GROUNDWATER AND SOIL SALINITY VARIATIONS IN A CANAL COMMAND AREA IN PAKISTAN y

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1 IRRIGATION AND DRAINAGE Irrig. and Drain. 58: (2009) Published online 28 July 2008 in Wiley InterScience ( GROUNDWATER AND SOIL SALINITY VARIATIONS IN A CANAL COMMAND AREA IN PAKISTAN y MUHAMMAD LATIF* AND MUHAMMAD ZAKRIA AHMAD Centre of Excellence in Water Resources Engineering, University of Engineering and Technology, G.T. Road, Lahore, Pakistan ABSTRACT This three-year study was undertaken to investigate the groundwater and soil salinity variation in a canal-irrigated area. Water and soil samples were collected along 54 tertiary canals located on six secondary canals (two each at head, middle and tail end) of a main canal. Data of crop yield and income of the farmers were also collected. The results show that electrical conductivity (EC) of groundwater increased from head to lower reaches along all the irrigation channels, i.e. main, the secondary and the tertiary canals. Similarly, the soil water EC e also increased with increased distance from the head of the irrigation system. Reduced canal water supply at lower reaches of the irrigation system forced the downstream water users to pump more groundwater, thereby increasing their irrigation cost. The deteriorating groundwater quality further adds misery to the downstream farmers by degrading productivity of their lands caused by excessive use of saline groundwater. Location of the water users along the canal irrigation system had an impact on their crop yield as well as income and these parameters decreased with increased distance from the head of the irrigation channels. For example, the net income of the tail-end farmers varied from 43% to 59% of the head-end farmers. Copyright # 2008 John Wiley & Sons, Ltd. key words: canal irrigation network; EC of groundwater and soil water; crop yield; farm income Received 12 January 2008; Revised 22 February 2008; Accepted 23 February 2008 RÉSUMÉ Cette étude de trois ans a été entreprise pour étudier la variation de la salinité des eaux souterraines et de l eau dans le sol dans un périmètre irrigué par des canaux. Des échantillons d eau et de sol ont été prélevés le long de 54 canaux tertiaires situés sur six canaux secondaires (2 en tête, au milieu et en extrémité) d un canal principal. Des données sur le rendement et le revenu des fermiers ont été également rassemblées. Les résultats montrent que la conductivité électrique des eaux souterraines a augmenté de l amont vers l aval le long de tous les canaux, principal, secondaires et tertiaires. De même la conductivité électrique de l eau dans le sol a augmenté avec la distance à la tête du système d irrigation. Une alimentation en eau réduite en extrémité de canaux oblige les utilisateurs aval à pomper plus d eaux souterraines augmentant de ce fait leur coût d irrigation. La mauvaise qualité des eaux souterraines augmente la misère des fermiers aval en dégradant la productivité de leurs terres par suite d une utilisation excessive des eaux souterraines salines. La localisation des utilisateurs le long du système d irrigation a eu un impact sur leur rendement et sur leur revenu; ces paramètres ont diminué avec la distance à la tête du système d irrigation. Par exemple, le revenu net des fermiers de l extrémité aval a diminué de 43% à 59% par rapport à celui des fermiers de l amont. Copyright # 2008 John Wiley & Sons, Ltd. mots clés: réseau d irrigation avec canaux; conductivité électrique des eaux souterraines et de l eau dans le sol; rendement; revenu agricole * Correspondence to: Muhammad Latif, Centre of Excellence in Water Resources Engineering, University of Engineering and Technology, G. T. Road, Lahore, Punjab 54890, Pakistan. drmlatif@yahoo.com y Variations de la salinité des eaux souterraines et du sol dans un périmètre irrigué au Pakistan. Copyright # 2008 John Wiley & Sons, Ltd.

