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Current policies leveraging financial incentives and improved irrigation efficiency to mitigate groundwater scarcity have not proven to curtail trends of resource depletion. Groundwater benefits cannot be appropriately valued solely on market forces, and so deeper policy consideration is warranted under a framework that considers the importance of groundwater across all its values to society. Understanding time preferences for groundwater management and preferences for alternative policies is vital to inform efficient policies. Furthermore, climate change remains politically controversial yet has important consequences for critical groundwater resources and their sustainable long-term management. Proliferating policy narratives concerning climate change could influence the way people think about managing groundwater resources. I present three empirical studies that address these issues. Chapter I examines irrigation efficiency technologies for improved outcomes using a market-based, spatially-dynamic optimization model to test the limitations of improvements alone and in tandem with typical environmental policy mechanisms. Improved efficiency induces some producers to plant more of water-intensive crops such as rice, and best-case improvements fail to counter trends of groundwater depletion over a 30-year horizon. Chapter II elicits public willingness to pay (WTP) for long-term groundwater management and for market and non-market groundwater services. I employ time-discounted choice models to endogenously estimate time preferences under different forms of discounting. This is the first non-market valuation to estimate heterogeneity in time preferences using flexible mixing distributions. I find significant WTP for water quality provision, buffer against long-term drought, jobs from agriculture, and provision of wildlife habitat that promotes fishing and duck hunting, while most people display evidence of hyperbolic or quasi-hyperbolic discounting. Individual parameter distributions for WTP and time preferences are not normally distributed. Chapter III continues the Narrative Policy Framework (NPF) tradition to test for systematic influences of narrative frames about climate change on elicited groundwater and policy preferences. In a Choice Experiment (CE), some respondents were exposed to a structuralist, culturally-biased narrative frame about climate change and groundwater resources. Using theories about cultural risk perception and motivated reasoning for systematic evaluation, I find evidence for a cultural incongruency effect but no evidence for a congruency effect. This suggests that people could respond more strongly to incongruence than to congruence in the case of groundwater policy preferences.

Furrow irrigation is a very common irrigation method for growing crops like soybean, cotton and corn in Arkansas. A major portion of this irrigation water is lost as runoff from the field significantly reducing the irrigation application efficiency. There are various methods of improving irrigation efficiency and one of the methods is using tail-water recovery. A tail-water recovery system utilizes tail-water recovery ditches or pits to collect tail-water which can be re-used for irrigation. However, this method is very labor intensive and has been found to be economically non-feasible for some farms in the past research studies. In order to reduce the cost of a tail-water recovery system, a new system was designed at the University of Arkansas, a Variable Flow Tail-Water Recovery System (VFTWRS). This system eliminates the need of tail-water recovery ditches or pits. It can be operated using grid power or photo voltaic (PV) modules. Application and system efficiency tests were performed in a 16 ha rice field planted in 76 cm × 76 cm rows. Application efficiencies of VFTWRS were compared with continuous furrow and surge irrigation methods. Results have indicated that application efficiency of furrow irrigation can be increased up to 93% using this designed tail-water recovery system. Application efficiency for continuous furrow irrigation was from 47% to 83%, 32% to 88% for surge irrigation, 81% to 97% for VFTWRS on electric grid as the energy source, and 23 to 96% for VFTWRS on PV modules as the energy source. Average percent of Nebraska Pumping Plant Performance Criteria were 98% and 77% for VFTWRS on grid and VFTWRS on PV modules, respectively. Net Present Value (NPV) and Discounted Payback Period (DPP) were analyzed for different scenarios with an interest rate of 4%. VFTWRS on grid was found to be the most economically feasible system with the highest NPV of $8,031 per hectare with a DPP of 2 years. VFTWRS on PV modules was a better alternative than VFTWRS on grid when the distance of the tail-water pump to the power source was greater than 900 m. In general, all of the designs of tail-water recovery systems which consisted of a tail-water ditch had lower NPV and higher DPP in comparison to VFTWRS operated using grid as well as PV modules.

