N.V. Pundarikanthan and C. Santhi, Centre for Water Resources, Anna University, Madras, India
Irrigation scheduling is one of the managerial activities that aim at effective and efficient utilization of water. A number of research findings and techniques related to irrigation scheduling are available today. Despite this, irrigation scheduling is only at inception level in most developing countries. This paper illustrates the status of irrigation scheduling and the constraints in the practice of scheduling at the field level from the perspective of a developing country, taking the case of Tamil Nadu in India.
The growing competition for water between the agricultural and non-agricultural sectors has increased the concern for the sustainability of the irrigated agriculture system. The need for increasing agricultural production demands an increase in the irrigated area regardless of the water resources availability for irrigation. Water has thus become a limiting factor in many of the irrigation projects. This necessitates an efficient and effective utilization of water through various water conserving methods.
Irrigation scheduling is a means of conserving water which helps in making decisions on allocation of quantity and timing of water supply commensurate with crop needs. It is one of the key activities that has the potential to improve performance of the system, especially its productivity, equity and stability (Chambers, 1983).
Research has made available a large number of findings useful for irrigation scheduling, such as those of crop water requirement estimation methods (Doorenbos and Pruitt, 1977), soil moisture depletion and allied procedures, water stress indicators, water and crop yield functional relationships, and the use of remote sensing techniques. These water-saving methods and techniques are not widely practised in developing countries, particularly in the southern part of India. Irrigation systems are fascinating and complex in nature, in the sense that each of these systems has its own characteristics in its physical conditions, climatic events, design criteria, institutional arrangements, resource availability, water rights, operational rules and sociocultural practices, and these characteristics are mostly interactive in nature. The introduction of any new procedure or technique and the degree of its success largely depend upon these system characteristics (Vaidhyanathan and Janagarajan, 1988). There are wide variations between the developed and developing countries in terms of these characteristics and therefore scheduling is still at inception levels in most of the developing countries like India. This paper addresses some of the constraints in the practice of irrigation scheduling at field level, from a perspective of irrigation systems in a developing country, taking the case of Tamil Nadu in south India. The irrigation systems in Tamil Nadu are jointly managed by the irrigation agency (above the outlet) and the farmers (below the outlet). Although there exists no well defined policy or management framework for scheduling in the state of Tamil Nadu, the prevailing practices such as crop localization, monsoon dependent water allocation, and duty based design and water distribution pose constraints in the practice of scheduling. These constraints are discussed in detail.
CONSTRAINTS IN PRACTISING IRRIGATION SCHEDULING
The concept of localization has been in practice for a long time in India. All along, the accepted practice has been to include all cultivable land under command in the ayacut. Once the land is identified as 'commendable' under an irrigation system, it remains as such forever in the revenue records and is eligible to draw water from the system forever. No special permit is necessary season after season and thus it confers permanency in irrigation. In general, the command areas are localized as 'wet' (for water intensive crops such as paddy, sugar cane and banana) and 'irrigated dry' (for crops such as groundnut, onion and cotton), leaving decisions on crop choices to farmers. This strategy constrains scheduling in two ways.
· This localization policy permits farmers to take the freedom of crop choices, even though it is authorized for a particular crop. Farmers grow one or more crops in a diversified manner according to their family needs, local expertise and market fluctuations.
· The localization policy, by way of conferring rights for water along with land, gives the farmers a notion that they acquire the riparian rights on the use of water, and they try to seek legal remedies whenever changes are introduced in the interests of better water management.
Localization, therefore, gives little scope for the government agency for revising the crop policy or operational procedures. For example, the Sathanur Irrigation System in Tamil Nadu is localized for groundnut, an irrigated dry (ID) crop, in the direct command of 14 750 ha. Farmers, however, prefer to grow paddy (for family needs or due to land suitability) and sugar cane (for high returns) in addition to the ID crop. These are grown in 30-35% of the command in a scattered way. Likewise, banana (a crop of high profitability) is grown in 15% of the command area of 34 794 ha in the Tamiravaruni System. The diversified cropping system constrains the regularization of water delivery.
Water allocation strategy
The strategy for water allocation and use of irrigation water in the south Indian systems has been neither demand based nor supply based, but location based (Mohanakrishnan, 1990). Seasonal and in-seasonal allocations depend on the resources available, crop seasons and priorities for water allocations prevailing in the particular location of the system. The irrigation engineers, usually the executive or assistant executive engineers, make the allocation decisions according to the 'water duty' specified at the heads of the main and branch/distributary canals and the command area under those canals. (Water duty is locally denoted as the number of acres that can be irrigated with a cusec of water during crop period.)
