- Email: [email protected]
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA
Agricultural Sciences in China
July 2009
2009, 8(7): 850-854
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA T L Thompson1, PANG Huan-cheng2 and LI Yu-yi2 1 2
Department of Plant and Soil Science, Texas Tech University, Lubbock TX 79409, USA Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences (CAAS), Beijing 100081, P.R.China
Abstract Water shortages within the western USA are resulting in the adoption of water-saving agricultural practices within this region. Among the many possible methods for saving water in agriculture, the adoption of subsurface drip irrigation (SDI) provides a potential solution to the problem of low water use efficiency. Other advantages of SDI include reduced NO3 leaching compared to surface irrigation, higher yields, a dry soil surface for improved weed control, better crop health, and harvest flexibility for many specialty crops. The use of SDI also allows the virtual elimination of crop water stress, the ability to apply water and nutrients to the most active part of the root zone, protection of drip lines from damage due to cultivation and tillage, and the ability to irrigate with wastewater while preventing human contact. Yet, SDI is used only on a minority of cropland in the arid western USA. Reasons for the limited adoption of SDI include the high initial capital investment required, the need for intensive management, and the urbanization that is rapidly consuming farmland in parts of the western USA. The contributions of SDI to increasing yield, quality, and water use efficiency have been demonstrated. The two major barriers to SDI sustainability in arid regions are economics (i.e., paying for the SDI system), including the high cost of installation; and salt accumulation, which requires periodic leaching, specialized tillage methods, or transplanting of seedlings rather than direct-seeding. We will review advances in irrigation management with SDI. Key words: subsurface drip irrigation (SDI), water-saving agriculture, western USA
INTRODUCTION Most of the western USA, west of 100° W longitude, has an arid or semi-arid climate. It is in this region that irrigation of crops is most common. However, increasing urban populations, drought, declining groundwater levels and loss of water storage in reservoirs are combining to put water resources within these regions at risk. Thus, the need for water-saving agriculture has never been so great. Improvements in irrigation system technology used Received 9 October, 2008
in the western USA include improvements in flood irrigation such as “surge irrigation” using gated pipe, in which water flow is interrupted during irrigation rather than maintaining continuous flow. This helps to ensure improved water distribution. Sprinkler irrigation is popular in the western USA. In many areas, especially in the southern High Plains of Texas, low-flow nozzles have almost entirely replaced high flow sprinkler nozzles. This method greatly reduces rates of water application and evaporation and improves uniformity of distribution. Where fields are sloped, some farmers will create “furrow-dikes”, which are small dams within
Accepted 19 May, 2009
T L Thompson, Tel: +1-806-742-2838, Fax: +1-806-742-0775, E-mail: [email protected]; Correspondence PANG Huan-cheng, Professor, Tel: +86-82109739, E-mail: [email protected] © 2009, CAAS. All rights reserved. Published by Elsevier Ltd. doi:10.1016/S1671-2927(08)60287-4
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA
furrows to control runoff. This can help to restrict movement and improve infiltration of irrigation or rain water. Drip irrigation is the most inherently efficient irrigation system available. With drip irrigation (surface or subsurface) growers can routinely achieve both application and water use efficiencies exceeding 85%. Recent improvements in dripper technology have resulted in drip irrigation tubing that is robust and can easily last in the field for 20 years or more with proper installation and maintenance.
