1. Environmental impact assessment of regional switchgrass feedstock production comparing nitrogen input scenarios and legume-intercropping systems

• Authors:
  • Tyler, D. D.
  • Keyser, P. D.
  • Allen, F. L.
  • Reed, D. L.
  • Taylor, A. M.
  • Ashworth, A. J.
• Source: JOURNAL OF CLEANER PRODUCTION
• Volume: 87
• Year: 2015
• Summary: As the use of second-generation biofuel crops increases, so do questions about sustainability, particularly their potential to affect fossil energy consumption and greenhouse gas emissions. This study used a life-. cycle approach to compare environmental impacts associated with three switchgrass (Panicum virgatum L) production scenarios: i) regional production from a pool of Tennessee farmers based on in-field inputs and biomass yield; ii) varying nitrogen (N)-input levels from a replicated field study for 8-yrs i.e., a 100% and 9% decrease, and an 81% and 172% increase from 'baseline levels' of N inputs used under objective i; and, iii) a legume-intercrop system compared to baseline levels in order to determine effects of displacing synthetic-N with legumes. When compared across all agricultural inputs, nitrogen fertilizer production and breakdown resulted in the greatest environmental impacts. Although fertilization increased lignocellulosic yields, a 100% reduction in N-inputs from baseline levels reduced the formation of carbon, methane, and nitrous oxides per unit of production, (or dry tonne of biomass over 10-yrs) compared to a 172% increase. Switchgrass yield response indicated a 'less is more' scenario, as inputs beyond the current recommended input level (67 kg N ha(-1)) are not environmentally remunerating. During switchgrass biomass production, inputs with lesser impacts included phosphorus, herbicides, pesticides, and diesel fuel. Legume-intercropping reduced greenhouse gas emissions and groundwater acidification (5% and 27% reduction in global warming potential and formation of acidifying species, respectively) compared with the 67 kg N ha irate. Although N-fertilizers impact environmental sustainability of regional switchgrass feedstock production, environmental consequences can be reduced under proper N-management i.e., <= 67 kg N ha(-1) or legume intercropping. However, given that the aim of second-generation feedstocks is to reduce the current reliance on fossil fuels, their production still requires fossil energy-based inputs. Consequently, greenhouse gas reductions and the extent of cleaner feedstock production during the agricultural biofuel supply chain is contingent upon input management and optimizing synthetic fertilizer usage. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.

2. Nitrogen and carbon transformations, water use efficiency and ecosystem productivity in monocultures and wheat-bean intercropping systems

• Authors:
  • Riseman, A.
  • Chapagain, T.
• Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
• Volume: 101
• Issue: 1
• Year: 2015
• Summary: Enhancing soil organic carbon (SOC), nitrogen (N) and water use efficiency (WUE) are significant challenges in intensive wheat production. An intercropping system combining wheat and grain legumes may help maintain SOC, soil mineral N and WUE while also providing an opportunity to sequester carbon (C) in low input organic systems. We grew wheat (Triticum aestivum cv. 'Scarlet') as a monoculture and intercropped with either common bean (Phaseolus vulgaris cv. 'Red Kidney', or cv. 'Black Turtle'), or fava bean (Vicia faba cv. 'Bell') in rows of 1:1, 2 wheat: 1 bean or broadcast arrangement without fertilizers for 2 years to assess the effects of genotype and spatial arrangement on biological nitrogen fixation and seasonal transfer, WUE, gross ecosystem photosynthesis (GEP), and net ecosystem productivity (NEP). Stable isotope methods (C-13 and N-15 natural abundance) were used to quantify C and N within the plant and soil system. Field CO2 exchange measurements used a dynamic closed transparent chamber connected to a portable CO2 analyzer. Intercropped plots had higher percent N derived from symbiotic N-2 fixation, and increased C and N accumulation compared to monocultured wheat. The fava bean cv. Bell intercrops showed increased nodulation (60-80 % more nodules) and percent N derived from symbiotic N-2 fixation (10-12 % higher) compared to common beans resulting in the fixation of 74 kg N ha(-1) biologically from the 1:1 arrangement. The highest rate of N-transfer (13 %) was observed in the wheat-fava bean cv. Bell combination when planted in the 1:1 arrangement. All intercrops accumulated more N in shoot biomass compared to monoculture wheat with wheat-fava bean cv. Bell (1:1 arrangement) accumulating the highest N (34 kg N ha(-1), i.e., 176 % higher) and C (214 g C m(-2) year(-1), i.e., 26 % higher). All plots fixed the most CO2 (i.e., greatest GEP) during mid-growth stage (50 days after seeding i.e., prior to flowering) however, wheat-fava bean cv. Bell in the 1:1 arrangement displayed the greatest NEP sequestering C at the seasonal daytime average rate of 208 mg C m(-2) h(-1) (i.e., 7 % higher than wheat monoculture plots). Intrinsic WUE of wheat, as indicated by delta C-13, was also improved when grown with fava bean cv. Bell or common bean cv. Red Kidney. This study demonstrated that intercropping wheat and fava bean is an effective strategy to achieve greater nitrogen fixation and transfer to the wheat counterparts, higher WUE, and ecosystem productivity than wheat monocultures in areas with low soil N and C. Furthermore, the wheat-fava bean cv. Bell (1:1 arrangement) was more productive than either the 2:1 or mixed planting arrangements.

