[nafex] mulching blueberries with woodchips

Michael Dossett phainopepla at yahoo.com
Mon Dec 24 13:41:44 EST 2012

Telling the difference between a chlorosis derived from excessive pH and one caused by poor drainage is actually fairly straight forward.  A combination of leaf tissue nutrient analysis and soil pH testing, in this case, was enough to confirm what was going on and verified the site history.  Overall, leaf tissue nutrient analysis is a great way to monitor what is going on and tells you far more than a simple soil test for nutrient analysis.
I noticed two things about your links to land grant university guidelines about wood chips that are worth pointing out.  One is that they are for the upper Midwest and the SE.  I already mentioned that pine-bark substrates and mulches were the rule of thumb for production in the SE.  This fits very well with their production systems and conditions.  The other thing I noticed about your links is that the actual guidelines (not the project report from the grant, which only compared woodchips to no mulch and did not compare to sawdust nor did it give actual guidelines) also recommended sawdust.  If you read my email, I noted that in the Pacific Northwest, the conventional treatment is sawdust, with or without compost underneath.  I'm not saying that woodchips won't work, but if you read what I wrote, where wood chips or hog fuel were used in side-by-side treatments under the same growing conditions as compared to sawdust with and without compost,
 sawdust performed better, therefor I would not recommend wood chips in this area.  This is based on observations from grower's experimenting on their own, as well as grower-managed replicated research plots and university-managed trials. The links you provided are not at all contradictory to the argument I was making, but don't provide enough information for people to decide which of these was better, only that either can be used as a mulch and that wood chips is better than no mulch at all.  Aside from potential differences in the types of wood and trees that chips may come from, wood chips and sawdust break-down differently and do different things for the soil and at different rates.  They tie-up nitrogen differently so that fertilization regimes will have to be adjusted, they need to be replenished at different rates, they alter C/N ratio of the soil differently, and in many areas where incorporation of sawdust is recommended, incorporating wood
 chips would also change porosity and drainage differently in addition to magnifying the effects already mentioned.  These all go into adjusting the production system, rather than merely one aspect and are likely to change with different growing climates.
Oregon State University currently has a project for organic blueberry production using weed mat as a weed control.  This is in various combinations with sawdust and compost mulches on their own as well, as above and below the weed mat.  One thing that has come out of the preliminary results, so far, is an effect on soil temperature and canopy temperature that is changing the rate of water use in the plants and also a change in the rate of loss of soil organic matter.  Not to mention the fact that voles loved the weed mat and the researchers found the need to bait under the mat to control them.  This is the sort of project that will be able to provide real recomendations for organic blueberry production down the road as it takes into account all aspects of the production system including fertility, irrigation, and soil management in addition to growth and yield.

Michael Dossett
Mission, British Columbia
phainopepla at yahoo.com

From: Alan Haigh <alandhaigh at gmail.com>
To: nafex at lists.ibiblio.org 
Sent: Sunday, December 23, 2012 1:17 PM
Subject: [nafex] mulching blueberries with woodchips

Michael, how can you tell the difference from a chlorosis derived from
excessive pH from one caused by poor drainage?.  I'm a little suspicious
that those low points may have been like low points in many fields-
possessing poor drainage.  Of course this is an obvious observation that
was probably explored.

Here in the northeast woodchips are often used to mulch blueberries in home
orchard settings, which is all I'm knowledgeable about and I fail to see
why they should ever create problems- relatives like rhododendrons are
routinely mulched with shredded wood as well and these plants thrive under
this treatment at scores of estates I've seen. .  The only trouble I've
had  with shredded wood is that it sometimes mats up and excludes rain
water- it just runs off the surface.

I don't completely trust the kind of anecdotal examples you supply (not
that I'm not offering the same thing with much smaller scale examples).
I'd need a lot more info about how mulch was applied and what the weather
and soil issues were- actually I'd need to see the site myself to be
satisfied.  Always the problem with contradicting anecdotes.

Here are several mostly landgrant university guidlines that do recommend
mulching blueberries with woodchips.  I'd be interested in any research
based info you have on the affects of mulching blueberries with woodchips
as I couldn't find any actual research on the subject.





>I have no doubt that what you say about humic acid production and mulching
blueberries may be true, but there are a lot of >variables at play, such as
what kind of mulch, or what kind of wood chips, and where the trees grew
etc.? Just as there are exceptions to every rule, there are circumstances
in which blueberries can be successfully grown in soils with a pH range
higher than the 4.5-5.5 typically recommended; however, as a general
guideline, most people will have the best shot at success if they follow
this.? I have been to literally hundreds of different blueberry operations
over the years, both in the NW and elsewhere?(there's more than 30,000
acres in blueberry production within a 45 minute drive of my house) and the
one thing I can say is that I absolutely cannot recommend wood chips as a
mulch for blueberries.? While some people may have success with it
elsewhere, in this area, every single field I've seen where they have
mulched with wood
chips or hog fuel, has underperformed, often times in comparison with the
same variety being grown by the same person just a few rows away with
conventional treatments of compost and sawdust.? As I've said, there are
always exceptions.? In Georgia and Florida, most of the commercial
blueberry production takes place in pine bark substrate, or with
incorporated pine bark in the soil.? They have developed a system where
this works for them, although they still have to acidify the soil.? In fact
one very large blueberry farm I visited in Florida last month was growing
primarily in a pine bark incorporated and mulched system with sulfuric acid
in the water to help acidify, and they still had iron deficiency in some
low spots in their fields.? It turns out that these spots were where there
were limestone tailings near the surface that had been left there decades
before, and they just couldn't get the soil and water acid enough in these
places to avoid
nutrient problems.
Every site is different and not all wood chips or other materials are the
same, and different cultivars certainly have a range of tolerances for
differing soil conditions and production practices.? I encourage people to
try to get their conditions as close to what the recommendations are as a
start, because I believe this will be their best chance for success.?
Having said that, sometimes you have to improvise and experiment to find
another solution, and I encourage people to do that too.
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