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Item Comparing nutrient leaching between standard and diverse pasture under sheep grazing : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand(Massey University, 2024) Chandrasiri, Nipuni KaushyaliCurrent intensive sheep farming in New Zealand has led farmers to focus on improving economic outcomes based on production. Thus, in such an environment, there is a potential risk to contaminate soil and waterways with nutrients, more specifically as nitrate. However, there is lack of knowledge on nitrate leaching in modern sheep farming systems, particularly in the context of using perennial diverse pasture mixes coupled with regenerative pasture management practices. The objective of this study was to compare the nitrate leaching concentrations and quantify nutrient losses in both diverse pasture and standard pasture systems under regenerative pasture management and contemporary pasture management over one year from January to December 2023. This study was conducted on a poorly-drained, fine-textured Tokomaru silt loam soil at Massey University’s Whenua Haumanu sheep farmlet study located at the Pasture Crop Research Unit, near Palmerston North, Manawatū, New Zealand. The study design was a randomised complete block design containing eight drainage paddocks (each approximately 0.25 ha) including two pasture types (standard and diverse) and two management practices (contemporary and regenerative) each with two replicates. Each paddock had an independent mole-pipe drainage system. Standard pasture treatments were sown with perennial ryegrass (Lolium perenne), white clover (Trifolium repens) and red clover (Trifolium pratense) and diverse pasture treatments were sown with a mix of 21 species which resulted in six dominant species including perennial ryegrass, cocksfoot (Dactylis glomerata), white clover, red clover, plantain (Plantago lanceolata) and chicory (Cichorium intybus). Regenerative pasture management treatments were managed with longer grazing intervals, higher post-grazing residuals and low to no mineral fertiliser and chemical use while contemporary pasture management treatments followed the Beef and Lamb New Zealand best practice grazing advice for sheep and used mineral fertiliser and chemicals as required. The drainage volume and concentrations of nitrate N, nitrite-N, ammonium-N and dissolved reactive phosphorus (DRP) in each drainage paddock were measured to estimate the nutrient loads. In addition, pasture growth rate and accumulated dry matter mass were monitored along with botanical composition. Due to improper functioning of one of the drainage pipes, the data from one replicate was not usable, so the data were analysed by comparing pasture types and ignored the effect of management type. The measured total cumulative drainage (mm) was higher (p<0.05) in diverse pasture treatment than the standard pasture treatment. The total loads of nitrate (kg N/ha) were higher (p>0.05) in standard pasture treatments (1.04 kg N/ha) than in diverse pasture treatments (0.73 kg N/ha). The diverse pasture treatment had visually greater pasture growth and accumulated dry matter yield, and greater herb contents than the standard pasture treatments which likely caused the numerically lower nitrate concentrations observed in the diverse pasture treatments than the standard pasture treatments. Overall, the measured loads of nitrate-N, nitrite-N ammonium-N and DRP in both treatments were very small (<1.0 kg /ha). These low loads in contaminants were likely because all the drainage paddocks were not grazed until late autumn as they were cut for hay and then allowed to recover early in the year. Therefore, the amount of urinary N loading that occurred during late summer, early autumn would have been minimal. Overall, diverse pastures have the potential to reduce nitrate leaching in sheep grazing systems.Item Nitrogen and phosphorus leaching losses under cropping and zone-specific variable-rate irrigation(CSIRO Publishing, 2023-12-19) Drewry JJ; Hedley CB; McNeill SJ; El-Naggar AG; Karakkattu KK; Horne DJ; Dickinson NContext. Agricultural land use is intensifying globally. Irrigation and other farm practices associated with intensification, such as cultivation, grazing, and fertiliser application, can increase nutrient losses. Variable rate irrigation (VRI) systems manage irrigation to spatially variable soils and different crops (zones). We lack knowledge on nutrient losses under zone-specific irrigation for mixed-cropping systems (combined crop and livestock grazing). Aims. This study evaluated drainage, nitrogen, and phosphorus leaching losses under zone-specific irrigation for a temperate mixed-cropping system. Methods. The study site had sheep grazing and crops including peas, beans, wheat, turnips, plantain, and ryegrass-white clover pasture. It had a variable-rate centre-pivot irrigator for two soil zones (free draining Zone 1; poorly drained Zone 2). Drainage flux meters (DFMs) collected drainage leachate, and samples for measurement of nitrogen (N) and phosphorus (P) concentrations. Soil water balance data and statistical modelling evaluated nutrient leaching losses over 5 years. Key results. The mean leaching load of NOx-N (nitrate + nitrite) across 5 years was 133 (s.d. 77) and 121 (s.d. 97) kg N/ha/year for Zone 1 and Zone 2, respectively. Similarly, the mean leaching load of reactive P across all years was 0.17 (s.d. 0.30) and 0.14 (s.d. 0.14) kg P/ha/year for Zone 1 and Zone 2, respectively. The nitrogen concentrations and loads generally had greater uncertainty in Zone 2. Conclusions. The DFMs worked well for the free draining sandy soil. However, fewer samples were collected in the silt soil, requiring the statistical modelling developed in this study. This study gave a reasonable estimate of annual leaching load