In general, the crop seasons are planned to coincide with the monsoons (southwest monsoon between June and September and northeast monsoon between October and December) in most of the irrigation systems in south India. For example, in a few systems like the Tamiravaruni and the Periyar - Vaigai in Tamil Nadu, the reservoirs fill with the progress of the monsoon and cultivation starts as the monsoon proceeds. Here there are two complex situations that make crop planning and allocation decisions difficult:
· Inflow may dwindle after an initial promise of a good monsoon:
· The monsoon may break a little late, and the initial promise is by itself not good.
In the first case, the current practice is to reduce the supply after the initial crop period, and this might affect the crop growth. In the second case, the date of release is postponed, anticipating the strengthening of the monsoon to the extent that the crop does not become affected. The allocation decisions thus cannot be made without some risk. Even the decisions as to when the season starts and when it ends, the important decisions at the macro level are not very easy to make. Farmers also make their decisions on crop choices and planting dates in the face of uncertainty of occurrence of rainfall and the building up of storage in the reservoir. This argument emphasizes that the 'timeliness dimension' is very complex in the case of scheduling in systems in which the crop seasons are monsoon based.
Nevertheless, under these situations, while preparing the schedule, the system manager makes assumptions regarding the extent of crop area, timings of land preparation and the transplantation. These assumptions do not coincide with the actual field practices, requiring a revision in the schedule. There is no in-built feedback mechanism to revise the schedule on a real-time basis.
Water distribution strategy
In south India, irrigation systems are jointly managed by the government agency and farmers. The responsibility of water distribution up to the outlet is in the hands of the government agency, and the beneficiaries take over the responsibility below the outlet.
Water is distributed at different parts of the canal network, such as branch canal and outlets, by the agency according to the duty specified. Distribution below the outlet in practice is generally to stand in queue when the lands below each turn-out are fed one after the other from head to tail. This is mostly done by mutual consent by a group of farmers. This kind of distribution practice followed by the farmers works satisfactorily as long as there is adequate waters, but it is very difficult during scarcities, leaving the tailenders to suffer.
Experience has shown that there are difficulties in the jointly managed irrigation systems. These are described below:
Systematic Scheduling: It has been noticed that in many systems the main system scheduling done by the irrigation agency and the on-farm scheduling practices adopted by the farmers do not match in terms of time of operation (Santhi, 1994). Examples of this situation can be seen in terms of the Sathanur irrigation project. The distributary canals are scheduled to be operated for a duration varying from 5 to 10 days according to the size of the command, whereas the on-farm schedule is prepared on a weekly basis (7 days) specifying timings for individual farmers (with the assistance of the Agricultural Engineering Department). This suggests that a systematic scheduling based on a bottom-up approach or top-down approach on a service agreement basis is very important for field implementation. This has been tried on a small scale in the Thindal area of the Lower Bhavani Irrigation System in Tamil Nadu through a farmers' association with the assistance of the Irrigation Community Organizers (ICOs) and it has been found to work well in the past decade. Once the water is delivered in the outlets by the irrigation agency, the farmers irrigate their farms according to the timings specified for them. The ICOs act as catalysts between the agencies involved and farmers. The ICOs assist the farmers in on-farm development works as well.
Revealed Farmer-Agency Perception: There are two aspects to the farmer-agency perception that are relevant here: one is that of adequacy and the other is of timeliness.
· Adequacy: In the farmers' perception it is time and again made out that there is inadequate water to the crops, when in fact, the measurements by the agency have proven otherwise. For example, the farmers of the Nathiyunni Channel command in the Tamiravaruni system have shown that stagnating water in the paddy fields is like building up a stock of water and that when it is not possible, they have a sense of inadequacy of water for the crop grown, as during the Kar season (June-September) of 1993. The research study done in the same channel during the same season reports that the Relative Water Supply (RWS), which is a measure of adequacy, has been computed as equivalent to 1.1, that is, 110% of the water requirement (Rajan, 1993). Yet, 84% of the farmers perceived the supply as having been inadequate for their crop. Similarly, in Sathanur, the irrigation interval suggested for the ID crop of groundnut was 15 days, whereas the farmers' perception was that of a week at the most, and thus they irrigated the crop once a week.
· Timeliness of Revealed Convenience: Farmers prefer to do the agricultural operations at their personal and managerial convenience depending on the availability of inputs/credit/labour. For example, the tailend farmers of the North Kodaimel Azhagian Channel of the Tamiravaruni system were able to transplant their paddy only after a month's delay in comparison with their counterparts at the head reaches during the Kar season in 1994. Because of labour shortage the transplantation could not be done. This subsequently delayed the harvest of that crop. Farmers have also shown a preference for not irrigating the fields at night, for personal convenience. It has also been seen that the farmers prefer to complete their cultural operations at a lower cost. As such, they try to use their own labour and minimize the hired labour. This might cause delay in the completion of the agricultural activities. Hence, the planned schedules could not be implemented effectively in the field.
The above explanations underline the need for service agreements between the agency and the farmers.
