Economic analysis of sprinkler and siphon tube irrigation systems, with implications for public policies

Agricultural water management ELSEVIER

Agricultural Water Management 32 (I 997) 259-273

Economic analysis of sprinkler and siphon tube irrigation systems, with implications for public policies Dennis Wichelns

a,*, Laurie Houston b, David Cone ’

a Department oj’Resource Economics, Unioersity oj’Rho& Island. Kingston, RI, USA b Department oj’Forest Resources, Oregon State University, Coruullis, OR, USA ’ Brouduiew Water District, Firebaugh, CA, USA

Accepted 4 July 1996

Abstract This paper examines the economic rationale for using sprinklers for initial irrigation events, while using siphon tubes for remaining irrigations on the same crop, using cost data and descriptive information from an irrigation district on the west side of California’s San Joaquin Valley. Many farmers in the region began using sprinklers for pre-irrigating cotton fields and for early irrigations on tomatoes, in response to reductions in water supply and rising water prices, during 1990 through 1994. However, most farmers continued using siphon tubes for summer irrigations on both crops. The fixed and variable costs of using sprinklers and siphon tubes are examined, and the potential improvements in crop yield that may be achieved when using sprinklers, to determine the economic rationale for these decisions. Results suggest that agencies wishing to encourage improvements in water management practices should implement policies that reduce the initial cost of sprinkler systems, while permitting farmers to choose the best combination of irrigation methods. 0 1997 Elsevier Science B.V. Keywords:

Irrigation systems; Economic analysis; Economic incentives; Water policy

1. Introduction

Public agencies in California and other western states have recommended that farmers improve their water management practices to increase the values generated with limited water supplies, and to reduce subsurface drain water in regions where salts,

* Corresponding author. 0378-3774/97/$17.00

0 1997 Elsevier Science B.V. All rights reserved.

PII SO378-3774(96)01271-

1

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selenium, or boron degrade the quality of receiving waters (US Bureau of Reclamation, 1990; Westcot, 1988). Potential improvements include better management of surface irrigation methods to reduce surface runoff and deep percolation, and the use of sprinklers to improve distribution uniformity. Sprinklers are more costly to purchase and operate than surface systems, but farmers may achieve water management goals more effectively with sprinklers, provided the systems are operated and maintained correctly (Hanson, 1987). For example, sprinklers utilize water more effectively than surface methods, when leaching salts through the soil profile (Bresler, 19811, and they move salts downward, rather than into the seed bed of row crops (Hoffman et al., 1990; Kruse et al., 1990). Sprinklers are also more appropriate for germinating some field crops such as tomatoes, because they can moisten the surface soil with minimal water deliveries (University of California, 1990). The improved leaching and the more uniform germination that are achieved with sprinklers may enhance crop yields. Improvements in distribution uniformity can reduce the total volume of water required during irrigation events, resulting in lower water costs, and enabling farmers to irrigate a larger area with limited water supplies. Farmers receive the benefits of any reductions in total water costs and improvements in crop yield that occur when irrigation water is delivered more uniformly with sprinklers. However, the benefits of reducing deep percolation and subsurface drain water, which include improvements in the quality of receiving waters, accrue largely to the public, rather than to individual farmers (Dinar, 1993; National Research Council, 1989). Hence, the number of farmers using sprinklers is usually less than the number desired by public officials seeking water conservation and drain water reduction goals. Public programs to encourage additional use of sprinklers include low-interest loans to assist farmers with the purchase of new sprinkler systems and leasing programs that enable farmers to use sprinklers for selected irrigation events, without purchasing new systems. In recent years, many farmers in California’s San Joaquin Valley have begun using sprinklers for pre-irrigation of cotton and melon fields and for early irrigations on tomatoes. They have also improved their management of surface methods during summer irrigations on most crops (Wichelns and Cone, 1992a). These actions have diminished the relative advantage of sprinklers in reducing water deliveries and drain water volume during summer irrigations. The irrigation strategies revealed by farmers represent actual, cost-effective responses to reductions in water supplies and rising water prices. Information describing the farmlevel economic rationale for implementing these improvements can guide water resource agencies in selecting policies that promote more rapid adoption of irrigation methods that generate public benefits. This paper examines the economic rationale for using sprinklers for initial irrigation events, while using surface methods for remaining irrigations. The goal is to determine the appropriate public policies for motivating farmers to increase their use of sprinklers, given the improvements that farmers have already achieved when using surface methods. In particular, policies are described that encourage farmers to deliver water efficiently, using either sprinklers or surface methods. Empirical estimates of irrigation costs and average water deliveries for cotton and tomatoes in a typical irrigation district in central California are also presented.

