Perennial clovers and ryegrasses as understorey crops in cereals

Perennial crops undersown in cereals provide ground cover from harvest of the cereal crop to sowing of the next crop. Such cover crops can e.g. reduce soil erosion, nutrient leaching and N fertiliser requirements of the succeeding crop. The objective of this thesis was to develop guidelines on how to prevent grain yield losses due to competition from the perennial crops or to increase the yield of the main crops. The effects of species and time of undersowing of perennial crops in spring cereals, and the management of an intercropping system in which winter oilseed rape or consecutive crops of winter wheat were established in a remaining crop of white clover, were studied. The biomass of undersown cover crops by the time of the harvest of spring barley was significantly reduced with each delay in the undersowing, but the increase in biomass during autumn was generally not affected. Italian ryegrass (Lolium multiflorum Lam) and perennial ryegrass (Lolium perenne L.) reduced the grain yield by 6 and 1%, respectively, but may both be suitable as cover crops with the appropriate main crop, time of undersowing and seed rate. Undersown white clover (Trifolium repens L.)/perennial ryegrass mixtures kept soil mineral N as low as pure ryegrass and improved the residual effect. This suggests that clover in the cover crops may reduce the N fertiliser requirements of the succeeding crop without increased N leaching. Grain yields were smaller in the wheat/clover system than with wheat alone when the wheat was direct drilled and larger when sown after stubble cultivation. Direct drilled wheat and rape yielded more with clover varieties less adapted to the cold climate than with varieties in common use in the area. Grain yield increased, weeds were efficiently controlled and the white clover crop maintained by applying herbicides that mainly act as germination inhibitors when a third consecutive wheat crop had 1–2 leaves. It was possible to conclude that (1) the tillage performed in conjunction with the sowing of wheat, (2) the weed control practice, and (3) the choice of clover variety, have large effects on the yield of the winter annuals in the intercropping system

Long-term fate of sewage-sludge derived cadmium in arable soils

The focus of this work was to improve knowledge of the long-term fate of cadmium supplied to arable soils by sewage sludge. Emphasis was placed on measured and modelled changes in the solubility and mobility of cadmium, resulting from long-term turnover of both sludge-derived and inherent organic matter of the soil. Measurements were conducted in a long-term sludge supplied field experiment, situated at Ultuna (60°N, 17°E), started in 1956. Furthermore, batch studies on soil samples and modelling exercises in WHAM were performed in order to study the speciation of cadmium in the soil-solution system. A comprehensive model -the SLAM model- was developed to increase the understanding of the influence of soil and sludge adsorption characteristics on cadmium solubility and bioavailability, and the migration rate of cadmium in soil profiles. The long-term sludge supplies had increased the solubility of cadmium, measured in crop cadmium concentration, as an effect of enhanced acidification and increased Cd concentration in the soil. A low Cd migration was measured, attributed to non-equilibrium Cd concentration in percolating water, a high cadmium sorption capacity in the subsoil and root driven Cd circulation in the soil profile. No increased Cd sorption capacity was measured in the sludge supplied soil, despite the almost doubled soil organic matter content. This might be partly attributed to the higher iron oxide and hydroxide concentration measured in the sludge, forming more stable complexes with soil humic compounds compared to cadmium complexes with soil humic compounds. A Monte-Carlo analysis of the SLAM model suggested that the major parameters affecting leaching and crop uptake of cadmium were the cadmium loading and the partitioning coefficient for sludge-derived inorganic material and parameters controlling the effect of pH on sorption. Long-term scenario simulations in SLAM identified critical factors influencing plant cadmium uptake: the cadmium concentration in the sludge, the adsorption capacity of the sludge in relation to the adsorption capacity of native soil and the proportion of the sludge adsorption capacity contributed by the inorganic fraction

On Asymptotics of Polynomial Eigenfunctions for Exactly-Solvable Differential Operators

In this paper we study the asymptotic zero distribution of eigenpolynomials for degenerate exactly-solvable operators. We present an explicit conjecture and partial results on the growth of the largest modulus of the roots of the unique and monic n:th degree eigenpolynomial of any such operator as the degree n tends to infinity. Based on this conjecture we deduce the algebraic equation satified by the Cauchy transform of the asymptotic root measure of the properly scaled eigenpolynomials, for which the union of all roots is conjecturally contained in a compact set.Comment: 36 pages, 37 figures, to appear in Journal of Approximation Theor

Regional valuation of infrastructure improvements. The case of Swedish road freight