This thesis comprises two small core studies and two lysimeter studies, which are aimed at understanding how incorporation of soil amendments at cultivation can increase soil water retention in New Zealand’s shallow stony soils. The overall objective was to determine the potential of this management practice to increase water retention of these vulnerable soils and to develop an understanding of the benefits and limitations of this practice in a spray irrigated system. Experiment 1 (Chapter 3) - A lab based study was initially conducted to determine the potential of a range of amendments to increase soil water retention. This experiment involved incorporating organic (dairy shed manure (DSM), municipal compost (MC), sphagnum moss (SM) and biochar (BC)) and synthetic (polyacrylamide-based hydrogel (PM), silicate gel (SI) and starch gel (ST)) amendments in to a Templeton silt loam soil that had been under long term intensive cropping management. The amendment application rate was 1% and 0.1% on a mass by mass basis for the organic and synthetic amendments, respectively. The original hypothesis was that incorporation of these amendments would increase the water-retaining mesoporosity of a cultivated silt loam and that water repellence and carbon mineralisation would not be increased relative to the control. This experiment confirmed the original hypothesis for some amendments. Mesoporosity and total mesopore volume increased relative to the control in the order of PM>SM>DSM>BC, and the remaining amendments failed to produce a significant increase. Contrary to the original hypothesis, both water repellence and carbon mineralisation were significantly increased relative to the control by the incorporation of DSM, although no other amendment had a significant effect on these properties. From analysis of changes in soil physical properties such as bulk density, total porosity and the volume change due to the strain of amendment addition it was concluded that these changes in mesoporosity were caused by two modes of action that were unable to be separated: (1) inter-particle pore spaces were created through soil and amendment particle interaction, (2) the introduction of amendments bought new intra-particle pore spaces within the new particles which held water within the mesopore range. The results and conclusions from this initial experiment allowed subsequent questions to be developed that contribute towards the original aim. Experiment 2 (Chapter 4) - If the concentration and volume of water-retaining mesopores is controlled by the introduction of new inter-particle pore and intra-particle pore spaces, what effect would 1) modifying the maximum particle size of the amendment have? and 2) modifying the application rate have? For this experiment a readily available amendment (municipal compost) was selected, screened to three different maximum particle sizes and incorporated at four rates to determine if reducing particle size would allow water retention to be increased at lower application rates than traditionally recommended. Increasing MC application rate increased both the concentration and net volume of mesopores, and maximum mesoporosity was achieved with the smallest MC particle size (

Research was conducted to assist in the improvement of irrigation efficiency on the shallow stony soils of Canterbury and identify the effect of current irrigation practice on the redistribution of solute within the soil profile. Irrigation treatments were measured using twenty-four undisturbed monolith lysimeters containing a stony Eyre shallow silt loam soil. Treatments included 15/10, 15/15, 30/20, 30/30, 60/40 and 60/60, being the respective soil deficit irrigation trigger/irrigation depth combinations (mm). The trial was split into three experiments. Experiment 1 began with a surface application of bromide tracer before exposing the lysimeters to the irrigation treatments for three months. Experiment 2 and 3 were designed to examine how the bromide had been redistributed within the pores during Experiment 1. Experiment 2 irrigated 250 mm depth continuously at 50 mm/hr to drain bromide in the macropores, while Experiment 3 irrigated 500 mm depth continuously at 2 mm/hr to drain bromide in the soil matrix. Over the three experiments, leachate was collected regularly and analysed for bromide. Preferential flow dominated solute leaching, occurring in the first drainage event irrespective of the application volume and frequency of irrigation, with leached bromide moving predominately through the macropore fraction of the soil. Treatments with greater irrigation quantities corresponded with more extensive preferential flow, drainage and for the most part, leaching in Experiment 1. Treatments irrigated to field capacity (FC) had greater leaching and drainage as well, as uniform irrigation of lysimeters in a treatment meant soil heterogeneity caused some lysimeters to exceed FC before others. Generally, there were no significant treatment effects on the cumulative bromide leached across the experiments, reflecting the dominance of preferential flow under the irrigation conditions studied. There was evidence that bromide distribution in the profile at the end of Experiment 1 was affected by treatments, with moisture status after irrigation having an effect on the bromide peak mass readings in Experiment 2, while the moisture deficit irrigation trigger influenced the bromide peak mass and cumulative mass readings in Experiment 3. However, effects were not consistent across treatments and experiments, making interpretations difficult. The results indicate that irrigation practices on Eyre shallow silt loam soils at 50 mm/hr needs to be adjusted for preferential flow, which has a dominant influence on solute distribution within the soil profile. Results imply that the 15/10 treatment had the least leaching as less extensive preferential flow means solute remains within the profile and has a greater opportunity to be immobilised.

