Sub-Surface Drip Irrigation:
Factors Affecting the Efficiency and Maintenance
Report No 1189/1/05
March 2005
EXECUTIVE
SUMMARY
INTRODUCTION
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.
OBJECTIVES
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:
- Determine
the blockage potential of different types of emitters under field, as
well as laboratory conditions.
- Establish
guidelines for the choice and management of sub-surface emitters, to
prevent blockage and root intrusion.
METHODS
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.
RESULTS
New
emitters
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%.
Experimental
site
•
Untreated blocks
In the
Treflan treated blocks, the emitters showed 74%less root intrusion than
the untreated blocks. The untreated blocks were 29.3% root intruded
against the 7,5% of treated block and there was also a significant
increase of root intrusion of 505% over the 42 month period in the
untreated blocks. The impact of the clogging in the untreated blocks
was evident with the 16% decrease in emitter delivery rate and the
worsening of the coefficient of variation (CVq) from an excellent 3,04%
to a very poor 56.36'%. There was also an average 34% of the emitters
that were not functional after the 42 month testing period.
•
Treated blocks
With the
treated blocks, root intrusion could not he prevented completely and
after the 42 month period. 16% drippers were not functional (that is.
However, 27% better than the untreated blocks). The impact of the
clogged drippers was that the CV dropped from an excellent 3,04% to a
poor 32.30% which was still 43% better than the untreated blocks.
However the average emitter deliver rate stayed fairly constant,
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:
- Technology
transfer and training of irrigators with practical demonstrations.
- The
compilation of a user's guide. which describes the complete development
process of an irrigation system at farm level, as well as norms for
minimum acceptable standards for irrigation equipment and services.
- A further
investigation is recommended where the water treatment methods for
water sources with a high clogging hazard are practically and
experimentally tested.
- A
user-friendly manual regarding the maintenance of sub-surface drip
irrigation systems should be compiled for the use by irrigators.
- Development
and refinement of the installation methods and equipment to ensure
accurate placement of the laterals in the underground is recommended.
- The
establishment of the causes in variation of emitter performance.
between sub-surface and surface applications.
- Influence
of different soil types and installation depths on emitter types.
- The
influence of lateral flushing methods in terms of clogging. e.g.
individual lateral flushing versus manifold based flushing.
Copies of this report are available from the Foundation, price
£20.00, less 20% for FWR members