Economic and agronomic strategies to achieve sustainable irrigation

The achievement of sustainable irrigation in arid regions requires greater attention to waterlogging, salinization, and degradation of ground and surface waters, which are among the problems that continue to threaten productivity and degrade environmental quality. We consider sustainability to be achieved when irrigation and drainage are conducted on-farm, and within irrigation districts, in a manner that does not degrade the quality of land, water, and other natural resources, either on-farm or throughout an irrigated region. Sustainability may also be described as maintaining the productive resources required for irrigation, so that future generations may have the same opportunity to use those resources as we do. Given the increasing importance of irrigated land for food production, the time has come when it is vital to intercept, reuse, and isolate drainage waters within the regions in which they are generated. Adoption of this strategy can be enhanced by policies that require farmers, and irrigation districts, to consider the off-farm impacts of irrigation and drainage. Such policies include linking water rights with salt rights to require the monitoring and management of both irrigation water and the salt loads in drainage waters. We review the knowledge gained since the early 1970s regarding the economic and agronomic aspects of irrigation and drainage, with a focus on drainage water reduction and sequential reuse of drainage water on salt-tolerant crops. Economic incentives that motivate farm-level and district-level improvements in water management are also reviewed. We conclude that adequate knowledge exists for implementing strategies that focus on water use and salt disposal within irrigated regions, and we recommend policies that will motivate improvements in productivity and enhance the likelihood of achieving sustainability.     

Economic evaluation of salinity,drainage and non-uniformity of infiltrated irrigation water

Salinity, drainage and non-uniformity of irrigation water are important components in determining optimal water application and related profitability. A crop-water production function assuming steady state conditions is incorporated in a long-run economic model to investigate the combined effects of salinity, irrigation uniformity and different drainage requirements at the field scale for the specific crop.The analysis was conducted for corn and cotton as sensitive and tolerant crops to salinity, respectively. Optimum applied water and associated profits, yield and drainage volumes were computed for each crop. The computations were done for the condition that no drainage system was required and also where a drainage system was required and the drainage water was disposed of to either a free off-farm facility or to an on-farm evaporation pond constructed on productive or non-productive land.The main findings are that type of drainage disposal system affects the optimal values of applied water, profits, yield and drainage volumes, except for uniform water applications and non-saline irrigation water. Another finding is that in the long run, under saline conditions and/or different drainage disposal systems, a sensitive crop such as corn is not profitable and goes out of production. In general the profit levels associated with the various drainage options are in the order of no drainage requirement ? free off-farm facility > on-farm evaporation pond on non-productive land > on-farm evaporation pond on productive land. Uniformity of irrigation water affects values of the analyzed variables and the effects are greatest for the cases of on-farm evaporation ponds. Pumping cost effects are quite small, but water price effects are more significant. Breeding the crops for increased salinity tolerance has little effect when irrigating with water of low salinity and/or low irrigation uniformity.     

太阳能暗管排水对银北灌区油葵土壤环境及产量影响

针对土壤盐渍化严重影响了宁夏银北灌区土壤环境和作物产量的问题,通过太阳能暗管排水区和非暗管排水区对比试验方法,着重研究了2017和2018两年太阳能暗管长时间持续排水对土壤环境和油葵产量的影响。结果表明:太阳能暗管排水可以有效改善土壤环境,使两年的地下水平均埋深分别增加4.5%和6.4%,地下水平均矿化度分别降低7.9%和9.0%,两年土壤平均脱盐率分别为4.7%和8.2%,对表层土壤的脱盐效果最为明显。同时提高了油葵产量和水分生产效率,两年油葵产量分别提高13.8%和21.6%,灌溉水分生产效率分别增加13.3%和21.8%,作物水分生产效率分别增加16.4%和22.9%。综合试验结果和经济成本考虑,油葵生育期灌水2次、播前灌水1次、冬灌1次,生育期5-9月持续排水,这是适宜惠农当地太阳能暗管排水条件下油葵的灌排制度。     

