1. Temperature dependence of organic matter solubility: Influence of biodegradation during soil-water extraction

• Authors:
  • Qiu, W.
  • Beare, M. H.
  • Curtin, D.
  • Chantigny, M. H.
  • Curtin, D.
  • Beare, M. H.
  • Qiu, W.
  • Chantigny, M. H.
• Source: Agronomyhttps://dl.sciencesocieties.org/publications/sssaj/articles/79/3/858 Journal
• Volume: 79
• Issue: 3
• Year: 2015
• Summary: Water-extractable organic matter has been shown to increase as temperature increases (from 20 to 80°C), with the rate of increase being soil dependent. We examined whether biodegradation during overnight soil-water extraction may influence the temperature response of extractable C and N. Dissolved organic N (DON) and C (DOC), and NH4-N were determined after 16 h of soil-water extraction at either 80 or 50°C (previous work in our laboratory suggested that biodegradation in soil-water suspensions peaks at ~50°C). For both DOC and DON, there were large differences among soils in their temperature responses (e.g., the increase in DON between 50 and 80°C ranged from 29 to 148 mg kg-1). More NH4-N was generated at 50 than at 80°C. Ammonium N produced at 50°C was largely attributable to mineralization (it was almost eliminated when microbial activity was suppressed by extracting with 2 mol L-1 KCI at 50°C). The small amounts of NH4-N found at 80°C were probably of abiotic origin (e.g., thermal degradation of soil organic N). Our results suggested that dissolved organic matter (DOM) was mineralized during the 50°C extraction. The release of DOM was thus underestimated at 50°C and, as a consequence, the temperature response of DOM between 50 and 80°C was overestimated (mineralization at 50°C accounted for most of the variability in the temperature response of DOM). We conclude that the temperature response of DOM can be affected by biodegradation during extraction and that an extraction at 80°C has the important merit that biodegradation during extraction should be negligible. © Soil Science Society of America, 5585 Guilford Rd., Madison Wl 53711 USA.

2. Modelling the influence of predicted future climate change on the risk of wind damage within New Zealand's planted forests.

• Authors:
  • Moore,J. R.
  • Watt,M. S.
• Source: Global Change Biology
• Volume: 21
• Issue: 8
• Year: 2015
• Summary: Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (ForestGALES) to an empirical growth model for radiata pine ( Pinus radiata D. Don) and a process-based growth model (CENW) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The CENW model was used to estimate site productivity for constant CO 2 concentration at 1990 values and for assumed increases in CO 2 concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1 B (mid-range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the ForestGALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO 2 concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances.

3. Evaluating biodegradability of soil organic matter by its thermal stability and chemical composition.

• Authors:
  • Curtin, D.
  • Beare, M.
  • Gillespie, A.
  • Gregorich, E.
  • Sanei, H.
  • Yanni, S.
• Source: Soil Biology and Biochemistry
• Volume: 91
• Issue: December 2015
• Year: 2015
• Summary: The stability of soil organic matter (SOM) as it relates to resistance to microbial degradation has important implications for nutrient cycling, emission of greenhouse gases, and C sequestration. Hence, there is interest in developing new ways to quantify and characterise the labile and stable forms of SOM. Our objective in this study was to evaluate SOM under widely contrasting management regimes to determine whether the variation in chemical composition and resistance to pyrolysis observed for various constituent C fractions could be related to their resistance to decomposition. Samples from the same soil under permanent pasture, an arable cropping rotation, and chemical fallow were physically fractionated (sand: 2000-50 m; silt: 50-5 m, and clay: <5 m). Biodegradability of the SOM in size fractions and whole soils was assessed in a laboratory mineralization study. Thermal stability was determined by analytical pyrolysis using a Rock-Eval pyrolyser, and chemical composition was characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the C and N K-edges. Relative to the pasture soil, SOM in the arable and fallow soils declined by 30% and 40%, respectively. The mineralization bioassay showed that SOM in whole soil and soil fractions under fallow was less susceptible to biodegradation than that in other management practices. The SOM in the sand fraction was significantly more biodegradable than that in the silt or clay fractions. Analysis by XANES showed a proportional increase in carboxylates and a reduction in amides (protein) and aromatics in the fallow whole soil compared to the pasture and arable soils. Moreover, protein depletion was greatest in the sand fraction of the fallow soil. Sand fractions in fallow and arable soils were, however, relatively enriched in plant-derived phenols, aromatics, and carboxylates compared to the sand fraction of pasture soils. Analytical pyrolysis showed distinct differences in the thermal stability of SOM among the whole soil and their size fractions; it also showed that the loss of SOM generally involved preferential degradation of H-rich compounds. The temperature at which half of the C was pyrolyzed was strongly correlated with mineralizable C, providing good evidence for a link between the biological and thermal stability of SOM.

