No-till versus ploughing -- does increased stratification help?

So this question has been bugging me for a while. I keep hearing recently, and I think I am correct that @martian is a proponent of this approach, that no-till is a vital way of sequestering carbon in the efforts to combat elevated atmospheric concentrations. Moreover, and perhaps more relevant to farming in the shorter term, is the claim that this extra SOC will dramatically improve the fertility (and therefore the productivity) of our soils.

There is only one problem with this, I think there's a good chance that no-till doesn't actually do the above. To get a really overview of the corpus of academic work on this area pretty much requires this to be your job, but having done a good few hours -- probably tens of hours -- reading around this subject, I come somewhat begrudgingly to hold this viewpoint.

There is a lot of erroneous information about SOM / SOC etc under plough and no-till systems. A lot of the errors come from incorrect sampling techniques. For example, sampling too shallowly and failing to correct for bulk density in the samples. Once those mistakes are corrected, the general picture shows surprisingly little difference between tillage and zero-tillage practices.

If it is the case, as a matter of fact, that there is no extra SOM due to zero-tillage, we can, I think, say with a good degree of certainty that zero-till causes a significant stratification of SOM which you do not see in plough based systems.

So, my question then is this: does the same amount of SOM concentrated near to the surface in a stratified way lead to a more fertile and productive soil? If so, should we be using SOM stratification as a more useful metric in assessing soil fertility rather than the error prone loss on ignition SOM tests?

Here's a paper which suggests that the answer to the last question should be "yes": http://www.sciencedirect.com/science/article/pii/S0167198702000181.
 
This is a very good study (long time period, good sample technique, relevant geography and climate) which exemplifies the lack of difference between cultivation and zero-till:

http://www.sciencedirect.com/science/article/pii/S0167880914000942.

On the plus side though, I have just spent the day at the NIAB winter conference with some very useful data coming out of the New Farming Systems JD750a project which shows zero-till in a more positive light.
 
I cant read your links but remember stratification in dry areas is probably more likely than our wet island.

Also are the plowing comparisons the one where they chuck the om under the plough and claim that tillage doesnt burn it up?

Finally OM isnt the be all and end all. Id be happy in some of my fields not to have much more OM as its doing enough now to function for my crops. Some fields need more but may never get there because i probably farm slightly too extractively. Id say OM is good but not beyond a certain point. Fertility is also important. They are not always hand in hand.

Im following Charles Darwin and his worm theory esp for this country
 
@SilliamWhale - so you do you think that more SOM (yes, it's too broad a term, I know) concentrated near the surface, rather than spread more evenly throughout the profile, generates a more productive soil?

I dont know. I suppose if you want to invoke the idea that mother nature is doing what comes naturally by taking co2 and putting it as C then yes I would. But there comes a point where more SOM could start to affect other stuff. If you think about how vegetation reaches a climax in this country at say beech and lime woodland and we are wanting to keep it at the grassland phase then maybe we need to admit OM isnt the key component?

But we all know you can grow great crops with poor soil om and you can grow great crops with poor soil structure as plough and power harrow men up and down the country prove. So maybe its by the by?
 

debe

Member
Location
Wilts
As someone who has too much time on their hands I've thought, and occasionally read about this little concept.

One theory I keep returning to is the idea that after a period of time (x) soil OM (y)under a certain system will reach an equilibrium. Where x and y vary according to cultivation method as in x and rotation as in y.

The value of zero till comes in maintaining a higher OM level (and all its perceived benefits) for that bit longer, before they return to the inevitable equilibrium.
 

martian

DD Moderator
BASE UK Member
Location
N Herts
I've just spent 2 days listening to talks at No till on the Plains (with another day tomorrow ) and I've heard some astonishing claims about levels of c sequestration.

I won't answer in full now as it takes me ages to tap out on my phone, but Dr Ray Weil (Prof Soil Science Univ Maryland and author of standard soil textbook over here) referred to this stratification. He went on to say that once you use cover crops properly this effect disappears and SOM levels increase throughout profile. Introduce livestock and figures go wild.

More later. ..
 

fudge

Member
Arable Farmer
Location
Lincolnshire.
As someone who has too much time on their hands I've thought, and occasionally read about this little concept.

One theory I keep returning to is the idea that after a period of time (x) soil OM (y)under a certain system will reach an equilibrium. Where x and y vary according to cultivation method as in x and rotation as in y.

The value of zero till comes in maintaining a higher OM level (and all its perceived benefits) for that bit longer, before they return to the inevitable equilibrium.
I completely agree with this assessment. I plough because it makes farming our soil easier, all the problems go in a hole, but there is no doubt that fields that were in grass until 2001 still have higher om content. This makes them easier to work and more resilient in wet weather but not necessarily higher yielding. The conclusion that I infer from this, admittedly empirical, evidence is that those who say that grassland holds more carbon than arable soils are correct. Stating the obvious really. I suppose if policy makers wanted to increase SOM they would limit the use of N, manure and bagged, to force farmers like me to adopt ley farming techniques.
 
Location
Cambridge
There is a good trial from FAR in NZ that showed when coming out of grass into cropping, the rate of SOM decrease significantly slower in no-till than when ploughed. But after, IIRC, 9 years, the SOM levelled out at the same % in both treatments.
 

conor t

Member
SOM is a function of roots and microbes tying up carbon in aggregates where it gains protection, so expecting modern crops with smaller root mass + less microbes its hard to see how no till alone can have any major difference.
 

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Simon C

Member
Arable Farmer
Location
Essex Coast
My main question is not about whether no-till builds higher organic matter levels overall. The question is, assuming that it does not, whether stratification of organic matter is a good or a bad thing.

The one thing we know for sure is that no-till reduces the losses of organic matter. If you don't keep artificially aerating the soil to depth, you won't be stimulating the bacteria that feed on it and therefore releasing CO2 into the atmosphere.

The other thing is that organic matter is no use if it is down below the aerobic layer, however deep that is. Even in permanent grassland, fence stakes don't rot all the way down, they give a very good idea of how far the air is getting into the soil and so ploughing OM down below this level is pretty stupid.

In the days of horse drawn ploughs running at four of five inches in mid winter when the soil was too cold for any microbial activity to be going on anyway, probably wasn't a big deal, but today's deep summer and early autumn ploughing is a whole different ball game.
 

fudge

Member
Arable Farmer
Location
Lincolnshire.
My main question is not about whether no-till builds higher organic matter levels overall. The question is, assuming that it does not, whether stratification of organic matter is a good or a bad thing.
Surely it's neither good or bad. If you're no tilling it is bound to be at the top. While it lasts!
 

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