growers@sgcotton.com.au Roger Tomkins - Greenmount Press

FIGuRE: 3 Relationship between EM34 and a) estimated deep drainage (mm/year), and b) log
estimated DD
furrows can be only a couple of hundred metres.
In the few instances where water storage reservoirs have been
constructed they are small. This is similarly the case with respect
to the more extensive prior stream channel which extends to the
northwest and due west past Wee Waa and Merah North.
Conversely, and on the clay plains proper, estimated DD is
small (less than 150 mm per year). This includes the clay plain
between Spring Plain and Bald Hill Roads. This is also the case at
the northern end of Doreen Lane. In these locations, irrigation
runs are consistently much longer between 600–800 metres. The
reason for this is because of the swelling nature of the Vertosols
and the alluvium appears to be thicker in these areas.
In addition, these areas are more commonly used to site large
water storage reservoirs. This is the case at ‘Auscott’ where two
adjoining storages have a combined approximate dimension of
1one square kilometre.
The relationship between EM34 and DD changes most rapidly
where DD ranges between 150–350 mm per year. Whilst the
spatial distribution of this DD range lies adjacent to the prior
stream channels, these areas represent for the most part soil of
the second and third terraced fan of Namoi alluvium. Irrigated
farms such as ‘Apple Trees’, ‘Glenarvon’, and ‘Beechworth’ fall
within these areas. Estimates of this magnitude also characterise
irrigated farms in The Gardens, north of Merah North and
Wee Waa and to the east of and including the ACRI. This
suggests WUE results collected from a lysimeter installed and
commissioned at the research station are most applicable to
these areas.
FIGuRE 4: Spatial distribution of estimated deep drainage (mm/year) using the EM34 calibration
shown in Figure 3
August–September 2012 The Australian Cottongrower — 45