3. The cost of emission mitigation by legume crops in French agriculture

• Authors:
  • Dequiedt, B.
  • Moran, D.
• Source: Ecological Economics
• Volume: 110
• Year: 2015
• Summary: This paper considers the cost of greenhouse gas mitigation potential of legume crops in French arable systems. We construct marginal abatement cost curves to represent this mitigation or abatement potential for each department of France and provide a spatial representation of its extent. Despite some uncertainty, the measure appears to offer a significant low cost mitigation potential. We estimate that the measure could abate half of the emission reduction sought by a national plan for the reduction of chemical fertilizer emissions by 2020. This would be achieved at a loss of farmland profit of 1.2%. Considering the geographical heterogeneity of cost, we suggest that a policy implementing carbon pricing in agriculture would be more efficient than a uniform regulatory requirement for including the crop in arable systems.

4. Best management practices in Northern agriculture: A twelve-year rotation and soil tillage study in Saguenay-Lac-Saint-Jean

• Authors:
  • Lafond, J.
  • Paré, M. C.
  • Pageau, D.
• Source: Soil and Tillage Research
• Volume: 150
• Year: 2015
• Summary: In the northern agroecosystem of Saguenay-Lac-Saint-Jean, cash crops such as barley, canola, and field pea are gaining popularity over traditional perennial crops like alfalfa. However, very little information is available on the relatively long-term effect of different crop rotations and soil tillage practices on crop yields and soil quality parameters. This study was conducted at the Normandin Research Farm of Agriculture and Agri-Food Canada. Five rotation types [1: Canola-Barley-Barley-Pea (C-B-B-P); 2: Canola-Pea-Barley-Barley (C-P-B-B); 3: Canola-Barley-Pea-Barley (C-B-P-B); 4: Pea monoculture; and 5: Barley monoculture] and two soil tillage practices [1: Chisel plough (CP) and 2: Moldboard plough (MP)] were evaluated. Canola monoculture of was not included. The study began in 1999 on a former alfalfa field and ended in 2010 after three four-year rotation cycles. Barley monoculture decreased yields by 600kgha-1 in the last five years, whereas field pea monoculture decreased yields by about 1000kgha-1 in most years. Barley monoculture did not significantly reduce grain yields compared to C-B-B-P and C-P-B-B, highlighting the importance of alternate crops every year. Soil tillage (CP versus MP) did not significantly affect yields for all crops in most years; and when it did have an effect, it showed inconsistencies by either increasing or decreasing grain yields. Soil tillage also had insignificant impact regardless of the rotation type involved. Rotation type and soil tillage had insignificant effect on soil organic matter content, whereas CP increased nitrate and phosphorus content in the 0-20cm soil layer. Rotation type had insignificant impact on soil physical properties, whereas CP improved soil water conductivity by 0.03cmh-1 for C-B-B-P and barley monoculture. Compared to MP, CP improved soil macro-aggregate (2-6mm) stability to water as well as aggregate mean weight diameter by about 15% for most of the rotations.

