Plant analysis as a tool to determine crop nitrogen status

An effective plant nutrient management strategy optimises nitrogen (N) use efficiency for minimised environmental impact, while ensuring an optimum N status of the crop for good product quality and maximum growth. Soil or plant analysis can be used to evaluate the strategy; however the use of plant analysis for this purpose has been limited. One reason is lack of reliable reference values for the critical concentration needed for optimal growth. This study builds on theories that relate ontogenetic changes in the critical N concentration to changes in the relation between mass and surface area of the entire plant and of individual leaves. Through the establishment of critical N concentrations on the basis of these theories, some of the drawbacks hitherto experienced with plant analysis, such as difficulties in defining growth stage or plant part to sample, can be avoided. The aim of this thesis was to establish critical N concentrations for white cabbage (Brassica oleracea L. var. capitata L. f. alba D.C.) on the basis of these theories. Multi-N-rate and multi-harvest experiments were conducted in the field and in a climate chamber. The results showed that the critical N concentration declined at the same rate (-0.33) as the plant's leaf area ratio (leaf area divided by plant mass), which is in agreement with the 2/3-Power rule or "skin-core" hypothesis. The critical N concentration (% of DM) on a whole plant basis was estimated to 4.5 (W1.5 t ha-1), where W is weight per unit area of plant dry matter exclusive of roots. Moreover, it was concluded that the unshaded horizontally orientated leaves of cabbage can be used for leaf area based plant analysis of individual leaves. The critical N concentration of these leaves expressed on an area basis was found to be 3.7 g N m-2, while that for the whole plant N on a leaf area basis was 4.7 g N m-2. The ratio of these two critical concentrations, 0.8, was similar to the leaf N ratio (leaf N/whole plant N) of young plants before self shading occurs

Land Use Influence on the Characteristics of Groundwater Inputs to the Great Bay Estuary, New Hampshire

This research examines the sources and factors affecting nutrient-laden groundwater discharge to the Great Bay Estuary. To further understand this relationship, examination of groundwater residence time, a review of historic land uses, and nitrate source tracking strategies were used. Seven submarine groundwater discharge (SGD) sites were selected, and groundwater monitoring networks were installed to examine the relationship between land use and groundwater quality at the discharge zones. Field activities were performed in the summer and fall of 2003 and 2004. Estuarine water intrusion in groundwater discharge samples confounded the analyses for major ion chemistry and boron isotopes. CFC-derived and modeled groundwater ages in the study area averaged 23.2 years (±15.0 years). CFC analysis enabled correlation of nitrate concentrations at the SGD sites with the historic land use coverage for the years 1974 (for most of the sites) or 1962 (SGD 58.4). Two types of correlation were made: 1) between the agricultural and residential land use for all observed nitrate concentrations in the recharge areas, and 2) correlation with the nitrate concentrations between developed and undeveloped land uses. Both statistical correlations (Kendall’s Tau and Spearman’s Rho) indicated a connection between the increase of residential land use of the last three decades with the high nitrate-bearing groundwater discharging to the Great Bay (NH). The geochemical composition of the SGD water was also investigated by using simple mixing models that attempted to explain the water chemistry characteristics of the targeted SGD sites. Based on these models it was concluded that overburden groundwater comprises 75% to 95% of the groundwater discharging at the SGD sites. A significant correlation (Tau’s, p=0.021) between nitrate-bearing groundwater and CFCderived groundwater ages was detected supporting the hypothesis that high nitrate bearing groundwater will be discharged to the Great Bay in the near future accounting for the increase of residential land use of 1990’s. Continuous monitoring of SGD sites was suggested to be included as part of the periodic environmental quality monitoring activities of the Great Bay. Long-term step-wise sampling for groundwater dating is required to develop a stronger chronological evolution of groundwater nitrate inputs. Further research should concentrate on detailing the overburden water chemistry, flow paths, and nitrogen loading characteristics

Real-time Tactical and Strategic Sales Management for Intelligent Agents Guided By Economic Regimes

