Tuesday, February 02, 2010

Proper irrigation of garden Soil Beds


I came across the question and answer you gave below (a previous post which
stated that 1" of water in the beds is needed each time you water - JK) and it
confused me somewhat. I have a question about putting an inch of standing water
on the beds every day. Conventual wisdom is an inch of water per week. Are we
to apply a weeks worth of water per day to the beds?

An example of the confusion many people experience with this subject can be
found in an article by Cornell University Agricultural Extension Division about
watering tomatoes. The author states that tomatoes need 1" of water per week at
a minimum. In the very next paragraph the article gets more specific and says
that a single tomato plant needs between 3 and 5 gallons of water per week.

On the surface, those two statements seem to be very inconsistent, but let's go
a little deeper. Traditionally, tomatoes are grown much farther apart than we
do in the Mittleider Method. In addition, traditional watering is done by
flooding the entire garden area.

Let's suppose a person's tomatoes are planted 2' apart, in rows that are 3'
apart in a bed that's 30' long. One hundred square feet of garden space would
contain about 16 plants, and would require 64 gallons of water per week
(assuming 4 gallons per plant).

Applying 1" of water to 100 square feet of garden would require 8 1/3 cubic
feet, or 62.5 gallons (1 cubic foot is 7.5 gallons), so that is consistent with
what Cornell recommends.

In the Mittleider Method 16 tomato plants - planted 9" apart - will take up 12
lineal feet in a soil-bed. The width of the planting area is 10"-12". Using a
12" width, it would require 1 cubic foot of water each time(12' long X 1' wide X
1/12' deep =1 cubic foot). That amounts to 7.5 X 7, or 52.5 gallons per week.

So, you can see that watering 1" per day in your soil-bed uses less water than
watering 1" per week by flooding. Confusion ended, right?

There is more to consider, so let's carry it a bit further. If you are growing
in heavy clay soil Cornell's recommended 1" per week may be sufficient, because
water drains very slowly from clay soil. But if your soil is loamy or sandy, or
if the temperatures are hot, the water will be gone from the top 8-12" of the
soil in less than a week, and your plants will be stressing.

Tomato plants grown under traditional watering conditions have to expend
substantial energy sending their roots deep into the soil, to follow the
receding water, and keep from dying. This is energy we prefer to use growing
and maturing fruit.

Furthermore, flooding the entire area wastes much of the water, and usually much
more than 1" depth is applied, wasting even more. Also, flooding makes the
aisles hospitable places for weeds to grow, increases humidity which invites
diseases, and the moisture, weeds, and cooler temperatures nurture the bugs.

All things considered, I believe Dr. Mittleider has it figured out very well,
even to the point of declaring that you will save 1/2 or more of the water you
traditionally used, and promising a better garden with fewer problems with
weeds, bugs, and diseases.

Jim Kennard