2 GROUNDWATER AND SOIL SALINITY IN A CANAL COMMAND AREA IN PAKISTAN 457 INTRODUCTION The need for more food and fibre is increasing all over the world due to population increase and people s changing eating habits. Canal water scarcity leads to use of more and more groundwater to fulfil crop water needs. Saline groundwater is a potential source for meeting growing irrigation requirements. Limited availability of fresh water, soil salinity and sodicity are the major bottlenecks in the sustainable development of agriculture sector in the Indus Basin of Pakistan. Canal water scarcity has compelled farmers to make greater use of saline groundwater that occurs extensively in the arid and semi-arid environments of India and Pakistan and other countries (Bhutta and Alam, 2006; Sharma and Minhas, 2006; Qadir et al., 2007; Qureshi, 2004). Indiscriminate and continuous use of poor-quality water often causes increase in soil salinity, sodicity and toxicity. In addition to the reduced productivity, the use of saline groundwater deteriorates the quality of produce and also limits the choice of cultivable crops. Concerted efforts at different research stations located in different agro-climatic zones have yielded valuable insights and viable technologies for a sustainable irrigation with poor-quality water (Minhas, 1996). Research efforts have demonstrated the possibilities of using such waters through selection of salt-tolerant crops, crop varieties and cropping patterns and by maintaining low levels of salts in the active root zone through appropriate irrigation schedules and water application methods (Ahmed et al., 2007; Karlberg et al., 2007; Kalra et al., 2007). Integrated use of canal water, groundwater and rainwater can help to mitigate harmful impacts of the salts. Salt-affected soils are common in countries situated in arid and semi-arid regions like Pakistan. The major constraints to irrigated agriculture in the subcontinent of Pakistan and India are scarcity of canal water and its unequal distribution, soil salinity and waterlogging, which have severally affected the production potential of vast areas in the region by creating a poor environment in the crop root zone (Bhutta et al., 1991; Smout and Gorantiwar, 2006). Khan et al. (2006) studied sustainability of three irrigation systems situated in different semi-arid regions in Australia, China and Pakistan. Groundwater use was found to be maximal in Pakistan (53%), whereas water uptake from shallow groundwater was highest in China (48%). Surface water use efficiency was lowest in Pakistan (32%) and it was highest (77%) in Australia. The authors concluded that under the existing operating conditions none of the three systems was sustainable. However, no alternative option was discussed to improve the existing conditions. Leaching of the undesirable salts cannot be effectively accomplished if there is scarcity of canal water supply. The canal irrigation systems in the subcontinent of India and Pakistan were designed by the British to combat famine and to benefit more farmers. These systems do not provide sufficient water for full crop water requirements (Johnson, 1982). In these systems water is allocated to the farmers according to Malhotra s model (1982), based on land holdings of the farmers. Some recent studies (Sharma and Oad, 1990; Latif and Sarwar, 1994; Khepar et al., 2000) showed that seepage losses have been ignored in the above model, which are the major cause of inequitable water distribution at a tertiary level in these countries. This leads to a monotonically decreasing amount of water received by downstream farmers. The present study was undertaken to investigate and analyse variations in the electrical conductivity (EC) of groundwater and soil salinity along with its impact on the income of farmers in a Table I. Main features of the selected secondary channels Serial no. Location on main canal Name of secondary channel Off-take RD a Command area (ha) Discharge (m 3 s 1 ) 1 Head Athail pur L Lalliani L Middle China L 11, Zafer Ke R Tail Rosa L Vahn L a RD stands for reduced distance for canal mile. 1RD¼ m (1000 ft). Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2009)

3 458 M. LATIF AND M. Z. AHMAD Table II. Number of irrigations applied from canal and groundwater in 2005 Tertiary canal Location on secondary canal Secondary canals along the main canal Athail Pur Lalliani China Zafer Ke Rosa Vahn Head Middle Tail Head Middle Tail Head Middle Tail Head Middle Tail Head Middle Tail Head Middle Tail 1 Head 4 a (0) b 3 (1) 3 (1) 5 (0) 4 (1) 3 (1) 5 (0) 4 (1) 3 (1) 5 (0) 4 (1) 3 (1) 4 (1) 3 (1) 3 (2) 4 (0) 4 (1) 4 (1) 2 5 (0) 3 (1) 3 (1) 5 (0) 3 (1) 3 (2) 4 (0) 3 (1) 3 (1) 5 (0) 3 (1) 3 (1) 4 (0) 3 (2) 3 (2) 4 (0) 4 (1) 3 (2) 3 4 (0) 3 (1) 3 (1) 4 (0) 3 (1) 2 (2) 4 (0) 3 (1) 3 (1) 5 (0) 3 (2) 3 (2) 4 (1) 3 (2) 2 (3) 4 (0) 3 (2) 3 (2) 4 Middle 5 (0) 3 (2) 3 (2) 4 (0) 3 (1) 2 (2) 4 (0) 3 (1) 2 (3) 4 (0) 4 (1) 3 (2) 4 (1) 3 (2) 1 (4) 3 (1) 3 (2) 2 (2) 5 4 (0) 3 (2) 3 (2) 3 (1) 2 (2) 2 (2) 4 (0) 3 (2) 2 (3) 3 (1) 3 (2) 2 (2) 3 (2) 3 (2) 2 (3) 2 (2) 2 (2) 2 (3) 6 5 (0) 3 (2) 3 (2) 3 (1) 2 (3) 2 (3) 3 (1) 2 (3) 2 (3) 3 (1) 2 (3) 2 (3) 2 (2) 2 (3) 2 (3) 1 (2) 1 (2) 0 (3) 7 Tail 1 (4) 2 (3) 1 (3) 2 (2) 1 (3) 1 (3) 1 (2) 1 (3) 0 (4) 1 (3) 0 (3) 0 (4) 1 (3) 1 (3) 1 (4) 1 (2) 0 (3) 0 (4) 8 2 (3) 2 (3) 2 (3) 1 (3) 1 (3) 1 (4) 1 (3) 1 (3) 0 (4) 1 (3) 0 (4) 0 (4) 2 (2) 1 (3) 0 (4) 1 (3) 0 (3) 0 (4) 9 2 (3) 2 (3) 1 (4) 1 (3) 1 (4) 1 (4) 1 (3) 1 (4) 0 (5) 1 (3) 0 (4) 0 (4) 2 (2) 0 (4) 0 (4) 0 (3) 0 (3) 0 (4) a Canal irrigation; b tubewell irrigation. Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2008)

