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Item Nutrient leaching under intensive sheep grazing : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Manawatu, New Zealand(Massey University, 2023) Maheswaran, SarminiThe use of some alternative forages may help sheep farmers to reduce nitrogen (N) leaching while increasing production. This thesis explores the effects of four forages (perennial ryegrass/white clover: RGWC; Italian ryegrass/white clover: IRWC; plantain/white clover: PWC; and a winter brassica) on sheep performance, urinary N excretion and N loss in drainage over two and a half years (Year 1: July to December 2019; Year 2: January to December 2020; Year 3: January to December 2021). This study was conducted on an artificially drained, fine textured Tokomaru silt loam soil at Massey University’s Keeble farm, near Palmerston North, Manawatu, New Zealand. The study design included four self-contained farmlets (each approximately 3.3 ha): three farmlets had 0.8 ha (24% of their grazing area) sown to include one of three alternative forages (IRWC or PWC or brassica), and the remaining 2.5 ha was sown in a perennial ryegrass/white clover sward. The entire area (100% of grazing area) of the fourth farmlet was sown in RGWC. Approximately 0.4 ha of each farmlet was located in a paddock where a series of 20 drainage plots (each 40 m by 20 m) were established to measure N leaching. Each of the alternative forages, and the RGWC, were sown on five of the drainage plots i.e., five replicates (combined area of 0.4 ha), which composed about one-half of the area of each alternative forage on each farmlet. The amount of N leached through a mole-pipe network on each drainage plot was also measured. Breeding ewe productivity including liveweight, condition score and lambing performance, as well as N excretion was also measured. In addition, forage growth and DM production were monitored along with chemical and botanical composition. The inclusion of alternative forages into the RGWC system did not affect animal performance. This was due, in part, to animal management. The N leached under various forages was, therefore, able to be compared without the confounding effects of differences in animal performance. The daily urinary N excretion per animal by sheep grazing PWC or brassica was lower (18 to 70%) than the daily urinary N excretion by sheep grazing RGWC or IRWC. It is likely that the diuretic effect of plantain and a lower N concentration in the brassica caused lower N concentrations in urine. Nitrate (NO₃⁻) leaching losses under RGWC, IRWC and PWC were very small in Years 1 and 2 (ranging from 0.4 to 0.8 kg N/ha). The poor persistence of IRWC and PWC at this site and the need to re-establish these forages on the plots resulted in greater NO₃⁻ leaching under these forages in Year 3, negating some of the advantages associated with these forages in Years 1 and 2. In contrast, NO₃⁻ leaching losses were greater under brassica forages (ranging from 0.4 to 6.4 kg N/ha) than under RGWC (ranging from 0.5 to 1.5 kg N/ha). Although sheep grazing brassica forages excreted less urinary N (on an individual animal basis), leaching losses under the brassica treatments were higher. In addition to the effect of cultivation, this increased leaching was likely because brassica plots were grazed for a more extended period during winter than other forages, and there was no crop (forage) cover until the spring resowing; therefore, the urinary N accumulated during winter grazing was displaced by subsequent drainage. With the assumption that the cropped area occupies a relatively small portion of the farm, grazing brassica is likely to result in a relatively small increase in whole farm NO₃⁻ leaching. Overall, NO₃⁻ leaching losses under sheep grazing forages were lower (ranging from 0.5 to 9.5 kg N/ha) than those reported under dairy cattle grazing forages, which suggests that sheep production may offer an alternative land use option for dairying areas where it is difficult to achieve the large reductions in NO₃⁻ leaching required to meet water quality objectives.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 Targeted duration controlled grazing - the effects of timing of grazing on nitrate leaching and treading damage : 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, 2019) Howes, JayDuration controlled (DC) grazing is successfully employed for two main reasons: to reduce N leaching and to protect pastures and soils from treading damage in wet conditions. These two objectives are currently very important for the New Zealand (NZ) dairy industry and this will only continue to increase with changing environmental expectations and legislation. However, while there have been a number of studies showing the benefits of DC grazing, there has not been any detailed research into the means to modify or improve the management of DC grazing systems. Therefore, the overall objectives of this research were to further the understanding of the advantages of targeted cow standoff from pastures during the late-summer to early-winter period and its effect on nitrate (NO3-) leaching, and to identify the relationship between soil water deficit (SWD), grazing duration and treading damage (related to standoff in winter to early spring). Two experiments were conducted on a fine textured Tokomaru silt loam soil at Massey University’s Dairy 4 Farm near Palmerston North, Manawatu, New Zealand. One experiment was conducted to investigate the interaction of grazing duration and SWD on soil damage and pasture