Drainage disposal and reuse simulation in canal irrigated areas in Haryana

Nearly 60 per cent of the geographical area of Haryana state in Indian Union is underlain by saline ground water. The intra-basin transfer of surface water in the early sixties for irrigation has disturbed the hydrodynamic equilibrium resulting in waterlogging and salinization in large parts of the state. The existing inland drainage basin conditions did not permit the disposal of drainage effluent. The reuse system was therefore, integrated with the drainage system. A model RESBAL was coupled with the calibrated and validated on-farm water management model FAIDS and run for eight years to optimally design a series of connected reservoirs for the disposal of drainage effluent from an area provided with a subsurface drainage system. The possibility of the reuse of the disposed water for irrigation, aqua culture and salt harvesting was also studied comprehensively in order to maintain proper salt balance in the root zone.     

Increasing water-use efficiency in rice production: farm-level perspectives

This paper describes the components of water use in rice-based production systems and identifies water used during land preparation, and seepage and percolation during crop growth as important sources of water `loss' from the system. Strategies for increasing farm-level water-use efficiency are discussed, including the problems of up-scaling from on-farm to system-level water savings.     

Agro-hydrological evaluation of on-farm rainwater storage systems for supplemental irrigation in Laikipia district,Kenya

Semi-arid agro-ecosystems are characterized by erratic rainfall and high evaporation rates leading to unreliable agricultural production. Total seasonal rainfall may be enough to sustain crop production, but its distribution and occurrence of intra-season dry spells (ISDS) and off-season dry spells (ODS) affect crop production. Rainwater harvesting (RWH) and management, especially on-farm storage ponds for supplemental irrigation offers an opportunity to mitigate the recurrent dry spells. Farm ponds are small runoff storage structures of capacities ranging from 30 to 100 m³ used mainly for supplemental irrigation of kitchen gardens, and sometimes for domestic and livestock water supply. The main objective of the study was to evaluate the hydrological and economic performance of farm ponds with the view of assessing their contributions to water and food security in semi-arid agro-systems of Kenya. Agro-hydrological evaluation of on-farm runoff storage systems entailed field survey, monitoring of water losses, analysis of rainy seasons and dry spell occurrence, soil moisture and water balance, estimation of supplemental irrigation requirement (SIR) and farm-level cost-benefit analysis of cabbage production using low-head drip irrigation system. Significant water losses through seepage and evaporation, which accounted on average for 30–50% of the stored runoff, is one of the factors that affect the adoption and up-scaling of on-farm water storage systems. Frequency analysis of rainfall revealed that there is 80% probability of occurrence of dry spells exceeding 10 and 12 days during the long rains and short rains, respectively. The occurrence of off-season (after rainfall cessation) dry spells was more pronounced than intra-seasonal (within the rainy season) dry spells. The length of intra-seasonal (10–15 days) was less than off-season dry spells (20–30 days). The occurrence of off-season dry spells coincides with the critical crop growth stage, in particular flowering and yield formation stages. A 50 m³ farm pond with a drip system irrigation system was found adequate to meet supplemental irrigation requirement for a kitchen garden of 300–600 m² planted with a 90 days growing period cabbages. The cost-benefit analysis showed that farm ponds are feasible solutions to persistent crop failures in semi-arid areas which dominant most countries in Sub-Saharan Africa (SSA).     