POTENTIAL AND PROBLEMS OF SDI FOR WATER-SAVING AGRICULTURE There are many ways to practice water-saving agriculture within the western USA. However, the potential for saving irrigation water in these regions is greatest with water-efficient irrigation methods such as subsurface drip irrigation (SDI). Currently, there are about 350 000 ha of commercial agriculture within the state of Arizona, all of it irrigated. Traditional irrigation has been by flood irrigation. However, within the past 10 years, significant amounts of subsurface drip irrigation have been installed, and now about 3-4% of irrigated acres have subsurface drip irrigation. Many studies have shown that SDI can result in saving 25-50% of the water used with flood irrigation. However, growers who have adopted SDI have done so not because of the water savings, but because of the many other advantages of SDI. These include, but are not limited to higher yield, higher quality of cotton and vegetable crops, ease of multiple harvests with vegetable crops, the ability to apply chemicals (fertilizers and pesticides) through the SDI tubing, and the reduction of plant diseases through maintaining a dry soil surface. The situation in West Texas is significantly different from that in Arizona. The sole source of agricultural irrigation water for the southern High Plains of Texas is the Ogallala aquifer. It is estimated that during the past 50 years of intensive irrigation, approximately 50% of the water originally present in the aquifer has been depleted. The result is that many areas are running short of water, and in those areas where water is still present, the water yield from groundwater wells has been significantly decreased. Farmers have therefore been forced to
851
switch from conventional center-pivot sprinkler irrigation to water-saving irrigation methods such as lowenergy precision application (LEPA), sprinkler irrigation, and subsurface drip irrigation. It is estimated that about 200000 ha of SDI that have been installed on the southern High Plains. In contrast to the current situation in Arizona, many West Texas farmers do not have access to enough water for optimum irrigation. Many crops in this area, especially cotton, are deficit-irrigated. Subsurface drip irrigation is the best method for deficit irrigation while minimizing crop stress and maximizing crop yield and quality. It is for this reason that SDI is being adopted so rapidly by farmers in West Texas. The use of SDI provides one potential solution to low water use efficiency and decreasing irrigation water quality. Subsurface drip irrigation offers many advantages for crop production. These advantages include increased water use efficiency, reduction of nitrate leaching compared to surface irrigation, higher yields, maintenance of a dry soil surface for improved weed control and crop health, the ability to apply water and nutrients to the most active portion of the root zone, protection of drip lines from damage due to cultivation and other operations, and the ability to safely irrigate with wastewater while preventing human contact (BarYosef 1999; Camp 1998; Lamm 2002; Enriquez et al. 2003; Phene 1995). Recent research has shown that with proper management, crop yields can be optimized with SDI while minimizing pollution through leaching losses of N (Thompson et al. 2000b, 2002b). Irrigation with SDI allows maintenance of low root-zone salinity, even when using irrigation waters containing appreciable salts (Oron et al. 1999; Oron et al. 2002). Two potential shortcomings of SDI are its high initial cost and the potential for the development of soil salinity. Installation of SDI systems may cost > US$2 500 ha -1 (Hanson and May 2003). Conversion from conventional irrigation systems requires high capital inputs and increases in time required for irrigation design implementation and management. Costs of conversion to SDI often prevent producers from seeing the benefits of its adoption. However, when amortized over the 10+ year life of the system the actual cost of SDI installation is less than $250 ha-1 yr-1. Proper management of SDI systems also requires higher time commitment and specialized training, which
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
852
usually impact the economics of conversion to SDI. Soil salinity is a common problem with SDI. Precise application of water and nutrients below the soil surface is a benefit of SDI, but leads to accumulation of salt near the soil surface. Net upward flow of water from the SDI emitter to the surface and loss of water to evaporation and transpiration can lead to high ECe values at the soil surface (Dasberg and Or 1999). Management of accumulated salts leads to increased demand on time and money to maintain high levels of productivity. Reduction of salts accumulated at or near the soil surface is often accomplished using sprinklers, which leads to increases in labor and capital inputs (Hillel 2000). Accumulation of salts in SDI-irrigated fields will always be a problem in arid and semi-arid regions where there is insufficient rainfall to leach salts. Specialized tillage methods, planting salt-tolerant crops, and transplanting within vegetable production systems can help to minimize salinity problems with SDI (Roberts et al. 2008).
