1. Soil nitrous oxide emissions as affected by long-term tillage, cropping systems and nitrogen fertilization in Southern Brazil

• Authors:
  • Piccolo, M. D. C.
  • Vieira, F. C. B.
  • Zanatta, J. A.
  • Gomes, J.
  • Bayer, C.
  • Dieckow, J.
  • Six, J.
• Source: SOIL & TILLAGE RESEARCH
• Volume: 146
• Issue: Pt. B
• Year: 2015
• Summary: Soil nitrous oxide (N2O) emissions are affected by management practices, but little information is available on the interactive effects of tillage, cropping systems and N sources in tropical and subtropical soils. In an 18-yr old experiment located in a subtropical Acrisol of Southern Brazil we conducted a sequence of two trials. The 1-year trial (October 2003-2004) was set to evaluate the long-term effects of tillage [CT: conventional; and NT: no-tillage] and cropping systems [O/M: black oat (Avena strigosa Schreb.)/maize (Zea mays L.); and V/M: vetch (Vicia sativa L.)/maize] on soil N2O emissions, either in the post-management period (45 days after desiccation and knife-rolling of winter cover crops) or in the whole year. The second and short-term trial (October-November 2004) was carried out to compare the impact of N sources [urea (mineral) and legume-residue of vetch (biologically fixed), both at 180kgNha-1] on soil N2O emissions during 53 days after cover-crop management. Air sampling was carried out by static chambers and N2O analysis by gas chromatography. In the 45-day post-management period of the 1-year trial, soil N2O emissions were practically not affected by tillage systems, but increased 4 times due to vetch residues (average of 0.40±0.08kgNha-1 in V/M versus 0.10±0.05kgNha-1 in O/M) and related with soil contents of NO3 --N, NH4 +-N, and dissolved organic C (DOC). Over the whole year, soil N2O emissions under CT were similar for grass- and legume-based cropping systems and averaged 0.43±0.17kgNha-1, while NT exacerbated N2O emissions in the legume-based cropping system (0.80±0.07kgNha-1 in V/M versus -0.07±0.06kgNha-1 in O/M). Maize yield was not affected by tillage, but increased from 2.32Mgha-1 in O/M to 4.44Mgha-1 in V/M. Yield-scaled N2O emissions varied from -33g N2O-NMg-1 grain in NT O/M to 179g N2O-NMg-1 grain in NT V/M, and were intermediate in CT soil (106 and 156g N2O-NMg-1grain in V/M and O/M cropping systems, respectively). In the short-term trial, the N2O emitted in excess relative to the control treatment (O/M without N fertilizer) was at least 3 times greater with urea-N (0.44% of applied N) than with legume-residue-Nsource (0.13% of applied N). Yield-scaled N2O emission after vetch residues management (67gNMg-1 grain) was half of that after urea-N application (152gNMg-1 grain). Partially supplying the maize N requirements with winter legume cover-crops may be a feasible strategy to mitigate soil N2O emissions in the subtropical conservation agriculture.

2. Soil quality, microbial functions and tomato yield under cover crop mulching in the Mediterranean environment

• Authors:
  • Brunetti, P.
  • Mancinelli, R.
  • Marinari, S.
  • Campiglia, E.
• Source: SOIL & TILLAGE RESEARCH
• Volume: 145
• Year: 2015
• Summary: An experiment concerning the biological and chemical responses of soil to cover crop mulching was carried out in two adjacent experimental fields (2012 and 2013) under different climatic conditions in the Mediterranean environment (Central Italy). The Monthly Aridity Index was calculated in order to verify the relationship between soil properties and climatic factors under three different cover crop mulches: Vicia villosa Roth (HV), Phacelia tanacetifolia Benth. (LP), and Sinapis alba L. (WM). A conventional management was also included in the experimental fields as control (C). Soil samples were collected at 0-20cm depth after the transplanting and the harvesting of tomato (May and August, respectively), in order to assess the initial and residual effects of mulching on soil quality. In the two experimental years, the amount of precipitation from May to August was 110mm in 2012 and 172mm in 2013. The average values of AI were 18 and 49 in 2012 and 2013, respectively. LP mulching was sensitive to low precipitation levels in terms of aboveground decomposition rate (the variation of dry matter from May to August 2012 was -53% in LP, 64% in HV and 69% in WM) and a lower tomato yield compared to the control in 2012 (4.2kgm-2 in LP and 5.2kgm-2 in C). WM mulching was sensitive to low precipitation in terms of soil nutrient storage (from May to August 2012 the variation of soil C was 19% in WM., 6% in C, -5 % in LP and 10% in HV; the variation of soil N was 44% in WM, 2% in C, -2% in LP and 13% in HV). Soil microbial activity and functional diversity were strongly affected by the climatic conditions in all mulching treatments. In particular, precipitation influenced soil C availability, which enhanced microbial functional diversity. In short, the effects of lacy phacelia, white mustard and hairy vetch mulching on soil quality, microbial functions and tomato yield were influenced by summer precipitation and temperature in the Mediterranean environment. © 2014 Elsevier B.V.

