Cotton strip assay detects soil microbial degradation differences among crop rotation and tillage experiments on Vertisols.

The cotton strip assay (CSA) is a simple and inexpensive method of evaluating management effects on soil microbial decomposition. The average loss of tensile strength of cotton strips buried 3 to 35 days in soils from two long-term tillage and crop-rotation experiments was of the order: cotton-wheat rotation > minimum-tillage cotton monoculture > maximum-tillage cotton monoculture. The study suggests CSA can be an effective indicator to delineate microbial activity, soil organic carbon or crop biomass as influenced by agricultural practices in cotton fields.

Perennial pastures reduce nitrous oxide emissions in mixed farming systems in a semi-arid environment.

Perennial pastures play a crucial role in mixed farming systems by supplying feed for livestock, restoring soil fertility, reducing deep drainage, providing an opportunity to manage herbicide-resistant weeds and breaking soil-borne disease cycles. However, to our knowledge there is no data on the role of perennial pastures in mitigating N2O emissions from the phased crop rotations in semi-arid environments. Two 4-year field experiments were conducted in a semi-arid environment in southern Australia to (a) evaluate the role of perennial pastures in mitigating N2O emissions in mixed farming systems, and (b) compare the cumulative N2O emissions from different pasture mixes. Results showed that the annual N2O emissions were 31% lower from chicory-based pastures and 12-17% lower from perennial grass-based pastures compared with lucerne-based pastures. During the pasture phase, actively growing pastures kept N2O emissions at a relatively low level (59 g N2O-N ha-1 year-1), but N2O emissions increased significantly upon termination of the pastures. Results showed that the N2O emitted during the summer (December to February) after the pastures were terminated accounted for 70% of the total N2O emissions in the final pasture year. Furthermore, perennial grass and chicory-based pastures were highly productive during favorable conditions, leading to a low N2O emission intensity. It is suggested that emphasis be placed on utilizing highly persistent species to foster a longer and more productive pasture phase, and to manage N-supply in the transition between pasture and crop phases as this is where the greatest risk of N2O emission exists.

Tail-drain sediments are a potential hotspot for nitrous oxide emissions in furrow-irrigated Vertisols used to grow cotton: A laboratory incubation study.

The impacts of soil properties and urea fertigation on nitrous oxide (N2 O) emissions from uncropped areas of furrow-irrigated Vertisol paddocks are unknown. We sampled soils from the head-ditch end (upslope) and sediments from the tail-drain end (downslope) of 10 Vertisols under irrigated cotton (Gossypium hirsutum L.) production in northeastern Australia. Four replicates of each sample were incubated in open-top polyvinyl chloride (PVC) chambers at 25 ± 2°C for 25 d. Nitrous oxide emissions were measured periodically after simulated irrigations on Days 0 and 15 with either water or, for soils, urea solution. Compared with the soils, sediments were enriched in silt, total organic carbon (TOC), total nitrogen (TN), ammonium N, and dissolved organic C (DOC) but had lower pH and sand content. Sediments emitted more N2 O than soils from the same paddocks after water irrigations. Nitrous oxide fluxes varied by two orders of magnitude between paddocks, with most variation explained by baseline nitrate N, TOC, pH (inversely), and sand content. Urea solution applied to soils at 30 kg N ha-1 irrigation-1 increased N2 O emitted, but more so after the second irrigation. In irrigated cotton systems, tail-drain sediments are a potential hotspot for N2 O emissions that has not previously been documented.

The global warming potential of straw-return can be reduced by application of straw-decomposing microbial inoculants and biochar in rice-wheat production systems.

