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A.J. van der Westhuizen and J.G. Annandale, Department of Plant Production and Soil Science, University of Pretoria, Hatfield, and N. Benadé, Fischer & Associates, Menlo Park, South Africa |
SUMMARYThe main obstacle which keeps the majority of farmers from scheduling is that they do not perceive the net benefit of scheduling to be positive. This results from not quantifying the net benefit at all or from not quantifying it correctly (Annandale et al., 1995). The hypothesis postulated is that farmers will apply scheduling technology if they perceive the net benefit to be sufficiently positive (Annandale et al., 1996). The requirements for a positive net benefit of scheduling are identified as, firstly, a need for procedures and appropriate input data for the quantification of net benefit, and secondly, a need for efficient and cost effective scheduling techniques. To satisfy these needs, Annandale et al. (1996) pursued a modelling approach to integrate the large number of variables describing the plant-soil-climate-management-economic situation, for which decisions are based on a single net benefit value as the bottom line. A management tool in the form of a computer program, TOM-MAN (Tomato Manager), has been developed. The program integrates a fairly mechanistic crop growth and soil water balance model (TOMYIELD) and an economic optimization model (TOM-ECON) and simulates the crop growth and development, marketable yield and quality, crop water requirements and the economic net benefit of processing tomatoes. By simulating the net benefit of different irrigation schedules, including the current practice, based on a user's own input data, TOM-MAN facilitates the selection of the optimum schedule and demonstrates its financial benefit. It is concluded that integration of economic optimization and technical irrigation scheduling models will enhance the application of irrigation scheduling technology. Research and development on irrigation scheduling programs should therefore be aimed at increasing benefits, reducing costs and facilitating the quantification of the net benefit of scheduling.
The majority of irrigation farmers are striving for increased profits and will therefore apply new technology if a net benefit (increased income after costs) is expected from its application. Although it is common knowledge that irrigation scheduling is already applied successfully by some farmers throughout the world, it is also a fact that the majority are not scheduling at all. From this situation, it is concluded that the majority of farmers do not expect a net benefit from applying irrigation scheduling technology (Annandale et al., 1995) In this paper, a cost-benefit approach is pursued as a means of encouraging the application of irrigation scheduling technology. The TOM-MAN management program, which has been developed for processing tomatoes as an example, is based on this approach. The program is not applied widely in practice yet, because the programming into a user friendly format is currently underway and input parameters are being established for a wide variety of crops irrigated in South Africa. The program is, however, ready for use with processing tomatoes in South Africa.
HYPOTHESIS
The hypothesis on which the approach is based is that farmers will apply appropriate scheduling techniques if they perceive the net benefit from their application to be positive. This hypothesis implies that in order to motivate farmers to schedule, they need to expect greater benefit than cost from scheduling. Annandale et al. (1995) investigated the reasons why the majority of farmers in the Marble Hall area (Mpumalanga Province, South Africa) do not schedule irrigations. The main crops planted in the area are wheat and green peas in winter; cotton, maize, soybeans, potatoes and tobacco during summer, and citrus. Irrigation is mostly applied by portable sprinkler and centre-pivot systems. Of the 425 farmers, 23.5% were interviewed during 1993. It was found that although the majority of farmers did expect savings on irrigation inputs and improvements in yield from proper scheduling, they did not regard scheduling to be worth the trouble. The value of the average expected benefit from improved scheduling was calculated and found to be in excess of R1000 ($US275) per hectare per year for low valued crops like wheat and cotton. This amount included expected increased yield (7%), savings on irrigation costs (10%) and potential additional income from using the saved water for planting bigger areas. This additional income is also called 'opportunity cost' for sub-optimal strategies. It was concluded that the main obstacle that kept the majority of farmers from scheduling was that these farmers did not perceive the net benefit of scheduling to be positive because they either did not quantify it at all or they did not quantify it correctly.
The reasons for not quantifying costs and benefits at all were that farmers either did not expect a benefit or they did not have the required input data. Incorrect quantification was primarily the result of disregarding the opportunity cost of saved resources.