production, while the other experiment compared NO3- leaching under a standard dairy grazing system and a grazing system that used targeted DC grazing (i.e. during late-summer to early-winter). Irrespective of drainage season and grazing treatment, the greatest NO3- concentrations in drainage occurred in the first seven to eight drainage events, which equated to the initial 50 to 100 mm of drainage. The majority of N losses following this were in the form of total organic nitrogen (TON). The average reductions in NO3- and TN leaching following targeted DC grazing in the summer to early winter periods of 2015 and 2016 were 28% and 20% respectively. The uniform return of slurry contributed to the DC treatment maintaining similar pasture production to the standard grazing treatment. Compared with year-round DC grazing, targeted DC grazing could be relatively inexpensive and so is likely to be a good mitigation option for N leaching in many cases, particularly on free draining soils where treading damage is uncommon. Treading damage can be easy to observe; however, it can be time consuming to measure and even more difficult to quantify in a spatially aware manner. Therefore, two new and contrasting methods of assessing treading damage were developed, namely, the visual scoring method and the pugometer. The advantage of the pugometer is that it can automatically capture spatial variability rapidly, which no current method is able to do. Only minimal treading damage and no reduction in pasture production was associated with cows grazing pasture at SWD > 2 mm, and this SWD appears to be a critical value, which farmers on fine textured soils, like the Tokomaru silt loam, could use to schedule grazing to protect soils and pastures from pugging damage. However, due to the need to maintain pasture quality there will be numerous occasions when the pasture on farms practising DC grazing will need to be grazed at a SWD < 2 mm. A modelling exercise revealed that up to 60% of a farm with standoff facilities could be damaged in an average season. While the damage inflicted on pastures may look unsightly, this may have little influence on overall accumulated (annual) pasture production. However, when the SWD was less than 2 mm, there were short-term losses in pasture production of approximately 500 to 1000 kg DM/ha under the grazing regimes studied here (i.e. 4- or 8-hour grazing duration and single and repeat damage events). If there is a need to graze in wet conditions (at or near saturation), then short durations (up to 4 hours) are recommended. Targeted DC grazing management provides the opportunity to achieve improved environmental outcomes, and the effectiveness of targeted DC grazing as a multi-purpose tool is not undermined by the need to graze in wet conditions.Item Effects of increasing cow urine deposition area on soil mineral nitrogen movement and pasture growth on a recent soil in the Manawatu region, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management at Massey University, Manawatū, Palmerston North, New Zealand(Massey University, 2017) Romero Ramírez, Stefanía YaninaThe cow urine patch is a major source of nitrate (NO₃⁻) leaching from grazed dairy pasture farms. Increasing the urine deposition area is a direct way of reducing the potential risk of this cause N leaching losses. Research is required to quantity the effectiveness of this mitigation across a range of different soil and climatic conditions. The objective of this study was to determine the effect of increasing the cow urine deposition area on NO₃⁻ leaching risk and short-term pasture accumulation on Recent soil in the Manawatu Region, New Zealand. A field trial was conducted, which consisted of three treatments evaluated on pasture plots: Urine (1 m2), Urine (0.2 m2) and No-urine. The two urine treatments received the same volume of 2.1 L urine/patch. Urine treatments were applied on the 6th of March 2017, and soil inorganic N was measured on three occasions; 15, 36 and 53 days after urine application (DAUA). At the third soil sampling time, which was 24 days after the drainage season was estimated to have commenced, the net inorganic N (inorganic N in the urine treatment minus the value for the No-urine treatment) in the 45-120 cm soil depth was 1.08 g net inorganic N/patch for the Urine (1 m2) treatment compared to 2.97 g net inorganic N/patch for the Urine (0.2 m2) treatment. Therefore, the Urine (1 m2) treatment resulted in a 63.6% reduction in the quantity of net inorganic N that was highly susceptible to leaching, compared to the more typical urine patch area of 0.2 m2. At a paddock scale, when net inorganic N from the urine treatments is multiplied by an estimate of the quantity of urine patches per hectare in a single grazing, this equates to a reduction of 2.53 kg N/ha from a single autumn grazing. It is expected that increasing urine deposition area at multiple grazings would result in greater reductions in the annual NO₃⁻ leaching risk. Over the two pasture harvests conducted in the trial, the pasture DM accumulation for the No-urine treatment produced an average of 3220 kg DM/ha. The two urine patch treatments achieved a similar level of pasture DM accumulation to that of the No-urine treatment. The lack of a pasture growth response from the added urine could have been influenced by the high clover content (35.9%) of the pasture, and in addition, there may have been adequate background soil mineral N levels, which together could have contributed to N not being growth limiting during the trial. This