Many enterprises that participate in dynamic markets need to make product pricing and inventory resource utilization decisions in real-time. We describe a family of statistical models that address these needs by combining characterization of the economic environment with the ability to predict future economic conditions to make tactical (short-term) decisions, such as product pricing, and strategic (long-term) decisions, such as level of finished goods inventories. Our models characterize economic conditions, called economic regimes, in the form of recurrent statistical patterns that have clear qualitative interpretations. We show how these models can be used to predict prices, price trends, and the probability of receiving a customer order at a given price. These “regime†models are developed using statistical analysis of historical data, and are used in real-time to characterize observed market conditions and predict the evolution of market conditions over multiple time scales. We evaluate our models using a testbed derived from the Trading Agent Competition for Supply Chain Management (TAC SCM), a supply chain environment characterized by competitive procurement and sales markets, and dynamic pricing. We show how regime models can be used to inform both short-term pricing decisions and longterm resource allocation decisions. Results show that our method outperforms more traditional shortand long-term predictive modeling approaches.dynamic pricing;trading agent competition;agent-mediated electronic commerce;dynamic markets;economic regimes;enabling technologies;price forecasting;supply-chain

Trading patterns in the European Carbon Market: the role of trading intensity and OTC transactions

International audienceThis paper examines the effect of trading intensity and OTC transactions on expected market conditions in the early development period of the European Carbon futures market. Past duration and trading intensity are used as information related order flow variables in modelling time between transactions in two new specifications of Autocorrelation Conditional Duration (ACD) models. This allows for specific investigation of non-linear asymmetric effects on expected duration and the impact of OTC transactions. Evidence is presented of two main types of trading episodes of increased and decreased trading intensity. Both have a significant impact on price volatility, which increases further if an OTC transaction intrudes. OTC transactions also play a dual role. They slow down trading activity in the short term (over the next five transactions) but increase it substantially in the long term (over ten transactions). Both the liquidity and information price impact components increase following an OTC trade, but the information impact is greater. Price volatility calms down faster than liquidity effects following an OTC trade, and this is more pronounced in ECX and in Phase II. The combined evidence points towards increased market depth, efficiency and maturity of the trading environment

Transport on complex networks: Flow, jamming and optimization

Many transport processes on networks depend crucially on the underlying network geometry, although the exact relationship between the structure of the network and the properties of transport processes remain elusive. In this paper we address this question by using numerical models in which both structure and dynamics are controlled systematically. We consider the traffic of information packets that include driving, searching and queuing. We present the results of extensive simulations on two classes of networks; a correlated cyclic scale-free network and an uncorrelated homogeneous weakly clustered network. By measuring different dynamical variables in the free flow regime we show how the global statistical properties of the transport are related to the temporal fluctuations at individual nodes (the traffic noise) and the links (the traffic flow). We then demonstrate that these two network classes appear as representative topologies for optimal traffic flow in the regimes of low density and high density traffic, respectively. We also determine statistical indicators of the pre-jamming regime on different network geometries and discuss the role of queuing and dynamical betweenness for the traffic congestion. The transition to the jammed traffic regime at a critical posting rate on different network topologies is studied as a phase transition with an appropriate order parameter. We also address several open theoretical problems related to the network dynamics

Immunity and Simplicity for Exact Counting and Other Counting Classes

Ko [RAIRO 24, 1990] and Bruschi [TCS 102, 1992] showed that in some relativized world, PSPACE (in fact, ParityP) contains a set that is immune to the polynomial hierarchy (PH). In this paper, we study and settle the question of (relativized) separations with immunity for PH and the counting classes PP, C_{=}P, and ParityP in all possible pairwise combinations. Our main result is that there is an oracle A relative to which C_{=}P contains a set that is immune to BPP^{ParityP}. In particular, this C_{=}P^A set is immune to PH^{A} and ParityP^{A}. Strengthening results of Tor\'{a}n [J.ACM 38, 1991] and Green [IPL 37, 1991], we also show that, in suitable relativizations, NP contains a C_{=}P-immune set, and ParityP contains a PP^{PH}-immune set. This implies the existence of a C_{=}P^{B}-simple set for some oracle B, which extends results of Balc\'{a}zar et al. [SIAM J.Comp. 14, 1985; RAIRO 22, 1988] and provides the first example of a simple set in a class not known to be contained in PH. Our proof technique requires a circuit lower bound for ``exact counting'' that is derived from Razborov's [Mat. Zametki 41, 1987] lower bound for majority.Comment: 20 page