122 Symes and Connellan: Water Management Strategies for Urban Trees Graphical presentation of soil moisture data allows absolute values to be read as well as the changes in soil moisture conditions to be readily interpreted. Examples of how soil moisture data can be used to provide a better understanding of aspects of the water management of complex landscapes include: • identification of active root zones in the soil profile • estimate of the Crop Coefficient (Kc ) value • influence of water logged conditions on plant growth • effectiveness of irrigation • effectiveness of rainfall • drainage characteristics of the soil Seasonal Adjustment of Site-specific Landscape Coefficients Based on the information shown by soil moisture sensing, RBG has now included seasonal differentials in its four scheduling regimes for garden areas: landscape coefficients are adjust- ed for winter, spring, summer, and autumn. This has reduced overwatering in the cooler times of the year, and particular- ly, the transitional periods from winter-spring-summer. For some areas, it was shown that under-watering occurred in the peak of summer that was difficult to remediate under current water scarcity and restrictions of Melbourne. The availability of soil moisture readings through the internet allows the actual soil moisture conditions to be monitored in real time and di- rect reference made to the condition of the plants. In periods of high temperatures and high evaporative demand this infor- mation allows informed water management decisions to be made. The soil moisture data generated allows key indicators to be used to aid in the water management of the landscape. SUBSOIL WATER STORAGE Subsoil Moisture Storage and Recovery is a methodology being developed through a research partnership among the RBG, Sentek Pty, Ltd., and the University of Melbourne to recharge subsoil moisture when the water is freely available as a reserve for trees. The severity of depletion of soil water reserves, over multiple dry years, is illustrated in Figure 4. Soil moisture sensing technology provides the means to study the effectiveness of the irrigation technique and the rate and depth of tree water use. This technique is being considered to optimize the use of stormwater, as this is usually more available in the late autumn-winter months when irrigation is not normally required. The concept is that stormwater is applied via irrigation to soil profiles in winter-spring to ‘bank’ water when stormwater supplies are more available (Figure 6), thus ensuring subsoil moisture is adequate for the forthcom- ing summer and to also minimize the use of potable water for irrigation. At study site 57, the graph shows soil moisture traces at each 10 cm layer of soil profile down to one meter depth under a specimen of Quercus aff. alba (Figure 7). It can be seen that water is not used at most depths during winter when the tree is dormant. However, after precipitation during July to August 2010, all layers of the soil profile including the subsoil have been recharged. The patterns of water extraction by the tree can be more easily seen from mid-December 2010, ©2013 International Society of Arboriculture with most intensive use in January 2011, especially for the deeper soil layers. These findings have led to the consider- ation of a split irrigation scheduling/water balance regime in the RBG. For example, the landscape coefficient (KL top 30 cm in December was calculated to be KL 0.5, but for the full profile it equated to KL 0.94. This means the turf zone could be managed at lower KL values while the trees are using ) for the subsoil reserves, thus saving potable water during summer. Based on the methodology described by Harris (1998) and Kopinga (1998), modeling of tree water needs in the RBG suggest that if soil moisture was at full capacity and acces- sible to 1000 mm soil depths, then the average Gardens tree could subsist for about 90 days in summer with no addition- al precipitation. This potentially extends to 150 days when considering species more adapted to drought conditions. The application of Subsoil Moisture Storage and Recovery has the clear potential to maintain tree health in water-scarce environ- ments, and minimize the use of supplementary potable water. Figure 6. Schematic of typical stormwater availability and irriga- tion demand. Figure 7. Soil moisture traces for the root-zone of Quercus aff. alba growing at RBG site 57. Note: Figure 5 shows individual soil moisture traces (mm/10cm) for the root zone of Quercus aff. alba at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 cm spacings from top to bottom in the graph. Previous to August 2010, soil moisture contents from 60cm to 100 cm were at or below permanent wilt- ing point. Recharging of soil moisture to 100 cm depth can be seen early on in August 2010. Tree water use is most visible to 100 cm depth from mid-December 2010 until late March 2011. The tree enters dormancy during April 2011 and soil profile begins recharging at this time.
May 2013
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
