OM decomposition is mainly microbe mediated process and is affected by soil temp., moisture, O2 and N2 content and quality and quantity of available carbon substrate and soil management practices. Soil organic carbon consists of various heterogeneous pools which differ in their stability and availability and are characterized by their turnover rates. Older, more recalcitrant C pools are less decomposable by microorganisms, in comparison to younger C pool. According to their turnover time various C pools contribute differently to soil CO2 as the major product of microbial decomposition. Thus, all the OM is not converted to CO2.

The terrestrial carbon cycle maintains a balance between photosynthesis and respiration. Carbon from the atmosphere is transferred to soil via ‘carbon fixing’ autotrophic organisms, (mainly photosynthesizing plants and photo and chemoautotrophic microbes) that synthesize atmospheric carbon dioxide into organic material. Fixed carbon is then returned to the atmosphere by a variety of different pathways that account for the respiration of both autotrophic and heterotrophic organisms. The reverse route includes decomposition of organic material by ‘organic carbon-consuming’ heterotrophic microorganisms that utilize the carbon of either plant, animal or microbial origin as a substrate for metabolism, retaining a part of carbon in their biomass and releasing the rest as metabolites or as CO2 back to the atmosphere. Plants benefit from root exudates mainly via improved acquisition of soil nutrients mobilized by microorganisms.

Dear Heba,

The process is not unidirectional, it is cyclic.

Yes, with increase in microbial biomass the demand for O2 will increase but on the same side the growth of vegetation will also increase.

This growth due to additional nutrients (fertility) will balance the enhance CO2 produced by microbes.

In this way nature balance itself.

However, the same is not true in the case of Lakes.

Thank you.

So, dear Vishal enhansin microbial biomass will increase soil carbon sequestration, right?

As temperature increases the primary plant productivity may be less than the respiration which mostly is a function of microbial activity. In this equation the net result would be the disappearance of organic matter leading to increase in global greenhouse gases.

Primary plant productivity can be made more resistant to rapid soil organic matter decay by the complexing of organic matter with clay referred to as organo mineral complex.

A vast swathe of the global has acid soil infertility which greatly comprises the plant productivity.

The equilibrium soil organic matter is a function of lime and clay content critical factors for generating the organo mineral complex.

The complexed soil organic matter is believed to cloak the material from microbial decay. The organo mineral complex made resistant to rapid decay and the neutralized pH favors primary plant productivity.

The majority of the land surfaces have some issues with acidity.

For a sequestering program needed to address greenhouse gases by liming acid soils and using methods to track and increase acid infertile soils into peak soil organic matter. In sandy soils beside the liming the amendment using silt and clay would be very useful.

Thanks so much dr. Paul for your valuable and helpful answer, but what about the alkaline soil like our soil in Egypt

Dear Heba Elbasiouny Under the alkaline soil condition pH and salts can be detrimental to water dynamics and plant productivity. Like many acid soils the soil organic matter is not optimized. The soil approach to climate change is to focus on limiting factors and target the increasing of living soil by increasing the soil organic matter level. This approach starts with a comprehensive soil testing and the elimination of deficiencies and toxicities. Originally the virgin soils had 5% or more soil organic matter and had little of the issues our current soil possess. When soil is alkaline and salty the ability to optimize plants through water is greatly limited. The first step in this situation is targeting limiting minerals and then developing a soil improvement plan with measurement. I like targeting soil organic matter since most cultivated soils have lost over 3 quarters of the original content. Many dryland soils are highly sandy with little organic matter and clay and silt to help stabilize them. Eliminating erosion and stimulating the organomineral complex provides a mechanism for regenerating the depleted soils and restoring the environment. This should be done holistically and systematically.

Thanks so much Dr Paul Reed Hepperly for this comperhensive reply.

Many many thanks. You are very right and we should work to solve this issue.

Dear Heba Y. Elbasiouny, If you have a good soil test I would be glad to review it and give some insights. I have worked in diverse soil conditions in various environmental conditions and have reviewed thousands of analyses and worked on remediation programs. Best wishes for the regeneration of your soil issues for the progress of your people. Sincerely, Paul Reed Hepperly

Thanks so much Dr. Paul Reed Hepperly for you kind invitation. It's my honor, for sure I will do. I will be glad if you send me your email.

My regards,

Heba Y. Elbasiouny, in continuation to the previous question, indeed it will increase but upto an optimum level beyond which effects are opposite.

Thank you!

Thanks so much Vishal Khanna for your valuable answer

Heba, the microbes break down the organic matter that is produced through photosynthesis. therefore we can not assume that the amount of CO2 produced by microbes would exceed the amount of CO2 absorbed by plants in any way.

isnt it so?

Yes Rasanja, you are right.

Thanks so much for sharing your answer.

