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    Design and fabrication of a climate-controlled lysimeter and testing of new controlled-release fertilisers : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PHD) in Agricultural Engineering and Environmental Sciences at Massey University, Palmerston North, New Zealand
    (Massey University, 2021) Gunaratnam, Abhiram
    Pastoral agriculture is the backbone of the New Zealand (NZ) economy and nearly 9 million hectares of land (33% of the total land area in NZ) is under pastoral farming. The higher and continuous applications of readily available N fertilisers to pastoral land use increase nitrogen (N) losses, which degrade the water and air quality. Controlled-release fertilisers (CRFs) have been shown to be an effective strategy to mitigate N losses in many parts of the world. This study was undertaken to develop different CRF formulations and test their effect on ryegrass under a simulated climate condition. A new controlled-environment lysimeter system was designed and fabricated, since lysimeter designs available in the literature are not suitable to conduct a controlled-environment study. The lysimeter was permanently capped to provide a confined space for controlling the microclimate of ryegrass, and equipped with sensors to monitor the environmental variables. An environmental controlling unit (ECU) was designed to emulate a climate model and control the environmental variables in the lysimeter. Taranaki region’s (spring season of the year 2013) climate model was selected to emulate in this design. The ECU modifies the ambient air according to the climate model and circulates it through 40 lysimeters using air conduits and distributors. The ryegrass was grown for three months under simulated climate conditions, and DM yield was measured. In addition, microclimate temperature, relative humidity (RH), evapotranspiration and drainage of each lysimeter during the experimental period were recorded. The performance of the ECU was tested by comparing the observed temperature and RH values of the plant proximity with setpoints of the climate model. In addition, the performance of the lysimeter system on recreating the climate model was tested by comparing the observed drainage, evapotranspiration, and DM yield values with the estimated values derived from the climate model. The root-mean-square error (RMSE) of temperature was 1.96 °C day⁻¹, which was marginally higher than the targeted temperature variation range of 1 °C day⁻¹. However, the RMSE of RH was 4.45% day⁻¹, which was within the targeted fluctuation range of 5% day⁻¹. These observations showed that the ECU satisfactorily controlled the environmental variables as per the climate model. The observed drainage, evapotranspiration and total DM yield were within the estimated values; 525 mm, 104 mm and 2167 kg-DM ha⁻¹, respectively. These results revealed that the selected Taranaki climate model was successfully emulated in the newly developed lysimeter system design. A low-cost, simple lysimeter soil retriever (LSR) design was fabricated to retrieve the soil, and its performance was examined. The soil moisture influenced the retrieval process, where lower disturbances for soil block structure and roots were observed for soil with high moisture (28%) than low moisture (13%). The linear actuator used in this design was powerful enough to perform soil retrieval and showed consistent performance after 80 soil columns were retrieved. Force given by the linear actuator did not damage the lysimeter body, but was sufficient to push the soil column out of the lysimeter. Therefore, this design is suitable to retrieve soil blocks from mini (<100 kg) and small (100-1000 kg) lysimeters. Different forms of CRFs were developed by coating urea with epoxy-lignite (Epox) or polyester-lignite (Poly) polymer composites. Each composite was coated three or five times, and therefore four CRFs were formulated depending on the type of composite and coating thickness; Epox3, Epox5, Poly3, and Poly5. The complete release of urea took place at 144, 408, 120 and 175 hours for Epox3, Epox5, Poly3 and Poly5, respectively, in water. Increasing the coating thickness prolonged the duration of urea release for both composites. Although no cracks were identified in all the CRF coatings, micropores were seen under high magnification in the scanning electron microscopy (SEM) images. The interactions between lignite and polymer were demonstrated using Fourier Transform Infrared Spectroscopy (FTIR) analysis. The lignite dominated in all coatings compared to the polymer, and lignite compositions were 2.1 to 5.3-fold higher than polymers in CRFs. The Epox5 showed overall better performance than other formulations. The CRF formulations which showed more controlled-release characteristics in water; Epox5 and Poly5, were selected to study their performance on ryegrass against urea