[Digestion] dosing for crops
david at h4c.org
Wed Dec 7 13:46:26 PST 2011
On 12/7/2011 2:59 AM, Les Gornall wrote:
> My first point of call for any fertiliser recommendations is
> 'FERTILISER RECOMMENDATIONS' otherwise known as RB209....
> From memory trials in Egypt in sandy soils crops were compared from
> digested and undigested manures for decades (Halwagi et al). The
> digestate crop yield was 15% better than the undigested manure crop
> yield after 15 years. In other words the soil was improving as a
> growing medium even in hot sandy soils.
I guess nothing ever dies in the Internet. Digital eternity?
I was interested in your mention of this, Les, and went spelunking,
thus encountering the fragment below
posted by you to this list, but a decade ago. Do forgive me therefore
for quoting it-- your ideas may well have changed, etc.-- but I
thought it was a useful addition to this discussion:
There are very few long term experiments relating plant growth
to the plant nutrients and micronutrients in digested vs
undigested organic wastes. - Have you ever tried to get a
grant for a 20 year research project?
However, you should read :
MOAWAD H., ZOHDY L.I., BADR EL-DIN S.M.S, KHALAFALLAH M.A.,
ABDEL-MAKSOUD H.K., 1984, "Assessment of anaerobically
digested slurry as a fertiliser and soil conditioner." in
[El-] Halwagi ed. Proc.Int. Conf. State of the art on Biogas
Technology Transfer and Diffusion, Cairo Nov. 17-24, Elsevier
The above appears to be the reference which memory prompted you to
cite, although perhaps it should be referenced as Moawad et al. You go on:
Also Zohdy L.I. et al 1984, "Repeated application of
anaerobically digested slurry and its effect on the yield and
NPK uptake of wheat, turnips and onion plants." (also in
Halwagi ed. above.)
These workers found that whilst the annual difference in crop
mass was greater for AD than unD manures, the difference was
not significant statistically-- But the positive difference
accumulated year on year for many years and so after 15 years
you would expect almost 15% more crop mass.
It seems to me that soils typically take 10,000 years to make
and 100 years to destroy. The aim of using AD is that the
decomposition of organic matter that would take place slowly
in the soil is done quickly in the digester. The AD effluent
is then used to rebuild the soil structure faster and more
efficiently than it is being destroyed by the agricultural
activity which itself depletes soil organics 100 times faster
than nature can repair the losses incurred by agriculture.
If we put undigested sludge on the soil the soil first has to
grow the bacteria for decomposition and typical growth rates
of bacteria in soil (in Northern Ireland) are one doubling per
year as determined by soil respiration experiments (see the
work of Prof. A. McFadden in the 1970's). There are also other
losses from 'slurry spreading', nitrogen is lost, (bound up as
microbial protein in AD effluent), clovers and nitrogen fixing
plants are severely inhibited and earthworm populations fail,
It is a big subject and one that is severely underfunded
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com
"Make no search for water. But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)
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