Sources and modes of action of invasive knotweed allelopathy : the effects of leaf litter and trained soil on the germination and growth of native plants

Invasive knotweeds, native to Eastern Asia, are among the most dominant plant invaders of European and North American temperate ecosystems. Recent studies indicate that one cause of this dominance might be allelopathy, but the possible sources and modes of action of this allelopathy are insufficiently understood. Here, we asked whether the invasive knotweed Fallopia × bohemica can exert allelopathic effects on native plants also through its leaf litter, or through persistent soil contaminants, and whether these affect the germination or growth of native plants. In a germination experiment with nine native species neither litter leachate, an aqueous extract of knotweed leaves added to the soil, nor trained soil with a history of Fallopia pre-cultivation suppressed the germination or early growth of natives. A mesocosm study with experimental native communities showed that the presence of F. × bohemica, although not a dominant in these communities, caused significant shifts of life-history strategy in two dominant natives, and that similar effects could be elicited through litter leachates or trained soil alone. However, there were hardly any effects on the biomass of natives. Our study indicates that knotweed allelopathy acts on the growth rather than germination of natives, and that soil contamination through persistent allelochemicals may not be a significant problem in habitat restoration. It also shows that allelopathic effects can sometimes be subtle changes in life-history and allocation patterns of the affected species

Sources of nitrogen for winter wheat in organic cropping systems

In organic cropping systems, legumes, cover crops, residue incorporation, and manure application are used to maintain soil fertility, but the contributions of these management practices to soil nitrogen (N) supply remain obscure. We examined potential sources of N for winter wheat (Triticum aestivum L.) in four experimental cropping systems established in 1997 on three soil types. Three of the four systems were under organic management. Topsoil N, depth of the A horizon, and cumulated inputs of N since 1997 were determined at plot level. Labile soil N pools (mineral N, potentially mineralizable N [PMN], microbial biomass N [MBN]) were monitored during two growth periods; at one site, biomass C/N ratios were also determined. Soil for labile N analysis was shielded from N inputs during spring application to isolate cumulated system effects. PMN and MBN were correlated across all sites and rotations (r2=0.72). The MBN corresponded to 46-85, 85-145 and 74-172 kg N ha-1 at the three sites and differed significantly between cropping systems, but MBN could not explain differences in wheat grain N yields. Instead, a multiple linear regression model explained 76 and 82% of the variation in grain N yields in organic cropping systems in 2007 and 2008, showing significant effects of, respectively, topsoil N, depth of A horizon, cumulated inputs of N, and N applied to winter wheat in manure. Thus, soil properties, and past and current management all contributed to winter wheat N supply

Boundary line analysis of the effect of water-filled pore space on nitrous oxide emission from cores of arable soil

The boundary line has been proposed as a model of the effects of a variable on a biological response, when this variable might limit the response in only some of a set of observations. It is proposed that the upper boundary (in some circumstances the lower boundary) represents the response function of interest. Boundary-line analysis is a method for estimating this response function from data. The approach has been used to model the emission of N2O from soil in response to various soil properties. However, the methods that have been used to identify the boundary are based on somewhat ad hoc partitions of the data. A statistical model that we have presented previously has not been applied to this problem in soil science, and we do so here to represent how the water-filled pore space (WFPS) of the soil affects the rate of N2O emission. We derive a boundary-line response that can be shown to be a better model for the data than an unbounded alternative by statistical criteria. Furthermore, the fitted boundary-response model is consistent with past empirical observations and modelling studies with respect to both the WFPS at which the potential emission rate is largest and the measurement error for the emission rates themselves. We show how the fitted model might be used to interpret data on soil volumetric water content with respect to seasonal changes in potential emissions, and to compare potential emissions between soil series that have contrasting physical properties

Evolution of soil and water conservation in rain-fed areas of China

AbstractRain-fed (dryland) farming is an ancient agricultural production system in China. It occurs widely across almost the whole country, especially in the Northwest and North China. The semi-arid Loess Plateau is the most important region of rain-fed farming in China, but unfortunately, soil erosion on the Loess Plateau area is the highest in China, and indeed amongst the highest in the world. This highlights the necessity for developing practices that can reduce soil and water erosion, improve soil water use efficiency, improve crop productivity, and reduce rural poverty in the region. Many techniques of soil and water conservation are being used in rain-fed areas of China, including such systems as mulch, ridge and furrow systems. The Appendix describes a unique system of soil and water conservation, called Shatian.Modern research on conservation tillage (No Till), although essential for reducing erosion, increasing crop productivity, and ameliorating poverty, is just beginning in China. Modern conservation tillage research started in the1990s' with support from Australia and other countries. The procedures, however, were modified to be in accord with local conditions and prevailing farmer experiences. With 10 years of experimentation, results show that the most successful conservation practice on the Western Loess Plateau is no till with stubble retention. This technique helps to conserve soil water, increases soil organic carbon, improves soil structure and water infiltration, reduces soil and water erosion, and improves crop productivity and sustainability of rain-fed farming systems. However, its adoption rate remains low due to barriers such as traditional attitude, insufficient rural extension, and so forth

Tall Fescue (\u3cem\u3eFestuca arundinacea\u3c/em\u3e) Stockpiling Response to N Fertilizer in Southern Virginia as Affected by Biological Soil Quality

