Organic Farmer Aug/Sept 2019

Irrigation treatment
Sprinkler
4-dripline per bed
3-dripline per bed
Fall 2018
Fresh yield (lb/ac)
12,406 a
11,378 b
10,950 b
Winter 2019
Irrigation treatment Fresh yield (lb/ac)
Sprinkler
1.5D-4B
1.5D-3B
13,281 a
12,414 ab
12,116 b
Table 1. Mean spinach fresh yield values of each irrigation treatment in each of the fall and winter experiments. Yields with different letters
significantly differ (p < 0.05) by Tukey’s test.
Figure 2. Visual comparison of the drip treatments versus the sprinkler treatment 38 days after planting in the fall experiment.
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organic production. Therefore, additional
strategies are needed to reduce
disease pressure, including irrigation
managements.
It is postulated that new irrigation
management techniques and practices
in spinach production may have a
significant economic impact to the leafy
greens industry through the control of
downy mildew. In addition to reducing
losses from plant pathogens, new
irrigation practices could reduce risks
to food safety (risks caused by overhead
application of irrigation water). For
instance, adapting drip irrigation for
high density spinach plantings could
be a possible solution to reduce losses
from downy mildew, improve crop
productivity and quality, and improve
crop water and fertilizer use efficiency.
Currently, no one uses drip irrigation
for spinach, and there is a lack of information
on the viability of drip irrigation
technology in spinach. This project aims
to evaluate the viability of drip irrigation
for organic spinach production and
assess its impact on the management of
spinach downy mildew.
Field Experiment
The field experiment was conducted
over two crop seasons (fall 2018
and winter 2019) at the University
of California Desert Research and
Extension Center in Holtville,
California (Figure 1, see page 10).
Two dripline spacings (three and
four driplines per 80-inch bed) was
studied versus sprinkler irrigation as
control treatment. A comprehensive
data collection was carried out to fully
understand the differences between
the irrigation treatments. Untreated
Viroflay spinach seeds were planted
in both seasons. True 6-6-2 (a homogeneous
pelleted fertilizer) and True
4-1-3 (a liquid fertilizer) were applied
as pre-plant fertilizer and as complementary
fertilizer through injection
into irrigation systems, respectively.
The emitter spacing on the dripline was
8-inch with nominal flow rate of 0.13
gph (gallons per hour) at 8 psi (pounds
per square inch). The beds were 80-inch
wide by 200 feet long. The experiment
was arranged in a randomized complete
block design with four replications. All
treatments were germinated by sprinklers.
In the winter trial, 6-spinach bed
was germinated and irrigated using
drip irrigation (four driplines per
80-inch bed) the entire crop season to
evaluate the possibility of using drip
throughout crop season including plant
establishment.
Fresh Biomass Yield
In the fall trial, mean fresh biomass
yield for the sprinkler treatment was
12,406 lb/ac (pound/acre), approximately
9 percent more than the
4-dripline in bed treatment (Table 1). In
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Organic Farmer August/September 2019