Is it possible to identify regional differences among shippers in their valuation of infrastructure improvements? The question is analysed within a random utility approach where parameters are estimated by a logit model. Data consists of a Swedish stated preference study from 1992. The results indicate that regional differences may exist but a considerable heterogeneity in the empirical material prohibit robust results in some cases. However, regional differences seem to exist when industrial mix, shipping distance and goods values are held constant. Independent of the limitations, the results should render implications to any infrastructure benefit analysis where parameters from spatial averages are used. The results are based on short term decisions and one should recognise that parameters may vary under mid- and long- term.Regional preferences; road transportation; freight demand; stated preference analysis; random utility models; logit model

Estimation of interregional freight flows with a gravity model by OLS estimation, Poisson and neural network specifications

In this paper we compare three different specifications of gravity models for inter regional freight flow prediction. The most used specification with OLS estimation is compared with a model where data are assumed to be Poisson distributed. We also compare these with a Feed Forward Back Propagation Neural Network. Data consists of freight flows between Norwegian counties. The attribute describing the nodes is population and distance in kilometers gives the friction on transport links. Since we here only are interested in inter regional flows all intra regional flows are excluded. Results are also compared with an earlier study by Bergkvist and Westin (1997) were all data were used. Estimations indicate that OLS compared to Poisson and Neural Network specifications will produce worse predictions. However, the question on how to compare performance is not undisputable and of great importance since different measures can produce quite different results, not just in scale but also in ranking. When non-linear models are used the lack of a simple interpretable R-square measure as in linear regression is evident. We therefore use different measures of performance and discuss their pros and cons. Bergkvist E. and Westin L. (1997) Estimation of gravity models by OLS estimation, NLS estimation, Poisson and Neural Network specifications. Submitted to "Analytical advances in Transportation Systems and Spatial Dynamics." Eds. Gastaldi M. and Reggiani A.

Resource effective control of Elymus repens

Preliminary results show that there is room for improvement within existing control methods of couch grass (Elymus repens (L.) Gould). It may be possible to reduce the number of stubble cultivations during autumn by timing the treatment, and to reduce the cultivation depth by using a goose foot cultivator (5 cm) instead of a disc cultivator (10 cm), without sacrificing couch grass control efficiency. The first year of the experiment, the use of a goose foot cultivator resulted in less nitrogen leaching than cultivation by disc. A reduced number of stubble cultivations potentially reduces nutrient loss, fuel consumption and the workload of the farmer. Our experiments with cover crops to control couch grass in cereals has yet to prove significant effects on couch grass control, but cover crops combined with goose foot hoeing did reduce nitrogen leaching by more than a third compared to cultivation by disc. Further data is necessary to see if the system can be used to effectively control couch grass without significant yield losses. Regardless, it can reduce nitrogen leaching and potentially provide other ecosystem services, e.g. control weeds other than couch grass

Negative effects of unlabeled response scales

This study used a novel research approach to investigate the effects of unlabeled response scales on response distributions. Instead of responding to standard questionnaire items respondents were asked to report given judgments on either semantic-differential (SD) or agree-disagree (AD) response scales, thereby showing the extent to which respondents agree upon where to place given judgments. Results from a survey-based study ( N = 418) show that respondents to a large extent disagree about where to place judgments on the response scale; the level of agreement for different judgment intensities ranged from 42% to 82% and the level of agreement is lower for AD than SD response scales. The low levels of agreement contribute to non-substantive variance in the data which increases the risk of attenuated or inflated correlations between constructs. Moreover, simulations of actual response distributions suggest that unlabeled response scales may lead to a strong bias in the form of underestimated shares of positive answers. Implications for research and marketing research practice of using unlabeled response scales are discussed and it is recommended that response categories on SD and AD items always should be labeled since this will reduce non-substantive variance and bias in the data

Gender-specific inclinations in a Cooperation Game - Implications for Negotiations

This study explores possible gender-specific inclinations, specifically inclinations for cooperation, fairness, discrimination, risk taking and sex stereotyping, all potentially fundamental to negotiation outcomes. The aim is that the findings may provide insight in observed gender inequality in organizational life. Participants in the study were engaged in matrix games with a Prisoners’ Dilemma-like payoff structure, but with variable degrees of possible cooperation. The games were played with the strategy method and all participants played against both women and men. The results showed no significant differences in level of cooperation between the sexes. Neither were there any significant differences in fairness or discrimination of or by either sex in the games. However, men were found to be more prone to taking risks compared to women, and both female- and male participants believed that men would take higher risks in the games. Differences in risk propensity may help explain why men do better in negotiations in organizational life, as men would be more inclined than women to enter risky negotiations and taking risks in negotiations. Thus policies aimed at lowering the risk of becoming unemployed, paired with policies to lower the risk of initiating salary negotiations, could potentially contribute to increased gender equality in organizational life