No abstract

2014). Influence of cutting time and stubble height on regrowth capacity of Juncus effusus and Juncus conglomeratus. Weed Research 54, 603-613.Fig. 1 Regrowth of shoots during the season 2009 from two ecotypes (western and eastern Norway) of Juncus effusus and J. conglomeratus, measured as dry weight of shoots per unit, in a growth chamber at 17.5°C. Each point represents shoot dry weight for one unit. The lines show quadratic functions for the given ecotype, species and stubble heights, based on the fitted model. © 2014 European Weed Research Society 54, 603-613 J. conglomeratus -West Norway (2010) J. effusus -West Norway (2010) J. effusus -East Norway (2010) J. conglomeratus -East Norway (2010) Fig. 2 Regrowth of shoots during the season 2010 from two ecotypes (western and eastern Norway) of Juncus effusus and J. conglomeratus at 17.5°C. Each point represents shoot dry weight for one unit. The lines show quadratic functions for the given ecotype, species and stubble heights, based on the fitted model.

Under northern conditions, winter survival of grass species for hay production is quite uncertain because of winter stresses to plants. Damage to plants may be caused by variability in snow cover, low temperatures, ice encasement and pathogens. Compared to renovation by ploughing, direct drilling without ploughing has some beneficial aspects and may be an alternative method for renovating hay fields. However, successful establishment of grasses without ploughing has been difficult to achieve both in scientific studies and under practical conditions. The objective of this investigation was to study whether a dead grass sod, killed by different winter injuries, may leak phytotoxins into the soil, thus causing the poor results observed by direct drilling in hayfields. Experiments, including soil water extraction and the use of bioassays, were conducted in growth chambers, to study the effects of the winter stresses frost, ice encasement, and snow mould on the accumulation of potentially phytotoxic biochemical compounds in the soil. Snow mould did not kill the grasses in the experiments and no phytotoxicity was measured. Although both ice encasement and low temperatures killed the grasses, only ice encasement caused phytotoxicity. The present investigation shows that the occurrence of phytotoxic substances, especially butyrate, after ice encasement may be a cause of poor establishment of direct-drilled grass plants after winter injuries. In serious cases of ice encasement this may justify a 1-2 wk delay of sowing, which in turn may result in reduced soil water for germination and may cause increased competition from other species. Key words: Hay fields, grassland, winter injuries, phytotoxic substances, allelochemicals

Summary The abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) has increased in coastal grasslands in Norway over recent decades, and their spread has coincided with increased precipitation in the region. Especially in water‐saturated, peaty soils, it appears from field observations that productive grasses cannot compete effectively with such rapidly growing rush plants. In autumn–winters of 2012–2013 and 2013–2014, a four‐factor, randomised block greenhouse experiment was performed to investigate the effect of different soil moisture regimes and organic matter contents on competition between these rush species and smooth meadow‐grass (Poa pratensis). The rush species were grown in monoculture and in competition with the meadow‐grass, using the equivalent of full and half the recommended seed rate for the latter. After about three months, above‐ and below‐ground dry matter was measured. J. effusus had more vigorous growth, producing on average 23–40% greater biomass in both fractions than J. conglomeratus. The competitive ability of both rush species declined with decreasing soil moisture; at the lowest levels of soil moisture, growth reductions were up to 93% in J. conglomeratus and 74% in J. effusus. Increasing water level in peat–sand mixture decreased competivitiveness of meadow‐grass, while pure peat, when moist, completely impeded its below‐ground development. These results show that control of rush plants through management may only be achieved if basic soil limitations have been resolved.