• Authors:
    • Lindquist, J. L.
    • Francis, C. A.
    • Wortman, S. E.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Achieving agronomic and environmental benefits associated with cover crops often depends on reliable establishment of a highly productive cover crop community. The objective of this study was to determine if cover crop mixtures can increase productivity and stability compared to single species cover crops, and to identify those components most active in contributing to or detracting from mixture productivity. A rainfed field experiment was conducted near Mead, NE, in 2010 and 2011. Eight individual cover crop species (in either the Brassicaceae [mustard] or Fabaceae [legume] family) and four mixtures of these species (two, four, six, and eight species combinations) were broadcast planted and incorporated in late March and sampled in late May. Shoot dry weights were recorded for sole crops and individual species within all mixtures. Sole crops in the mustard family were twice as productive (2428 kg ha -1) as sole crops in the legume family (1216 kg ha -1), averaged across 2 yr. The land equivalent ratios (LERs) for all mixtures in 2011 were >1.0, indicating mixtures were more productive than the individual components grown as sole crops. Improved performance in mixture may be related to the ecological resilience of mixed species communities in response to extreme weather events, such as hail. Partial LERs of species in the mustard family were consistently greater than those in the legume family, indicating that mustards dominated the mixtures. Results provide the basis for yield-stability rankings of spring-sown cover crop species and mixtures for the western Corn Belt.
  • Authors:
    • Dyer,Lisa
    • Oelbermann,Maren
    • Echarte,Laura
  • Source: Journal of Plant Nutrition and Soil Science
  • Volume: 175
  • Issue: 3
  • Year: 2012
  • Summary: The Argentine Pampa is one of the major global regions for the production of maize (Zea mays L.) and soybean (Glycine max L. [Merr.]), but intense management practices have led to soil degradation and amplified greenhouse-gas (GHG) emissions. This paper presents preliminary data on the effect of maize-soybean intercrops compared with maize and soybean sole crops on the short-term emission rates of CO2 and N2O and its relationship to soil moisture or temperature over two field seasons. Soil organic carbon (SOC) concentrations were significantly greater (p < 0.05) in the maize sole crop and intercrops, whereas soil bulk density was significantly lower in the intercrops. Soil CO2 emission rates were significantly greater in the maize sole crop but did not differ significantly for N2O emissions. Over two field seasons, both trace gases showed a general trend of greater emission rates in the maize sole crop followed by the soybean sole crop and were lowest in the intercrops. Linear regression between soil GHG (CO2 and N2O) emission rates and soil temperature or volumetric soil moisture were not significant except in the 1:2 intercrop where a significant relationship was observed between N2O emissions and soil temperature in the first field season and between N2O and volumetric soil moisture in the second field season. Our results demonstrated that intercropping in the Argentine Pampa may be a more sustainable agroecosystem land-management practice with respect to GHG emissions.
  • Authors:
    • Grant, T.
    • Carre, A.
    • Eady, S.
  • Source: Journal of Cleaner Production
  • Volume: 28
  • Issue: June
  • Year: 2012
  • Summary: Most agricultural products are produced on farms where there is a mix of activities, resulting in a range of co-products. This raises the issue of how best to model these complex production systems for Life Cycle Assessment, especially where there are benefits imparted by one activity in the mixed farming system to another. On the mixed farm studied, there were significant two-way reference flows (representing 288 t CO2-e/year or 10% of the total farm emissions) between activities producing distinct products (wool, meat, grain) and these were modelled using system expansion. Cropping and sheep activities were modelled as separate sub-processes in the farming system, with unique inputs and outputs identified for each. Co-production from the sheep activity was modelling using allocation, comparing biophysical and economic relationships. Using an economic allocation resulted in different estimates of global warming impact for sheep co-products, with figures varying by 7-52%. When compared to biophysical allocation, economic allocation shifted the environmental burden to the higher value co-products and away from the high resource use products. Using economic allocation, for every kilogram of wool produced there was an estimated 28.7 kg of CO2-e emitted. Amongst the live animal products, the stud rams had the highest estimated carbon footprint (719 kg CO2-e/ram). Amongst the crops, estimates of emissions for the cereal grains averaged 202 kg CO2-e/tonne grain, canola 222 kg CO2-e/tonne and lupins 510 kg CO2-e/tonne, when modelled to include the benefits of the mixed farming system. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
  • Authors:
    • Alves, B. J. R.
    • Hauggaard-Nielsen, H.
    • Gresshoff, P. M.
