80 years of research in the Goulburn Valley (part 8)

Soil structure: Soft stable porous soil was considered very important for high yields in a high-density irrigated orchard.

(Continued from last issue)
Soil structure
In contrast to soils for fruit production in Europe and North America, soils in north-central Victoria are old and highly weathered.
The irrigated surface soils set hard when dry and the subsoils are massive clays with low permeability and drainage, and restrict roots.
The research was directed towards creating and maintaining an environment that did not restrict roots.
The research included:
• the distribution of applied irrigation water within the soil, and uptake of water by roots
• encouraging roots, fauna and microorganisms to improve the structure of surface soils
• improving the physio-chemical properties and drainage of the subsoils
• determining soil aeration needed for root growth.
Development of a suitable soil structure for irrigated fruit trees depends on the roots, fauna and microorganisms within the soil; and maintaining and improving soil stability with gypsum (calcium sulphate).
This is sometimes needed to soften surface soils and to improve their structure.
Soil stability is improved and pores can be created chemically by sticking together (flocculation) of clay particles by the addition of gypsum.
When organic residues as organic matter (OM), are added to soil, and large pores are formed by fauna and roots, the soil is opened up to give rapid water movement.
When concentration of OM is low (less than 2%) in soil, the soil packs up early in the irrigation season, and water infiltration is low.
Considerable modification and stabilisation of the soil structure resulted in a new system of soil management.
What was needed in the surface soil?
• High infiltration and permeability of soil during late spring and summer, because trees need plenty of water while actively growing and producing fruit.
• Well-aerated soil to add oxygen, and to remove toxic gases (e.g. carbon dioxide, methane).
• Minimum competition from summer weeds when trees are actively growing.
• Adequate wetness in soil to promote root growth of young trees.
• Optimum temperature for roots.
• No diseases.
• Maximum volume of surface soil available, since roots do not grow in the subsoil.
• Incorporation of organic matter into the soil without cutting roots.
With rising costs and growers finding it harder and harder to find skilled workers to do the job, to do it efficiently, and to do it correctly, we believed, mechanisation was a strategy to stay competitive.
Therefore, we needed to determine what modification was required to the structural features of the frame and canopy of the free-standing tree, to reduce damage to fruit that are mechanically harvested, so that we could develop research programmes for ensuing years in the proper order of priority.
While the trees still needed to produce heavy yields, mechanical harvesters would be much more effective when the trees had been deliberately shaped to simplify mechanisation.
(continued next month)

See this article in Tree Fruit July 2019

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