Availability of rain water is lower than the total water requirement for several crops, while the use of ground water is under discussion. This creates the need to either find alternative water sources, or decrease the required amount of water. This project investigated with model calculations the options to produce year-round tomatoes without the use of additional water, by decreasing transpiration, regain of transpiration water, or by using water collected by energy production via hydrogen. An increased size rain water basin up to 3000 m3/ha strongly decreases the required amount of additional water. Reflection of sun-light at higher irradiation strength than 600 W/m2 and increasing relative humidity (measures from Het Nieuwe Telen) decrease the water requirement. Measures to regain transpired water (balanced ventilation, active dehumidification and closed greenhouse) also lead to a decreased requirement for additional water. A completely closed greenhouse does not require additional water, but the energy demand for dehumidification increases. Investments in these technologies are only financially interesting when also the picture for energy is right. Hydrogen as fuel has potential, but production of water from this energy source is a by-catch and should not be the main reason for investment.

Pesticide emissions to surface water from greenhouses with crops grown on substrates in open or closed systems may be significant. It is important, therefore, to test models such as the Greenhouse Emission Model (GEM), which was developed to assess these emissions as part of the Dutch authorization procedure for use of plant protection products in greenhouses. GEM was tested using an experiment in which imidacloprid and pymetrozine were applied via drip irrigation to stone wool mats growing sweet pepper. The irrigation system in such greenhouses consists of a mixing tank to prepare the nutrient solution and a series of tanks to treat and recirculate the drain water back to the mixing tank. Emissions may occur because (part of) this recirculation water may be discharged or leached to the surface water. GEM assumes that all tanks are perfectly mixed. GEM further assumes that the water in these mats is perfectly mixed and that the pesticide behavior can be simulated by assuming one perfectly mixed reservoir. The model predicted breakthrough of both pesticides out of the mats earlier than measured, and the measured maximum concentrations were approximately two times lower than predicted. We considered a series of possible causes, including a smaller water volume in the mats, a higher plant uptake factor, and sorption to the stone wool. The model performance improved by representing the mats as a sequence of two equally large tanks with plant uptake restricted to the first tank. We recommend to study the solute transport process and the distribution of plant roots in the mats in more detail to further underpin the hypothesis used and improve the model. After this first validation, the GEM model might also be used in other countries to forecast emissions of PPPs to surface water.

A soilless culture system (SCS) is a technique used for plant production that has recently become increasingly popular [...]

In this study a greenhouse has been designed for optimal production in the coastal area close to Algiers. Data showed that there are two main options for optimal production of tomatoes and similar products like cucumber. A choice can be made for winter production in a heated greenhouse or summer production with air-conditioning and CO2 injection. The estimated production is fairly similar for both seasons but the costs for summer production are 30% higher. The investment costs for the summer production scenario are higher but running costs are lower, since in summer less additional water and energy are needed for the production. To reduce the use of water and related costs we recommend to grow on substrate, re-circulate the water and collect the rainwater in a water basin. The growth of salad or strawberries might be an alternative for cultivation in early winter or early spring in greenhouses without heating.

In the cultivation of amaryllis (Hippeastrum) every year about 350 m3/ha of rinsing water is released during the regeneration (flushing) of the substrate during crop interchange. This rinsing water contains on average 75 kg N/ha/year and is therewith higher than current emission standards for nitrogen. Three solution approaches were studied to decrease the emitted amount of nitrogen: 1. Prevention/decrease emission of rinsing water; 2. Reuse of rinsing water during cultivation; 3. Decrease nitrogen in rinsing water. Most important bottlenecks are protection against bulb scale mite, the low uptake of sodium by the crop and the low tolerance towards sodium in the nutrient solution. By endless reuse of the substrate and zero liquid discharge during cultivation, the only discharge of sodium is via the rinsing water after the cultivation cycle. Replacement of substrate is expensive and not sustainable. Capture of rinsing water and reuse during cultivation after selective removal of sodium can only be feasible at the middle long term if installations for selective removal of sodium are optimized and cheaper. Cascading of rinsing water only decreases the amount of water discharged, not the amount of nitrogen (load). Rinsing during cultivation increases the risks for plant health. Redesign of the cultivation system with a smaller substrate volume and bulb singulation (every bulb in a separate root compartment, pot) can be a solution for the longer term.

Cleansing and disinfection products are applied to clean pipes in soilless growing systems. These product may potentially inhibit growth. It was investigated which test method is most suitable (effect, reproducibility, expenses, costs). The phytotox testing method appeared to be best. A number of products (chlorine products, other cleansing products, hydrogen peroxide with stabilizer, ozone) were tested in commercially used concentrations and lower ones if needed to avoid growth inhibition. Bleach and cleansing products cause large inhibition and should be avoided to enter the circulating water flow. Disinfection products don’t give growth inhibition in concentrations lower as commercially advised. Ozone did not give inhibition or stimulation of growth. Within the project a few products are tested. In future others can be tested on demand. It has not been investigated if the product has its claimed effect.

