There are major changes afoot in Saudi Arabia. One key strategy is to convert the country from an economy that is dependent on oil to one with a broader basis.
The aim is to increase incomes and economic and social development and to create more jobs for the relatively young population by making agricultural production more sustainable. To begin with, the focus will be on improving the efficiency of water and energy usage and reducing the use of pesticides in the production of fruit, vegetables and dates by applying modern technology and providing training for local growers. At present, 80 percent of the available water in the country goes to agriculture and horticulture.
Partly due to the success of the Estimadah project, in which our Greenhouse Horticulture business unit is working on improving water efficiency in greenhouses, the Saudi Ministry of the Environment, Water and Agriculture has asked us to carry out a major four-year project with demo farms set up at existing operations all over the country. We will be responsible for setting up the project as well as for data collection, analysis and communication.
Raspberries and blackberries are relatively new crops under glass, so knowledge in this area is as yet in very short supply. Woody small fruit growers therefore still have a lot of questions on aspects such as the best climate, energy-saving and the ideal light levels to use.
But more information on the effects of assimilation lighting, light colours, optimum light distribution in the canopy, storage of plant material, substrates and nutrition would also be very welcome. To meet this need, we are launching an in-depth study in September. In it we will be growing two varieties of each crop under diffuse and clear glass.
The crops will be lit using top lighting and interlighting with LEDs. For the interlighting, three different light colours will be compared with each other. Among other things, we will be measuring photosynthesis under different light and CO2 levels. We will also be studying the distribution of assimilates to the generative and vegetative parts of the plant. The influence of the lighting treatments on the plants’ resistance to pests and diseases and the effects on the microorganisms around the roots will also be determined. We will of course also be looking at production, quality and energy usage.
One of the main tasks of the Smart Materials project was completed last year. Greenhouse simulation models were used to explore the potential effect of smart covering materials with switchable optical filters on microclimate, use of resources and crop performance.
Until recently, the only way to modify the amount and quality of light reaching the crop in a greenhouse was to use temporary coatings or screens. Three main groups of filters were identified and simulated: filters reflecting both PAR and NIR radiation, filters selectively reflecting only the NIR part, and filters reflecting the FIR spectrum.
Different climate regions and types of coverings were analysed to factor in a range of scenarios. The results highlight a significant potential improvement in microclimate and yield associated with the use of switchable optical filters for all the analysed climates, even if the optical properties are less than ideal.
For some of the simulated filters there are other alternatives available which perform equally well (thermal/energy saving screens). Further research is needed to analyse the technical and economic feasibility of these theoretical filters.
Viruses are among the smallest pathogens infecting other living organisms. Plants are also susceptible to a large number of viruses that can cause serious diseases.
Viruses consist solely of a piece of genetic material (RNA or DNA) and a protein coat, or capsid. They therefore cannot survive independently and need other organisms to multiply and spread. Plant viruses replicate in plant cells and use insects (especially aphids and whitefly), mites, nematodes, soil fungi and even humans and our tools to move from one host to another. There are specific interactions between viruses and their vectors. Cucumber mosaic virus (CMV) is transmitted by aphids, for example, and tomato spotted wilt virus (TSWV) by thrips.
Therefore, controlling viral diseases not only entails starting with clean and certified plant material but also involves monitoring and controlling the transmitters (vectors) of plant viruses. Vigilance is essential, because new viral diseases can appear in plants when changes in populations of viruses and their vectors give rise to new situations.
Predatory mites are the most important natural enemies used for biological pest control in greenhouse horticulture.
Many of these predatory mites are mass-reared on prey mites that feed on fungi growing on bran. In collaboration with companies in the Netherlands and Spain, we investigated whether predatory mites could also be reared directly with artificial diets based on insect proteins. High-quality proteins from sources such as black soldier flies and mealworms were found to be suitable food sources.
However, formulating these semi-liquid diets wasn’t easy as the predatory mites were unable to consume diets offered in microcapsules. The next step, therefore, was to focus on diets for prey mites. Several species of prey mites were reared on diets with different nutritional values. When administered on plants, the prey mites reared on high-protein diets produced predatory mite populations five times the size of those feeding on bran-reared prey.
These nutritious prey mites can therefore enhance pest control by quickly boosting populations of predatory mites.
The Sweeper consortium was invited to hold the first live demonstration of its new sweet pepper harvesting robot at the De Tuindershoek greenhouse horticulture firm in IJsselmuiden. The so-called ‘Sweeper robot’ is the world’s first harvesting robot for sweet peppers to be demonstrated in a commercial greenhouse. An audience of over 40 interested parties watched the harvesting robot pick its first commercially-grown sweet peppers.
