What is the correct interpretation of these results? Just
by looking at the results it is impossible to say, unless the
percentage of leachate is known.
If the leachate percentage is low (e.g., 10 per cent) the
result in the leachate can mean that irrigation amount is
insufficient and that the amount of irrigation water has
to be increased. If the percentage of leachate is high (e.g.,
70 per cent) the same results can mean that fertilization level is too high and has to be decreased. The same
rule applies for all elements in the leachate solution.
Note that test results of nutrients are always expressed as
concentration, and it is worthwhile to consider also the
amounts in order to correctly interpret results. For example, a concentration of 100 ppm nitrogen in 17 ounces of
leachate solution means 50 milligrams (because one ppm
= one milligram per quart).
The same concentration in seven ounces of water translates into 20 milligrams. Thus, the result 100 ppm may not
be used as is, but should sometimes be converted into the
actual amount of the element tested.
In order to effectively compare leachate solutions content,
it is important to consistently use leachate samples that
reach same percentage of irrigation water.
EC Monitoring
The EC of the water indicates the total concentration of
salts in it. Comparing the EC of irrigation water to EC of
leachate solution collected from containers is a valuable
practice. Testing the EC of irrigation water confirms that
the actual EC resembles the planned EC.
Testing the leachate solution gives indication of adequacy
of irrigation water amounts as well as fertility levels. When
the EC of the leachate solution is noticeably higher than
the EC of the irrigation, it usually indicates salinity buildup
in the container, either due to over-fertilization or due to
too low irrigation water amounts. When the EC of the leachate solution is much lower than the EC of the irrigation
water, it could indicate nutrient deficiencies.
A commonly acceptable difference between EC of leachate solution and irrigation water is 0.5-1 dc/m, depending on crop type.
pH Monitoring
The pH of the irrigation water and leachate should be tested as
soon as possible after irrigation is over.Waiting too long might
result in an incorrect reading, since CO2 from air dissolves in
water, creating bicarbonates and increasing pH levels.
It is very important to understand that pH of irrigation water
is rarely the actual pH that the plant sees. There are various reactions taking place near the roots, influenced by nutrient concentrations in the growing media and in the irrigation water.
As a result, pH in the root zone changes frequently.
Nevertheless, the pH of the leachate
solution can give a rough, yet
accessible, indication of the status in the media, and is therefore
widely used.
When the pH of the leachate drops
below an optimal level, or even to a
harmful level (below five), ratios between
nutrients in the irrigation water should be assessed, mainly
ammonia/nitrate ratio. A higher ammonia/nitrate ratio
usually results in a lower pH in the root zone as well as
in the leachate solution. Other causes of low pH may be
excess of potassium, calcium or magnesium. MY
A