DOC and DON from grass-clover - results from a field experiment

The C and N dynamics in perennial grass-clover mixtures are not fully understood although such mixtures dominate temperate grassland. The co-existence of clover and grass involves both competition for and transfer of nutrients between the species. The nutrients that are competed for and transferred may originate from leaky root systems, from a rapid turnover of the fine root systems, or from degradation of more stabile organic material. The aim of the present study was to investigate the origin of dissolved organic C and N in perennial grass-clover mixtures. In an existing grass-clover ley, field mezotrons (cylinders with a diameter 30 cm) were installed in the spring of 2003 to depths of 20, 40 and 60 cm. Suction cups was installed beneath the mezotrons in order to sample the soil solution during the growth season. In late June 2004 cross-labelling of clover and grass populations in the mezotrons was done by leaf labelling (5 days) of either grass or clover using 15N- and 14C-labelled urea. During the following 3 months the percolating soil solution was sampled either after heavy rain or after irrigation of the mezotrons and the content 15N- and 14C-labelled compounds were determined. Leaf material was harvested at tree times during the growth season and at the end of the growth season the mezotrons was excavated and the distribution of 15N and 14C in the plants and soil determined. 14C was detected in the percolating soil solution imediately after leaf-labelling was initiated, with the highest amounts occuring from labelled grass. The peak of 14C reached the depths of 20 and 40 cm between 3-10 and 5-15 days respectively after labelling was initiated while no 14C was detected beneath the 60 cm mezotrons. The majority of 14C in soil solution was identified to be 14CO2 originating either from root respiration or from biomass respiration of 14C-labelled root parts or root exudates. The transfer of 14C was higher from grass to clover than vice versa. This transfer of 14C properly occurs as 14CO2 exchange between the leaves or in the root zone. Transfer of 15N was highest from clover to grass, while the transfer from grass to clover was negligible. These observations confirm previous investigations of 15N transfer between grass and clover. No clear connection was found between the transfer of 14C and 15N. After excavation of the mezotrons 14C was found in higher amounts and at larger depths in the soil for grass compared to clover. The results from this experiment point to that in a grass-clover ley carbon would primarily originate from grass and nitrogen would come from clover. The depths at which 14CO2 is found in the soil solution seem to be somewhat related to the depth of 14C-labelled root material meaning that the rooting profile of a crop influence the deposition of carbon and nitrogen in the soil matrix. These findings add significant new dimensions to our current understanding of processes governing the build up of soil fertility under grass-clover leys

Nanomaterials in food and agriculture: The big issue of small matter for organic food and farming

Nanotechnology is the study of very small matter, of materials where one dimension is less than 100 nanometres. Surveys reveal that consumers are generally ignorant of nanotechnology, are concerned of its risks versus benefits, expect labelling of products incorporating nanotechnology, and a big issue for respondents is particularly the use of nanotechnology in food. Organic standards of Australia, Canada, Demeter-International and the UK’s Soil Association exclude nanomaterials, however a general nanotechnology exclusion across the organics sector is lacking

The contribution of grass and clover root turnover to N leaching

Sources of inorganic and organic N leaching from grass-clover mixtures at field sites in Denmark, Germany and Iceland were investigated. Grass or clover was labelled with 15N-urea four times (autumn 2007, spring, summer and autumn 2008) prior to the leaching season in autumn and winter 2008. Soil water was sampled at 30 cm depth and analyzed for 15N-enrichment of dissolved inorganic N (DIN) and dissolved organic N (DON). Most 15N was recovered in DON for both labelled grass and clover at all sites. At the Danish site, grass and clover contributed more to the DON pool than the DIN whereas the opposite was observed at the German and Icelandic sites. The results show that both clover and grass contribute directly to N leaching from the root zone in mixtures, and that clover contribution is higher than grass. Furthermore, the present study indicates that roots active in the growth season prior to the drainage period contribute more to N leaching than roots active in the growth season the previous year, which is consistent with estimates of root longevity at the three sites

In field N transfer, build-up, and leaching in ryegrass-clover mixtures

Two field experiments investigating dynamics in grass-clover mixtures were conducted, using 15N- and 14C-labelling to trace carbon (C) and nitrogen (N) from grass (Lolium perenne L.) and clover (Trifolium repens L. and Trifolium pratense L.). The leaching of dissolved inorganic nitrogen (DIN), as measured in pore water sampled by suction cups, increased during the autumn and winter, whereas the leaching of dissolved organic nitrogen (DON) was fairly constant during this period. Leaching of 15N from the sward indicated that ryegrass was the direct source of less than 1-2 percent of the total N leaching measured, whereas N dynamics pointed to clover as an important contributor to N leaching. Sampling of roots indicates that the dynamics in smaller roots were responsible for N and C build-up in the sward, and that N became available for transfer among species and leaching from the root zone. The bi-directional transfer of N between ryegrass and clover could however not be explained only by root turnover. Other processes like direct uptake of organic N compounds, may have contributed

Short-term nitrous oxide emissions from pasture soil as influenced by urea level and soil nitrate

