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Item Reducing agricultural nitrate leaching : investigating the performance of denitrification bioreactors in New Zealand conditions : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science [Agriculture] at Massey University(Massey University, 2023) Ratcliffe, HarryDenitrifying woodchip bioreactors are a tool that is used in the agriculture sector to reduce undesired nitrate-nitrogen (NO₃-N) concentrations in subsurface drainage water before entering downstream environments. As well as their ability to reduce the NO₃-N pollutant, denitrifying bioreactors tend to produce other unwanted pollutants such as nitrogen dioxide (N₂O), carbon dioxide (CO₂), and methane (CH₄). This thesis presents research from 2 pre-installed denitrification bed bioreactors in the Manawatu-Whanganui region of New Zealand. The aim of this research was to measure the performance of these bioreactors in terms of nitrate removal rates and nitrate removal efficiency, as well as measuring any unwanted pollutants produced. Nitrate removal performance was assessed by measuring the nitrate concentrations flowing into the bioreactor and comparing them to the nitrate concentrations flowing out. The difference between these values, per unit time, is the nitrate removal rate (NRR). To recreate different New Zealand seasonal conditions different flow rates were changed, hence, the length of time the dissolved solutes remained in the bioreactors (hydraulic retention time or HRT) also changed. Measurements were undertaken to see if these changes in flow rates had any effect on nitrate removal, N₂O, CO₂, and CH₄ production. Results indicated that during the spring of 2022, the denitrifying bioreactors removed an average of 2.25 and 3.70 grams of NO₃-N per m³ of water per day, with an average nitrate removal efficiency (NRE) of 76.3 and 76.5%. Relatively smaller fractions of 1.81 and 0.77% of the NO₃-N removed was converted to N₂O within the bioreactors. Of the N₂O produced, 99.5 and 99.8% was dissolved and leached in the outflow, whilst 0.5 and 0.2% was released as a gas. This supports previous literature from Rivas et al., (2019), stating that bioreactors produce high NO₃-N removal rates with relatively low N₂O emissions, with the main export pathway of N₂O via outflow of water in dissolved form. Results also indicated that, for both bioreactors, there is strong correlation that as HRT decreased, NRR exponentially increased. As HRT increased, the ratio of N₂O-N produced to NO₃-N removed decreased, with an R-squared value of 0.8007 proving significant correlation. The average CO₂ produced was 6.13 and 0.441 g CO₂-C/m³ /day and the average CH4 produced was 5.10E-04 and 3.17E-03 g CH₄-C/m³ /day. The concentrations of CO₂ and CH₄ produced by the bioreactor were difficult to compare to average concentrations produced from agricultural land in New Zealand due to varying climate, soil, and pasture species. Varying the HRTs of the 2 bioreactors produced no significant effect on CO₂ or CH₄ production.Item 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, AbhiramPastoral 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.Item Automated body condition scoring of dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Manawatū, New Zealand(Massey University, 2018) O'Connor, AaronThis research demonstrates the development and implementation of an automatic body condition scoring system for dairy cattle that can operate in a real-world environment. Body condition scoring is a subjective method used for measuring changes in energy reserves in many animals, including dairy cattle. These energy reserves can be measured by analysing specific regions on the cow to estimate the amount of fat the animal is carrying. This information allows for greater management of the herd by adjusting the feeding strategies to ensure that each cow is at an optimal condition score. Maintaining an optimal condition throughout the year has implications for milk yield, reproductive performance, animal welfare, and overall farm profits. Current condition scoring methods are manual and are highly subjective, time consuming, expensive, and require a high level of training and competency. These limitations have created a demand for an accurate and objective scoring system. This research presents an automated system that utilises a single camera to be placed above the path of the cow at the entrance or exit to a milking platform or weigh scale. When the cow passes in view of the camera, the features are automatically extracted and converted to a conditions score. Tests have shown that the system successfully predicted the condition score within half a point of the true score for 83% of the 710 cows scored, and 96% within one point.