Extreme weather at Unifarm: with so many crops, how do you ensure they stay wet or dry enough?

Published on
July 27, 2023

Rain, sun, hail and wind are part and parcel of crop trials in open fields. But extreme weather can affect the results of a trial. Gerard Derks and Joep Laan of Unifarm's Outdoor Cultivation Department do everything they can to give the crops whatever they need. How do they go about it?

‘We had weeks of taking it easy, and then it was a race against time,’ is how Gerard Derks and Joep Laan sum up the spring of this year. Along with two other colleagues, they manage the 20 to 25 people who look after the Unifarm experimental farm located at the Wageningen campus. Initially, the persistently wet fields meant the whole team were twiddling their thumbs, because the crops for WUR trials and external clients couldn’t be planted yet. When the rain stopped, it was finally time to start sowing and planting. ‘Everything had to happen at once. We were working around the clock, but we made it,’ says Derks, surveying the crops.

The wet spring was immediately followed by a long period of hot and dry weather, which soon meant the crops weren’t getting enough rain. With the soil drying out, it was difficult for the young plants to establish root systems. This meant the Unifarm team were also extra busy with watering the trial fields, on top of all the sowing and planting. The trial fields cover about 30 hectares out of the 250 hectares of arable land managed by Unifarm. And whether they’re using sprinklers or applying water in other ways, the team often have to use a tailor-made approach because each trial field is different.

Workload peaks

Extreme weather, such as drought and excessive rainfall, is becoming more and more common due to global warming. Derks and Laan are noticing the difference too, as weather extremes cause peaks in their own workload. It means they have to deploy the whole team at the same time to ensure that crops are sufficiently watered, for example, or to get the sowing and planting done. Derks and Laan sometimes work long days and also work on weekends when necessary. ‘But that's just part of farming,’ they say.

We watered often, but not all the plants made it.
Joep Laan

Derks and Laan walk to a field with strips of pumpkin plants and maize stalks. It’s a trial to see how different varieties of pumpkin plants grow when combined with maize in the same field. ‘Some of those plants have limp leaves,’ Laan points out. ‘That tells us they were struggling right after they were planted out. We watered often, but not all the plants made it.’ The less successful plants were those that were exposed to the sun pretty much all day, while the plants located in the shade of the rows of maize did better. In those spots, the soil doesn’t dry out as fast.

Influence on experiments

‘It can sometimes be a challenge to keep the plants alive,’ Laan continues. ‘Drought can have a huge impact on the trials.’ It’s very rare for a trial to fail because of this, but researchers conducting trials at Unifarm do need to take it into account when analysing their results. In most trials, researchers want to test something under “normal” conditions. Laan and Derks therefore create those conditions by making sure the plants get enough water during dry periods. But it’s almost impossible to totally prevent any damage.

In some trials, drought isn’t a problem. Those trials are about investigating the difference in yield between irrigated and non-irrigated fields. Or the crop in the trial might be one that is very tolerant of drought, such as quinoa. Laan and Derks pause at a trial involving a mix of different varieties of quinoa. ‘Quinoa is becoming more popular in the Netherlands,’ says Laan. ‘Not just because people like to eat it, but also because it’s an interesting crop for growers to consider if there’s a growing likelihood of extreme drought.’

Tight planning

However, only a minority of trials are unaffected by drought. Derks and Laan make clever use of a range of tools to ensure the success of as many trials as possible. Each crop has specific needs and every field is designed in a specific way. But coping with drought is mostly about efficiency. So it’s not just about preventing drought damage in every trial, but also about optimising your use of people and tools. That takes a lot of planning.

There are water points all over Unifarm’s fields where groundwater can be pumped up from about 60 metres below the surface. Thick, 100-metre hoses lie coiled and ready to be brought to these points whenever crops need spraying. ‘During those dry weeks, they were constantly in use. ‘We had elaborate schedules to ensure that all the fields were supplied with water to the best of our ability,’ explains Laan.

Efficient watering

On many plots, Derks and Laan use sprinklers that spray water around, just as most farmers do. It’s a cheap method, but it’s not very efficient, because some of
the water evaporates or blows away before the crop has had a chance to absorb it.
The team therefore also has access to other types of sprinklers. These are used
for specific trials.

During droughts, our colleagues spend all day moving these systems around. It’s quite labour-intensive.
Gerard Derks

In a potato field, for example, a 34-metre-wide sprinkling system drives across the rows of plants. In a trial featuring grass at different cutting lengths, only one half is being watered, using a smaller system that waters the grass evenly. ‘During droughts, our colleagues spend all day moving these systems around,’ says Derks. ‘It’s quite labour-intensive.’ Other trials at Unifarm use drip irrigation, where a hose placed alongside each row of plants provides the exact amount of the required water and nutrition.

Extreme rainfall

Periods of drought are often followed by intense rain, sometimes including hail and gusts of wind. On one occasion, a foil tunnel with plants growing in it was damaged beyond repair. ‘Twice in the past four years, that entire tunnel has become airborne,’ says Derks. ‘For the 15 years before that, there was never a problem.’ There’s now a windbreak to protect the tunnel from gusts of wind. ‘This year, the storms were not too bad here, but the trial site in Lelystad was less fortunate. Several trees were blown over there, on trials that were actually researching the effect of trees on arable farming,’ says Laan.

Derks and Laan are now planning to spend some time focusing on water retention, because heavy rainfall can sometimes be followed by another period of drought. ‘Water runs off too quickly here,’ says Laan, indicating to the west. Running from east to west, the land at Unifarm slopes down by at least a few metres. Retaining water in the dry soil can help to provide moisture to crops for longer, thus preventing damage. The plan is to build retention weirs at several places to stop water before it flows away. ‘In the past, water needed to be able to drain away quickly, but now we also want to be able to retain it,’ says Laan.

Providing certainty

Years of experience has taught Derks that every innovation opens up the possibility of more trials. When he started 40 years ago at one of Unifarm’s predecessors, he was happy just to acquire a pump and a few pipes. ‘Now there’s a whole network of underground pipes. You need to be sure that certain trials can
succeed, even under extreme weather conditions.’ ‘But if we have to deal with
an irrigation ban, that’ll really be a challenge,’ says Laan.