Minimisation or remediation: A cost benefit comparison of two approaches for managing irrigation-induced deep percolation

We compare the net present costs of two approaches for managing irrigation-induced deep percolation under border-check irrigated pasture: (1) conversion from border-check irrigation to sprinkler irrigation to minimise deep percolation and (2) installation of a subsurface drainage system to extract excess deep percolation under the existing border-check system. Results for a dairy farm in northern Victoria, Australia, show that conversion to sprinkler irrigation is the more cost-effective approach. The net present cost of the second approach varies across an irrigation landscape, depending on the most suitable subsurface drainage and disposal system that can be used for a particular location. Where an aquifer is high yielding and of low salinity and thus drainage water is suitable for reuse on farm, tubewell drainage and farm reuse of drainage water provides a viable alternative to conversion from border-check irrigation to sprinkler irrigation. Where tubewell drainage or farm reuse is not feasible, sprinkler irrigation is more cost-effective than border-check irrigation with subsurface drainage.     

Modeling a farm population to estimate on-farm compliance costs and environmental effects of a grassland extensification scheme at the regional scale

We used a farm-level modeling approach to estimate on-farm compliance costs and environmental effects of a grassland extensification scheme in the district of Ostprignitz-Ruppin, Germany. The behavior of the regional farm population (n = 585) consisting of different farm types with different production orientations and grassland types was modeled under the presence and absence of the grassland extensification scheme using the bio-economic model MODAM. Farms were based on available accountancy data and surveyed production data, while information on farm location within the district was derived from a spatial allocation procedure. The reduction in total gross margin per unit area was used to measure on-farm compliance costs. A dimensionless environmental index was used to assess the suitability of the scheme to reduce the risk of nitrate-leaching.Calculated on-farm compliance costs and environmental effects were heterogeneous in space and farm types as a result of different agricultural production and site characteristics. On-farm costs ranged from zero up to almost 1500 Euro/ha. Such high costs occurred only in a very small part of the regional area, whereas the majority of the grassland had low on-farm costs below 50 Euro/ha. Environmental effects were moderate and greater on high-yield than on low-yield grassland. The low effectiveness combined with low on-farm costs in large parts of the region indicates that the scheme is not well targeted. The soft scheme design results from an attempt to achieve environmental and rural development objectives with only one scheme. Improving the efficiency of the scheme would require designing separate instruments for the two distinct objectives. This is in line with the Tinbergen rule, which states that consistent economic policy requires that the number of instruments equals the number of targets.     

An economic analysis of irrigation systems

Summary An array of irrigation systems are available which can be broadly classified as being gravity flow or pressurized. Pressurized irrigation systems provide better control on the amount of applied water and, in most cases, better irrigation uniformity than gravity flow systems. They also have a higher initial capital cost than gravity flow systems and an analysis is required to determine whether the improved performance of pressurized systems justifies the additional costs. An economic analysis was done on several irrigation systems which included consideration of farm management costs associated with a given irrigation system, shifts in crop yield and drainage volumes associated with the optimal management of each irrigation system, and costs associated with disposal of drainage waters. Cotton was selected as the crop for analysis. Irrigation uniformity is a significant determinant to the results. Although irrigation uniformities can be highly variable based on design, maintenance and management, a typical uniformity for each irrigation system was selected. For the conditions of the analysis, gravity flow systems were calculated to be more profitable than pressurized systems if there was no constraint on the amount of drainage water generated or cost for its disposal. Imposition of costs for drainage water disposal induced a shift whereby pressurized systems became more profitable than gravity flow systems.     

黄河下游灌区农田排水再利用效应模拟评价

在田间试验观测基础上,采用SWAP模型分析黄河下游簸箕李引黄灌区农田排水再利用下的土壤盐分季节性变化以及地下水位对土壤盐分剖面分布的影响,模拟农田排水补灌对作物产量的效应。研究结果表明,咸排水补灌引起的土壤盐分积聚主要在冬小麦生长期,夏玉米生长期内并不明显,有效地控制地下水位有助于减少土壤盐分累积量,维系作物根区的盐分平衡。利用含盐量为4mg/cm3以下的农田排水在冬小麦生长后期水分亏缺阶段进行补灌,可在基本不影响随后夏玉米产量的基础上,不同程度地改善冬小麦产量。对缺水严重的黄河下游引黄灌区,农田排水再利用是缓解水资源供需矛盾、改善作物产量的一种有效水管理措施。     