INFRASTRUCTURE, CANALS AND FLOW CONTROL SYSTEMS
The design as well as the operation of the distribution network in practice in the southern region of India is based on the average 'duty'. To date, a duty of 60 acres per cusec for wet and 120 acres per cusec for irrigated dry crop are adopted for designing the distribution system. The duties adopted at different levels of the canal network in the case of the Sathanur Irrigation System are given below as an example.
Sathanur left bank canal
Duty at the head of the main canal
Duty at the head of the major distributary
Duty at the head of the minor distributary
Duty at the head of the outlet level
Duty-based design and operational procedures do not give due consideration (a) for the 'conveyance losses' occurring in the canal network, and (b) for meeting the 'crop water requirements in time'.
· The average duty considers that the lengths and conditions of the canals are the same and therefore the losses are considered to be uniform. However, they are not so in almost all of the systems in Tamil Nadu.
· Figure 1 shows that the delivery of water according to the duty and the crop water requirements at different stages (for groundnut, estimated at 50% efficiency) differ in quantity over time in the case of the Sathanur system. Interventions have to be made in the scheduling procedure by considering the crop water requirements and the conveyance losses occurring in the system such that they match with the existing design. This requires meteorological instruments, flow control and measuring devices and communication facilities for collection of data, elements which are not there in most of the system.
FIGURE 1 - Water required and supplied in the distributary canals of 6R and 10R in the LBC DY6R: Distributary 6R; DY10R: Distributary 10R
This paper has highlighted the following points as constraints in the practice of irrigation scheduling in the case of irrigation systems in Tamil Nadu in India, from the experience of a developing country. This paper also suggests a few priorities for developing countries.
· The localization policy in practice for a century permits farmers to make one or more crop choices. The diversified cropping system (rice and non-rice crops) with different crops in differing growth stages and varying areal extent under the same sluice/outlet makes irrigation scheduling a difficult task in the field, considering the controls available in the system at the outlet heads and there being no measuring devices to enable the required quantum of water.
· Decisions on the start of the crop season, extent of the area allocated for irrigation, end of the season and crop planning are very difficult, as the reservoir storage and cultivation proceeds with the monsoons in most of the systems in the state.
· In the case of jointly managed systems, there are no service agreements between the agency and the farmers at present. They are important for managing the different perceptions of the farmers and the agency involved.
· The design and operation procedures of the irrigation systems in the state are duty based. Scheduling has to be done with suitable interventions, like introducing the crop water requirement concepts, allowing for losses in the network and using measuring devices.
These conclusions have been drawn from our research activities in many of the irrigation systems in Tamil Nadu. Nevertheless, irrigation scheduling is a key for improving the management of the irrigation system. Scheduling is gradually becoming recognized as a subject of importance in this country. However, not all the available scheduling techniques can be transferred. The physical, institutional, economical and sociocultural characteristics of the irrigation systems vary widely in the case of the south India, and they require their own categories of facilities, interventions and priorities.
What needs to be done in a developing country?
Three options emerge from a consideration of the issues from the viewpoint of any developing country. They are:
· Facilities and databases as a prerequisite: It is fairly common that the irrigation systems in the country lack facilities in terms of equipment and databases. Meteorological stations on representative sites in the system commands, moisture measuring equipment, measuring devices along the canal network, controllable distribution networks and communication facilities are necessary to obtain timely and reliable data. A good database system has to be maintained to improve operations through good information.
· Capacity building through training: There is a need to develop the capacity of the farmers (through associations) and the officials alike in concepts of crop water requirements and water saving methods for efficient utilization of the water. Effort have already been made in this direction. The Irrigation Management Training Institute in Tamil Nadu is training officials and the farmers on a representative basis.
· Feedback mechanism: The system design, allocation and distribution procedures are made with certain assumptions and approximations. The delivery schedules prepared on such assumptions and approximations may not hold good in field implementation. There is thus a need to build up a feedback mechanism in the system procedures to obtain the field information through interactions with farmers and make corrections on a real-time basis.
Doorenbos, J. and Pruitt, W.O. 1977. Crop water requirements. FAO Irrigation and Drainage Paper 24. FAO, Rome.
Mohanakrishnan, A. 1990. Selected Papers on Irrigation. Irrigation Management Training Institute, Trichy, India.
Rajan, A.P. 1993. Performance Evaluation of the Run-of-the River Irrigation System - A New Approach. Ph.D. thesis, Anna University, Madras, India.
Chambers, R. 1983. Managing Canal Irrigation. Oxford Publications, New Delhi.
Santhi, C. 1994. Development of a Management Information System for Sathanur Irrigation System. Internal Review, Anna University, Madras, India.
Vaidhyanathan, A. and Janagarajan, S. 1988. Irrigation Management in two different surface Irrigation Systems in Tamil Nadu. Draft Report, Madras Institute of Development Studies, Madras, India.