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-- [ From: Jack Hillen * EMC.Ver #2.5.02 ] --
------- FORWARD, Original message follows -------
Date: Sunday, 20-Oct-96 02:14 PM
From: Jack Hillen \ Internet: (jackh@fishnet.net) To:
Multiple recipients of list IRRIGATION-L \ Internet: (irrigation-
l@listserv.gmd.de)
Subject: Re: Benefits of straw mulch in orchards
-------- REPLY, Original message follows --------
> Date: Friday, 18-Oct-96 08:18 AM
>
> From: Hortech Services Pty Ltd \ Internet: (hortech@www.ats.com.au)
> To: Multiple recipients of list IRRIGATION-L \ Internet:
> (irrigation-l@listserv.gmd.de)
>
> Subject: Benefits of straw mulch in orchards
>
> Does anybody have or know of any information on the benefits of mulching
trees
> with specific respect to soil water relations ?
>
> I presently have a EnviroSCAN system installed on an Avocado orchard.
>
> One probe with sensors at 10,20,40,70 cm under a mature Hass tree, un-
mulched.
>
> Another probe in adjacent row with sensors at 10,20,40,70 cm under a
mature
> Hass tree, with straw mulch up to 4 inches thick.
>
> So far,
> 10 cm - unmulched dries out faster than mulched
>
> 20 cm - unmulched dries out slightly faster than mulch
>
> 40 cm & 70 cm - water extraction rates comparable if not slightly faster
in
> mulched.
>
> Irrigations - same sprinkler, 12 hours in unmulched reached 70 cm and
beyond.
> 12 hours mulched did not reach 20 cm and even did not saturate 10 cm.
>
> The straw is only been placed around the tree within the last month. I
> suspect the slower loss of moisture at 10 cm in the mulched trees may be
due
> to either
> 1. condensation under the mulch
> 2. higher levels of CO2 in top soil due to breaking down of mulch. I
suspect
> the roots in top 10 cm are competing with microbes for O2 and may explain
> reduction in activity.
>
> Many growers comment on the visible benefits of mulch on the soil moisture
at
> surface. But has anybody have soil moisture data to verify the claims ?
The
> grower at which this trial is being conducted feels the data contradicts
the 20
> years of thought on mulching of trees. Especially where the mulched trees
are
> redirecting their extraction activity to the deeper soil profiles.(Or am I
> seeing capillary rise caused by the condensation processes under the mulch
? )
>
> Any feedback would be most appreciated.
>
> Kind Regards
>
>
>
> Peter Broomhall
> Horticulural Consultant
>
> Hortech Services Pty Ltd
> a.c.n. 060 406 957
> P.O. Box 370
> Kallangur QLD 4503
> Australia
>
> P: +61 418 708 573
> F: +61 7 3886 0389
>
> hortech@ats.com.au
>
-------- REPLY, End of original message --------
Peter,
As a Hass avocado grower of some 24 years, I might be able to shed some
light on your readings. First of all it is important to understand where
avocado trees come from. They are a subtropical rain forest type of tree.
The Hass avocado tree is shallow rooted, and is in need of frequent
irrigations. If you take a shovel and dig down into the root system, you
will find that mature Hass avocado trees have most of their feeder roots in
the top 20 to 30 cm. The trees will grow to a height of 10 to 15 meters
and have a diameter about the same. The natural structure of the tree is
that the lower branches grow down to the ground. The tree sheds copious
amounts of leaves all year. This forms a natural mulch, much to the benefit
of the top feeder roots, i.e. moisture levels in the soil are not depleted
as rapidly by solar and wind influence. I think it would stand to reason
that the uptake of irrigation water by the tree would influence the top 30
cm more than the lower levels. This appears to be reflected in your data.
The avocado tree information above, is for California, USA, trees.
Since a commercial avocado tree is a union of two different avocado trees,
and the type of root system we use may not be the same as yours, you might
want to check the root depth on a few of your trees to see if it is the same