SCHOOL OF LAND , CROP AND FOOD EFFECTS OF ARTIFICIAL AMENDMENTS IN POTTING MEDIA ON ORTHOSIPHON ARISTATUS (CAT’S WHISKERS) PLANTS UNDER WATER DEFICIT STRESS Nguyen Trung Ta A report submitted as a requirement for the degree of (Master of Agricultural Studies) in The University of Queensland School of Land, Crop and Food Sciences Faculty of Natural Resources, Agriculture and Veterinary Science The University of Queensland, Gatton November, 2008 DECLARATION OF ORIGINALITY The work reported in this research project report has been carried out by the undersigned. Where reference has been made to the results of other workers, appropriate acknowledgment of the source of information has been made. Author…………………………………… This is to certify that the academic style and manner of presentation of the research project report are appropriate to the discipline, that all requirements of The University of Queensland in relation to the deposition of records of research have been met and that the information contained in the report is a true representation of the data collected. Project Supervisor…………………………. i ACKNOWLEGEMENTS I would like to thank Professor Daryl Joyce who devoted his time to my work. I am indebted to him for his supervision, support and patience throughout this project. Thanks are also due to Mr Allan Lisle for his assistance with data analysis. Many thanks also to Mr Quang-Son Dinh for his assistance with this report and the experiments. Special thanks to technicians and general staff at the School of Land, Crop and Food Sciences. They supported me with equipment and materials. Finally, I gratefully acknowledge the support of my father, mother, sisters and brothers, who cared, worried and encouraged me while I was doing this work. ii ABSTRACT Synthetic soil conditioners have long been used with a view to improving soils and other growing media. Among these, polyacrylamide gel (PAG) and urea-formaldehyde resin foam (UFRF) are commonly utilised for enhancement of soil water holding capacity. However, there is little or no information comparing and contrasting them. This project investigated the growth of Orthosiphon aristatus grown in either composted pine bark or sand treated with UFRF and/or PAG, including under transient water deficit stress. Effects of these soil amendments on media physical properties (viz. bulk density, water content and air-filled porosity) were also assessed for composted pine bark and sand. UFRF and PAG [30% and 0.1% (v/v), respectively; manufacturers recommended rates] were incorporated into the composted pine bark or sand for potted O. aristatus. Effects on plant growth parameters were observed under water withholding intervals. Plant growth and shoot number were not increased by adding PAG. UFRF also did not improve shoot length and number of plants, and the number of opened flowers. PAG incorporation actually reduced shoot number of O. aristatus. The combination of UFRF plus PAG reduced plants shoot biomass in experiment 1 but not in experiment 2. No significant effects of UFRF and/or PAG on plant media water content were recorded at field capacity (FC). PAG retained more moisture than other treatments at wilting time during plant water deficit stress cycles. UFRF and especially UFRF plus PAG prolonged the time to plant wilting of O. aristatus by 4-15 hours compared to control and PAG alone in experiment 1 with composted pine bark. However, UFRF and/or PAG did not increase time to wilting for plants in experiment 2 with composted pine bark or sand. UFRF and/or PAG did not increase plant available water for plants in both composted pine bark and sand. Stomatal conductances (Gs) were generally similar in all water deficit stress cycles. In terms of media physical properties, bulk densities were reduced and air-filled porosity increased by UFRF incorporation. PAG incorporation also reduced bulk density of sand but not the composted pine bark. PAG did not increase air-filled porosity of both composted pine bark and sand. Volumetric soil water content of both iii composted pine bark and sand was not increased by UFRF. UFRF plus PAG incorporation did not have greater effects on bulk density and air-filled porosity than either UFRF or PAG incorporation alone. In conclusion, UFRF slightly delayed the onset of water deficit stress in O. aristatus, whereas PAG did not. Bulk densities and air-filled porosity