Time spent in the field this irrigation season, has alerted the Netafim Field Team of the extremely poor and worsening quality of available irrigation water in certain areas. According to Dexter Neethling, Product Manager at Netafim South Africa, water quality has noticeably deteriorated this summer. This statement is based on visual assessments of filters during filter maintenance in-season. “For the first time ever, we have found various organisms growing inside a working filter, where there is no light and high pressure.” Many of these filters were assessed in the Western Cape, but the trend of declining water quality is not limited to this province.
On the topic of deteriorating water quality, there are two phenomena at work. Firstly, there is a definite trend that water quality is deteriorating year by year. This can, of course, be attributed to many factors. Willem Smit, National Sales Manager at Netafim South Africa, reports that discussions concerning the long-term decline in water quality attributes it to a long list of negative factors. Some of these factors are due to poor municipal management, some due to poor farming practices and others to climate-related matters.
Examples of a high load of physical contaminants in water caught in the discs of irrigation filters.
Reported causes of declining water quality include:
- Poorly functioning municipal sewage systems that lead to sewage ending up in rivers and dams.
- Informal settlements next to riverbanks that lead to pollution of rivers or dams, as well as groundwater.
- Increased growth of invasive plant species on water surfaces, killing the natural life in the water.
- Poor quality borehole water that is used for agricultural irrigation due to increased agricultural expansion and drought conditions. This has a negative impact on natural water resources.
- Over irrigation and the negative effect of drainage water and leaching.
- Climate change that leads to extreme weather events. Extremely high rainfall, for example, fills dams with a high concentration of organic material.
- Mining and industrial effluent water contaminating natural water resources.
The second phenomenon is one faced by irrigation farmers in many an irrigation season. As resources are used during the season, the quality of water from the relevant water source often declines as the concentration of quality-reducing properties increase.
Charl van Reenen, Agronomy Manager at Netafim South Africa, explains that the latest irrigation season experienced in the Western Cape is a very good example of this phenomenon. Charl shares his theory as possible explanation for the extremely poor water quality experienced in certain areas of the Western Cape this summer. “I believe it can be attributed to the high rainfall we had during the last winter and the very long, dry and windy summer we are now experiencing.”
“During the winter months, all the dams filled up after the high rainfall. High quantities of organic material and leached elements ended up in these dams. As the irrigation season commenced, farmers started irrigating and the rate of water extraction from dams increased as the season progressed. As the rate of water extraction increases, it can happen that the extraction rate exceeds the refilling rate of dams and reservoirs. This means that dams and reservoirs remain half-full during the hot spells in the season. These low dam levels then create ideal growing conditions for organisms such as algae, leading to higher occurrences of algae blooms and a generally higher load of organic material in the water source.” According to Van Reenen this occurrence was a major problem during the irrigation season that led to several challenges with filtration.
Water Quality and Agriculture
Successful agricultural irrigation fully depends on the adequate availability of water of a quality fit for crop irrigation. As agricultural practices become more intensive, and as pressure on water sources continue to increase, more and more questions around water quality are being raised. Water allotment concerns, the quantity and quality of water available to agriculture, and the pressure on agriculture to reduce water, can and must be debated from political, geographical, climate-related and many other perspectives. We are concerned with two key facts. Firstly, that the water available for irrigation is often of poorer quality and secondly, that farmers must be increasingly precise in the way they use water.
The greatest concerns with poor quality irrigation water are damage to the crop and soil on the one hand, and damage to the irrigation system on the other hand. In the drive towards increased use of precision irrigation, based on increasing water-scarcity and burgeoning input costs, it is important to place focus on water quality, our understanding of water quality and water quality management.
Netafim’s guidelines for filtration selection.
Understanding Water Quality
The concept of water quality concentrates on the physical, chemical, and biological properties that will determine whether it is fit for a variety of uses. In irrigation, these are factors that will determine crop suitability, irrigation system selection, the risk of emitter clogging, filtration requirements and fertigation. The composition and quality of water is complex, and a range of factors must be considered. The parameters that determine water’s suitability for irrigation are:
- pH
- Salinity
- Hardness
- Alkalinity
- The ratio of sodium, calcium, and magnesium
- The concentration of specific minerals
- Total dissolved solids
- Total suspended solids
Water Quality and Precision Irrigation
A successful farming enterprise is one of the most complex economic activities as success depends on such a wide-ranging list of factors that any attempt to compile a complete list would be futile. Irrigation is but one aspect of planning and execution and depends on a massive diversity of factors. Irrigation planning and execution will be based on data from the long list of necessary analyses done and decisions made during the holistic project planning phase. Water analysis is one of these. Very importantly, a properly designed and planned irrigation system that is managed correctly, must ensure total control of water and nutrition delivery and levels. Such a system must accommodate all the variables that impact a farming enterprise, be it soil types, climatic conditions, water quality, energy availability and much more. A holistic approach is crucial in this regard.
Farmers and industry role players must remember that no irrigation or filtration decisions can be made without sufficient knowledge of the water source and water quality. When we embark on developing an irrigation system for a new development, one of the first questions asked will be about the quality of the available water. This is why a water analysis must be done as part of the planning phase of any crop project. Furthermore, it is very important to continuously monitor water quality as quality may vary during the production period as seasons and other influencing factors change.
