THE rain-fed agriculture is an enterprise of high risks and is exposed to many soil and environmental threats. The sustainability of rain-fed agriculture is, in fact, management of risks involved in cultivation and that should be the focal point of policy makers, knowledge imparting institutions and ultimately the farming community.
Taking this sustainability aspect in perspective of Pakistan agriculture, 67 per cent population lives in rural areas (1998, Census of Pakistan), with insufficient food of low quality and natural resources being exploited ruthlessly.
How best the rain-fed areas are used and at the same time sustain productivity is really a big challenge. Out of 79.6 million hectares the total area of Pakistan, 22.1 million hectares is cultivated (Agricultural Statistics of Pakistan, 2006). The three-fourth of the cultivated area is irrigated and one quarter is rain-fed (Barani). The rainfall in Pakistan is highly variable and is recorded as low as 10 mm in hot deserts of Cholistan and Thar to as high as 1500 mm per annum in foothill of Himalayas.
The farming in dry land areas is subjected to soil erosion, degradation of vegetation cover, desertification, low crop productivity, substandard livestock and poor farm management and consequently low economic return to farming community.
Because of these constraints and risks involved in rain-fed agriculture, till recent past the main focus was on irrigated agriculture, and rain-fed agriculture was neglected. However, the barani areas are such a vast and valuable resource that it was not possible to ignore these rain-fed areas any more. Dry land areas sustain 80 per cent of livestock, contribute to 12 per cent wheat, 23 per cent rapeseed and mustard, 53 per cent barley, 65 per cent gram, 69 per cent sorghum and 89 per cent groundnut. As such rain-fed areas offer hope of sustainable agriculture.
Keeping in view the significance of Barani areas, the Barani Commission was constituted to explore the possibility of development of rain-fed areas. The commission in its report in 1976 emphasised the need of trained manpower, problem-orientated research and measures to devise ways and means for uplift of the poor rural masses in rain-fed region.
The soils in rain-fed areas are subjected to water erosion and wind erosion to varying degree. Out of total water erosion area of 11.17 million hectares, 1.9 million, .0059 million, 6.57 million and 2.63 million hectares are affected in Punjab, Sindh, NWFP inclusive of northern areas and Balochistan, respectively. Out of this eroded area only 0.398 million hectares are affected by sheet and slight rill erosion, while remaining area is moderately to severely affected by rill and gully erosion.
In Potohar region during intense rain Kohan, Bhanu, Kansi, Sowan and Harrow rivers take away huge sediments rendering 12,000 to 30,000 acres arable land unsuitable for cultivation every year (Barani Commission report, 1976). In high rainfall areas water erosion predominates, while in low rainfall areas wind erosion is main impediment to sustainable agriculture. The total area affected by wind erosion is 4.7 million hectares. The area affected by wind erosion in Punjab, Sindh, Balochistan and the NWFP is 3.8 million, 0.64 million, 0.28 million and 36,000 hectares, respectively.
This is evident from data of water and wind erosion, that water erosion is most predominant in NWFP, while reverse statement is valid in case of wind erosion. An area of 2.6 million, 0.49 million and 1.6 million hectares are slightly, moderately and severely affected by wind erosion. The rain-fed areas are susceptible to water and wind erosion and need proper management practices. The soil is a natural resource of immense significance and should be utilised in a way that quality of soil is not degraded.
The soil and water resources need to be conserved to ensure sustainability of rain-fed agriculture. The soil eroded by water is conserved by integration of cultural practices, vegetation measures and engineering techniques. The cultural practices include deep ploughing, conservation tillage and furrow cultivation. The crops that fit the rainfall pattern may be cultivated. The pasture may be established on marginal lands. The vegetation cover is the first defence against erosion and run off and must be adopted earnestly.
The soil in rain-fed area is usually uneven, with variable degree of slope. The local word Potohar means, undulating and uneven. The levelling of such lands may not be feasible and costly as well, the soil is to be managed in situ or as it is, hence terracing and contour practices may be adopted. The engineering measure may be temporary or permanent in nature. The water ways, spill ways, drainage ways and diversion channels are constructed to control run off water and conserve the soil. The permanent engineering work involves masonry work, the check dam and retaining walls are constructed to plug the gully. The gully may be plugged by vegetation cover.
The flowing silt is arrested and gully is plugged over time. The principles of wind erosion control are four folds; protect the soil surface with cover preferably vegetation cover, may be grasses, roughen the soil surface to slow down wind velocity and trap drifting soil, produce stable soil aggregates to resist force of wind and install wind barrier, by growing trees, shrubs and tall growing crops. The application of soil stabilisers/soil conditioners may prevent wind erosion, but these chemicals should be cost effective. The top down soil conservation approach need to be replaced with bottom up approach that suit the farmer’s convictions and resources.
