Digging Deeper: planting of walnut trees

Through the 'Digging Deeper' series, you can follow the developments and results of Inagro's own agroforestry plot from the front row. The nut trees were planted in mid-February with the necessary care and attention, as these trees will eventually be an important source of income. In this edition, you can read more about the planting, we look at the costs and show how we monitor hibernating insects in the soil.

Plot takes final shape

The nut trees on our agroforestry plot have been planted. A little later than originally planned, but still on time. The early frost period in December, followed by a very wet start of 2023, forced us to exercise a little more patience. On 13th of February, our plot underwent a true metamorphosis. Five rows of trees now run across the plot, totaling 47 nut trees (Juglans regia 'Broadview'). On the south-western flank, we previously planted a mixed hedge as windbreak and to promote biodiversity on the plot.

Correct planting is crucial

Planting the trees is done with the same attention and care as planting or sowing crops. In the long run, trees are an important source of income for our agroforestry system. So a good start is crucial. We describe the planting step by step.

Protect the roots. The roots were covered with soil as long as possible during planting to protect them from the drying wind and sun. Half an hour of exposure is often enough to make roots die.
Make spacious planting holes. The manually dug planting holes were spacious enough allowing the root wig fitting in neatly. The sides were loosened a little. From the bottom of the pit, we drilled an additional hole about half a meter deep with a post drill and then refilled it with loose soil. This way, we break through the plough sole or other hard-to-penetrate layers and roots grow more easily in depth. No soil conditioner was added in the planting pit.

Attention to the roots when planting. When filling the planting holes, we regularly shook the trees up and down so that the loose soil spread well between the roots and no air cavities were created. The grafting point (recognizable by a thickening just above the roots) is well above the ground. This prevents the upper stem from developing its own roots.
Protection against herbivory. We protect the young plants against damage by (small) game. There are many systems on the market. We chose semi-rigid PVC spirals because they are easy to install and grow with the tree. This allows us to easily prune away stem growth.

Place support posts. For each tree, we provided two sturdy acacia stakes (spiked, 10-12 cm diameter) far enough away from the trunk. Binding material was twisted into an eight to avoid contact between trunk and support post. When installing support posts after planting the tree, as was the case here, be careful not to damage the roots when drilling the holes. The stakes play a double role. They support the tree, but also serve as protection during machining operations in the tree strip and field.
Pruning after planting? Certainly not! You only prune walnut trees when they are fully in leaf and the sap flow decreases again, otherwise they 'bleed'. More specifically, only prune them in the period June - October.
Fertilization. Applying an organic fertilizer to tree beds is not a must, but it can give young trees a boost. Soon, we will apply a wheelbarrow of champost to each tree bed.

The planting in pictures

A team of four got the job done in one working day. Below are some images of the planting. Click on the photos for a full view.

The cost?

We bought 3,355 euros worth of materials (planting material, support stakes, binding material, tree protection). We outsourced the planting and it was carried out for 1,850 euros (32 man-hours for the trees, 10 man-hours for the hedge). So for the planting of our 1.4-hectare agroforestry plot, we paid a total of 5,205 euros (including VAT).

Looking at the hedge and the trees separately, the total cost of planting the mixed hedge was 620 euros (planting material + labour) and that of the trees 4,585 euros (planting material + protection + labour), giving a cost of 97.5 euros per tree. Planting material was collected from the grower by ourselves, this is not included in the cost.

TIP: As an active farmer, you can have your agroforestry planting subsidized by the Department of Agriculture & Fisheries. Subject to certain conditions, you will be reimbursed up to a maximum of 80% of your planting costs (planting material, tree protection and labour costs).

Tree seeks farmer

The management of the trees and the tree strip will be done by Inagro, but for the intercropping we will work with local farmers in the coming years. This way, we also want to introduce them to the system and collect their experiences. Contacts are currently being made with farmers who are willing to cultivate between the tree rows of our plot. For this year, we are still looking for farmers who want to grow leeks on our agroforestry plot.

What happened on the site since the last 'Digging Deeper'

In addition to planting the trees, monitoring was also done again. Shortly after the trees were planted, we took samples to see which insects and other invertebrates hibernated in the soil of our plot. At three different distances from the tree row (in the row, 6m and 12m), we dug out a fixed volume of soil and incubated this for several months at room temperature in the lab. All insects emerging from these samples are collected and determined. By repeating this annually, we determine the impact of the trees on the presence of these invertebrates and also see how far in the field this impact extends.