D. Wichelns et d/Agricultural

2. Changes

in irrigation

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261

methods

The primary source of irrigation water for farmers on the west side of California’s San Joaquin Valley is the federal Central Valley Project that delivers surface water collected in Lake Shasta through the Delta formed by the Sacramento and San Joaquin Rivers to delivery canals that serve more than 250000 ha of farmland (Fig. 1). Water supplies were reduced significantly during 1990 through 1994, due to persistent drought conditions and environmental policies that limited the volume of water diverted from the Delta. These reductions in water supply encouraged many farmers to replace surface irrigation methods with sprinklers for selected irrigation events. Farmers using sprinklers to pre-irrigate cotton fields and to germinate tomatoes used less water, on average, than farmers using surface methods (Wichelns and Cone, 1992a). However, most farmers continued to use surface methods for summer irrigations of cotton and tomatoes, even though many farmers had purchased sprinkler systems. Farmers using surface methods during the summer improved their management practices and achieved average water deliveries similar to those achieved by farmers using sprinklers. These observations suggest that during pre-irrigation of cotton, and during early irrigations of tomatoes, the variable cost of using sprinklers may be less than the variable cost of using surface methods. If this is not the case, then farmers must perceive that the soil enhancement or yield increasing benefits of sprinklers and the value of water saved during those events offset the higher variable costs. The value of water saved is enhanced when the supply of water is limited, relative to available land, because additional hectares can be planted and irrigated. The evidence also suggests that during summer irrigations of cotton and tomatoes, the variable cost of using sprinklers must exceed the variable cost of using surface methods, even after accounting for any water savings, soil enhancement, or yield increasing benefits that are generated by using sprinklers during those irrigations. It is possible to irrigate cotton with sprinklers, throughout the summer, and farmers will choose to do this if the variable cost is less than that of using surface methods. The cost of using

California

San

Joaquin Valley

Broadview Water District

Fig.

I Location of Broadview Water District.

D. Wicheins et ul./Agkultural

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Table 1 Water supply, water prices, and irrigation

Water Management 32 (1997) 259-273

methods in the Broadview

Water District,

1989 through

1994

crop year

Proportion of contractual surface water supply (%)

Price of water delivered to farm mmouts ($ per 1000 m3)

Proportion of cotton fields pre-irrigated with sprinklers (%)

Proportion of cotton fields irrigated with sprinklers in summer (%)

Proportion of tomato fields germinated with sprinklers (o/o)

1989 1990 1991 1992 1993 1994

100 50 25 25 50 35

17.17 23.92 35.89 36.63 26.07 35.05

0.0 0.0 26.7 52.6 43.8 44.4

0.0 0.0 26.7 14.3 18.4 13.9

0.0 28.6 100.0 100.0 100.0 92.9

sprinklers on tomatoes in summer can be quite high, because placing water directly on the plants and fruit promotes fruit molds, late blight, and early blight (University of California, 1990). The empirical information analyzed in this study was collected in the 3642 ha Broadview Water District, located near Fresno, CA, on the west side of the San Joaquin Valley (Fig. 1). Broadview has a water supply contract with the US Bureau of Reclamation for annual delivery of 33.3 X lo6 m3 of surface water. Broadview does not have a viable source of groundwater and the average annual precipitation in the district is only 203 mm. The district’s water supply was reduced by 50% in 1990, and by 75% in 1991 and 1992, due to persistent drought conditions in California (Table 1). Supply was increased to 50% of the contractual volume in 1993, when the rainfall received in northern California was sufficient to replenish surface water reservoirs. Broadview received only 35% of its contractual supply in 1994, when rainfall was less than normal, and the volume of water diverted from the Sacramento/San Joaquin River Delta was reduced to protect water quality and endangered species. Clearly, Broadview farmers have had significant economic incentive to improve water management practices in recent years. Data describing the cost of purchasing and operating sprinklers and surface systems were collected during interviews with Broadview farmers. They described their current water management practices and the labor requirements for irrigating cotton and tomatoes. Investment costs were obtained from actual invoices for the purchase of sprinkler and gated pipe systems by Broadview farmers during 1992 and 1993. Further details of the data collection procedure are described in Wichelns et al. (1996). The unit price of water delivered to farm turnouts in Broadview increases when the total volume supplied by the Bureau of Reclamation is reduced, because the Bureau’s total cost of operating and maintaining the delivery system must be recovered through the sale of less water. The price of water rose from $17.17 per 1000 m3 in 1989, to $23.92 per 1000 m3 in 1990, when the supply was reduced by 50% (Table 1). The price rose to $35.89 per 1000 m3 in 1991 and to $36.63 per 1000 m3 in 1992, when supply was reduced by 75%. The price declined to $26.07 per 1000 m3 in 1993, when supply