In the Netherlands recirculation of the nutrient solution is statutory required in soilless culture systems. The goal is to achieve a zero liquid discharge, it means no solution with fertilizers, pesticides and/or cleansing products are allowed to be discharged to surface or ground water or the sewage system. It also means that products added to the system should be taken up by the plants or broken down. The objectives of this research were to investigate i) if frequently used cleansing products accumulate in the nutrient solution and may harm growth of the plants, and ii) if the used concentrations of cleansing products were able to eliminate pathogens in the circulating nutrient solution. Gerbera was used as a pilot crop. The research was divided in four steps. As a first step growers and consultants were inquired (1) about the use of cleansing products additional to the traditional disinfection methods. It was followed by laboratory experiments (2) to test a few cleansing products in various concentrations against plant pathogens. A next step was a greenhouse experiment in which gerbera plants were infected with Fusarium oxysporum (3). Finally sampling at commercial farms (4) was performed to investigate if accumulation did really appear. The inquiry showed that nearly all growers were using, additional to UV or heat treatment for disinfection, cleansing products such as hydrogen peroxide, bleach, chlorine dioxide or ECA water. They were mainly used for cleaning of the pipework. From the laboratory experiments it appeared that the concentration to eliminate the pathogen was much higher as the concentration used to clean the pipe work. In the greenhouse experiment two cleansing products (hydrogen peroxide, chlorine dioxide) were added in five concentrations with two replicates and compared with a control. All treatments were infested with F. oxysporum, except for the control. During the short growing cycle there were no symptoms of F. oxysporum at the plants. However, it appeared that the higher the concentration of added cleansing products the worse the state of the plants, decreasing plant growth. Additionally, bleach showed high sodium concentrations, while the iron chelate was broken down by the hydrogen peroxide. Looking to the cleansing products at commercial farms hardly any accumulation could be measured. It was concluded that the low concentrations applied in commercial practice do not accumulate to toxic levels while a side effect of cleansing products against pathogens cannot be expected.

According to the EU Water Framework Directive the emission of nutrients and plant protection products to water bodies should be reduced dramatically. In practice threshold values for water bodies are exceeded due to leakages, discharges and unexpected problems from greenhouse facilities. Nitrate eutrophicates surface water. In the Netherlands nutrient solution recirculation in soilless cultivation is obliged and discharge is regulated to yearly crop specific nitrogen concentrations. However, water authorities still measure exceedances in surface water, leading to an interest real-time measurement of nitrogen or nitrate to have data faster available. Adjustments in nutrient recipes in greenhouses are based on a 7-14 days analysis of drainwater by sending it to a laboratory. This practice is suboptimal since the loss in nutrients is higher than necessary and it might even reduce crop development. Besides it is time consuming and often expensive. In areas where the results of the laboratory are not fast available, a nitrate sensor may even play an important role in creating the right solution for the plants. With a real-time measuring nitrate sensor, it is possible to fertigate more accurately which increases the harvest/quality of the crop with a lower environmental footprint. Besides, such a nitrate sensor has also a large scientific value since the dynamic nitrate uptake by the crop can be studied at a scale of minutes instead of days. A start has been made to analyse available methods for measuring nitrate, and in this study we will present an innovative optical fibre based nitrate sensor using an algorithm which has been tested in a greenhouse setting at field conditions. This UV-VIS spectroscopy system in combination with the developed model can be used for online monitoring of nitrate concentrations in hydroponic solutions, without the use of any reagents or need for recalibration, to enhance the efficiency and safety of greenhouse systems with respect to water reuse and recycling.

In hydroponic cultivation, monitoring and quantification of nutrients is of paramount importance. Precision agriculture has an urgent need for measuring fertilization and plant nutrient uptake. Reliable, robust and accurate sensors for measuring nitrogen (N), phosphorus (P) and potassium (K) are regarded as critical in this process. It is vital to understand nutrients’ interference; thusly, a Hoagland fertilizer solution-based orthogonal experimental design was deployed. Concentration ranges were varied in a target analyte-independent style, as follows: [N] = [103.17–554.85] ppm; [P] = [15.06–515.35] ppm; [K] = [113.78–516.45] ppm, by dilution from individual stock solutions. Quantitative results for N and K, and qualitative results for P were obtained.