5. Nitrous oxide emissions from perennial grass-legume intercrop for bioenergy use

• Authors:
  • Stoddard, F. L.
  • Simojoki, A.
  • Makela, P.
  • Jaakkola, S.
  • Santanen, A.
  • Saikkonen, L.
  • Epie, K. E.
• Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
• Volume: 101
• Issue: 2
• Year: 2015
• Summary: Bioenergy cropping, like all agricultural practices, may lead to the release of greenhouse gases. This study was aimed at determining biomass and energy yields of reed canary grass (RCG) (Phalaris arundinacea), galega (Galega orientalis) and a mixture of these, and to relate these to fluxes of nitrous oxide (N2O), a potent greenhouse gas, emitted from the soils. Plots including a bare fallow as control were established in 2008. Gases emitted from the soil surface were collected in closed chambers from May 2011 to May 2013, except during periods of snow cover, and analysed by gas chromatography. Seasonal and annual cumulative emissions of N2O and CO2 equivalents per unit energy yield were calculated. Soil moisture content, nitrate (NO3 (-))-N and ammonium (NH4 (+))-N were also determined. Both species composition and crop yields affected energy yields and N2O emission from the soil. The annual cumulative emissions from mixture were marginally lower than those from fertilized RCG soils. Fertilized RCG produced twice as much biomass and correspondingly higher nitrogen and energy yields, so its low emission of N2O per Mg of dry matter was not significantly different from that of the mixtures. Cropping an RCG-galega mixture for biofuel may replace N fertilizer input since it resulted in lowering N2O fluxes, but requires management to maintain grass as the major component in order to minimize N2O emissions. In a time of climate change, low-input bioenergy crops may be a suitable strategy for land left uncropped after ploughing for one season or longer.

6. Intercropping enhances soil carbon and nitrogen.

• Authors:
  • van der Werf, W
  • Zhang, F. S.
  • Six, J.
  • Cong, W. F.
  • Hoffland, E.
  • Li, L.
  • Sun, J. H.
  • Bao, X. G.
• Source: GLOBAL CHANGE BIOLOGY
• Volume: 21
• Issue: 4
• Year: 2015
• Summary: Intercropping, the simultaneous cultivation of multiple crop species in a single field, increases aboveground productivity due to species complementarity. We hypothesized that intercrops may have greater belowground productivity than sole crops, and sequester more soil carbon over time due to greater input of root litter. Here, we demonstrate a divergence in soil organic carbon (C) and nitrogen (N) content over 7 years in a field experiment that compared rotational strip intercrop systems and ordinary crop rotations. Soil organic C content in the top 20 cm was 4%1% greater in intercrops than in sole crops, indicating a difference in C sequestration rate between intercrop and sole crop systems of 18486 kg C ha -1 yr -1. Soil organic N content in the top 20 cm was 11%1% greater in intercrops than in sole crops, indicating a difference in N sequestration rate between intercrop and sole crop systems of 4510 kg N ha -1 yr -1. Total root biomass in intercrops was on average 23% greater than the average root biomass in sole crops, providing a possible mechanism for the observed divergence in soil C sequestration between sole crop and intercrop systems. A lowering of the soil delta 15N signature suggested that increased biological N fixation and/or reduced gaseous N losses contributed to the increases in soil N in intercrop rotations with faba bean. Increases in soil N in wheat/maize intercrop pointed to contributions from a broader suite of mechanisms for N retention, e.g., complementary N uptake strategies of the intercropped plant species. Our results indicate that soil C sequestration potential of strip intercropping is similar in magnitude to that of currently recommended management practises to conserve organic matter in soil. Intercropping can contribute to multiple agroecosystem services by increased yield, better soil quality and soil C sequestration.

