Think carefully before applying fertilisers to your orchard, particularly chemical fertilisers. Consider first whether it is really necessary. It can do more harm than good not only to the trees but also to the grassland. Frequent applications of fertiliser, even good old farmyard manure, can disrupt the nutrient balance of the grassland. This can have a detrimental affect on plant species diversity which in turn can lead to a decline in pollinating insects. Fertilisers can also harm the trees by interfering with their associations with beneficial fungi such as mycorrhizae – the subject of this blog.
The word mycorrhizae comes from Greek and literally means ‘fungus roots’. These harmless fungi attach themselves to the roots of trees (and plants) and develop into an extensive network of fine, thread-like filaments known as mycelium. (There can be up to 20 metres of mycorrhizal filaments per teaspoon of soil). Mycelium extends the tree’s reach and provides it with access to a much larger surface area for the absorption of water and mineral nutrients. In return, the tree provides the mycorrhizae with a fairly constant meal of carbohydrates.
This mutualistic relationship helps the tree maintain its vigour even during periods of stress, such as drought. Trees with a well-established mycorrhizal root system are much more efficient at absorbing nutrients and water from the soil. In addition, the mycorrhizae act as natural block to the passage of root pathogens.
Applying fertiliser provides the tree with a temporary abundance of nutrients which can encourage it to abandon its association with these beneficial fungi. However, if the orchard has always been fertilised it is probably better to continue as mycorrhizae may never have been established in the first instance.