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was increased to 50% of the contractual volume. In 1994, the price rose to $35.05 per 1000 m3, when supply was reduced to 35% of the contractual volume. Detailed data describing the irrigation method used on each field in the district were collected for 1989 through 1994. These data describe a significant shift from surface methods to sprinklers, particularly during pre-irrigations of cotton and early irrigations of tomatoes. Prior to 1991, most farmers in Broadview used siphon tubes with earthen head ditches, or gated pipe, for pre-irrigation of cotton fields, and for all summer irrigations on cotton and tomatoes. In 1989, for example, 29 of 32 cotton fields in Broadview were pre-irrigated using siphon tubes, while three fields were pre-irrigated using gated pipe. In 1990, siphon tubes were used to pre-irrigate 29 of 33 cotton fields, and gated pipe was used on the remaining four fields. This pattern began to change in 199 1, when eight of 30 cotton fields (26.7%) were pre-irrigated using sprinklers, and 20 fields were pre-irrigated with siphon tubes. The proportion of cotton fields pre-irrigated with sprinklers has increased to an average of 46.9% during 1992 through 1994 (Table 1). Sprinklers were first used for summer irrigations of cotton in Broadview in 1991, when farmers used sprinklers for at least one summer event on eight of 30 cotton fields (26.7%). In the summer of 1992, farmers used sprinklers for at least one event on only three of 21 cotton fields (14.3%), even though the district received only 25% of its contractual water supply. Sprinklers have been used on fewer than 20% of all cotton fields during the summers of 1992 through 1994 (Table 1). These data suggest that many farmers who use sprinklers for pre-irrigating cotton prefer surface methods for summer irrigations. Farmers irrigating tomatoes in Broadview have developed a similar preference for using sprinklers for selected irrigation events. Broadview farmers usually irrigate tomatoes very soon after planting, to germinate the seeds. This germination event is usually followed very quickly by a pre-emergent irrigation that provides enough moisture to prevent the clay loam soils from sealing and inhibiting the emergence of the young tomato plants. The goal during each event is to deliver just enough water to maintain soil moisture. Some farmers deliver a single irrigation at this time, rather than two events, if spring rains are sufficient to achieve the goal of either the germination or the pre-emergent irrigation. Prior to 1990, all farmers in Broadview used surface methods to deliver the germination and pre-emergent irrigations on tomatoes. During 1991 through 1993, all farmers used sprinklers for these events, and all fields but one were irrigated using sprinklers in 1994 (Table 1). Some farmers use sprinklers for one or two additional events on tomato fields, but all farmers switch to surface methods before the fruit begins to ripen, as recommended for control of fruit molds, late blight, and early blight (University of California, 1990). Broadview farmers have improved their irrigation efficiencies on cotton, in recent years, by irrigating more frequently with smaller volumes of water in each irrigation event. The typical cotton irrigation regime has changed from three irrigations in summer, with an average delivery of 200 mm per event, to four irrigations with an average delivery of 110 mm per event (Wichelns and Cone, 1992a). Irrigation efficiencies have increased from an average of 0.69 during 1986 through 1989, to an average

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efficiency of 0.84 during 1990 through 1994. Much of this improvement has been achieved by using sprinklers for pre-irrigations and early summer irrigations, reducing the lengths of run from 800 m to 400 m when using surface methods, and reducing set times from 24 h to 12 h during most irrigation events.

