Sustainable Yet Highly Productive Arable Farming

The Netherlands strives for sustainable and highly productive food production. In other words: achieving good production with less fertilizers, water and pesticides and more crop and biodiversity. WUR is researching ecology-based arable farming, in the form of strip cultivation and mixed cultivation.

In the Netherlands we are used to seeing uniform plots of land with only ryegrass, maize, potatoes or wheat. But along the A6 near Almere, motorists can see a mosaic of different crops next to each other on one field. Here, ERF BV, Flevoland Reserve Grounds Operator, practices strip cultivation.

ERF BV is the largest organic vegetable grower in the Netherlands. The company manages 1,000 hectares of arable land in Flevoland and has been experimenting with strip cultivation on part of the company since 2015. ERF grows potatoes, field beans and various vegetables there, such as celeriac, parsnip, Brussels sprouts, broccoli and cauliflower. Dirk van Apeldoorn, researcher at Farming Systems Ecology and Open Cultivation at WUR, takes measurements and provides advice.

Plus strip cultivation
First, ERF started growing different potato varieties next to each other in strips of 6 meters, just like different vegetables. The company then started testing strip cultivation with different widths - 6, 12 and 24 metres. These are logical widths, says Van Apeldoorn, because the machines for fertilization, crop care and harvesting have multiples of 6 meters in width. He discovered that the yields in strips remained the same compared to monoculture and that the labor efficiency for organic farming also remained the same. However, an important plus was that the crops in strips of 6 meters suffered less from diseases and pests.

Farm of the Future Lelystad
Since 2010, WUR has also been involved in strip cultivation in the testing ground for agroecology and technology in Lelystad. This living lab is a breeding ground for new techniques that are used on the Farm of the Future in Lelystad. There, Van Apeldoorn was surprised to find that the potatoes in strips of 3 meters yielded 25% more per hectare than an entire field with potatoes on the clay near Lelystad. In Wageningen, on sandy soil, strip cultivation yielded 12% more potatoes per hectare. The researcher: 'We think that useful soil fungi play a role in this higher production, but this requires further research.' At ERF, which grows potatoes in 6-metre strips, the researchers did not encounter this increase in yield.

Strip cultivation requires craftsmanship
'We are only at the beginning of strip cultivation,' says Van Apeldoorn. 'And don't expect us to do tests and then tell the strip growers what to do on their farm. Which crops and combinations are good depends very much on the local conditions. Strip cultivation requires a lot of skill from the farmers. They must learn to look at the ecological conditions, accept complexity and learn to manage variation.'

For this reason, so far mainly organic farmers have invested in strip cultivation. Van Apeldoorn: 'In conventional agriculture you are assured of a good yield if you use good varieties and apply fertilizer and crop protection at the right time; you control the cultivation from A to Z that way. In organic cultivation you don't have those controls and you have to observe more what happens in the field and take that into account next year. What works for one farmer may not work for another. That is why strip cultivation is a greater challenge for conventional arable farmers.'

More farmland birds with strip cultivation
Nevertheless, conventional farmers are now also participating in WUR's practical network of 50 farmers who will apply strip cultivation. Including an arable farmer from the Veenkoloniën who grows potatoes, grain and sugar beet. He used to grow potatoes in crop rotation on an entire field, now he will grow potatoes in strips of 27 metres. 'This farmer is not interested in fewer pesticides, he already grew without insecticides,' says Van Apeldoorn. 'With strip cultivation he wanted more farmland birds.' The alternation between potatoes and grain in the fields is good for the field birds, because they breed in the grain and look for food in the open field. Previously, a black desert remained after the harvest of the potatoes and wheat, but with the strips the birds always have food and shelter. Bird counts already show that this farmer's approach works.

Tuition fees are also paid during the voyage of discovery. According to the literature, maize is a suitable strip crop to alternate with grain or legumes. But when organic farmers started to include maize in their strip plan, the crows ate up all the seeds. You can grow corn in strips, Van Apeldoorn teaches, but then you have to plant conventional corn seed with a coating, because the crows don't eat those. Another discovery: you shouldn't put spinach next to the potatoes if the spinach is used for baby food. Because you don't want pieces of poisonous potato leaves to end up in the Olvarit.

Strip cultivation versus mixed cultivation
Strip cultivation is a crowbar in the transition to sustainable agriculture, says Van Apeldoorn. It's not perfect, but doable for many farmers. A step further is mixed cultivation. With mixed cropping you grow two crops that have a favorable influence on each other together or in rows of 1 to 1.5 meters wide. Wopke van der Werf and Tjeerd Jan Stomph of WUR are doing research into this.