RESEARCH ADVANCES OF SDI FOR WATER-SAVING AGRICULTURE Field researches with SDI were conducted to evaluate various outcomes of production of high-value crops, such as watermelon, lettuce, broccoli, cauliflower with SDI (Pier and Doerge 1995; Thompson and Doerge 1996; Thompson et al. 2000a, b, 2002a, b). The objective of these researches was to evaluate simultaneously the agronomic, economic, and environmental outcomes of crop production with SDI. The results showed that excessive N or water applications resulted in high amounts of N loss, and this N was probably lost from the soil profile. Therefore, good water and fertilizer management is still necessary when using SDI. It could be concluded from these experiments that production of high-yielding vegetable crops is compatible with environmental protection. A long-term evaluation of SDI demonstration/research project was established at the University of Arizona’s Maricopa Agricultural Center. The results of demonstration project showed that high frequency irrigation with SDI benefited summer-grown watermelon crops, but did not benefit winter-grown broccoli crops compared to low-frequency
T L Thompson et al.
irrigation with SDI. Providing for high-frequency SDI irrigation for summer-grown crops (irrigation at least once/day) to maintain soil water tension near 10 cbar should result in higher yield of watermelons. However, the combination of generally lower water use and higher yields with SDI have resulted in substantially higher water use efficiency with SDI than with surface irrigation. With high-frequency SDI, cumulative water use efficiency was twice that with surface irrigation. Thus, twice as much crop was produced using the same amount of water with high-frequency SDI than with surface irrigation. The results of this project have demonstrated that the use of SDI in Arizona crop production can consistently result in higher water use efficiencies and higher economic returns than surface flood irrigation. Continued use of SDI in arid regions will inevitably lead to salt accumulations detrimental to crop growth, unless salt accumulation can be minimized. Salt accumulation may pose the single largest constraint to the sustainable use of SDI in Arizona. Detrimental salt accumulations can be avoided by a) cultural techniques with some crops (e.g., pre-irrigation followed by removal of the bed cap with cotton), b) periodic leaching with sprinklers, or c) transplanting of high-value crops. Methods for managing salt without the use of sprinklers include transplanting and bed shaping. Using transplants may eliminate the need for sprinklers during establishment, because the root ball is placed from 5 to 10 cm below the zone of highest salt accumulation. However, sprinklers are often used with transplants to prevent desiccation, because several hours may be required for water to move from the drip tape to the root zone. Transplants may eliminate the need for sprinklers to manage salts, but require high capital inputs and may not improve the economic sustainability of SDI. Bed shaping has been introduced as a means to manage salt accumulation above the drip tape. This method involves forming the beds to a peak and preirrigating to move salts toward the peak. The tops of the bed are then removed into the furrow leaving behind soil of low ECe. Direct seeding of some largeseeded crops can then occur without inhibition of emergence. Small seeded crops that require precision planters cannot usually be direct-seeded into moist beds. Bed shaping procedures may prove effective in some
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA
crop rotations by eliminating the need for sprinklers, but the excess water needed to pre-irrigate beds may be less economically feasible, depending on water cost (Roberts et al. 2008).
CONCLUSION To be sustainable, SDI must 1) achieve substantially higher water use efficiency than surface irrigation methods, 2) increase crop yield and quality, 3) be economically viable, 4) contribute in a positive way toward environmental protection, and 5) not lead to development of adverse soil properties (salinity, sodicity). Many authors have shown that SDI is superior to most other irrigation methods with respect to points 1, 2, and 4. However, the economic viability of SDI depends on several factors under the control of the grower, including SDI system life, crop produced, water savings, and application cost savings. However, there are other factors, not under the grower’s control, including water cost and crop prices, that profoundly affect the economics of SDI. In arid regions, there is usually insufficient rainfall to leach salts from the zone of soil above the SDI tape. In this zone, detrimental salinity may result. In most cases, use of SDI in arid regions requires the periodic use of sprinklers to leach salts. The contributions of SDI to increasing yield, quality, and water use efficiency have been demonstrated. The two major barriers to SDI sustainability in arid regions are economics, including the high cost of installation and low cost of water; and salt accumulation, which demands periodic leaching, specialized tillage methods, or transplanting.