Vegetables are grown in the peri-urban zone throughout Australia in diverse soil types and climates. Irrigation allows cropping throughout the year. Competition for water and adverse environmental impacts from irrigation will increasingly influence access to water and the price paid. These forces are particularly strong in the Sydney Region, where improved irrigation techniques are urgently needed. A review of literature showed that sub-surface drip irrigation (SDI) has the potential to achieve high water use efficiency and crop yields, as well as reduce drainage and runoff and the associated environmental risks. However, disadvantages of SDI include ‘tunnelling’, poor soil surface wetting, and risky crop establishment. The research reported in this thesis, evaluated ways to overcome these problems, including a new product (KISSSTM) that has a narrow band of impermeable material below the drip tape, and geotextile above. It was hypothesised that the impermeable layer would create a temporary watertable, from which the upward flux of water would be greater than in conventional SDI and the drainage less. The research questions were: 1. Does an impermeable layer beneath the drip tape (modified SDI) improve surface soil water conditions and crop establishment, compared with conventional SDI? 2. Does the modified SDI (M.SDI) offer any advantage over using conventional SDI (C.SDI) with increasing irrigation amount or frequency? A further objective was to determine how irrigation management with the modified SDI should take account of soil type and evaporative demand. Field experiments at Richmond, NSW compared C.SDI and M.SDI on a sandy soil in autumn (mean pan evaporation 2 mm/day) and spring (mean evaporation 6 mm/day) to investigate lettuce crop establishment. The treatments were two drip tape types (M.SDI, C.SDI) and three irrigation frequencies (1, 2 and 4 times per day). Irrigation application volume was calculated by using a crop factor of 0.4 in autumn. In spring, crop factors of 0.4 and 0.8 were compared. Modified SDI improved crop establishment compared with conventional SDI. The difference in seedling survival was numerically small but significant (p is less than 0.05), indicating a superior environment for establishment in the M.SDI. This was reflected in higher leaf appearance rates in the spring experiment. In both experiments, leaves were longer and wider with the M.SDI, and plant fresh weights were greater at the end of the crop establishment period. The differences in fresh weight were substantial, with the M.SDI system recording average increases over the C.SDI of 16% and 25% in the autumn and spring experiments, respectively. Plants were also more uniform with the M.SDI. In both experiments, plant weight was closely related to volumetric soil water content, regardless of the source of variation in water content: tape type, crop factor, irrigation frequency, or location within the plot. Soil water and plant weight responded to increased irrigation frequency (IF) and crop factor (CF, included in spring only) with both tape types. The effects of CF and IF were additive within tape types. So, whilst the negative effect of reduced irrigation amount can be offset by increased irrigation frequency, the best growth was obtained where both were high. However, for every combination of CF and IF, plant growth with the modified SDI exceeded the conventional SDI. With the combination of high irrigation frequency (4/day) and a high crop factor (0.8), the modified SDI resulted in a 35% increase in plant fresh weight over conventional SDI. Importantly, at high irrigation frequency (4/day) but with only half the amount of irrigation (CF 0.4 versus 0.8), plant weight with modified SDI was similar to conventional SDI (actually 10% greater). Soil water content was also more uniform in the M.SDI treatment. A glasshouse experiment quantified the components of the water balance under irrigation with conventional and modified sub-surface drip irrigation, in sand and sandy loam soils under different evaporation demand. A tension table in the base of each large pot (50x35x5 cm) was used to maintain a suction of -60 cm at the base. Each treatment was subjected to a sequence of different irrigation frequencies, one per two days; and one, two and four per day. Data for drainage and soil water were recorded daily, and averaged over the last three days when daily drainage approached steady-state for any irrigation frequency. The M.SDI system generally resulted in lower drainage than with the C.SDI, regardless of soil type, irrigation frequency, evaporative demand, and irrigation rate. As the amount of daily irrigation (I) was known and equal for all treatments, soil evaporation (Esoil) was estimated from drainage (D) using the simplified soil water balance equation: Esoil = I – D. Thus soil evaporation was the inverse of drainage. The upward flux of water to meet the evaporative demand was greater in the M.SDI, and it was greater with more frequent irrigation. Soil water content and potential were both higher with the M.SDI. They were also higher with frequent irrigation, as in the field experiment. Overall, the M.SDI had less drainage than conventional SDI, greater upward flux of water (soil evaporation), and wetter surface soils. The findings are consistent with the hypothesis that an impermeable layer beneath the drip tape creates a temporary watertable, increasing the upward flux of water. Both the field and glasshouse experiments showed the benefit of dividing the daily irrigation requirement into smaller, more frequent pulses, for both types of drip tape, regardless of the soil types and climates investigated. Whilst increased