Dear Tlhokomelo, we have been using these conservation measures in Brazil for a long time now. You will find many references on the literature, regarding No-til, which I prefer to call it Minimum tillage, since there is some disturbance of the soil, once you plough it. The main thing is that once you use these conservation practices, besides decreasing soil erosion, you will increase the amount of organic matter in the soil, that means you increase carbon content.

Best wishes,

Prof. Antonio Guerra

Department of Geography

Federal University of Rio de Janeiro

www.lagesolos.ufrj.br 

Thank you Sir  Jose Teixeira Guerra

A follow up question please. On the literature i discovered that total organic carbon content decrease with depth and according to the trial i conducted, active or labile carbon pool does the opposite which is increasing with depth. I'm currently busy with the project report that need to be submitted any time soon. My only problem is that i cannot find the literature to support my finding . The only thing i could do is to speculate! Simply because the most previous and the current research is more based on determination of Total organic carbon without paying attention on the active carbon.

Dear Motema,

To evaluate the potential of no-tillage management to increase the stock of total organic C in soils of the Pampas region in Argentina, 40 crop fields under no-tillage and conventional tillage systems and seven undisturbed soils were sampled.

(1) Total organic C, their fractions and stratification ratios and the C storage capacity of the soils under different managements were assessed in samples to a depth of 30 cm, in three layers (0–5, 5–15 and 15–30 cm). The differences between the C pools of the undisturbed and cultivated soils were significant (p < 0.05) and most pronounced in the top (0–5 cm) soil layer, with more active C near the soil surface (undisturbed > no-tillage > conventional tillage). Based on the stratification ratio of the labile C pool (0–5/5–15 cm), the untilled were separated from conventionally tilled areas.

(2) Much of the variation in potentially mineralizable C was explained by this active C fraction (R2 = 0.61) and by total organic C (R2 = 0.67). No-till soils did not accumulate more organic C than conventionally tilled soils in the 0–30 cm layer, but there was substantial stratification of total and active C pools at no till sites. If the C stratification ratio is really an indicator of soil quality, then the C storage potential of no-tillage would be greater than in conventional tillage, at least in the surface layers. Particulate organic C and potentially mineralizable C may be useful to evaluate variations in topsoil organic matter.

I hope you find this input interesting and useful.

Reference:

Álvarez CR, Costantini AO, Alfredo B, Taboada MA, Boem FHG, Fernández PL and Prystupa P (2011) Distribution and vertical stratification of carbon and nitrogen in soil under different managements in the Pampean region of Argentina. R. Bras. Ci. Solo, 35:1985-1994.

This is lovely. Thank you Sir! 

Interesting discussion . Here arev some good works relating the discussion...

Abstract ; To assess the impact of different types of soil tillage on the density, biomass, and community composition of earthworms, a long-term field study was performed in which soils were tilled in different ways for ten years. This study included five different types of tillage: (i) plough, (ii) grubber, (iii) disc harrow, (iv) mulch sowing, and (v) direct sowing. At the end of the experiment the earthworm density, biomass, and community composition, and the SOC (soil organic carbon) content were determined. The results show that density, biomass, and community composition of earthworm populations varied in relation to the type of soil tillage used. The density of anecic earthworm species decreased when soils were managed byconventional ploughing, relative to reduced tillage practices, whereas conversely the density of endogeic species increased. Additionally, the varying types of soil tillage influenced the abundance and biomass of different earthworm species in different ways. The density of Aporrectodea caliginosa was positively influenced by ploughing, whereas Aporrectodea longa, Lumbricus castaneus, and Satchellius mammalis showed a positive relationship to the grubber and Allolobophora chlorotica to direct sowing. We attribute these changes to modifications in the vertical distribution of SOC and varying potentials for mechanical damage of earthworms by tillage. A decrease in tillage intensity modified the vertical SOC distribution in the topsoil and consequently revealed positive effects on earthworm biodiversity, thus sustaining soil functioning. Source : Gregor Ernst*, Christoph Emmerling,European Journal of Soil Biology 45 (2009) 247–251

