Digging Deeper: Trees and leeks are competing for space
Through the Digging Deeper series, you can follow the developments and results of Inagro's own agroforestry plot from the front row. In this edition, you'll learn more about the leek yield on our plot, the battle against excess water, and the activities and other events on-site since the last update.
No effect of young trees on leek production and quality
This year, a farmer from the region cultivated leeks between the rows of trees on our agroforestry plot. The impact of the trees on leek yield was immediately one of the many questions we wanted to answer.
In early October, we manually took samples at various distances from the tree rows, each time in quadruplicate. We removed the outer leaves of the leeks, shook out the root clump, and weighed the leeks. On average, we recorded a yield of 60.89 tons (uncleaned) leeks per hectare. A good yield and comparable to other conventional plots in the region. We observed no difference in yield in the proximity of the tree rows (see figure below). Not abnormal, given the limited size of our young walnut trees. Based on visual observations, we also noted good leek quality across the entire plot.
Loss of cultivation area is currently decisive
The layout of our agroforestry plot with rows of trees and hedges, as well as the need for additional harvesting lanes for leeks (see left figure), meant that only 84% (1.176 ha) of the total plot (1.4 ha) could effectively be cultivated with leeks.
Assuming a uniform yield of 60.89 tons/ha across the entire plot, this corresponds to a production of 71.60 tons at plot level and a production loss of 13.64 tons of leeks due to the layout of the plot. Based on an average market price of 0.7 euros/kg and a cultivation-related cost of 0.5 euros/kg (seedlings, labor, crop protection, harvest, ...), this means a financial loss of 2.728 euros on this plot. Since our walnut trees are not yet productive, this is not yet compensated by nut income.
Numbers may be a slight overestimate as we are working with yield figures for uncleared leeks.
Drone images show a fairly homogeneous crop stand
This fall we released drones above the plot to determine the NDVI (Normalized Difference Index). This is a graphical representation of the vitality of your crop. Simply put, the greener the map, the more biomass and the healthier your crop or vegetation. On the NDVI maps below, you can see:
- The tree rows are clearly visible (dark green color), and there are no zones where the leeks significantly perform worse. In the center, we see a slightly greener color (7/9/2023), corresponding to a clay zone. All in all, a fairly homogeneous crop stand over the plot.
- The greener color (11/10/2023) on the east side of the plot is due to higher weed pressure.
- The circled red spots are the areas where the leeks were harvested for yield determinations
These drone images confirm previous conclusions, where we observed no differences in yield across the plot and little damage from diseases or thrips.
Water... and even more water
With the leek yield sampling completed, it was tme for the farmer to proceed with the actual harvest... but then came the rain. A lot of rain.
From mid-October to the end of November, the plot received over 320 l/m² of water. Certain sections were submerged, and harvesting was impossible across the entire plot. Ditches were dug to drain the water, but an initial attempt by the farmer to harvest around mid-November failed. At the time of writing, the leeks still could not be harvested. Oslo, the leek variety planted here, is inherently a robust and disease-tolerant variety, but time is gradually running out for harvesting...
Partial replanting of trees
Waterflooding is not only concerning for the leeks, but the situation is far from ideal for the trees as well. The wet months in early 2023 took their toll even before summer. Despite careful attention during planting, we saw exceptionally many trees fail before summer. Recently, the dead walnut trees were excavated, and we saw that the roots had rotted due to excessive water (see photo). Approximately half of the walnut trees will need to be replanted next winter. From soil maps, we infer that the dropout is mainly concentrated in an area where we have a clayey soil rather than loamy sand. In that same zone, most problems with waterflooding were also observed.
To avoid a similar scenario next year, we are focusing on maximum drainage by digging ditches. We prefer not to drain because in summer, we want to retain water on the plot. Replanting the trees on raised ridges could also be an option, but we found it practically unfeasible on such a short-term basis.
Agroforestry and water
Inagro recently started as a Belgian partner in the European LIFE project AFaktive, where we examine the potential of agroforestry in terms of water management, especially as an adaptation to prolonged drought on the one hand and periods of intense rainfall on the other. We do this together with ILVO and AWAF (Association pour la promotion de l'agroforesterie en Wallonie et à Bruxelles). Besides Belgium, Germany and the Netherlands are also represented in this project.
Perhaps we can gain valuable new insights here that will also advance us on our own plot?
What happened on the field since the last edition of 'Digging Deeper'?
