Xubo Zhang

Simulation of nitrous oxide emissions at field scale using the SPACSYS model.

Nitrous oxide emitted to the atmosphere via the soil processes of nitrification and denitrification plays an important role in the greenhouse gas balance of the atmosphere and is involved in the destruction of stratospheric ozone. These processes are controlled by biological, physical and chemical factors such as growth and activity of microbes, nitrogen availability, soil temperature and water availability. A comprehensive understanding of these processes embodied in an appropriate model can help develop agricultural mitigation strategies to reduce greenhouse gas emissions, and help with estimating emissions at landscape and regional scales. A detailed module to describe the denitrification and nitrification processes and nitrogenous gas emissions was incorporated into the SPACSYS model to replace an earlier module that used a simplified first-order equation to estimate denitrification and was unable to distinguish the emissions of individual nitrogenous gases. A dataset derived from a Scottish grassland experiment in silage production was used to validate soil moisture in the top 10 cm soil, cut biomass, nitrogen offtake and N2O emissions. The comparison between the simulated and observed data suggested that the new module can provide a good representation of these processes and improve prediction of N2O emissions. The model provides an opportunity to estimate gaseous N emissions under a wide range of management scenarios in agriculture, and synthesises our understanding of the interaction and regulation of the processes.

Sustainable grassland systems: a modelling perspective based on the North Wyke Farm Platform

Summary The North Wyke Farm Platform (NWFP) provides data from the field‐ to the farm‐scale, enabling the research community to address key issues in sustainable agriculture better and to test models that are capable of simulating soil, plant and animal processes involved in the systems. The tested models can then be used to simulate how agro‐ecosystems will respond to changes in the environment and management. In this study, we used baseline datasets generated from the NWFP to validate the Soil‐Plant‐Atmosphere Continuum System (SPACSYS) model in relation to the dynamics of soil water content, water loss from runoff and forage biomass removal. The validated model, together with future climate scenarios for the 2020s, 2050s and 2080s (from the International Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES): medium (A1B) and large (A1F1) emission scenarios), were used to simulate the long‐term responses of the system with three contrasting treatments on the NWFP. Simulation results demonstrated that the SPACSYS model could estimate reliably the dynamics of soil water content, water loss from runoff and drainage, and cut biomass for a permanent sward. The treatments responded in different ways under the climate change scenarios. More carbon (C) is fixed and respired by the swards treated with an increased use of legumes, whereas less C was lost through soil respiration with the planned reseeding. The deep‐rooting grass in the reseeding treatment reduced N losses through leaching, runoff and gaseous emissions, and water loss from runoff compared with the other two treatments.

A synthetic analysis of greenhouse gas emissions from manure amended agricultural soils in China

Application of manure has been recommended as an effective strategy to to mitigate climate change. However, the magnitude of greenhouse gases emission derived by application of manure to agricultural soils across environmental conditions still remains unclear. Here, we synthesized data from 379 observations in China and quantified the responses of soil nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) emissions to manure (Org-M) in comparison to chemical fertilizers (Min-F) or non-fertilizers (Non-F). The results showed that N2O, CO2 and CH4 emissions were significantly affected by Org-M compared to Min-F (percentage change: −3, +15 and +60%, P < 0.05) and Non-F (percentage change: +289, +84 and +83%, P < 0.05), respectively. However, at the same amount of total N input, Org-M decreased soil N2O emission by 13% and CH4 emission by 12%, and increased soil CO2 emission by 26% relative to Min-F in upland soils. For paddy soils, N2O, CO2 and CH4 emissions differed by −3%, −36% and +84% between Org-M and Min-F (i.e., Org-M minus Min-F). Thus, practices such as application of manure instead of chemical fertilizer and decreasing nitrogen input rate need to be highly considered and optimized under different soils and climate conditions to mitigate GHGs emission in China.

