Increased yield and yield stability in variety mixtures of spring barley

In the DARCOF II BAR-OF project, six variety mixtures are studied in organic as well as conventional growing systems in the period 2002 to 2005. The focus has been on competitive ability of the component varieties in addition to their disease resistance. This study is included in a European Network on sustainable low-input cereal production focusing on varietal characteristics and crop diversity (SUSVAR - COST 860), initiated in 2004. The following is based on papers presented at two SUSVAR workshops

Hyperscaling in the Domany-Kinzel Cellular Automaton

An apparent violation of hyperscaling at the endpoint of the critical line in the Domany-Kinzel stochastic cellular automaton finds an elementary resolution upon noting that the order parameter is discontinuous at this point. We derive a hyperscaling relation for such transitions and discuss applications to related examples.Comment: 8 pages, latex, no figure

Mean-field model of the ferromagnetic ordering in the superconducting phase of ErNi_2B_2C

A mean-field model explaining most of the details in the magnetic phase diagram of ErNi_2B_2C is presented. The low-temperature magnetic properties are found to be dominated by the appearance of long-period commensurate structures. The stable structure at low temperatures and zero field is found to have a period of 40 layers along the a direction, and upon cooling it undergoes a first-order transition at T_C = 2.3 K to a different 40-layered structure having a net ferromagnetic component of about 0.4 mu_B/Er. The neutron-diffraction patterns predicted by the two 40-layered structures, above and below T_C, are in agreement with the observations of Choi et al.Comment: 4 pages, 3 figures (Revtex4

Characteristics of spring barley varieties and crop diversity for organic farming and variety testing

Results from Danish spring barley variety trials including about 50-120 varieties and variety mixtures on three locations over three years under organic as well as conventional farming systems demonstrate the importance of genotype-environment interactions. This has implications for potential future organic VCU-testing; here results are shown for grain yield. Further, grain yield results from of six variety mixtures and their 14 component varieties indicate that variety mixtures may be less influenced by genotype-environment interactions compared to pure line varieties

Percolation and epidemics in a two-dimensional small world

Percolation on two-dimensional small-world networks has been proposed as a model for the spread of plant diseases. In this paper we give an analytic solution of this model using a combination of generating function methods and high-order series expansion. Our solution gives accurate predictions for quantities such as the position of the percolation threshold and the typical size of disease outbreaks as a function of the density of "shortcuts" in the small-world network. Our results agree with scaling hypotheses and numerical simulations for the same model.Comment: 7 pages, 3 figures, 2 table

Stability of variety mixtures of spring barley

Six 3-component variety mixtures of spring barley and their component varieties have been grown in 17 different environments (3 years, 3 locations, 3 different growing systems). For three of the six mixtures, the grain yield was significantly higher than the average yield of its components; in none of the mixtures it was significantly lower. The variation in grain yield over environments of all variety mixtures was compared to the variation of all component varieties. The six mixtures were on average more stable than the 14 component varieties grown in pure stands with respect to actual yield as well as to rank values of yield

Physical State of Water in Plant Xylem Vessels

The vapor pressure psychrometer was used as a tool to study the physical state of water in plant xylem vessels. The experimental procedure involved measuring the change in diffusion pressure deficit (DPD) of corn and tomato plants when the stem was cut. When the DPD was greater than 4 bars in tomatoes and 28 bars in corn, the water in xylem vessels no longer appeared to flow in response to hydrostatic pressure gradients. The limiting value of DPD increased as the xylem radius decreased. A mechanism is suggested which describes the physical state and the movement of water through xylem tissue under high DPD. The proposal is based on the pressure difference across a curved air-water interface and on the concept of an electrostatic double layer with its associated osmotic pressure