Sunday, April 19, 2015

Preparing for Drought

Defining drought is an elusive task.  We know it when we see it.  Wilted plants.  Plants failing to thrive.  Dry streams and river beds.  Swamps that one can walk across.

Up-to-date Crop Moisture Index charts available HERE
One attempt to quantify drought is the Crop Moisture Index.  It portrays the moisture available in the top five feet (1.6 m) of soil.  A fine loam soil can easily hold the equivalent of up to 12" (300mm) of rain in the top five feet.  A growing crop of corn needs every bit of it.  The corn's moisture requirements typically exceeds the precipitation during the growing season by 10"-to-15".  That water must come from somewhere.

One nuance of the Crop Moisture Index is that a moisture deficiency is unlikely to be fixed by a single rain.  It takes an extra 5" and 10" of rain, over a long enough of a period for it to soak in to fix a Crop Moisture Index shortfall.

Another deficiency of the Crop Moisture Index maps is that the scale of these maps is too crude.  Drought can be a profoundly local phenomena.  I have seen corn fields where half had received an inch of rain from a July thunderstorm cell and the other half had not.  The corn in the moister half was 18" taller than the corn that stayed dry.  The transition area, the corn that received some rain but not the full inch was about six rows wide....about 20 feet. 

You might challenge me by suggesting other factors were the cause.  However, the transition was arrow straight and cut across the field diagonally, west-southwest, the direction of that the thunderstorm cell had been traveling.  And diagonally is not a pattern associated with different hybrids or a misapplication of fertilizer.

Half the field was suffering drought.  The other half was happy.  That cannot be captured in a map where the tiles are 5000 square miles.

Trail of utility trenching is easy to see.  Drought damage may be due to the synergy of nutrient poor soil and lack of moisture.  Nutrient starved plants cannot punch their roots down 5 feet and harvest all of the moisture that is available to their healthier neighbors.

Similar juxtapositioning of drought/not-drought can happen due to soil types or soil depth.  One often sees that where foundations have been built and the subsoil was dozed out over low spots.  It is also apparent where trenches have been dug and back-filled with non-native soils.

Up-to-date U.S. Drought Monitor charts available HERE
This map shows another way of quantifying drought.  It is the equivalent of the BCS system for rating college football teams.  It attempts to take data from a variety of sources and synthesize a "best definition".

It suffers the same problems of crude scale that the CMI map has.

Walk around and kick the dirt

The way to tell if you have a drought, or are on the verge of a drought, is to walk around and kick some dirt.  Check out the ephemeral swamps and ponds and road-side ditches.

A gardener can soften the edges of a drought with a little bit of lead time.  It is like driving on a slippery road;  the time to make adjustments is before you are into Deadman's Curve.

One function of rain is to carry fertilizer down to the root zone.  I am spreading Nitrogen early this year.  I would usually wait for the trees to be budding out to ensure that the trees took up the Nitrogen rather than any grasses growing beneath them.  A tree in a strong state of nutrition will have energy to grow more root hairs and to drive their roots deeper into the subsoil.  They build up carbohydrate reserves because they do not extend shoot growth.  They bank those reserves instead.

A gardener can also make some decisions to plant his/her seed further apart.  Each plant mines a block of soil commensurate with its spacing relative to other plants.  Seeding rates that result in high plant density give each plant a smaller block of soil from which to extract moisture and nutrients.

In the woods I have been doing "release" cuttings.  That is, I have been removing trees where the trees are crowded and are mutually suppressing each other's growth.  I remove less desirable species.  I remove trees with poor form.  The remaining trees end up with bigger blocks of soil from which to extract moisture.

Weed control becomes even more critical during a drought.  Weeds are more competitive growers than the gardener's vegetables or flowers.  For fruit trees, this often means more aggressive use of a herbicide like glyphosate to clear larger patches of ground cover from beneath the trees. 

Mulch is your friend.

Wind breaks are your friend.

When you water, remember that you need to lay down inches of water.  Put out some shallow, disposable, aluminum pie pans in a semi-random pattern and time how long it takes them to fill. That is how long you need to run the sprinklers each week. I use impulse sprinklers and I need to run them six hours to lay down enough water.

The pie pans are also a good method to adjust the calibration on your impulse sprinklers.  It is difficult to not over-water the center and under-water the edges when you calibrate by eye.  (Detail:  some pie pans have little holes in their bottom.  Avoid those pans when you use them for this purpose.)

The last two years have been excellent for rain but there are no guarantees in the gardening game.  I am preparing for a dry summer because it has been a very dry spring on my ten acres of paradise.

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