October 1, 2007	Monday	Ramazan 18, 1428

SOIL is the non-consolidated mineral material on the immediate surface of the earth that serves as a natural medium for the growth of land plants. Soil provides mechanical support, nutrients, moisture and oxygen to plant roots.

Mineral materials (48-49.5 per cent), organic matter (0.5-2 per cent), water (25 per cent) and air (25 per cent) make up the soil mass. The mineral components consist of primary and secondary minerals, amorphous substances and fragments of parent rocks. The organic component includes soil fauna and flora, plant roots, plant residues and humus.

The mineral and organic matter constitutes the reserve for nutrients and provides physical anchorage for the plants. The liquid phase is mainly responsible for nutrient transport in the soil. The gaseous phase provides oxygen for respiration of plant roots and soil organisms.

Salt is the savour of foods but the scourge of agriculture, in excess it kills growing plant. Salt-affected soil is a collective term which encompasses saline, sodic and saline sodic soils.

Out of 22.15 mha total cultivated area, about 6.68 mha is salt affected in Pakistan. In Sindh province, salt-affected soils cover an area of 2.11 mha which is more than 36 per cent of total cultivated area of Sindh.

Concerted efforts for reclamation of salt affected soils are vital to increase the irrigated areas coupled with efficient water use in order to enhance and sustain the agricultural production to feed the burgeoning population. Various measures and methods are in practice for reclaiming saline, sodic and saline-sodic soils. The prevalent method of reclaiming salt-affected soils in Pakistan is the removal of excess salt to a desired level in the root zone by leaching soil through heavy (flood) irrigations and use of chemical amendments (gypsum and sulphuric acid).

The best way of reclaiming the saline soil is to level the land, improve drainage though chisel plough and apply heavy irrigations for leaching soluble salts. Chemical amendments (gypsum and sulphuric acid) are used in saline-sodic and sodic soils in addition to deep ploughing and heavy irrigations. It is recommended that before using chemical amendments, soils should be analysed for gypsum requirements. Free of cost soil and water testing facility is being provided by Farm Advisory Centres of FFC located at Mirpur Khas, Vehari, Kasur, Gujranwala and Char Sadda.

Reclamation of salt-affected soil is extremely difficult even if chemical amendments are used and cannot be accomplished unless sub-soil opened by deep ploughing or chiseling. Appropriate deep ploughing is necessary to avoid harmful salt accumulation by improving drainage and soil porosity and increasing leaching.

Mould board plough, disc plough, chisel plough and sub-soiler are the primary tillage implements which are used for deep ploughing. In Sindh, “panjphali” is the only implement which is used for deep ploughing. The implements (moldboard plough, disc plough and panjphali) which cut, invert and pulverise the soil should be avoided especially in the soils of Sindh province because of lying of major quantity of salts in upper soil depth (4 to 12 inches). During the operations of deep ploughing, when implements cut and invert the soil, the salts come on the surface of the soil which badly affects the germination of field crops.

The chisel plough is a common tool to get deep tillage with limited soil disruption. The main function of this plough is to loosen and aerate the soils while leaving crop residue at the top of the soil. This plough is used to reduce the effects of compaction and to help break up hardpan. Unlike many other ploughs the chisel will not invert or turn the soil. Because of these attributes, the use of a chisel plough is considered to be more sustainable than other types of plough, such as the mould board plough and disc plough.

The chisel is a plough with a rigid curved or straight shank with relatively narrow shovel points. It is also called heavy duty deep cultivator. The shanks are arranged on heavy frames in staggered rows from nine inches to 12 inches apart to allow trash to pass them without choking. Most chisel ploughs are provided with coil cushion springs in conjunction with the clamps. Locally made chisel plough consists of three or five tines on heavy frame. The chisel plough is typically set to run up to a depth of eight to 12 inches.

The plough works best when the soil is firm and dry, by shattering the compacted layers and breaking up the large clods. If too wet, the shank opens a narrow groove and rolls up large chunks of wet soil which dry hard. When planning to plough with a chisel it is important to bear in mind that 10 to 15 horsepower per shank will be required. Sub-soiler is a form of chisel plough designed to penetrate to a greater depth. Chisel plough can work effectively at 10 inches deep. Sub-soiler, if necessary, will penetrate 20 to 30 inches to break up compacted layers of soil to permit better root and moisture penetration. A lot of power (40-60 hp) is needed to pull one shank of a sub-soiler at a depth of 20 inches in heavy soil.