| Management & Utilization of problem soils |
Water logging……………………………………………..
· Water logging is a state at which soil becomes saturated with water for a period that affects yield & quality of crops.
· When land becomes waterlogged, all the available are spaces, both capillary & non capillary, are field with water resulting in deficiency in soil aeration which hampers plants growth.
Causes of water logging………………………………………………….
· Over irrigation.
· Canal irrigation in areas adjoining agricultural lands where subsoil water table steadily rises.
· Inadequate drainage.
· Surface flooding.
· Presence of high water table.
· During monsoon & soon after some areas remains totally submerged by the discharge of the rivers & accumulation of runoff from the surrounding catchment.
· Water logging conditions are also caused in depressions along roads, canals & railway sides during rainy season.
· Sea water comes to a particular area during high tidal surges.
Types of water logging………………………………………………….
Gupt (2000) mentioned 4 categories. These are—
· Category 1: areas having higher water table within 0.5m depth from soil surface.
· Category 2: areas having surface drainage congestion but not having high water table.
· Category 3: areas having both high water table & surface water drainage congestion.
· Category 4: coastal areas subjected to periodic inundation by salty sea water.
Luna (1989) classified water logging as follows—
· Water logging condition caused by stragnant water.
· Water logging condition caused by impeded but mobile water.
· Swampy areas.
· Marshy areas & saline muddy areas.
However, water logging can be grouped as following types—
1) Water logging due to permanent submersion of land. Such as ponds, rivers, etc.
2) Water logging from periodical submersion such as coastal & estuarine land inundation by soil water or runoff of freshwater over lands etc.
3) Temporary water logging by stagnation of water as a result of heavy rainfall.
4) Water logging by coming out of water table to the surface & swampy areas in valleys are mostly caused by the phenomenon.
5) Water logging from artificial irrigation of agricultural lands in polders areas.
Major water logged areas in BGD……………………………………………..
· The chanal Beel in Natore.
· The Haor basin, the eastern part of Sylhet, Mymensingh & Moulovibazar.
· The Kaptai Lake in Chittagong.
· Riverine flood plains of Ganges, Brahmaputra, Meghna, Tista & other small rivers of the country.
· Haors, Beels, baors & other natural & artificial ponds.
· The coastal areas of Chittagong, Cox are Bazar, Noakhali, Patuakhali, Barisal & the Sunderbans.
Problems due to water logging…………………………………………………..
· It creates anaerobic condition in soils for which microbial activity is hampered.
· The availability of nutrient elements in soil is reduced & leaching loss is higher.
· Increases soil pH in coastal & dry area which leads salinity & alkalinity.
· Pollutes soil water & favors excessive weed growth.
Choice of species …………………………………for water logged areas
· In periodically wet sites………..Hijal, Jam etc.
· In Road, Canal & Railway sides……..Eucalyptus robusta, Syzygium cumini etc.
· In Beel areas of west Bengal…………Hijal, Jarul, Sissoo, Pitali, Kerong, Khoir, Arjun etc.
· In fresh water logged areas…………..Jarul, Ficus glabrata, Pitali etc.
· In saline water logged areas…………Keora, Baen, Kakra etc.
Planting techniques for water logged areas……………………………..
· Before launching afforestation program in such areas, all type of tall grasses & weeds should be stubbed out. This will reduce the competition for food & chances of fire during dry season.
· 2/3 years old tall sapling must be planted. They must be raised in nursery containers filled with earth, sand & form yard manure mixture.
· In areas where water depth is less than 1m, ridge & furrow method of planting gives good results. In scattered patches of waterlogged areas & burrow pits along canals & railway lines, it is advisable to raise methods about 1m diameter at the base & 50cm at the top.
· Planting should be done in dry season during October-November, so that by the time of next rainy season, plants are established to combat the effect of water logging.
· In many cases, surface & sub surface drainage can be provided depending upon field conditions.
Measures to reduce water logging in an area…………………………………………………….
· Construction of dams & embankments along the coast to restrict saline to enter the agricultural lands. Could be an effective measure of reducing the water logging.
· Providing adequate number of bridges & culverts, along the roads, railroads, highways, across the canal etc could be a handy measure against water logging.
Planting techniques for coastal areas of BGD……………………………………………
1) Site conditions of coastal areas:
· Coastal sands are found in all around the coasts, including the sea front of the mouths of big rivers as in the Sunderbans.
· Soils are unstable & permeability is higher.
· The depth of water table & lime content various from place to place. Sometimes water table is very near to the grounds.
· Water is slightly to moderately brackish.
· Atmospheric humidity is along most of the coasts, the rainfall is adequate during the monsoon & heavy in the Chittagong area.
2) Site preparation:
· As the soil very loose, no site preparation I usually required. Coarse grasses need to be thinned out before planting.
3) Fixing blowing sand:
· For the successful undertaking of the planting, stabilization of sand is necessary.
· This can be done by using sand binding grasses as Saccharum spontaneum, Aristica pennata etc, shrubby plants such as Calotropis & Pandanus, or herbaceous plants such as Aloe can be used.
4) Species suitability:
· Casuarina equisetifolia (jhau) is very suitable for this condition in Bangladesh, because it grows more quickly, hardy & easy to raise.
· Planting naked rooted species usually gives good success.
· Pongamia pinnata (kerong) can also be planted in the coastal sands.
· Cocos nocifera & borassus flabellifer can also be planted in sites which are established by jhau.
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