[Terrapreta] Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions

[Sean K. Barry]

Hi Elliot,

I've read the paper you referred to us  ...

Biol Fertil Soils (2007) 43:699–708
Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions
Marco A. Rondon, Johannes Lehmann, Juan Ramírez & Maria Hurtado

I found it on Dr. Lehmann's Cornell site.

There was a confusing set of statements in the ABSTRACT ?

Bean yield
increased by 46% and biomass production by 39% over the
control at 90 and 60 g kg-1 bio-char, respectively. However,
biomass production and total N uptake decreased when biochar
applications were increased to 90 g kg-1.

They must have meant ... 30 and 60 g kg-1 in that first sentence?

I read the paper similar to the way you did.  All the levels of bio-char addition raised the C/N ratio and lowered available Nitrogen.  
But, the BNF plants still did a better job at fixing N than the control (no biochar).  Overdosing the charcoal amendments up to 90 g kg-1 seemed to cause the N-fixing beans to fix less N and grow less than at the 30 or 60 g kg-1 biochar levels.

These
results suggested that biological N fixation (BNF) is
enhanced by bio-char amendments.

...

Several studies indicate that biochar
is an excellent support material for Rhizobium
inoculants.

...

It is hypothesized that bio-char improves BNF by common
beans due to decreased N availability, increased pH as well
as nutrient availability, and greater mycorrhizal infection.

Does the nitrogen derived from the atmosphere (NdfA) look like it might be a key to the BNF increases?  The NdfA went up in all the biochar amended soils, presumably because the Rhizobium (Actinobacteria) got more active in soils.

Do BNF plants look like the ultimate first crop to put into biochar enhanced soils, or what?  They will fix more N, which can be tilled back into the soil.  Then, will that repair that initial high C/N ratio in the soil sooner?  After that C/N balance is restored below what?, 20?, then other crops could do better, maybe?

The ground bio-char was added and
very well mixed with the soil just immediately before
filling the pots. Water was then applied to the pots to reach
a 60% field capacity, and the pots were allowed to stabilize
during 4 weeks before planting, replenishing evaporated
water twice a week.

I wonder why they let the pots of soil/biochar mix sit wet for 4 weeks before planting?  The Rhizobium inoculate was in the beans, not the soil, right?  What were they allowing to stabilize?

Apart from the stimulating effect of low N availability,
increased availability of other nutrients contributed to
greater BNF of beans.

It is very odd, I think that nitrogen fixation by BNF plants goes up with decreased N availability in the soils?!  I don't understand why that is?  Why is it a stimulating effect?

Foliar concentrations and uptake of
B and Mo (Ca and P only slightly) indicated better
availability of these elements which are known to increase
BNF (Carpena et al. 2000; Giller 2001) when bio-char was
added to soil. 

...

This application of 60 g kg-1 is equivalent to an application
of 121.5 mg bio-char per hectare ha-1 or 97.2 mg C ha-1 if
calculated for the plough layer of 0.15 m with an average
bulk density of 1.35 mg m-3.

^That looks like a somewhat optimized recipe for an amount of biochar application and it's HUGE; ~122 tonnes per hectare in the top 15 centimeters!  They talked about how this 60 g kg-1 level looked like the optimal rate for the best BNF and biomass production from the beans.  I think anyone would be lucky to be able to get 10 tonnes per hectare of biochar from charring up Savanna biomass standing on that land before cropping it with soybeans.

Conclusions

Nitrogen fixation significantly improved by moderate rates
of bio-char additions. The reason for the improved BNF
was mostly an effect of the improved availability of B and
likely of Mo, and to a lesser extent, ...

I don't know why, but they give the attribution for improved BNF mostly to the increased availability of Boron and Molybdenum micronutrients when biochar is added to the soil ?

Thanks for the reference, Elliot.  It's a very interesting paper.

Regards,

SKB
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/terrapreta_bioenergylists.org/attachments/20071004/5cae85f1/attachment.html