Sub-Surface Drip Irrigation: Factors Affecting the Efficiency and Maintenance
Report No 1189/1/05
Drip irrigation is considered as the most efficient irrigation system, but there is proof from literature that this system can also be as in-efficient as any system. due to bad water quality. mismanagement and maintenance problems. Clogging of the emitters is one of the most serious problems associated with sub-surface drip irrigation and various approaches in preventing the clogging of emitters include filtration, flushing. chemical treatment of the irrigation water and chemical treatment of the soil surrounding the dripper lines, as well as the chemical treatment of the lateral polymers. Through this project. guidelines were developed to enable irrigators with sub-surface drip irrigation systems to apply good management and maintenance schedules to enable them to adhere to the conditions of the National Water Act regarding the efficient and beneficial use of water in the public interest.
The National Water Act (Act 36 of 1998) makes provision for water to be protected, used, developed, conserved, managed and controlled in a sustainable and equitable manner to the benefit of all people in South Africa. Currently, sub-surface drip systems account for about 7 500 hectares of the total of 140 000 hectares of drip irrigation in South Africa. To assist the users to utilise their systems effectively, the research was carried out with the following objectives:
An extensive literature study on all facets that can influence the different types of emitters under field conditions was undertaken. Aspects that are addressed in this study include water quality. water treatment methods: inherent factors that effect emitter performance. filtering. system maintenance, system installation and design.
Three drip irrigation companies' drip irrigation equipment was used in the research project. The companies are Agriplas. Netafim and T-Tape. The performance of these new emitters, five models in total. was evaluated under controlled conditions in the hydro laboratory of the ARC-Institute for Agricultural Engineering.
With regard to the field evaluation, two areas in southern Africa were identified, namely the Mpumalanga Lowveld and Swaziland. In these areas, a total of five systems were identified. These systems' performance was evaluated in the field on one occasion and the farmers were contacted again after three years to obtain their experiences. Apart from the performance evaluations, data was also collected of the maintenance schedules. Water samples were taken for water quality analysis. Questionnaires. which were completed with the farmers, supplied most of the background information.
The new regular emitters' coefficient of variation (CVq) varied from an 2.1% to a 2.4% with an average of 2.2%. The pressure compensated emitters' average CVq was 3.2%.
• Untreated blocks
Conclusions and recommendations
Proper installation and maintenance are of utmost importance for the successful long-term operation of any sub-surface drip irrigation system.
It is recommended that water quality analysis be carried out to identify the potential clogging problems due to water quality. This will assist in emitter type and filter selection and to develop proper preventative measures. The use of a root growth inhibitor is also of critical importance with a sub-surface drip system to prevent root intrusion.
Details are given for solutions of specific clogging problems. choice and management of equipment, to help ensure effective water utilisation. Design principles, operation and maintenance information for best management practices. are recommended. The importance of a complete design report with details of the system's specifications. maintenance requirements and installation guidelines is emphasized.
No formal capacity building in terms of postgraduate students took place. but through the study the research team's knowledge was enhanced tremendously and a fair amount of capacity building within the industry and that of producers took place through interaction.
The following aspects need further attention: