No abstract

Nitrate (NO(3)) loss from arable systems to surface and groundwater has attracted considerable attention in recent years in Ireland. Little information exists under Irish conditions, which are wet and temperate, on the effects of winter cover crops and different tillage techniques on NO(3) leaching. This study investigated the efficacy of such practices in reducing NO(3) leaching from a spring barley (Hordeum vulgare L.) system in the Barrow River valley, southeast Ireland. The study compared the effect of two tillage systems (plow-based tillage and noninversion tillage) and two over-winter alternatives (no vegetative cover and a mustard cover crop) on soil solution NO(3) concentrations at 90 cm depth over two winter drainage seasons (2003/04 and 2004/05). Soil samples were taken and analyzed for inorganic N. During both years of the study, the use of a mustard cover crop significantly reduced NO(3) losses for the plowed and reduced cultivation treatments. Mean soil solution NO(3) concentrations were between 38 and 70% lower when a cover crop was used, and total N load lost over the winter was between 18 and 83% lower. Results from this study highlight the importance of drainage volume and winter temperatures on NO(3) concentrations in soil solution and overall N load lost. It is suggested that cover crops will be of particular value in reducing NO(3) loss in temperate regions with mild winters, where winter N mineralization is important and high winter temperatures favor a long growing season.

The hypothesis that the increased use of the powdery mildew-resistance gene mlo has caused the increase in spotting diseases of barley over the past 20 years was tested in field trials. Near-isogenic lines with alleles of the Mlo gene for susceptibility or resistance to mildew in two parental backgrounds were trialled at four sites in Scotland and two in Ireland that were prone to spotting diseases, over 3 consecutive years. Mildew was controlled by sprays with quinoxyfen. Disease levels were low in the trials, the two most important diseases being scald caused by Rhynchosporium secalis and ramularia leaf spot caused by Ramularia collo-cygni . There were high levels of abiotic spotting. Lines with mutant mlo alleles consistently developed less Rh. secalis and Ra. collo-cygni , but more abiotic spots. This study indicates that the mlo mildew-resistance gene has not alone been responsible for the rise in spotting diseases over the past 20 years. Possible reasons for the rise are discussed, including the interaction of the mlo gene with the environment.

The objectives of this work were to determine the effects of initiating application of fertilizer nitrogen (N) to winter wheat at different growth stages (GSs) on grain yield and N use efficiency (NUE). A factorial experiment was carried out in two growing seasons (2011 and 2012) with five timings of first N application (GS 24/26 [tillering], GS 30, GS 31, GS 32 or GS 37) and an unfertilized control, two sowing densities (100 and 400 seeds/m 2 ) and a cattle slurry treatment (with or without slurry). The latter was included to simulate variation in soil N supply (SNS). Delaying the first application of N from the tillering stage until GS 30 had no significant effect on grain yield in either year. Further delaying the initial N application until GS 31 caused a significant yield reduction in 2011, in comparison to GS 30 application, but not in 2012. Differences in efficiency of recovery and use of fertilizer N by the crop among the first three application timings were small. There was no evidence to support alteration in the timing of the first application of N in response to low plant density. Slurry application did not influence SNS, so the interaction between SNS and fertilizer N application timing could not be determined. It is concluded that in order to maximise yield and NUE, the first N application should be applied to winter wheat between late tillering and GS 30 and that delaying the first N until GS 31 can lead to yield reductions compared to the yield obtained with earlier application.

A comparative study was conducted on earthworm communities in a conventional winter wheat monocropping system and a low-input intercropping system in which successive crops of winter wheat were direct-drilled into a permanent white clover sward. Earthworm abundance, biomass and species composition under the two cropping systems in the second and third years of successive cropping were assessed each spring and autumn in farm-scale field plots at four sites using formalin and electrical extraction methods. The wheatclover cropping system supported larger earthworm communities (overall mean abundance 548 individuals m -2 , 137 g biomass m -2 ) than conventional wheat monocropping (194 individuals m -2 , 36 g biomass m -2 ). Between one and five more earthworm species were recorded in the wheatclover system than in the wheat system at three out of the four study sites. Wheatclover cropping especially favoured species belonging to the epigeic and epigeic/anecic ecological groups such as Lumbricus castaneus, L. festivus, L. rubellus, juvenile Lumbricus and Satchellius mammalis. Earthworm communities in the wheatclover cropping system were comparable in size and species composition to communities normally found in perennial grassland-type habitats such as pastures and grass-legume leys.