Acknowledgements The help from colleagues and students, past and present, is gratefully acknowledged. In particular, I acknowledge Tom Doerge, Scott White, Ron Godin, Trent Roberts, Ed Martin, Jim Walworth, and Russ Tronstad. This paper is funded by 948 Program of Ministry of Agriculture, China (2006-G52).
References Bar-Yosef B. 1999. Advances in fertigation. Advances in Agronomy, 65, 2-77.
853
Camp C R. 1998. Subsurface drip irrigation: A review. Trans ASAE, 41, 1353-1367. Dasberg S, Or D. 1999. Applied Agriculture: Drip Irrigation. Springer-Verlag, New York, NY. Enriquez C, Alum A, Suarez-Rey E, Choi C Y, Gerba C P. 2003. Survival of bacteriophages MS-2 and PRD-1 in turfgrass irrigated by subsurface drip irrigation. Journal of Environmental Engineering, 129, 852-857. Hanson B R, May D. 2003. Drip irrigation increases tomato yields in salt-affected soil of San Joaquin Valley. California Agriculture, 57, 132-137. Hillel D. 2000. Salinity Management for Sustainable Agriculture: Integrating Science, Environment and Economics. The World Bank. Washington D.C. Lamm F R. 2002. Advantages and disadvantages of subsurface drip irrigation. In: Proceedings of International Meeting on Advances in Drip/Micro Irrigation. Puerto de La Cruz, Tenerife, Canary Islands, Dec. 2-5, 2002. Instituto Canario de Investigaciones Agrarias, Canary Islands. p. 13. Oron G, De Malach Y, Gillerman L, David I, Rao V P. 1999. Improved saline-water use under subsurface drip irrigation. Agricultural Water Management, 39, 19-33. Oron G, DeMalach Y, Gillerman L, David I, Lurie S. 2002. Effect of water salinity and irrigation technology on yield and quality of pears. Biosystems Engineering, 81, 237-247. Phene C J. 1995. The sustainability and potential of subsurface drip irrigation. In: Freddie Lamm, ed, Microirrigation for a Changing World. American Society of Agricultural Engineers, St. Joseph, MI. pp. 359-367. Pier J W, Doerge T A. 1995. Concurrent evaluation of agronomic, economic, and environmental aspects of trickle irrigated watermelon production. Journal of Environmental Quality, 24, 79-86. Roberts T L, White S A, Warrick A W, Thompson T L. 2008. Tape depth and germination method influence patterns of salt accumulation with subsurface drip irrigation. Agricultural Water Management, doi:10.1016/j.agwat.2008.01.003 Smith M. 1995. Irrigation scheduling: From theory to practice. Proceedings of the ICID/FAO Workshop on Irrigation Scheduling Rome, Italy, 12-13 September. Thompson T L, Doerge T A. 1996. Nitrogen and water interactions in subsurface tricle-irrigated leaf lettuce. II. Agronomic, economic, and environmental outcomes. Soil Science Society of America Journal, 60, 168-173. Thompson T L, Doerge T A, Godin R E. 2000a. Nitrogen and water interactions in subsurface drip-irrigated cauliflower. I. Plant response. Soil Science Society of America Journal, 64, 406-411. Thompson T L, Doerge T A, Godin R E. 2000b. Nitrogen and water interactions in subsurface drip-irrigated cauliflower.
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
854
T L Thompson et al.