    • Boddey, R. M.
    • Peoples, M. B.
    • Jensen, E. S.
    • Morrison, M. J.
  • Source: Agronomy for Sustainable Development
  • Volume: 32
  • Issue: 2
  • Year: 2012
  • Summary: Humans are currently confronted by many global challenges. These include achieving food security for a rapidly expanding population, lowering the risk of climate change by reducing the net release of greenhouse gases into the atmosphere due to human activity, and meeting the increasing demand for energy in the face of dwindling reserves of fossil energy and uncertainties about future reliability of supply. Legumes deliver several important services to societies. They provide important sources of oil, fiber, and protein-rich food and feed while supplying nitrogen (N) to agro-ecosystems via their unique ability to fix atmospheric N-2 in symbiosis with the soil bacteria rhizobia, increasing soil carbon content, and stimulating the productivity of the crops that follow. However, the role of legumes has rarely been considered in the context of their potential to contribute to the mitigation of climate change by reducing fossil fuel use or by providing feedstock for the emerging biobased economies where fossil sources of energy and industrial raw materials are replaced in part by sustainable and renewable biomass resources. The aim of this review was to collate the current knowledge regarding the capacity of legumes to (1) lower the emissions of the key greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) compared to N-fertilized systems, (2) reduce the fossil energy used in the production of food and forage, (3) contribute to the sequestration of carbon (C) in soils, and (4) provide a viable source of biomass for the generation of biofuels and other materials in future biorefinery concepts. We estimated that globally between 350 and 500 Tg CO2 could be emitted as a result of the 33 to 46 Tg N that is biologically fixed by agricultural legumes each year. This compares to around 300 Tg CO2 released annually from the manufacture of 100 Tg fertilizer N. The main difference is that the CO2 respired from the nodulated roots of N-2-fixing legumes originated from photosynthesis and will not represent a net contribution to atmospheric concentrations of CO2, whereas the CO2 generated during the synthesis of N fertilizer was derived from fossil fuels. Experimental measures of total N2O fluxes from legumes and N-fertilized systems were found to vary enormously (0.03-7.09 and 0.09-18.16 kg N2O-N ha(-1), respectively). This reflected the data being collated from a diverse range of studies using different rates of N inputs, as well as the large number of climatic, soil, and management variables known to influence denitrification and the portion of the total N lost as N2O. Averages across 71 site-years of data, soils under legumes emitted a total of 1.29 kg N2O-N ha(-1) during a growing season. This compared to a mean of 3.22 kg N2O-N ha(-1) from 67 site-years of N-fertilized crops and pastures, and 1.20 kg N2O-N ha(-1) from 33 site-years of data collected from unplanted soils or unfertilized non-legumes. It was concluded that there was little evidence that biological N-2 fixation substantially contributed to total N2O emissions, and that losses of N2O from legume soil were generally lower than N-fertilized systems, especially when commercial rates of N fertilizer were applied. Elevated rates of N2O losses can occur following the termination of legume-based pastures, or where legumes had been green- or brown-manured and there was a rapid build-up of high concentrations of nitrate in soil. Legume crops and legume-based pastures use 35% to 60% less fossil energy than N-fertilized cereals or grasslands, and the inclusion of legumes in cropping sequences reduced the average annual energy usage over a rotation by 12% to 34%. The reduced energy use was primarily due to the removal of the need to apply N fertilizer and the subsequently lower N fertilizer requirements for crops grown following legumes. Life cycle energy balances of legume-based rotations were also assisted by a lower use of agrichemicals for crop protection as diversification of cropping sequences reduce the incidence of cereal pathogens and pests and assisted weed control, although it was noted that differences in fossil energy use between legumes and N-fertilized systems were greatly diminished if energy use was expressed per unit of biomass or grain produced. For a change in land use to result in a net increase C sequestration in soil, the inputs of C remaining in plant residues need to exceed the CO2 respired by soil microbes during the decomposition of plant residues or soil organic C, and the C lost through wind or water erosion. The net N-balance of the system was a key driver of changes in soil C stocks in many environments, and data collected from pasture, cropping, and agroforestry systems all indicated that legumes played a pivotal role in providing the additional organic N required to encourage the accumulation of soil C at rates greater than can be achieved by cereals or grasses even when they were supplied with N fertilizer. Legumes contain a range of compounds, which could be refined to produce raw industrial materials currently manufactured from petroleum-based sources, pharmaceuticals, surfactants, or food additives as valuable by-products if legume biomass was to be used to generate biodiesel, bioethanol, biojet A1 fuel, or biogas. The attraction of using leguminous material feedstock is that they do not need the inputs of N fertilizer that would otherwise be necessary to support the production of high grain yields or large amounts of plant biomass since it is the high fossil energy use in the synthesis, transport, and application of N fertilizers that often negates much of the net C benefits of many other bioenergy sources. The use of legume biomass for biorefineries needs careful thought as there will be significant trade-offs with the current role of legumes in contributing to the organic fertility of soils. Agricultural systems will require novel management and plant breeding solutions to provide the range of options that will be required to mitigate climate change. Given their array of ecosystem services and their ability to reduce greenhouse gas emissions, lower the use of fossil energy, accelerate rates of C sequestration in soil, and provide a valuable source of feedstock for biorefineries, legumes should be considered as important components in the development of future agroecosystems.