were reduced and increased, respectively, by adding UFRF but not PAG. These changes, as might be repeated, did not increase available water for plants. In future work, optimum incorporation rates of UFRF and PAG could be integrated for composted pine bark and sand. iv TABLE OF CONTENTS DECLARATION OF ORGINALITY i ACKNOWLEGEMENTS ii ABSTRACT iii TABLE OF CONTENTS v LIST OF TABLES viii LIST OF FIGURES ix LIST OF APPENDICES xi LIST OF ABBREVIATIONS xii CHAPTER 1 1 INTRODUCTION 1 1.1. BACKGROUND 1 1.2. THE PROBLEM 2 1.3. OBJECTIVES 3 CHAPTER 2 5 LITERATURE REVIEW 5 2.1. SOIL-PLANT-AIR CONTINUUM (SPAC) 5 2.1.1. Soil water 5 2.1.1.1. Water holding capacity (WHC) 5 2.1.1.2. Water flow 6 2.1.2. Root and shoot growth 8 2.1.2.1. Root growth 8 2.1.2.2. Shoot growth 8 2.1.2.3. Root: shoot ratio 9 2.1.3. Air water 10 2.1.3.1. Vapour pressure deficit 10 2.1.3.2. Air movement 11 2.2. PLANT WATER USE 11 2.2.1. Water use efficiency 11 2.2.2. Water deficit stress 12 2.3. SOIL CONDITIONERS TO ENHANCE SOIL PHYSICAL PROPERTIES 12 2.3.1 General functions 12 2.3.1.1. Wet-ability and infiltration rate 13 v 2.3.1.2. Soil aeration and drainage 14 2.3.1.3. Soil water holding capacity 14 2.3.2. Major soil conditioner types 15 2.3.2.1. Natural inorganic materials 15 2.3.2.2. Natural organic materials 17 2.3.2.3. Synthetic materials 19 2.3.3. Utility in improving SPAC relations 24 2.3.4. Synthetic soil amendments and the environment 25 2.3.4.1. Polyacrylamide gel 26 2.3.4.2. Urea formaldehyde resin foam 26 2.4. CONCLUSION 27 CHAPTER 3 28 MATERIALS AND METHODS 28 3.1. INTRODUCTION 28 3.2. MATERIALS AND METHODS 28 3.2.1. Plant materials 28 3.2.2. Experiment preparation 28 3.2.3. Potting media treatments 29 3.2.4. Transient water deficit treatments 29 3.2.5. Data collection 30 3.2.6. Physical properties determination 31 3.2.7. pH and EC 31 3.2.8. Experimental design and analysis 32 CHAPTER 4 35 RESULTS 35 4.1. PHYSICAL PROPERTIES OF COMPOSTED PINE BARK AND SAND 35 4.1.1. Physical properties 35 4.1.2. pH and EC 35 4.2. EXPERIMENT 1 37 4.2.1. Growth phase 37 4.1.2. Stress phase 37 4.1.3. Shoot biomass 40 4.1.4. Stomatal conductance 40 vi 4.3. EXPERIMENT 2 43 4.3.1. Growth phase 43 4.3.2. Stress phase 44 4.3.3. Shoot biomass 48 4.3.4. Stomatal conductance 48 CHAPTER 5 51 DISCUSSION 51 5.1. SUBSTRATE CHARACTERIZATION 51 5.2. PLANT GROWTH 52 5.2.1. Plant height 52 5.2.2. Shoot number 54 5.2.3. Flowering time and open flower number 55 5.2.4. Shoot biomass 55 5.3. WATER DEFICIT STRESS TOLERANCE 56 CHAPTER 6 58 CONCLUSION 58 BIBLIOGRAPHY 59 APPENDICES 75 vii LIST OF TABLES Table 2.1. The amount of N fixed by some plants in the sub-tropics and tropics. 18 Table 2.2. Soil aggregates with and without arbuscular mycorrhizal fungi 19 Table 2.3. Effects of various synthetic soil amendments on soil physical properties. 22 Table 2.4. Effects of various synthetic soil amendments on soil water contents 22 Table 4.1. Estimated physical properties, pH and electrical conductivity of composted pine park and sand 36 Table 4.2. O. aristatus shoot height increments between beginning and end of water stress cycles and time to flowering in composted pine bark (experiment 1). .37 Table 4.3. Time to wilting of O. aristatus and relative pot weight loss during the water deficit cycles in composted pine bark (experiment 1). 39 Table 4.4. Volumetric water content of composted pine bark at field capacity and wilting time, and plant available water (experiment 1). 41 Table 4.5. Shoot biomass of O. aristatus grown in composted pine bark (experiment 1). 43 Table 4.6. O. aristatus shoot height increments between beginning and end of water stress cycles and time to flowering in composted pine bark and sand (experiment 2). 45 Table 4.7. Time to wilting of O. aristatus and relative pot weight loss during the water deficit cycles in composted pine bark and sand (experiment 2). 47 Table 4.8. Volumetric water content of composted pine bark and sand at field capacity and wilting time, and plant available water (experiment 2). 49 Table 4.9. Shoot biomass of O. aristatus growing in composted pine and sand (experiment 2). 50 viii [...]