3. Economic

analysis

The fixed and variable costs of sprinklers and siphon tubes are examined for cotton and tomatoes, to determine the farm-level rationale for choosing among these systems. Gated pipe and drip systems are not included in this analysis because they are not used by a large number of Broadview farmers. At present, most farmers are choosing either sprinklers or siphon tubes. The costs of purchasing and maintaining these systems have been estimated using the Broadview information. The amortized capital costs are estimated using a real interest rate of 4% and a useful life of I2 years for siphon tube systems and 10 years for sprinkler systems. An annual maintenance cost equal to 10% of the initial purchase price is added to the amortized capital cost to determine the total annual cost of each system. Wage rates, water prices, and energy costs are those reported in farmer interviews. Most farmers in Broadview use 400 m furrow lengths when irrigating cotton with siphon tubes, and 240 m furrow lengths when irrigating tomatoes. The initial cost of components for a siphon tube system large enough to irrigate a 61 ha field is $2070 ($34 ha- ‘> when using 400 m furrows, and $2588 ($42 ha-‘) when using 240 m furrows. (Table 2). The system includes either 540 plastic siphon tubes (for 400 m furrows) or 675 plastic tubes (for 240 m furrows), and the tarps and wooden stakes that are used to check the flow of water in earthen head ditches. The initial cost of a typical sprinkler

Table 2 Estimated

fixed costs of selected irrigation Initial cost of system components ($ ha- ’)

Siphon tubes ’ 400 m furrows 34 240 m furrows 42 Sprinklers 809 Sprinklers and siphon tubes ’ 400 m furrows 843 240 m furrows 851

methods in the Broadview Total fixed costs a 6 ha- ‘1 182-772 190-780 809 991-1581 999- 1589

Water District Average annual costs b @ha- ‘) 37- I59 39-161 181 2 188340 220-342

a Total fixed costs include the initial cost of system components and the cost of laser leveling. which ranges from $148 ha- ’ on fields requirin g relatively little work, to $738 ha- ’ on fields requiring a large amount of soil to be cut and filled; b average annual costs include the amortized cost of system components and laser leveling, and an annual maintenance cost which is 10% of the initial cost of components and laser leveling. A real interest rate of 4% is used when amortizing the initial system costs. A useful life of 12 years is assumed for siphon tube systems, while a useful life of 10 years is assumed for sprinkler systems; ’ most Broadview farmers use 400 m furrow lengths when irrigating cotton and 240 m furrow lengths when irrigating tomatoes.

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system that includes 1207 m of 25.4 cm mainline pipe, 4828 m of 7.62 cm lateral pipe with risers, a booster pump with diesel engine, and other system parts is $49 341 ($809 ha-’ ). Farmers using both siphon tubes and sprinklers on the same field will invest either $5 1411 ($843 ha- ’> or $5 1929 ($85 1 ha- ’) in system components. Many farmers in the San Joaquin Valley laser level their fields, periodically, to improve the efficiency of surface irrigation systems. The cost of laser leveling a 61 ha field in Broadview, as reported in farmer interviews, ranges from $9000 ($148 ha-’ ) to $45 000 ($738 ha- ’). The higher costs are incurred when larger volumes of soil must be moved within a field to achieve the desired slope and uniformity. Most Broadview farmers use sprinklers only for pre-irrigation of cotton and melon fields, and for the early seasonal irrigations on cotton and tomatoes. These farmers will likely laser level all of their fields, to improve irrigation uniformity whenever siphon tubes are used. The cost of laser leveling is, therefore, included in the fixed cost of irrigation when farmers use siphon tubes alone, or in combination with sprinkler systems. The estimated total fixed cost of irrigation (system components plus laser leveling) ranges from $182 to $772 ha- ’ when farmers use 400 m furrows, and from $190 to $780 ha-’ when farmers use 240 m furrows (Table 2). The fixed cost of irrigation for farmers who use sprinklers for all irrigations on cotton, and who choose not to laser level their fields, includes only the $809 ha-’ for system components (Table 2). The fixed cost of using siphon tubes and sprinklers on the same fields ranges from $991 to $1581 ha-’ when using 400 m furrow lengths, and from $999 to $1589 ha- ’ when using 240 m furrow lengths. As expected, the highest fixed costs of irrigating occur when farmers use both sprinklers and siphon tubes on fields that require a large amount of laser leveling. We also note that the total fixed cost of irrigating with siphon tubes approaches the total fixed cost of irrigating with sprinklers when a large amount of laser leveling is required to prepare a field for surface irrigation. The estimated total fixed costs of siphon tube and sprinkler irrigation systems are amortized over their expected useful life, and a 10% annual maintenance fee is added to determine the average annual cost of using these systems. The average annual cost of using siphon tubes ranges from $37 to $159 ha-’ when using 400 m furrows, and from $39 to $161 ha- ’ when using 240 m furrows (Table 2). The average annual cost of using sprinklers for all irrigations is $181 ha- ’, if laser leveling is not required. The average annual cost of using both siphon tubes and sprinklers will range from $218 to $340 ha-‘, when using 400 m furrows, and from $220 to $342 ha- ‘, when using 240 m furrows. The variable costs of irrigating include the cost of water and labor, and the energy required to operate the booster pump when using sprinklers. Labor costs are higher for sprinkler systems because the pipe must be delivered to the field and returned to storage after individual events, or at the end of the summer irrigation season. In addition, the lateral lines of a sprinkler system must be moved once or twice per day, when irrigating a 61 ha field. The cost of line movers adds about $30.00 ha-’ to the total variable cost of each irrigation event and the energy cost is $12.34 per 1000 m3. The average water cost for each irrigation method is estimated using water delivery data observed in Broadview during 1991 through 1994.