II. Agronomic, economic, and environmental outcomes. Soil Science Society of America Journal, 64, 412-418.
186-192. Thompson T L, Doerge T A, Godin R E. 2002b. Subsurface drip
Thompson T L, Doerge T A, Godin R E. 2002a. Subsurface drip irrigation and fertigation of broccoli: I. Yield, quality, and
irrigation and fertigation of broccoli: II. Agronomic, economic, and environmental outcomes. Soil Science Society of America
nitrogen uptake. Soil Science Society of America Journal, 66,
Journal, 66, 178-185. (Edited by ZHAO Qi)
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
July 2009
2009, 8(7): 850-854
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA T L Thompson1, PANG Huan-cheng2 and LI Yu-yi2 1 2
Department of Plant and Soil Science, Texas Tech University, Lubbock TX 79409, USA Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences (CAAS), Beijing 100081, P.R.China
Abstract Water shortages within the western USA are resulting in the adoption of water-saving agricultural practices within this region. Among the many possible methods for saving water in agriculture, the adoption of subsurface drip irrigation (SDI) provides a potential solution to the problem of low water use efficiency. Other advantages of SDI include reduced NO3 leaching compared to surface irrigation, higher yields, a dry soil surface for improved weed control, better crop health, and harvest flexibility for many specialty crops. The use of SDI also allows the virtual elimination of crop water stress, the ability to apply water and nutrients to the most active part of the root zone, protection of drip lines from damage due to cultivation and tillage, and the ability to irrigate with wastewater while preventing human contact. Yet, SDI is used only on a minority of cropland in the arid western USA. Reasons for the limited adoption of SDI include the high initial capital investment required, the need for intensive management, and the urbanization that is rapidly consuming farmland in parts of the western USA. The contributions of SDI to increasing yield, quality, and water use efficiency have been demonstrated. The two major barriers to SDI sustainability in arid regions are economics (i.e., paying for the SDI system), including the high cost of installation; and salt accumulation, which requires periodic leaching, specialized tillage methods, or transplanting of seedlings rather than direct-seeding. We will review advances in irrigation management with SDI. Key words: subsurface drip irrigation (SDI), water-saving agriculture, western USA
INTRODUCTION Most of the western USA, west of 100° W longitude, has an arid or semi-arid climate. It is in this region that irrigation of crops is most common. However, increasing urban populations, drought, declining groundwater levels and loss of water storage in reservoirs are combining to put water resources within these regions at risk. Thus, the need for water-saving agriculture has never been so great. Improvements in irrigation system technology used Received 9 October, 2008
in the western USA include improvements in flood irrigation such as “surge irrigation” using gated pipe, in which water flow is interrupted during irrigation rather than maintaining continuous flow. This helps to ensure improved water distribution. Sprinkler irrigation is popular in the western USA. In many areas, especially in the southern High Plains of Texas, low-flow nozzles have almost entirely replaced high flow sprinkler nozzles. This method greatly reduces rates of water application and evaporation and improves uniformity of distribution. Where fields are sloped, some farmers will create “furrow-dikes”, which are small dams within
Accepted 19 May, 2009
T L Thompson, Tel: +1-806-742-2838, Fax: +1-806-742-0775, E-mail: [email protected]; Correspondence PANG Huan-cheng, Professor, Tel: +86-82109739, E-mail: [email protected] © 2009, CAAS. All rights reserved. Published by Elsevier Ltd. doi:10.1016/S1671-2927(08)60287-4
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA
furrows to control runoff. This can help to restrict movement and improve infiltration of irrigation or rain water. Drip irrigation is the most inherently efficient irrigation system available. With drip irrigation (surface or subsurface) growers can routinely achieve both application and water use efficiencies exceeding 85%. Recent improvements in dripper technology have resulted in drip irrigation tubing that is robust and can easily last in the field for 20 years or more with proper installation and maintenance.