Abstract ;Stabilizing or improving soil organic carbon content is essential for sustainable crop production under changing climate conditions. Therefore, soil organic carbon research is gaining momentum in the Mediterranean basin. Our objective is to quantify effects of no tillage (NT) and conventional tillage (CT) on soil organic carbon stock (SOCs) in three soil types (Vertisol, Cambisol, and Luvisol)

within Central Morocco. Chemical analyses were used to determine how tillage affected various humic substances. Our results showed that, after 5 years, surface horizon (0–30 cm) SOC stocks varied between tillage systems and with soil type. The SOCs was significantly higher in NT compared to CT (10% more in Vertisol and 8% more in Cambisol), but no significant difference was observed in the Luvisol. Average SOCs within the 0–30 cm depth was 29.35 and 27.36 Mg ha−1 under NT and CT, respectively. The highest SOCs (31.89 Mg ha−1) was found in Vertisols under NT. A comparison of humic substances showed that humic acids and humin were significantly higher under NT compared to CT, but fulvic acid concentrations were significantly lower. These studies confirm that NT does have beneficial effects on SOCs and quality in these soils. Source : Applied and Environmental Soil Science ,Volume 2014, Article ID 654796, 8 pages

Hope , you find them useful..

Dear Tlhokomelo, cultivation will increase oxidation, and so result in the breakdown of organic matter which has an an associated increase in CO2 release. However, these differences between the treatments are likely to be transitory. Over time the OM content of the three treatments will trend towards the same point of equilibrium, with gradually decreasing rates of decomposition. In general, if organic matter is incorporated into a soil, you will find that after a couple of years, that 95% of the OM will have been oxidised. In contrast, peat soils with a very high OM content occur in areas that are cold and waterlogged, where oxidation rates are very low.

Regards,

Dear Motema, I do not know up to what soil depth you are considering in your studies but my experience is in surface soil (0-15 cm), you may get more active C in no-till soil followed by stubble land then tilled soil. But if you look at sub surface soil (below 45 cm depth), you may get more active C in tilled/plough soils than stubble and no-till soil. There is a possibility to get some conflicting results when you are considering the soil layer between 30 and 45 cm depth. But one thing is very clear that the active C in the soil is absolutely depends on the microbial activity , moisture content , the C content of your stubble and the vegetation on the soil surface.

Interesting feedback Dr Tarafdar, very impressive indeed . Why do take organic carbon alone as ultimate effect of  tillage versus non-tillage..? Does it really act so precisely as an index of  biological properties of soil, as a function of labile fraction of soil organic carbon...? 

 As per the current literature(colleagues also cited good references), most of the changes in organic carbon content were seen in surface layers 0-5cm or 0 - 15 cm under conservation agriculture(zero or minimum tillage).In the deeper layers there was no much change.However depth of root penetration and amount  of organic matter added through roots may have some influence on carbon content.Biological activity may also extend upto that depth.The following paper and references  cited in the paper may help.

Tillage and soil carbon sequestration-What do we really know? Baker,J.M. et al .Agriculture Ecosystem and Environment.118(2007):1-5.Available online at www.sciencedirect.com

Dr. Srivastava, yes, labile organic carbon fraction may act precisely as an index of biological properties of soil as biological activity of soil, in general,  strongly correlated with available carbon content in the soil 

Thank you everyone for the feed back. 

A follow up question!

I'm fully aware that organic matter contain different fractions of which active or labile carbon is one them and regarded as the most important one. This active carbon is subdivided into Particulate organic carbon, dissolved organic carbon and microbial biomass to mention the few. My main concern is what makes it so distinct as compared to order fraction and why attention is only bases on total organic carbon while active carbon is mobile and quickly react on soil management practices??

Total organic C represent the C stock in the soil, which with time becomes active  or labile to take part in the soil management practices.  Total organic C also very much linked with  the microbial build up and nutrient transformations as well as enzymatic activities in the soil. Therefore, generally, more attention was focused on total organic C rather than active or labile fractions. 

Dear Tlhokomelo Motema,

As above mentioned by Tarafdar sir that Total Organic C represents the C sequestration potential of soil due to certain management practices followed in the field but it is not a sensitive indicator of soil quality. for eg. Two soils may have the same total organic matter content, but a soil with 50 % of its total soil organic matter present in the labile pool suggests a more biologically active soil, with greater potential for nutrient turnover, and better soil structure, than a soil with just 5 % of its total organic matter in labile fractions. Similarly, a soil that has a high proportion of its total carbon present in the recalcitrant organic pool is likely to be less fertile than a soil with the same total carbon content but a lower proportion of recalcitrant organic carbon 

In a study by Huang etal 2015, the results showed that concentrations of SOC, soil total N (STN), and soil organic N (SON) were higher at 0–5 cm depth but lower at 5–10 cm depth under No  Tillage than conventional tillage (CT), while at 10–20 cm depth the differences were not significant.