests and weeds are bad farming practices as they cause harmful effects on soil and other natural resources and human health. On the other hand, the good farming practices are in harmony with natural processes and cause no harm to environment, natural resources, and human health. Good farming practices also reduce farming effort to the minimum as they do not involve farming activities against natural processes. Why bad practices are mainstream is no secret. The industrial agriculture has aggressively promoted use of mechanical equipment for soil preparation and use of chemicals for fertilizers and pest/weed control. As farmers are blinded by the high yield propaganda, they are unable to see the loss of soil which is their main asset. It calls for big efforts at various levels to nudge farmers to switch to good farming practices as explained earlier.

Good farming practices not only improve soil carbon sequestration but also farm-productivity. The potential of SCS in removing atmospheric carbon is about 2 GT C per year which can be achieved with good farming and management practices. Farmers may have nothing against good FPs since they are good for both farmers and climate. This perspective primes farmers to adopt good FPs and global community to support them for good FPs. With carbon sequestration being an ecosystem service, it is possible that farmers may claim compensation for rendering ecosystem services. But once they realize that good FPs provide not only ecosystem services but also maximize crop yield, they would happily embrace good FPs. However, there is a case for financial support to them during the first 3 years of transition to compensate for loss of income during this period when yield is less. There can be no going back once they find the new practice to be in their interest, more so if provided with training and orientation on good practices. Then they can become strong followers of good FPs for life. Under such revolutionary change, even the industrial agriculture will be compelled to change its business strategy from toxic farming to ecological farming services and products. Thus, all stakeholders viz. farmers, industry, and global community will support eco-farming resulting in better crop yields and SCS leading to better atmosphere with reduced carbon dioxide. The world can thank farmers and their supporters for such an inexpensive climate solution which can operate alone or in parallel with other climate solutions. All this would be possible by leveraging the soil microbial creatures who are at their best when farming practices are good. So, thank you, microbes for compelling all to follow good FPs.

Acknowledgments

No financial support is received in connection with publishing this document. The author feels grateful to following individuals/organizations acknowledging the support from them:

1. Principal Editor Michael Aide for kind guidance to the author for revising the script.

2. Karmen Daleta, Author Service Manager for extension of deadlines for submission.

3. IntechOpen for inviting the author to contribute a chapter on the subject.

Conflict of interest

It is confirmed that there is no conflict of interest in authoring this work.