IRRIGATION SCHEDULING FOR SWEET PEPPER - Management, Performance, and Applications of Micro Irrigation Systems - page 177

ages 900 cm/day [11]. Bulk density, porosity, hydraulic conductivity, moisture content
at 0.33 and 15 bars pressure, and AWHC were obtained from undisturbed cores in the
laboratory.
Measured soil pH soil was between 4 and 5. Laboratory incubation tests were
performed to determine the proper amount of lime needed to be applied to the soil to
increase the pH to around 6.5 in the limed treatments; this amount was 7.4 tons lime/
ha. The fi rst year the pH did not respond as expected in the limed plots, and therefore,
this may have contributed to there being no signifi cant difference observed in the esti-
mated nitrate losses by leaching between the lime and no-lime treatments. The second
year the amount of lime applied to the limed treatments was doubled (14.8 tons lime/
ha) and pH levels rose as expected.
Figure 2 shows a comparison of the evapotranspiration derived from pan and Pen-
man-Monteith methods during Year 2. ET pan was observed to have higher variability
than ETc. For reference, Fig. 2 also shows the ETc based on long-term average climate
data for Isabela, PR. The seasonal ET (mm per season) was 447 for the Epan methods,
402 for Penman-Monteith method based on weather station data and 511 for Penman-
Monteith based on long-term data, respectively.
FIGURE 3 Estimated and measured volumetric soil moisture content between March 27th and
July 9th 2002 and January 27th and June 12th, 2003.
The water balance equation (the Eq. (1)) was calibrated for the site conditions.
Figure 3 shows the simulated and measured average soil moisture content for Year 1
and Year 2. The measured moisture contents shown in Fig. 3 represent the vertically
averaged moisture content over all 16 plots. The minimum and maximum measured
soil moisture content is also shown in Fig. 3. Vertically averaged values of the in-
situ-measured fi eld capacity equal to 0.39 and 0.35 were used in the Year 1 and Year
2 analyzes, respectively, (averages from Table 1). It was necessary to use a value of
RO/R = 0.25, reasonable agreement between the estimated and measured soil moisture
content. During Year 1, the beginning of the season was quite wet. On April 6, 2002, a
176 mm rainfall occurred, which caused severe fl ooding of the study area. During Year
2, a rainy period occurred during April 5th through April 18th with fl ooding observed
in the fi eld plots. The largest rainfall of the season occurred on April 10, 2003 equal
to 97 mm.