Realizing the Potential of Integrated Irrigation and Drainage Water Management for Meeting Crop Water Requirements in Semi-Arid and Arid Areas

In situ use of ground water by plants is one optionbeing considered to reduce discharge of subsurfacedrainage water from irrigated agriculture. Laboratory, lysimeter, and field studies havedemonstrated that crops can use significant quantitiesof water from shallow ground water. However, moststudies lack the data needed to include the crop wateruse into an integrated irrigation and drainage watermanagement system. This paper describes previousstudies which demonstrated the potential use of groundwater to support plant growth and the associatedlimitations. Included are results from three fieldstudies which demonstrated some of the managementtechniques needed to develop an integrated system. The field studies demonstrated that approximately 40to 45% of the water requirement for cotton can bederived from shallow saline ground water. Thatregulation of the outflow will result in increasinguse. Implementation of integrated management ofirrigation and subsurface drainage systems is a viableand sustainable alternative in the management ofsubsurface drainage water from arid and semi-aridareas only if soil salinity can be managed and if thesystem is profitable.     

On-farm labour allocation and irrigation water use: case studies among smallholder systems in arid regions

On-farm measurements and observations of water flow, water costs and irrigation labour inputs at the individual parcel level were made in case studies of smallholder irrigation systems in sub-Saharan Africa and south-eastern Arabia. The systems, in which the water source supplied either single or multiple users, were analysed to address the fundamental issues of labour allocation for on-farm water management as this has important consequences for the success of such systems. Results show that the costs associated with accessing water influenced labour input, because when they were low the farmers tended to increase the irrigation rate and reduce the amount of time they spent distributing the water within their parcels. Conversely when water costs were high, lower flow rates and more time spent in water distribution were observed, and this resulted in more uniform irrigation and higher irrigation efficiency. Also, opportunities and demands for farmers to use their labour for activities other than irrigation can lead them to modify operational or physical aspects of the system so that they can reduce the time they spend distributing water within the parcels, particularly when the water is relatively cheap. Awareness and better understanding of how farmers may allocate their labour for water management will lead to more effective planning, design and management of smallholder irrigation systems.     

Water and nutrient use efficiency of a low-cost hydroponic greenhouse for a cucumber crop: An Australian case study

The Australian greenhouse industry is primarily dominated by low-cost hydroponic greenhouses for delivery of water and nutrients to plants to grow a variety of vegetable crops including cucumber and tomato. The nutrient rich drainage water from these greenhouses is generally released into the local environment causing pollution concerns. This study was initiated to investigate the opportunities in recycling drainage water to increase water and nutrient-use efficiency of hydroponic greenhouses and reduce the environmental impact of the drainage water discharge. Results indicated that a total of 4.15 ML/ha of irrigation water was applied during the 13 weeks crop growing period of which 2.56 ML/ha was drained off and 1.59 ML/ha was used to meet the crop evapotranspiration demand. The study showed that the recycling of the drainage water resulted in a 33% reduction in potable water used for irrigation in cucumber production. The drainage water contained 59% applied N, 25% applied P and 55% applied K and illustrated the potential for nutrient recovery and production cost savings through the reuse of drainage water. This case study demonstrates that some relatively simple changes in irrigation practices within greenhouse systems to recycle drainage water can considerably improve sustainability of low-cost hydroponic greenhouses and help minimise the environmental footprint of the greenhouse industry.     