POTENTIAL AND PROBLEMS OF SDI FOR WATER-SAVING AGRICULTURE There are many ways to practice water-saving agriculture within the western USA. However, the potential for saving irrigation water in these regions is greatest with water-efficient irrigation methods such as subsurface drip irrigation (SDI). Currently, there are about 350 000 ha of commercial agriculture within the state of Arizona, all of it irrigated. Traditional irrigation has been by flood irrigation. However, within the past 10 years, significant amounts of subsurface drip irrigation have been installed, and now about 3-4% of irrigated acres have subsurface drip irrigation. Many studies have shown that SDI can result in saving 25-50% of the water used with flood irrigation. However, growers who have adopted SDI have done so not because of the water savings, but because of the many other advantages of SDI. These include, but are not limited to higher yield, higher quality of cotton and vegetable crops, ease of multiple harvests with vegetable crops, the ability to apply chemicals (fertilizers and pesticides) through the SDI tubing, and the reduction of plant diseases through maintaining a dry soil surface. The situation in West Texas is significantly different from that in Arizona. The sole source of agricultural irrigation water for the southern High Plains of Texas is the Ogallala aquifer. It is estimated that during the past 50 years of intensive irrigation, approximately 50% of the water originally present in the aquifer has been depleted. The result is that many areas are running short of water, and in those areas where water is still present, the water yield from groundwater wells has been significantly decreased. Farmers have therefore been forced to
851
switch from conventional center-pivot sprinkler irrigation to water-saving irrigation methods such as lowenergy precision application (LEPA), sprinkler irrigation, and subsurface drip irrigation. It is estimated that about 200000 ha of SDI that have been installed on the southern High Plains. In contrast to the current situation in Arizona, many West Texas farmers do not have access to enough water for optimum irrigation. Many crops in this area, especially cotton, are deficit-irrigated. Subsurface drip irrigation is the best method for deficit irrigation while minimizing crop stress and maximizing crop yield and quality. It is for this reason that SDI is being adopted so rapidly by farmers in West Texas. The use of SDI provides one potential solution to low water use efficiency and decreasing irrigation water quality. Subsurface drip irrigation offers many advantages for crop production. These advantages include increased water use efficiency, reduction of nitrate leaching compared to surface irrigation, higher yields, maintenance of a dry soil surface for improved weed control and crop health, the ability to apply water and nutrients to the most active portion of the root zone, protection of drip lines from damage due to cultivation and other operations, and the ability to safely irrigate with wastewater while preventing human contact (BarYosef 1999; Camp 1998; Lamm 2002; Enriquez et al. 2003; Phene 1995). Recent research has shown that with proper management, crop yields can be optimized with SDI while minimizing pollution through leaching losses of N (Thompson et al. 2000b, 2002b). Irrigation with SDI allows maintenance of low root-zone salinity, even when using irrigation waters containing appreciable salts (Oron et al. 1999; Oron et al. 2002). Two potential shortcomings of SDI are its high initial cost and the potential for the development of soil salinity. Installation of SDI systems may cost > US$2 500 ha -1 (Hanson and May 2003). Conversion from conventional irrigation systems requires high capital inputs and increases in time required for irrigation design implementation and management. Costs of conversion to SDI often prevent producers from seeing the benefits of its adoption. However, when amortized over the 10+ year life of the system the actual cost of SDI installation is less than $250 ha-1 yr-1. Proper management of SDI systems also requires higher time commitment and specialized training, which
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
852
usually impact the economics of conversion to SDI. Soil salinity is a common problem with SDI. Precise application of water and nutrients below the soil surface is a benefit of SDI, but leads to accumulation of salt near the soil surface. Net upward flow of water from the SDI emitter to the surface and loss of water to evaporation and transpiration can lead to high ECe values at the soil surface (Dasberg and Or 1999). Management of accumulated salts leads to increased demand on time and money to maintain high levels of productivity. Reduction of salts accumulated at or near the soil surface is often accomplished using sprinklers, which leads to increases in labor and capital inputs (Hillel 2000). Accumulation of salts in SDI-irrigated fields will always be a problem in arid and semi-arid regions where there is insufficient rainfall to leach salts. Specialized tillage methods, planting salt-tolerant crops, and transplanting within vegetable production systems can help to minimize salinity problems with SDI (Roberts et al. 2008).