4 GROUNDWATER AND SOIL SALINITY IN A CANAL COMMAND AREA IN PAKISTAN 459 large-scale canal irrigation system in Pakistan. No doubt the results are site specific but these can be applied to other areas in Pakistan and elsewhere with similar conditions. METHODOLOGY AND DATA COLLECTION Site selection This study was undertaken in the command area of the main branch lower (MBL) canal, keeping in mind that canal water is the primary source for irrigating crops and the area is easily approachable. The canal is located in central Punjab in Pakistan and it off-takes at RD 433 þ 958 from the Bambanwala Ravi Bedia Depalpur (BRBD) link canal. This is a perennial canal, having a design discharge of 49 m 3 s 1. The command area of this canal is ha. Six secondary canals were selected, two each at head, middle and tail locations of the main canal (Table I). A total of 54 tertiary canals (watercourses) were selected, i.e. three tertiary canals each at the head, middle and tail of six secondary canals. For income calculations 486 farmers were selected, while nine farmers were selected along each tertiary canal. Figure 1. EC of groundwater along tertiary canals (watercourses) of different secondary canals during first year of the study (2005). (a) Athail pur channel, (b) Lalliani channel, (c) China channel (d) Zafer ke channel, (e) Rosa channel, (f) Vahn channel Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2009)

5 460 M. LATIF AND M. Z. AHMAD Data collection Information about the irrigation system and the irrigated area were obtained from the Irrigation Department. In water and soil samples were collected from each of the 9 6 tertiary canals along their head, middle and tail reaches once during each year. Soil samples were taken by using an auger up to 90 cm depth at 15 cm depth intervals. Six samples were collected from each sampling location, making a total of 324 (9 6 6) samples. Chemical analysis of all the water and soil samples was performed as discussed by Ahmad (2006). Data regarding number of irrigations applied, source of irrigation water, farm operations, inputs used, total expenses and yield of wheat crop were collected from selected farmers. Wheat was selected since all the farmers sow it, as it is a staple food. Figure 2. Average EC of groundwater along different secondary canals on the main canal for 3 years. (a) 1 st year (2005), (b) 2 nd year (2006), (c) 3 rd year (2007) Figure 3. Average distribution of groundwater EC in the study area during 3 years ( ) Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2008)

6 GROUNDWATER AND SOIL SALINITY IN A CANAL COMMAND AREA IN PAKISTAN 461 Groundwater use RESULTS AND DISCUSSION Data were collected on the number of irrigations applied to wheat from canal water as well as groundwater (Table II). It is apparent from the table that three to five irrigations were applied. The number of irrigations applied from the canal is greater at the heads of the secondary canals than at their middle or tails. The same is true along the tertiary canals. Normally four to five irrigations were applied at the heads of the secondary canals by canal water. The number of irrigations from canal water dropped to zero or one at the very tail reaches and there is a corresponding increase in the number of irrigations by tubewell. With greater use of groundwater, the cost of irrigation of the lower riparians increases many times, as discussed by Latif (2007). EC of groundwater The EC of groundwater varied highly and it ranged from less than 1 to more than 10 ds m 1 in different years. As an example, groundwater EC during 2005 at head, middle and tail ends of the tertiary canals along six secondary canals, as shown in Figure 1 plots (a) (f), tends to increase from head to tail end along almost all the tertiary canals. At the head of tertiary canal number 7 of secondary canal number 1 there is a progressive farmer who has three pumps up to 175 m (575 ft) deep (EC of deeper groundwater is low in the study area but tubewells of most farmers are shallow). Similarly, a deep pump was also installed jointly by a group of farmers at the tail of this tertiary canal. Figure 4. Mean, median and percentile EC of groundwater for 3 years ( ) along tertiary canals Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2009)

