Broccoli, strawberries, summer flowers, flower bulbs and trees do not need soil to grow. They can also be grown in water or on substrate, and that is better for the environment. However, the costs are too high for many crops. Researchers from Wageningen UR and Proeftuin Zwaagdijk (Agricultural Research Centre) are trying to do something about this.
'Twice as much with half the input' is a slogan that concisely summarises the challenge for 21st-century agriculture. During this century, the world population will continue to grow and people will make higher and higher demands on their food supply. Twice as much means that food production will have to double. Half the input means that the inputs for food production will have to be drastically reduced. Present-day agriculture uses too much artificial fertiliser, water and land to ensure sustainable management of our planet. Sustainability must be improved, at least by a factor of two.
This sounds like an enormous challenge: producing food at least four times more efficiently. Is that possible? In any case, technology does not appear to be the biggest problem. Motivated by environmental regulations, scientists from Wageningen UR and Proeftuin Zwaagdijk are working on a project with the aim of bringing this aim closer to reality for Dutch horticulture. From a global perspective, this sector already uses land and other inputs very efficiently.
As part of the programme Teelt de grond uit, researchers are looking for ways to grow vegetables, flower bulbs, fruit, flowers and trees without soil. The aim is to develop cultivation systems that combine environmental benefits with a high yield per hectare or improved quality. The initial reason for the research was the strict environmental regulations affecting Dutch growers such as the Water Framework Directive and the Nitrates Directive. On some types of soil, it is virtually impossible to continue to comply with the increasingly stringent directives. It is therefore time for a radically different approach, known as a system shift.
Janjo de Haan from Applied Plant Research is leading the programme. ‘In theory, you can realise a major improvement in sustainability.’ For example, if you grow crops in closed systems that are separate from the soil, there is no longer any leaching of nitrates to groundwater or surface water. ‘The need for crop protection agents will probably be greatly reduced as well.’ The new cultivation systems, for instance, are completely weed free. ‘So you don't have to use any herbicides. What's more, if crop protection agents are required, then they can be applied directly via the water in which the plants grow. So there is no spraying that could contaminate the surface water.’
Flower bulb growers
In the project, De Haan is working together with Matthijs Blind from Proeftuin Zwaagdijk. This experimental station has extensive experience with cultivation on water. ‘In 2007, we began studying the production of leafy vegetables on water. Growers in our area who force tulips for cut flowers wanted to know if they could also use their installations (the bulbs grow in water) for other crops. Tulips are generally forced in the spring, and for the rest of the year the installations often remain idle. This is why we looked at other crops such as summer flowers. Later on, we were approached by outdoor vegetable growers who said that the regulations had become so strict that they were being compelled to grow their crops differently. We wanted to help them get started.’
The first experiments immediately resulted in a great deal of interest from growers and special interest groups, says Blind. ‘We had many positive responses. The Product Board for Horticulture financed a three-year research project. For the Ministry of Agriculture, Nature and Food Quality (LNV) that was an important step; the Ministry wants to see more participation from the sector.’ In the meantime, Blind has tested many crops on water. ‘We are now primarily focusing on specialty crops, such as coloured lettuces and multi-leaf lettuces. But we have also experimented with endive, Chinese cabbage, parsley, broccoli, spinach and many other ornamentals and vegetables. During these experiments, the most important question was whether the crops would grow with their roots in water. We were successful with nearly all crops; only larkspur (a summer flower) is still a problem. But all the vegetables we have tried so far have worked. Rocket (arugula) didn't work at first, but now we can grow that crop as well.’
Ponds
The system at Zwaagdijk uses tanks with non-circulating water, similar to ponds in the ground. The plants float on plastic carriers, with their roots dangling in the water and their foliage growing above the clean plastic. There also systems with plants in gutters, but Blind says these are less robust. ‘In gutters, the water is supplied through thin tubes. If the water supply is interrupted even briefly, then you have a problem.’
Applied Plant Research (PPO) in Vredepeel is testing comparable systems for leek production. De Haan: ‘In 2008, we tested six systems. In 2009, we continued with three of these systems, and this year we are testing an additional two systems. The floating system is currently the most promising method. We use tubes to ensure that the leeks grow vertically.’ The biggest problem with growing on water is not technical, but financial. For example, most leafy vegetables are so inexpensive that it is not cost-effective to make large investments in cultivation systems. This is why the possibilities for the more expensive varieties of lettuce were first investigated at Zwaagdijk.
PPO researcher De Haan: ‘ We are working towards the current cost of production. For many crops, this is still some distance away, but cultivation on water would be profitable in the short term if you can clearly demonstrate the added value of the system. Perhaps this will be possible with a different type of leek. In any case, a major advantage of growing leeks on water is that they are completely free of soil and sand.’
It could also become possible by marketing vegetables differently. For example, the Albert Heijn supermarket chain sells herbs growing in a small pot in the fresh produce section, along with lettuce produced in a similar fashion. The herbs and the lettuce stay fresh longer. ‘Perhaps there are similar possibilities for other products, for which consumers will also pay more.’ One way to earn back the investment is the possibility of growing multiple crops per year. De Haan: ‘Lettuce growers currently harvest two to three crops per year on soil, but they could harvest four or five crops on water. For leeks, growers generally harvest only a single crop, but on water they could perhaps harvest three or four.’ By growing the seedlings closer together when they are small and giving them more room as they grow, the growers can achieve much higher planting densities than is now the case, and can therefore produce more.
Landscape
The new system is very promising. However, an important question is whether consumers will accept crops grown on water. Are Dutch consumers looking for new technological advances, or do they prefer lettuce that is grown the old-fashioned way? ‘This is certainly a point of attention’, says De Haan. ‘Will consumers accept this new system, or will there be protests, such as those against watery greenhouse tomatoes (Wasserbomben) and high-tech pig farming?’ In any case, he believes that flavour will not be a problem. ‘This depends much more on the chosen variety than on the cultivation method and the soil.’
One problem for growers could be the objections of nearby residents and municipalities that see changes to their familiar landscape. Instead of freshly ploughed fields, they will see large reservoirs of water with white plastic rafts for the plants. Blind from Proeftuin Zwaagdijk predicts that farmers will wait to make plans for the large-scale application of these systems until they have clarity about the land-use regulations. On the other hand, he doesn't expect that many consumers will lose any sleep about a possible shift to cultivation on water.
‘Greenhouse tomatoes are all grown without soil. However, the outdoor systems will look strange to people for a while. You have to properly communicate why you are making this change, especially the fact that it is good for the environment because there is less leaching of fertilisers and pesticides. Moreover, we will probably need less land, because you can produce more efficiently. That extra land can be used for wildlife habitats and recreation.’
All in all, Blind sees a promising future for cultivation on water. ‘In five years, it is likely that the systems will already be applied on a fairly large scale in the Netherlands. The best part is that you do not need good farmland. You can grow crops on almost any type of land, as long as it is solid enough to hold the water reservoirs and the machinery.’ The benefits do not have to be limited to the Netherlands. Blind: ‘Because you need less water, such systems are highly suitable for areas with scarce water or poor soil. You can also think about using them in urban agriculture. With a robust system, you could even grow vegetables on the roofs of apartment houses.’