The Sweeper robot was designed to harvest sweet peppers in a cultivation system based on single plant stalks in a row, a crop without clusters and in little foliage near the fruits.
In earlier test set-ups in a commercial greenhouse with a V-type double-row cultivation system the harvesting robot achieved a harvesting percentage of 62%. Based on these test results, the Sweeper consortium expects to be able to bring the commercial sweet pepper harvesting robot to the market in about four or five years.
Further research required
Until then, further research will be needed to enable the robots to work faster and achieve a higher success percentage. Additionally, commercially viable cultivation systems must be developed that are more suitable to the robotic harvesting of crops. The test and research results are not only suitable for the automatic harvesting of sweet peppers; the data can also be used to robotise the harvesting of other crops.
International research partnership
Sweeper is a partnership between Wageningen University & Research (WUR), sweet pepper farm De Tuindershoek BV, the Umea University in Sweden, the Ben-Gurion University in Israel, the Research Station for Vegetable Cultivation and Bogaerts Greenhouse Logistics in Belgium. The study receives financial support from the EU’s Horizon 2020 programme and is also funded by the Dutch Horticulture and Propagation Materials Top Sector.
Successor of CROPS
The Sweeper robot is the successor of CROPS (Clever Robots for Crops), an EU project launched by WUR, in which WUR and the other participants developed a robot that can make a distinction between a sweet pepper plant’s fruit, leaves, stalks and main stems. As a result, the robot can harvest sweet peppers without damaging the fruit, leaves, stalks or stems.
Source and photo: www.sweeper-robot.eu. Video: Wageningen UR greenhouse horticulture.
The Plantalyzer is a unique tool for accurately estimating vine tomato crops. It counts the number of vine tomatoes on the plant in the greenhouse and provides reliable information for an accurate estimate of the harvest.
The system was developed in close collaboration with Wageningen University & Research. It uses special cameras to measure the bottom two to three leaf-free trusses. The system maps the trusses per stem, the number of fruits per truss and the colour of each fruit. The Plantalyzer thus provides insight into numbers and colour stages. Linking this information to practical greenhouse data produces an accurate estimate of the harvest.
The tool is able to measure large areas of tomatoes, counting both quantity and maturity. The system does that tirelessly every day, always in exactly the same way, and works fully automatically.
Stand number: 11.115
A range of chemicals are used to keep greenhouse pipework clean. They include bleach, hydrogen peroxide, chlorine dioxide and ECA water.
Growers are concerned that the use of these substances could have side-effects. With the regulations on discharging becoming ever tighter, residues could accumulate in concentrations that could be harmful to the plant, and they may even have side-effects on pathogens. This issue was investigated last year as part of the “Prevention and Control of Leaching from Greenhouses“ PPP. It started with a survey conducted among a number of gerbera growers, followed by laboratory trials in which various concentrations of products were applied to a live fungus on a Petri dish. Then two products were used in a gerbera trial to investigate whether accumulation occurred. The initial results are encouraging: for the first time, we are gaining an understanding of the behaviour of these products in comparable conditions.
In 2018 we will be seeking additional funding from grower cooperatives and product suppliers so that we can test more products. More knowledge on this subject is urgently needed, not just for gerbera but also for other greenhouse crops.
Photosynthesis takes place in the leaves but the products that are made – sugars – have to be transferred to other parts of the plant. This is carried out by the phloem transport system. The temperature of the organs that receive the sugars plays an important role in the speed of transportation and hence the useful conversion of sugars. Disruption in the relationship between production and their further processing can lead to problems.
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The shift towards closed growing systems is forcing growers to take a critical look at their sodium figures. Would higher sodium levels affect the crop? And could sodium be “harvested” and removed from the system that way? The answer to both questions is “yes”, initial Dutch research results indicate.
When the sodium concentration in drain water rises above 5 mmol/l, almost every grower will discharge the water. Ideas on acceptable concentrations are based loosely on the results of research carried out in the past, in which a very generous safety margin was applied. But nowadays we live in different times: zero-emission growing is getting ever closer and discharging drain water costs money. So now is a good time to take another look at the margins within which you can work safely. This was the background to the sodium study carried out by Wageningen University & Research in the Netherlands as part of the “Prevention and Control of Leaching from Greenhouses” research programme.
Sodium is not an essential element for the plant and can be toxic in high concentrations. It also competes with the uptake of potassium and calcium. Too much sodium in the irrigation water can cause blossom-end rot in fruiting vegetables by inhibiting calcium uptake.