4. Mineralization of soil carbon and nitrogen following physical disturbance: A laboratory assessment

• Authors:
  • Hernandez-Ramirez, G.
  • Scott, C. L.
  • Beare, M. H.
  • Curtin, D.
  • Meenken, E. D.
• Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
• Volume: 78
• Issue: 3
• Year: 2014
• Summary: Uncertainty persists regarding the influence of physical disturbance on mineralization of soil organic matter. This study examined how disturbance affects mineralization in soils with different management histories and textures. Results from a 100-d incubation (20°C, -10 kPa) using cores (0-15 cm deep; 5-cm diameter) from a field trial at Lincoln, New Zealand with different agronomic treatments in the previous 5 yr (pasture, arable cropping, and chemical fallow) confirmed that mineralization is strongly influenced by management history (C mineralized ranged from 390 mg kg-1 in fallow soil to 1570 mg kg-1 under pasture). However, there was no difference in C or N mineralization between disturbed (sieved <4 mm) and intact cores. In another experiment, comparisons of mineralization in intact and disturbed (<4 mm) cores from 14 arable and pasture fields with either silt loam or clay loam texture also showed no effect of disturbance. In a final experiment, large, air-dry aggregates (19-40 mm) from two soil types (silt loam and clay loam) were fragmented using a compressive force and the resulting subaggregates separated into size classes (<0.25, 0.25-1, 1-2, 2-4, 4-9.5, and 9.5-13.2 mm) by dry sieving. Mineralization increased only when aggregate size was below a certain threshold value (∼3 mm diameter); mineralization was ∼25-50% greater in fine (≤1 mm) vs. large (4-40 mm) aggregates, likely due to exposure of previously-occluded organic matter. Unless a substantial quantity of fine aggregates is generated, the influence of physical disturbance may be small.

5. Decadal changes in soil carbon and nitrogen under a range of irrigation and phosphorus fertilizer treatments

• Authors:
  • Mudge, P. L.
  • Pronger, J.
  • Dodd, M. B.
  • Schipper, L. A.
  • Moss, R. A.
  • Upsdell, M.
• Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
• Volume: 77
• Issue: 1
• Year: 2013
• Summary: We determined decadal changes in soil carbon (C) and nitrogen (N) due to different irrigation regimes and phosphorus fertilization of pastures. Archived soil samples (0-75 mm) collected annually from two long-term trials in New Zealand were analyzed for %C and %N from three P input treatments (ranging from 0 to 376 kg superphosphate ha-1 yr-1, 1952-2009) and three irrigation treatments (unirrigated and irrigated when soil moisture content fell below either 10 or 20%, 1959-2002). In the fertilizer trial, soil C increased linearly from 2.7 to 4.2%, and there was no difference in rates of increase in C between treatments, despite much greater aboveground production when P was added. This lack of difference was attributed to higher stocking rates on treatments with higher production, and to the possibility that root inputs (which differed less between treatments) was a more important control of soil C accumulation. Nitrogen (%) was lower in the unfertilized than fertilized treatments due to lower clover N fixation, which was constrained by P availability. Soil C (%) was significantly greater in the unirrigated treatment than the irrigated treatments throughout the trial. Aboveground production was much greater in the irrigated than dryland treatment but root biomass was lower. Irrigation must have increased C and N losses, possibly via increased respiration rates during seasonally dry periods. Our study showed that P fertilizer application did not result in an increase in surface soil C and that flood irrigation resulted in a constrained increase in surface soil C content.

