Aug 9 - 15, 2010

Deserts constitute a greater part of arid zones of the world. They were considered useless for agricultural cultivation, but modern plant physiology approaches have revealed their agricultural potentialities. Recent developments in hydrology show the presence of groundwater resources in the deserts, which could be exploited for irrigation.

Low and medium salinity groundwater can be used for irrigation on most of the desert soils, where a certain amount of leaching occurs. High salinity water can be used for irrigation on the sandy soils with adequate drainage.

Sandy deserts provide an excellent media for quick percolation of water and chemical amendments further improve the conditions for saline agriculture. One-third of the earth's surface, 47 billion hectare, is classed as arid or semiarid land.

In Pakistan, it is estimated that about 57.1 million ha is arid and 17.11 million ha semiarid. Low rainfall and extremely high summer temperatures are the characteristic feature of these tracts. Life of the people is very tough and hard, the most prominent feature of which is poverty. Scanty rainfall and severity of the climate make them poorer still.

Due to people's requirements of fuel wood, timber, and fodder, all of these areas have been under very heavy biotic pressure. Vegetations have almost disappeared and owing to poor site quality and increase in human and cattle population, it is very difficult to re-green these desert areas without a scientific plan and some sustained effort.

The main desert areas located in arid and semiarid of the country are Thar in Sindh, Thal, Cholistan in Punjab and Chagi-Kharan in Balochistan, which range with a total area of eight million hectares. These drier areas are extensively distributed due to biotic pressure and are subject to heavy wind erosion. Desert habitats are mostly influenced by global warming and increasing aridity due to prolonged drought induced by phenomena related to climate change. Below is the short description of the plant species grown in the desert areas of the country.

Thar Desert lies between Indus River and Run of Kutch. It covers an area of 2.65 million hectares in Tharparkar, Nawabshah, Khairpur, Sukkur, and Sanghar districts. The area comprises of sand dunes of 20-200 meters in elevation. Climate of the desert is very arid with annual rainfall between 100-300 mm. The rainwater flowing down the sand hills does not move as runoff, but is absorbed in the surface ground. It is subsequently lost largely in the atmosphere by evaporation and transpiration and the rest percolates down in the ground in small quantities. Cultivation to a limited extent is done on rainwater. The crops grown on rainwater are bajra and castor. Maximum temperature upto 45oC is recorded in May-June, while January and February are the coldest months (2-5oC).

Wind erosion is a characteristic feature of the Thar desert. The movement of wind determines sand dunes formation in summer, which is a natural phenomenon. Illicit cutting and heavy grazing of trees/shrubs are accelerated fast the erosion scenario. Some of important species found n the Thar desert are: Acacia arabica, Acacia senegal, Cactus tamarisk, Cenchrus biflorus, Eleushine flagellifen, Euphorbia caducifolia, Lasiurus sindicus, Panicum turgidum, Prosopis cineraria, Salsola foetida, Tecoma undulate, and Ziziphus mauritiana.

In Thar only those places where groundwater for human and cattle consumption is available are populated. The economy of Thar depends largely on grazing. Many tracts are uninhabitable mainly for want of drinking water.

Thal desert stretches over an area of 2.6 million ha. in Khushab, Mianwali, Bhakkar, Leiah, Muzaffargarh and Jhang districts. The tract is covered by the piedmont of the salt range in the north, the Indus River flood plains in the west, Jhelum and Chenab River flood plains to the east. The maximum temperature recorded in the tract are about 44oC. The heavy wind movements affect the amount and distribution of rainfall in the desert, which is mostly received during monsoon. It varies from 135mm in the south to 350mm in the north-eastern region of the tract.

The soils are alluvial with sandy textured sand dunes covering 50 to 60 per cent of the area. The most common species are Acacia jacquemontii, Aristida depressa, Calligonum polygonoides, Cenchrus ciliaris, Cymbopogon jwarancusa, Eleusine flagellifera, Leptadenia spartium, Prosopis cineraria, Suaeda fruticosa, Salvadora oleides, Tamarix articulata, and Ziziphus jujuba.

Cholistan Desert is located in the southern part of Punjab. It covers an area of 2.6 million hectares with the districts of Bahawalpur and Rahim Yar Khan. Climate is characterised by hot summers and cold winters. Maximum temperature is 49oC. Rainfall is erratic and ranges from 100 -200 mm annually. Soils of the tract are saline and gypsiferous. The plant species grown are Calligonum polygonoides, Cymobopogon jwarancush, Cenchrus ciliaris, Capparis aphylla, Eleusine flagellifera, Lasiurus sindicus, Prosopis cineraria, Salvadora oleoides, and Ziziphus mummularia.

The Chagi-Kharan covers an area of 23,000 km2 in upland Balochistan, stretching over Chagi and Kharan districts. Climate of the tract is very arid and sub-tropical. Long hot summer (45oC) and cold winter (5oC) and low precipitation control the growing pattern of vegetation. Average annual rainfall varies between 80-170 mm, which is primarily received during monsoon. Vegetation of the area is predominantly Tamarix aphylla, Prosopis cineraria, Calligonum polyonoides, Cenchrus ciliaris, Cymobopogon jwarancusa, Eleusine flagellifera, and Sulvadora oleoides. The productivity of range lands has deteriorated due to heavy local as well as nomadic livestock grazing.

The desert areas of the country can be successfully utilised for growing vegetable as well as other crops hydroponically (without soil) using amended nutrient solution.