[Digestion] dosing for crops

David david at h4c.org
Wed Dec 7 13:46:26 PST 2011

Les, all,

On 12/7/2011 2:59 AM, Les Gornall wrote:
> Wayne,
> 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 
<http://www.repp.org/discussion/digestion/200002/msg00130.html>, also 
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 :

        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
        App.Sci. 499-519.

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,
        reducing recycling.

        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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