Nitrogen excreted by cattle during grazing is a significant source of atmospheric nitrous oxide (N2O). The regulation of N2O emissions is not well understood, but may vary with urine composition and soil conditions. This laboratory study was undertaken to describe short-term effects on N2O emissions and soil conditions, including microbial dynamics, of urea amendment at two different rates (22 and 43 g N m-2). The lower urea concentration was also combined with an elevated soil NO3- concentration. Urea solutions labelled with 25 atom% 15N were added to the surface of repacked pasture soil cores and incubated for 1, 3, 6 or 9 days under constant conditions (60% WFPS, 14°C). Soil inorganic N (NH4+, NO2- and NO3-), pH, electrical conductivity and dissolved organic C were quantified. Microbial dynamics were followed by measurements of CO2 evolution, by analyses of membrane lipid (PLFA) composition, and by measurement of potential ammonium oxidation and denitrifying enzyme activity. The total recovery of 15N averaged 84%. Conversion of urea-N to NO3- was evident, but nitrification was delayed at the highest urea concentration and was accompanied by an accumulation of NO2-. Nitrous oxide emissions were also delayed at the highest urea amendment level, but accelerated towards the end of the study. The pH interacted with NH4+ to produce inhibitory concentrations of NH3(aq) at the highest urea concentration, and there was evidence for transient negative effects of urea amendment on both nitrifying and denitrifying bacteria in this treatment. However, PLFA dynamics indicated that initial inhibitory effects were replaced by increased microbial activity and net growth. It is concluded that urea-N level has qualitative, as well as quantitative effects on soil N transformations in urine patches

The new import regulation; More reliability for imported organic products? in The New EU Regulation for organic food and farming: (EC) No 834/2007

The European market for organic products is growing at a dynamic pace. Increasingly, processing and marketing companies are entering this market, which has a very promising future. However, organic farm production at the inter-European level has not increased at the same rate as the market for organic products

Lack of increased availability of root-derived C may explain the low N2O emission from low N-urine patches

Urine deposition on grassland causes significant N2O losses, which in some cases may result from increased denitrification stimulated by labile compounds released from scorched plant roots. Two 12-day experiments were conducted in 13C-labelled grassland monoliths to investigate the link between N2O production and carbon mineralization following application of low rates of urine-N. Measurements of N2O and CO2 emissions from the monoliths as well as δ13C signal of evolved CO2 were done on day -4, -1, 0, 1, 2, 4, 5, 6 and 7 after application of urine corresponding to 3.1 and 5.5 g N m-2 in the first and second experiment, respectively. The δ13C signal was also determined for soil organic matter, dissolved organic C and CO2 evolved by microbial respiration. In addition, denitrifying enzyme activity (DEA) and nitrifying enzyme activity (NEA) were measured on day -1, 2 and 7 after the first urine application event. Urine did not affect DEA, whereas NEA was enhanced 2 days after urine application. In the first experiment, urine had no significant effect on the N2O flux, which was generally low (-8 to 14 μg N2O-N m-2 h-1). After the second application event, the N2O emission increased significantly to 87 μg N2O-N m-2 h-1 and the N2O emission factor for the added urine-N was 0.18 %. However, the associated 13C signal of soil respiration was unaffected by urine. Consequently, the increased N2O emission from the simulated low N-urine patches was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots

EU Ecolabel for food and feed products – feasibility study

The environmental impacts of the production and processing of food, feed and drinks make up between 20% and 30% of the total environmental impacts of consumable goods in the EU. In the case of eutrophication (the accumulation of nutrients in water causing a reduction in oxygen availability) they account for as much as 58% of the total impacts. The EU Ecolabel is a voluntary scheme that forms part of overall EU policy to encourage more sustainable consumption and production. To date, the EU Ecolabel scheme has developed criteria for products in the non-food sector. The Regulation that governs the scheme (66/2010) aims to extend the EU Ecolabel into new product categories including food. However, the Regulation stipulates that before extending to the food sector, a feasibility study should be undertaken

Food for Thought about Environmental Values and Food Demand

It is a controversial discussion whether consumers are taking care of environmental issues when buying food. This question seems to be of significance to understand the demand for organic products, and thus many investigations have been made in this field. However, no strong relationship between attitudes and knowledge about environmental issues on the one hand and consumption behaviour on the other hand could be confirmed yet, and still there is a gap in thorough understanding of the demand for eco-friendly produced food. In this text it is discussed to what extent people are both willing and enabled to consider environmental footprints in their food choice by applying recent surveys of environmental preferences and food labels

On the tree-root-soil-continuum - temporal and spatial coupling of the belowground carbon flux

The direct flux of current assimilates from the tree canopy to the belowground compartment drives roughly half of the soil respiratory activity in boreal forests. This thesis focuses on temporal and spatial aspects of the carbon (C) flux within the tree-root-soil continuum in temperate and boreal forests. I used the stable isotopes 13C and 15N to follow C from the canopy to the belowground compartment and the flow of nitrogen in the reverse direction. The C isotope composition of photosynthate varies diurnally, but such variations could not be observed in soil-respired CO2. Labelling of small (up to 4.5 m) Pinus sylvestris trees with 13CO2 showed that it took two days for the photosynthate to reach the soil. The velocity of the phloem flux was c. 0.1 m h-1. This flux of C is absolutely vital for the production of sporocarps by ectomycorrhizal fungi, as shown by their paucity in plots with girdled trees. It is also likely to be important for other soil microorganisms; addition of a labile 13C labelled C source revealed a lack of labile C substrates in girdled plots. The reduction in the abundance of ectomycorrhizal sporocarps from the edges to the centre of girdled plots and a 15N uptake experiment showed that lateral spread of ectomycorrhizal roots was on average 4 to 5 m from the trunks. Thus, it can be expected that an area of c. 60 m2 of soil is under the influence of direct flux of current assimilates from the tree canopy of a single tree. Areas of influence of several trees overlapped. I conclude that canopy and soil processes are coupled with time lags of a few days. The direct impact of plant photosynthate should be considered more often in studies of soil. The 13CO2 labelling study demonstrated that it is now possible to follow at a very high resolution the fate of this C into the belowground system