Valentini A. Pappa

UK emissions of the greenhouse gas nitrous oxide

Signatories of the Kyoto Protocol are obliged to submit annual accounts of their anthropogenic greenhouse gas emissions, which include nitrous oxide (N2O). Emissions from the sectors industry (3.8 Gg), energy (14.4 Gg), agriculture (86.8 Gg), wastewater (4.4 Gg), land use, land-use change and forestry (2.1 Gg) can be calculated by multiplying activity data (i.e. amount of fertilizer applied, animal numbers) with simple emission factors (Tier 1 approach), which are generally applied across wide geographical regions. The agricultural sector is the largest anthropogenic source of N2O in many countries and responsible for 75 per cent of UK N2O emissions. Microbial N2O production in nitrogen-fertilized soils (27.6 Gg), nitrogen-enriched waters (24.2 Gg) and manure storage systems (6.4 Gg) dominate agricultural emission budgets. For the agricultural sector, the Tier 1 emission factor approach is too simplistic to reflect local variations in climate, ecosystems and management, and is unable to take into account some of the mitigation strategies applied. This paper reviews deviations of observed emissions from those calculated using the simple emission factor approach for all anthropogenic sectors, briefly discusses the need to adopt specific emission factors that reflect regional variability in climate, soil type and management, and explains how bottom-up emission inventories can be verified by top-down modelling.

Nitrous oxide mitigation in UK agriculture

Nitrous oxide (N2O) makes the single largest contribution to greenhouse gas (GHG) emissions from UK and European Union agriculture. Ambitious government targets for GHG mitigation are leading to the implementation of changes in agricultural management in order to reduce these emissions (mitigation measures). We review the evidence for the contribution of those measures with the greatest mitigation potential which provide an estimated 4.3 t CO2e ha−1 y−1 GHG reduction in the UK. The mitigation options considered were: using biological fixation to provide nitrogen (N) inputs (clover, Trifolium), reducing N fertilizer, improving land drainage, avoiding N excess, fully accounting for manure/slurry N, species introduction (including legumes), improved timing of mineral fertilizer N application, nitrification inhibitors, improved timing of slurry and manure application, and adopting systems less reliant on inputs. These measures depend mostly on increasing the efficiency of N fertilizer use and improving soil conditions; however, they provide the added benefit of increasing the economic efficiency of farming systems, and can often be viewed as “win-win” solutions.

Biochar field testing in the UK: outcomes and implications for use

Background: There is a lack of biochar field trials in temperate climate regions. Wood biochar was applied during 2009–2011 to seven field experiments on five working farms in the UK, for arable, legume, horticultural and root crops. Results: Three trials showed no significant (p > 0.05) effect on crop yield, two showed positive effects of 5–6%, one showed a very strong increase of 100% and one showed a decrease of 2–16%. A meta-analysis of effect sizes was conducted for all treatments (n = 47), which showed a significant (p < 0.05) positive effect, increasing average yield by 0.4 t ha-1. Biochar application rates of 20 t ha-1 or under led to the greater benefits. Conclusion: This paper shows that, in some situations, biochar can bring benefits in modern temperate farming.

Legumes intercropped with spring barley contribute to increased biomass production and carry-over effects

Intercropping systems that include legumes can provide symbiotically fixed nitrogen (N) and potentially increase yield through improved resource use efficiency. The aims of the present study were: (a) to evaluate the effects of different legumes (species and varieties) and barley on grain yield, dry matter production and N uptake of the intercrop treatments compared with the associated cereal sole crop; (b) to assess the effects on the yields of the next grain crop and (c) to determine the accumulation of N in shoots of the crops in a low-input rotation. An experiment was established near Edinburgh, UK, consisting of 12 hydrologically isolated plots. Treatments were a spring barley ( Hordeum vulgare cvar Westminster) sole crop and intercrops of barley/white clover ( Trifolium repens cvar Alice) and barley/pea ( Pisum sativum cvar Zero4 or cvar Nitouche) in 2006. All the plots were sown with spring oats ( Avena sativa cvar Firth) in 2007 and perennial ryegrass in 2008. No fertilizers, herbicides or pesticides were used at any stage of the experiment. Above-ground biomass (barley, clover, pea, oat and ryegrass) and grain yields (barley, pea and oat) were measured at key stages during the growing seasons of 2006, 2007 and 2008; land equivalent ratio (LER) was measured only in 2006. At harvest, the total above-ground biomass of barley intercropped with clover (4·56 t biomass/ha) and barley intercropped with pea cvar Zero4 (4·49 t biomass/ha) were significantly different from the barley sole crop (3·05 t biomass/ha; P P P

A Comparative Nitrogen Balance and Productivity Analysis of Legume and Non-legume Supported Cropping Systems: The Potential Role of Biological Nitrogen Fixation.

