In their new research article, Mina Anders (University of Göttingen, Germany) and colleagues compared the effects of agronomic practices, including agronomic inputs (irrigation and managed honey bees), orchard design without external inputs (spatial orchard structure), and landscape factors on nut production in South African macadamia orchards.
The need for sustainable agricultural practices
Conventional agricultural intensification causes biodiversity loss and environmental degradation. To reduce these impacts, we need sustainable and environmentally friendly agricultural practices. One option is ecological intensification, the replacement of human-produced inputs such as pesticides and fertilisers with natural processes such as pollination and biological pest control.
This research investigated how pollination services can be improved at minimal cost. We assessed nut set – the number of flowers that actually develop into fruit – at two different stages: initial nut set (3 to 5 weeks after flowering) as an indicator of pollination success, and final nut set (18 to 20 weeks after flowering) as an indicator of yield outcomes.
Bees could do better – pollination limitation
As a mass flowering crop, macadamia is highly dependent on pollination. Compared to experimental pollinator exclusion, insect pollination boosted initial and final nut set by 304% and 23% respectively. However, nut set was pollination limited as hand pollination further increased initial and final nut set by 737% and 367% respectively. This means that the pollination service provided by pollinating insects was worth improving.
Who pollinates macadamia flowers?
We observed flower visits by pollinators, 95% of which were honeybees. Surprisingly, the cover of semi-natural habitats in the surrounding landscape was more important in increasing these visits than the number of managed honeybee colonies. We suspect that a large proportion of the honeybees were wild and originated from the surrounding habitat.
How can we improve bee pollination?
Firstly, higher flower visitation rates led to higher initial nut sets. We found that special orchard design can improve pollination and, thus, nut set. These measures do not require external inputs (after planting the orchard block).
Macadamia trees are usually planted in rows. When the orchard is adjacent to a semi-natural habitat, a perpendicular orientation of the planted macadamia rows towards the edge of the orchard increased the initial nut set more than threefold compared to a parallel row orientation. A perpendicular orientation makes it easier for bees leaving the semi-natural habitat to enter the orchard, as they tend to fly along the rows of trees.
In addition, initial nut set was 80% higher at the edge of semi-natural habitats than in the centre of the orchard. Moreover, a mixture of different macadamia varieties in the same orchard block enhance cross-pollination of the varieties resulting in higher nut sets that in single-variety blocks. In contrast, agronomic practices such as irrigation did not increase either initial or final nut set.
Summary
We found that pollination services were a prerequisite for high yields in macadamia. They could be improved without further agronomic inputs, but with an intelligent planning of the orchard design in advance. Given the urgency to reduce the environmental impacts of agricultural production, we highlight the high potential for ecological intensification through smart orchard design and the restoration and conservation of semi-natural habitats in the orchards and their surrounding landscape.
Read the full Open Access article, “Smart orchard design improves crop pollination“ in Journal of Applied Ecology