REQUIREMENTS FOR TECHNOLOGY TRANSFER IN IRRIGATION SCHEDULING
In order to convince farmers to apply irrigation scheduling technology, the farmers need to be motivated to quantify the costs and benefits, which they will be if they expect a net benefit. Then they must be able to do it correctly and they must have sufficient, correct and applicable input data. In order to ensure a sufficiently positive net benefit, efficient scheduling techniques are required and the cost of scheduling should not be too great. These requirements imply a need for the quantified integration of a large number of variables describing the plant-soil-climate-management-economic situation for which a decision needs to be made, based on a single net benefit value as the bottom line. A modelling approach is pursued in order to meet all the above mentioned requirements. TOM-MAN integrates several variables to calculate net income per unit limiting resource, for the purpose of selecting an optimal irrigation schedule. TOM-MAN also offers a tool for the accurate implementation of scheduling in order to improve the efficiency of irrigation at a reasonable cost.
DESCRIPTION OF THE TOM-MAN PROGRAM
TOM-MAN consists of a crop growth simulation model (TOMYIELD) and an economic optimization model (TOM-ECON). TOMYIELD is based on the generic crop version of the soil water balance model initially described by Campbell and Diaz (1988) with more detail in Campbell and Stockle (1993) and Benadé et al. (1995). This model has been modified by Annandale et al. (1996) to simulate the growth and development of processing tomatoes as well as the fresh yield, quality and water use. TOM-ECON then uses the simulated output yield, quality and water use to estimate required inputs (irrigation, fertilizer, labour, transport) and calculate the net benefit (gross income less total costs) of the simulated schedule. By running TOMYIELD and TOM-ECON for a range of recommended irrigation schedules, TOM-MAN can then calculate the net benefit of each, and select the economically optimum schedule. This is then used as a guideline for the management of the irrigation using the real-time scheduling procedure, which is also a part of TOM-MAN.
TOMYIELD uses a mechanistic modelling approach to describe the soil-plant-atmosphere continuum. Crop water use is calculated by taking both the supply of water from the soil-root system, and the demand from the canopy-atmosphere system into account. Penman-Monteith reference crop evaporation (Smith, 1991), is used if required inputs are available, otherwise a modified Priestley-Taylor estimate of evaporative demand is calculated from daily maximum and minimum temperatures.
The main function of TOM-ECON is to establish the optimum irrigation strategy for application by TOM-MAN during routine scheduling. TOM-ECON quantifies the costs of TOMYIELD simulated inputs required for different irrigation management strategies, as well as the income generated from the simulated outputs (yield and quality). In order to optimize for a specific situation, which may differ from region to region, farm to farm and even field to field, the user can enter the applicable cost of inputs and the quality based fruit price structure. Because TOM-ECON's simulation of the net benefit is based on TOMYIELD's simulated yield and quality, the accuracy of TOMYIELD's simulation is of utmost importance.
The different cost items are classified as either fixed overhead costs, fixed or variable running costs, cost of risk or opportunity cost. Cost per hectare is calculated for each cost item. Gross income per hectare is also calculated from simulated yield and quality. Net income is calculated per unit of land area, volume of irrigation water, and ton yield. The user then selects the resource (land, water or contract tonnage) which is most limiting. TOM-ECON then sorts the irrigation strategies, based on the selected criteria, in descending order. Finally, the user selects the best irrigation strategy which is applicable to the particular situation. The selected strategy is taken as the irrigation guideline for scheduling irrigation.
TOM-MAN is therefore a tool for optimizing net income from different irrigation schedules, as well as for accurate real-time scheduling of irrigations. The quantification of the net benefit from scheduling is facilitated by comparing simulated net income for the most profitable strategy with that from the current (unscheduled) situation.
FACILITATING THE QUANTIFICATION OF THE NET BENEFIT OF SCHEDULING
Farmers will normally only be interested in the quantification if they expect a positive outcome, have the ability and if the required input data is available. The way in which TOM-MAN assists the user in each one of these fields is discussed below.