  • Authors:
    • Cockfield, G.
    • Maraseni, T. N.
  • Source: Agricultural Water Management
  • Volume: 103
  • Year: 2012
  • Summary: Irrigated cropping helps stabilise farm and regional income and contributes to productivity gains but the net benefits should include the full cost of water and greenhouse gas (GHG) emissions. This study examines the costs and returns of switching from a dryland rotation for four crops in the Darling Downs region of Australia, to a rotation of the same crops under irrigation, including greenhouse gas (GHG) values. The value chain, including all inputs was identified and emissions estimated using a range of studies and models. Over four year cropping cycle, the irrigated system would result in more than six times the emissions than from the dryland system. If GHG and water prices are not embedded in the production process, irrigation is more profitable per hectare. In this scenario, the landholder makes more than twice as much from the irrigated crops, with gross margins for the dryland and irrigated crop rotations of $1597 and $3490/ha, respectively. If the value of GHGs is included, the gap closes but irrigated crops are still more profitable. If however, a relatively high cost of the water, based on price ranges from the last decade, is included, then dryland crops are financially preferable. These results could be useful in designing national mitigation and water buy-back policies, both of which are being developed in Australia.
  • Authors:
    • Boyd, N. S.
    • Brennan, E. B.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Long-term research on cover crops (CC) is needed to design optimal rotations. Winter CC shoot dry matter (DM) of rye (Secale cereale L.), legume-rye, and mustard was determined in December to February or March during the first 8 yr of the Salinas Organic Cropping Systems trial focused on high-value crops in Salinas, CA. By seed weight, legume-rye included 10% rye, 35% faba (Vicia faba L.), 25% pea (Pisum sativum L.), and 15% each of common vetch (V sativa L.) and purple vetch (V. henghalensis L.); mustard included 61% Sinapis alba L. and 39% Brassica juncea Czern. Cover crops were fall-planted at 1x and 3x seeding rates (SR); 1x SR were 90 (rye), 11 (mustard), and 140 (legume-rye) kg ha(-1). Vegetables followed CC annually. Cover crop densities ranged from 131 to 854 plants m(-2) and varied by CC, SR, and year. Year, CC, and SR affected DM production, however, the effects varied across the season and interactions occurred. Averaged across years, final DM was greater in rye and legume-rye (7 Mg ha(-1)) than mustard (5.6 Mg ha(-1)), and increased with SR through January. Dry matter production through the season was correlated significantly with growing degree days (GDD). Legumes contributed 27% of final legume-rye DM. Season-end legume DM was negatively correlated with GDD at 30 d, and legume DM in the 3x SR increased during years with frequent late-season rainfall. Seed costs per Mg of final CC DM at 1x SR were approximately three times higher for legume-rye than rye and mustard.
  • Authors:
    • Mancinelli, R.
    • Radicetti, E.
    • Campiglia, E.
