Efficiency of water supply to plants is crucial for their development, but how have techniques and products changed this?

The way growers use water in the future will be dictated by changes to abstraction laws that are expected to come into force by the early 2020s. These regulations will underpin any changes in technological developments including the ways in which growers irrigate their crops.

As a result, much of the development and future research work will have to be focused on helping growers deliver more efficient ways of being more precise with their irrigation management. This means that efficiency is key when it comes to irrigation.

According to the Fertigation Bible, a document put together by the FERTINNOWA project-aimed at providing useful information to the glasshouse sector, the combined use of fertigation with pressurised irrigation systems, such as drip or advanced sprinklers, provides numerous potential practical advantages to the grower.

Amongst the most important advantages, of combined fertigation and pressurised irrigation, are the reduction and often elimination of mechanical fertiliser application with the associated labour savings, reduced total irrigation volumes, automation of both irrigation and nutrient application, and the potential for a much more precise control over and nutrient application throughout a crop.

Currently, and increasingly in the future, horticulture in the UK will be conducted in the context of reduced water supply and the implementation of regulations to reduce environmental impacts. In addition to the practical and economic advantages of, increasing environmental, political and consumer pressure to reduce water use and the loss of nutrients to natural water bodies will make fertigation increasingly attractive to growers.

The RIGA project (www.rigaproject.eu) funded in the frame of the CIP-Eco-innovation scheme has developed new irrigation systems with anti-microbial and anti-roots (trifluralin free) functionalities to pursue the following objectives:

To reduce the algae and diseases in irrigation water, which may cause biofilm formation inside the tubes, by the addition of anti-microbial additives, according to the biocide standards: 98/8/CE and RD 1054/2002, in the extruded micro-irrigation pipes

To reduce the clogging of the drippers by roots, using additives with low toxicity as an alternative to trifluralin. Drippers will be impregnated with these additives during the manufacturing process through injection.

Managing all aspects of irrigation is crucial not only because of mounting pressure from retailers, consumers and government to reduce the environmental impacts associated with growing crops, but also to reduce fertiliser and water costs and use irrigation more intelligently to increase production, says Nick Field of CMW Horticulture.

“Protected cropping already uses water more efficiently that open field production, but even so significant volumes of water and fertilisers are lost in run-to-waste irrigation systems in glasshouses and tunnels, particularly in the rapidly expanding soft fruit sector. Yet proven technologies to safely collect and recycle irrigation drain are readily available to provide worthwhile cost savings as well as improvements in production,” he tells The Commercial Greenhouse Grower.

Worried about the disastrous effects that irrigation drain was having on the environment in the canals in the Westland, the Dutch government introduced legislation more than 20 years ago to ensure that recycling irrigation water became standard practice. The knowledge and technologies resulting from that radical step are now being used all over the world, though in the absence of legislation elsewhere and the relatively high upfront investment in drain collection and disinfection systems, means that in the UK there is still some way to go before implementation is at the same level as in the Netherlands. “Nevertheless, steadily increasing fertiliser costs and restrictions in water extraction rights mean that irrigation water recycling is now a hot item in the UK too. Little wonder, as recent Dutch data has indicated that the total cost of recycled irrigation water, taking into account both the savings in water and fertiliser costs and the capital cost of the necessary new equipment, can be around 20%,” says Mr Field.

A typical system for the recycling irrigation water in glasshouses or tunnels (called a ‘closed’ system) consists of a number of extra components in addition to the standard water storage tank for ground water and/or rainwater, fertiliser injection and pH control, drip irrigation and crop gutters. These are:

  • Drainwater collection tank
  • Sterilisation system (usually UV or pasteurisation)
  • Storage for treated water
  • Addition to the standard EC/pH control to allow accurate mixing of the recycled water containing residual fertiliser with clean water before final trimming the required target level

“There are also significant gains to be made by managing the irrigation system better – i.e. applying water at the right time and in the ideal quantity. In this respect, knowledge gained from the growing popularity of Next Generation Growing (NGG) has proved to be very useful,” he adds. “Tomato growers in particular are keen to ‘steer’ the crop either vegetatively (more growth) or generatively (more production). NGG experience has shown that applying too much water encourages excess vegetative growth, but this can be avoided by using the technology available. In fact, most specialist crop advisers agree that the plant should be kept in balance at all times and that precise irrigation is an important tool in achieving good balance,” he says.

Ideally, irrigation water should be applied in response to actual demand. In the past, demand has been somewhat crudely connected to computerised tools such as radiation sum i.e. determining irrigation need in relation to the cumulative amount of radiation measured. This is all very well up to a point, but more recent developments enable growers to anticipate irrigation demand more accurately in relation to plant physiology (in particular transpiration and photosynthesis) Priva have a number of solutions for this. Their Groscale can measure the actual uptake of water and nutrients in real time and combine this with radiation sum, drain measurement and their Root Optimizer software to estimate transpiration and therefore ensure that the plant receives the correct amount of water at exactly the right time. Time of day, season and stage of the crop are all taken into account, according to Mr Field.

“However, it’s also important not to lose sight of the basics. So weekly samples of the drain water should be taken and analysed to ensure that there is no build of potentially harmful elements such as sodium. And however sophisticated the hardware and software might be, good crop performance is very dependant on the performance of the drip system. – it’s essential that the whole system has been designed to deliver equal quantities through each individual dripper – modern protected cropping is all about achieving the same conditions for all the plants in a structure, both in terms of the temperature and humidity above the crop and the water and nutrient content in the root zone,” he says.

So, while it makes sense to think about recycling irrigation water based on costs alone, that’s not the whole story, because there are significant gains to be made in increased production. Moreover, retailers and consumers increasingly expect their fresh produce to be produced in an environmentally friendly way, and government is becoming increasingly keen to legislate to protect water supplies and the environment.

“The day when recycling irrigation water becomes a requirement is no longer in the distant future,” says Mr Field.

According to Phillip Ashton at Rotomation UK, the use of boom irrigation is continuing to increase. “For several years now, we have seen a steadily increasing demand for our boom irrigation as growers try to find areas where automation can increase efficiency and reduce labour costs. Watering and spraying crops by hand is a very time-consuming job even more so when the weather is as good as it has been this year,” he says.

“The Urbinati boom irrigation is the perfect solution. Urbinati are one of the largest suppliers of boom irrigation worldwide. The Urbinati boom irrigation can be used for watering a crop, spraying with chemicals and feeding. The growers are able to program the boom with the panel in each bay, or with a hand held remote as they walk the crop and then leave them to work automatically while they get on with other tasks,” he adds.

Growers can select the time that they want the crop to be watered, the amount of water to use, how many times to water it and select certain areas within a bay to give more or less water to, meaning that it’s not only the large-scale mono-crop growers that benefit from this system. “Small and medium sized growers can also benefit as they can put multiple crops with different requirements in one bay. The uniformity of the watering and spraying is much more accurate than what is achievable by hand or by using spray lines, which can leave some areas of the crop with too much or too little treatment,” says Mr Ashton.