The overall objective of this study was to determine the influence of
intermittent water application via overhead irrigation on water and N leaching,
substrate water distribution, and plant growth in a pine bark substrate.
Intermittent irrigation was defined as the application of a plants' daily water
allotment in multiple applications with prescribed intervals between
applications. Specifically, experiments were conducted to determine: 1) the
influence of water application rate and pre-irrigation substrate moisture content
on water application efficiency, 2) the influence of the number of intermittent
applications and interval duration between applications on application
efficiency, 3) substrate water distribution after intermittent irrigation, 4) efficiency
of intermittent irrigation in unamended and sand-amended pine bark, and 5)
influence of intermittent irrigation on plant growth. In all experiments, Marigold
(Tagetes erecta L. 'Apollo') was grown in unamended or sand-amended pine
bark in 3.8-liter containers. After saturation, bark was allowed to dry via
evapotranspiration to targeted moisture deficits after which irrigation treatments
were applied via a simulated overhead irrigation system. In experiments
evaluating intermittent irrigation, water was applied intermittently (multiple
applications with intervals between applications) or continuously (single
application). After 1 h drainage, collected leachate was measured and
analyzed (in two experiments) for electrical conductivity, N03-N and NH4-N and
water application efficiency (percentage of applied water that is retained in the
substrate) determined. There was an inverse linear relationship between water
application rate and efficiency. Leachate N (total) increased linearly as
application rate increased. Efficiency increased curvilinearly and leachate N
(total and concentration) increased linearly as pre-irrigation substrate moisture
content decreased. Efficiency of intermittent irrigation was greater than
continuous irrigation over a range of pre-irrigation substrate moisture contents,
and in both unamended and sand-amended pine bark. Intermittent efficiency
increased linearly as interval duration between applications increased.
Efficiency of five 60 ml applications was greater than three 100 ml applications.
Gravimetric moisture content of the bottom third of the substrate was greater
with intermittent than continuous irrigation. Intermittent efficiency was greater in
pine bark than in sand-amended pine bark when the water deficit from
container capacity was the same for both substrates. Repeated intermittent
irrigations resulted in less water and N leaching compared to continuous
irrigation. Intermittent irrigation did not result in substrate nutrient accumulation
and had no adverse effect on plant growth. Fresh and dry root weights and
shoot and root N concentrations were greater with intermittent irrigation than
continuous irrigation.
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