Orchard soil health
of you who read chapter three of The
with me this week
will probably feel like you were drinking from a fire hose. The
took me days to digest and I suspect I'll be trying out Phillips'
techniques for the next several years. Feel free to comment about
other parts of the chapter (of which there were many), but I want to
focus my post on soil health this week.
It's very handy to read
this chapter with soil test results in hand. I
didn't actually test my orchard soil last winter, but I have test
results from the back garden, which started with the same
type of soil,
even if it has been treated slightly differently over the years.
Here are the relevant portions of the test results:
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Phillips follows an
Albrecht-like ratio approach to soil health, focusing on the relative
(rather than absolute) amounts of nutrients. When I got my
results back for the garden, all of the cations were listed as "very
high", so I figured I was fine. But Phillips notes that if
there's too much magnesium (Mg) in relation to the calcium (Ca) in the
soil (for example), plants will accidentally take up magnesium while
looking for calcium and may end up deficient in the latter. In
addition, he points out that calcium tends to spread soil apart, which
can be handy for drainage and aeration in clay
soil, while magnesium pulls soil particles together (useful in
sand, but not elsewhere).
The optimal Ca:Mg ratio
(compared using the percent of base saturation figures, not the
absolute ppm figures) is 5:1 for sandy soil and 7:1 for clay. As
you can see, my ratio is 4.5:1, meaning that some of my drainage issues
might be improved by boosting calcium. However, since my pH is
already too high, I don't want to just add lime, so I'll need to look
into gypsum, which increases calcium content in soil without sweetening
Similarly, you want to
consider the ratio of phosphorus (P) to potassium (K). Phillips
recommends P:K values of 2:1 to produce the most nutrient-dense fruits,
although 1:1 is okay in young orchards. My P:K value of 0.9:1 is
typical and signifies a need to boost phosphorus levels without
increasing the soil's supply of poassium. I'm going to have to do
some research into phosphate amendments to see which ones won't raise
our pH, but Phillips lists black rock phosphate, colloidal phosphate,
Tennessee brown phosphate, bonemeal, and bone char as possibilities.
If your head's awhirl
with numbers, here are some non-numeric soil factors to consider.
As I've mentioned previously, the goal in orchard soils is to boost
fungi at the expense of bacteria, which Phillips explains results in
more nitrogen being available in the form of ammonia.
Bacterially-dominated soils tend to have nitrogen in the form of
nitrates, which results in happy-looking trees and big fruits,
but low nutrient density and flavor, along with more susceptability to
disease. Phillips recommends keeping your soil fungally-dominated
by making special compost for the orchard out of deciduous wood chips
slow-composted with animal manures.
When should you apply
that compost? I've always thought that early spring was the best
time, but Phillips gets more scientific. He explains that the
white feeder roots that suck up nutrients are even more ephemeral than
leaves --- they generally only live 14 to 60 days before dying
back. Trees produce multiple flushes of feeder roots throughout
the year, generally during periods when growth on top of the tree has
slowed, and if you time your compost applications to match root growth
periods, you'll get more nutrients to the tree. Trees focus on
blooms in early spring, roots in mid spring, leaves in early summer,
and roots in late summer and fall. Cutting herbaceous plants
under the tree canopy (like grass or comfrey) during peak root growth
can help feed your tree at just the right time, and so can spreading
compost in autumn when half of the leaves have fallen. Meanwhile,
a heavy mulch in the fall can keep the roots growing later into the
winter, and can also muffle spring warmth so trees bloom up to ten days
later and miss fruit-killing freezes.
If you can handle
another eye-opening chapter, we'll read chapter 4 "Orchard dynamics"
for next Wednesday. Those new to the club might want to check out
previous chapters on beginning
a holistic orchard
for designing a holistic orchard. And, as always, I'm
looking forward to hearing your thoughts on this fascinating subject.