7 462 M. LATIF AND M. Z. AHMAD Conditions were much worse at the last two secondary canals (Figure 1(e) and 1(f)), which are located at the tail reach of the main canal. A similar trend of increasing EC of groundwater along the lower reaches of the irrigation channels was found during 2006 and The average EC of groundwater along each secondary canal is presented in Figure 2(a) (c) over 3 years. Groundwater EC varied from 0.5 to 0.67 ds m 1 at heads to more than 5 ds m 1 at their lower ends. The worst condition prevails at the lower ends of the last two secondary canals situated at the end of the main canal. Figure 5. Average EC e of the soil extracts of different secondary canals during the first year (2005). (a) Athail pur channel, (b) Lalliani channel, (c) China channel (d) Zafer ke channel, (e) Rosa channel, (f) Vahn channel Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2008)

8 GROUNDWATER AND SOIL SALINITY IN A CANAL COMMAND AREA IN PAKISTAN 463 The groundwater EC data may be classified into suitable, marginal and unsuitable class, as shown in Figure 3. The results show that 53% of water samples had EC below 1.5 ds m 1, whereas 32% of samples had EC in the range ds m 1 and 15% of samples had EC greater than 3.0 ds m 1. According to FAO (1985) guidelines for irrigation water quality, EC of the irrigation water between 0.75 to 3 ds m 1 cause an increasing problem, whereas a severe problem is caused if EC exceeds 3 ds m 1. The EC is greater than 1.5 ds m 1 in almost one-half of the study area, thus causing a reduction in crop yield, as discussed in last section of this paper. Figure 6. Average soil salinity along different secondary canals on the main canal for 3 years. (a) 1 st year (2005), (b) 2 nd year (2006), (c) 3 rd year (2007) Figure 7. Average percent distribution of soil salinity in the study area during 3 years ( ) Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2009)

9 464 M. LATIF AND M. Z. AHMAD Means, medians and percentiles of the EC data were also calculated and the results are presented in Figure 4. Means ranged from 0.93 to 2.48 ds m 1, whereas standard deviation varied from 0.42 to 1.73 ds m 1, respectively, at head and tail end of the tertiary canals. Vertical bars show 10th and 90th percentiles. Boxes in the figure show 25th and 75th percentiles. It is once again evident from this figure that EC of groundwater and its variability increase from head to lower reaches of the irrigation channels. Soil water EC e The average values of EC e at heads, middles and tails of the tertiary canals along each secondary canal are plotted in Figure 5(a f) for the first year of the study. EC e of the soil profile increased from head to tail of all tertiary canals. Similarly, average EC e of the soil profiles of the six secondary canals along the main canal are plotted in Figure 6(a c) for 3 years. Again, the EC e increased from head to lower reaches of all the secondary canals as well as along the main canal following the pattern of groundwater EC, as discussed in the preceding section. Figure 7 shows that 75% of soils had EC e less than 2 ds m 1, while 25% of the soils were more saline. The latter are situated at the tail end of the irrigation channels. Profiles of EC e for the last secondary canal (Vahn) are plotted in Figure 8. The EC e values are low and uniform at the head of the tertiary canal (no. 46) located at the head of the secondary channel but the values are higher and decrease with depth in the command areas of all other tertiary channels on the last secondary canal. The latter trend is found when less water is applied for leaching of salts. Under such conditions salts accumulate in the upper soil layers as found in these fields. Yield of wheat and income The wheat yield varied from 3.41 to 2.21 tons ha 1, while net income of the farmers ranged from Rs to Rs 4140 per ha. That is, the net income of the tail-end farmers is only one-quarter of their head-end counterparts. Figure 8. Average soil salinity profiles under the command area of last secondary canal (Vahn) during 3 years ( ) Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2008)