3. Carbon sequestration in agricultural soils via cultivation of cover crops - A meta-analysis

• Authors:
  • Don, A.
  • Poeplau, C.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 200
• Year: 2015
• Summary: A promising option to sequester carbon in agricultural soils is the inclusion of cover crops in cropping systems. The advantage of cover crops as compared to other management practices that increase soil organic carbon (SOC) is that they neither cause a decline in yields, like extensification, nor carbon losses in other systems, like organic manure applications may do. However, the effect of cover crop green manuring on SOC stocks is widely overlooked. We therefore conducted a meta-analysis to derive a carbon response function describing SOC stock changes as a function of time. Data from 139 plots at 37 different sites were compiled. In total, the cover crop treatments had a significantly higher SOC stock than the reference croplands. The time since introduction of cover crops in crop rotations was linearly correlated with SOC stock change (R2=0.19) with an annual change rate of 0.32±0.08Mgha-1yr-1 in a mean soil depth of 22cm and during the observed period of up to 54 years. Elevation above sea level of the plot and sampling depth could be used as explanatory variables to improve the model fit. Assuming that the observed linear SOC accumulation would not proceed indefinitely, we modeled the average SOC stock change with the carbon turnover model RothC. The predicted new steady state was reached after 155 years of cover crop cultivation with a total mean SOC stock accumulation of 16.7±1.5Mgha-1 for a soil depth of 22cm. Thus, the C input driven SOC sequestration with the introduction of cover crops proved to be highly efficient. We estimated a potential global SOC sequestration of 0.12±0.03PgCyr-1, which would compensate for 8% of the direct annual greenhouse gas emissions from agriculture. However, altered N2O emissions and albedo due to cover crop cultivation have not been taken into account here. Data on those processes, which are most likely species-specific, would be needed for reliable greenhouse gas budgets.

4. In situ net N mineralisation and nitrification under organic and conventionally managed olive oil orchards

• Authors:
  • Garcia-Ruiz, R.
  • Hinojosa, M. B.
  • Gomez-Munoz, B.
• Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
• Volume: 101
• Issue: 2
• Year: 2015
• Summary: Olive oil orchard occupies a great percentage of the cropland in southern Spain. Thus, changes in nitrogen (N) fertilization might have a great effect on N dynamics at least at regional scale, which should be investigated for a sustainable N fertilization program. In situ net N mineralization (NM) and nitrification (NN) were investigated during a year in comparable organic (OR) and conventional (CV) olive oil orchards of two locations differing their N input. Soil samples were collected in two soil positions (under and between trees canopy) and both buried-bags and soil core techniques were used to quantify both microbial rates. There were differences in NM and NN between sites mainly due to differences in soil total N (TN), and potential mineralisable N (PMN). In all cases NM and NN were higher in soils under tree canopy. NM and NN were higher in OR than in CV managed orchards in the location with high soil TN. Soil TN and PMN explained together a 50 % of the variability in soil N availability, which suggests that these two variables are good predictors of the potential of a soil to provide available N. The highest rates of soil N availability were found in spring, when olive tree demand for N was at its maximum. Annual soil N availability in olive groves was in all cases higher or similar than tree demand suggesting that soil annual supply of N should be taken into account in order to develop sustainable N fertilisation strategies for olive crops.

5. Greenhouse gas emissions from conventional and organic cropping systems in Spain. II. Fruit tree orchards

• Authors:
  • Alonso, A.
  • Guzman, G.
  • Aguilera, E.
• Source: AGRONOMY FOR SUSTAINABLE DEVELOPMENT
• Volume: 35
• Issue: 2
• Year: 2015
• Summary: Fruit tree orchards have a historical and economic importance for Mediterranean agriculture, notably in Spain. Fruit tree orchards have the potential to mitigate global warming by sequestrating carbon (C) and providing renewable fuels. Actually, there is few information on the benefits of organic practices. Therefore, we analyzed the greenhouse gas contribution of 42 pairs of organic and conventional perennial cropping systems, including citrus, subtropical trees, other fruit trees, treenuts, vineyards, and olives, using life-cycle assessment (LCA). The assessment was based on management information from interviews and involved the estimation of soil carbon sequestration, specific Mediterranean N2O emission factors, and the consideration of coproducts. Results show on average a 56 % decrease of greenhouse gas emissions under organic versus conventional cropping, on an area basis. On a product basis, greenhouse gas emissions decreased by 39 % on average. These findings are explained mainly by C sequestration in soils, which is due in turn to higher C inputs by cover cropping and incorporation of pruning residues.