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3.1. Cotton irrigations Farmers in the San Joaquin Valley pre-irrigate cotton fields to leach accumulated salts from the root zone and to establish deep moisture that can be used by the crop in late summer, when it is difficult to conduct irrigations quickly enough to keep pace with high rates of evapotranspiration. The water holding capacity of clay loam soils ranges from 108 mm to 175 mmm-’ of soil depth (California Fertilizer Association, 19951, and a useful guideline for leaching salts from soils in areas with saline high water tables is 83 mm of water m-’ of soil depth (Hanson et al., 1993). Therefore, the desirable pre-irrigation depth for cotton fields in Broadview ranges from 191 mm to 258 mm. Rainfall can provide a portion of this water requirement in some years, but most farmers in the region do not consider expectations regarding rainfall when scheduling pre-irrigations. The average depth of cotton pre-irrigations in Broadview was greater than 330 mm in 1989 and 1990, when siphon tubes were used on all cotton fields. Farmers began improving water management practices in 1991, achieving average pre-irrigation depths of 323 mm with siphon tubes and 226 mm with sprinklers (Table 3). The average pre-irrigation depth achieved with sprinklers has been significantly less than the average depth achieved with siphon tubes in all years since 1991. The average pre-irrigation depths on all cotton fields, durin g 1991 through 1994, are 279 mm with siphon tubes and 168 mm with sprinklers. Farmers using siphon tubes for all summer irrigations on cotton have reduced the average water delivery from 698 mm in 1989 to 491 mm in 1994 (Table 3). In 1991, some farmers began using sprinklers for at least one irrigation event during the summer. The average depth of summer irrigations on these cotton fields is not significantly different from the average depth achieved when siphon tubes are used throughout the summer, during 3 of the most recent 4 years (Table 3). The average depth of summer irrigations on all cotton fields during 1991 through 1994 is 483 mm with siphon tubes and 504 mm when sprinklers are used for at least one event. The variable cost of pre-irrigating cotton with siphon tubes and 400 m furrows includes $69.39 ha-’ for day and night irrigators, and $89.94 ha-’ for water, when water is priced at $32.43 per 1000 m3 (Table 4). The cost of night irrigators is included in these estimates because most farmers in Broadview hire night irrigators to monitor water deliveries carefully, to prevent excessive surface runoff. Day and night irrigators perform the same tasks, but in previous years most farmers chose not to incur the additional cost of monitoring irrigation deliveries during the night. The total variable cost of pre-irrigating cotton with siphon tubes is $159.33 ha-‘. The labor cost of pre-irrigating with sprinklers ($89.40 ha-’ ) is higher than for siphon tubes, but the water cost is lower. The total variable cost of using sprinklers, including the cost of energy, is $157.35 ha-‘, when water is priced at $32.43 per 1000 m3. The variable cost of using sprinklers to pre-irrigate cotton fields exceeds the variable cost of using siphon tubes, when water is priced below $31.00 per 1000 m3 (Fig. 2). Above this price, the reduction in water deliveries offsets the higher costs of labor and energy. The farm-level price of water in Broadview was $35.89 per 1000 m3 in 1991 and $36.63 per 1000 m” in 1992, when many farmers began using sprinkler systems for