OM decomposition is mainly microbe mediated process and is affected by soil temp., moisture, O2 and N2 content and quality and quantity of available carbon substrate and soil management practices. Soil organic carbon consists of various heterogeneous pools which differ in their stability and availability and are characterized by their turnover rates. Older, more recalcitrant C pools are less decomposable by microorganisms, in comparison to younger C pool. According to their turnover time various C pools contribute differently to soil CO2 as the major product of microbial decomposition. Thus, all the OM is not converted to CO2.

The terrestrial carbon cycle maintains a balance between photosynthesis and respiration. Carbon from the atmosphere is transferred to soil via ‘carbon fixing’ autotrophic organisms, (mainly photosynthesizing plants and photo and chemoautotrophic microbes) that synthesize atmospheric carbon dioxide into organic material. Fixed carbon is then returned to the atmosphere by a variety of different pathways that account for the respiration of both autotrophic and heterotrophic organisms. The reverse route includes decomposition of organic material by ‘organic carbon-consuming’ heterotrophic microorganisms that utilize the carbon of either plant, animal or microbial origin as a substrate for metabolism, retaining a part of carbon in their biomass and releasing the rest as metabolites or as CO2 back to the atmosphere. Plants benefit from root exudates mainly via improved acquisition of soil nutrients mobilized by microorganisms.

Following

Mohammed JARULLAH Farhan

Hudhaifa maan Al-Hamndi

Nooral Dean M. Muhawish

Awss Khairo

Abdulmajeed Al-Maeni

The organic matter decomposition is microbial process, under reduced condition they emit more co2 to the atmosphere as like in paddy field. suitable soil management practices may reduce the CO2 emission and we can observe more sequestration.

Sunita Gaind, thanks so much for your comprehensive answer. So it is like a circle and depends on the balance between photosynthesis (or in the other meaning pathways of C sequestration) and other pathways of C releasing to the atmosphere.

Thanks, Paramesh Venkatesh, but it is is known that wetlands have a higher ability to sequester more C than dry soil because of a low decomposition rate. On the other hand, CH4 emission is higher there.

I totally agree that improving management practices is a critical matter in this issue.

As noted the net sequestration is the difference between the net photosynthesis and the net respiration. As Paramesh Vendatesh alludes that the decomposition can govern the net equation.

A difficult part of this globally is elevated global temperature can increase respiration at a greater rather than photosynthesis making remediation more of an uphill challenge. Indeed in the perma frost areas the melting landscape is belching accumulated sequestered organic matter as previously trapped carbon carbon dioxide and methane.

We can have excellent photosynthesis but if the respiration values exceed it the carbon battery of the soil becomes depleted that the soil organic matter decreases.

If temperature and oxygenation is lowered the respiration is reduced and this can favor greater conservation and building of the soil organic matter resource

. Sunita Gaind alludes that as fresh organic matter becomes decomposed into humus the materials are stabilized and will be more refractory in the soil. We stress that the organomineral complex or the joining of and cementing of clay to organic matter through cationic bridges favoring persistent aggregation of soil particles is another mechanism which stabilizes beneficial soil organic matter.

In terms of practices 1) no till farming, 2)manuring, 3) composting, 4) liming, 5) cover cropping,6) mulching, 7) intensive rotational pasture systems such as holistic grazing and 8) agrofestry are systems of agriculture which can promote the change of the system to counteract rather promote global warming through greenhouse sequestration rather than net emissions.

If a system of teaching producers and giving incentive to producers could go a long way to remediating the soil issues which plague our world and allow society to address the run away greenhouse gas elevation we are currently plagued with.

The tried and true industrial efficiency strategy is what ever can be measured can be improved. The importance here is on one hand few producers are even aware of the importance of soil organic matter let alone are knowing its measurement values. The baseline of actual situation and the development of plans for its increase is mostly recognized by organic farmers but certainly in a minority situation. The improvement of the soil needs to start with soil conservation plans and development of crop rotations. In the prevailing monoculture production the use of no tillage has advanced but the use of rotation and cover cropping has lagged. Both conventional and organic farmers can be greatly benefited by the soil focus rather than purely focusing on inputs.

Soils with a high content of stable organic matter are powerful carbon sinks. Therefore, reducing tillage (even better would be eliminating tillage completely), maximizes carbon retention by soils. Developing an agriculture that relies on perennial crops (Natural Systems Agriculture as The Land Institute in Salina, Kansas) is proposing, is a sustainable model for regenerative agriculture, where carbon is 'banked' in the soil, rather than being spewed into the atmosphere.

I agree with

Bruno Borsari

Paul Reed Hepperly, thanks so much for your valuable and comprehensive answer every time, I already suppose the case of high temperature with a fast decomposition of organic matter and I totally agree with you and Bruno Borsari that management practices should be considered. But I have a question, what about soil cooling (without a greenhouse), is there any method or material application to cool soil to avoid such circumstances? Is this will be available and valuable in locations that have higher than 40-50-celsius degrees, or this just sophisticated and inapplicable suggestion?