irrigation amount and irrigation frequency both increased soil water content and plant growth, the best performance was when both irrigation amount and frequency were high. Frequent irrigation (4/day) was essential to obtain the improved crop growth with the M.SDI and a high crop factor in the spring experiment. These positive responses to tape type and irrigation frequency were obtained at relatively low and high evaporative demand (2, 6 mm/day), and in soils with different texture (coarse sand, sandy loam). So the modified drip tape and more frequent irrigation appear to be reliable, broad recommendations. No specific recommendation can be made on the present data regarding irrigation frequency in relation to evaporative demand, although it might be expected that under very high demand more frequent irrigation will be required unless the modified drip tape can be made to hold a greater volume of water against drainage. In relation to the first objectives of the study, it is concluded that the modified SDI (KISSSTM) improves surface soil water content and uniformity, and has the potential to overcome the plant establishment problems associated with conventional SDI. It does so whilst saving water and reducing environmental risk (drainage and/or runoff). With respect to research question 2, irrigating with more water, or more frequently, did improve seedling growth, but the modified drip tape (KISSSTM) retained an advantage in terms of both establishment and growth at any combination of irrigation amount and frequency. Further research is required to develop guidelines for using the M.SDI in specific soils and climates, especially for heavier-textured soils and more extreme evaporation.

A novel electrostatic spray nozzle, termed the Lektraspray Nozzle, was evaluated to assess its suitability for pesticide application in the greenhouse industry. The nozzle is based on the vortical nozzle principle, releasing the spray liquid into a low pressure/high volume airstream through a flexible emitter tube. The encompassing airstream shatters the liquid into small droplets and transports them to the target. The experimental work identified that the nozzle could deliver a droplet spectra with a Volume Median Diameter (VMD) of approximately 75 μm for a range of liquids and viscosities. Charging the droplets had a minor effect on the VMD, although typically improved the droplet spectra. The nozzle could be operated satisfactorily with or without electrostatically charging the droplets. The VMD could be changed simply by increasing/decreasing the liquid flow rate and/or adjusting the air pressure of the encompassing airstream. Small adjustments to the air pressure (4.5 to 14 kPa) will allow the production of an acceptable droplet spectra over a large range of liquid flow rates (30 to 1000 ml/min). The results of a limited number of tests using the Lektraspray nozzle on plants indicated that electrostatic charging could significantly influence the deposition of droplets on the underside of the leaves, providing the foliage was not "dense". However no significant increase in the total amount deposited on the plant was noted when the droplets were charged. The results from spraying a "dense" foliage plant (Pittosporum eugenioides) indicated the need to adjust the charge/air pressure relationship of the spray nozzle to increase underleaf deposition and improve droplet penetration into the plant canopy. After evaluating the experimental work on the Lektraspray nozzle, and considering the simplicity and ruggedness of the nozzle, the conclusion was that it should be seriously considered as an alternative spray application technique for use where controlled environment spraying is required. In particular - the greenhouse industry.

The overall objective of this study was to evaluate the performance of selected furrow irrigation models for field conditions in south-east Australia. The other important aspects which were examined during this study include: developing a methodology for estimating of infiltrating characteristics, assessing the applicability of the Manning and other similar equations for flows in furrow irrigation, investigating the variation of shape factor during irrigation developing methodology for estimation of recession time and exploring the sensitivity of the models to the input parameters. Field experiments were conducted at Walla Park in northern N.S.W. and on two selected paddocks at the University Farm, Richmond, in western Sydney,Australia, over a period of three years. The validity of the assumption that the shape factor of advancing water front during furrow irrigation varies between 0.7 and 0.8 was investigated using field data collected from irrigation events monitored in the study. It was found that the average values of the shape factor varied from 0.96 to 1.80 at Walla Park site, from 0.56 to 0.80 at Field Services unit paddock site and from 0.78 to 0.84 at Horticulture Farm paddock site. The value of shape factor was affected by uniformity of furrow cross section along the length, the value and uniformity of furrow slope, furrow length and infiltration characteristics of soil. This means it is difficult to recommend a typical value for the shape factor for a given field situation.The performance of the models for prediction of advance and recession characteristics and runoff were evaluated using different indices of performance. In general, it was found that the Walker-HD and ZI model was the most satisfactory for the field conditions encountered in this study. This finding can provide a basis for initiating work on developing design criteria and management strategies for furrow irrigation in south-east Australia.