Design of Agricultural Irrigation Systems

Irrigation systems are used to replace water used by the crop’s evapotranspiration (ET), The objective of a well-designed irrigation system is to apply water (and often chemicals) in an efficient, effective, and timely manner in order to optimize crop production.

Efficiency is defined broadly here to consider economic, labor, management, and production system constraints, as well as conservation of natural resources. Another key concept, application efficiency, refers to how much of the total water (gross amount) applied is available to the crop for use.

Every type of irrigation system has an application efficiency, expressed as percentage value less then 1, that describes its efficiency in delivering applied water to the plant’s root zone. Timeliness refers to a system’s capability to deliver water (or chemicals) when required and in the amounts required to optimize crop production.

Our job at POLY DRIP is to determine the individual system components and the conditions under which they will be operated. This includes the types of components required, their sizes, method of operation, and other characteristics such as pressure ratings, resistance to chemicals to be injected, etc.

Additionally, local site-specific conditions such as elevation change, source water availability and chemistry, soil structure and infiltration rate, current crop cultural practices, and initial assessment of grower capabilities must also be factored in. Failure to consider all of these factors may result in the design of an inefficient irrigation system unsuited to the grower’s needs and abilities or even system failure.

What Do We Need To Get Started?

1. Topographic Map: Depending of the extent of the proposed project, this can be as simple as a hand drawing (not necessarily to scale) that includes all pertinent information (ex. Plant spacing, row spacing, accurate dimensions being noted of target areas, distance to water source). More complex projects require, in addition to the above, a scaled drawing of the site (we can create this drawing using GPS technology) with elevations recorded on a systematic grid pattern.
2. Water Supply Evaluation: You/We must determine “how much” is available. If a supply is presently in use or readily available, a flow curve must be generated by “flow testing” (we can walk you through this process) that will tell us exactly what volumes and pressure combinations are available. Important: knowing either value alone will not work! We must have an accurate measurement of your supply’s dynamic flow information.
3. Water Quality Evaluation: Equally important is quality (suitability) of your water for irrigation purposes. An irrigation water analysis (plus iron) from a reputable testing laboratory is a must for determining on the front end what modifications (if any) will be necessary to make your water “better” (more suitable) for irrigation. Some common problems include elevated sodium levels, high PH, high alkalinity (total carbonates), “hard” water”, the presence of algae (surface water), iron and iron bacteria. >> More
   
   Any of these can cause major problems ranging from equipment plugging to tying up available (you paid for them) nutrients that your crop needs to flourish. Excessive sodium levels can have destructive, long-term effects on soil structure. Since water sources and quality can change over time, it is important to take water samples on a somewhat regular basis. The recommended range of irrigation water pH and substrate solution pH for production depends on the crop being grown.
   
   In general, pH should range from 5.2 to 6.8 for irrigation water and 5.4 to 6.3 for substrate solution. If the pH and alkalinity are high, your water may need acid treatment prior to use on crops. The chart represents the influence of PH on the availability of essential nutrients in a soilless mix .