May 2019 WCN Digital Edition

Figure 2. Illustration of amount of water applied orchards with a good 90 percent DU (left) vs poor 70 percent DU (right). In this illustration, the target
amount of water applied is 1.0 inch. The difference in water applied across the orchard with 90 percent DU is 0.22 inches. The difference increases to 0.72
inches in the orchard with 70 percent DU, with the wettest trees receiving twice as much water as the driest trees.
Continued from Page 10
Impact of Poor DU will be
Reflected in Orchard Health
and System Run Times
Figure 2 shows a difference in
applied water to an orchard where
the DU is 90 percent versus a DU of
70 percent. In a scenario where the
irrigator is targeting 1 inch of applied
water in a block with a 90 percent DU,
the applied water in the driest quarter
of the orchard was 0.9 inches, while the
wettest quarter of the orchard received
1.12 inches—a difference of 0.22 inches
between the driest and wettest quarters
of the orchard.
However, an irrigator targeting 1 inch
of applied water in a block with a 70
percent DU will see the driest quarter of
his orchard receive 0.7 inches, whereas
the wettest quarter of the block receives
1.42 inches of water. In this scenario, the
wettest quarter of the block is receiving
TWICE as much water as the driest.
Management in a block where trees are
receiving wildly different amounts of
water becomes complicated because key
events such as hull split and harvest can
vary in duration and timing depending
on tree water status. Equally, if not
more important, fertigation of nutrients
such as nitrogen will not be uniform
and increase the risk of leaching in the
wettest areas of the block.
A low DU will also impact your
bottom line because you will need
to run your irrigation system
longer to ensure that the driest
quarter of your block receives the
target application amount. Table
2 shows an example of the weekly
evapotranspiration (ET) use of
almonds, pistachio and walnuts
Crop
Almonds
Pistachios
Walnuts
Continued on Page 14
Past Week
Water Use
1.6
1.7
1.4
["MANAGEMENT IN A
BLOCK WHERE TREES
ARE RECEIVING WILDLY
DIFFERENT AMOUNTS
OF WATER BECOMES
COMPLICATED..."
Adjusted for System Efficiency
70%
Table 2. Sample from an ET irrigation report from August 2018. The columns under ‘Adjusted for System
Efficiency’ show how much more water needs to be applied to ensure that the trees in the driest quarter of
the block receive the amount of water shown under the ‘Past Week Water Use’ column.
2.3
2.4
1.9
80% 90%
2.0
2.1
1.7
1.8
1.8
1.5
[
12
West Coast Nut May 2019