WATER LOGGING & SALINITY CONTROL
Sep 17 - 23, 2007
WATER LOGGING: Water logging occurs when soil pores stay filled with water causing oxygen deficiency that impairs the root growth and its ability to absorb nutrients. Water logging results due to high water table, excess watering and seepage and leakage from canals and water reservoirs. Bunds should be constructed in coastal, in rive rain areas and areas adjacent to the water reservoirs.
SALINITY OF SOIL: Worldwide nearly 20 percent of irrigated area is salt affected. It is characterized by the presence of Sodium at levels that lead to poor physical properties and fertility problems, threatening agricultural productivity.
Poor irrigation and agronomic practices have caused salinity, sodicity and water logging affecting 40-50 percent of the world's 270 million hectares of land currently under irrigation. When the land is no more cultivated and is left uncultivated, organic matter in the soil declines, soil erosion increases and the soil becomes saline rapidly.
Providing soluble Calcium helps amelioration of the affected soils to replace excess Sodium. The excess Sodium is either displaced by leaching from the root zone by excess irrigation, processing that requires soil permeability and provision of a natural or artificial drainage system, or is taken up and consumed by crops.
The first and foremost requirement is to establish salt testing laboratories in good number, if possible at least at Tehsil level to determine the extent of salinity in respect of a particular soil and then to apply necessary strategy to reclaim the land. There is no single technique or agricultural system that will be applicable to areas affected by salinity. It requires a combination of a number of agronomic and management practices, keeping in view a comprehensive investigation of soil characteristics, water monitoring (rain-fall, irrigation water and water table) as well as local conditions including climate, crops, economic, social, political and cultural environment, as also existing farming systems. Several practices combined together form an integrated system, which includes:
LEACHING: Leaching of irrigation water or rain-water is practiced to prevent accumulation of salt in the root zone. Leaching, as much as possible, should be minimized to avoid rising ground water and soil run-off.
DRAINAGE: When underlying layers are permeable, natural drainage may function effectively otherwise artificial drainage may be arranged to drain out the extra water and salt sediments, also by constructing drenches at suitable places.
SUB-SURFACE DRAINAGE: Sub-surface drainage is meant to control ground water table at a specified safe depth. This consists of open ditches or tiled drains or perforated plastic pipelines.
MOLE DRAINAGE AND VERTICAL DRAINAGE: This is to carry out excess drainage by pumping out excess water from tube-wells and bringing down the surface and sub-surface water level besides lowering and removing the salts concentration from the soil.
MECHANICAL METHODS: Mechanical methods are used to improve infiltration and permeability in the soil surface and root zone to control saline and sodic conditions
These include deep ploughing, land leveling, tillage, sub-soiling and planting procedures.
The soil permeability loosens the soil aggregates, improves the physical conditions of the soil layers and increases air space and hydraulic conductivity important for land reclamation.
PLANTING PROCEDURES: These procedures loosens the soil aggregates, improves its condition and the layer. Planting on sloping beds or raised furrows in single or double rows prove helpful in getting stands and positive results in salinity control.
CHEMICAL PRACTICES: Using chemical amendments and mineral fertilizers like Gypsum, Ammonium Sulphate and Sulphuric acid are commonly used. Proper and balanced amounts of mineral fertilizers should also be used.
BIOLOGIAL PRACTICES: These practices include using organic matter, farm manure, growing leguminous crops, mulching, application of crop residue and growing salt tolerant crops. Salt tolerant crops include Barley, Canola, Wheat, Sugar Beet, Millet, Rice, Flax alfalfa, Lucerne, Sweet clover, salt tolerant forage and grasses to be used by animals. Thus vegetative bio-medication of sodic and saline soils is used for enhancing productivity and environment conservation.
CROP RESIDUE APPLICATION: It is one of the easiest and cheapest method to improve water infiltration, provide green manure to the soil and make it porous and better the prospects of productivity.
ALLEY CROPPING: It is considered one of the most effective agro-forestry arrangement to grow crops between rows of leguminous plants, trees or shrubs. It is a technique called alley cropping. However, to prevent these plants and trees from overshadowing and affecting crops, they should be pruned frequently and when their leaves and branches are spread on ground, they decompose and serve as mulch. This decomposition provides nitrogen and phosphorus to the soil, and trees continuously pump nitrogen from deep in the soil and make them available to the crops.
PADDY/RICE CROP: Rice plants are an exception to many other plants/crops as they transfer air to roots and are able to grow well even when roots are submerged for long periods.
Almost one third of Pakistan's irrigated agriculture is affected by salty soils and experts are of the considered opinion that if these soils remain unchecked and untreated, the high levels of salinity could lead to abandonment of 25% of the country's cultivable land, which is immensely needed to meet the food requirements of our ever increasing population.
It is heartening to note that Kausar A. Malik, a Pakistani scientist with the Nuclear Institute for Agriculture and Biology in Faisalabad sometime ago developed a pasture grass to counter the situation of salinity in Pakistan, called Kallar grass in ordinary parlance, which is a high salt tolerant perennial grass that has the quality to grow well under water logged conditions. It helps permeability of the soil, provides green manure and sufficient amount of suitable organic matter, besides harbouring nitrogen fixing bacteria that obtains 60-80 percent of the nitrogen requirement from the air. The scribe, who has a small slice of land in Punjab, found Kallar grass effective to rehabilitate his salt affected land. However, if Junter, a leguminous fodder is also sown along with the aforesaid grass, it proves a better combination for more efficient and effective amelioration of the soil, besides serving as a source of suitable green fodder for the livestock.
Investment is essentially required for improvement of surface irrigation systems (such as furrow irrigation, border irrigation or basin irrigation) or pressurized systems including sprinkler, drip irrigation or precision leveling, land leveling and applying other practices described above for reclamation of the salt affected land. The Government should arrange to give interest free loans to resource-scarce farmers for reclamation of their water-logged and salt affected areas as these people are unable to make a concerted effort continuously and steadfastly spending from their own pocket and also to repay the loans with high interest. They need to be aided before achieving sustainability.