https://hdl.handle.net/10182/39 Thu, 25 Jan 2018 15:18:28 GMT 2018-01-25T15:18:28Z https://hdl.handle.net/10182/8889 Ammonium sorption and ammonia inhibition of nitrite-oxidizing bacteria explain contrasting soil N₂O production Venterea, R. T.; Clough, Timothy J.; Coulter, J. A.; Breuillin-Sessoms, F.; Wang, P.; Sadowsky, M. J. Better understanding of process controls over nitrous oxide (N₂O) production in urine-impacted 'hot spots' and fertilizer bands is needed to improve mitigation strategies and emission models. Following amendment with bovine (Bos taurus) urine (Bu) or urea (Ur), we measured inorganic N, pH, N₂O, and genes associated with nitrification in two soils ('L' and 'W') having similar texture, pH, C, and C/N ratio. Solution-phase ammonia (slNH₃) was also calculated accounting for non-linear ammonium (NH₄⁺) sorption capacities (ASC). Soil W displayed greater nitrification rates and nitrate (NO₃⁻) levels than soil L, but was more resistant to nitrite (NO₂⁻) accumulation and produced two to ten times less N₂O than soil L. Genes associated with NO₂⁻oxidation (nxrA) increased substantially in soil W but remained static in soil L. Soil NO₂⁻was strongly correlated with N₂O production, and cumulative (c-) slNH₃ explained 87% of the variance in c-NO₂⁻. Differences between soils were explained by greater slNH₃ in soil L which inhibited NO₂⁻oxidization leading to greater NO₂⁻ levels and N₂O production. This is the first study to correlate the dynamics of soil slNH₃, NO₂⁻, N₂O and nitrifier genes, and the first to show how ASC can regulate NO₂⁻ levels and N₂O production. © 2015 Macmillan Publishers Limited. Thu, 16 Jul 2015 00:00:00 GMT https://hdl.handle.net/10182/8889 2015-07-16T00:00:00Z https://hdl.handle.net/10182/8794 The effect of the lime-molybdenum interaction on some properties of pasture soils Harris, A. J. Molybdenum is the most recent addition to the list of those elements essential for plant growth. Such insignificant amounts are required to give benefit on deficient areas that results from its application are truly amazing, yet, where it is found to be necessary, application of this trace element may mean the difference between low and high pasture production. It appears that molybdenum will continue to be used in this country for numerous trials have indicated that as far as pasture production is concerned, a few ounces of molybdenum give results as good as several tons of lime in many cases. This work is an attempt to show the differences, if any, in soil structure, earthworm populations, organic matter content, mineralisation of soil nitrogen, exchangeable manganese content, and phosphate fixing power of the soil due to treatment in the field with lime and with molybdenum. Sat, 01 Jan 1955 00:00:00 GMT https://hdl.handle.net/10182/8794 1955-01-01T00:00:00Z https://hdl.handle.net/10182/8789 Carbonaceous soil amendments to reduce plant uptake of Cd in NZ’s agricultural systems Mamun, Shamim Al Cadmium (Cd) is a non‐essential trace element that accumulates in agricultural soils through the application of Cd-rich phosphate fertiliser and industrial activity. Plants can accumulate Cd to concentrations that sometimes exceed food safety standards presenting a human health risk. Cadmium is readily taken up by plants and can be transferred to grazing animals. In many agricultural systems, Cd concentrations in leafy vegetables and the offal products of grazing animals are at or above food safety standards. There is no practical means of removing Cd from contaminated agricultural soils. Various soil amendments have been used to reduce plant Cd-uptake, but these have mostly focused on heavily contaminated soils and mine tailings. This work aimed to determine whether low cost carbonaceous amendments could effectively reduce Cd uptake by crop plants in agricultural soils with moderate levels of Cd contamination. We used two contrasting market garden soils (a silt loam and a brown granular allophanic soil) for these experiments, where Cd concentrations in selected vegetables were occasionally above food safety standards (0.1 mg/kg fresh weight). Batch sorption experiments were used to determine the ability of the soils and potential soil amendments to bind Cd from a solution of 0.05M Ca(NO3)2. The sorption experiments revealed that composts and lignite bound an order of magnitude more Cd than soils and other potential soil amendments. For all materials, sorption increased with increasing pH of the ambient solution up to a pH of 7.5. Pot trials were used to determine the effect of various composts, lignite and lime on the uptake of Cd by spinach (Spinacia oleracea L.), lettuce (Lactuca sativa L.), onion (Allium cepa L.) and potato (Solanum tuberosum L.). All composts, added at a rate of 2.5% or 5% (w/w) reduced plant Cd uptake by up to 60%. The composts did not induce a deficiency in the uptake of plant nutrients, including essential trace elements such as zinc, and copper. Composts invariably increased plant biomass. An incubation experiment, including treatments with increased temperature and nitrogen as well as regular disturbance, was used to determine the likely longevity of the Cd-immobilising properties of the composts. After one year of incubation, there was no significant release of Cd from the compost-amended soils, despite a significant reduction in soil carbon. A pot trial using incubated soil also