More soil life in the greenhouse
Information
The Wubben family farm in Nootdorp, the Netherlands, has been growing nerines and amaryllis on around 20 ha since 1961. Last year, they incorporated a variety of catch crops into their crop rotation for the first time. Rowan Timmer (DSV) visited Paul Wubben, along with his son Kevin and nephew Ronald Wubben, who are also actively involved in the business. They discuss their initial experiences of growing catch crops in the greenhouse.
From fallow land to green manure
“Between two Nerine growing cycles, the soil lies fallow for 8 to 9 weeks. Our adviser suggested we introduce a catch crop. The soil usually dries out considerably between two phases of flower cultivation, which reduces soil life and fertility. That’s why we decided to give catch crop cultivation a go. After some initial scepticism due to the extra effort involved, sowing the catch crop and subsequently incorporating it into the soil proved simple after all.”
Wubben opted for a combination of the TerraLife® cover crops BetaSola and WarmSeason. “We tested two different mixtures to see how they would perform during an eight-week greenhouse growing cycle. We chose BetaSola because of its deep root system. A second variant was a mixture of BetaSola and WarmSeason, to achieve greater diversity.” Both mixtures flowered quite late. “And that’s a good thing, because as soon as they start to flower, they become attractive to thrips.”
Adjusted irrigation
The first attempt at growing catch crops did not go to plan. “We irrigated for too long, which caused the oil radish to die off,” says Paul Wubben. Nevertheless, the farmers immediately recognised the benefits and, on the advice of Rowan Timmer, decided to make a second attempt using an adjusted irrigation strategy. “We irrigated at the start but stopped completely later on in the growing season. That worked much better. The BetaSola was sown on 18 February and is now looking fantastic,” says Paul Wubben with satisfaction.
A new approach: focusing on soil life
We used to steam the soil deeply and kill everything off to create as sterile an environment as possible,” explains Ronald Wubben. “Now we are doing exactly the opposite: preserving soil life.” Steaming is now limited to the soil’s surface, and the subsoiler is no longer driven through the soil. “The cover crop loosens the soil, so we no longer need to drive the tractor into the greenhouse. It is better for soil resilience if the layers remain on top of one another rather than being torn apart. We now also want to launch a trial in which we stop steaming part of the area altogether.”
“Given the current state of knowledge, it no longer seems appropriate to steam the soil or leave it fallow.”
Visible effects of cover cropping
“We have noticed that the soil absorbs more water when a cover crop is used. We observed this after just one growing season. Radishes loosen the soil. We have also noticed an increased share of soil organic matter and a lovely, crumbly structure.”
But that is not all: the main crop benefits from it too. “Overall, we’ve noticed stronger growth in the nerines. They produce more leaves and are more firmly rooted in the soil than before, as they can establish themselves better. Furthermore, the soil becomes saturated less quickly, meaning more oxygen is available,” says Paul Wubben. “We’re experiencing fewer losses in the main crop and retaining significantly better-quality, larger tubers. We have also been able to harvest significantly more stems. We are convinced that the cover crops have made a positive contribution to this.”
Crop rotation in turbo mode
“This plot used to be grassland. After the greenhouse was built, we grew crops on fresh soil for the first time. The harvest in that year was excellent,” explains Paul Wubben. “By using a crop rotation system with catch crops, we try to achieve the same ‘fresh soil’ effect.”
The cover crops are integrated into the crop rotation when the greenhouse has been emptied for at least six weeks. The mixtures are sown on the surface using a granule seed drill and then lightly raked in. The cultivation process is completed by chopping the plants down to about 10 centimetres above the ground using a flail mower. Within a few days of this, effective microorganisms are applied to accelerate decomposition and stimulate soil life. “This makes the nutrients from the catch crop available more quickly to the subsequent main crop,” says Paul Wubben.
Incorporating the catch crop
Photo series: The cover crop mixtures are chopped up using a flail mower. This chops the plants down to a height of approx. 10 cm.
The result of green manuring: well-rooted, crumbly soil that visibly retains moisture despite reduced irrigation. Ready for the next crop of nerines.
“We are using the catch crop to try and achieve the ‘fresh soil’ effect.”
Challenges in growing catch crops under glass
“In our first trial, we had problems with thrips,” explains Kevin Wubben. “This was because the plant had entered the generative phase. The solution is to chop the crop before this phase begins. It is also important to monitor the thrips closely. We now have a plan in place for this and are using biological pest control with predatory mites.”
“We do not fertilise the catch crops, as they themselves act as fertiliser for our crop rotation. Growing catch crops has been so successful for us that we will be applying this method to all our Nerin crops in future,” concludes Paul.
Source: Ellen Heesen und Rowan Timmer, both DSV