means, but the indicators of their within-year variation were not reliable, partly due to differences in sampling frequency. With some exceptions, there was generally more NOx-N leaching from the free draining Zone 1. VRI provided a system to control irrigation-related drainage and leaching in these soil zones. Implications. Drainage flux meters are more reliable in well-drained than in poorly drained soil. Given the lack of published studies, this study has improved knowledge of nutrient losses under zone-specific irrigated mixed-cropping systems in a temperate climate.Item Comparison of maize silage and traditional forage crops in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatū Campus, New Zealand(Massey University, 2022) Thant, Aung MyoCattle wintering systems using crops including grazing kale, swede, and fodder beet crops in situ have resulted in soil and water quality deterioration. Nitrate leaching is the most common problem due to the high deposition of urine N driven by excess N intake. Alternative cropping systems offer a potential solution to reduce these environmental problems while maintaining or maximising productivity. We proposed maize silage as an alternative crop because it has high yield potential, flexible feeding requirements, compliments the nutritive value of pasture, and is potentially suitable for more regions in New Zealand in the future due to climate change. However, research needs to determine whether maize silage yield, feed quality and potential nitrate losses during production and utilisation means it is a viable alternative to in situ grazed forage crops in these areas. Field experiments were conducted at Massey University, Tokoroa and Kiwitea to determine forage yield and feed quality, management effects and site differences in 2018/19 and 2019/20. Crop yields and forage N content were utilised to simulate urine N loads from the feeding of these forage crops. The excreted N loads were analysed in APSIM (Agricultural Production Systems sIMulator) to predict nitrate leaching losses. Maize produced significantly higher yields compared with the winter forage crops at all Massey University trials while producing competitive yields at Tokoroa and Kiwitea. Yields ranged from 10,940 to 30,417 kg DM/ha for maize whilst wide and lower yield ranges were observed for the winter forage crops (4,579 to 22,928 kg DM/ha). Irrigation increased yields of forage crops by 29-63%. Similarly, nitrogen fertiliser increased yield by 30%, on average. The faster canopy development of maize has the advantage of intercepting more radiation in summer and suppressing weeds, contributing to greater growth and yield despite a shorter crop season. All forage crops produced forage with good metabolisable energy content (MJ/kg DM); higher values in swede (10.1-14.5) and fodder beet (10.8-14.9) whereas intermediate values in kale (8.9-12.7) and maize (9.9-12.2). However, maize was the highest energy-yielding crop, ranging from about 200-316 GJ/ha while other crops varied from 34 to 217 GJ/ha. Protein content in kale (7.5-16.6% DM) and swede (11.4-18.2% DM) were adequate for non-lactating cows whereas maize (5.4-9.2% DM) and fodder beet (7.6-11.2% DM) were lower than recommended protein levels for dairy cows but offering an opportunity to reduce urinary N excretion. Maize also had recommended fibre content. With higher sugar contents, swede and fodder beet were poor in fibre sources, potentially prone to rumen acidosis unless considered mixed diet with high fibre feed. APSIM modelling indicated that maize would produce the lowest urine N output while swede the highest in simulated feeding. Accordingly, N loads/ha was higher for winter forage crops especially when good yields were produced. When common feeding practices were considered, i.e., off-paddock maize feeding (no urine N deposition) and on-paddock grazing of winter forage crops (high urine N deposition), simulated nitrate losses from maize cropping systems were the lowest. Predicted nitrate losses were 21 and 32 kg N/ha for maize under irrigated and non-irrigated conditions. A ryegrass cover crop further reduced simulated nitrate losses by 20-30%. Predicted nitrate losses for fodder beet, kale, and swede crops were 126, 162, 154 kg N/ha under irrigated conditions and 72, 201, 199 kg N/ha under non-irrigated conditions, respectively in grazing systems.Item Nitrate leaching mitigation options in two dairy pastoral soils and climatic conditions in New Zealand(MDPI (Basel, Switzerland), 17/09/2022) Matse DT; Jeyakumar P; Bishop P; Anderson CWNThis lysimeter study investigated the effect of late-autumn application of dicyandiamide (DCD), co-poly acrylic-maleic acid (PA-MA), calcium lignosulphonate (LS), a split-application of calcium lignosulphonate (2LS), and a combination of gibberellic acid (GA) and LS (GA + LS) to reduce N leaching losses during May 2020 to December 2020 in lysimeter field sites in Manawatu (Orthic Pumice soil) and Canterbury (Pallic Orthic Brown soil), New Zealand. In a second application, urine-only, GA only and GA + LS treatments were applied during July 2020 in mid-winter on both sites. Results showed that late-autumn application of DCD, 2LS and GA + LS reduced mineral N leaching by 8%, 16%, and 35% in the Manawatu site and by 34%, 11%, and 35% in the Canterbury site, respectively when compared to urine-only. There was no significant increase in cumulative herbage N uptake and yield between urine-treated lysimeters in both sites. Mid-winter application of GA and GA + LS reduced mineral N leaching by 23% and 20%, respectively in the Manawatu site relative to urine-only treated lysimeters, but no significant reduction was observed in the Canterbury site. Our results demonstrated the potential application of these treatments in different soils under different climate and management conditions.