10 GROUNDWATER AND SOIL SALINITY IN A CANAL COMMAND AREA IN PAKISTAN 465 Table III. Summary of crop yield and income of farmers of different secondary canals during first year (2005) Location at canal Name of secondary canals Location at secondary canal Tertiary canal Average yield of wheat (tons ha 1 ) Net income (Rs c ha 1 ) Location along tertiary canal Location along tertiary canal Head Middle Tail Head Middle Tail Head Athail Pur Head 1, 2, (100) a 3.07 (97) 3.01 (95) (100) b (85) (78) Middle 4, 5, (100) 2.86 (96) 2.95 (99) (100) (80) (80) Tail 7, 8, (100) 2.86 (94) 2.83 (93) (100) (91) (77) Average 3.06 (100) 2.93 (96) 2.93 (96) (100) (85) (78) Lalliani Head 10, 11, (100) 3.01 (95) 2.95 (93) (100) (79) (70) Middle 13, 14, (100) 2.77 (94) 2.73 (93) (100) (80) (70) Tail 16, 17, (100) 2.70 (96) 2.67 (95) (100) (83) (77) Average 2.98 (100) 2.83 (95) 2.79 (93) (100) (80) (72) Average of two channels 3.02 (100) 2.88 (95) 2.86 (95) (100) (83) (75) Middle China Head 19, 20, (100) 2.95 (99) 2.80 (94) (100) (85) (68) Middle 22, 23, (100) 2.70 (95) 2.67 (94) (100) (81) (68) Tail 25, 26, (100) 2.73 (96) 2.64 (92) (100) (76) (64) Average 2.90 (100) 2.80 (96) 2.70 (93) (100) (81) (67) Zafer Ke Head 28, 29, (100) 2.77 (97) 2.64 (92) (100) (84) (69) Middle 31, 32, (100) 2.58 (97) 2.49 (93) (100) (79) (66) Tail 34, 35, (100) 2.46 (98) 2.40 (95) (100) (87) (67) Average 2.68 (100) 2.60 (97) 2.51 (94) (100) (83) (67) Average of two channels 2.79 (100) 2.70 (97) 2.61 (93) (100) (82) (67) Tail Rosa Head 37, 38, (100) 2.67 (96) 2.64 (95) (100) (80) (72) Middle 40, 41, (100) 2.61 (99) 2.52 (95) (100) (90) (74) Tail 43, 44, (100) 2.40 (95) 2.37 (94) (100) (74) (63) Average 2.65 (100) 2.56 (97) 2.51 (95) (100) (82) (70) Vahn Head 46, 47, (100) 2.52 (94) 2.43 (91) (100) (77) (62) Middle 49, 50, (100) 2.43 (95) 2.37 (93) (100) (78) (66) Tail 52, 53, (100) 2.40 (91) 2.30 (87) (100) (66) (52) Average 2.62 (100) 2.45 (93) 2.37 (90) (100) (74) (60) Average of two channels 2.64 (100) 2.50 (95) 2.44 (92) (100) (78) (65) Overall average 2.82 (100) 2.69 (96) 2.63 (94) (100) (81) (70) a Average yield in percent with respect to head. b Average net income in percent with respect to head. c US $1 ¼ 61 rupees. Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2009)

11 466 M. LATIF AND M. Z. AHMAD Figure 9. Average crop yield and farmers net income along each secondary canal during the first year (2005). (a) Athail pur channel, (b) Lalliani channel, (c) China channel (d) Zafer ke channel, (e) Rosa channel, (f) Vahn channel The average crop yield and farmers net income in 2005 are given in Table III. Crop yield dropped with distance along all the irrigation channels, i.e. the tertiary and secondary canals as well as the main canal. Average values of crop yield and farmers income along the tertiary canals of each secondary canal are plotted in Figure 9(a f) for further elaboration. Yield and income are decreasing from head to lower reaches along all the irrigation channels, i.e. the tertiary canals, secondary and main channels. It is interesting to note that yield of wheat is not much different from head to tail reaches of the tertiary canals. The reason is that the farmers on the lower reaches used more groundwater to fulfil their crop water requirements and pumping of groundwater is more than Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2008)

12 GROUNDWATER AND SOIL SALINITY IN A CANAL COMMAND AREA IN PAKISTAN 467 Figure 10. Average net income of farmers of different secondary canals along the main canal for 3 years. (a) 1 st year (2005), (b) 2 nd year (2006), (c) 3 rd year (2007) 25 times costlier than canal water (Latif, 2007). Due to more use of groundwater, irrigation cost of these farmers is increased and consequently net income of the lower-reach farmers was reduced accordingly. The average net income of the farmers along the secondary canals is plotted in Figure 10(a c) for 3 years. The difference in net income of the farmers varied from 93% to 43% in 2005 along the secondary channels. The solid line in the figure shows the average income along the secondary canals, which also follows a falling trend from head to tail end of the main canal. CONCLUSIONS The analysis of groundwater quality data showed that groundwater salinity increased from head to lower reaches of all the irrigation channels, i.e. the main, secondary and tertiary canals. The groundwater is of suitable quality only in about one-half of the command area. In the rest of the area, groundwater is either marginally fit for irrigation or it Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2009)

