The choice of drip line is a key step in setting up an irrigation system. How many times have you had drippers near the main pipe that deliver more water while those at the ends deliver less water? How many times has it happened that during harvesting, the quantities collected within the same field are not uniform? How many times, with minimum row lengths, is a 20mm drip line or even a pressure-compensating drip line used?
In this article, we will try to highlight some key concepts for choosing a drip line.
The choice of drip line must always start from the water requirements of the crop, and thus the liters per hour of the dripper, and the type of soil which can determine both the distance between one dripper and another and its flow rate.
Next, the size of the drip line is chosen, either 16mm or 20mm for rigid lines, and 16mm or 22mm if we are talking about Tape or Layflat Hose. I hear many people choose a larger drip line thinking that the drippers will deliver more water; this is completely wrong. The choice of drip line dimensions is determined based on the maximum length of the rows, and furthermore, to achieve almost homogeneous uniformity, the working pressure should be 1 bar. In this way, you will have more or less homogeneous uniformity from beginning to end.
I often hear people working at high pressures thinking they will get better delivery, but this is incorrect. Most drip line manufacturers provide tables from which the maximum achievable distances for each type of drip line can be extrapolated.
Let's take an example to better understand the concept:
Consider two different types of drip lines:
1) Light Drip Line 16mm with dripper spacing at 30cm and a flow rate of 1.5 lt/h at 1 Bar pressure;
2) Light Drip Line 16mm with dripper spacing at 30cm and a flow rate of 0.8 lt/h at 1 Bar pressure;
These two drip lines have the same performance, but simply the distance at which they can be applied to the rows changes; with the first, we will have a maximum achievable distance of 148m, while with the second, we will have a maximum distance of 180m. From this, we can see that as the dripper's flow rate increases, the maximum distance to which we can lay the drip line decreases.
If we were to work with more pressure, let's assume 2 bar, the 0.8 lt/h drippers would increase their flow rate up to 1.11 lt/h, and considering the reasoning made previously, in this case, with an increase in working pressure and thus an increase in the dripper's flow rate, the maximum achievable distance would no longer be 180m but 155m; therefore, the crops at the end of the field will receive less water and thus, likely, yield less.
The same applies to the chosen drip line dimensions, which exclusively affect the achievable distance.
To understand this other concept, let's consider two light drip lines with the same characteristics:
1) Light Drip Line 16mm, dripper spacing at 30cm, flow rate 1.5 lt/h;
2) Light Drip Line 22mm, dripper spacing at 30cm, flow rate 1.5 lt/h;
In this case, we have two drip lines with the same characteristics but different dimensions; with the 16mm drip line, as seen previously, we will have a maximum achievable distance of 148m, while with a 22mm drip line, we will have a maximum distance of about 190m.
From this example, it is clear that the tube dimension only and exclusively determines the maximum achievable distance. Therefore, when choosing a drip line, in addition to the factors described previously, the maximum distance to which the irrigation system must be extended must be considered.
The discussion changes if we talk about "pressure-compensating" drip line. In this case, the situation changes. Let's start with the type of dripper. A pressure-compensating dripper refers to a dripper that has a membrane inside that compensates for pressure increases. So in this case, the flow rate will be the same regardless of pressure increase. Considering this, a pressure-compensating drip line should be considered when greater distances are to be achieved and/or when there are particular terrain slope situations that do not allow for uniform emitter flow.