Planten van prei op het agroforestryperceel

Digging Deeper: A closer look at leek in agroforestry

Through the 'Digging Deeper' series, you can follow the developments and results of Inagro's own agroforestry plot from the front row. Last month and a half was dominated by the planting of leek as intermediate crop. In this edition, you can read more about the first practical experiences and, together with Inagro's cultivation manager, we take a closer look at growing leek in agroforestry.

What does practice teach us?

Questions on agroforestry mainly focus on crop yield and quality, but there can also be many practical challenges associated with growing between rows of trees.

Now that we are effectively working with leek as intercropping on our agroforestry plot, a first evaluation of the practice is in order.

Aanplant van prei op het onderzoeksperceel agroforestry van Inagro

Field preparation and planting

We can be brief about the field preparation (tillage, pulling ridges and punching) for growing and planting leek. The (young) rows of trees did not complicate the work.

Preiruggen worden getrokken op het agroforestryperceel

Extra attention to tree strips

The tree strips with perennial herbs do require some extra attention.

  • After planting the leek, chemical weed treatments were already carried out according to the conventional cultivation method. However, if good practice is followed (spraying in good weather conditions, use of drift-reducing caps, etc.), the impact on these strips will be minimal. This is important because these strips are there to attract beneficial insects!
  • When spreading manure pellets, it’s also important to protect the tree strips as much as possible to prevent them from becoming overgrown by weeds.
Bloeiende boomstrook agroforestryperceel

Loss of cultivation area

The biggest impact of the tree rows lays in the loss of cultivation area. Besides the direct loss of cultivation area, the tree rows also have their impact on the cultivation zone between the tree rows. Harvesting leek is done at the side of the tractor. Harvesting therefore requires an uncultivated strip. Without tree rows on the plot, one uncultivated strip is sufficient.

Inzetstrook voor oogst van prei in agroforestry

On our agroforestry plot however, a new uncultivated strip was needed for each zone between two tree rows. The cultivation zone between the tree rows is 7 machines wide each time, i.e. four ridges per machine.

  • We chose to use the middle machine row as the cultivation strip each time. These uncultivated strips immediately also serve as spraying lanes.
  • On the outer sides of the plot, the grass strips along the hedges serve as inserts.

In total, we had to provide 4 additional inserts on our plot, which ultimately allowed us to use 5% less than the foreseen growing space. If we include the uncultivated tree lanes and the hedges with grass strips, a total of 84% of our plot is cultivated with leek.

Dronefoto agrofestryperceel

How does Inagro's crop manager look at leeks in agroforestry?

The trees are still young and little impact on cultivation can be expected this year. Together with Geert Desmedt, cultivation manager for leeks and cabbages at Inagro, we look ahead anyway. 'I find it important to give innovation in my field of work a chance and to think constructively together. Our leek cultivation in agroforestry is an example of this,' Geert states.

Yield along the row of trees

As cultivation manager, Geert is responsible for monitoring all the leek plots at Inagro, including the leeks on the agroforestry plot. He immediately makes it clear that the combination of leeks and trees will bring a number of challenges.

'In the longer term, trees will indeed have their impact on leeks. Firstly, I think of competition for light and water. We can expect lower yields along the tree rows as a result.' Here, Geert refers to field experience in the region where leeks are grown near existing tree rows along plots. 'I cannot immediately put an estimate of the percentage yield loss, because with agroforestry the situation is slightly different. There you can mitigate the competition between crop and tree by cleverly orienting the tree row or applying root pruning.' Geert therefore hopes that this plot will offer some more insight on this matter.

Prei langsheen de bomenrij op agroforestryperceel

My job is to give innovation in my field a chance and to think about it constructively. So also regarding agroforestry.

Geert Desmedt

Crop manager leek and cabbage, Inagro

Geert Desmedt Teeltverantwoordelijke prei Inagro

And what about the quality of leeks?

Geert also points out the potential impact on quality. Consumers, and therefore buyers, prefer leeks with a nice dark green leaf colour. 'A lack of light causes the leaves to be paler in colour. Especially for the fresh market and auction, the leaf colour determines the price.' Near trees, you also run the risk of falling leaves ending up in the shaft of the leeks. Something Geert occasionally sees happening when cultivating leeks along rows of poplar or willow. 'These leaves can be manually removed when washing the leeks, but the higher processing cost deters industrial buyers.'

A possible solution for this, according to Geert, lies in the choice of varieties. 'This year we are putting autumn leeks, but in the future we might switch to summer leeks or early autumn leeks. That way the leeks are already harvested when the leaves fall off and when the nuts are harvested,' Geert clarifies. 'Potentially, the larger leaves of walnut trees also get into the shaft of leeks less easily and this problem is smaller than we think now.'

Geert Desmedt Teeltverantwoordelijke prei Inagro

Walnuts and leeks: a good combination?

On the choice of walnut, Geert is certainly positive. 'Of all the trees, I think walnut is one of the best possible choices in our situation.' As main reasons, he cites walnut's relatively open crown and late leafing as somewhat limiting its competition for light.

To financially compensate for the loss of cultivation area, Geert also stresses the importance of trees as production. 'Especially with intensive vegetable cultivation on fertile and expensive plots, there needs to be an interesting source of income linked to the trees as well. Nuts are definitely a contender in that respect,' Geert concludes.

Noten als inkomstenbron in agroforestry

In addition to challenges, there are also benefits!

Besides the many concerns, Geert also sees a number of potential benefits linked to leeks in agroforestry. 'Through leaf fall the trees will add extra carbon to the soil thus improve fertility and water balance,' he says. But first and foremost, Geert is curious about the impact in terms of pest control. 'The tree strips with perennial herbs and grasses can host a lot of natural pest controllers on the plot. Whether this also leads to a lower pest pressure of thrips, leek fly or leek leafminer and thus a decrease in pesticide use is a question I would like to see answered in the future'. With that, Geert once again underlines the importance of the economic picture.

Bloeiende boomstrook trekt natuurlijke plaagbestrijders aan

Geert stresses that there are still many question marks at the moment and currenty we often have to rely on expectations and estimates. 'There aren't many figures to back it all up. For that reason, I'm already looking forward to the knowledge and practical experience that our agroforestry plot will provide.' That ever shrinking profit margins limit the space for alternative systems such as agroforestry among our growers, he finds regrettable. 'This is precisely why I think it's important that we work on this with Inagro and can provide growers with well-founded advice now and in the future.'

Plot in the spotlight

The agroforestry plot attracted a lot of curious visitors again recently. About 80 farmers visited the plot during the spring edition of the organic field day at Inagro and were introduced to agroforestry.

In addition, recordings for 'Tournée Provinciale' on Rural TV also took place. In this documentary, our plot is put in the spotlight! The documentary will be broadcast in August, so be sure to keep an eye out for it!

Agroforestry interview plattelandstv

What happened on the field since the last edition of 'Digging Deeper'?

Leek planting work and cultivation care were the main activities in the field over the past period. In addition, biodiversity monitoring also continued and we installed window traps for the first time to catch and identify flying insects. Incidentally, the drought also forced us to water the newly planted hedge. We are happy to provide some ambient pictures below.
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