To produce early and high yields of good quality fruit, fruit trees need lots of feeder roots in the surface soil so they can take up plenty of water and nutrients.
To enable this, the surface soil should be deep, soft, stable, well-structured, well-drained, fertile, and cool in summer. Here are steps to achieve that.
The following steps will help you to plan any new planting of fruit trees.
4 Hill-up the surface soil (continued from last issue)
Make good use of the shallow surface soil by hilling (ridging) it up along the rows so that the depth of good quality free-draining soil available to the tree roots is increased.
Hilling-up can increase up to four times the volume of surface soil in the row as compared with no hilling-up.
Most feeder roots grow in the surface soil, so when the surface soil is shallow, these roots are severely restricted. Few roots grow in the compacted surface soil in the traffic lanes between rows of fruit trees. If the land is also flat, the soil can easily be waterlogged in wet conditions.
To solve these problems, use a road grader to take the wasted surface soil from the traffic lanes, and hill-up the surface soil before you plant the fruit trees. This increases the volume of soil for the feeder roots to explore, and the sloping hills also allow excess rain water to run off. Surface drainage is as important as irrigation.
5 Sow ryegrass onto the beds or let voluntary weeds develop
This will decrease slumping and creates a good environment within this area of topsoil, because tree roots are confined to a relatively small area of soil.
This step must be carried out in early autumn to ensure that the ryegrass or weeds become established before the winter sets in.
Use irrigation water to germinate and establish ryegrass or weeds.
6 Spray out ryegrass or weeds before you plant fruit trees
Ryegrass or weeds are needed to keep the hilled-up surface soil covered to avoid impact from heavy rain, avoid impermeable crusts from forming and to stabilise the soil.
Kill the ryegrass or weeds in spring, because they compete with fruit trees for water and nutrients during the growing season. The dead roots of ryegrass or weeds and associated fungal hyphae create pores and stabilise the surface soil.
Also:
Do not walk on the hills.
If possible, 1 to 5 are best done a year before planting.
Restricting root growth
This is then followed by restricting root growth to control tree vigour and impose cropping.
Root restriction provides orchardists with a useful tool for tree growth manipulation
Strategies to achieve root restriction include close planting of fruit trees, regulating the supply of irrigation water, applying growth regulators, using rootstocks which induce precocity (if available), pruning, and keeping the soil in optimal condition to implement the long-term effects of root restriction on controlling root growth, tree vigour and fruit production.
Close planting restricts roots
Fruit trees with confined root systems do not grow much and if properly cared for in regard to water and nutrients, can remain healthy for a very long time.
Fruit trees planted closely together experience root competition. Root distribution, as well as abundance of roots, is influenced by the root growth of other trees planted close by.
Roots will in preference always grow into areas of soil free of competition from other fruit trees.
It must be assumed that the roots exude or produce substances that are inhibitory to root growth of fruit trees of the same species or variety.
High-density planting suppresses tree growth, and while competition for sunlight may cause shoots to extend and result in taller fruit trees, girth of the trunk, expressed as trunk cross-sectional area (TCA), is decreased.
The weight of above ground parts of a tree, excluding the fruit, is proportional to TCA, and thus, root competition decreases vegetative growth above the ground.
(continued next month)
See this article in Tree Fruit Jan 2018
