Increasing population growth, waterlogging and salinity converting the arable land into non-agricultural uses

By Dr.S.M.Alam and M.A. Khan
Mar 01 - 07, 1999

Our agricultural land is facing many problems and some of the major problems are the conversion of arable land into non-agricultural uses, waterlogging and salinity and land erosion scenarios are the most disastrous of the present day crisis.

The total land area of Pakistan is nearly 197 million acres, while the population growth rate is 3.1 per cent annually. As our total land area is fixed, which cannot be increased, therefore, with rapidly expanding population pressure on it, it is also increasing quickly. As a result, our current and potential agricultural land is reducing and shrinking tremendously. It has been estimated that throughout the country, everyday approximately 500 acres (1 acre = 4,840 square yards) of farmland is taken out of agriculture by the expansion of settlements, roads, factories and many other non-agricultural activities. It is predicted that if this trend continues then after every decade approximately a million acre or more of crop land would be taken out of agriculture in our country. In USA, for example, nearly 8,000 acres of farmland is lost each day due to non-agricultural uses.

Arable land is a basic and major resource for the production of human food. But it seems that the expansion of human population and human activities are reducing the availability of land, suitable for food production at an alarming rate. Expanding population demands more food on one side and devours agricultural land on the other side, which is a matter of great concern for everyone.

Out of total land area, 80 million hactres, 21 million hectares is cultivable. Of the total cropped areas 16.2 million hectares (77%) is irrigated and 6.01 million hectares is rain-fed. The annual rainfall in Pakistan varies from less than 100 mm in Sindh to more than 750 mm in the foothills and northern mountains. About 60% of this rainfall occurs during monsoon. In spite of a number of drainage and salinity, menace control schemes being undertaken, the salinity and waterlogging problems positively persist and each year 40,000 hectares of irrigated land is lost to waterlogging and salinity. On the one hand, the nation needs more food to fulfill the demands of its increasing population while on the other hand, each year the cultivable commanded area (CCA) is decreasing due to this twin menace.

Pakistan is quite outstanding country in the world with regard to its well-knit irrigation system which covers from upper parts of the country, down to the mouth of Indus in the south. Irrigated areas (nearly 16.0 million hectares) are generally limited to the Indus plain and river Indus and its tributaries are the main source of irrigation water of this 12.09 million hectares are canal irrigated 3.35 million hectares by tubewells and another 0.6 million hectares by other sources. Of the total area under irrigated agriculture, about 9.6 million hectares is arid, 3.8 million semi-arid and the remaining area is characterized by sub-humid. No doubt, irrigation system has increased agricultural production but on the other hand has created the problems of salinity and waterlogging.

Percolated irrigation water has raised the underground water level and subsequently has waterlogging. Excessive salinity of the underground water has also harmful effects on the soil body. Ascent of dissolved minerals of irrigation water through capillary action increases the soil at salinity and damages its fertility. It is rightly said that waterlogging is the cancer of the soil. Because of poor soil drainage and improper irrigation practices, the huge amount of arable land is waterlogged and has became saline now. This problems has destroyed millions of acres of farmland in the country. Waterlogging and deposition of whitish crust of salts are changing farmland into unproductive land and many areas, the crop fields are reduced considerably. Reports say that during every five minutes, one acre fertile farmland is taken out from agriculture, because of this problem. Such land losses must be checked by draining the affected areas and by planting there hydrophytes.

Over the years, about 40 per cent of the irrigated cropping land in Pakistan, which produces around 90 per cent of the total agricultural output of the country has come under waterlogging. This makes the land non-cultivable and poses a serious threat to the agriculture sector and to the country, as agriculture is the bloodline of Pakistan's economy. Salinity and waterlogging are adversely affecting agriculture at alarming rate in Pakistan. These maladies have overlapped over more than 6 million hectares in the country. These two problems are inter-linked and co-exist at most of the places. Experts' reports say that the impact of waterlogging on crop yields is startling. A decrease in the depth of water level within five feet inhibits root growth and causes yields of all major crops to decline rapidly. The impact of salinity on agriculture productivity is similarly severe, robbing Pakistan of about 25 per cent of its potential production of major crops. This is happening in the most productive and fertile agricultural areas of the country and it is clear that unless the twin menace of waterlogging and salinity is countered on an urgent basis and with a new approach, agriculture productivity of the country would be lowered. The reason of these two problems is mainly because of irrigation without drainage. The situation bas been compounded by over-irrigation which many farmers carry out in the belief that it would help increase produce. Considering that 80 per cent of Pakistan's cultivated area of about 17 million hectares is irrigated network, the Indus River irrigation system, the threat to agriculture is not just serious, it is grim and could result in emptying the country's food basket. Implications of waterlogging and salinity can be described in one word: "disastrous."

It is not that the problem has been left unattended. Numerous efforts have been made in the past 40 years to counter waterlogging and salinity and retrieving lost or damaged fields. All campaigns in this direction, however, suffered from two shortcomings. One, while affected lands were restored for cultivation, the malaise continued spreading engulfing other areas. Two, overtime, drainage channels constructed to rehabilitate land, got clogged for lack of maintenance. Nature has gifted us highly diverse and favourable environmental conditions for agricultural practices. But, unfortunately, the yield per acre and per capita is very low as compared to many other countries of the world. This is mainly due to illiteracy, ignorance, lack of improved strains, poor health of farmers. By eliminating these hurdles, the productivity of the land can be improved manifolds. For economic well-being of the country, these maladies must be removed through effective planning, otherwise, agriculture would remain in stress and food supply problems would become much serious with the passage of time.

The productive capacity of a soil is often related to the properties inherent without soil. Erosion removes top-soil and exposes sub-soil, thereby changing its characteristic productivity. Removal of soil by erosion and subsequent incorporation of underlying material by tillage reduces the organic matter. Reduction of organic carbon is associated with reduction in profile NO3-N and CEC. The contents of P. Zn, Fe and Mn decrease as severity of erosion increase. The physical properties such as water holding capacity and infiltration capacity are reduced due to soil erosion which consequently further enhances the process. The soil structure is highly variable throughout the country and largely affects its erodibility. Soils of some areas are several times more erodible than others. The soil structure and water holding capacity can be improved by green manuring, whereas heavy manuring reduces the soil erodibility upto 5 times. Soil erodibility can also be reduced by developing vegetation cover, because root system of plants penetrates into the soil and binds its particles in proper place.