Addition of nitrogen enhances stability of soil organic matter in a temperate forest

Physicochemical protection of soil carbon provided by soil aggregates is critical to carbon (C) sequestration in terrestrial ecosystems. However, the stability of soil organic matter (SOM) in terrestrial ecosystems in response to atmospheric nitrogen (N) deposition is unclear. In this study, N was added to a forest soil dominated by deciduous trees on Changbai Mountain, China, at three different rates (0, 25 and 50 kg N ha−1 year−1) from 2007 to 2012. Its effect on C content and stabilization was evaluated by soil fractionation and stable isotope (δ13C) analyses. The results showed that large macroaggregates (2–8 mm) decreased and small macroaggregates (0.25–2 mm) increased with increasing rates of N addition, whereas soil C content remained unchanged. Irrespective of the N treatments, the C content of soil organic matter (SOM) fractions differed significantly between large and small macroaggregates, which suggests that the size of aggregate classes regulates C content in the SOM fractions. A slight increase in the C content of microaggregates within macroaggregates (Mm) and that of silt and clay fractions was recorded with the addition of N at 50 kg N ha−1 year−1. This increase also occurred in the silt and clay fraction within microaggregates (Intra-SC). Unprotected C (comprising the free light fraction (Free-LF) and coarse particulate organic matter (CPOM)) accounted for 18.9% only of the total C and decreased in response to the addition of N. The δ13C signature and C/N ratios obtained for SOM fractions showed that newly formed C was transferred from POM to Intra-SC. Overall, our results suggested that long-term addition of N might promote stabilization of C by increasing small macro- and micro-aggregation within macroaggregates in temperate forest soil. Highlights Investigated stability of soil organic matter in response to long-term N addition in a deciduous forest. Physicochemical protection of soil organic matter by aggregates changed after N addition. Soil organic carbon in microaggregates within macroaggregates increased with N addition. Long-term N addition might promote C stabilization in temperate forest soil.

Experimental observation of the Cu-rich phase in nanocrystalline Fe73.5Cu1Mo3Si13.5B9 alloy

Strong experimental evidence reveals that we have found a new crystalline Cu-rich phase with a size of 4-5 nm in nanocrystalline Fe73.5SCu1Mo3Si13.5B9 alloy at optimum magnetic stage. Experimental work was carried out using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The Cu-rich phase possesses f.c.c. structure and exists randomly in orientation. Its volume fraction and Cu content increase as the annealing temperature is increased, while its size increases slightly. When the annealing temperature increases to 600 degrees C, the size and volume fraction of Cu-rich phase reach 5.5 nm and 2.5%, respectively; at the same time, its lattice parameter is 0.3620 nm

Long-term straw decomposition in agro-ecosystems described by a unified three-exponentiation equation with thermal time

Understanding drivers of straw decomposition is essential for adopting appropriate management practice to improve soil fertility and promote carbon (C) sequestration in agricultural systems. However, predicting straw decomposition and characteristics is difficult because of the interactions between many factors related to straw properties, soil properties, and climate, especially under future climate change conditions. This study investigated the driving factors of straw decomposition of six types of crop straw including wheat, maize, rice, soybean, rape, and other straw by synthesizing 1642 paired data from 98 published papers at spatial and temporal scales across China. All the data derived from the field experiments using little bags over twelve years. Overall, despite large differences in climatic and soil properties, the remaining straw carbon (C, %) could be accurately represented by a three-exponent equation with thermal time (accumulative temperature). The lignin/nitrogen and lignin/phosphorus ratios of straw can be used to define the size of labile, intermediate, and recalcitrant C pool. The remaining C for an individual type of straw in the mild-temperature zone was higher than that in the warm-temperature and subtropical zone within one calendar year. The remaining straw C after one thermal year was 40.28%, 37.97%, 37.77%, 34.71%, 30.87%, and 27.99% for rice, soybean, rape, wheat, maize, and other straw, respectively. Soil available nitrogen and phosphorus influenced the remaining straw C at different decomposition stages. For one calendar year, the total amount of remaining straw C was estimated to be 29.41 Tg and future temperature increase of 2 °C could reduce the remaining straw C by 1.78 Tg. These findings confirmed the long-term straw decomposition could be mainly driven by temperature and straw quality, and quantitatively predicted by thermal time with the three-exponent equation for a wide array of straw types at spatial and temporal scales in agro-ecosystems of China.