Page 72 - Soil Degradation, Conservation and Remediation

58 2 Physical Deterioration of Soil

Fig. 2.3 Waterlogging in agricultural land (Photo courtesy of Dr. Richard Doyle)
2.3.1 Causes of Waterlogging

Natural conditions responsible for waterlogging include heavy rains, low lands, clay

soils, flooding, and presence of impervious subsoil. Human activities that create or
aggravate waterlogging include faulty irrigation, inadequate drainage, and surface
sealing as well as deep soil compaction by tillage implements.
Wetlands are naturally and permanently waterlogged, but we are primarily con-
cerned with arable lands because waterlogging hampers the growth of most crop plants.
The most important causes of waterlogging are the poor drainage due to compaction
(Fig. 2.3 ) and the rise of the groundwater table. Compaction including surface sealing,
crusting, hardsetting, and deep compaction results from organic matter depletion,
structure deterioration, dispersion, compression, and consolidation. These processes
occur due to inappropriate tillage and applied pressure by the heavy load of farm
machineries (Sect. 2.2.3.1 ). Soil compaction reduces hydraulic conductivity, thereby
reducing both infiltration and percolation. Rainwater or irrigation water cannot move to

the groundwater table deep in the regolith and drain away. In some situations, water
accumulates and the groundwater table rises toward the surface of the soil in absence
of significant base flow. Usually, a small area is irrigated in small farm holdings, so that

over-irrigation is done and high percolation compels the groundwater table to rise.
Rising groundwater table prevents root respiration and restricts their functioning.
Elevated groundwater table may also create salinity and reduce crop yield.

In soils where there is a deep compaction, plant roots are confined to the loose sur-
face soil, and excess irrigation water cannot pass readily through the impervious layer.
It creates shallow root system and leads to waterlogging. In some cases, an impervious
stratum may occur below the top layers of pervious soils. In this case also, water seeping