“There are three input streams,” project manager Wim Voogt explains. “Sodium can enter in the water, with fertilisers and in some organic substrates such as coco. The crop absorbs some of it and the rest leaches out into the drain water. Some crops, such as cucumber, tomato, aster, carnation and gerbera, absorb a lot of sodium. Others absorb barely any, such as rose, orchid and sweet pepper.”
Drain water containing sodium can be reused providing the concentration is not too high. Voogt: “That begs the questions: Are the standards from the past still relevant today? And can you ‘teach’ the plant to handle salt?” The EC of the recirculating water partly stems from the nutrient solution and partly from ballast salts. “With tomato and cucumber, you need an EC of at least 1-1.7 mS/cm for the nutrient supply. But growers often work with an EC of 2.5-3, or even more for tomatoes. So there’s leeway for extra salt there,” he says.
To explore the limits, he first carried out a trial with sweet pepper, with tomato following this year. Sodium was added to the basic nutrient solution in increments rising from 2 to 10 mmol/l (10 mmol is extremely high and is regarded as unacceptable in practice).
But the surprising result was that the sweet peppers performed well even at the highest level (see figures 1 and 2). Voogt: “The yield per square metre, the number of fruits and the fruit weight remained the same at all concentrations. Because we anticipated problems with calcium uptake at high Na concentrations, with the associated higher risk of blossom-end rot, we increased the calcium level in the nutrient solution in some of the treatments. But even that turned out to be unnecessary. So our conclusion was that it is possible to grow with higher sodium levels. The Supervisory Committee for Research followed the study with a critical eye but didn’t see any problems. This year we will be looking at tomato with even more extreme values, up to 15 mmol/l.”
The second part of the research project looks at the question of whether you can “harvest” sodium. If you can store the element safely in the crop, it will ultimately end up in the composter and you will be rid of it. The more you can remove this way, the less you will need to discharge.
The plant can take up more Na if you allow the concentration to rise at the roots, but this inhibits nutrient uptake. So you need a workaround: a split-root system (SRS) (see diagram). One half of the roots gets the regular nutrient solution and the other half gets the drain water with rising Na concentrations.
Voogt again: “We know from previous research with these types of systems that water uptake drops as the EC rises, while nutrient uptake increases the more you supply, in other words, the higher the EC. Based on this idea, we want to develop a cultivation system in which half the roots are in a gutter with a normal nutrient solution and low sodium, allowing the plant to take up water and nutrients freely. The other half of the root system is in a gutter with rising sodium concentrations. The proportion of the drain water to be discharged is added to the second gutter.”
When presented with a high supply, the plant will take up high levels of sodium and there will be less remaining in the system. The researcher this year ran trials with tomato and cucumber with Na in a range of 0-15 mmol/l with two EC increments (2.8 and 4.2) in one half of the roots, and with no Na and an EC of 2.8 in the other. The results were surprising (see figures 3 and 4). “This way you can remove sodium from the system with no negative impact on growth. We certainly don’t have answers to all the questions yet, but we now have proof that the principle works,” the researcher says.
There is a catch, however. Despite the fact that the two halves of the root system are separate, sodium was found to have made its way into the other gutter. “It travels up the xylem and passes into the stem. Then it flows down again through the phloem and is secreted by the roots, but not in high enough amounts to reverse the removal effect. In net terms, a lot more sodium still finds its way into the leaves than is secreted,” he says.
Leave more leaves
To begin with, the growers on the supervisory committee were sceptical about how the system could be implemented in practice. But it is feasible, according to Voogt: “You only have to equip a small part of the greenhouse with a split-root system. That’s plenty. The annual costs aren’t too high and it’s a good way of reducing the amount of water that has to be discharged. The project still has a year to go, so we have plenty of time to flesh this out.”
The system should also be ideal for Mediterranean regions where irrigation water is often salty. But you can also harvest more salt without technical adaptations, he adds. “As long as leaves transpire, sodium goes into them. Tomato growers currently aim for 11-15 leaves on the plant to keep the leaf/fruit ratio constant. But if you leave the leaves on the plant for longer, you can get more sodium out of your system. That could be a reason to leave a few more leaves on the plant.”
Growing with higher sodium levels looks possible for sweet pepper. Trials with tomato will follow this year. A split-root system enables sodium to be harvested out of the system and removed with the crop. In this system, one half of the roots gets the regular nutrient solution and the other gets the drain water with rising Na concentrations. Both growing with higher sodium levels and storing sodium in the crop reduce the need to discharge drain water.
Text: Tijs Kierkels
Images: Wilma Slegers and Wageningen University & Research