Moisture is most limiting factors in crop husbandry in dry land areas and each and every drop of water is to be conserved for successful crop production. The rain-fed agriculture depends on how to capture rainfall and make efficient use of rain water. During intense rainfall the runoff of water is quite common, and occurs as a rule rather than exception, specifically in soils with low infiltration induced by soil compaction and crust formation. The runoff water takes the top fertile soil away, leaving the soil barren for plant growth.
The conservation of water is important for productive rain-fed agriculture and is accomplished by appropriate tillage, soil mulching, and application of crop residues as cover on soil surface to eliminate evaporation losses, vegetation and crop cover and adoption of cultivation techniques such as terracing, ridges and contour practices. The conservation of water is essential in all rain-fed area, but more so in dry areas. In arid regions with rainfall less than 250mm, the farmers must be conversant with the technology of conservation of all available water.
In order to conserve adequate water, sub-soiling, chiselling and deep tillage is practiced. In this way more water infiltrate into the soil and more root penetration occur that has access to more water over a large area. The success of crop production in rain-fed area is directly related to quantity of water conserved in soil, Hence bunds or check border should be erected around the field, the field may be deep ploughed, so that maximum rain water can infiltrate into the soil and is conserved for the next crop. Water harvesting is essential for rain-fed agriculture. Water harvesting is collection and storage of precipitation, the rain water. The risk involved in rain-fed agriculture is minimised by proper water harvesting, water harvesting in an area may be 20-90 per cent of precipitation received in that area depending on slope, intensity of rainfall and soil characteristics.
The Cholistan desert in Punjab and the Thar desert in Sindh are dependent on rain water. The inhabitant of these deserts had been using water harvesting techniques since distant past. The water harvesting techniques are site specific and most appropriate one must be adopted in a locality under consideration.
In rain-fed areas there is a great scope of runoff agriculture. The rainwater is taken away by runoff to other areas, where it is stored and used for crop production. The runoff takes place in upper part of catchments and is collected at lower part of it. In water harvesting at other places infiltration in reduced at original site and as such runoff is increased for more water harvest on adjacent areas. The runoff is accelerated by vegetation removal and soil compaction. The area is also treated with chemical soil sealant and water repellent materials in order to increase runoff. The farmers in Cholistan in Punjab and Thar in Sindh collect rainwater in depression called Tarries. The shape and size of such rainwater reservoir depend on size of catchments and type of soil in a locality. The farmers also store water in underground tanks locally known as Tonka, that are made by hard clay.
In underground tanks, water loss by evaporation practically does not occur. The shallow well upto the depth of 20m are also dug in depression, where rainwater is collected in sufficient quantity. These dug well are recharged by percolating water in soil. Farm tank or pond is another method of water harvesting. The pond may be excavated in existing depression of the farm and soil so obtained may be used for embankment. The pond may be made impermeable by use of chemical sealants and soil cover such as wax and asphalt that will minimise water loss. The pond may be sealed with local available material to check seepage, covered to control evaporation and designed to prevent silting. With improved practices in catchments it is feasible, to harvest water as low as 10 mm rainfall.
The flood water harvesting, snow harvesting and dew harvesting are other resources of harvesting that deserve attention. In Dera Ghazi Khan District of Punjab, and in Balochistan hill torrents occur. The rainfall is received in short intense storm in form of flood. This flowing water should be spread over adjacent plains for crop production, range and pasture improvement. The water resources are scarce and will be more acute in future, because of the gap between demand and supply. Hence water needs to be conserved/harvested efficiently for optimum crop production.
No plan for uplift of farming community can be useful, unless farmers are actively involved in that activity, so is the case with water harvesting. The participatory approach involving stack holders to take part in water harvesting to conserve / harvest every drop of water is essential. The local people should be provided technical know how and financial assistance for construction and development of rainwater harvesting system in the respective region.
In successful crop production under rain-fed conditions, there are two options, either conserve/harvest enough water for optimum plant growth or grow crops that have minimum water requirements and give more yield with less water. The crops with low water requirements and high water use efficiency are to be propagated in rain-fed areas.
The crop species selected should be such that fit the rainfall pattern. Integrated farming system is appropriate for all levels of technologies from subsistence farming to large, highly technical commercial farming enterprises, The crop plants that can tolerate heat and resist drought / stress environment, yet had acceptable productivity and contribute to economic stability by reducing risks involved in rain-fed agriculture, are to be propagated. The conventional crops are to be supplemented with high value fruits and vegetable crops or agro-forestry, olive, saffron, salicornia and sea buckthorn cultivation may be other alternatives, depending on land capability classes.
The soils in rain-fed areas are usually class III and IV land capability class and had moderate to severe limitation for general crop production and deserve appropriate management practices. Vitiver grass known as Khus Khus is effective in soil and water conservation and may be adopted in suitable localities. The appropriate moisture conservation/water harvesting will ensure water availability to crops sown in rain-fed region.
The water available in dry areas may be utilised by highly efficient and effective irrigation techniques such as drip or sprinkler irrigation for successful crop production in rain-fed areas.