Notes by Milton Spurling

Department of Agriculture

Milton B Spurling graduated at the end of 1945 and was appointed as a Horticultural Research Officer to the Department of Agriculture in January 1946. I was not yet 21 years so I could not be appointed permanently as an “adult” in the Department of Agriculture.

Initially undertook a major research project investigating leafdrop in Washington Navel oranges which lead to a longer and larger investigation of the water requirements of citrus and evaluating irrigation methods for citrus and other horticultural crops. The research project was funded by Murray Citrus Growers Association.

With the selection of Loxton as the site for horticultural war service land settlement I was required to develop the specifications for irrigation methods and irrigation timing and water requirements for the crops. Much of the work was conducted at the Berri Experimental Orchard as there was no water reticulated on the proposed development area at Loxton – it was resumed wheat growing land of sand dunes and heavier soils in the swales.

A soil survey by CSIRO produced the soils map for an area of about 12,000 acres and this was to form the basis for crops to be grown and irrigation methods to be used.

Sprinkler systems were evaluated at Berri Experimental Orchard and as soon as water was available at Loxton the design criteria for furrow irrigation were established as well. The water requirements of crops were established on the mature crops at Berri Experimental Orchard, and at Waikerie using fruit growth measurements to indicate when trees were developing moisture stress and correlating these tree response measurements with evaporimeter records which were then used to indicate irrigation timing. It was clear early on, that citrus were the most demanding of water and being evergreen needed water all the year round. So the work was concentrated on citrus anticipating that stonefruit and vines would be satisfied if citrus were adequately catered for.

To determine how much water needed to be applied per irrigation, the root distribution of citrus trees was determined by trenching alongside mature trees on a range of soils representative of those in in the Loxton Irrigation Area, being the Barmera Sand, Berri Sand and Waikerie Sand soil types. Trenches to 5 feet deep were dug by hand and the root systems physically mapped. Then the amount of water to “wet” the depth of soil occupied by roots was established by infiltration studies.

The resultant work determined the cause of the citrus leafdrop problem.  In the older settlements irrigation schedules were based on the needs of the vines – 5 or 6 general irrigations per year – and this meant that once the crops were off the vines and before the spring bud burst, irrigations were not needed by the vines. Hence the citrus were usually not irrigated either. In the case of Valencia oranges the trees were carrying fruit all the year round and water could be drawn from the fruit as a buffer when the trees started to develop moisture stress. Washington Navel oranges on the other hand, once the fruit was harvested in late autumn, early winter, did not have this fruit buffer on the trees. What the root distribution studies and the water requirement studies found was that during winter and early spring, while the surface soil might be kept moist by winter/spring rain and give the appearance of not requiring irrigation, in fact the deeper rootzone was depleted and in late August-September trees developed moisture stress even though the surface soil was moistened by rain. Any burst of warm weather and the Washington Navel trees shed their leaves.

As my appointment was funded by a research grant from the citrus industry it was very satisfying to have established the cause of the leafdrop and provide the evidence to justify special irrigation for citrus in early August.

The root distribution studies provided the basis for determining which soils at Loxton (and later Cooltong) were suitable for which crops. In fact the areas suitable for fruit crops at Loxton was reduced significantly (by about 40%) because areas which were too shallow were excised from the plantings.

Soils suitable for citrus were suitable for sprinkler irrigation and heavier soils were designed for furrow irrigation - the optimum gradients for efficient furrow irrigation were determined experimentally once water was reticulated in the main A channel  system on the Northern end of the settlement to be planted in 1948. Stonefruit fitted in between citrus and vines as to these soil requirements and were usually designed for sprinkler irrigation.

The planning of the Loxton Irrigation Area was determined to avoid mistakes of earlier settlements – choosing soils suitable for crops, using irrigation methods and irrigation frequency to give efficient irrigation, allocating block size to give economically viable areas according to the value of crops from 25-35 acres, choosing planting material – propagated trees and vines - from established high quality mature plantings were all taken into account.

A factor which was new to horticultural land development was predicting frost liability. Recording sites in the Berri-Loveday Irrigation Areas for which frost liability was known from previous history, were selected and minimum recording thermometers were installed at a standard height, 1 meter above soil level.

Concurrently, lines of thermometer recording sites were set out in the Loxton Irrigation Area locating these at known contour heights from the highest point (now in Loxton North) to the lowest points in the valleys between the sand dunes. It was known that while some severe frosts were associated with a tongue of cold air blowing across the countryside irrespective of contour heights (adiabatic frosts) that the most frequent frosts were still air frosts (inversion frosts) and these could be correlated with contour height i.e. cold air flowed down into valleys and if this cold air could not escape to the river valley then a severe frost pocket resulted.

Besides recording the minimum temperatures on nights when inversion conditions favoured frosts, the drift lines for cold air were established by lighting smoke generators while the frost conditions applied and the cold air drift lines were mapped. This was facilitated by the fact that all fences had been removed over the area of the proposed settlement and by this time – late 1947 – I had been appointed to the district as a resident advisor and was living in one of the old farm houses within the area to be developed. On frosty nights I could drive across country to set smoke generators going in contour saddles and suspect valleys and then map the smoke traces as soon as it was light enough to see before sunrise dissipated the frost conditions.

After two seasons of these records a frost liability map for the whole of the Loxton Irrigation Area was produced identifying areas in which citrus may be economically damaged and so planted to deciduous tree fruits and particularly to identify cold air drift lines which should not be impeded by windbreaks or buildings. Plans to beautify the Loxton-Berri road by tree plantings were modified to avoid interfering with cold air drift lines.

The results of this frost liability study were used in the extension of the Loxton Irrigation Area south of the town and in the development of Golden Heights and Sunlands near Waikerie.

Another series of research projects at Loxton and on the Nuriootpa Viticulture Station were to have a significant influence on viticultural practices also related to frost management of vines.

Measuring the minimum temperatures reached over various soil surfaces and a range of ground covers established that a 3° to 4° C difference at crop height resulted from leaving cover crops (after oats and peas or broad beans) standing rather than discing the ground cover down before frosts occurred. The temperatures over a largely loosely cultivated surface were lower than over a compacted surface.

So the recommended management practice became – turn in cover crops before the frost danger period and let the soil surface consolidate to reduce the frost hazard.

The other significant recording was that the minimum temperatures reached during an inversion frost were lowest at ground level and increased rapidly with height above ground so that increasing the height of vine trellises reduced frost hazard. As a result there was a significant shift to higher trellises for vineyards.  For example the Barossa vines which had been trellised at 12-15” above ground were taken up to 18” or 2 feet. New plantings in frost prone areas like Coonawarra were trellised at heights of 3 or 4 feet.

To provide guidance to growers on horticultural developments, forty acres of land near the town of Loxton were selected as a site for a research station to eventually replace the Berri Experimental Orchard as a source of research facilities to service the new settlement.  Meteorological recording commenced as early as possible as this new site and the research station became the location of the laboratories for a whole range of needs in the area. An early development which was to have immeasurable value to the fruit industries especially citrus was the building under the oversight of Noel Richardson of an insectory and the development of biological control measures against scale insects of citrus.