The rehabilitation of an irrigation system along the Yellow River

The People's Victory Irrigation System which diverts water from the Yellow River of China covers a total irrigable area of 59 000 ha. The system encountered some serious problems in the first decade of its operation — salinity and waterlogging of irrigated land, siltation of irrigation and drainage channels, as well as a low efficiency of water use. This paper describes a series of structural and functional measures which have been adopted in the past 24 years for the rehabilitation of the system, including: improvement of the existing drainage system and construction of new drainage system on agricultural land, conjunctive use of surface and groundwater supplies, a comprehensive programme to reduce the levels of siltation as well as the implementation of improved water management practices. A model for the optimal operation of the system by using system analysis theory as an aid in reducing the operation and maintenance (O & M) costs has been developed in recent years. The results are that the soil salinity has been controlled and the agricultural production has increased whilst the efficiency of water use has improved and the siltation levels reduced. Experience gained on this system has been successfully used in developing and managing other irrigation projects along the lower reaches of the Yellow River. The proposed procedure of solving the said optimal model has also embodied some benefits from reducing O & M costs in operation.     

Economic incentives reduce irrigation deliveries and drain water volume

This paper describes the application of an economic incentive program to achieve water quality objectives by motivating improvements in farm-level water management practices. The program includes farm-specific water allotments, tiered water pricing, and low-interest loans for purchasing irrigation equipment. The implementation of this program in a California water district has resulted in significant reductions in irrigation deliveries and drain water volume. Since the program was implemented, average irrigation depths have declined by 25% on cotton fields, 9% on tomatoes, 10% on cantaloupes, 30% on seed alfalfa, and 29% on grain fields. The average volume of drain water collected each year in subsurface drainage systems has declined from 4.8 million m³ during 1986 through 1989 to 2.6 million m³ during 1990 through 1993. These results confirm that economic incentives can be effective in generating improvements in water quality.     

Irrigation water distribution and long-term effects on crop and environment

The response of three water delivery schedules, representing various levels of flexibility, on crop production, water saving, soil salinization, drainage volumes and watertable behavior was examined. A physical-based transient soil water and solute transfer model, Soil–Water–Atmosphere–Plant (SWAP), was used as a tool. The evaluations were made for un-restricted and restricted water supply situations considering three different watertable conditions prevailing in the fourth drainage project (FDP) of the Punjab, Pakistan. From the simulation results it is apparent that on average the effect of irrigation schedule flexibility on crop yields is not very significant. However, compared to a fixed schedule provided un-restricted canal water supplies are available, the productivity of irrigation water supply (Y_act/I_rr), is up to 30% higher for the on-demand schedule. The on-demand schedule capable of complying with the temporal variations in climate is also more effective in water saving, reducing drainage volumes and controlling rising watertables if farmers follow guidelines and do not over-irrigate. In the present water deficient environment of the Indus basin, the benefits of the on-demand schedule and a fixed schedule are comparable. In the absence of sufficient canal water supplies, infrastructure and a well-designed and effective monitoring and communication system, moving towards the on-demand system will be un-productive. For the long-term sustainability of the irrigation system, improvements in the performance of the present water allocations and on-farm water management practices seems to be more necessary.     

Relationship between salinity and efficient water use

The relationship between salinity and water use efficiency is highly dependent upon which definition of water use efficiency is used. The two common definitions, yield per unit evapotranspiration and yield per unit applied water, both have significant deficiencies and can lead to erroneous conclusions. Thus, the analysis of efficient use of saline waters invokes a broader analysis than merely computing water use efficiency. An array of models is available to simulate the effects of various irrigation management strategies with saline waters. Based on results computed from these models, which consider the osmotic and matric potential effects on plant growth, strategies can be developed to effectively use saline waters in crop production. The cyclic strategy of using waters of different salinities can effectively be used in maintaining crop rotations which include both salt-sensitive and salt-tolerant crops. The major deficiency of the models is that they do not account for the effects of water quality on soil physical conditions with consequent effects on crop production. Indeed, the most limiting factor in use of saline waters on soils may be deterioration of soil physical conditions. The deterioration of soil physical conditions does not result from using the high-salinity waters per se but from subsequent rainfall or low salinity waters. Thus far the emphasis on using saline waters on crop production has centered on yields and less attention has been given to the long-term consequences on soil physical conditions. This factor requires further research and should be a focus of attention in future experiments. Relatively high saline water tables can be maintained without drainage if a non-saline source of water is available, and irrigation amounts can be controlled. This strategy might invoke the necessity for shifting irrigation systems from surface to pressurized systems. Eventually, some salt must be removed from the system. It is probably more efficient to allow it to become very concentrated and remove small volumes to be disposed of in some manner rather than apply it to productive land.     

