Hysteresis of cocopeat-perlite mixture under root zone cooling system for growing butterhead lettuce (pdf tiada security)

• Main Author: Fazlil Ilahi, Wan Fazilah
• Format: Thesis
• Language: English
• Published: 2017
• Online Access: http://psasir.upm.edu.my/id/eprint/71197/1/FK%202017%2063%20-%20IR.pdf; http://psasir.upm.edu.my/id/eprint/71197/

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).