Type and time of autumn tillage with and without herbicides at reduced rates in southern Sweden: 1. Yields and weed quantity

Environmental as well as economic incentives support the use of integrated weed management (IWM) systems for crop production. In order to reduce the input of agrochemicals for weed control, it may be possible to combine reduced doses of herbicides with appropriate tillage strategies and still maintain acceptable weed population levels. The purpose of this study was to compare the efficiency of different tillage strategies, with and without herbicides at 50% of normal rates, on weed populations and crop yields. The influences of type and time of stubble cultivation, harrowing and mouldboard ploughing were followed in eight long-term field trials in southern Sweden from 1988 until the spring of 1994. The crop rotations were dominated by spring-sown oats (Avena sativa L.) and barley (Hordeum distichon L.). Although significant site-by-year-by-treatment interactions were found, certain trends in influences of tillage on weeds and yields were identified. Weed density and weight often decreased in the order: stubble cultivation without ploughing > solely ploughing > stubble cultivation succeeded by ploughing. Grain yields of oats and barley varied 6–50% among tillage systems and the highest yields were often obtained in plots where ploughing succeeded stubble cultivation. Effects of tillage on weeds or yields were usually not influenced by herbicide application. Although only subnormal herbicide rates were used, weed density and weight were mostly reduced by 70–90%, while yields increased by 10–20%. In the spring of 1994, 1 year after the last herbicide application, densities of annual broad-leaved weeds were 40–65% lower in plots previously treated by herbicides than in non-treated plots, and differences among tillage systems were still significant. This study shows the advantage of combining herbicides at reduced rates with stubble cultivation and ploughing.     

Differences in CO2 and N2O emission rates following crop residue incorporation with or without field burning: A case study of adzuki bean residue and wheat straw

In the context of sustainable soil-quality management and mitigating global warming, the impacts of incorporating raw or field-burned adzuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) and wheat (Triticum aestivum L.) straw residues on carbon dioxide (CO₂) and nitrous oxide (N₂O) emission rates from soil were assessed in an Andosol field in northern Japan. Losses of carbon (C) and nitrogen (N) in residue biomass during field burning were much greater from adzuki bean residue (98.6% of C and 98.1% of N) than from wheat straw (85.3% and 75.3%, respectively). Although we noted considerable inputs of carbon (499 ± 119 kg C ha^–1) and nitrogen (5.97 ± 0.76 kg N ha^–1) from burned wheat straw into the soil, neither CO₂ nor N₂O emission rates from soil (over 210 d) increased significantly after the incorporation of field-burned wheat straw. Thus, the field-burned wheat straw contained organic carbon fractions that were more resistant to decomposition in soil in comparison with the unburned wheat straw. Our results and previously reported rates of CO₂, methane (CH₄) and N₂O emission during wheat straw burning showed that CO₂-equivalent greenhouse gas emissions under raw residue incorporation were similar to or slightly higher than those under burned residue incorporation when emission rates were assessed during residue burning and after subsequent soil incorporation.     

Assessment of genetic diversity in cultivars and wild accessions of Luohanguo (<Emphasis Type="Italic">Siraitia grosvenorii</Emphasis> [Swingle] A. M. Lu et Z. Y. Zhang), a species with edible and medicinal sweet fruits endemic to southern China,using RAPD and AFLP markers

Genetic variation of wild populations and cultivars of Luohanguo (Siraitia grosvenorii), a plant species endemic to southern China, was assessed using random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers. Based on the results for 130 individuals from seven populations, a high level of genetic diversity of Luohanguo was observed at the species level. The percentage of polymorphic loci (P) was 89.4%, Nei’s gene diversity (H _e) was 0.239, and Shannon’s information index (H _o) was 0.373 based on the combined AFLP and RAPD data. There was a high degree of genetic differentiation, with 45.1% of the genetic variation attributed to differences between the populations. The genetic diversity of the Luohanguo cultivars is much lower than that of wild populations (P = 41.8%, H _e = 0.141, H _o = 0.211), and a distinct genetic differentiation is observed between the cultivars and wild accessions. The pool of genetic variation in the wild populations provides an excellent gene resource for Luohanguo breeding.