D. Wichelns ef ul./Ap-i~ulturul Table 3 Average irrigation depths for pre-irrigation 1989 through 1994

and summer irrigations

Siphon tubes

Year

Wurer Monugement 32 (1997) 259-273

Sprinklers

Comparing (t-statistic)

(mm)

(n)

(mm)

(n)

1989 341 I990 332 1991 323 1992 268 1993 250 1994 274 Summer irrigations b

29 29 20 8 15 17

n/a n/a 226 140 149 158

8 10 14 16

1989 1990 1991 1992 I993 1994

29 21 17 13 24 26

n/a n/a 448 536 521 512

8 3 7 5

Pre-irrigation

on cotton fields, Broadview

261

Water District,

the means

a

698 546 445 485 512 491

3.34 * * 6.93 ~6.60 * = 1.76 * -

-0.13 - 1.78 -0.31 - 0.53

a The number of fields that are pre-inigated with sprinklers or siphon tubes is not always the same as the number of fields irrigated with these methods during the summer, because some fields are irrigated using gated pipe, and those fields are not included in these tables. For example, two of the fields that were pre-irrigated with siphon tubes in 1989 were irrigated with gated pipe during the summer; bsprinklers were nsed for at least one summer irrigation on these cotton fields. Significant differences in mean irrigation depths: ‘, P < 0.05 or * s , P < 0.01.

Table 4 Estimated Item

variable costs of selected irrigation Siphon tubes @ha-‘)

Pre-irrigating cotton Water 89.94 Labor 69.39 Energy 0.00 Total 159.33 Summer irrigations of cotton Water 159.13 Labor 112.58 Energy 0.00 Total 271.71 Early irrigations on tomatoes Water 89.94 Labor 53.97 Energy 0.00 Total 143.91

events for cotton and tomatoes

in the Broadview

Sprinklers @ha-‘)

Difference @ha-‘)

54.36 89.40 13.59 151.35

- 35.58 20.01 13.59 - 1.98

159.13 28 1.64 39.78 480.55

39.78 208.84

56.34 121.77 14.08 192.19

- 33.60 67.80 14.08 48.28

The cost of water is $32.43 per 1000 m3, the cost of energy to pressurize a sprinkler m3, and the cost of labor is $7.80 h- ’

Water District

0.00 169.06

system is $12.34 per 1000

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Water Management 32 (1997) 259-273

Variable Costs ($/ha) 260

,

100

’

16

24

57

65

Sprinklers Siphon Tubes 1 -

Fig. 2. Variable costs of pre-inigating

cotton.

pre-irrigating cotton (Table 1). These prices are sufficient to justify using sprinklers for pre-irrigating cotton, provided that farmers can also recover the higher fixed costs of owning and maintaining the sprinkler systems. Some farmers in Broadview purchased supplemental water from the California Emergency Drought Water Bank in 1992 and 1994. The price of that water was $81.89 per 1000 m3 in 1992 and $95.67 per 1000 m3 in 1994, providing additional incentive for those farmers to use sprinklers for pre-irrigation. The annual cost of owning and maintaining a sprinkler system adds $18 1 ha- ’ to the fixed cost of irrigation for farmers who use sprinklers for pre-irrigations and early irrigation events, while using siphon tubes for later irrigations (Table 2). A yield increase of 111 kg ha -’ is required to recover this increment in fixed cost when cotton is priced at $1.63 kg-‘, which is the average price received for cotton during 1986 through 1994. It is not possible, with the available data, to determine if such a yield increase can be attributed to using sprinklers for pre-irrigations and early seasonal irrigations of cotton. In fact, the average yield of cotton in Broadview follows a time trend similar to the average yield of cotton in Fresno County (Fig. 3). However, the average yield of cotton on fields pre-irrigated with sprinklers in Broadview was slightly higher than the average yield on fields pre-irrigated with siphon tubes, during 1991 through 1994 (Table 5). In 2 of those years, the difference in yield is statistically significant. While many factors contribute to observed differences in crop yields, it is possible that farmers using sprinklers for pre-irrigation may have improved their yields. If this is true, then the higher fixed costs of using sprinklers may be justified by a combination of yield improvements, water savings, and a reduction in the amount or frequency of laser leveling required to achieve the desired irrigation uniformity. The variable cost of four summer irrigations on cotton is $271.71 ha- ’ when using siphon tubes and $480.55 ha-’ when using sprinklers (Table 4). The labor cost of using