Straw-return methods that neither negatively impact yield nor bring environmental risk are ideal patterns. To attain this goal, it is necessary to conduct field observation to evaluate the environmental influence of different straw-return methods. Therefore, we conducted a 2-year field study in 2015-2017 to investigate the emissions of methane (CH4) and nitrous oxide (N2O) and the changes in topsoil (0-20 cm) organic carbon (SOC) density in a typical Chinese rice-wheat rotation in the Eastern China. These measurements allowed a complete greenhouse gas accounting (net GWP and GHGI) of five treatments including: FP (no straw, plus fertilizer), FS (wheat straw plus fertilizer), FB (straw-derived biochar plus fertilizer), FSDI (wheat straw with straw-decomposing microbial inoculants plus fertilizer) and CK (control: no straw, no fertilizer). Average annual SOC sequestration rates were estimated to be 0.20, 0.97, 1.97 and 1.87 t C ha-1 yr-1 (0-20 cm) for the FP, FS, FB and FSDI treatments respectively. Relative to the FP treatment, the FS and FSDI treatments increased CH4 emissions by 12.4 and 17.9% respectively, but decreased N2O emissions by 19.1 and 26.6%. Conversely, the FB treatment decreased CH4 emission by 7.2% and increased N2O emission by 10.9% compared to FP. FB increased grain yield, but FS and FSDI did not. Compared to the net GWP (11.6 t CO2-eq ha-1 yr-1) and GHGI (1.20 kg CO2-eq kg-1 grain) of FP, the FS, FB and FSDI treatments reduced net GWP by 12.6, 59.9 and 34.6% and GHGI by 10.5, 65.8 and 37.7% respectively. In rice-wheat systems of eastern China, the environmentally beneficial effects of returning wheat straw can be greatly enhanced by application of straw-decomposing microbial inoculants or by applying straw-derived biochar.

Indirect N2O emissions from groundwater under high nitrogen-load farmland in eastern China.

Current estimates of global indirect N2O emissions are based on a relatively small dataset and remain a major source of uncertainly in the global N2O budget. Nitrogen (N)-enriched groundwater from agricultural fields may act as an important source of indirect N2O emissions as it discharges to adjacent watershed areas. During 2015-2017, dissolved N2O concentrations in groundwater were measured and indirect N2O emission factors (EF5g) calculated under three typical high-N land-use types (vineyard, vegetable field and paddy field) in eastern China. The average dissolved N2O concentrations in groundwater were 58.1 ±â€¯40.4, 18.5 ±â€¯11.5 and 0.72 ±â€¯0.27  µg N L-1 for vineyard, vegetable field and paddy field, respectively. The dissolved N2O was over-saturated and was therefore a net source of N2O to the atmosphere. The indirect N2O emission factors (EF5g) of vineyard (0.0091) and vegetable (0.0092) fields were much higher than the current Intergovernmental Panel on Climate Change (IPCC) default value of 0.0025 which indicated that these land-uses may have led to indirect N2O emissions from the underlying groundwater. In contrast, the EF5g of the paddy field (0.0019) was slightly lower than the default EF5g proposed by IPCC (2006) and contributed minimal indirect N2O emissions to the atmosphere. However, the current IPCC method may have overestimated the contribution of groundwater N2O to the global N cycle because it took residual but not initial groundwater NO3--N concentration into account when calculating EF5g. Therefore, we proposed the adoption of an improved method for calculating the EF5g and compared it to the current IPCC (2006) method using data from the present study and other published data. The results of the comparison showed that the improved method was more scientifically appropriate measurement for calculating EF5g.

A comparison of methane and nitrous oxide emissions from inland mixed-fish and crab aquaculture ponds.

