Page 46 - GRIHA Manual Volume II - Introduction to National Rating System

38 GrIha Manual: Volume 2

Methodology

The soil should be tested at a laboratory accredited by the Indian Council of Agricultural Research
(ICAR) for primary plant nutrient and pH. In case the soil test conducted yields a result that is not up
to the requisite standard, then the following steps may be considered.
# Landscape architect/horticulturist recommendations should be adopted for improving deficient
nutrients, timing of application of fertilizers, and warning of excessive nutrient levels.
# If the soil has a low pH (<6.0) add lime (agricultural lime and not quick lime or slaked lime) to
adjust to 6.5 or higher (up to 7.5). Some details are provided in the following points.
• The pH value of a soil type is inluenced by the kinds of parent materials from which the
soil was formed. In other words, soils that have developed from basic rocks generally have
higher pH values than those formed from acidic rocks.
• Rainfall also afects soil pH. Water passing through the soil leaches basic nutrients such
as calcium and magnesium from the soil. They are replaced by acidic elements such as
aluminium and iron. For this reason, soils formed under high rainfall conditions are more
acidic than those formed under arid (dry) conditions. This is another reason why soils must
be preserved and protected from rainfall erosion.
• A pH level of around 6.3–6.8 is also the optimum range preferred by most soil bacteria,
although fungi, moulds, and anaerobic bacteria have a broader tolerance and tend to
multiply at lower pH values.
• Therefore, more acidic soils tend to be susceptible to souring and putrefaction, rather than
undergoing the sweet decay processes associated with the decay of organic matter, which
immeasurably benefit the soil. These processes also prefer near-neutral conditions.

# If the soluble salt content is greater than 500 parts per million (PPM), the soil should not be used
for the purpose of landscaping. Some details are provided in the following points.
5
• Salinization of soil occurs due to several reasons such as
B High levels of salt in the soil
B Disruption of the natural landscape that causes the water table to shift, carrying salts
with it.
B Effects of climate change such as excess evaporation of saline water due to high
temperatures and later deposition as precipitation in distant areas.
B Human activity such as construction and land clearing (especially around dam sites
when the hydro-geological conditions also undergo alteration over a period of time and
can render arable land unproductive/infertile.
B Saline soils can be categorized into three broad types.
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# Saline soil, pH <8.5, EC (ds/m) >4, ESP <15
7
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# Saline-sodic soil, pH <8.5, EC (ds/m) >4, ESP > 15
# Sodic soil, pH >8.5, EC (ds/m) <4, ESP >15
• Saline soil can be improved by using the following methods.
B For these soils with electrical conductivity of more than 4 dS m–1, provision of lateral
and main drainage channels of 60 cm deep and 45 cm wide and leaching of salts could
reclaim the soils.

5 Source , last accessed on 1 February 2010.
6 Source , last accessed on 1 Feruary 2010.
7 Electrical conductivity
8 Exchangeable sodium percentage