Page 111 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 99

The management of soil water can be conducted at least by three methods:
(a) irrigation or drainage, (b) soil tillage, and (3) soil mulching. Irrigation is
important when the soil water contents are relatively low and must be moistened
by addition of water. This method may raise the soil moisture content to the level
needed to increase the activities of soil enzymes. Conversely, when the soils are
waterlogged, decreasing the amount of water in soils is needed. Drainage can be
conducted so that the soil water content may reach the level pertinent to particular
activities of soil enzymes.
Sometime soils are compacted with a bulk density too high so that the
porosity and pore size distribution are not suitable to increase the activity of soil
enzymes. At this condition, water can not diffuse into the soil body because the
soils are lacked of pores and may have poor pore size distribution. To cope with
this problem, soil tillage is a very good method. With tillage, the soil bulk density
may decrease and soil pores may retain enough water. With this, the activities of
soil enzymes may significantly increase. However, smaller size pores are needed to
retain more water and inhibit water drainage by gravitation, which may lower the
soil water content.
Water in soils might be preserved so that most of the water are retained in
soils untill it is used by plants. One of the method to do this is soil mulching. In
addition to lower the soil erosion, soil mulching may inhibit the evaporation of
water from the soil surfaces. The requirement for good mulches: (a) are
abundantly available in the environment, (b) do not disturb the field activity of
agriculture, and (c) are not sources of potential weeds, pests, and deseases. Straws
of paddy is one of the best mulching materials. Some other mulching materials are:
papers, plastic sheets, stones, and woods.
Soil temperature varies dependent on the geographycal location and
climate. Therefore, soil temperature must be properly managed, particularly
related to the existing soil enzymatic activities. Generally, the are two methods can
be utilyzed to manage the soil temperature. The first method is to use the
temperature pattern along any season as a guide to predict the soil enzymatic
activities. The second method is to manipulate the soil temperature either by
increasing or decreasing the soil temperature to obtain a maximum value of
enzymatic activities.
The main source of soil heat is sunlight. Therefore, the method to regulate
the soil temperature may use the soil properties that may vary the heat absorption.
Several factors that may influence the absorption of heat are: soil color, soil cover,
direction to sunligt and hills, and soil depth. Soils with dark color absorb 75% of
incoming heat while pale color soils may absorb only 25% of incoming heat. The

Abdul Kadir Salam - 2014