13 468 M. LATIF AND M. Z. AHMAD is hazardous (unfit). The soil salinity (EC e) almost follows the pattern of groundwater salinity. The soil profile EC e values were low and uniform except for the last secondary canal, where the salinity was high, and it decreased with increase in depth. The crop yield and net income decreased along all the irrigation channels (i.e. the main, secondary and tertiary canals) but decrease in net income was much more than decrease in crop yield. NOTES In Pakistan, a secondary irrigation canal is called a distributary. A minor is a small secondary canal that off-takes from the secondary canal. A tertiary canal is called a watercourse. Rs ¼ Pakistan rupee; US $1 ¼ Rs 61. ACKNOWLEDGEMENTS The authors wish to acknowledge the Higher Education Commission and the Government of Pakistan for funding support. REFERENCES Ahmad MZ Secondary soil salinity development and its impact on irrigated environment in a selected canal command area. MPhil thesis, Centre of Excellence in Water Resources Engineering, University of Engineering and Technology, Lahore, Pakistan. Ahmed BAO, Yamamoto T, Rasiah V, Inoue M, Anyoji H The impact of saline water irrigation management options in a dune sand on available soil water and its salinity. Journal of Agricultural Water Management 88: Bhutta MN, Alam MM Prospectives and limits of groundwater use in Pakistan. In Proceedings of Groundwater Research and Management: Integrating Science into Management Decisions, Groundwater Governance in Asia Series 1; pp Bhutta NM, Latif M, Kijne JW A study of water distribution from a branch to distributary canals: a case study of Gugera Branch. Journal of Irrigation and Drainage Systems 5(3): Food and Agriculture Organization (FAO) Water Quality for Agriculture. FAO: Rome; Johnson SH III Large-scale irrigation and drainage system in Pakistan: a study of rigidities in public decision making. Food Research Institute Studies 18(2): Kalra N, Debashis C, Ramesh KP, Jolly M, Sharma PK An approach to bridging yield gaps, combining response to water and other resource inputs for wheat in northern India, using research trials and farmers fields data. Journal of Agricultural Water Management 93: Karlberg L, Rockstrom J, Annandale JG, Steyn JM Low-cost drip irrigation: a suitable technology for Southern Africa? An example with tomatoes using saline irrigation water. Journal of Agricultural Water Management 89: Khan S, Rana T, Cui Y, Blackwell J Can irrigation be sustainable? Journal of Agricultural Water Management 80: Khepar SD, Gulati HS, Yadav AK, Barar TPS A model for equitable distribution of canal water. Journal of Irrigation Science 19: Latif M Spatial productivity along a canal irrigation system in Pakistan. Irrigation and Drainage 56(5): Latif M, Sarwar S Proposal for equitable water allocation for rotational irrigation in Pakistan. Journal of Irrigation and Drainage Systems 8: Malhotra SP The Warabandi System and Infrastructure. Publ. no. 157, Central Board of Irrigation and Power: New Delhi, India. Minhas PS Saline water management for irrigation in India. Agricultural Water Management 30: Qadir M, Sharma BR, Bruggeman A, Choukr-Allah R, Karajeh F Non-conventional water resources and opportunities for water augmentation to achieve food security in water scarce countries. Agricultural Water Management 87: 2 22 (available at Qureshi AS Protecting food and livelihood security through groundwater management: challenges and opportunities. In International Symposium on Community-Based Approaches for Towards Integrated Water Resources Management, United Nations Development Programme, Islamabad, Pakistan; Sharma DR, Minhas PS Management options and polity guidelines for use of poor quality groundwater in agriculture. In Proceedings of Groundwater Research and Management: Integrating Science into Management Decisions, Groundwater Governance in Asia Series 1; Sharma DN, Oad R Variable time model for equitable irrigation water distribution. Agricultural Water Management 17: Smout KI, Gorantiwar SD Productivity and equity of different irrigation schedules under limited water supply. Journal of Irrigation and Drainage Engineering, ASCE 132(4): Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: (2008)