Hysteresis of cocopeat-perlite mixture under root zone cooling system for growing butterhead lettuce (pdf tiada security)
Cocopeat is one of the leading coconut by-products known for its special characteristics; high water holding capacity, excellent drainage and absence of weeds and pathogen, however it has high water holding capacity which may not provide adequate aeration for plant root. It is common in soilless...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/71197/1/FK%202017%2063%20-%20IR.pdf |
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| Summary: | Cocopeat is one of the leading coconut by-products known for its special
characteristics; high water holding capacity, excellent drainage and absence of weeds
and pathogen, however it has high water holding capacity which may not provide
adequate aeration for plant root. It is common in soilless culture to mix perlite with
cocopeat on order to improve aeration. The ratio of mixing these two materials needs
to be determined in order to provide a better cocopeat-perlite mixture for plants.
Moreover, little attempts had been made to observe the hysteretic phenomena in
cocopeat medium and the theory used in soil physics cannot be directly applied for
container medium. Plant heat stress is more economically reduced by root zone
cooling (RZC) method compared to other environmental technique such as air
temperature cooling. This study focuses on the water retention curve (WRC) and
hysteresis for the cocopeat-perlite mixture in two conditions; with and without RZC.
The aim is to understand the behaviour of the hydraulic properties of cocopeatperlite
mixture so that the irrigation schedule for butterhead lettuce can be
established.
An extensive study on physical properties of the cocopeat-perlite mixture were
analysed in the laboratory for its particle size distribution, bulk and particle densities,
porosity, water holding capacity, wettability and hydraulic conductivity. These
properties were analysed to choose the most suitable ratio of cocopeat-perlite
mixture as a growing medium. Available water content derived from WRC and
hysteresis retention curves measurements were used to estimate irrigation scheduling
for butterhead lettuce. Irrigation interval was calculated from the crop water
requirement and the medium available water. In order to determine the effectiveness
of RZC, comparisons of butterhead lettuce growth grown in the selected cocopeatperlite
mixture with and without RZC treatments were conducted. Results had shown that the best cocopeat-perlite mixture was 3 cocopeat: 1 perlite.
This ratio had the highest porosity (63.22%) and water holding capacity (920%), and
lowest hydraulic conductivity (0.09 cm/s) compared to other ratios. These properties
are significant in providing suitable environment for plant growth. From the
hysteresis curve, the first main drying and wetting cycle of cocopeat-perlite mixture
(3:1) without RZC, showed an unclosed hysteretic loop in term of water retention
properties with a gap of 16% (0 kPa) and 9% (10 kPa) of water ratio. However,
reversible and closed hysteretic loop was observed for the second drying and wetting
cycle. Under RZC treatment, retention and hysteresis curves shifted upward from the
normal curves which resulted in an increase in volumetric water content for suction 0
to 10 kPa. The hysteresis loop of the first cycle was anticlockwise which was
contradictory with the normal clockwise hysteresis loop obtained earlier. The first
main drying and wetting cycle showed a closed hysteretic loop in terms of water
retention properties with a maximum gap of 15% at 5 kPa. The optimum
temperatures in the medium with RZC treatment were between 12°C and 19°C at 10
cm below the medium surface during hot ambient temperatures between 10 am and 4
pm daily. Medium temperatures remain below 22.8°C after this period. Irrigation
management without considering hysteresis had resulted in three days of irrigation
interval for both medium treated with and without RZC. However, when hysteresis
was considered in the irrigation management, the irrigation interval reduced to two
days for medium without RZC and one day for medium with RZC treatment.
Considering hysteresis in the irrigation management is significant to estimate the
accurate irrigation interval. In this study, yields were found greatest for butterhead
lettuce grown in RZC compared to those grown in ambient temperatures without
RZC. The cocopeat-perlite mixture (3:1) had provided an optimum growth condition
for butterhead lettuce with RZC treatment at low temperatures (between 12 and
19°C). |
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