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269

Mglha 1.9

1.3 1

1986

1987

1988

1989 BWD --

1990

1991

1992

1993

1994

FresnoCounty

Fig. 3. Average cotton yields in Broadview

and Fresno County,

1986 to 1994.

sprinklers includes $148.01 ha-’ for day and night irrigators, and $133.63 ha-’ for line movers, while the labor cost of siphon tubes includes $104.87 ha-’ for day and night irrigators, and $7.71 ha-’ for opening and closing head ditches and tailwater ditches. Farmers would need to achieve an additional yield increase of 128 kg ha- ’, to justify using sprinklers for summer irrigations, even if they already own a sprinkler system. These cost data likely explain why most Broadview farmers used siphon tubes for summer irrigations of cotton during 1991 through 1994.

3.2. Tomato irrigations The cost of delivering the germination and pre-emergent irrigations on tomato fields with siphon tubes and 240 m furrows includes $53.97 ha-’ for labor and $89.94 ha-’ for water, when water is priced at $32.43 per 1000 m3 (Table 4). The total variable cost is $143.91 ha-‘. The labor cost of delivering the same events with sprinklers is significantly higher ($12 1.77 ha- ’) because the sprinkler pipe must be delivered to the field and removed after the irrigations are completed. The total variable cost of using

Table 5 Average_ _ vields of cotton and tomatoes

in the Broadview 1989

Average yield of cotton fields pre-irrigated with siphon tubes (Mgha- ’) Average yield of cotton fields pre-irrigated with sprinklers (Mg ha- ’) Average yield of tomatoes (Mgha-

’>

1.68

Water District. 1990 1.71

n/a

n/a

84.96

69.04

1991

1989 throuah 1992

1994 1993

1994

1.60

1.80

1.80

1.77

I .87

1.90

1.89

I .80

69.27

78.90

89.89

95.04

The average yield on cotton fields irrigated with sprinklers is significantly greater fields irrigated with siphon tubes in 1991 (P < 0.01) and 1993 (P < 0. IO).

than the average yield on

270

D. Wichelru et ul./Ap-iculturul Variable 350

Wuter Munupmmt

32 (19971259-273

Costs ($/ha)

r

24

32

41

49

57

65

73

81

136

148

Water Price ($/I 000 m3) Sprinklers

Siphon Tubes

-

Fig. 4. Variable costs of early irrigations on tomatoes.

sprinklers is $192.19 ha-‘, when water is priced at $32.43 per 1000 m3. This is 34% higher than the variable cost of using siphon tubes for the same events. Siphon tubes remain less expensive than sprinklers for the pre-emergent and emergent irrigations on tomatoes, until the water price rises to $79.00 per 1000 m3 (Fig. 4). Therefore, at current water prices in Broadview, farmers using sprinklers for these events must be expecting an increase in crop yield that justifies the higher fixed and variable costs of using sprinklers. The variable cost of using sprinklers is $48 ha-’ greater than the variable cost of using siphon tubes. When this is added to the fixed cost differential of $181 ha-‘, the difference in total cost is $229 haa’. This can be recovered if yields are increased by 4.12 Mg ha- ’, when the tomato price is $55.56 Mg- ’, which is the average price received for tomatoes during 1986 through 1994.

60 1966

1967

1988

1989 Broadview -

1990

1991

1992

1993

1994

Fresno County

Fig. 5. Average tomato yields in Broadview and Fresno County. 1986 to 1994

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The average yield of tomatoes in Broadview has increased from about 74 Mg ha- ’ during 1989 through 1991 to more than 89 Mgha - ’ in 1993 and 1994 (Table 5). The average yield of tomatoes has also increased during these years in Fresno County (Fig. 5). The Broadview tomato data do not permit comparison of yields by technology within the same year because all farmers used sprinklers during 1991 through 1993, and all but one farmer used sprinklers in 1994. However, the average yield has increased by about 15.5 Mgha- ’ in recent years, and an increase of only 4.1 Mgha-’ is required to justify the higher costs of using sprinklers for the germination and pre-emergent irrigations. It is possible that the current preference for using sprinklers for these events is driven by improvements in crop yield. However, it is not possible to test this hypothesis using the data currently available from the Broadview Water District. Data describing tomato yields and irrigation methods, by field, in Broadview and Fresno County are required for this task.