They just published an article in which they review the results of 226 intercropping field experiments around the world. A few remarkable conclusions emerged from this. Successful mixed crops achieve 28% more yield than you would expect from the sum of the two crops separately. So they reinforce each other's production. As a result, you need an average of 19% less land for the same yield with mixed crops compared to monocultures, the researchers conclude.

They are talking about successful combinations of corn alternated with legumes, such as soy, lentils or field beans. Legumes also do well with wheat, because they fix nitrogen and are a good green manure. A combination of maize and wheat is also interesting, especially winter wheat, because you can then harvest the wheat in July and the maize in October. By combining early and late cultivation, you use the entire growing season and use light, water and nutrients more efficiently, the experiments show.

Advantages and problems of mixed crops
The advantages of mixed crops are obvious, says Van der Werf. They provide comparable production with a smaller environmental impact – less fertilizer and plant protection products – and more biodiversity. The climate risks of mixed crops – crop failures due to heat and drought, for example – are also often smaller, because farmers spread their risks in this way.

Yet intercropping plays a very modest role in the food supply. Mixed cultivation mainly occurs in developing countries. French farmers sporadically grow mixed crops of pea and wheat, and mixed crops of maize with grains or vegetables are still grown on small fields in parts of China, but are on the decline due to the modernization and mechanization of agriculture. The problem with mixed cultivation is that all agricultural machines are designed for monocultures. In fact, the entire cultivation system – varieties, fertilizers, crop protection – is aimed at optimizing individual crops and not combinations of crops.

Precision farming
That is why it is now also up to the machine builders to make mixed crops possible. These are smaller machines that recognize different crops and can provide tailor-made treatment. This brings us to the domain of precision agriculture, where farmers use cameras, sensors and satellite data to care for their plants and remove harmful weeds. In the case of mixed cultivation, this concerns robots that can recognize several crops, herbs and flowers (good for pest suppression) and weeds and have a treatment plan for each.

In this technological development, we must distinguish between strip cultivation and mixed cultivation, says Peter Groot Koerkamp, ​​professor of Agrotechnology. 'With strip cultivation you continue to do linear operations during sowing, weeding, spraying and harvesting,' he says. 'You harvest everything, but you no longer carry out that activity over a width of 48 or 27 metres, but over a width of 3 meters or less. In practice, that means that you have to reduce the working width of machines, and that is a trend break.'

In the meantime, weed robots are already being developed for fields of 3 meters wide, which can spray herbicides very accurately based on sensors, completely autonomously. And the first potato harvester that can drive on 3-metre strips is now being tested. 'There is no 3-metre beet harvester yet, but that is only a matter of time. Main disadvantage for the arable farmer: they are more expensive at the moment.'

The biggest challenge according to Groot Koerkamp are the harvesting machines. You need driving paths between the strips, just like now with monocultures, but with machines with a reach of 27 meters you need fewer driving paths than with machines of 3 metres. If you continuously drive heavy machinery over these driving paths, you get soil compaction, which is bad for soil quality and production. Smaller and lighter harvesting machines offer a solution, but even in that case the spuds must be removed with heavy tractors. 'We have to stop using heavy bunker harvesters that harvest and transport the potatoes at the same time, but we do not yet have another system for transporting the potatoes without soil compaction.'

New logistics field concepts
Groot Koerkamp is thinking of new logistical concepts in the field, such as a moving conveyor belt system that brings all the potatoes to the top of the fields. However, that idea is still in the stage of a group of students making a sketch.

However, with mixed cultivation, the technicians have to throw the linear model overboard. 'Then we have to deal with several crops, herbs and weeds. We then have to determine which of several plants should stay or go, and we also have to manage the competition between plants.'

The technology for this is now being developed. For example, the start-up Saia Robotics , run by Wageningen PhD student Ruud Barth, developed a broccoli harvesting machine that autonomously determines which broccoli is ripe and which needs to be harvested. 'With this technology you could also mix crops and harvest them separately with the same machine,' says Groot Koerkamp.

The old trend in agrotechnology was increasingly larger and heavier machines that could combine mowing, threshing and transport, for example. The new trend is smaller light machines, where functions such as sowing, harvesting and transport are being decoupled again, says Groot Koerkamp. At the same time, Dirk van Apeldoorn sees an agricultural trend. 'We are going to reduce the size of the agricultural plots and cultivate ecologically and intensively within those plots.'