6. The efficacy of winter cover crops to stabilize soil inorganic nitrogen after fall-applied anhydrous ammonia.

• Authors:
  • Armstrong, S.
  • Lacey, C.
• Source: JOURNAL OF ENVIRONMENTAL QUALITY
• Volume: 44
• Issue: 2
• Year: 2015
• Summary: There is a dearth of knowledge on the ability of cover crops to increase the effectiveness of fall-applied nitrogen (N). The objective of this study was to investigate the efficacy of two cover crop species to stabilize inorganic soil N after a fall application of N. Fall N was applied at a rate of 200 kg N ha -1 into living stands of cereal rye, tillage radish, and a control (no cover crop) at the Illinois State University Research and Teaching Farm in Lexington, Illinois. Cover crops were sampled to determine N uptake, and soil samples were collected in the spring at four depths to 80 cm to determine the distribution of inorganic N within the soil profile. Tillage radish (131.9-226.8 kg ha -1) and cereal rye (188.1-249.9 kg ha -1 N) demonstrated the capacity to absorb a minimum of 60 to 80% of the equivalent rate of fall-applied N, respectively. Fall applying N without cover crops resulted in a greater percentage of soil NO 3-N (40%) in the 50- to 80-cm depth, compared with only 31 and 27% when tillage radish and cereal rye were present at N application. At planting, tillage radish stabilized an average of 91% of the equivalent rate of fall-applied N within the 0- to 20-cm, depth compared with 66 and 57% for the cereal rye and control treatments, respectively. This study has demonstrated that fall applying N into a living cover crop stand has the potential to reduce the vulnerability of soil nitrate and to stabilize a greater concentration of inorganic N within the agronomic depths of soil.

7. A short-term assessment of carbon dioxide fluxes under contrasting agricultural and soil management practices in Zimbabwe.

• Authors:
  • Lambert, D. M.
  • Thierfelder, C.
  • Hicks, B. B.
  • Sauer, T. J.
  • O'Dell, D.
  • Logan, J.
  • Eash, N. S.
• Source: Journal of Agricultural Science (Toronto)
• Volume: 7
• Issue: 3
• Year: 2015
• Summary: Two of the biggest problems facing humankind are feeding an exponentially growing human population and preventing the accumulation of atmospheric greenhouse gases and its climate change consequences. Refined agricultural practices could address both of these problems. The research addressed here is an exploration of the efficacy of alternative agricultural practices in sequestering carbon (C). The study was conducted in Zimbabwe with the intent to (a) demonstrate the utility of micrometeorological methods for measuring carbon dioxide (CO 2) exchange between the surface and the atmosphere in the short-term, and (b) to quantify differences in such exchange rates for a variety of agricultural practices. Four Bowen ratio energy balance (BREB) systems were established on the following agricultural management practices: (1) no-till (NT) followed by planting of winter wheat ( Triticum aestivum), (2) NT followed by planting of blue lupin ( Lupinus angustifolios L.), (3) maize crop residue ( Zea mays L.) left on the surface, and (4) maize crop residue incorporated with tillage. Over a period of 139 days (from 15 June to 31 October 2013) the winter wheat cover crop produced a net accumulation of 257 g CO 2-C m -2, while the tilled plot with no cover crop produced a net emission of 197 g CO 2-C m -2 and the untilled plot with no cover emitted 235 g CO 2-C m -2. The blue lupin cover crop emitted 58 g CO 2-C m -2, indicating that winter cover crops can sequester carbon and reduce emissions over land left fallow through the non-growing season. The micrometeorological methods described in this work can detect significant differences between treatments over a period of a few months, an outcome important to determine which smallholder soil management practices can contribute towards mitigating climate change.

8. Enhanced efficiency urea sources and placement effects on nitrous oxide emissions

• Authors:
  • Gao XiaoPeng
  • Asgedom,H.
  • Tenuta,M.
  • Flaten,D. N.
• Source: Agronomy Journal
• Volume: 107
• Issue: 1
• Year: 2015
• Summary: The effects of band placement of enhanced efficiency fertilizers (EEF) on nitrous oxide (N 2O) emissions are uncertain. Placement and EEF on N 2O emissions from spring wheat ( Triticum aestivum L.) at two locations in Manitoba, in 2011 and 2012 were examined. Treatments were a no N control and 80 kg N ha -1 at planting of five combinations of placement and granular N source: broadcast-incorporated urea (Urea I) and, subsurface side-banded urea (Urea S; each row side-banded), midrow-banded urea (Urea M; placement between every other set of rows), midrow-banded environmentally smart nitrogen (ESN, Agrium, Inc.) (ESN M), and midrow-banded SuperU (Koch Industries Inc.) (SuperU M). Planting in 2011 was delayed 40 d compared to 2012. Planting coincided with higher soil temperature and moisture resulting in three- to sevenfold more growing season N 2O emissions (SigmaN 2O) in 2011 than 2012. In 2011, SuperU M and ESN M reduced SigmaN 2O, emission factor (EF) scaled by N-applied EF, and yield-scaled N 2O emission intensity (EI) by 47, 67, and 55%, respectively, compared with Urea I. In 2011, increasing placement concentration of N in order broadcast-incorporation, side-banding, and midrow-banding tended to decrease SigmaN 2O, EF, and EI of granular urea, but not statistically significant. The SigmaN 2O and nitrate exposure (NE), were significantly correlated over the site-years, indicating N availability from treatments in part determined emissions. Grain yield and crop N uptake were unaffected by sources and placement. These results suggest for early season wet and warm conditions, EEF N sources can reduce emissions compared with granular urea. Further studies are required to clarify placement effects on N 2O emissions.

