The Range, Distribution and Implementation of Irrigation Scheduling Models and Methods in South Africa
Report No. 1137/1/05
January 2005

Irrigation scheduling is accepted as the process to decide when to irrigate crops and how much water to apply and is assumed to play an important role in the general improvement of water use efficiency on the farm. However, the adoption of objective irrigation scheduling worldwide is still on a limited scale. The idea that there is a single key to the adoption of irrigation scheduling as a component of efficient water use on the farm is simplistic. It implies that science has all the answers, and we as scientists just need to convince the farmers of its value.

This project was introduced with the purpose of identifying social, cultural, economic and technological factors, which inhibit the adoption of irrigation scheduling practices on the farm. Understanding and gaining insight into some of the human factors that determine individual irrigation farmers’ decisions to either adopt or reject the implementation of irrigation scheduling will help to plan and design effective propagation strategies for the implementation of irrigation scheduling amongst irrigators. A large number of irrigation scheduling methods and models are available in South Africa as discussed in Chapter 2. They include various soil, atmospheric and plant monitoring techniques as well as a range of scheduling methods based on soil-water balance and computer simulation models. To appreciate the variety of irrigation scheduling methods and models currently available to farmers, advisors, consultants and extensionists it was necessary to categorize the scheduling method according to their application.

Secondly, the adoption of irrigation scheduling amongst commercial and small-scale farmers was investigated with the purpose of identifying the possible human and socioeconomic factors that may influence the adoption thereof. This investigation was done on macro (scheme) level as well as micro (on-farm) level. Important human and socioeconomic factors were identified that influence the adoption of irrigation scheduling practices. An overview of the service currently rendered by irrigation consultants is provided and the important information and learning sources that irrigators generally use were investigated.


Five objectives were set out in the original proposal.
  1. Investigate and describe the variety, range and scope of models and methods of irrigation scheduling in South Africa.
  2. Investigate, analyse and describe the levels of application by a cross section of subsistence and commercial farmers, institutions and advisors of a selection of irrigation scheduling models and methods.
  3. Investigate, analyse and describe the reasons from a cross section of subsistence and commercial farmers, institutions and advisors, for using the different irrigation scheduling methods and models.
  4. Investigate, analyse and describe why irrigators discontinue with the implementation of irrigation scheduling.
  5. Make recommendations concerning the propagation and institutionalising of the proper sustained implementation of irrigation scheduling methods and models.

The overall approach for meeting the objectives is summarized in Figure 1.

Step 1
There are a vast number of irrigation scheduling methods and models available to help the farmer with decisions regarding when the crops require water and how much irrigation needs to be applied. These include the various soil, plant and atmospheric monitoring techniques as well as a range of scheduling methods based on soil-water balance and simulation models. Step I was to identify the irrigation scheduling methods and models that are available for the South African irrigation farmer, and to categorize these methods and computer models according to their possible use. Irrigation farmers in their irrigation management decisions often use intuition, which was acknowledged in the framework used for categorization.

Step 2
A quantitative assessment was conducted on a national basis amongst 332 irrigation schemes, which provides an overview of the implementation and distribution of irrigation scheduling methods, and models amongst commercial and small-scale farmers on a scheme level (macro level) in the nine provinces of South Africa. It served to identify the different institutions and agencies that provide support to farmers with the implementation of irrigation scheduling (Step 2).

Step 3
Objectives three to five of the project focused on the intervening variables that operate as direct determinants of adoption or rejeclion of irrigation scheduling practices. Perceptions, attitudes and needs of irrigation professionals (consultants, advisors, industry experts and irrigation specialists) and irrigators regarded as opinion leaders in their respective areas. formed the basis for the 70 semi-structured interviews that were conducted (Step 3). Each of these interviews were recorded on tape and transcribed afterwards.

