permaculture

[Robyn Francis <erda@nor.com.au>]

Fresh sawdust can have a C/N ratio of up to 500:1 this reduces with aging
and composting.

While sawdust can be an excellent mulch, it's important to realise it can
impact on N balance and plant uptake--to be forewarned is to be forearmed--
monitor the plants and act promptly if there's symptoms of N deficiency, or
take proactive measures such as partial pre-composting, adding compost
before the mulch (buffer effect) or apply diluted urine, liquid cook manure
or other suitable N source.

Apparently the high lignin content (27%) in sawdust also has a high N demand
to break down.

Research has found fresh sawdust mulch can result in N-deficiency in crops,
though not as severely as when incorporated into the soil.

Robyn


On 27/10/07 6:33 PM, "Dieter Brand" <diebrand@yahoo.com> wrote:

> Composting does occur at a range of C/N ratios, but, according
>   to what I understand, optimal composting conditions are near
>   a ratio of 25/1. Using the compost heap as example, which is
>   easier to understand, I have understood this to mean, that, if
>   the ratio is for example 100/1 then all of the N will be used to
>   compost part of the C, going through successive cycles until
>   the ideal ratio is reached, at which time full blown composting
>   will take place. Hence, the higher the C contents the more
>   time needed for the composting.