Agriculture Reference
In-Depth Information
We are still missing iron (Fe), which is also a minor element. Using
iron chelate (FeDTPA) that has 10% elemental iron, we need 2 grams in a
10-gallon tank to add 5 ppm of iron. You now have your nutrient formula-
tion complete with all 13 essential elements.
WATER ANALYSIS
Before making up the nutrient solution you should have a water analysis
of the local water supply to determine the levels of these 13 elements in
the raw water. Adjust your formulation for the presence of any of these
elements in the water. For example, if the raw water has 10 ppm of cal-
cium, then simply subtract this amount from the original formulation. All
of these elements are in ratios, so it is easy to calculate any changes.
Taking our example of 10 ppm of Ca in the raw water, then we want
180 - 10 = 170 ppm of additional calcium using calcium nitrate. We adjust
the formulation as follows: (170/180) × 31 gm = 29 gm of calcium nitrate.
At the same time the level of nitrogen provided by the reduced calcium
nitrate will fall to (29/31) × 126 ppm = 118 ppm. That is, there is 8 ppm
less of nitrogen. That would not influence our optimum level of nitrogen.
If there were a larger drop of greater than 10% we would need to add that
from another source such as potassium nitrate.
pH OF NUTRIENT SOLUTION
The pH scale measures the relative acidity or alkalinity of a solution or
medium. The scale has a range from 0 (extremely acid) to 14 (extremely
basic). These sorts of levels you will not encounter. Most plants prefer a
slightly acid condition between 5.8 and 6.5. The pH affects the plants'
ability to take up its essential elements from the nutrient solution. It also
influences the solubility and capacity for the nutrient solution to retain its
individual elements in solution.
There are a number of ways to monitor the pH of your nutrient solution.
Your choice of testing system depends upon the amount of accuracy and
reliability in detection you require. Although sophisticated pH test meters
may be accurate within 1/100 of a pH unit, they really are not practical for
other than laboratory use. They also need constant calibration and are very
delicate to handle. They will cost from $300 to $500 and upward. Simpler,
more durable handheld pH meters and “pen” types that have accuracy
within 0.1 pH units are available for under $100 to $200 (Figure 5.6 and
Figure 5.7). They too, however, must be calibrated frequently and always
kept moist.
My preference is to use good pH indicator paper that has a range between
4.0 and 7.0. This paper is accurate to within 0.3 units. My favorite is Merck
