European legume crops are assumed to provide a range of environmental benefits including reduced greenhouse gas emissions, reduced nitrate leaching and lower energy consumption in agriculture. However, there is a lack of information on the range and scale of these benefits.
Both above- and below-ground biodiversity can be effected by legume crops, and the decline in bumblebee species across USA and Europe has been related to changes in agricultural practise, specifically the move away from crop rotation involving legumes. Reduced tillage and crop rotation systems incorporating legumes have been shown to increase the abundance and biodiversity of soil macro-invertebrates significantly.
This work package will assess the effect of similar legume systems on above-ground biodiversity along a transect of climate zones from the UK to Scandinavia. Pollinator, soil macro-invertebrate and above-ground flora abundance and diversity will be assessed and related to ecosystem services, namely pollination, biological pest control by polyphagous ground predators, organic N inputs and higher plant biodiversity.
There are also environmental risks associated with increased planting of legume crops, such as the incidence of soil borne legume pathogens such as Aphanomyces euteiches which causes root rot of alfalfa and pea, the presence of which maybe under reported in European soils due to inadequate sampling and isolation techniques, and aerial fungi of the Ascochyta genus.
Soil N2O emissions
A two-tier system of measurement will be adopted including minimum monthly data collection for all sites (as outlined in the EU Nitro Europe (NEU) protocol) together with weekly measurements of N2O and CH4 fluxes for selected sites. In all cases the methodology of Smith et al. (1995) will be used adopting best practice procedures as outlined in Rochette & Eriksen-Hamel, (2008). As far as possible a greater frequency of sampling will take place after specific management events. For those experimental sites where access to a GC/ECD/FID system is not available, samples will be sent for analysis to the two central laboratories at Trinity College Dublin and SAC, Edinburgh. To aid in modelling of N2O fluxes simultaneous measurements of soil parameters will also be conducted, these being soil water content, soil temperature and soil nitrate and ammonium concentration. Soil bulk density will be determined to allow calculation of Water Filled Pore Space for correlation studies. At three selected sites, small plots and established monoliths will be incubated with 15N and the fate of the labeled nitrogen determined by GC/Stable Isotope Mass spectrometry. In accordance with Carter and Ambus (2006), the first published study of 15N labeled N2O through N fixation, labeling of soils will be carried out in controlled environment growth cabinets and determination of incorporation of 15N into N2O will be carried out in both the short and long-term to evaluate turnover of legume roots in the soil. Growth conditions within the cabinets will be manipulated to mimic as far as possible seasonal changes in temperature, monthly rainfall and light intensity. Furthermore the use of both small pots and established monoliths taken from sites selected from WP1 will allow determination of 15N incorporation into N2O in new and established legume systems.
In grazed pastures, forage legumes may increase N-leaching from the soil by virtue of their high N-content being converted to urine, and subsequent nitrification of this urine to nitrate. In other legume systems increased N-leaching from soils may also occur if the high-N legume residues are returned to the soils. This may particularly be the case for legumes grown as a green manure crop. No simple and single method for soil solution sampling exists but in general the use of porous suction cup samplers coupled with continual measurements of soil water balance using tensiometers/neutron probes has been favoured (Gehl et al., 2005). Here porous-cup solution samplers are inserted below the rooting zone to collect leached nitrate and tensiometers or neutron probes inserted at varying depths are used to determine drainage. To determine the extent of nitrate leaching in cropping systems, the methodology of Gehl et al, (2005) will be used incorporating simple porous cup samplers and tensiometers. Sampling of soil leachate will be as far as possible every seven days.
Four parameters have been chosen that would best describe biodiversity in terms of ecosystem services, namely pollinators and pollination services, biological pest control by polyphagous ground predators, organic N input and higher plant biodiversity.
All research partners except LEI WUR are involved in WP3. Tasks are led by Mike Williams, Mike Jones and Jane Stout of TCD, Ireland.