... have potential implications for other species under transient water deficit stress In this general context, effects of UFRF and PAG on soil water supply for plant uptake under transient water deficit stress conditions were evaluated This study also measured effects of these specific amendments at manufacturers recommended rates on the physical properties of sand and organic potting mixes Therefore, the... conditions Drought stress encourages roots to penetrate more deeply to seek moisture from depth in the soil profile (Reid, 1990) For instance, in the drought stress condition non-irrigated Vicia faba crop responded to water deficit by reducing its rate of height increase and decreasing its rate of leaf-area expansion, but the rate of root growth still increased from about day 78 after sowing (Husain... contribute to soil improvement and rehabilitation In this context, the conservation and judicious use of soil water can play an important role for sustainable plant production, especially under drying conditions Thus, any factor which enables plants to better withstand water deficit stress via improvement in physical properties of soils and growing media, including WHC, will improve plant growth and development... functions Sub-optimal soil physical properties like low IR, poor drainage, runoff and erosion are main factors contributing to soil degradation An approach for soil conservation and rehabilitation to improve soil physical properties is application of soil conditioners Soil conditioners consist of both natural and synthetic materials that can sustain important soil functions For example, soil conditioners... growth and crop production Various water saving measures have been investigated General strategies involve physical monitoring and the introduction of regulations to address users with low efficiency (Frederiksen, 1992), including legal water restrictions (Handreck, 2008) In developing countries, other methods may involve relocation of people to reduce population pressures in high risk areas (McWilliam,... vital in the face of scarce water A broad range of approaches are applied to maintain substrate productive capacity The success of substrate conservation and improvement is intimately linked to maintaining or creating aggregates That is, this physical characteristic is important not only for nutrient reserves, but also for water retention Improvement of substrate physical properties, including water. .. enhance water infiltration in relatively well-drained soil (Franklin et al., 2006) Khan et al (2000) reported that plants are impaired as soon as the oxygen supply in soils is limited due to poor aeration Clay can be used for improved soil aeration and drainage On one hand, high clay content can maintain standing water during the growing season in rice fields (Tsubo et al., 2007), On the other, high clay... P1 and constant Ks (Jury and Horton, 2004) Q= Ks A ∆P (3) L Infiltration rate (IR) is important in terms of soil management because it indicates how much water enters the soil surface from rainfall, irrigation or contaminant spill and how much water is runoff (McLaren and Cameron, 1996; Radcliffe and Rasmussen, 2002; Jury and Horton, 2004) IR is the volume flux of water flowing into soil profiles per... solutions have not brought about significant water savings for specific crops and gardens, especially in the current scenario of climatic change Soil and growing media quality and conservation are pivotal to any 1 sustainable agriculture and horticulture program Management of soil and other growing media to maintain or create substrate aggregates in support of water and nutrient retention for plants... physical properties of organic potting mix UFRF is claimed to increase air-filled porosity and water infiltration of heavy soils and water retention in light soils (Baader, 1999), but it has not been adequately characterised in sand or organic potting mix Therefore, questions remain as to which soil amendment is more beneficial to the physical properties of sand and organic potting mix media 1.3 OBJECTIVES . SCHOOL OF LAND , CROP AND FOOD EFFECTS OF ARTIFICIAL AMENDMENTS IN POTTING MEDIA ON ORTHOSIPHON ARISTATUS (CAT’S WHISKERS) PLANTS UNDER WATER DEFICIT STRESS Nguyen Trung. O. aristatus turgor in drought conditions may have potential implications for other species under transient water deficit stress. In this general context, effects of UFRF and PAG on soil water. composted pine bark or sand treated with UFRF and/or PAG, including under transient water deficit stress. Effects of these soil amendments on media physical properties (viz. bulk density, water content