6. Conservation tillage systems: a review of its consequences for greenhouse gas emissions

• Authors:
  • Smith, P.
  • Williams, M.
  • Forristal, D.
  • Lanigan, G.
  • Osborne, B.
  • Abdalla, M.
  • Jones, M. B.
• Source: Soil Use and Management
• Volume: 29
• Issue: 2
• Year: 2013
• Summary: Conservation tillage (CT) is an umbrella term encompassing many types of tillage and residue management systems that aim to achieve sustainable and profitable agriculture. Through a global review of CT research, the objective of this paper was to investigate the impacts of CT on greenhouse gas (GHG) emissions. Based on the analysis presented, CT should be developed within the context of specific climates and soils. A number of potential disadvantages in adopting CT practices were identified, relating mainly to enhanced nitrous oxide emissions, together with a number of advantages that would justify its wider adoption. Almost all studies examined showed that the adoption of CT practices reduced carbon dioxide emissions, while also contributing to increases in soil organic carbon and improvements in soil structure.

7. Climate regulation in New Zealand: contribution of natural and managed ecosystems.

• Authors:
  • Dymond, J. R.
  • McNeill, S.
  • Andrew, R. M.
  • Kirschbaum, M. U. F.
  • Ausseil, A. G. E.
  • Carswell, F.
  • Mason, N. W. H.
• Source: Ecosystem services in New Zealand: conditions and trends
• Year: 2013
• Summary: This chapter reviews all stocks and fluxes of carbon in New Zealand, and reviews biophysical regulation through surface albedo. The terrestrial environment provides a climate-regulation service by assimilating, transforming, and adjusting to emissions of greenhouse gases that could otherwise lead to undesirable changes in global climate. Quantifying this service requires accounting for both stocks and flows. While greenhouse gas emissions and removals are reported in the national inventory, this inventory accounts only for human-induced changes in greenhouse gases, and omits some natural processes and ecosystems; for example, indigenous forest and scrub are not included but represent the largest biomass carbon pool in New Zealand. Emissions are mainly attributed to the energy and agricultural sectors, while removals come from exotic forestry and natural shrubland regeneration. Erosion plays a role as a carbon sink through natural regeneration of soil carbon on slopes. Biophysical regulation occurs through absorption or reflection of solar radiation (albedo). Forests tend to absorb more radiation than crops or pasture, thus contributing to a lesser extent to global warming. Government currently provides some mechanisms to incentivise sustainable land management in favour of increased forest area on lands unsuitable for agriculture. However, carbon stocks are also at risk of being lost through degradation of natural ecosystems, and this requires active management and mitigation strategies.

8. Quantifying the climate-change consequences of shifting land use between forest and agriculture

• Authors:
  • Thakur, K. P.
  • Tate, K. R.
  • Saggar, S.
  • Kirschbaum, M. U. F.
  • Giltrap, D. L.
• Source: Science of The Total Environment
• Volume: 465
• Issue: November
• Year: 2013
• Summary: Land-use change between forestry and agriculture can cause large net emissions of carbon dioxide (CO2), and the respective land uses associated with forest and pasture lead to different on-going emission rates of methane (CH4) and nitrous oxide (N2O) and different surface albedo. Here, we quantify the overall net radiative forcing and consequent temperature change from specified land-use changes. These different radiative agents cause radiative forcing of different magnitudes and with different time profiles. Carbon emission can be very high when forests are cleared. Upon reforestation, the former carbon stocks can be regained, but the rate of carbon sequestration is much slower than the rate of carbon loss from deforestation. A production forest may undergo repeated harvest and regrowth cycles, each involving periods of C emission and release. Agricultural land, especially grazed pastures, have much higher N2O emissions than forests because of their generally higher nitrogen status that can be further enhanced through intensification of the nitrogen cycle by animal excreta. Because of its longevity in the atmosphere, N2O concentrations build up nearly linearly over many decades. CH4 emissions can be very high from ruminant animals grazing on pastures. Because of its short atmospheric longevity, the CH4 concentration from a converted pasture accumulates for only a few decades before reaching a new equilibrium when emission of newly produced CH4 is balanced by the oxidation of previously emitted CH4. Albedo changes generally have the opposite radiative forcing from those of the GHGs and partly negate their radiative forcing. Overall and averaged over 100 years, CO2 is typically responsible for 50% of radiative forcing and CH4 and N2O for 25% each. Albedo changes can negate the radiative forcing by the three greenhouse gases by 20-25%. (C) 2013 Elsevier B.V. All rights reserved.