  • Source: Crop Protection
  • Volume: 33
  • Year: 2012
  • Summary: Organic mulches could be a part of a wide strategy of integrated weed management in vegetable production systems. A 2-year field experiment was carried out in Central Italy with the aim of assessing the effect of grass and legume mulches, coming from winter cover crops, combined with herbicide or mechanical hoeing on weed control, on weed community (density and aboveground biomass of each species), and yield of a pepper crop. Hairy vetch (Vicia villosa Roth), oat (Avena sativa L) and their mixture were sown in early autumn and suppressed in May. The cover crop aboveground biomass was cut and arranged in strips which were used as beds for pepper seedlings transplanted in paired rows. A conventional treatment kept bare during the cover crop growing season with two different levels of nitrogen fertilizer on pepper (0-100 kg ha(-1) of N) was also included. Three weed control treatments were applied between the paired pepper rows 30 days after transplanting: a weed free treatment, glyphosate or mechanical hoeing. Dry matter production at cover crop suppression ranged from 5.3 t ha(-1) in oat to 7.1 t ha(-1) in hairy vetch/oat mixture and the N accumulation ranged from 56 kg ha(-1) in oat to 179 kg ha(-1) in hairy vetch. Within the pepper paired rows, mulch treatments reduced weed density and biomass throughout the pepper cropping season. At harvest, weed density and aboveground biomass within the pepper paired rows ranged from 1.7 to 4.6 plants m(-2) and 28 and 133 gm(-2) of DM, respectively. Oat mulch had the highest weed suppression ability and the lowest species richness. Shannon's index and Shannon evenness. Between the pepper paired rows the mulch treatments had the highest species richness and the most diverse weed community in chemical compared to mechanical weed control. The densities of Portulaca oleracea L and Polygonum aviculare L. were the highest under chemical and mechanical control, respectively. The weeds did not hinder pepper production in hairy vetch and hairy vetch/oat mixture where the yield was similar to that obtained in a conventional weedfree system fertilized with 100 kg ha(-1) of N. Therefore the use of hairy vetch mulches in combination with reduced mechanical or chemical weed control could be a feasible strategy in order to control weeds and to produce high yields in a pepper crop. (C) 2011 Elsevier Ltd. All rights reserved.
  • Authors:
    • Bakshawain, A. A.
    • Abusuwar, A. O.
  • Source: African Journal of Microbiology Research
  • Volume: 6
  • Issue: 14
  • Year: 2012
  • Summary: A field experiment was carried out during 2009/2010 and 2010/2011 seasons at Hada Al-Sham experimental Farm of King A/Aziz University in Jeddah, Saudi Arabia. The objective was to evaluate the effect of some chemical fertilizers on productivity and nutritive value of Sorghum Sudanense Var. Panar intercropped with Cowpea ( Vigna unguiculata L. Walp) in an adverse condition of soil and irrigation water. The chemical fertilizers applied were 50 kg/ha of urea (46%N), 50 kg/ha of triple superphosphate (46% P), 50 kg/ha of KNO 3, 50 kg/ha of NPK (20:20:40) and a control for check. Sudan grass and Cowpea were sown as sole crops and as a mixture. Treatments were laid out in a split plot design with the fertilizer treatments in the main plots and the intercropping treatments in the subplots. Parameters measured were plant height and nutritive value for the Sudan grass, fresh and dry yields and the land equivalent ratio (LER). The chemical fertilizers had no significant (P≤0.05) effect on productivity but significantly improved forage quality. Intercropping of Sudan grass and Cowpea significantly (P≤0.05) increased forage productivity and improved forage quality and land equivalent ratio (LER). Cowpea was not a good competitor as it disappeared following the first cut in the first season.
  • Authors:
    • Armentano, G.
  • Source: L'Informatore Agrario
  • Volume: 68
  • Issue: 1
  • Year: 2012
  • Authors:
    • Smith, P.
    • Hillier, J.
    • Walter, C.
    • Malin, D.
    • Garcia-Suarez, T.
    • Mila-i-Canals, L.
  • Source: Environmental Modelling & Software
  • Volume: 26
  • Issue: 9
  • Year: 2011
  • Summary: Agriculture and deforestation contribute approximately one third of global greenhouse gas emissions. Major sources of emissions in this sector are from loss of soil carbon due to repeated soil disturbance under typical crop cultivation, fossil fuel use in the production of synthetic fertilisers, direct and indirect soil nitrous oxide emissions from fertiliser application, pesticide manufacture and use, and fossil fuel combustion in machinery use (e.g. tractors, irrigation, etc). Although knowledge of emissions sources aids in the determination of potential mitigation strategies (reduced or no-till methods, use of N-fixing leguminous crops in rotations, use of lower emissions fertilisers), there currently exist limited decision support and knowledge transfer tools to enable the farmer or grower to make choices appropriate to existing management practices. In this article we present a model, and open source software tool called the "Cool Farm Tool" integrating several globally determined empirical models in a greenhouse gas calculator. The software, in requiring inputs of which a farmer typically has good knowledge (and no more), has a specific farm-scale, decision-support focus. Due to its use of only readily available farm data, there is considerable scope for its use in global surveys to inform on current practices and potential for mitigation.