research has demonstrated that increasing cow urine deposition area in autumn has potential to be an effective mitigation for decreasing N leaching losses from grazed dairy pastures. Further research is required to investigate the effects of increasing cow urine deposition area at multiple grazings, in order to determine the effect of this mitigation option on annual NO₃⁻ leaching and pasture production.Item Assessment of the transport and transformation of nitrogen in the unsaturated and saturated zones under two dairy farms in the Manawatu River catchment : a thesis presented in partial fulfilment of the requirements for the degree of Master in Environmental Management at the Institute of Agriculture and Environment, Massey University, Palmerston North, Manawatu, New Zealand(Massey University, 2015) Espanto, Patrick Benson BThe importance of dairy farming in New Zealand is reflected in the country’s export and gross domestic product earnings. While the economic and food production benefits are evident, there is an increasing concern about the effects of excess nutrient runoff on water quality and ecosystem health. Studies on the transport and transformation of nutrients, specifically nitrogen, are limited or mainly focused on the management and reduction of nutrient losses from the root zone. This is also the case in the Manawatu River catchment of New Zealand. The goal of this study was to assess the transport and transformation of nitrogen in the unsaturated (below the root zone) and saturated zones using field measurements, a tracer test, and identification of redox conditions in the shallow groundwater. Two sites were chosen in the Manawatu River catchment: Site 1 (Massey Dairy Farm No. 1, Palmerston North) and Site 2 (Te Matai Road, Whakarongo). Soil-water and groundwater were extracted using 12 porous cups (0.3, 0.6, 1.0, 2.0 m bgl) and four piezometers (5.8, 6.3, 7.4, 8.7 m bgl) installed at Site 1, and six piezometers (12, 18, 33, 51, 66, 87 m bgl) installed at Site 2. The extracted water samples were analysed for nitrate-nitrogen (NO3-N) and other water quality parameters. The average NO3-N concentrations in the unsaturated zone (0.3 – 2.0 m bgl) decreased with depth. At Site 1, a tracer test was conducted in November, 2013, using an application of urea (467 kg N/ha) and bromide (206 kg Br/ha). After fertiliser application, NO3-N concentrations increased in the root zone. The bromide reached only until the 2-m depth porous cup in January, 2014, after a total irrigation depth of 478 mm. The early appearance of bromide in the 0.3 m depth root zone suggested preferential flow, a pathway that speeds up transport of potential contaminants in the groundwater. The observed data of NO3-N, dissolved oxygen (DO), iron, manganese, and sulphate were utilised to assess the redox condition in groundwater at both sites. The decreasing NO3-N concentrations with increasing depth indicated dilution and/or the occurrence of denitrification in the groundwater. The groundwater redox conditions were mixed oxic-anoxic in the 5.8 – 51 m bgl and mainly anoxic below 51 m groundwater depth.Item Measuring and modelling the fate of fertilizer and soil nitrogen in a cropping system : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1983) Iqbal, Hayath MohammedFuture trends in New Zealand cropping, anticipate an increased use of fertilizer nitrogen (N). In order to more efficiently utilise N in cropping systems, a better understanding of the N processes and their significance under New Zealand conditions, is required. To achieve such understanding, several small scale experiments were conducted. Preliminary experiments, investigating the fate of N-15 urea applied to barley and oats, were conducted using soil cylinders. Total recovery of N-15 in plant and soil components varied between 50 to 90 percent. Initial urea N transformations were rapid, and most of fertilizer N uptake by plants occurred in the first five weeks following its application at sowing. Plants took up a greater proportion of their total N as native soil N. N-15 assay on soil and plant samples containing N-15 in excess of about 1 atom percent, was performed satisfactorily with emission spectrometry. The data obtained by the use of soil cylinders, were representative, particularly of short term field behaviour. A five-week study was undertaken to account for the extent and pattern of immobilisation and leaching of N-15 urea applied to a barley crop. Two irrigation treatments (wet and normal) were imposed. Approximately 90% of the applied N was recovered. One week after application, 86% of urea N had been hydrolysed, while after two weeks 36% of it had been immobilised into organic matter. The increased leaching of N from the wet lysimeters compared with the normal lysimeters was at the expense of plant N uptake, having little effect on the amount of N immobilised. Net mineralisation of native soil N was calculated as 1.2 kgN/ha/day. Using the data obtained from the preceding investigation, a five-week N model was developed. The model successfully predicted the increased leaching of fertilizer N from the wet compared with the normal lysimeters. The reduced plant uptake of fertilizer N, resulting from this increased leaching from the wet lysimeters, was also quite successfully modelled. The model indicated that the amount of fertilizer N leached was strongly dependent on the timing of rainfall in relation to the time of fertilizer application. A crop season model was developed by extending the five-week model to cover a full growth season