High sustained production
When root restriction is combined with management of the fruit trees, the soil and the method of irrigation, high-density plantings can be highly productive and easy to manage for a long time. You can achieve this by:
•Maintain a good soil structure
Keep the soil in optimal conditions to implement the long-term effects of root restriction on controlling root growth, tree vigour and fruit production.
Gypsum applied every 2 or 3 years plus the weed mulch will keep the surface soil soft, permeable and well-aerated.
•Mulch
In hot dry climates with shallow soils, a thick organic mulch helps to conserve water and cools the soil down. This decreases both irrigation and heat stress and improves performance of the trees. However, some water is lost through deep-drainage.
In grassed orchards, mowers that feed the clippings sideways towards the tree rows, effectively mulch the tree rows.
•Crop load
Mature and semi-mature fruit trees with heavy crop loads produce much fewer shoots than fruit trees with light crop loads do. Hence, crop loading (stimulating the set and retention of adequate fruit on the tree) is one of the most economic and environmental sensitive methods of controlling excessive shoot growth.
Cropping has a profound effect on controlling tree size, primarily through decreased root growth, a consequence of roots being the weakest competitor between fruit and roots for leaf photosynthates.
By manipulating crop load, you are able to manipulate the balance between cropping and vegetative growth.
Cropping is one of the most practical and effective means of controlling growth. Managing crop load to avoid either under or over cropping in the establishment years of a high-density planting is critical and requires good horticultural skills.
Interdisciplinary research
Originally it was believed that the only significant functions of roots was to facilitate the uptake of water and nutrients from the soil and to anchor the tree to one position. However, it is now realised that roots have other important functions.
The scientific study of root growth has lagged behind that of shoots, flowers and fruits—almost certainly because of the difficulties encountered in conducting studies within the soil.
The first authoritative root studies were reported in 1939. More research work was done on root systems and the distribution and effectiveness of roots of fruit trees in the 1970s and 1980s.
The information provided in this article is a good example of soil science interacting with tree physiology to gain more knowledge that can then be translated into better management decisions for tree fruit production.
See this article in Tree Fruit July 2018