Step 4
By combining the findings of the macro-level study and the insights gained from the semi-structured interviews conducted with key individuals in the irrigation fraternity, a more focused approach was followed in the identification of human factors and constraints that impact on the adoption of irrigation scheduling practices of commercial and small-scale farmers. The quantitative survey amongst a random sample of 134 commercial farmers from eight different provinces (Northwest. Eastem Cape, KwaZulu Natal, Western Cape, Limpopo, Northern Cape. Free State and Mpumalanga) represented the micro level of the study (Step 4). Step 4 also comprised the investigation and description of the irrigation practices and scheduling methods used by small-scale farmers as well as their perceptions and possible reasons (human, social, and economic) for adopting or rejecting the use of irrigation scheduling methods. Interviewing key informants on several of the small-scale irrigation schemes formed the second phase of this investigation. Four small-scale irrigation projects were selected for more detail investigations and assessments, to illustrate the different approaches followed in the training and development of small-scale irrigation farmers in the use of irrigation scheduling practices.

Step 5
The data, insights and findings gained from the different interviews and surveys amongst commercial and small-scale irrigation farmers were incorporated in the conclusions and recommendations (Step 5).

Identify irrigation scheduling methods and models
available for the South African irrigator
Quantitative assessment of the implementation and distribution of irrigation scheduling methods(macro level)
Semi-structured interviews with irrigation consultants andextensionists rendering an irrigationscheduling service
Quantitative survey to determine the human factors that influence adoption of irrigation practises on farm
(micro level)
Conclusions and recommendations

Figure 1    A framework to illustrate the overall approach for meeting the objectives of this study. Steps 2 and 3 were carried out concurrently with iteration between the project team, farmers and respondents from the irrigation industry.


The report comprises seven chapters. Chapter 1 describes the rationale behind the introduction of irrigation scheduling to the farmer, as one of the elements of efficient water use on the farm. The three main focus areas of the project, namely the identification and classification of irrigation scheduling methods and models commonly used in South Africa, national survey of the implementation and distribution of irrigation scheduling methods and models on an irrigation scheme level, and the micro level assessment of the human factors and constraints that influence the adoption or rejection of irrigation scheduling are discussed in Chapter 2, 3, 4, and 5. Chapter 6 deals with the different approaches which farmers follow to solve problems and the different information sources that farmers use to leam about irrigation practices.

The timing and depth criteria used in irrigation scheduling can be established by using several approaches to scheduling based on soil water measurements, use of soil water balance estimates, atmospheric measurements and plant stress indicators in combination with simple rules, observations or very sophisticated models. The various irrigation scheduling methods and approaches available in South Africa were classified according to a framework based on the mode of operation and the possible users of the specific method or technique (Chapter 2). Irrigation scheduling techniques and methods were classified into the following categories: intuition, atmospheric based quantification of evapotranspiration (ET), soil water measurement, plant based monitoring and integrated soil water balance approach which includes pre-programmed irrigation methods as well as real time scheduling approaches. Some of these methods and techniques were found to be “transferable” to farmers, while others will only be considered as research tools.

The survey amongst 332 irrigation schemes (which included 51 small-scale irrigation schemes) showed that 18% of the farmers are applying objective scheduling practices, while the majority of irrigators rely on the use of intuition or subjective irrigation scheduling (Chapter 3). Subjective irrigation scheduling is based on instinct, knowledge. experience and confidence gained over many years of farming. The great variation in irrigation figures reported (0-100%) suggests that farmers perceived irrigation scheduling as either one of the following approaches:
The findings of the survey reveal several important relationships regarding the implementation of irrigation scheduling:
The acceptability of the implementation of irrigation scheduling on-farm was evaluated through a quantitative survey conducted among 134 commercial irrigation farmers (Chapter 4). It is evident from the study that socio-economic factors like the age of the farmer, experience of irrigation, and the level of education play an important role in the general willingness of a farmer to trial and perhaps on a later stage adopts or rejects irrigation scheduling methods. Farmers with relatively more experience in irrigation management tend to be more willing to rely on their own experience, knowledge, observations and intuition than on the use of objective scheduling methods.

Farmers generally perceived the efficient use of irrigation water on the farm as being the major reason for the adoption of irrigation scheduling practices on the farm, and not just the conservation of irrigation water per Se. Perceived indicators of efficient use of irrigation water on the farm include the improvement of the quality of high value crops, increasing of production yields, decreasing of energy (diesel and electricity) operational costs and improvement of the management efficiency of nitrogen and other nutrients. Accuracy, reliability, ease of implementation and affordability are some of the important technological characteristics of scheduling methods and devices that were identified by the farmers,

As farmers advance through a leaming process of evaluation, trialing and experimenting with specific irrigation scheduling methods, some will change practices and discontinue some irrigation methods, while others will change the implementation of irrigation scheduling methods from the one to the other. 57% of the respondents changed their irrigation scheduling methods since they started scheduling, while 12% of the respondents indicated the discontinuance of objective irrigation scheduling.

