Mitigation of indirect environmental effects of GM crops

Currently, the UK has no procedure for the approval of novel agricultural practices that is based on environmental risk management principles. Here, we make a first application of the ‘bow-tie’ risk management approach in agriculture, for assessment of land use changes, in a case study of the introduction of genetically modified herbicide tolerant (GMHT) sugar beet. There are agronomic and economic benefits, but indirect environmental harm from increased weed control is a hazard. The Farm Scale Evaluation (FSE) trials demonstrated reduced broad-leaved weed biomass and seed production at the field scale. The simplest mitigation measure is to leave a proportion of rows unsprayed in each GMHT crop field. Our calculations, based on FSE data, show that a maximum of 2% of field area left unsprayed is required to mitigate weed seed production and 4% to mitigate weed biomass production. Tilled margin effects could simply be mitigated by increasing the margin width from 0.5 to 1.5m. Such changes are cheap and simple to implement in farming practices. This case study demonstrates the usefulness of the bow-tie risk management approach and the transparency with which hazards can be addressed. If adopted generally, it would help to enable agriculture to adopt new practices with due environmental precaution

Using a growth model-based drought stress index for assessing drought tolerance in multi-environment sugar beet variety trials

Non peer reviewe

Cost efficacy in measuring farmland biodiversity : lessons from the Farm Scale Evaluations of GMHT crops

Measuring farmland biodiversity is time-consuming and costly. Operational data from the Farm Scale Evaluation of genetically modified crops project were collated to identify the financial and time costs of each of the 14 protocols used. A subset of 113 of the 266 experimental sites was used. The mean overall cost per site was £19 453 (£ of 2002). Laboratory time was almost 2.5 times that in the field. The most costly protocol was soil surface invertebrates because it required species level identification. The ‘bees and butterflies’ protocol at £418 per site was particularly cost-effective. The six vegetation protocols accounted for 65% and the six arthropod protocols accounted for 29% of the total costs. The recommended reduction from 12 to 3 transects would have saved £1356 per site, 6% of total budget. A minimalist approach using the single-season seedbank protocol would cost £3437 per site. The effect of geographical spread of sites on cost was small because of clustering of sites and the large number of protocols. Careful selection of ecological indicators can save considerable resourcesPeer reviewe

Management of genetically modified herbicide tolerant sugar beet for spring and autumn environmental benefit

When used in genetically modified herbicide–tolerant (GMHT) crops, glyphosate provides great flexibility to manipulate weed populations with consequences for invertebrates and higher trophic levels, for example birds. A range of timings of band and overall spray treatments of glyphosate to GMHT sugar beet were compared with a conventional weed control programme in four field trials over 2 years. Single overall sprays applied between 200 and 250 accumulated day degrees (above a base air temperature of 3°C; °Cd) and band applied treatments applied at 10% or 20% ground cover within the crop rows generally gave significantly greater weed biomass and seed rain than conventional treatments, while later band sprays (more than 650 °Cd) reduced seed return. Two overall sprays of glyphosate produced low weed biomass and generally lowest seed return of all treatments but tended to give some of the highest yields. However, the early overall sprays (200–250 °Cd) and band sprays gave as good or better yields than the conventional and were generally equivalent to the two overall–spray programme. Viable seeds in the soil after the experiment were generally higher following the early overall (200–250 °Cd) and the band spray treatments than following the conventional. The results show that altered management of GMHT sugar beet can provide alternative scenarios to those of the recent Farm Scale Evaluation trials. Without yield loss they can enhance weed seed banks and autumn bird food availability compared with conventional management, or provide early season benefits to invertebrates and nesting birds, depending on the system chosen. Conventional weed control does not have the flexibility to enable these scenarios that benefit both agriculture and environment, although there may be some options for increasing weed seed return in autuPeer reviewe

Hadean crustal evolution revisited: new constraints from Pb–Hf isotope systematics of the Jack Hills zircons

Detrital zircon crystals from the Jack Hills metasedimentary belt, Western Australia, are the only surviving vestiges of Hadean crust and represent an extraordinary archive into the nature of the early Earth. We report the results of an in situ isotopic study of 68 Jack Hills zircons in which the Hf and Pb isotope ratios were measured concurrently, allowing a better integration of isotope tracer information (176Hf/177Hf) with crystallization age (207Pb/206Pb). These data are augmented by Hf isotope data from zircons of the surrounding Narryer gneisses (3.65–3.30 Ga) and from Neoarchaean granites that intrude the Jack Hills belt. The detrital zircons define a subchondritic εHf–time array that attests to a far simpler evolution for the Hadean Earth than claimed by recent studies. This evolution is consistent with the protracted intra-crustal reworking of an enriched, dominantly mafic protolith that was extracted from primordial mantle at 4.4–4.5 Ga, perhaps during the solidification of a terrestrial magma ocean. There is no evidence for the existence of strongly depleted Hadean mantle, or for juvenile input into the parental magmas to the Jack Hills zircons. This simple Hf isotope evolution is difficult to reconcile with modern plate tectonic processes. Strongly unradiogenic Hf isotope compositions of zircons from several Archaean gneiss terranes, including the Narryer and Acasta gneisses, suggest that Hadean source reservoirs were tapped by granitic magmas throughout the Archaean. This supports the notion of a long-lived and globally extensive Hadean protocrust that may have comprised the nuclei of some Archaean cratons

Using multi-environment sugar beet variety trials to screen for drought tolerance

Drought is a major limitation to sugar beet yield in many rainfed areas. Varieties with increased drought tolerance would improve productivity, but breeding specifically for drought tolerance is time-consuming and expensive. Here we explore a complementary approach based on evaluation of data collected from multi-environment sugar beet variety trials (METs). The approach was to assign a drought stress index (DSI) to each trial, and then plot the regression of relative yield performance of each variety against a range of DSI. Varieties were classed according to their intercept (yield potential under low-stress conditions) and their slope (which indicates relative drought tolerance or susceptibility). The database consisted of 121 trials of 137 varieties conducted on 38 sites from 1989 to 1999. Three different methods to calculate DSI were compared; the preferred method was based on the cumulative daily ratio of actual to potential evapotranspiration because it was the best predictor for measured sugar yield losses in 25 years of rainfed/irrigated trials at Broom's Barn. The actual evapotranspiration for each trial was derived from a crop growth model using site-specific soil and weather inputs. Line comparison regression analysis revealed 20 varieties that showed significant positive or negative slopes, including seven varieties with average yield potential, but better than average yields under dry conditions. Conversely, there were 10 varieties that had good yield potential but showed poor performance under drought. ANOVA of trials testing some of these varieties within a single year showed that the 'crossover' behaviour was statistically significant and consistent across years. Results confirm the diversity for drought tolerance within sugar beet germplasm. This approach of assessing MET data using the DSI as an environmental descriptor can be used by breeders to evaluate drought tolerance and yield stability in current breeding material. (c) 2005 Elsevier B.V. All rights reserved.Peer reviewe