R Dunn

Influence of microbial activity on plant-microbial competition for organic and inorganic nitrogen.

To investigate how the level of microbial activity in grassland soils affects plant–microbial competition for different nitrogen (N) forms, we established microcosms consisting of a natural soil community and a seedling of one of two co-existing grass species, Anthoxanthum odoratum or Festuca rubra. We then stimulated the soil microbial community with glucose in half of the microcosms and followed the transfer of added inorganic (15NH415NO3) and organic (glycine-2-13C-15N) N into microbial and plant biomass. We found that microbes captured significantly more 15N in organic than in inorganic form and that glucose addition increased microbial 15N capture from the inorganic source. Shoot and root biomass, total shoot N content and shoot and root 15N contents were significantly greater for A. odoratum than F. rubra, whereas F. rubra had higher shoot and root N concentrations. Where glucose was not added, A. odoratum had higher shoot 15N content with organic than with inorganic 15N addition, whereas where glucose was added, both species had higher shoot 15N content with inorganic than with organic 15N. Glucose addition had equally negative effects on shoot growth, total shoot N content, shoot and root N concentrations and shoot and root 15N content for both species. Both N forms produced significantly more shoot biomass and higher shoot N content than the water control, but the chemical form of N had no significant effect. Our findings suggest that plant species that are better in capturing nutrients from soil are not necessarily better in tolerating increasing microbial competition for nutrients. It also appears that intense microbial competition has more adverse effects on the uptake of organic than inorganic N by plants, which may potentially have significant implications for interspecific plant–plant competition for N in ecosystems where the importance of organic N is high and some of the plant species specialize in use of organic N.

Ecologically sustainable fertility management for the maintenance of species‐rich hay meadows: a 12‐year fertilizer and lime experiment

Increased use of artificial fertilizers has caused widespread loss of species-rich grasslands throughout Britain and mainland Europe. Species-rich meadows are traditionally managed by hay cutting, use of farmyard manure (FYM) and occasional liming, but sustainable fertility management to maintain their botanical diversity is ill defined. This study measured vegetation responses to fertilizers and lime applied over 12years to species-rich upland and lowland mesotrophic hay meadows in the UK. Treatments consisted of three rates of FYM applied annually or triennially, inorganic fertilizers giving equivalent amounts of N, P and K to two of the annual and two of the triennial FYM treatments, and lime applied either alone or with annual or triennial FYM. Farmyard manure at 24tonnesha(-1)year(-1) reduced total species richness and the richness of positive indicator species at both meadows and increased aggregate cover of negative indicator species. Lower rates of FYM application were also detrimental at the lowland meadow, but not at the upland one. Inorganic fertilizers were no more damaging to plant species richness than equivalent FYM treatments. At the upland meadow, vegetation quality was maintained by continuing past FYM inputs (12tha(-1)year(-1)), but improved at lower rates. At the lowland meadow, which has no recent history of fertilizer use, rates equivalent to only 4tonnes FYM ha(-1)year(-1) were sustainable. Evidence was slight of vegetation adapting to increased inputs at either meadow. Between-meadow differences in vulnerability to treatments apparently reflected differences in site-specific factors, particularly past management, rather than differences in plant community type.Synthesis and applications. Relatively modest fertility inputs can reduce the ecological value of meadows with no recent history of such inputs, whereas moderate inputs of fertilizer and lime will be ecologically sustainable in meadows adapted to a long history of application. Decisions on sustainable levels of fertilizer use to maintain or enhance botanical diversity of grassland should be based on knowledge of soil physical and chemical status and past fertility management. Inorganic fertilizers are no more damaging than farmyard manure when applied at equivalent amounts of N, P and K. Relatively modest fertility inputs can reduce the ecological value of meadows with no recent history of such inputs, whereas moderate inputs of fertilizer and lime will be ecologically sustainable in meadows adapted to a long history of application. Decisions on sustainable levels of fertilizer use to maintain or enhance botanical diversity of grassland should be based on knowledge of soil physical and chemical status and past fertility management. Inorganic fertilizers are no more damaging than farmyard manure when applied at equivalent amounts of N, P and K.

Modelling field scale spatial variation in water run-off, soil moisture, N2O emissions and herbage biomass of a grazed pasture using the SPACSYS model

In this study, we evaluated the ability of the SPACSYS model to simulate water run-off, soil moisture, N2O fluxes and grass growth using data generated from a field of the North Wyke Farm Platform. The field-scale model is adapted via a linked and grid-based approach (grid-to-grid) to account for not only temporal dynamics but also the within-field spatial variation in these key ecosystem indicators. Spatial variability in nutrient and water presence at the field-scale is a key source of uncertainty when quantifying nutrient cycling and water movement in an agricultural system. Results demonstrated that the new spatially distributed version of SPACSYS provided a worthy improvement in accuracy over the standard (single-point) version for biomass productivity. No difference in model prediction performance was observed for water run-off, reflecting the closed-system nature of this variable. Similarly, no difference in model prediction performance was found for N2O fluxes, but here the N2O predictions were noticeably poor in both cases. Further developmental work, informed by this studys findings, is proposed to improve model predictions for N2O. Soil moisture results with the spatially distributed version appeared promising but this promise could not be objectively verified.

Intercropping flowering plants in maize systems increases pollinator diversity

Maize is a poorly competitive crop. Accordingly, soil preparation and high application rates of herbicides are required to reduce early competition with weeds. This leaves a large amount of bare ground with few flowering weeds, providing a poor farmland habitat for pollinators. The present study evaluates the effect of four different maize management regimes on pollinator diversity and community composition. Flowering plants intercropped with maize attracted pollinators, helping to support pollinator communities. Similar intercropping techniques using a grass ground cover did not increase pollinator density, demonstrating that pollinator richness, density and diversity is intrinsically linked to the presence of flowering plants. A maize system with a diverse intercrop may make it possible for pollinators to thrive; however, these systems may only be sufficiently attractive to bring pollinators in temporarily from the surrounding areas. These results show that there can be significant improvements to pollinator diversity, density and community composition as a result of modifying maize cultivation practices; however, these benefits must be balanced with yield penalties of approximately 60% to farmers.