Browsing by Author "Creamer, Rachel E."
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Item Open Access Interactions between phosphorus fertilisation and soil biota in managed grasslands systems(Cranfield University, 2012-05) Massey, Paul Andrew; Creamer, Rachel E.; Ritz, K.The application of phosphorus (P) fertilisers to grassland systems is a common practice to increase and sustain grassland productivity. This is requisite for satisfying the nutritional needs of grazing animals and increasing dairy and livestock output. The costs of such fertilisers are increasing and the demands for such fertiliser will also most likely rise following governmental targets set in Ireland to increase national agricultural output. However, the application of P fertiliser to grassland systems can contribute to the eutrophication of water-courses, since fertiliser applications can result in the accumulation of P at the soil surface. One potential way to facilitate plant P acquisition in grasslands may be associated with the soil biota. In particular, the soil microbial biomass is recognised as a potential P pool that can provide a source of bioavailable P to the plant community. The soil biota may also facilitate the incorporation of P from the soil surface into the soil profile, since earthworms can actively increase the transport of P-rich soil material from the surface belowground. This project thus aimed to discern how P fertilisation affects microbial biomass nutrient pools and biologically-mediated P incorporation in grassland systems, and how this relates to plant P yields. To investigate this aim, two research questions were proposed: (i) is the soil biota affected by commonly adopted P fertiliser strategies in grassland systems?; (ii) what consequence does this hold for P acquisition by the plant community? An experiment was conducted to examine how the soil biota responded to different rates of inorganic P fertilisation in two grassland sites of contrasting soil types over an 18 month period. This revealed that increasing P fertilisation did not affect microbial biomass P concentrations in the soil. However, an effect was observed upon plant P yield, in which greater plant P yields were obtained proportional to the P fertiliser rate. Two laboratory experiments were conducted to further investigate this lack of effect. These utilised soil from the same grassland sites and examined how nutrient additions to the soil affected microbial biomass nutrient pools and activity. Results from these experiments supported evidence from the field experiment, since the application of P fertiliser did not affect microbial biomass nutrient pools following fertiliser application, and supplementation of carbon (C) + P substrate to the soil did not invoke respiratory responses between P fertiliser treatments. Nevertheless,supplementation with C + nitrogen (N) and C+N+P substrates was found to suppress microbial respiration. This was attributed to greater C assimilation by the microbial community in these particular substrate-induced respiration treatments. In order to investigate biologically-mediated P incorporation, a glasshouse-based mesocosm scale experiment was carried out using two contrasting soils. Bulk soil (1 – 30 cm depth range) was derived from a nutrient poor grassland system, whereas the soil for the 0 – 1 cm depth range was taken from an intensive system that was seven times greater in labile inorganic P concentration. Three treatments were applied to mesocosms in an incomplete factorial design, involving the inclusion of earthworms, different botanical diversities (unplanted, monoculture or mixed plant community) and different fertiliser types (organic or inorganic). The absent factorial combinations involved the application of earthworms to unplanted mesocosms. With respect to the earthworm treatment, results revealed that the presence of earthworms reduced labile P concentrations in the 0 – 1 cm depth range of soil. The presence of different botanical diversities or fertiliser types did not affect microbial biomass nutrient pools, whilst the presence of mixed plant communities did increase plant P yields. However, microbial and nematode community structures were affected in an idiosyncratic manner by both botanical diversity and fertiliser type. This project demonstrated the significance of grassland management regimes in governing microbial biomass P concentrations. In particular, it was revealed that the frequent defoliation of the sward appeared to uncouple the microbial community from both fertiliser inputs and possibly plant P yields. The fact that an increase in plant P yield with increasing P fertilisation was noted in the absence of microbial responses suggests that the soil biota may not be crucial for plant P acquisition in such intensive inorganic-fertiliser based regimes. This suggestion was also supported by the mesocosm experiment, since plant P yields differed between botanical diversities but no effects were observed on microbial biomass P concentrations. Furthermore, this project showed the potential of the earthworm community to reduce P concentrations in the volume of soil which poses the greatest risk to water quality. The collective evidence highlights the need for further understanding of the consequences of inorganic-based fertiliser management systems, since current strategies may not adequately account for management effects on soil biological P cycling.Item Open Access Modelling Soil Bulk Density using Data-Mining and Expert Knowledge(Cranfield University, 2013-04) Taalab, Khaled Paul; Corstanje, Ronald; Whelan, Michael; Creamer, Rachel E.Data about the spatial variation of soil attributes is required to address a great number of environmental issues, such as improving water quality, flood mitigation, and determining the effects of the terrestrial carbon cycle. The need for a continuum of soils data is problematic, as it is only possible to observe soil attributes at a limited number of locations, beyond which, prediction is required. There is, however, disparity between the way in which much of the existing information about soil is recorded and the format in which the data is required. There are two primary methods of representing the variation in soil properties, as a set of distinct classes or as a continuum. The former is how the variation in soils has been recorded historically by the soil survey, whereas the latter is how soils data is typically required. One solution to this issue is to use a soil-landscape modelling approach which relates the soil to the wider landscape (including topography, land-use, geology and climatic conditions) using a statistical model. In this study, the soil-landscape modelling approach has been applied to the prediction of soil bulk density (Db). The original contribution to knowledge of the study is demonstrating that producing a continuous surface of Db using a soil-landscape modelling approach is that a viable alternative to the ‘classification’ approach which is most frequently used. The benefit of this method is shown in relation to the prediction of soil carbon stocks, which can be predicted more accurately and with less uncertainty. The second part of this study concerns the inclusion of expert knowledge within the soil-landscape modelling approach. The statistical modelling approaches used to predict Db are data driven, hence it is difficult to interpret the processes which the model represents. In this study, expert knowledge is used to predict Db within a Bayesian network modelling framework, which structures knowledge in terms of probability.This approach creates models which can be more easily interpreted and consequently facilitate knowledge discovery, it also provides a method for expert knowledge to be used as a proxy for empirical data. The contribution to knowledge of this section of the study is twofold, firstly, that Bayesian networks can be used as tools for data-mining to predict a continuous soil attribute such as Db and that in lieu of data, expert knowledge can be used to accurately predict landscape-scale trends in the variation of Db using a Bayesian modelling approach.