The use of irrigation water as a vehicle for fertilising crops has been a common practice in intensive farming for decades, and more recently it has also crept into extensive farming. However, it wasn’t until the last few years that it began being implemented in green spaces, although here it has a different set of benefits related to savings on fertiliser and labour, and improvements in homogeneity, regularity and control when growing vegetables.
Although fertigation meets the basic need of providing crops with fertilisers , it also allows us to control a range of chemical parameters related to the irrigation water, such as its electrical conductivity (EC, which is linked to its concentration of salt) and its pH. The use of reusable water and localised irrigation systems has shone a light on previously unknown virtues of the system. As such, a fertigation system also allows us to add phytochemicals (chemigation) and products for treating water (disinfectants such as chlorine and peroxides, among others).
Advantages of fertigation
Unlike in farming, the goal of fertilisation in green spaces is not to reap a larger harvest. Conversely, landscape gardeners are negatively impacted by excessive vigour, which translates to increased expenditure on cutting and pruning work, as well as excessive growth that fosters the transmission of parasites and diseases. Therefore, its goal is to bring about sustained and controlled growth that reduces costs and risks. The importance, then, is placed on ornamental performance and financial goals. Just as the cost of fertiliser in classic systems is linked to the number of applications, with fertigation these costs can even drop as we increase the frequency of applications, as the devices work automatically and they are smaller in size. This allows us to fertigate in each irrigation cycle, achieving a consistent concentration of nutrients throughout the season, which results in greater balance in the availability of nutrients over time without experiencing peaks and troughs in soil fertility.
Greater availability of nutrients
Fertigation helps us increase the availability of the nutrients that we supply to the plants, setting pH levels that are optimised to their absorption and providing an immediate response to fertilisation by applying ready-dissolved nutrients to the soil. We can also see how the nutrients are better absorbed by leaves when applied via sprinklers or diffusers.
On an environmental level, it is also worth noting that it reduces the amount of fertiliser that is lost due to runoff or washing, as it works with solutions that are extremely dissolved. This implies a reduced environmental impact as it causes less contamination of surface water and underground aquifers, all while saving on the amount of fertiliser used, in addition to decreased levels of pollution resulting from its manufacture and distribution.
Different formulae can be created quickly and efficiently in order to adapt to the season, the plants’ development and any issues that may have arisen. Therefore, it is possible, for example, to provide more nutrients that are easily dissolved after a rainfall or less if intense rainfall is expected, while we can also correct growth patterns by reducing the supply of a particular nutrient. It may prove especially useful when using recycled water with a high sodium content, as it allows us to add more calcium and magnesium, which help reduce the sodium absorption ratio (SAR).
We can see, then, that the current course of development of irrigation in green spaces – where localised (and even underground) irrigation and progressively worse water conditions (high salinity, conductivity, hardness and pH) are increasingly common – is linked to the treatment of this water, making it fit for purpose via fertigation.
Fertigation equipment in green spaces
With everything from Venturi injectors to automatic fertigation control, and not forgetting dosing pumps with advanced controls, there is a wide range of products that we can use to inject fertilisers into our irrigation network. However, given that a single installation can have parts in varying conditions, particularly important for those related to the pressure and flow rate of the different sectors of the network, or that different parts may be in use at the same time, we recommend using constant flow rate or proportional dosing pumps, thus avoiding as much as possible the use of devices whose performance may not be sufficient if the pressure conditions were to change, such as (non-proportional) Venturi injectors or hydraulic dosing pumps, even though these play an important role in horticulture.
One of the simplest devices is the proportional hydraulic dosing pump. With this type of injector, the energy absorbed by the pump from the loss of pressure depends on the flow rate passing through it and the pressure of the network at the point where the dosing pump is located, so that the greater the pressure and flow rate, the greater the head loss, even though the losses are lower than those generated by a Venturi injector with a similar flow rate.
Proportional hydraulic dosing pumps can be installed in line or in a bypass, and the exact configuration will depend on the circumstances surrounding the installation. With in-line installation, all of the water in the entire irrigation system flows through the dosing pump’s hydraulic motor. This way we reap all the benefits of properly regulated proportional dosing, which offers us plenty of possibilities in terms of percentages, with there being dosing pumps with regulation from 0.025% up to 10%. These devices are easy to install and the head loss is moderate.
The main drawbacks of this system are the head loss they generate and the flow rate limitations when installed in line, as some models have a maximum capacity of 20,000 l/h. However, the cost of these devices soars if we want a capacity of greater than 10,000 l/h.
When proportional hydraulic dosing pumps are installed in a bypass, only a part of the water flow is accessed by the pump. This allows us to inject large flows at a reduced cost and makes them easy to install, even with large flow rates. However, they do result in a head loss that affects the water in the entire network (and not just the water that passes through the hydraulic motor), and we lose this dosing pump’s main advantage, as we are unable to guarantee proportional dosing given that we cannot control which part of the water flows through which part of the bypass.
Active injection devices, however, allow us to forget all about the impact of changes to network flow rate or pressure. Many active fertiliser injection systems use electric motors, meaning that they can accurately control the injection. Nowadays, two main types of injection pumps are used in these systems: piston pumps and diaphragm pumps, which are able to accurately control the injection by adjusting the movement of the piston or diaphragm and the frequency of the injections.
Automated fertigation control
If we establish optimal pH levels, we increase the system’s efficiency, boosting nutrient uptake, preventing fertilisers or salts dissolved in water from precipitating and helping keep the irrigation system in good condition.
Balanced solutions can be dosed by electronically controlling the fertigation, which allows us to optimise concentrations of and ratios between nutrients, create balanced solutions and even alter concentrations and balances for each valve, which can be used to manage specific types of species. In fact, in gardening irrigation systems, it is common for some valves (or sectors) to be used for sectors with grass, while others are used for parterres with vivacious plants, hedges or trees, and we can decide on the duration, concentration and even pH of the solution that we are going to use to irrigate each of these sectors based on our intended objectives for them.
We can now buy electronic dosing systems that are capable of simultaneously applying different fertilisers in proportion to the volume of the irrigation water, while controlling the conductivity and pH at the same time by injecting an acid into the line. These systems, which automatically control the frequency and volume of the injection, adapt the dose to a wide range of flow rates, up to a maximum of 800 m/h, and to pressures of up to 15 bar, which meet all nutritional needs for everything from small gardens to large sports fields.
We can find electronic proportional systems in large installations, which work with highly variable flow rates and where the concepts of pre- and post-irrigation are difficult to apply, achieving different proportions and pH levels depending on the location or moment when the fertiliser or corrector is applied by working in coordination with the irrigation programming system. However, the benefits of fertigation can also be applied to smaller installations that use unsophisticated yet reliable systems through the use of electromagnetic dosing pumps with a low flow rate, which can be activated by the network’s water flow and by fertigation programmers, which allows us to make the most of our small patch of land at a much lower cost, extending the life of our valves and emitters and helping reduce the costs associated with maintenance and ornamental improvements.
