Process of Desertification

 

The dry region of Bangladesh has a high population density, which ranges from 500 persons per km 2 in Dinajpur to 900 persons per km2 in Kushtia, as against 755 persons per km2 for the country (GOB, 1997). The Barind Area covers 15 thanas of Rajshahi and 29 thanas of Bogra, Rangpur, Dinajpur and Pabna district with a population of 5.038 million. There prevails a special kind of weather having high temperature from mid June to October. Virtually there is no rainfall from November to February. Soil of the area becomes hard like iron during dry season whereas it melts like wax with a very little rainfall.

 

The Madhupur Tract is spread over Dhaka, Tangail, Jamalpur and Mymensingh districts. During 1983-84 and 1997 period, an 11 percent decline in total cultivable area, and specifically a 14 percent decline in cultivated area is observed. The level of land degradation and its extent vary seasonally and yearly and by region as well as the pressure on the land are not the same either. In the whole of Bangladesh, the degradation status is revealed as light - 42%, moderate - 48% and strong - 10%.

 

Using extensive soil sampling the nutrient grades of different agro-ecological zones (AEZs) was established on the basis of the levels of various nutrients (N, P, K, S, Zn, Mg) present. It was observed that there was only one AEZ, Young Brahamaputra - Jamuna Flood Plain, which could be classified as good. There were thirteen AEZs with fair nutrient status, while the rest (18) fell in the grades of poor and very poor. A good soil should have organic contents of more than 3.5%. But in Bangladesh most soils have less than 1.7%, some soils have less than 1% organic matter. In Bangladesh, the average by 20 - 46% from about 2% to 1% over the past 20 years of intensive cultivation.

Considering National Agricultural Research System (NARS) database, organic matter content of the soils of dry region has been summarized in Table 1.1 from BARC, 1998.

 

Table1.1 Status of Organic Matter in the Soils of the Dry Regions

 

 

Barind Tract are deficient in P for HYV rice (about 0.77 M ha). Medium level response was also observed in soils of Madhupur Tract having a total area of about 0.42 M ha. Barind and Madhupur Tract area deficient in K for HYV rice having a total area of about 1.20 M ha. Soil fertility decline has occurred due to removal of nutrients as well as uneven fertilizer application without accounting for soil characteristics. Some area affected by wind erosion mainly in the district of Rajshahi and Dinajpur region during drier months of the year. Most of the topsoils in the cultivated/ deforested areas of the terraces, and floodplains are acidified to a variable extent. Intensive acidification is also identified in the heavy clays in the Lower Atrai Basin and in some broad valleys within the Barind and Madhupur area.

 

Lowering of Groundwater Tables
The groundwater table goes below 8.95 m to 18.56 min dry season in and around Shibganj, Chapai Nawabganj and Iswardi. It indicates that most of the shallow tubewell goes below the suction lift capacity in the peak irrigation period. The trend of groundwater flow in Chapai Nawabganj and Rajshahi is to the southeast. The groundwater moves towards east and southeast in Pabna, Meherpur and Kushtia area.

 

Recharge to groundwater in the northwestern part varies from 210 mm to 445 mm It is observed that the loss of groundwater takes place from October to December. In the western and central part, the river is gaining from the surrounding aquifer in all the period except the wet season (IAEA-BAEC-BWDB, 2000). With ever increasing ground water extraction for irrigation in this region during the dry season in recent years and no increase in rainfall in that period, the ground water level may fall to the extent of not getting fully replenished in the recharge season causing overdraft. The ground water levels beneath Dhaka City have fallen steadily over the last twenty-five years in response to continuously increasing abstraction. Water levels have dropped and reached a maximum depth of 20 meters below ground surface in 1989 (from about 3 meters in 1965).

 

Degradation of Soil Fertility
Flooding leading to inundation of the plain lands is a major factor in retaining and enhancing soil fertility in the deltaic country. Soil degradation is said to be occurring in Bangladesh due to the intensification of crop cultivation and the advance of monoculture rice and providing imbalanced nutrient base to their crop. Soil fertility is degraded due to indiscriminate and inefficient use of chemical fertilizer and pesticides. Soil fertility decline has occurred due to removal of nutrients as well as uneven fertilizer application without accounting for soil characteristics.

 

The degradation results in a gradual decrease of soil quality. River erosion is posing threats for both sustainability of agricultural and human habitation in Bangladesh. Population increase puts pressure on non-crop ecosystems such as forests and wetlands to convert them to croplands. The sharply reduced flow below Farakka indiscriminate withdrawal of water at Farakka during the lean period creates a serious water crisis in the affected areas and aggravates salinity in the entire Khulna-Jessore region. Saline intrusion has degraded soil and ecosystem, leading to decreased agricultural production and increased poverty.