7. Effects of free-air CO 2 enrichment (FACE) on the uptake and utilization of N, P and K in Vigna radiata.

• Authors:
  • Hao, X. Y.
  • Han, Y. H.
  • Lin, E. D.
  • Li, H. Y.
  • Zong, Y. Z.
  • Han, X.
  • Li, P.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 202
• Year: 2015
• Summary: Elevated [CO 2] stimulates plant growth, which in turn demands more nutrients to sustain it. The nutrient demand of N-fixing plants may differ from that of other plants under elevated [CO 2]. We conducted an experiment to determine how elevated [CO 2] affected N, P and K content, assimilation of nutrients and accumulation of metabolites in the legume mung bean [ Vigna radiata L.]. We investigated the effect of 55019 mol mol -1 [CO 2] on N, P, K uptake and utilization by mung bean at the free-air carbon dioxide enrichment (FACE) experimental facility in north China. At maturity, N concentration in whole plants decreased by 4.4%, but P and K concentration was unchanged at elevated [CO 2]. The weight of nodules per plant significantly increased at elevated [CO 2] but N, P, K-use efficiency for seed and the ratio of seed yield to cumulative absorption of N, P and K was unaffected. These results indicate that under elevated [CO 2] the mechanisms governing N absorption and metabolism in mung bean was different from that for P and K. The nutrient dynamics between different elements of overall plant biomass and the soil nutrients pool could, therefore, be changed in future by elevated [CO 2].

8. Effects of contrasting catch crops on nitrogen availability and nitrous oxide emissions in an organic cropping system.

• Authors:
  • Sorensen, P.
  • Petersen, S. O.
  • Li, X. X.
  • Olesen, J. E.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 199
• Year: 2015
• Summary: Legume-based catch crops (LBCCs) may act as an important source of nitrogen (N) in organic crop rotations because of biological N fixation. However, the potential risk of high nitrous oxide (N 2O) emissions needs to be taken into account when including LBCCs in crop rotations. Here, we report the results from a one-year field experiment, which investigated N availability and N 2O emissions as affected by three LBCCs, i.e., red clover (CL), red clover-ryegrass mixture (GC) and winter vetch (WV), two non-LBCCs, i.e., perennial ryegrass (GR) and fodder radish (FR), and a control (CO) without catch crops. The effect of two catch crop management strategies was also tested: autumn harvest of the catch crop versus incorporation of whole-crop residues by spring ploughing. LBCCs accumulated 59-67 kg N ha -1 in their tops, significantly more than those of the non-LBCC, 32-40 kg N ha -1. Macro-roots accounted for >33% of total N in the catch crops. In accordance with this, LBCCs enhanced the performance of the succeeding unfertilised spring barley, thus obtaining a grain yield of 3.3-4.5 Mg ha -1 compared to 2.6-3.3 Mg ha -1 grain yield from non-LBCC and the fallow control treatments. Autumn harvest of catch crops, especially LBCCs, tended to reduce crop yield. The annual N 2O emissions were comparable across treatments except for fodder radish, which had the highest N 2O emission, and also the highest average yield-scaled N 2O emission, at 499 g N 2O-N Mg -1 grain. Although the sampling strategy employed in this study introduces uncertainty about the spatial and temporal variability, differences in seasonal emission patterns among catch crops were captured and harvest of catch crops in late autumn induced significantly higher emissions during winter, but lower emissions after residue incorporation in spring. In comparison with non-LBCC, LBCCs have the potential to partly replace the effect of manure application in organic cropping systems with greater crop production and less environmental footprint with respect to N 2O emissions. However, harvest of the catch crops may reduce crop yield unless the harvested N is recycled as fertiliser to the crops in the rotation.

9. Traditional rainwater management system ('Haveli') in Vertisols of central India improves carbon sequestration and biological soil fertility.

