Manage with low allocation
From the November 2007 edition of Agriculture Today.
The critical water shortage and resultant low allocations have forced many irrigation managers to pay more attention to their practices, systems, and the use of technology to maximise water use efficiency.
Now is the time for orchard and vineyard managers to evaluate a range of critical issues.
They are realising how important an efficient irrigation system is to meet production potential and to apply available water most effectively.
Routine checking of emitter pressure and discharge is becoming standard practice. An irrigator in Sunraysia recently flushed his system for the first time in 15 years and reduced discharge variation from 30 to 15 per cent.
Over time, system performance will decline to some degree in all irrigation systems. Systems which are regularly flushed, chlorinated, have adequate filtration and are initially well designed, are more able to maintain an excellent level of performance.
Variability is accentuated when less than optimal levels of irrigation are applied over an extended period. Variability due to uneven and inefficient irrigation systems, and therefore rootzone salinity levels, is something that managers do have a high level of control over; for this reason checking the performance of systems is becoming a routine management practice.
Rootstocks are another source of variability within a vineyard. Low water conditions have provided the opportunity to rigorously determine the drought tolerance of various rootstocks.
Some rootstocks are significantly better at tolerating low water applications than others.Where a range of rootstocks exist, managers have begun altering their irrigation systems by installing additional submains to segregate blocks of these rootstocks into individual valve units.
The interest in pumps operated by variable speed motors has increased recently. Managers monitoring crop water use with, for example, a range of winegrape varieties, have recognised that each variety has its own specific water requirements.Some blocks have received additional water in the past to allow existing pumps to operate most efficiently.
For wine grape growers, variation in water requirements may be due to variety, age, desired wine style, soil type and rootstock.
Similarly, citrus growers have observed a big variation in irrigation requirements of mandarins between March and May compared to navel varieties, and the significantly lower requirement of non-bearing trees.
Set valve combinations may also change, as well as routine calendar irrigation scheduling, as water is shuffled around the vineyard in the most efficient manner possible.
Soil moisture monitoring is a must, particularly if uncommon management practices such as removing canopy or fruit are adopted as water saving or survival measures.
The moisture measurement graphing capacity of these tools allows an accurate assessment of the water saving effects of various management practices.
Managers with severely restricted allocations are being required to make tough decisions and prioritise their blocks in order of importance. Management decisions on specific blocks should be based on a number of issues, including economics, and the winery’s priorities now and in the future. Other issues include contract limits, historical water requirements, existing plant health, vigour and rootstock.
Managers may have to get used to vineyards and orchards with lower than optimal water allocations in the coming seasons. Many were caught out last season by not fully understanding their operation’s water requirements. They lacked appropriate records of the requirements of individual blocks and varieties to refer to when water budgeting and prioritising was required.
Contact Jeremy Giddings, Dareton, (03) 5019 8421, jeremy.giddings@dpi.nsw.gov.au