The potential of biological nitrogen fixation (BNF) to provide sufficient N for production has encouraged re-appraisal of cropping systems that deploy legumes. It has been argued that legume-derived N can maintain productivity as an alternative to the application of mineral fertilizer, although few studies have systematically evaluated the effect of optimizing the balance between legumes and non N-fixing crops to optimize production. In addition, the shortage, or even absence in some regions, of measurements of BNF in crops and forages severely limits the ability to design and evaluate new legume–based agroecosystems. To provide an indication of the magnitude of BNF in European agriculture, a soil-surface N-balance approach was applied to historical data from 8 experimental cropping systems that compared legume and non-legume crop types (e.g., grains, forages and intercrops) across pedoclimatic regions of Europe. Mean BNF for different legume types ranged from 32 to 115 kg ha−1 annually. Output in terms of total biomass (grain, forage, etc.) was 30% greater in non-legumes, which used N to produce dry matter more efficiently than legumes, whereas output of N was greater from legumes. When examined over the crop sequence, the contribution of BNF to the N-balance increased to reach a maximum when the legume fraction was around 0.5 (legume crops were present in half the years). BNF was lower when the legume fraction increased to 0.6–0.8, not because of any feature of the legume, but because the cropping systems in this range were dominated by mixtures of legume and non-legume forages to which inorganic N as fertilizer was normally applied. Forage (e.g., grass and clover), as opposed to grain crops in this range maintained high outputs of biomass and N. In conclusion, BNF through grain and forage legumes has the potential to generate major benefit in terms of reducing or dispensing with the need for mineral N without loss of total output.

Pea cultivar and wheat residues affect carbon/nitrogen dynamics in pea-triticale intercropping: A microcosms approach

The underlying mechanisms by which legume cultivars contribute to nitrous oxide (N2O) generation are poorly understood. The aim of the present study was to explore the effects of two pea cultivars (Zero4 and Nitouche) intercropped with triticale, with or without wheat (Triticum aestivum) residues incorporation, on soil C and N dynamics, on bacterial community structure and their links with N2O emissions. Monocrops and bare soil (no plant) treatments were used as an additional control in order to account for the level of mineralisation between treatments. Changes in total C and N contents and in some functionally-related soil pools (microbial biomass C and N, basal respiration, KCl-exchangeable ammonium and nitrate, potentially mineralisable N, DOC, ecophysiological indexes) were followed throughout a 97-day microcosm experiment carried out on a loamy arable soil. ARISA community fingerprinting of soil extracted DNA and GHG emissions were carried out at two key stages (pea flowering and harvest). The addition of residues to the soil resulted in only small changes to the total C and N pools the Nitouche monocrop, which was found to have the highest potentially mineralisable N (13.4μgg-128d-1) of the treatments with added residue. The different pea cultivar selectively affected N2O emissions, with highest emissions associated with the cultivar Nitouche in the absence of residues. The two intercropping treatments of triticale/pea were significantly different either with residues or without, especially the triticale/Zero4 which had the lowest values (356gN2O-Nha-1). Similar patterns were also observed in below ground data. ARISA analysis showed that monocropped legumes and the Triticale-based treatment clearly grouped on separate clusters to the added residue treatment. We hypothesize that in pea-based intercrops variations in carbon supply from different cultivars may contribute to differences in N2O emissions and thus influence the choice of suitable cultivars, to optimize nutrient cycling and sustainable crop management.

Evaluation of the field performance, nitrogen fixation efficiency and competitive ability of pea landraces grown under organic and conventional farming systems

ABSTRACT In the present study, three pea Greek landraces Schinousa (AUASCHIN001), Andros (AUAANDRO001), and Amorgos (AUAAMORG001), and the commercial variety Onward were grown following either conventional or organic farming practices. The main objective of the study was to assess the suitability of these three landraces for organic cultivation as compared with a standard commercial variety. The total fresh pod yield produced by AUASCHIN001 and AUAAMORG001 was significantly lower than that obtained from ‘Onward’ and AUAANDRO001. Furthermore, the three landraces exhibited a higher competition to weeds than the commercial variety. Under organic farming conditions, AUASCHIN001 and AUAAMORG001 produced appreciably less shoot biomass than ‘Onward’ and this resulted in commensurate decreases in the total amount of BNF (biological nitrogen fixation) in their plant tissues, although the percentage of nitrogen (N) fixed from the atmosphere was significantly lower in ‘Onward’. AUAANDRO001 rendered the highest amounts of BNF in the organic farming systems, which was similar to that produced by ‘Onward’ in the conventional system. These results indicate that the tested landraces and especially AUAANDRO001 are more adaptable to low soil N levels and high weed competition, and thus they are more suitable for organic cultivation than ‘Onward’ which performs best in conventional cropping systems.