In areas near the coastline there is interest in using Ocean Thermal Energy Conversion as an alternatives means of energy generation not so dependent on fossil fuel resources. The pumping of water which is cool at the deeps is brought up to the surface and harvesting of the differential energy results an alternative energy source. The water brought up from the deep is cool and excellent for propagating marine algae and animal life as food resources This type of water can be a source of cooling the soil environment and harvesting the atmospheric water through condensation.

Another way to lower the soil temperature is by the covering of it by reflective mulch and the sub drip irrigation under the mulch. Methods like wind breaks can be part of the environmental modification which may be needed. Much of conversion of organic materials by earthworms can be fostered by centralizing the activity underneath shade trees and letting earthworms be primary labor for organic matter conversion.

Earthworms need water and calcium and near neutral pH in most cases.

Great work.

Congratulations.

Dr. Paul, many many thanks for richness this discusion.

My best regards,

Heba Y. Elbasiouny

Microbial biomass carbon is a measure of the carbon ( C ) contained within the living component of soil organic matter (i.e. bacteria and fungi). Microbes decompose soil organic matter releasing carbon dioxide and plant available nutrients

Article Soil microbial biomass carbon and carbon dioxide response by...

This is a very good question and indeed a real dilemma. Soil microbial activity is absent in most discussions about climate warming ! Why ?? We could even state that microbial activity is crucial for controlling global climate warming. Ignoring microbial activity in this context is really surprising as global soils may contain double as much carbon as the atmosphere. They are certainly the largest sinks for atmospheric CO2 and organic C. The amount of C stored in the soil depends on the balance between carbon inputs (plant detritus, fertilisers, soil and fauna microbes decomposition, etc.) and carbon outputs from microbial respiration. Due to the terrific increase of world population from 1.3 billion in 1850 to almost 8.0 billion people nowadays (!), much more farmland was created mainly from forest lands with much more C stored and much more CO2, methane and other climate gases were released. With further climate warming soil microbial activity will increase even further and even more C will be released. This is a viscous circle.

Therefore it will be essential to elaborate and adopt agronomic management strategies aimed at reducing emissions of climate gases as the following examples:

Decreasing the level of soil disturbance through no-tillage, even if this may lead to higher use of herbicides; improving soil microbial activity and diversity ; maintaining continuous plant cover on soils all over the year. By such management strategies well adapted to the different climate and soil conditions, it should be possible to better control the balance between C inputs and C sequestration in the soils and outputs through emissions.

Thanks so much, Dr. Nirmala S.V.S.G for sharing you answer

Thanks so much, Dr. Alvin Alexander for your answer.so there is an agreement about the balance between C inputs and outputs in addition to adopting good management practices to mitigate gas emissions from soil.

The idea that soil potentially is the largest carbon sink is somewhat tricky. When soils are being diminished in the soil organic sources the potential sink acts instead of being a sink acts as a source of elevated greenhouse gases. The tillage revolution of the agricultural revolution was an initial source of elevated not acting as a sink and today there are many more soils which are sources rather that sinks. I am in agreement with the enormous potential for soil to become a sink practically because it has been a source for thousands of years now. Perhaps one of micro organism types which might be most important are mycorrhizae whose ability to produce glomalin glycol protein with know resistance to quick decay produces a useful mechanism for cementing carbon gains. The action of glomalin is to join together soil assemblages which is associated with lowered erosion and persistence from rapid decay. Mycorrhizae are extremely useful bioindicators for soil health considerations and predictive of ability for the soil to become a sink rather than a source of greenhouse gases.

The presence of glomalin related source protein is directly realted to increased soil organic carbon. The protein covers the soil aggregates and makes them persistent and resistant. The extraction of the glomalin shows the substance related to black heart properties of living soil and the extracted soil is bleached with deteriorated physical chemical and biological properties.

Very good addition Dr. Paul Reed Hepperly

To maintain a balance between the carbon sequestered by the soil and the carbon respired by the same it is vital to foster the microbial diversity in the soil, while (as it was already said), minimizing (and even better) eliminating tillage. Also the diversity of the biomass (crop residues) metabolized by soil microbiota plays a pivotal role in enhancing the diversity of soil organisms. The processes about carbon transformation into humus are solidly linked to diversity (of biota and of the substrate) and evolution by natural selection rules as well upon these.

That's great, thanks so much Dr. Bruno Borsari for your sharing

It all depend on the quality the residue/organic material added to the soil. If the decomposition process occurs at a speed nearly equivalent to the natural decomposition process, excess carbon dioxide issue is resolved.