In the production of cut flowers and pot plants there are slow developments towards closed growing systems with recirculation of the surplus nutrient solution. In some countries, such as in The Netherlands, legislation to reduce discharges is a steering factor, as well as the advantages of a disease free start, higher potential production and quality. Crops such as rose and gerbera with less than 10 plants per m2 are now grown in completely closed growing systems and are on their way towards zero liquid discharge. Crops such as freesia, amaryllis and chrysanthemum, are still experimenting with soilless culture systems. Phalaenopsis is the most important pot plant grown in The Netherlands and is on the way towards a closed growing system. This chapter discusses the progress made, key challenges and how they are being overcome.

Growers worldwide often lack means to find the economically soundest order of investing. Authorities face similar problems when deciding which developments to stimulate. For Dutch greenhouse horticulture, models for production, climate, revenue and costs, allow selection of an optimal investment order. This approach was widened into "Adaptive Greenhouse Methodology" which allows evaluation of worldwide climate and greenhouse technology combinations. However, running the models requires expert skills. Our goal was to deliver a simplified software tool, which would allow horticultural suppliers, researchers and growers to autonomously rank alternative investments, for a specific combination of region, greenhouse design and crop. The Investment Order Tool was developed in cooperation with selected horticultural supply companies for the regions Almeria in Spain and the Jordan Valley. In Spain, a flat roofed Parral type greenhouse was compared to an industrial multi-span greenhouse. In Jordan a single tunnel greenhouse was compared to an industrial multi-span greenhouse with passive crop based cooling. The Investment Order Tool uses a one-time run of the Adaptive Greenhouse Methodology based on local information. This data set allows further off-line calculations. All adaptions in greenhouse construction and cultivation system are defined as relative production changes from the local standard. The adaptations are provided with their specific costs and benefits. The investments compared include: reverse osmosis; substrates; nutrient dosing; climate-adapted cultivars; recirculation of drainage water; ventilation capacity; shading screens and thermal screens. The Investment Order Tool informed growers on the investment order with the highest return on investment and the investment order with the lowest demand for capital. Nursery specificity was realized by permitting user defined yield and market price level per month and by defining a first and second class for product quality. It is hoped the Investment Order Tool encourages growers and local authorities to base investment decisions on increasingly solid knowledge.

Greenhouses are expanding fast in arid and semi-arid regions, among other reasons, because of the water savings that can be realized compared to open field cultivation. However, it is difficult for growers to recognize the optimum greenhouse design. Many competing aspects must be weighed against each other such as the structure, the cover and the climate control equipment. Obviously, the optimum design must be tailored for each specific crop and growing cycle and availability of resources (land, water, energy, labor, etc.). Simulation models can assist in this process, saving time and money. Wageningen University & Research, BU Greenhouse Horticulture has developed the Adaptive Greenhouse Methodology. It combines the use of greenhouse climate and resources simulation models, with crop growth and economic models, to solve the problem of designing the optimum greenhouse for each specific scenario in the world. In the present work we present the results of the application of this methodology to the specific case of the production of greenhouse soilless tomato in two regions in Jordan in the mid tech range: the highlands and the Jordan Valley. Results show that different mid tech designs could potentially provide yield levels of up to 35 and 27 kg m-2 in the Highlands and the Jordan Valley, respectively. The final design is similar in the two locations.

To achieve a zero emission of water with nutrients and plant protection products, recirculation of water in the greenhouse system is obligatory and discharge should be minimized. In this study it was investigated if applied cleaning products may accumulate to harmful concentrations and hamper plant growth. An enquiry amongst growers gave insights in the use of various products. This enquiry showed that most products are used in low concentrations to remove biofilm from piping. Laboratory tests have been executed to investigate if a side effect could be seen to eliminate pathogens. It appeared that the applied, low, concentrations to clean the pipework had no side effect in eliminating of pathogens. In a greenhouse experiment it appeared that sodium, chloride and chlorate can potentially accumulate, while chelates are partly broken down. Measurements at commercial gerbera farms showed that no accumulation took place to harmful concentrations.

Agriculture in Lebanon consumes most of the country's fresh water resources. Officials, organizations and related stakeholders mostly approve a water consumption use by irrigation of about 60 to 75% of the renewable and non-renewable water resources. Protected cultivation is still practiced largely in simple individual tunnels. Water use efficiency is very low, but protected cultivation and soilless cultivation may increase it. In this project first steps are made to demonstrate to Lebanese growers how to improve traditional tunnel cultivation and to introduce new techniques. The adaptive greenhouse concept was followed here: analysis of local climate, analysis of growth in present tunnels and modeling effects of new growing techniques in tunnels together with simple innovations: sidewall ventilation, insect netting, bumblebees for pollination, soilless cultivation, high wire cultivation, steering growth on climate and passive heating. Finally, four greenhouse tunnels were built at the LARI site in Tal Amara, two improved ones and two traditional. In both types there was one tunnel with soil and one with soilless cultivation. Two short crops (tomato in spring/summer; cucumber in autumn) gave preliminary indications about the potentials in relation to yield and quality of produce. An improved water use efficiency could not yet be achieved. This first year of cultivation was a year of learning for all parties involved, both technically and cultivation level. Growers and technicians visited the site several times to get informed about the different techniques.