RESEARCH ADVANCES OF SDI FOR WATER-SAVING AGRICULTURE Field researches with SDI were conducted to evaluate various outcomes of production of high-value crops, such as watermelon, lettuce, broccoli, cauliflower with SDI (Pier and Doerge 1995; Thompson and Doerge 1996; Thompson et al. 2000a, b, 2002a, b). The objective of these researches was to evaluate simultaneously the agronomic, economic, and environmental outcomes of crop production with SDI. The results showed that excessive N or water applications resulted in high amounts of N loss, and this N was probably lost from the soil profile. Therefore, good water and fertilizer management is still necessary when using SDI. It could be concluded from these experiments that production of high-yielding vegetable crops is compatible with environmental protection. A long-term evaluation of SDI demonstration/research project was established at the University of Arizona’s Maricopa Agricultural Center. The results of demonstration project showed that high frequency irrigation with SDI benefited summer-grown watermelon crops, but did not benefit winter-grown broccoli crops compared to low-frequency
T L Thompson et al.
irrigation with SDI. Providing for high-frequency SDI irrigation for summer-grown crops (irrigation at least once/day) to maintain soil water tension near 10 cbar should result in higher yield of watermelons. However, the combination of generally lower water use and higher yields with SDI have resulted in substantially higher water use efficiency with SDI than with surface irrigation. With high-frequency SDI, cumulative water use efficiency was twice that with surface irrigation. Thus, twice as much crop was produced using the same amount of water with high-frequency SDI than with surface irrigation. The results of this project have demonstrated that the use of SDI in Arizona crop production can consistently result in higher water use efficiencies and higher economic returns than surface flood irrigation. Continued use of SDI in arid regions will inevitably lead to salt accumulations detrimental to crop growth, unless salt accumulation can be minimized. Salt accumulation may pose the single largest constraint to the sustainable use of SDI in Arizona. Detrimental salt accumulations can be avoided by a) cultural techniques with some crops (e.g., pre-irrigation followed by removal of the bed cap with cotton), b) periodic leaching with sprinklers, or c) transplanting of high-value crops. Methods for managing salt without the use of sprinklers include transplanting and bed shaping. Using transplants may eliminate the need for sprinklers during establishment, because the root ball is placed from 5 to 10 cm below the zone of highest salt accumulation. However, sprinklers are often used with transplants to prevent desiccation, because several hours may be required for water to move from the drip tape to the root zone. Transplants may eliminate the need for sprinklers to manage salts, but require high capital inputs and may not improve the economic sustainability of SDI. Bed shaping has been introduced as a means to manage salt accumulation above the drip tape. This method involves forming the beds to a peak and preirrigating to move salts toward the peak. The tops of the bed are then removed into the furrow leaving behind soil of low ECe. Direct seeding of some largeseeded crops can then occur without inhibition of emergence. Small seeded crops that require precision planters cannot usually be direct-seeded into moist beds. Bed shaping procedures may prove effective in some
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
The Potential Contribution of Subsurface Drip Irrigation to Water-Saving Agriculture in the Western USA
crop rotations by eliminating the need for sprinklers, but the excess water needed to pre-irrigate beds may be less economically feasible, depending on water cost (Roberts et al. 2008).
CONCLUSION To be sustainable, SDI must 1) achieve substantially higher water use efficiency than surface irrigation methods, 2) increase crop yield and quality, 3) be economically viable, 4) contribute in a positive way toward environmental protection, and 5) not lead to development of adverse soil properties (salinity, sodicity). Many authors have shown that SDI is superior to most other irrigation methods with respect to points 1, 2, and 4. However, the economic viability of SDI depends on several factors under the control of the grower, including SDI system life, crop produced, water savings, and application cost savings. However, there are other factors, not under the grower’s control, including water cost and crop prices, that profoundly affect the economics of SDI. In arid regions, there is usually insufficient rainfall to leach salts from the zone of soil above the SDI tape. In this zone, detrimental salinity may result. In most cases, use of SDI in arid regions requires the periodic use of sprinklers to leach salts. The contributions of SDI to increasing yield, quality, and water use efficiency have been demonstrated. The two major barriers to SDI sustainability in arid regions are economics, including the high cost of installation and low cost of water; and salt accumulation, which demands periodic leaching, specialized tillage methods, or transplanting.