of a barley crop, and the model was verified with data from a large scale field trial. The model prediction for N leaching losses, demonstrated better accuracy than for plant N uptake. The model has the potential to provide a continuous evaluation of possible adverse effects caused by unanticipated factors such as excessive rainfall, on plant N uptake. The crop season model was further developed to predict long term changes in the N cycle of a double cropping system, in a soil that was previously under pasture. The model predicted quite accurately the N loads as well as the N concentrations in tile drainage effusing from experimental field plots. In general, the measured and predicted data for nitrate concentrations in tile drainage of field plots indicated that nitrate concentrations in tile effluent usually exceed 15 to 20 mgN/litre, regardless of fertilizer addition. The addition of fertilizer could increase these levels two-fold but only for a short time. The utility of the model as a research tool was illustrated.Item Nitrogen loss through denitrification in soil under pasture in New Zealand : a thesis submitted 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, 1996) Luo, JiafaDenitrification is an important process in the N cycle that can affect the efficiency of use of soil nutrients and also the impact of agricultural activities on the wider environment. There have been few studies on the losses of N by denitrification from pasture soils. The current study was undertaken to investigate N loss through denitrification in a New Zealand pasture, and to examine relationships between denitrification and other environmental and soil factors. Denitrification was measured using the acetylene inhibition technique by incubating soil in a closed system. A study on the effect of storage concluded that a soil's moisture status and the duration of storage can affect the denitrification activity, as measured by a short-term assay. This effect can operate by changing both denitrification enzyme activities and the availability of substrate. Denitrification activities were greatest in the surface soil and generally decreased with depth in the soil profile. The decrease in denitrification activity with depth could be also attributed to both a decrease in enzyme activity and also decreasing availability of C and NO3-N. High coefficients of variation (CV) and skewed distributions of denitrification rate were always observed in the field. The log-normal distribution generally provided a better fit than the normal distribution for denitrification rates measured in the field. The variance in denitrification rate changed temporally, and depended on the soil moisture content and the grazing pattern. Amendment of soil cores with NO3-N and soluble-C, either singly or together, substantially decreased the skewness of the frequency distribution of denitrification rates. Denitrification rates varied according the location in the paddock. Highest rates were detected in the floor of a gully and in a gateway area. Denitrification rates followed a marked seasonal pattern, with higher rates being measured during the wet winter and lower rates during the dry summer. Higher denitrification rates were also observed during brief periods after rainfall events in the summer. An annual N loss of about 4.5 kg N ha-1 through denitrification was estimated in this dairy-farm paddock. Block grazing with cows at a high stocking rate increased the denitrification rate between 3 and 14 days after grazing under seasonally moist conditions. However, the total N loss through denitrification induced by grazing during that period was still very small, compared with the N returned by the grazing animals. Correlation and multiple regression analyses revealed that relationships between single core measurements of denitrification rates and other edaphic factors in the field were poor for the combined data set. However better relationships between denitrification rate and NO3-N concentration in the individual soil cores existed at high soil moisture contents, and better relationships between denitrification rate and respiration rate existed at low soil moisture contents. Mean denitrification rates from individual dates were positively correlated to soil moisture content. Regression equations derived from the mean-value data for each sampling date improved the prediction of the observed denitrification rate, compared to those from the individual data sets. Soil moisture content and NO3-N concentration accounted for 51% of the observed variability in denitrification rate in the field. Experiments conducted to obtain insights into factors regulating denitrification, by removing possible limitations to denitrification during the incubation, found that the addition of NO3-N solution to soil cores stimulated denitrification rates in all seasons. This result suggested that the NO3-N concentration, or more importantly, the accessibility of NO3-N to the denitrification sites in the pasture soil may have limited denitrification. Denitrification rates also increased when soluble-C was added to the soil cores, but the magnitude of the effect depended on other edaphic factors A separate study demonstrated that the presence of acetylene during the denitrification measurement also inhibited the nitrification process, and consequently could affect the NO3-N availability for denitrification in the soil. However, this study also indicated that inhibition of nitrification by acetylene did not affect short-term measurement of denitrification rate.