The effect of water supply uncertainty on farmers’ choice of crop portfolio

This paper analyzes the effect of water supply uncertainty on farmers’ choice of crop portfolio. The paper presents an innovative model to estimate the value of uncertainty of water supply, and then tests the model using data from Israel. The modeling results provide support to the hypothesis that uncertainty induces farmers to prefer crops whose growth requires less agricultural capital accumulation, despite their lower profitability (agricultural capital referring to trees and other plants which take a significant period of time to mature). This is due to the risk that in a given year water supply will fall below a certain minimal level, thereby causing loss of all accumulated capital. The paper also examines a government intervention policy for mitigating uncertainty: use of reclaimed wastewater in crop irrigation as a supplement for freshwater supply. The costs associated with constructing the required wastewater reclamation and supply facilities are compared to the benefits of additional farm income earned through a more certain on-farm water supply. It is shown that under certain conditions implementation of this policy is indeed economically worthwhile.     

Agricultural and environmental changes after irrigation management transfer in the Develi Basin,Turkey

Develi Basin is a semi-arid basin in central Turkey where water sustains both irrigated agriculture and an internationally important wetland, the Sultan Marshes. Agricultural and environmental changes in the Develi Basin have occurred since irrigation management was transferred in 1994 from a state authority (DSI) to irrigation associations (Kovalı and Ağcaaşar IAs). In this paper we evaluate the practices of the IAs using extensive data from interviews with farmers and IA officials, as well as data from reports prepared by DSI and the IAs, using comparisons with case studies reported in the scientific literature. Irrigated areas and surface water use in the Develi Basin showed significant fluctuations from 1995 to 2003. The area allocated to high water-consuming plants increased. Maintenance activities became dependent on fee collection rates. Quality of the irrigation water did not changed significantly. Ground-water levels, flow rates from springs, and water levels in the Sultan Marshes all dropped. Overall analyses indicate that the water requirements of the Sultan Marshes have not been met, while water use for irrigation has been effective but not efficient. To reconcile agricultural and wetland water requirements, a basin-wide approach in water planning is recommended. Amounts of water to be allocated to the IAs and wetlands need to be clearly defined. DSI has to monitor canal maintenance by the IAs more closely, and IAs need to be given more responsibilities for future rehabilitation of the canals. Realistic water pricing, increased reliability of irrigation scheduling, higher on-farm irrigation efficiency, and in the long-term, modernization of the irrigation system need to be considered.     

An economic perspective on the potential gains from improvements in irrigation water management

In recent years, several researchers have introduced new terms describing irrigation efficiency to enhance the information available when evaluating water policy alternatives. Some of the definitions expand the physical boundary considered when evaluating water use, while others account for the changes in water quality that occur as drainage water is reused in an irrigated area. While the concepts of basin, global, and effective efficiency have enhanced our understanding of water use in agriculture, public officials may derive incorrect policy implications when reviewing empirical estimates of those measures, particularly if information describing the economic impacts of water use and allocation decisions is not available. For example, some authors suggest that when estimates of basin-wide efficiency approach 100%, there is little opportunity to save water by improving water management and achieving higher levels of classical, farm-level efficiencies in upstream portions of an irrigated region. However, there may be significant opportunities to increase the net values generated with limited water resources by improving the distribution of water among farmers and reducing the negative, off-farm effects of irrigation and drainage activities. Economic analysis is helpful in identifying those opportunities and in designing policies that encourage farmers and water agency personnel to improve water management practices in ways that enhance social net benefits.