Changing from low- to mid- and high-tech greenhouses and from soil to soilless cultivation require adapted cultivation measures for tomato and sweet pepper. Major differences are the automated regulation of ventilation (opening of windows), radiation (using screens or whitewash), fertigation and irrigation, a high wire plant training system and plant propagation in substrate. All topics are extensively described. A checklist for the grower facing all these new and unknown phenomena is added to minimize the chance on mistakes.

Surface waters in Dutch agricultural and horticultural areas do not meet the requirements of the European Water Framework Directive for good chemical and ecological water quality. Emission of nutrients and plant protection products (PPPs) from agricultural activity contributes to this. The Dutch government issued emission standards for nitrogen, evolving to zero discharge in 2027 for all greenhouse crops. However, to reduce the leaching of PPPs to surface and ground waters on the short-term, additional legislation came into force January 1, 2018. This regulation obliges Dutch growers to use purification equipment for the removal of 95% plant protection products (PPPs) when discharging drain water to sewage or surface water. This stimulates growers to look critically at opportunities to reduce the amount of discharge water, thus lowering the investment and operational costs of purification equipment. In this article, we describe the implementation of the obligated purification for different types of cultivation systems, including the development of an approval protocol for purification equipment. Depending on the amount of discharged water and company size, growers will choose between either applying an installation at the company level or cleaning the water cooperatively with a group of locally located companies. Another option, especially suitable for infrequent small amounts of discharge water, is rental of a mobile purification unit. In any of these three cases, the growers must use an approved installation. The installation and the applied technical specifications (for example ozone dosage) need to be tested with so-called Standardised Water following a strict protocol. An installation is approved by a governmental committee if tested correctly with a purification efficacy of 95% for each of the 11 active ingredients of PPPs in Standardised Water.

In 2018 a new greenhouse for low energy demand crops was developed and constructed. It consisted of an air bubble fi lm cover on a greenhouse with continuous roof ventilation and included a screen. Goal is to reduce the energy consumption and to improve production. Raspberry was chosen as pilot crop for a group of crops which might be grown in a greenhouse in future. In 2019 two cultivations took place with raspberry cultivar Diamond Jubilee. The fi rst year goals were achieved, there was a low energy use (5.7 m3/m2 compared to an expected 5 - 8 m3/m2), a high production (7.1 kg/m2 compared to an expected 6 kg/m2) and a good cultivation in containers. Plant density has to be optimized and varied between 1.8 and 2.2 canes/m2. Economically the greenhouse is cheaper as glass but especially the high ventilation capacity offers a high potential.

Zero liquid discharge (ZLD) should be the future for soilless production. In The Netherlands emission of nutrients and plant protection products to surface water is the main reason to investigate the potentials of cultivation methods without any discharge. In a few other countries water pollution issues is the main motive, but for a majority water shortage and the increasing competition for water of an acceptable quality is reason for the growing need for water efficient cultivation methods. During four years ZLD was investigated for cucumber (2014, 2017) and sweet pepper (2015, 2016). The primary goal was to reuse all drain water, while maintaining a similar yield and quality as in the traditional growing method with regular discharges. To achieve ZLD all practical reasons for growers to discharge the nutrient solution had to be anticipated before. In the ZLD trials technical and strategic solutions were jointly tested and further developed into an adapted growing strategy without any discharge. A number of factors could be mentioned as main reasons for discharge: sodium in the supply water, discharge of filter rinsing water, unbalances in the nutrient solution, no recirculation of the drainwater in the beginning of the cultivation, no disinfection equipment, too low drain storage capacity, appearance of calamities (technical failures) and the amount of remnant nutrient solution left in slabs and tanks at the end of the cultivation. The next step was demonstrating the technical and strategic solutions in a cultivation. In 2014 and 2015 we showed that ZLD-cultivation in stone wool substrate was possible without loss of yield and quality. In 2016 and 2017 the more challenging coir substrate was used to investigate the influence of buffering and sodium accumulation. It appeared that ZLD was possible without loss of production or quality. Appearing problems were more in the field of management of water flows than lack of technical equipment. Special care should come for technical failures of equipment, mostly not enough storage capacity is available.