and diammonium phosphate (DAP) in the climate-controlled lysimeter system. The total DM yield, root DM distribution, herbage N recovery and nitrogen utilisation efficiencies (NUE) were not significantly different between N treatments. Although N₂O emission and nitrate leaching losses were not significantly different between N treatments, the values were very low in comparison to the values obtained in similar studies reported in the literature. An investigation was carried out to find out the reason for these observed low N₂O and nitrate levels with different hypotheses. The only hypothesis tested that showed a significant relationship with these observed results; the high iron content of sand could have decreased the nitrate in leachate and N₂O emission. In this study, a 2 x 4 factorial design was used with two types of sand (low and high iron sand) and four N levels (0, 50, 100 and 200 kg-N ha⁻¹). It was found that high iron sand significantly lowered (P<0.05) the nitrate leaching at all N levels compared to low iron sand, except for the 0 kg-N ha⁻¹ treatment. The N2O emission was significantly lower (P<0.05) for high iron sand than low iron sand, only at the 200 kg-N ha⁻¹ application level. These observations support the hypothesis, that iron is involved in nitrate reduction and the possible mechanism was dissimilatory nitrate reduction (DNR) pathway. A new controlled-release fertiliser (Ver-1) was developed by Verum Group Ltd using lignite and urea. In this study, the effectiveness of two different types of CRFs (Epox5 and Ver-1) and two levels of iron application (239 and 478 kg-FeSO4 ha-1) on controlling N losses were tested in lysimeters where ryegrass was grown. The Epox5 and Ver-1 significantly (P<0.05) reduced N leaching losses by 37% and 47%, respectively, whereas only Epox5 significantly (P<0.05) increased N₂O emission compared to the urea treatment. Iron treatments were not effective in controlling N losses, which suggests that the expected DNR pathway was not prominent in this study. The DM yield and NUE were not significantly increased by CRFs and iron applications compared to the urea treatment. The hierarchical clustering analysis revealed that Ver-1 was the best treatment for controlling N leaching losses. Future research is recommended to investigate (a) the mechanism which underlies the reduction of nitrate in high iron content sand, (b) the effectiveness of iron application on N leaching losses on different soils, and (c) the performance of new CRFs formulations (Epox5 and Ver-1) at the field level.
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    Polymer coated controlled release agrichemicals as mitigation tools in pastoral farming : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2010) Bishop, Peter Andrew
    Controlled release coating technology and nitrification inhibitors offer potential mitigation options, for the reduction of pastoral nitrate leaching. Previous published research on this topic was reviewed indicating two potential areas of new research and development around two main hypotheses: • That polymer coated urea can allow high urea N applications in winter reducing application costs, nitrate leaching, herbage N content and urine N return to pasture. • That polymer coated nitrification inhibitor dicyandiamide (DCD) can increase the longevity of DCD in soil and effectively inhibit nitrification of dairy urine affected soils. To facilitate this research a range of coated urea and nitrification inhibitor dicyandiamide (DCD) products were produced using low cost, reactive layer, polyurethane (RLP) and were assessed in laboratory and field studies. The mechanism of urea release from modified RLP coated urea was investigated, leading to the development of a comprehensive model of release, based on the porous water repellent nature of the RLP coating. The “hydraulic convection” model was validated using water extraction and under field conditions for modified RLP coated urea. In, field trials (June-Nov 2007) using Italian ryegrass, a single application of 150 kgN ha-1 of palmitic acid modified RLP coated urea (5UCU) reduced winter nitrate leaching by 7 kgN ha-1 compared to uncoated urea and reduced peak herbage N levels over this period (150 days). Using an empirical N partitioning model for grazing cows, the reduction in herbage N was predicted to reduce urine N return by 5 to 10 kgN ha-1 over the 150 day trial. The effectiveness of laboratory prepared controlled release nitrification inhibitor dicyandiamide (PDCD) was tested as a surface application in repacked core studies on two soils contrasting in organic matter content and anion sorption capacity, Manawatu fine sandy silt and Dannevirke silt loam. The data from this trial was used to develop a model to explain DCD movement and degradation soils, which predicted that PDCD can potentially increase DCD longevity by 120 days at 20 oC over uncoated DCD.