revealed that the beneficial effects of compost for reducing plant Cd uptake persisted for at least one year. The results indicated that mechanical disturbance of the soil may have resulted in the dissolution / suspension of iron moieties that subsequently occluded Cd on the surfaces of soil colloids. Lignite generally reduced plant biomass and its effect on plant Cd-uptake was variable. In some cases, lignite caused a significant increase in plant Cd uptake. This was attributed to acidification, probably caused by oxidation of sulphide compounds in the lignite. Potentially, lignite-lime mixtures may be effective, however, the costs of lignite are significantly greater than composts. Using lime to increase the soil pH from 6.0 to 6.5 generally reduced the Cd concentration in soil solution and in vegetables. However, this effect was not consistent, with some treatments causing an increase in plant uptake. Moreover, liming significantly reduced the uptake of essential micronutrients, especially zinc, which offsets its usefulness as a tool to reduce Cd uptake. I conclude that biological wastes, especially composts, are an underutilised resource that can not only reduce plant Cd-uptake but also improve plant production. Future research should include field trials to determine the performance of Cd in field conditions as well as agronomic practicalities. Mon, 06 Mar 2017 00:00:00 GMT https://hdl.handle.net/10182/8789 2017-03-06T00:00:00Z https://hdl.handle.net/10182/8776 Lessons learned from liquefaction of the Canterbury Earthquake Sequence (2010-2011) to inform paleoliquefaction studies Giona Bucci, Monica Liquefaction affects late Holocene, loose packed and water saturated sediment subjected to cyclical shear stress. Liquefaction features in the geological record are important off-fault markers that inform about the occurrence of moderate to large earthquakes (> 5 Mw). The study of contemporary liquefaction features provides a better understanding of where to find past (paleo) liquefaction features, which, if identified and dated, can provide information on the occurrence, magnitude and timing of past earthquakes. This is particularly important in areas with blind active faults. The extensive liquefaction caused by the 2010-2011 Canterbury Earthquake Sequence (CES) gave the geoscience community the opportunity to study the liquefaction process in different settings (alluvial, coastal and estuarine), investigating different aspects (e.g. geospatial correlation with landforms, thresholds for peak ground acceleration, resilience of infrastructures), and to collect a wealth geospatial dataset in the broad region of the Canterbury Plains. The research presented in this dissertation examines the sedimentary architecture of two environments, the alluvial and coastal settings, affected by liquefaction during the CES. The novel aim of this study is to investigate how landform and subsurface sedimentary architecture influence liquefaction and its surface manifestation, to provide knowledge for locating studies of paleoliquefaction in future. Two study cases documented in the alluvial setting showed that liquefaction features affected a crevasse splay and point bar ridges. However, the liquefaction source layer was linked to paleochannel floor deposits below the crevasse splay in the first case, and to the point bar deposits themselves in the second case. This research documents liquefaction features in the coastal dune system of the Canterbury Plains in detail for the first time. In the coastal dune setting the liquefiable layer is near the surface. The pore water pressure is vented easily because the coastal dune soil profile is entirely composed of non-cohesive, very well sorted sandy sediment that weakly resists disturbance from fluidised sediment under pressure. As a consequence, the liquefied flow does not need to find a specific crack through which the sediment is vented at the surface; instead, the liquefied sand finds many closely spaced conduits to vent its excess of pore water pressure. Therefore, in the coastal dune setting it is rare to observe discrete dikes (as they are defined in the alluvial setting), instead A horizon delamination (splitting) and blistering (near surface sills) are more common. The differences in styles of surface venting lead to contrasts in patterns of ejecta in the two environments. Whereas the alluvial environment is characterised by coalesced sand blows forming lineations, the coastal dune environment hosts apparently randomly distributed isolated sand blows often associated with collapse features. Amongst the techniques tested for the first time to investigate liquefaction features are: 3D GPR, which improved the accuracy of the trenching even six years after the liquefaction events; thin section analysis to investigate sediment fabric, which helped to discriminate liquefied sediment from its host sediment, and modern from paleoliquefaction features; a Random Forest classification based on the CES liquefaction map, which was used to test relationships between surface manifestation of liquefaction and topographic parameters. The results from this research will be used to target new study sites for future paleoliquefaction research and thus will improve the earthquake hazard assessment across New Zealand. Thu, 13 Apr 2017 00:00:00 GMT https://hdl.handle.net/10182/8776 2017-04-13T00:00:00Z