Agriculture Reference
In-Depth Information
FIGURE 1
Location of field site at Isabela, PR.
The experimental site of 0.1 ha was divided into four blocks, each block divided
into four plots, one for each treatment, for a total of 16 plots. The plots measure 67
m 2 . The treatments included two lime levels (lime and no lime) and two fertigation
frequencies (F1 and F2). Each plot had four beds covered with plastic (silver side ex-
posed) with two rows of sweet pepper plants per bed. The transplanted sweet peppers
were grown in rows 91 cm apart, 30 cm apart along rows, with beds 1.83 meter on cen-
ter. This gave a plant population of approximately 37,000 plants per hectare. There was
an initial granular application of triple super-phosphate of 224 Kg/ha and 80 Kg/ha of
10-10-10 fertilizer. Peppers were planted from March 11th through March 13th, 2002
and January 27 through January 31th, 2003. KNO3 and urea were injected through
the drip irrigation system throughout the season at different frequencies (weekly [F1]
or bi-weekly [F2]). The total nitrogen applied during the season was 225 Kg/ha. After
transplanting, soil samples were taken bi-weekly at 20 cm increments, down to an 80
cm depth from each plot to be analyzed for moisture content and nitrogen concentra-
tion. Each date in which soil samples were collected, whole plants were harvested for
growth data. Periodic pesticide applications were made to control weeds and insects
affecting crop growth.
14.2.2 WATER BALANCE
A water balance approach [Eq. (1)] was used in this study to estimate percolation past
the root zone.
PERC = R - RO + IRR - ET c + ΔS
(1)
where: PERC is percolation below the root zone, R is rainfall, IRR is irrigation, RO is
surface runoff, ET c is crop evapotranspiration, and ΔS = S1 - S2, where S1 and S2 are
the water stored in the soil profile at times 1 and 2, respectively. The units of each term
in Eq. (1) are in mm of water per day. Rainfall was obtained from a tipping bucket-
type rain gauge located on the Isabela Experiment Station property. The rain gauge
was located within a weather station complex located approximately 0.4 km from the
study area. The weather station consisted of a 10 meter (high wind resistant) tower
with lighting protection, data logger and radio communication system, and sensors
 
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