Mixing groundwater with surface water (joint use) is widely practised by Punjab farmers but as canal supplies have declined and demand for irrigation has increased, excessive groundwater abstraction has led to rapidly declining water levels, which in some areas is already leading to a conversion to turbine pumping, and quality deterioration.
According to Punjab Irrigation and Power Department (PIPD)'s update study reports, the lower the water table, the greater the risk of drawing on saline water. In 1960 'hazardous' groundwater was found in less than 8,000 hectares of LBDC but by 2005 groundwater listed as 'marginal or unfit' was affecting 402,000 hectares, approximately half the area of the LBDC.
Farmers use mix canal water and poor quality groundwater to avoid soil salinisation in the short term, but with declining canal supplies and increasing cropping intensity the observed rate of groundwater deterioration is unsustainable.
The present cropping pattern requires about 6,410 MCM (5.2 MAF) of irrigation per annum. Cotton is the main user 1,479 MCM (1.2 MAF) followed closely by wheat. Rabi fodders and rice each require 740 MCM (0.6 MAF). At the mogha outlet and the tubewell, irrigation supplies are 3,700 MCM (3.0 MAF) and 4,809 MCM (3.9 MAF) respectively. Allowing for field efficiency, losses of about 0.66 (efficiencies of tubewell and canal supplies differ slightly) an overall irrigation deficiency of about 14 percent was estimated for Lower Bari Doab Canal (LBDC), Cultivable Command Area (CCA), varying between the head (3 percent) and the tail (up to 20 percent).
Crop yields are generally lower than potential (especially the main crops rice, wheat and cotton, but with some notable exceptions including spring maize and multi-cut fodders), and the main constraints are insufficient irrigation and small farm size. About 11 million tons of production is achieved annually in the LBDC command area, excluding livestock. This includes 2.2 million tons of cereals, 1.5 million tons of vegetables & fruits, 4.9 million tons of fodders, 1.8 million tons of sugarcane and 420 thousand tons of cotton. LBDC command area is one of the major sources of agriculture production in Punjab.
The climate in the LBDC command is semi arid and comprises two agro-ecological zones based on rainfall which is relatively higher in the north-east (340 mm pa) than the south-west (225 mm pa), and which mainly affects Kharif cropping. Rice is grown in the higher rainfall zone, while cotton is grown further south. Soils are deep and medium to fine textured throughout the area, but fertility has been reduced by intensive cultivation and decades of irrigation.
The present cultivated command area (CCA) of the canal is 1,737,843 acres (703,580 ha). There are 275,000 farms in the command area and the average farm size is 2.6 ha (6.3 acres). 57.5 percent of the farms are small farms, occupying 20 percent of the cultivable area with an average holding of 0.9 ha (2.24 acres). 30 percent of all farms in the medium category of 5 ha occupy 34 percent of the farmland. The large farms are only 13 percent of all farms but occupy 46 percent of the cultivable area.
The present cropping intensity is 170 percent and the gross cropped area is 1.19 million ha (2.95 million acres), 86 percent in Kharif and 85 percent in Rabi including double counting of the perennial crops; orchards and sugarcane. The cropping intensity in the selected subproject areas (Dhulwan and Jandraka) is higher than the overall intensity of LBDC. The highest acreage, 55 percent is under wheat during the Rabi followed by cotton at 34 percent in the Kharif. Fodders occupy about 14 percent of the area throughout the year. Maize occupies 14 percent followed by rice, 12 percent of cultivable command. The potential for intensive cropping is high in areas of good water supply. In Okara and Sahiwal division the cropping sequence of combinations of maize/rice/potato reaches 200 percent intensity over large areas.
Studies of conjunctive irrigation in the sub-project areas (based on the 2005 tubewell census) showed that the sanctioned delivery of canal water at the Mogha outlet is in the order of two acre feet per acre but only about 60 percent is received. In a few areas the canal system has deteriorated so much that farmers rely entirely on tubewell pumping for irrigation. Throughout LBDC CCA, tubewell pumped volume tends to exceed canal deliveries, and is in the order of 2 to 3 acre feet per acre. The marginal rate of substitution of use by farmers is 1.25 units of canal water to one unit of groundwater. This is a useful expression of greater application efficiency, reliability and timeliness of groundwater compared to canal water.
In the head of the system, study mentioned, particularly in areas favoured by good groundwater recharge the overall tubewell density is high, about 9.3 ha (23 acres) per tubewell. The overall tubewell density in the tail of the system is lower, about 21.4 ha (53 acres) per tubewell.
Tubewell density is higher on the saline aquifer (16.6 ha (41 acres) per tubewell) than the sweet aquifer (23.5 ha (58 acres) per tubewell), but here tubewells pump less than one third of the volume of tubewells over the sweet aquifer; the constraint is the volume farmers can mix with canal water to make what is perceived to be a "safe" application. Farmers mix at a ratio of 1:3, or one unit of poor quality water to 3 units of canal water. The residual for sale from tubewells operating on the saline aquifer is less than one third of that on the sweet aquifer.
Electricity powered pump sets have a lower density than diesel powered pump sets and the volume pumped per annum is greater because the marginal costs of pumping are lower. The density of electricity powered tubewells is less because they are pumping more and selling more water. Electricity powered pump sets have a higher utilisation rate (30%) than diesel (12 percent) and pump more than twice the volume of water (150 acre feet pa) than diesel (60 acre feet pa).
Tubewells are owned by landholders with relatively larger farm sizes. In the head of the system tubewell owning farms are about 30 percent of all farms and farm 42 percent of the area. In the tail of the system tubewell owning farms are only about 11 percent of the total number of farms and farm about 26 percent of the area. Owners of electricity powered tubewells have a larger farm size (6.5 ha) than diesel pump set owners (4 ha).
Water pumped over and above the irrigation requirement of the tubewell owner's farm is sold to neighbouring farms. Sales are about 50-60 percent of the total volume pumped and appear to provide up to 70 percent of the irrigation supply of non-tubewell owners.
However, in the tail of the system there is insufficient density for the water market to reach all farms, and it may be that 40 percent of the area relies entirely on canal water.
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