Brett Rosenzweig - Industry Development Officer In The Orchard
T he next few months leading up to harvest will again be a critical time for irrigation management. The Bureau of Meteorology predicts a drier and hotter than normal period from November to January. The official summary at 30th October 2014 is: • A drier than normal November to January is more likely over the northern and eastern mainland. • For the month of November, a drier than normal month is more likely over the northern half of Australia, with the chances of a wetter or drier November roughly equal over most of the south. temperature outlooks indicate a warmer than normal season for both daytime and night-time temperatures across most of Australia. • Climate influences include warmer than normal temperatures in the tropical Pacific Ocean, near normal tropical Indian Ocean temperatures, and normal to cooler than normal sea surface temperatures off Australia’s northern coasts. The next update is scheduled for the 27th November and can be found on the Bureau’s website at: http://www.bom.gov. au/climate/outlooks/#/overview/summary. Everyone knows moisture stress can have an impact on final yield. Moisture stress from fruit set until pit hardening will limit the overall fruit size and moisture stress from pit hardening until harvest will impact the overall kernel size and weight (Figure 1). In simple terms if moisture stress occurs before pit hardening, fruit growth is reduced. Therefore no matter how much irrigation and fertigation occurs after pit hardening, the end result will always be the same - small kernels. If moisture stress occurs after pit hardening the result can be pinched, shrivelled, misshapen or small kernels. If moisture stress at any stage during the fruit/kernel growth can impact negatively on kernel size and weight at harvest, is there any stage • The November to January
the kernel loses moisture after hull split, the variation in kernel weight becomes evident. There is also the possibility that the final kernel weight accumulation can occur in the period from early hull split to harvest. Both of these theories haven’t been analysed as part of the project and further confirmation is needed. Based on the simple principle that moisture stress has a direct impact on
during the season which can have the most impact and therefore should be given the most attention in regards to irrigation scheduling? The short answer is NO - once you lose the opportunity for fruit/kernel growth you can’t get it back. Figure 2 (opposite page) highlights the kernel dry weight accumulation during the 2011-12 growing season at the RDI Trial located at Lake Powell, Victoria.
Figure 1: Parts of an almond.
final yield, it’s critical to keep on top of irrigation scheduling this summer. With the possible increase of extreme heat events in the future a review of irrigation system capacity and/or scheduling requirement is warranted. A recent calculation by Ben Brown estimated for the 2013-14 season highlighted how many days an irrigation system could not match tree demand based on varying application rates. Assuming a total application of 14ML/ Ha for the season, an irrigation system with an application rate of 0.91mm/hr (10.87 mm/day) had 21 days that didn’t meet water demand. On the other hand, an irrigation system with an application rate of 1.17 mm/hr (14.04mm/day) would have four days that didn’t meet water demand. A well designed irrigation system with adequate capacity is critical to deal with the variable nature of heatwaves.
The amount of combined irrigation and effective rainfall applied ranged from 1336mm for the wet treatment (1296mm irrigation and 40mm effective rainfall) to 703mm for the RDI55 treatment (663mm irrigation and 40mm effective rainfall). Kernel dry weight accumulation is the same for each of the treatments until early hull split in January. From then until harvest (final weight measurement) the weight accumulation slows dramatically for those treatments with increasing levels of deficit (stress). The results of kernel dry weight accumulation for the 5 years of the RDI trial are shown in Figure 3 (opposite page). The decreased weight accumulation in the 55% treatments occurred regardless of whether the deficit occurred as a sustained deficit all season (SDI55) or a targeted deficit between fruit set and post-harvest (RDI55). The graphs suggest there is a lack of dry matter accumulation or oil content during the season and when
How robust are your strategies for limiting moisture stress and potential impact on yield?