A COMPLETE PULSE IRRIGATION GUIDE
Thousands of years ago (right up until the present day) farmers irrigated their crops using the flooding or furrow method, watering their crops every two to three weeks.
150 years ago, irrigation evolved through the introduction of sprinklers, which made it possible for farmers to irrigate at intervals of one week or one and a half weeks.
Almost 60 years ago, Netafim™ developed drip irrigation and the interval between irrigations changed yet again. At first, intervals were every week (imitating sprinkler irrigation systems), but with time and acquired knowledge, this interval was reduced to every 3 to 4 days and later every 2 to 3 days.
In recent years, with the introduction to the market of drippers with low flow rates and resistance to clogging, we can find many farmers who program their irrigation with daily frequencies or two-day intervals.
With the development of new cultivation technologies and the introduction of substrate agriculture, it began to be understood that due to the low level of water retention, daily irrigation was not viable, since much of the water (and nutrients) percolated and could not be used by the crop. This led to the development of the “pulse irrigation” concept.
With each innovation, we have seen greater efficiency in water and nutrient usage, followed by a significant improvement in results.
Pulse irrigation creates favorable conditions in a crop’s root zone, promoting better plant growth. Creating aeration in the root zone helps enhance the plant’s photosynthesis activity. Plant roots play a major role in growth under various conditions. Proper irrigation enables the creation of a favorable aerated environment.
A wide body of research and soil water distribution studies have concluded that aeration in the root zone increases crop yields. Thus, the effect of pulse irrigation on various aspects such as crop growth, soil water distribution, and root zone aeration proposed by numerous researchers are reviewed.
The first research study looking at pulse irrigation was conducted in 1974, and subsequently, many more studies followed. Karmeli and Peri (1974) suggested pulse irrigation as an irrigation technique that achieves a relatively low application rate while using an irrigation device with a higher application rate.
Pulse irrigation is composed of a series of irrigation time cycles where each cycle includes two phases, the operating phase followed by the resting or non-operative phase. As a function of the irrigation parameters and the number of cycles in the irrigation, the variables of the pulse pattern, the real irrigation time, the resting time, and the total time of a single pulse were defined.
One method determines the number of cycles in one pulse irrigation to be in the range of 5-10 or more cycles per day.
What Is Pulse Irrigation?
Pulse irrigation aims to match the application rate of the irrigation system with the absorption rates of the soil/substrate by applying water in cycles of short duration followed by a “rest” period which allows the soil/substrate/plant to absorb applied water before additional water is added.
Given that a crop requires differing amounts of water throughout the day, depending on factors such as temperature, relative humidity, radiation, wind, etc., it is important to tailor the water supply as closely as possible to these changing needs.
Pulse irrigation creates favorable conditions in a crop’s root zone, promoting better plant growth. Creating aeration in the root zone helps enhance the plant’s photosynthesis activity. Plant roots play a major role in growth under various conditions. Proper irrigation enables the creation of a favorable aerated environment.
Evapotranspiration During A Day
This graph illustrates how evapotranspiration may vary at different times of the day. Optimal irrigation would supply the precise amount of water needed at each moment:
Standard irrigation systems apply water at rates greater than can be absorbed and held by the soil and substrates, especially when we talk about soilless substrates. Substantial amounts of run-off can result, hence the need for adequate drainage.
Is There A Definition For The Time Of An Irrigation Pulse?
The maximum pulse length is not limited. It will be determined by the flow rate of the emitter in use and the specific requirements of the crop. On the other hand, it is crucial to pay close attention to the minimum irrigation duration for each irrigation pulse. As we will discuss later, the minimum pulse time must be taken into account if all emitters are to perform their function efficiently.
As a general guideline, we set the minimum duration for each irrigation pulse at two minutes. In such cases low flow drippers provide a significant advantage; since they take more time to supply the same amount, they can function with greater efficiency.
An alternative approach is to use high-flow drippers, activating them for short cycles (no less than two minutes in duration). This can also increase their resistance to clogging.
Wet Soil Volume
The most active rootlets grow better and faster in soil or substrate offering the optimal conditions, and a precise balance of air and moisture. If the farmer could ensure a 100% homogeneous volume of soil, this would create the ideal growing environment.
Hence, it is essential to use an emitter that caters to these requirements by ensuring optimal distribution and uniformity on the surface of the soil.
Crops can be found in various growing environments, such as cultivation channels, small or large pots, bags, etc. each possessing their own unique requirements.
Netafim’s product portfolio includes emitters that supply a single irrigation point (Drippers), 2 to 8 irrigation points ("Spiders"), and the innovative NetBow™, which can cover larger areas (with 4 or 8 irrigation points distributed in a circle).
When To Use Pulse Irrigation
This decision is up to the farmer to make Typically pulse irrigation will be used for greenhouse or nursery crops grown on substrates. This is due to the fact substrates have very low water retention, thus supplying small amounts of water many times a day instead of a larger amount a few times a day, will be very beneficial.
While various types of substrates are used with differing levels of water retention (the choice of the substrate ultimately depends on the farmer), each type will still retain a minimal amount of water.
The influence of substrate type over water holding capacity:
The pulse irrigation system is also used in crops (grown in pots/bags) that are cultivated in open fields (for example strawberries, and blueberries). In this case, the system is the same and the changes are the shift dimensions. In general, in open fields, the plots are much larger, and the topography can have a greater influence.
Many fruit crops (Mango, Coffee, Citrus, etc.) around the world and other crop types have used pulse irrigation to improve growing conditions and crop yields. Most of these experiences have produced very positive results.
In pulse irrigation of orchards in open fields we do not find a deficiency in the retention of water in the soil (since these crops are not cultivated on substrates), however, we do have the possibility of improving the humidity/air ratio around the most active rootlets, by keeping the soil at its peak condition at all hours of the day.
NOTE -
The pulse irrigation system requiring the most attention is the one using the CoolNet™ emitter to cool the interior of greenhouses; here, the pulses are very short in duration (one (1) second) and the frequency, depending on the climatic conditions in the zone, can reach several tens of pulses per hour.
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