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The terms of reference for this project required the measurement of the unstressed water use and ancillary variables of at least 4 types of fruit tree/orchard crops at selected sites to enable modeling using available South African or international models. Furthermore, the conditions stipulated that the selection should be representative of sub-tro...
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... CR1000 data logger, connected to two AM16/32 multiplexers (Campbell Scientific Inc., Logan, UT, USA), was programmed to initiate the heat pulses and record hourly data from the respective thermocouple pairs. This instrumentation, together with relay control modules to regulate the heat pulses and batteries to power the system, were all housed in heavy steel boxes for security reasons ( Figure 6). To account for lateral stem growth the HPV probes were removed and repositioned to their correct depths at the start of the growing season (October) and periodically thereafter to account for stem growth or unintentional movement / accidental removal of the probes. ...
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... summer measurement period was subject to large variations in weather conditions, which facilitated the collection of a representative range of data. The summer temperatures ranged from 16.7°C to 44.4°C with an average of ET of 3.45 mm.day -¹ (Figure 60). The highest recorded rainfall in this period was 119.5 mm in the middle of January 2012. ...
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... soil water content was measured using CS616 probes at two different locations and three different depths (0.3, 0.5 and 0.9 m), together with irrigation and rainfall volumes (Figure 65 and Figure 66). There was a marked difference in readings from the various depths in the 2010/11 season in row 5 (north), but this differentiation in water content with depth down the profile was not as evident at the start of the 2011/12 season. ...
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... serves to illustrate the difficulties faced when trying to estimate tree water use from the soil water balance based on soil water measurements. There was a close relationship between applied water (irrigation) and water used (transpiration) for much of both seasons in the 'Rustenburg' Navel orchard, with rainfall + irrigation and only irrigation moving above the 1:1 line late in the season, i.e. applied water exceeding transpiration, when irrigation volumes were increased ( Figure 67). As rainfall is low in this region there is very little difference between the irrigation and irrigation + rainfall plots, with the grower trying to make optimal use of the limited rainfall. ...
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... volumetric water content within the tree row and in between the tree rows exhibited more variation over the summer rainfall period, where responses to rainfall events were evident and when irrigation volumes were higher ( Figure 68 and Figure 69). There was a distinct decline in soil water content following the cessation of rainfall events in autumn and winter and an increase following the resumption of the rainy season. ...
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... volumetric water content within the tree row and in between the tree rows exhibited more variation over the summer rainfall period, where responses to rainfall events were evident and when irrigation volumes were higher ( Figure 68 and Figure 69). There was a distinct decline in soil water content following the cessation of rainfall events in autumn and winter and an increase following the resumption of the rainy season. ...
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... are preliminary estimates as it is difficult to parameterise the model without measured data. Using these estimates total ET for the 2010/2011 season was 696 mm, 3% of which was soil evaporation (Figure 76a). In the second season (2011/2012) the total ET during the season was 786 mm, 12% of which was evaporation (Figure 76b). ...
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... these estimates total ET for the 2010/2011 season was 696 mm, 3% of which was soil evaporation (Figure 76a). In the second season (2011/2012) the total ET during the season was 786 mm, 12% of which was evaporation (Figure 76b). These low rates of evaporation suggest that very little of the water applied to the orchard was lost through evaporation and applied volumes matching transpiration may not necessarily cause water stress in the orchard. ...
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... were conducted from August 2010 until July 2013 in a 9-year old nectarine orchard (Prunus persica) at a commercial farm ("Ou Stasie") located near the town of Wolseley (33˚2533˚25' 0.59" S and 19˚1419˚14' 44.84" E, elevation = 318 masl) in the winter-rainfall Western Cape region of South Africa ( Figure 85). The orchard was 140 m by 200 m (2.8 ha) in extent ( Figure 86). It was planted with 'Alpine' nectarines on SAPO 778 rootstock. ...