Motivation to quantify
When benefits arising from the application of new technology are not immediately and clearly visible, the transfer of technology is slow (Rogers, 1983). Because this is the case with irrigation scheduling, there is a need for the demonstration of the expected outcome of different possible schedules. The demonstration of irrigation schedules in practice is very expensive and time consuming. Using TOM-MAN, different irrigation strategies can be compared by simulating the expected water requirements, yield and quality of each. The net benefit is then calculated for each schedule for final comparison. If simulated optimal net income is greater than growers' current net income, they should be motivated to apply scheduling technology.
Correct quantification procedures
TOM-MAN has a standardized procedure to quantify net benefit which minimizes the possibility of errors and the omission of certain cost items. Users are guided through an interactive procedure to supply their own input data. The further benefit of the approach is that expertise required is reduced and the process is speeded up to save the users time.
Availability of sufficient and correct input data
The applicability of input data is of the utmost importance, because situations vary greatly between places and from time to time, while users need to make decisions for their own circumstances. By enabling users to supply their own input data in respect of the soil, climate, crop (processing tomato) and economics, the expected water use, yield and quality is simulated for their specific conditions. This represents the best possible set of input data for the calculation of users' net income.
ENSURING A SUFFICIENTLY POSITIVE NET BENEFIT FROM SCHEDULING
To ensure a positive net benefit, scheduling should offer sufficient benefit after cost. From this it follows that, on the one hand, the technique should maximize benefits, and on the other the costs of scheduling should be minimized.
Maximizing benefits from scheduling
TOM-MAN increases net benefit by improving the technical efficiency of irrigation scheduling and by offering additional fringe benefits.
Improved technical efficiency
The full benefits from irrigation scheduling will only be achieved if water requirements are estimated and applied accurately. A fairly mechanistic simulation model is therefore used in order to estimate water requirements as accurately as possible. The model allows the user to insert measured values of soil water content, fractional interception of solar radiation and dry mass of the different plant organs in order to check and correct simulated values.
Additional fringe benefits
The potential benefits from irrigation scheduling programs can be increased by transforming traditional scheduling programs into management tools to improve efficiency in different fields of management. TOM-MAN, apart from predicting the timing and quantity of the next irrigation, offers the following fringe benefits:
· the delegation of routine scheduling to lower levels of management is enabled by simplifying the input of daily weather data and the amount of rain and irrigation measured per field. This enables efficient irrigation scheduling without employing highly trained staff;· a record of calculated recommendations, water use and input data is kept in TOM-MAN'S database for future use. This information enables managers to check on the extent to which recommended irrigations were applied. The information is also valuable for cost allocations in budgetary control;
· expected water use and yields can be generated for forward planning;
· in situations where quantity and timing of water deliveries need to be estimated and ordered in advance, TOM-MAN calculates this based on predicted or recommended irrigations. The program also prints a standard water order form, which is normally done manually.
Minimizing the cost of scheduling
The major costs of irrigation scheduling are the direct costs of equipment, management time for routine calculations and control measurements, as well as the cost of expertise. These costs are minimized by TOM-MAN by reducing the need for soil water control measurements through increased accuracy of simulations. The time required for routine scheduling is reduced by the computerization of all calculations. The cost of expertise is reduced by reducing the level of required expertise at on-farm level. Normally the application of the principles included in TOM-MAN would require experts in crop growth, soil science, atmospheric demand, irrigation requirements and economics. TOM-MAN greatly reduces this required expertise by enabling trained users to apply all these principles without having to understand the detail. The required expertise is also reduced by having the input parameters for different crops, soils and irrigation systems available in TOM-MAN'S database. The database is utilized by selecting per field the crop, soil type, climatic area and irrigation system. TOM-MAN then automatically selects the appropriate parameters for the simulation. Crop parameters for processing tomatoes were generated during a series of growth analysis trials by Annandale et al. (1996), for green peas by Annandale et al. (1995) and for several agronomic and pasture crops by Barnard et al. (1996). A current research project is establishing crop parameters for a wide variety of vegetable, agronomic and perennial crops.
EXAMPLE OF MODEL APPLICATION ON TOMATOES
This example demonstrates how TOM-MAN was applied to calculate the net benefit of scheduling and to select an optimum schedule for processing tomatoes. Four different irrigation schedules were defined as indicated in Table 1.