The irrigation industry sets important standards for water analysis and irrigation water suitability in its Irrigation Design Manual, published by the Agricultural Research Council and The Water Research Commission in cooperation with other industry bodies. It is very important, says Van Reenen, that these standards are adhered to. “A farming operation is a massive investment; therefore every necessary step must be taken in planning, execution, and management to protect this investment. Furthermore, there is a lot of pressure on farmers to uphold food security as populations continue to increase. We cannot afford failed farming operations due to steps that are skipped and standards that are ignored. Be sure to involve the necessary experts in the planning process of the irrigation system and greater crop project planning.”
Speaking of standards, says Neethling, it is very important that filtration standards are strictly adhered to when selecting an irrigation filtration system. “The poor water quality experienced this season once again proves the importance of proper filter selection and knowing what quality of water you are working with before designing your irrigation system.” Filtration requirements must be clearly communicated by the manufacturer of the irrigation system, and specifically the emitter. “It is crucial that these filter requirements are obeyed as it will ensure the longevity and optimal operation of the system. In addition, do not neglect the filtration guidelines communicated by the manufacturer of irrigation filters.
Finally, remember the importance of using quality filtration systems. Do not cut corners when planning the filtration section of an irrigation system. The success of filtration will determine the efficiency and sustainability of the entire system. Do not allow filters to cause a weak link in a well-designed system.”
Filtration and Beyond
A filter’s job is to prevent solid particles of a predetermined size and larger from entering the irrigation system. The goal is to protect the emitter and the efficiency of the entire system. As water passes through the filter, unwanted solid particles are caught in the selected filter types, be it disc, screen, or media.
Asked how filtration is influenced by deteriorating water quality, Neethling confirms that quality irrigation filters will be able to deal with the situation at hand easily; if these filters were selected according to the correct standards, installed correctly, are operated to standard and properly maintained. “Maintenance plays a crucial role in the filtration of irrigation water and becomes even more important as water quality deteriorates. Poorer water quality will mean that your filter is working harder and must backflush more often. This increases wear and tear on the filter. It is important to go through the maintenance checklist frequently and determine if any problems can be handled preventatively to ward off future problems, inefficient operation or even breakdowns. This further includes proactive and reactive maintenance actions such as doing peroxide treatments on filters to combat the organism growth in the filter.”
Beyond filtration, there are practical system design and installation aspects that can assist in managing the quality of irrigation water that enters the system. Neethling explains that installations are often encountered where the suction point is installed at the bottom of the dam. “This automatically leads to poorer water quality as particles that have settled in the dam, are sucked into the system. A solution such as a floating suction point makes a massive difference in this regard. Wind direction must also be considered in the positioning of the suction point. The suction point must be positioned on the side of the dam that the wind most commonly comes from. As the wind blows over the dam, particles are collected, if the suction point is positioned at the other end of the dam, these particles will be sucked into the irrigation system.”
Van Reenen adds that there are many aspects of poor water quality that cannot be improved with filtration. “High EC, or a high occurrence of total dissolved solids (TDS), can only be treated with reverse osmosis. This is however not a feasible solution in the agricultural industry, due to scale and cost. If the problem concerns elements such as iron and manganese, the problem can be treated with a practical solution.” He explains that the water must be exposed to oxygen as long as possible before it is used for filtration. This gives the elements the necessary time to oxidise, flocculate and settle in the dam or other water source. This can be managed by aerating the water source and/or having a settling dam on the farm. Challenges such as the high occurrence of silt can also be managed with a settling dam and giving the silt sufficient time to settle in the dam.
The management of water on the farm, of course, goes beyond what has been discussed here and includes a long list of possible actions that can be taken to solve the problem at hand. The farmer can face many challenges during the season. This may include algae blooms, increased sand loads in water and more.
Water Quality Classification
Water Quality Factors and their impact on the suitability of water for irrigation.
The tip of the iceberg as discussed here, reminds us of the importance of involving the necessary experts in the planning phase of a crop development, as well as operation and maintenance in the case of unusual problems. We are further reminded of the value of a strong irrigation industry that sets the necessary standards for excellence, leading irrigation companies making advanced technologies available, and research bodies that support the industry with increased in-depth knowledge.
If we are not proactive now to manage our water resources sustainably, dire consequences will follow. Water scarcity and declining water quality pose a risk to our social order, food and economic security and ultimately human existence. We believe that we can only take the lead in this regard as a united industry. Massive value lies in strategic partnerships among agribusinesses to ensure sustainable agriculture. We must dare to partner for success, make it happen and finally create an impact.
The ability of filter to remove solid particles from water, has little to no effect in the case of certain physical, chemical and biological factors occuring in the available water. In these cases, prefiltration and/or pre-treatment will be necessary to ensure the suitability of the water for irrigation use.
This includes conditions such as:
Physical
- High sand load greater than 2 ppm
- Very high sand load greater than 20 ppm
- High total suspended solid load (TSS) greater than 150 ppm
Biological
- Algae bloom threat
Chemical
- High iron content greater than 0.3 ppm in underground water or greater than 0.8 ppm in surface water
- High manganese content greater than 0.3 ppm in underground water or greater than 0.3 ppm in surface water
