Comparative evalualtion of evapotranspiration parameters in a naturally ventilated polyhouse and open field
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Date
2017
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Department of Irrigation and Drainge Engineering, Kelappapji College of Agricultural Engineering and Technology, Tavanur
Abstract
Studies on the water requirement of horticultural crops in polyhouses are
scarce and despite the water scarcity, irrigation is mainly scheduled according to
farmer’s experience. Canopy development and management of some polyhouse
horticultural crops is quite different from that outdoors. Differences in plant
spacing, crop height and aerodynamic properties may affect the crop coefficient
values. Moreover, the proportion of diffuse radiation in polyhouse is different from
that outdoors. Thus it is questionable whether the standard crop coefficient values,
determined experimentally outside polyhouse can be used directly to determine the
evapotranspiration of the greenhouse crops. Complete data on meteorological
parameters inside poly houses is very rarely obtained and it causes lot of
limitations in applying indirect estimation methods of ET0 based on climatological
data.
Field experiment on the comparative evaluation of evapotranspiration
parameters in a naturally ventilated polyhouse and open field was conducted in a
naturally ventilated polyhouse and open field in the research plot of the
Department of Irrigation and Drainage Engineering, in KCAET campus, Tavanur.
In the study, Non-Weighing Mini-Lysimeters were used to determine
evapotranspiration parameters and to develop crop-coefficient curves for Okra.
Comparison with indirect methods was also done in order to assess the
dependability of climatic data for evapotranspiration estimates. The study
compares the data for open field and poly house conditions in order to quantify the
effect of micro climatic variations.
ETo estimated using climatological methods viz reduced pan, FAO -56
Penman-Monteith, FAO Blaney- Criddle and Thornthwaite were compared with
measured lysimetric data using simple error analysis and linear regression. Out of
all methods FAO-56 Penman-Monteith provides quite good agreement with
evapotranspiration obtained by lysimetric data with a high correlation coefficient
of 0.88 and 0.87 for polyhouse and open field conditions respectively. Studies on
crop morphological parameters indicated that plant growth and yield parameters
were not significantly different for polyhouse and open field conditions.
Seasonal average ETo for polyhouse and open field were 4.74 and 5.02
mm/day. Seasonal average ETc values of Okra for polyhouse and open field
conditions were 3.90 and 4.31mm/day. The calculated values of Kc for the initial,
mid and late season stages were 0.58, 0.94 and 0.67 in polyhouse. Open field
values were 0.61, 0.98 and 0.72 for different stages respectively. It was observed
that polyhouse Kc values were lower than the open field. The variations in micro
climate inside poly houses with reduced solar radiation and wind velocity
combined with higher humidity and temperature may have contributed to lesser
ET. The results implied that water requirement is lower inside the polyhouse
compared to open field conditions.
The results of this study can be used as a guideline in the computation of
water requirement of poly house crops instead of depending on open field accepted
values for Tavanur region. If the poly house irrigation is scheduled in such a way
as to apply the right quantity of water enough to meet the evapotranspiration
requirements of crops, considerable water saving can be achieved. The quality of
produce is high, duration of crop season is longer and year round cultivation is
possible inside poly houses which implies significant saving in water without
compromising yield and product quality.
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