4. Policy implications Many Broadview farmers have displayed a clear preference for using sprinklers for pre-irrigating cotton and germinating tomatoes. A regional education or extension program that informs other farmers of the potential advantages of using sprinklers during these events will encourage more widespread use of sprinklers. However, such a program will be neither appropriate nor successful in motivating sprinkler use during summer irrigations of tomatoes due to potential disease problems. An appropriate public policy in this case is to ensure that water is priced correctly so that farmers have an economic incentive to deliver water efficiently, using any irrigation method. Farmers who are not yet using sprinklers for pre-irrigation may not perceive that yields may be improved sufficiently to recover the fixed costs. Therefore, public agencies wishing to encourage the use of sprinklers during pre-irrigations should consider interest rate subsidies to reduce the fixed costs of owning sprinklers. As an example, the amortized cost of a sprinkler system is reduced by $1,640 ($27.00 ha-’ > when the interest rate is reduced from a market rate of 10% to a subsidized rate of 5%. This reduces the minimum yield increase required to recover the fixed costs of a sprinkler system and the annual payments required to finance the purchase. The variable cost of using sprinklers for summer irrigations of cotton is greater than the variable cost of using siphon tubes, at any water price, because there is no significant difference in water deliveries with these methods. Therefore, the higher labor costs of using sprinklers are not recovered by water savings. Here, again, the appropriate public policy is to ensure that water is priced correctly. Water marketing programs also provide farmers with a significant opportunity cost for water delivered to fields. In recent years, both the relative scarcity of water and participation in water markets have generated many improvements in water management practices. Increasing block-rate pricing structures (tiered water prices) for irrigation water are appropriate when the off-farm impacts of irrigation generate a public cost that is not included originally in the farm-level cost of water (Dinar et al., 1989; Letey et al., 1988). For example, if excessive deep percolation generates subsurface drain water that

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must be recirculated or disposed into receivin g waters, the public cost of inefficient irrigation may exceed the farm-level cost. Tiered pricing requires that water districts charge a higher unit price for water delivered in excess of specific volumes or equivalent average depths. This structure enables districts to encourage all farmers to limit water deliveries to crop water requirements and leaching fractions, while not penalizing farmers who irrigate efficiently (Wichelns, 1991). Tiered water pricing also provides an incentive for farmers to choose efficient combinations of irrigation methods and management levels, while not requiring the adoption of specific irrigation techniques (Wichelns and Cone, 1992b).

5. Conclusions Many farmers in the Broadview Water District have switched from surface methods to sprinklers for pre-irrigating cotton fields and for early irrigations of tomatoes. The variable costs of pre-irrigating cotton with sprinklers are less than when using siphon tubes at current water prices in Broadview. The variable cost of irrigating tomatoes with sprinklers exceeds the variable cost of using siphon tubes, but all farmers have used sprinklers for germination and pre-emergent events in recent years. Crop yield data suggest that farmers may be improving their yields by using sprinklers for pre-irrigating cotton fields and for early irrigations on tomatoes. In addition, water saved by using sprinklers during these events can be used to irrigate additional area when water supply is limited relative to the available land area. Low-interest loans for purchasing new systems and tiered pricing of irrigation water will encourage additional farmers to adopt sprinklers for specific irrigation events, without penalizing farmers who already irrigate efficiently. Public policies to promote sprinkler use during summer irrigations of cotton and tomatoes may be ineffective because the variable cost of using sprinklers greatly exceeds the variable cost of using siphon tubes during these events. In addition, many farmers have improved their ability to deliver water with surface methods, and the average irrigation depths for sprinklers and siphon tubes are not significantly different during the summer. Therefore, the appropriate public policy is to ensure that water prices and allocations reflect the true cost of water resources, to encourage farmers to irrigate efficiently during all irrigation events, using surface methods or sprinklers.

Acknowledgements This research was supported by the Rhode Island Agricultural Experiment Station, the USDA Cooperative State Research Service, and the Water Conservation Office in the California Department of Water Resources. The authors appreciate the comments of Stephen K. Swallow, Thomas F. Weaver and Marca Weinberg regarding earlier versions of the manuscript. This paper is Rhode Island Agricultural Experiment Station Contribution Number 3203.

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