• Authors:
  • Rawat, A. K.
  • Sahu, R. K.
  • Rao, D. L. N.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 200
• Year: 2015
• Summary: Farmers in Central India practice a unique rain water management system ('Haveli') based on impounding rain water in the fields during three months monsoon season (June-September) and draining out in October. Winter crops, mainly grain legumes are then grown that utilize the soil moisture conserved in the soil profile. We monitored the soil physico-chemical and fertility properties, C and N mineralization, microbial populations and biomass and soil enzymes in the 0-30 cm soil layer at ten sites over three years at four stages viz., prior to submergence in summer (PS), during water-logging (WL), after drainage (AD) and after legume cropping (AC). Anaerobic conditions during water-logging (for 11 weeks) led to extensive losses of soil carbon amounting to 1900 mg C kg -1 soil but no significant change in soil N. Post-drainage and decomposition of weeds (for 6 weeks), there was an increase in soil C of 3700 mg C kg -1 and soil N of 74.1 mg N kg -1 soil. Overall in 17 weeks, there was a net increase of 1800 mg C kg -1 (+30.5%) and 87.5 mg N kg -1 (+20.1%) amounting to soil C and N accretion rate of 15.1 mg C kg -1 soil day -1 and 0.74 mg N kg -1 soil day -1. Microbial biomass decreased by 19.7% during 11 weeks of water logging and improved by 54% in the 6 weeks aerobic phase; an overall increment of 23.5% (31 mg microbial C kg -1) in 17 weeks. Prolonged water-logging induced severe stress on microbial processes. However, post-drainage, there was significant improvement in microbial populations, nitrogen mineralization, soil enzymes and soil fertility. There were strong relationships between soil enzymes and microbial carbon; and, nitrogen mineralization and soil carbon. Results unequivocally demonstrated the benefits of rain-water conservation in Vertisols for carbon sequestration and nitrogen accretion and improvement of soil biological quality.

10. Soil N 2O emissions under N 2-fixing legumes and N-fertilised canola: a reappraisal of emissions factor calculations.

• Authors:
  • Haigh, B. M.
  • Rowlings, D. W.
  • Scheer, C.
  • Herridge, D. F.
  • Schwenke, G. D.
  • McMullen, K. G.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 202
• Year: 2015
• Summary: Introducing nitrogen (N)-fixing legumes into cereal-based crop rotations reduces synthetic fertiliser-N use and may mitigate soil emissions of nitrous oxide (N 2O). Current IPCC calculations assume 100% of legume biomass N as the anthropogenic N input and use 1% of this as an emission factor (EF)-the percentage of input N emitted as N 2O. However, legumes also utilise soil inorganic N, so legume-fixed N is typically less than 100% of legume biomass N. In two field experiments, we measured soil N 2O emissions from a black Vertosol in sub-tropical Australia for 12 months after sowing of chickpea ( Cicer arietinum L.), canola ( Brassica napus L.), faba bean ( Vicia faba L.), and field pea ( Pisum sativum L.). Cumulative N 2O emissions from N-fertilised canola (624 g N 2O-N ha -1) greatly exceeded those from chickpea (127 g N 2O-N ha -1) in Experiment 1. Similarly, N 2O emitted from canola (385 g N 2O-N ha -1) in Experiment 2 was significantly greater than chickpea (166 g N 2O-N ha -1), faba bean (166 g N 2O-N ha -1) or field pea (135 g N 2O-N ha -1). Highest losses from canola were recorded during the growing season, whereas 75% of the annual N 2O losses from the legumes occurred post-harvest. Legume N 2-fixation provided 37-43% (chickpea), 54% (field pea) and 64% (faba bean) of total plant biomass N. Using only fixed-N inputs, we calculated EFs for chickpea (0.13-0.31%), field pea (0.18%) and faba bean (0.04%) that were significantly less than N-fertilised canola (0.48-0.78%) ( P<0.05), suggesting legume-fixed N is a less emissive form of N input to the soil than fertiliser N. Inputs of legume-fixed N should be more accurately quantified to properly gauge the potential for legumes to mitigate soil N 2O emissions. EF's from legume crops need to be revised and should include a factor for the proportion of the legume's N derived from the atmosphere.