is a scale that chemists use to measure acidity. Values below 7
are considered acidic, values above 7 are alkaline ( the opposite of
acidic) and 7 is neutral. Most plants grow best in slightly acidic
soil, usually between values of 5.8 and 6.5, a few have special pH
that are too acidic must be corrected by applying limestone. The pH
value does not tell how much limestone is needed, this is calculated
from the active acidity measurement. Alkaline soils require
special nutrient management
soluble salts analysis indicates whether there is a buildup
of salts in the soil. It is not a measure of nutrient availability.
Soils with soluble salts below 1250 ppm are suitable for most crops.
Between 1250 and 2500 ppm, sensitive crops can be affected, above
2500 ppm only salt tolerant plants can be grown. Salt buildup occurs
in dry areas and areas irrigated with high-salt water, it does not
occur under high rainfall conditions. Salt buildup can also occur in
Exchange Capacity (CEC) indicates the ability of the soil to
hold onto nutrients. Values are often lower than 5 meq/100g for
sandy soils and can be above 30 meq/100g in clays and soils with
high organic matter content. In soils with low CEC values, nutrients
(especially nitrogen, boron and potassium) can be easily leached out
during rainfall. On these soils, it is better to apply small,
regular doses of these nutrients than to apply a few large doses.
Calcium/Magnesium and Magnesium/Potassium ratios indicate if
there are imbalances among these nutrients. For example, if the
Ca/Mg ratio is high, the calcium will reduce plant uptake of
magnesium even if there is enough magnesium in the soil. If the
ratio is good, but the total amount of both nutrients are low, they
must be applied.
Matter can reduce the effectiveness of some pesticides, the
extent depends on the actual product. Organic matter levels are
sometimes used to select pesticide application rates.
Levels are presented in an easy to understand chart, or an
guide should be supplied
by the laboratory. If a nutrient level is in the “low”
range, then it is too low for optimum growth and should be applied.
In the “very low” range, high application rates
are required to achieve good growth . In the “optimum”
range, you are unlikely to get a response to the nutrient, but we
may recommend a maintenance dose to replace what will be removed by
the crop. In the “high” range, the nutrient level
is high enough to cause nutrient imbalances; applying it is not only
a waste of money but it may actually harm the crop.
Nitrogen Analysis is often not as reliable as the other
nutrient analyses. Crop response to nitrogen is influenced by local
weather conditions, therefore it is usually better to use the
results of local trials where available.