TABLE 1 - Allowable depletion in matric potential (kPa) at 300 mm depth for different irrigation strategies
|
Schedule |
Crop development |
||||||||||
|
Establishment |
Flowering |
Ripening |
Maturity |
||||||||
|
1 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
20 |
|
2 |
20 |
20 |
20 |
20 |
20 |
20 |
75 |
75 |
75 |
75 |
75 |
|
3 |
20 |
75 |
75 |
75 |
75 |
75 |
75 |
75 |
20 |
20 |
20 |
|
4 |
30 |
75 |
50 |
50 |
50 |
50 |
50 |
1 500 |
1 500 |
1 500 |
1 500 |
The farmer's current irrigation schedule (normal practice in the industry) is included as strategy number one. TOM-MAN simulated the yield, quality (on which price is based) and water used for each strategy. The net income is calculated per unit of water, land and yield. TOM-MAN then sorted the results according to the most limiting factor (water, land area or yield contract), which is selected by the user. The results are presented in the output table (Table 2), which has in this case been sorted for limited water.
The simulation indicates that the net income per hectare can be increased from the current R 11 516 of strategy 1 to R 13 613 if strategy 2 is followed. This 18% increase of R 2 097 ha-1 represents the net benefit arising from the application of the particular schedule and should motivate a profit-seeking farmer to consider the application of the technology seriously.
TABLE 2 - Net income with an opportunity cost of R3 m-3 of saved water
|
Schedule |
Net income per unit resource |
Simulated values |
||||
|
water |
land area |
yield |
yield |
quality |
water use |
|
|
4 |
3.02 |
13 252 |
203 |
65.27 |
4.60 |
4 390 |
|
3 |
2.56 |
13 508 |
179 |
69.98 |
4.30 |
4 890 |
|
2 |
2.53 |
13 613 |
176 |
71.55 |
4.27 |
4 990 |
|
1 |
2.19 |
11 516 |
161 |
71.58 |
4.27 |
5 270 |
CONCLUSIONS
The primary reason why farmers do not schedule is because they do not perceive the net benefit of scheduling to be positive. In order to motivate farmers to schedule, they need to expect a sufficiently positive net benefit. It should also be quantified correctly. The scheduling technology must be efficient in achieving the potential benefits while the cost of applying the scheduling technique should be reasonable. The benefit from irrigation scheduling can be increased by transforming traditional scheduling programs into management tools which can assist irrigation management in general.
An economic cost-benefit approach can be implemented successfully to integrate the technical and economic variables which influence decisions on the application of irrigation scheduling technology. Integrated mechanistic simulation models, packaged as user friendly computer programs and supported if necessary by scheduling services, will enhance the transfer of sophisticated irrigation scheduling technology.
REFERENCES
Annandale, J.G., van der Westhuizen, A.J. and Olivier, F.C. 1995. Die fasilitering van tegnologieoordrag deur verbeterde besproeiingsriglyne vir groente en 'n meganistiese gewasmodelleringsbenadering. Verslag aan die Waternavorsingskommissie. WNK Verslag Nr 476/1/95.
Annandale, J.G., van der Westhuizen, A.J. and Benadé, N. 1996. Irrigation management for economic optimization of processing tomato production. Report to the Water Research Commission. In press.
Barnard, R.O., Rethman, N.F.G. and Annandale, J.G. 1996. The screening of crop, pasture and wetland species for tolerance to polluted water originating from coal mines. Report to the Water Research Commission. In press.
Benadé, N., Annandale, J.G. and van Ziji, H. 1995. The development of a computerized management system for irrigation schemes. Report to the Water Research Commission. WRC Report No 513/1/95.
Campbell, G.S. and Diaz, R. 1988. Simplified soil water balance model to predict crop transpiration. In: Drought Research Priorities for Dryland Tropics. (F.R. Bidinger and C. Johanson). pp. 15-26.
Campbell, G.S. and Stockle, C.O. 1993. Prediction and simulation of water use in agricultural systems. (67-73). Ch 10. In: International Crop Science. 1. CSSA, Madison, WI 53711.
Rogers, E.M. 1983. Diffusion of Innovations. Free Press, New York.
Smith, M. 1991. Expert Consultation on Revision of FAO Methodologies for Crop Water Requirements. FAO, Rome.