9. Sugarbeet yield and quality when substituting compost or manure for conventional nitrogen fertilizer

• Authors:
  • Johnson-Maynard, J. L.
  • Lentz, R. D.
  • Brown, B.
  • Lehrsch, G. A.
  • Leytem, A. B.
• Source: Agronomy Journal
• Volume: 107
• Issue: 1
• Year: 2015
• Summary: To grow sugarbeet ( Beta vulgaris L.) profitably, producers must effectively manage added N, whether from inorganic or organic sources. Our objective was to determine if equivalent sugarbeet root and sucrose yields could be achieved when substituting dairy cattle ( Bos spp.) manure, either composted or stockpiled, for conventional N (urea) fertilizer. First-year treatments at Site A (Parma, ID) included a control (no N), urea (202 kg N ha -1), compost (218 and 435 kg estimated available N ha -1), and manure (140 and 280 kg available N ha -1). Site B (Kimberly, ID) treatments were a control, urea (82 kg N ha -1), compost (81 and 183 kg available N ha -1), and manure (173 and 340 kg available N ha -1). Compost and manure were incorporated into two silt loams, a Greenleaf (fine-silty, mixed superactive mesic Xeric Calciargid) at Parma in fall 2002 and 2003 and a Portneuf (coarse-silty, mixed superactive, mesic Durinodic Xeric Haplocalcid) at Kimberly in fall 2002. Sugarbeet was planted the following spring. Sucrose yield averaged across years and organic N rates at Site A was 12.24 Mg ha -1 for urea, 11.88 Mg ha -1 for compost, and 11.20 Mg ha -1 for manure, all statistically equivalent. Doubling the organic N rates at Site A increased the yield of roots up to 26% and sucrose up to 21%. Applying organic amendments in place of urea affected neither root nor sucrose yields but, at one location, decreased sugarbeet quality, though without hindering sucrose recovery. Sugarbeet producers can use compost or manure to satisfy crop N needs without sacrificing sucrose yield.

10. Tillage and cover cropping affect crop yields and soil carbon in the San Joaquin Valley, California

• Authors:
  • Southard, R. J.
  • Horwath, W. R.
  • Shrestha, A.
  • Mitchell, J. P.
  • Madden, N.
  • Veenstra, J.
  • Munk, D. S.
• Source: Article
• Volume: 107
• Issue: 2
• Year: 2015
• Summary: Rising costs and air quality regulations have created interest in California's San Joaquin Valley (SJV) in production systems that reduce tillage operations and soil disturbance. From 1999 to 2009, we evaluated conventional (CT) and reduced tillage (RT) systems for a cotton ( Gossypium hirsutum L.)/tomato ( Solanum lycopersicon Mill.) rotation with (CC) and without (NO) cover crops in a Panoche clay loam soil (fine-loamy, mixed, superactive, thermic Typic Haplocambid) in Five Points, CA, in terms of yield, soil C, and the NRCS soil conditioning index (SCI). The RT reduced tractor operations by 50% for tomato and 40% for cotton. Cover cropping produced 38.7 t ha -1 of biomass. Tomato yields were 9.5% higher in RT vs. CT systems and 5.7% higher in NO vs. CC systems. The CT cotton yields were 10.0% higher than RT yields and 4.8% higher in NO systems, but yield patterns were not consistent from 2005 to 2009. Soil C content was uniform (0-30-cm depth) in 1999 (19.72 t ha -1) and increased in all systems in 2007 (t ha -1): RTCC 29.11, CTCC 26.36, RTNO, 24.09, and CTNO 22.65. Soil C content of RT and CT systems did not differ, but was greater in CC than in NO systems. In the 0- to 15-cm depth, RT increased soil C, indicating stratification, and also increased C in the occluded light and mineral fractions. The SCI was positive for RT treatments, predicting a soil C increase, and negative for CT systems, predicting a soil C decline, but measured soil C content increased in all systems. Results show that RT maintains or increases yields relative to CT, and CC stores more soil C than NO.