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From Planting to Harvest -
A study of water requirements of olives,
from planting to first commercial harvest
by James De Barro
June 2005
RIRDC Publication No 05/039 RIRDC Project No. DEB-2A
Executive Summary
“I don’t know what I may
seem to the world, but as to myself, I seem to have been only like a boy
playing on the seashore and diverting myself in now and then finding a smoother
pebble or a prettier shell than ordinary, whilst the great ocean of truth lay
all undiscovered before me” - Issac Newton
Not wanting to generalise, but most irrigation enterprises irrigating any type of crop from annual to perennial species can improve in the efficiency of their irrigation delivery. No doubt there are irrigators who actively seek peak performance of their irrigation equipment and invest considerably in improved infrastructure for pumping, and storing water which improves water, fertiliser and, in some instances, herbicide delivery. However there is still considerable room for even the elite irrigation operations to improve in the timing of irrigation delivery and the volumes applied per irrigation if possible to regulate. Whilst there is still a national lack of experienced consulting personnel to provide accurate advice and undertake appropriate research into irrigation scheduling and specific volume application, rapid advances since the mid to late 1990’s has taken place and irrigators should utilise and learn from their knowledge to improve their water application efficiency.
The phrase ‘irrigation efficiency’ seems to be fast losing its meaning as it is readily interpreted as the act of efficiently pumping water onto a crop at least cost or with least wastage of pumped water, whereas once it inferred applying water based on crop needs. It may be time to modify this phrase to explicitly define the action of applying irrigation specific to the crop’s requirements based upon its daily water use through its growth phases and cycles.
Such a phrase could be ‘prescribed irrigation’. This research shows that appropriate timing of prescribed volumes of irrigation provides adequate supplies to service the crop requirements whilst minimising water wastage. Prescribed irrigation is a simple process enhanced by the use of soil moisture monitoring devices to determine the volume to apply to attain particular depths of penetration to service the demands of the active root zone. Irrigation scheduling using particular devices is not a new phenonomen but it is one that is readily overlooked as an optional extra in an irrigation operation rather than a fundamental tool with the same importance as the pump and pipe work.
Prescribed irrigating is a skill that can be learnt by the irrigator by trial and error and can be enhanced by experienced professional assistance. Such professional assistance should be knowledgeable regarding the appropriate tool to monitor soil moisture levels with the cost of the tool being secondary to its suitability. The ease of device installation, type of irrigation system, ease of data retrieval and resolution of the data determine suitability. Prescribed irrigation is a fine tuning of the irrigation infrastructure and optimises the efficiency.
An enhancement of prescribed irrigation is to understand the soil moisture holding capacity of the active root zone, which can be judged from the soil moisture device. By using readily available computer software that permits calculation of evapotranspiration using models such as the modified Penman Monteith model, the daily water use potential of the olive tree at any stage of development can be calculated and hence permit timing of irrigation based on cumulative water use compared to the available water storage in the active root zone. There is no need to become ‘bogged’ down in the theory of such models but provided the appropriate advice is available this approach to prescribed irrigation is accurate and successful.
This research project highlights what is suspected to be a common occurrence in irrigation operations, especially those embarking on the irrigation of a new type of crop, irrigating for the first time or irrigating to “be sure” that the financial investment to establish the irrigation enterprise results in a visually thriving enterprise. The degree of irrigation of the commercial olive orchard studied was significantly higher than the research site studied, yet there was no detectable or significant difference between the trees either annually through the four years of monitoring or at the time of the first commercial harvest. The over irrigation appeared to have no detrimental or beneficial impact on the trees.
State Governments are having an increasing regulatory role over the irrigation industries and are not as active in designated research and extension into areas such as prescribed irrigation as they could or should be. This is not a specific criticism of the State’s role but just a fact of the services they can fund and a sign of our times. Consequently it is up to the industry itself (i.e. the industry associations as well as individual entities) to progress towards prescribed irrigation via research such as this project as well as private investigations using sound experienced advice.
This research reveals that as much as there is talk of irrigation efficiency the message is not being understood or listened to.
Last updated: June 2005
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http://www.rirdc.gov.au/reports/NPP/05-039sum.html