Cattlemen in the eastern USA profitably utilize endophyte-infected tall fescue (Festuca arundinacea) for fall-stockpiled winter grazing. Ergot alkaloid concentration in fescue tends to decline in winter. This improves the quality of fescue for grazing when the supply of other forage becomes limited on most farms. Tall fescue dry matter yields generally respond favorably to nitrogen (N) inputs, but response can be limited with summer application due to accumulation of biologically available N in soil. Research is needed to characterize a diversity of pastures for response to N fertilizer during fall stockpiling. Biological soil quality can be estimated with a simple measure of soil respiration following rewetting of dried soil (Franzluebbers et al., 2000). The flush of CO2 following rewetting of dried soil has been related to the quantity of N mineralized during longer term incubations (Franzluebbers and Haney, 2006) and to N uptake in field studies of forage growth (Haney et al., 2001). Soil was collected from a set of pastures in southern Virginia to characterize biological soil quality and determine dry matter yield response to fertilizer N inputs

Pasture Management Strategies for Sequestering Soil Carbon - Final Report

Pasturelands account for 51 of the 212 Mha of privately held grazing land in the USA. Tall fescue is the most important cool-season perennial forage for many beef cattle producers in the humid region of the USA. A fungal endophyte, Neotyphodium coenophialum, infects the majority of tall fescue stands with a mutualistic association. Ergot alkaloids produced by the endophyte have negative impacts on cattle performance. However, there are indications that endophyte infection of tall fescue is a necessary component of productive and persistent pasture ecology. The objectives of this research were to characterize and quantify changes in soil organic carbon and associated soil properties under tall fescue pastures with and without endophyte infection of grass. Pastures with high endophyte infection had greater concentration of soil organic carbon, but lower concentration of biologically active soil carbon than pastures with low endophyte infection. A controlled experiment suggested that endophyte-infected leaf tissue may directly inhibit the activity of soil microorganisms. Carbon forms of soil organic matter were negatively affected and nitrogen forms were positively affected by endophyte addition to soil. The chemical compounds in endophyte-infected tall fescue (ergot alkaloids) that are responsible for animal health disorders were found in soil, suggesting that these chemicals might be persistent in the environment. Future research is needed to determine whether ergot alkaloids or some other chemicals are responsible for increases in soil organic matter. Scientists will be able to use this information to better understand the ecological impacts of animals grazing tall fescue, and possibly to identify and cultivate other similar associations for improving soil organic matter storage. Another experiment suggested that both dry matter production and soil microbial activity could be affected by the endophyte. Sampling of the cumulative effects of 20 years of tall fescue management indicated that soil organic carbon and nitrogen storage were greater with than without endophyte only under high soil fertility. This extra carbon and nitrogen in soil due to the presence of the endophyte was further found to be located in intermediately sized soil aggregates, which are important for reducing water runoff and improving water quality. These results suggest that well-fertilized tall fescue pastures with a high percentage of plants infected with the endophyte have the potential to help offset the rising carbon dioxide in the atmosphere. This research has also shown positive ecological implications of tall fescue-endophyte association

Phonological and lexical influences on phonological awareness in children with specific language impairment and dyslexia

Children with dyslexia and/or specific language impairment have marked deficits in phonological processing, putting them at an increased risk for reading deficits. The current study sought to examine the influence of word-level phonological and lexical characteristics on phonological awareness. Children with dyslexia and/or specific language impairment were tested using a phoneme deletion task in which stimuli differed orthogonally by sound similarity and neighborhood density. Phonological and lexical factors influenced performance differently across groups. Children with dyslexia appeared to have a more immature and aberrant pattern of phonological and lexical influence (e.g., favoring sparse and similar features). Children with SLI performed less well than children who were typically developing, but followed a similar pattern of performance (e.g., favoring dense and dissimilar features). Collectively, our results point to both quantitative and qualitative differences in lexical organization and phonological representations in children with SLI and in children with dyslexia

Surface-Soil Aggregation and Organic C and N Fractions Under Paired Grassland and Cropland Sites in the Southeastern USA

Grasslands are expected to deliver ecosystem services by sequestering soil organic C, improving soil health and water quality, and minimizing soil erosion. Data to support these ecosystem services from contemporary managed grasslands are relatively scant, and so on-farm measurements would help bolster assessment across more diverse environmental settings. This study was conducted to compare soil properties from paired landuse of croplands and grasslands in a diversity of Major Land Resource Areas – the Piedmont, Blue Ridge, and Blackland Prairie of the southeastern USA. Four separate pastures on three collaborating farms were sampled at depth of 0-10 cm. Four samples from a neighboring cropland field were paired with these pastures. A variety of soil chemical, physical, and biological properties were determined. Soil chemical properties were occasionally different between land management systems on one of the three farms, but few consistent differences occurred across farms. Dry-stable mean-weight diameter (MWD) was not different between paired land management systems, but water-stable MWD was dramatically reduced at all three locations with cropland compared with pasture. Soil stability index (water-stable MWD divided by dry-stable MWD) averaged 0.64 mm mm-1 under cropland and 0.91 mm mm-1 under pasture, suggesting that pastures had a highly stable soil surface that was resistant to erosion and likely contributed to high water infiltration. Soil organic C and N fractions (i.e., total, particulate, and mineralizable) were all significantly greater under pasture than under cropland, indicating that these pastures were indeed storing more C and N, and contributing to greater soil biological activity. This study provides evidence that well-managed grasslands can sequester soil organic C and N, improve soil surface stability conditions to foster water infiltration and reduced runoff, and may have important implications for habit development for soil-dwelling organisms