(IPPM) in Vegetables - Vegetableipmasia.org

Resource Manual on IPPM in Rice
World Education Philippines, Inc.
To further explain the idea of soil pH, a more general analogy can be used. Imagine the
soil as a huge pantry or a place for storing food in the house. The pantry must be a goodenough
cabinet, cool enough to maintain the freshness of the food kept in it. Similarly,
the soil has to have the good qualities for it to be an appropriate storage place for
nutrients. In the case of sandy soil or a soil under high rainfall conditions, the nutrients
are often leached or dissolved. Thus, the pantry turns out to be a poor place for storing
food. In this case, putting OM back into the soil is just like stocking the pantry with
food. An ideal soil with a good mixture of sand, silt, clay and organic matter, therefore,
is like a large pantry that allows storage for many kinds of food. If the soil pH is too low
or too high, storage of nutrients will be difficult and the pantry will be empty. Thus, to
increase soil nutrients, pH level must be maintained at a desirable balance.
Improving Acid Soils
Lime is the most common material used to neutralize acid soils. Lime in pure form is
calcium carbonate (CaCO 3 ). What is important in lime is not the calcium (Ca++),
although calcium is a required nutrient for plant growth. Rather, it is the carbonate
(CO 3 ) that helps balance the pH level of acid soils. It does this by combining with the
hydrogen ion (H+). Each carbonate molecule combines with two hydrogen ions, and in
this way the lime cleans up the excess H+ and raises the soil pH toward neutral.
The formal description of the reaction goes as follows:
2 CaCO 3 + 3H+ 2Ca++ + HCO 3 - + H 2 CO 3
For every two molecules of CaCO 3 , 3 ions of hydrogen (3H+) are taken up (lowering the
pH), producing 2Ca++ (which are now available for storage in the soil, or uptake by the
plant), and one molecule each of bicarbonate (H 2 CO 3 ) and HCO 3 -.
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