Acknowledgements The help from colleagues and students, past and present, is gratefully acknowledged. In particular, I acknowledge Tom Doerge, Scott White, Ron Godin, Trent Roberts, Ed Martin, Jim Walworth, and Russ Tronstad. This paper is funded by 948 Program of Ministry of Agriculture, China (2006-G52).
References Bar-Yosef B. 1999. Advances in fertigation. Advances in Agronomy, 65, 2-77.
853
Camp C R. 1998. Subsurface drip irrigation: A review. Trans ASAE, 41, 1353-1367. Dasberg S, Or D. 1999. Applied Agriculture: Drip Irrigation. Springer-Verlag, New York, NY. Enriquez C, Alum A, Suarez-Rey E, Choi C Y, Gerba C P. 2003. Survival of bacteriophages MS-2 and PRD-1 in turfgrass irrigated by subsurface drip irrigation. Journal of Environmental Engineering, 129, 852-857. Hanson B R, May D. 2003. Drip irrigation increases tomato yields in salt-affected soil of San Joaquin Valley. California Agriculture, 57, 132-137. Hillel D. 2000. Salinity Management for Sustainable Agriculture: Integrating Science, Environment and Economics. The World Bank. Washington D.C. Lamm F R. 2002. Advantages and disadvantages of subsurface drip irrigation. In: Proceedings of International Meeting on Advances in Drip/Micro Irrigation. Puerto de La Cruz, Tenerife, Canary Islands, Dec. 2-5, 2002. Instituto Canario de Investigaciones Agrarias, Canary Islands. p. 13. Oron G, De Malach Y, Gillerman L, David I, Rao V P. 1999. Improved saline-water use under subsurface drip irrigation. Agricultural Water Management, 39, 19-33. Oron G, DeMalach Y, Gillerman L, David I, Lurie S. 2002. Effect of water salinity and irrigation technology on yield and quality of pears. Biosystems Engineering, 81, 237-247. Phene C J. 1995. The sustainability and potential of subsurface drip irrigation. In: Freddie Lamm, ed, Microirrigation for a Changing World. American Society of Agricultural Engineers, St. Joseph, MI. pp. 359-367. Pier J W, Doerge T A. 1995. Concurrent evaluation of agronomic, economic, and environmental aspects of trickle irrigated watermelon production. Journal of Environmental Quality, 24, 79-86. Roberts T L, White S A, Warrick A W, Thompson T L. 2008. Tape depth and germination method influence patterns of salt accumulation with subsurface drip irrigation. Agricultural Water Management, doi:10.1016/j.agwat.2008.01.003 Smith M. 1995. Irrigation scheduling: From theory to practice. Proceedings of the ICID/FAO Workshop on Irrigation Scheduling Rome, Italy, 12-13 September. Thompson T L, Doerge T A. 1996. Nitrogen and water interactions in subsurface tricle-irrigated leaf lettuce. II. Agronomic, economic, and environmental outcomes. Soil Science Society of America Journal, 60, 168-173. Thompson T L, Doerge T A, Godin R E. 2000a. Nitrogen and water interactions in subsurface drip-irrigated cauliflower. I. Plant response. Soil Science Society of America Journal, 64, 406-411. Thompson T L, Doerge T A, Godin R E. 2000b. Nitrogen and water interactions in subsurface drip-irrigated cauliflower.
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.
854
T L Thompson et al.
II. Agronomic, economic, and environmental outcomes. Soil Science Society of America Journal, 64, 412-418.
186-192. Thompson T L, Doerge T A, Godin R E. 2002b. Subsurface drip
Thompson T L, Doerge T A, Godin R E. 2002a. Subsurface drip irrigation and fertigation of broccoli: I. Yield, quality, and
irrigation and fertigation of broccoli: II. Agronomic, economic, and environmental outcomes. Soil Science Society of America
nitrogen uptake. Soil Science Society of America Journal, 66,
Journal, 66, 178-185. (Edited by ZHAO Qi)
© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.