9. A multi-criteria based review of models that predict environmental impacts of land use-change for perennial energy crops on water, carbon and nitrogen cycling

• Authors:
  • Thomas,Amy R. C.
  • Bond,Alan J.
  • Hiscock,Kevin M.
• Source: Global Change Biology Bioenergy
• Volume: 5
• Issue: 3
• Year: 2013
• Summary: Reduction in energy sector greenhouse gas GHG emissions is a key aim of European Commission plans to expand cultivation of bioenergy crops. Since agriculture makes up 1012% of anthropogenic GHG emissions, impacts of land-use change must be considered, which requires detailed understanding of specific changes to agroecosystems. The greenhouse gas (GHG) balance of perennials may differ significantly from the previous ecosystem. Net change in GHG emissions with land-use change for bioenergy may exceed avoided fossil fuel emissions, meaning that actual GHG mitigation benefits are variable. Carbon (C) and nitrogen (N) cycling are complex interlinked systems, and a change in land management may affect both differently at different sites, depending on other variables. Change in evapotranspiration with land-use change may also have significant environmental or water resource impacts at some locations. This article derives a multi-criteria based decision analysis approach to objectively identify the most appropriate assessment method of the environmental impacts of land-use change for perennial energy crops. Based on a literature review and conceptual model in support of this approach, the potential impacts of land-use change for perennial energy crops on GHG emissions and evapotranspiration were identified, as well as likely controlling variables. These findings were used to structure the decision problem and to outline model requirements. A process-based model representing the complete agroecosystem was identified as the best predictive tool, where adequate data are available. Nineteen models were assessed according to suitability criteria, to identify current model capability, based on the conceptual model, and explicit representation of processes at appropriate resolution. FASSET, ECOSSE, ANIMO, DNDC, DayCent, Expert-N, Ecosys, WNMM and CERES-NOE were identified as appropriate models, with factors such as crop, location and data availability dictating the final decision for a given project. A database to inform such decisions is included.

10. Effect of biochar on soil physical properties in two contrasting soils: An Alfisol and an Andisol

• Authors:
  • Camps-Arbestain, M.
  • Herath, H. M. S. K.
  • Hedley, M.
• Source: GEODERMA
• Volume: 209
• Year: 2013
• Summary: Improving soil physical properties by means of biochar application has been proposed in recent publications. The objective of this study was to investigate to what extent the addition of corn stover (CS) and biochars produced from the pyrolysis of corn stover feedstock (CS) at 350 and 550 degrees C temperatures (CS-350, CS-550) affected aggregate stability, volumetric water content (theta(V)), bulk density, saturated hydraulic conductivity (Ks) and soil water repellency of specific soils. Organic amendments (CS, CS-350, CS-550) were incorporated into a Typic Fragiaqualf (TK) and a Typic Hapludand (EG) soils at the rate of 7.18 t C ha(-1), which corresponded to 17.3, 11.3 and 10.0 t biochar ha(-1) for the CS, CS-350 and CS-550 treatments, respectively. After 295 d of incubation (1295), soils were sampled as (i) undisturbed samples for bulk density and Ks; and (ii) mildly disturbed samples for theta(V) (at -15, -1, -0.3, -0.1, -0.08, -0.06, -0.04, and -0.02 bar), aggregate stability and soil water repellency. The theta(V) at time 0 (TO) was also determined at -15, -1 and -0.3 matric potentials for the different treatments. Biochar application significantly increased (P < 0.05) aggregate stability of both soils, the effect of CS-550 biochar being more prominent in the TK soil than that in the EG soil, and the reverse pattern being observed for the CS-350 biochar. Biochar application increased the By at each matric potential although the effect was not always significant (P < 0.05) and was generally more evident in the TK soil than that in the EG soil, at both T0 and T295. Biochar addition significantly (P < 0.05) increased the macroporosity (e.g., increase in theta(V) at -0.08 to 0 bar) in the TK soil and also the mesoporosity in the EG soil (e.g., increase in theta(V) from -1 to -0.1 bar). Both biochars significantly increased (P < 0.05) the Ks of the TIC soil, but only CS-350 biochar significantly increased (P < 0.05) the Ks in the EG soil. Biochar was not found to increase the water repellency of these soils. Overall results suggest that these biochars may facilitate drainage in the poorly drained TIC soil. However, the present results are biochar-, dose- and soil-specific. More research is needed to determine changes produced in other biochar, dose and soil combination, especially under field conditions.