Inland aquaculture ponds in China collectively cover 2.57 million ha, so emissions of the greenhouse gases methane (CH4) and nitrous oxide (N2O) from these ponds may constitute a significant contribution to global warming. During 2016 and 2017, CH4 and N2O fluxes and a range of pond-water and sediment properties were measured in replicated (n = 4) "mixed-fish" and "crab" aquaculture ponds in southeast China. Annual CH4 and N2O emissions were 64.4 kg C ha-1 and 2.99 kg N ha-1, respectively, from the "mixed-fish" ponds, and 51.6 kg C ha-1 and 3.32 kg N ha-1, respectively, from the "crab" ponds. Emission differences between pond types were significant (p < 0.05) for both gases. CH4 fluxes from the "crab" ponds were significantly increased by the presence of aquatic vegetation, but N2O fluxes were not affected. Emissions of N2O were estimated to be 0.54% and 0.71% of the total nitrogen input (in the feed) for the "mixed-fish" and "crab" ponds, respectively. The net economic benefit-scaled sustained-flux global warming potential (NEB-scaled SGWP) of the "crab" ponds was 61.6% higher (p < 0.05) than that of the "mixed-fish" pond. Our CH4 and N2O emissions results suggest that aquaculture ponds can be important contributors to regional and national GHG inventories, with aquaculture type an important factor in total GHG impact. Further CH4 and N2O flux research is needed at aquaculture ponds across China to better establish the range of potential GHG impacts, and to confirm the importance of the influencing factors identified in this study.

Modeling the impact of crop rotation with legume on nitrous oxide emissions from rain-fed agricultural systems in Australia under alternative future climate scenarios.

Limited information exists on potential impacts of climate change on nitrous oxide (N2O) emissions by including N2-fixing legumes in crop rotations from rain-fed cropping systems. Data from two 3-yr crop rotations in northern NSW, Australia, viz. chickpea-wheat-barley (CpWB) and canola-wheat-barley (CaWB), were used to gain an insight on the role of legumes in mitigation of N2O emissions. High-frequency N2O fluxes measured with an automated system of static chambers were utilized to test the applicability of Denitrification and Decomposition model. The DNDC model was run using the on-site observed weather, soil and farming management conditions as well as the representative concentration pathways adopted by the Intergovernmental Panel on Climate Change in its Fifth Assessment Report. The DNDC model captured the cumulative N2O emissions with variations falling within the deviation ranges of observations (0.88±0.31kgNha-1rotation-1 for CpWB, 1.44±0.02kgNha-1rotation-1 for CaWB). The DNDC model can be used to predict between modeled and measured N2O flux values for CpWB (n=390, RSR=0.45) and CaWB (n=390, RSR=0.51). Long-term (80-yr) simulations were conducted with RCP 4.5 representing a global greenhouse gas stabilization scenario, as well RCP 8.5 representing a very high greenhouse gas emission scenario based on RCP scenarios. Compared with the baseline scenarios for CpWB and CaWB, the long-term simulation results under RCP scenarios showed that, (1) N2O emissions would increase by 35-44% for CpWB and 72-76% for CaWB under two climate scenarios; (2) grain yields would increase by 9% and 18% under RCP 4.5, and 2% and 14% under RCP 8.5 for CpWB and CaWB, respectively; and (3) yield-scaled N2O-N emission would increase by 24-42% for CpWB and 46-54% for CaWB under climate scenarios, respectively. Our results suggest that 25% of the yield-scaled N2O-N emission would be saved by switching to a legume rotation under climate change conditions.

Climate and soil properties limit the positive effects of land use reversion on carbon storage in Eastern Australia.

Australia's "Direct Action" climate change policy relies on purchasing greenhouse gas abatement from projects undertaking approved abatement activities. Management of soil organic carbon (SOC) in agricultural soils is an approved activity, based on the expectation that land use change can deliver significant changes in SOC. However, there are concerns that climate, topography and soil texture will limit changes in SOC stocks. This work analyses data from 1482 sites surveyed across the major agricultural regions of Eastern Australia to determine the relative importance of land use vs. other drivers of SOC. Variation in land use explained only 1.4% of the total variation in SOC, with aridity and soil texture the main regulators of SOC stock under different land uses. Results suggest the greatest potential for increasing SOC stocks in Eastern Australian agricultural regions lies in converting from cropping to pasture on heavy textured soils in the humid regions.