Significant differences in the general awareness of computer models exist between irrigators that belong to the objective irrigation-scheduling group and those from the subjective irrigation-scheduling group. Twenty nine percent of respondents that belong to the group of objective scheduling were aware of computer models, while only 5% of the respondents involved in subjective scheduling could name an irrigation scheduling model. Respondents who do not use computer-scheduling models either perceive it as being too difficult to apply on the farm (37%) or are not practically adapted for their specific circumstances (35%). Twenty five percent of the respondents indicated the lack of the necessary computer skills, which prevent them from the use of this technology on farm.

Although the majority (64%) of respondents indicated the regular evaluation of distribution uniformity of irrigation systems on the farm, many farmers are still reluctant to allocate the necessary time for this management activity. Farmers in general are positive towards the implementation of volumetric charges, however the practical implementation of such an approach raised concerns.

The majority of small-scale farmers do not perceive irrigation scheduling as an important production constraint (Chapter 5). They are preoccupied with the persisting bafflers to progress, which include lack of credit, infrastructure, and access to markets, land tenure, vandalism and theft and extension support. Many of the extensionists involved in the survey admitted that they lack the necessary knowledge and skills in irrigation management, and are consequently not in a position to render an effective service to farmers.

Extensionists and irrigation professionals often referred to the “dependency syndrome” that the majority of small-scale irrigators are suffering from. In an effort to break away

from this syndrome, farmers need to take the responsibility for and ownership of their own development. This can only be done through proper institutionalization and establishment of farmer representative bodies, such as, the Farmer Support Units found in Taung, commodity groups in Tshiombo and the block committees operating on the Bethlehem apple project. Farmers need to perceive the support from advisors and extensionists as being of temporary nature, and to develop the necessary urgency and motivation to be capacitated and empowered through the regular interaction and dialogue between farmers and extensionists.

Irrigation farmers access a variety of sources of information and belong to various information networks (Chapter 6). This study reiterated the fact that farmers do not operate in isolation but rather in a social and business situation in which the individual’s position is progressively influenced as a result of others. Different information sources were identified which irrigation farmers access and that fit the different farming styles as well as the lifecycle-stage of the farmer:
The study reveals that commercial irrigation farmers rely mainly on information from the local co-operative, private consultants, industry experts and fellow farmers, while the majority of the small-scale irrigators depend more on information from the departmental extensionists. A significant relationship exists between the number of information sources used and the implementation of the type of irrigation scheduling methods which, implies that farmers involved in the use of objective scheduling methods are more willing and prepared to seek additional information sources outside the irrigation area than the farmers involved in subjective scheduling methods.

The irrigation farmers identified desirable attributes of extensionists, consultants and advisors that play a crucial role in the uptake of information about new irrigation. Some of the attributes which were identified include the following: their credibility, integrity, technical competence, vision and focus of the farmer within the bigger picture furthermore aspects such as the understanding of the context of the farmer and his specific farming style, effective communication with the farmer, skills and knowledge to effectively interpret irrigation data into a format that is understandable to the farmer to be significant.


This project helped to quantify the scale of implementation of irrigation scheduling amongst commercial and small-scale farmers. Based on the data, it is clear that perceptions, attitudes and beliefs influence the adoption behaviour of farmers regarding the use of irrigation scheduling methods and techniques.

One of the most valuable insights derived from this project was the identification of the vast difference in perception regarding irrigation scheduHng and what it involves. Some of the farmers perceive irrigation scheduling as a means of finding solutions to their problems, and will therefore make use of the most scientific and sophisticated methods that are available, while the majority of irrigation farmers are more interested in the use of irrigation scheduling to identify ‘troubles or problems” (trouble shooting) experienced with irrigation. These farmers are therefore not always interested in absolute accuracy and sophisticated equipment, because no relative advantages could be perceived from the use of it. Therefore, it is inevitable that farmers will differ in their selection of the most appropriate scheduling method and technique, as their needs will be based on the relative technology level of operation required on the farm.