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Item Maintaining the hyper-arid forests of Abu Dhabi by sustainable irrigation using treated sewage effluent in conjunction with groundwater : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil and Environmental Sciences, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand(2019) Al Yamani, WafaThe late H.H Sheikh Zayed bin Sultan Al Nahyan, the founding President of the United Arab Emirates sought to ‘green the desert’ through planting of trees. These forests in the hyperarid desert of Abu Dhabi depend on irrigation with groundwater (GW). A wide range of valuable ecosystem services are delivered by the forests. In the 2017 State of the Environment Report, Environment Agency – Abu Dhabi (EAD) noted that “… considerable water resources are required to maintain these forests”. Over-consumption of GW, and the increasing salinity of the aquifers means that the GW of Abu Dhabi is under threat. To manage sustainably the GW resources, in 2016 the government of Abu Dhabi passed Law 5 on GW management and identified the requirement for limits to be placed on GW allocation for vegetation. The means to realise reductions in GW use are: minimised irrigation schedules for GW; and the replacement of GW with treated sewage effluent (TSE). To achieve this, a Government-to-Government partnership was established between EAD and the New Zealand Government. The NZ partners are Maven International and Plant & Food Research. This doctoral research was carried out under this larger partnership. The actual water uses, ETc, of the 3 major forest species of Al Ghaf, Al Sidr and Al Samr were measured by heat-pulse sapflow methods in trees irrigated with either GW or TSE. The impacts on ETc and tree health of the lower salinity TSE are detailed. The complex links between tree water-use, the reference ETo, and trees’ phenology are described. Relationships between the crop factor, Kc (=ETc/ETo), and tree canopy characteristics were inferred using a light-stick to measure the percentage light intercepted by the trees’ canopy. From this research, guidelines have been proposed for Law 5 for the water-allocation limits for these 3 species. These guideline values for GW are based on 1.5 ETc to account for a 25% factor-of-safety, and a 25% salt-leaching fraction. For TSE, there is no need for salt leaching. These recommendations will lead to GW savings of 35-70% compared to current practice. Eventually TSE should replace GW to sustain the forests.Item Management practices and technologies for reducing nitrogen and phosphorus losses from soils receiving farm dairy effluent : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University, Palmerston North, New Zealand(Massey University, 2012) Hanly, James AnthonyThe loss of nutrients to the aquatic environment caused by the irrigation of farm dairy effluent (FDE) is a prominent and contentious feature of dairy farming in New Zealand. This thesis investigates management practices and technologies with potential to reduce nitrogen (N) and phosphorus (P) losses in drainage water from mole and pipe drained dairy pasture soils irrigated with FDE. Farm dairy effluent management was both monitored, using remote sensing technologies, and modelled on a case study farm. During the winter and spring of 2008, an estimated 7,890 m3 of FDE was applied in excess of the soil water deficit (SWD). System constraints were the cause of about two-thirds (5,070 m3) of this over-applied FDE volume. It was estimated that as much as 502 kg TN and 83 kg TP could have been lost to surface waters due to inadequate infrastructure. The two main system constraints were the farm’s insufficient FDE storage capacity (2,000 m3) and the inability of the farm’s irrigator to apply small application depths (<8 mm). Furthermore, this study highlighted the significant loss of nutrients that can occur under FDE irrigation and reinforced the need for tools to assist farmers with FDE management. A number of tools were developed to help farmers manage FDE irrigation. The use of a soil water balance, incorporating actual farm daily rainfall, is an effective method for informing the scheduling of FDE irrigations. Also, the risk of over-application of FDE to soils caused by travelling irrigator breakdowns or stoppages was substantially reduced by the use of a breakdown alert and automatic shut-off system developed and evaluated in this study. Given the elevated risk of P losses from soils treated with FDE, a method of capturing P from drainage waters was investigated. A field experiment was conducted to quantify the ability of Papakai tephra, installed into mole and pipe drainage systems, to remove P from drainage waters. This drainage system reduced TP losses in drainage by about 50% (c. 0.14 kg P/ha) over a drainage season, which equated to a 2.8 kg P reduction for a 20-hectare effluent block. As farmers frequently crop effluent block soils, the effect of summer forage cropping on nutrient losses was quantified. The practice of spring cultivating long-term dairy pasture, summer forage cropping and autumn regrassing increased the quantity of TN measured in drainage water, over three drainage seasons (2006 to 2008), by 84% (21 kg N/ha), compared to long-term pasture. If this study had commenced in spring with a more typical pattern of rainfall and drainage, this increase is estimated to have only been about 23.7% (5.9 kg N/ha). Based on these results, summer forage cropping is estimated to increase whole-farm drainage water N losses by about 5%, when 10% of a farm’s area is cultivated each year. Of the management practices and technologies studied, the greatest opportunity to reduce the losses of N and P to surface water from the case study farm’s effluent block, is through investment in FDE system infrastructure, particularly adequate storage capacity, and the use of decision support and fail-safe tools to assist the implementation of deficit irrigation of FDE.