Agro-ecosystems In China Research Articles

Diversity and Antibiotic Resistance of Triticale Seed-Borne Bacteria on the Tibetan Plateau.

The Tibetan Plateau is located in southwestern China. It has many important ecological functions, such as biodiversity protection, and is an important grassland agroecosystem in China. With the development of modern agriculture and animal husbandry, antibiotics are widely used to treat humans and livestock, and antibiotics cannot be fully metabolised by both. Antibiotics eventually find their way into the environment, affecting other parts of grassland agroecosystems. Triticale (Triticosecale wittmack) is an artificial hybrid forage that can be used for both grain and forage. This study revealed the diversity of seedborne bacteria in triticale on the Tibetan Plateau and the resistance of the bacteria to nine antibiotics. It identified 37 representative strains and successfully obtained the spliced sequences of 36 strains of the bacteria, which were clustered into 5 phyla and 16 genera. Among them, 18 strains showed resistance to at least one of the 9 antibiotics, and the colony-forming unit (CFU) abundance of antibiotic-resistant bacteria (ARB) accounted for 45.38% of the total samples. Finally, the bacterial motility and biofilm formation ability were measured, and their correlation with bacterial resistance was analysed. The results showed that the bacterial resistance did not have an absolute positive correlation with the motility or biofilm formation ability.

Plastic film mulching increases crop yields and reduces global warming potential under future climate change

Identifying suitable cropping systems and planting areas with high yields and low greenhouse gas (GHG) emissions to adapt to climate change is essential for sustainable agricultural development. The DeNitrification-DeComposition (DNDC) model and the Coupled Model Inter-comparison Project Phase 6 (CMIP6) dataset were used to evaluate the impact of climate scenarios on the crop yields and global warming potential (GWP) of maize, winter wheat, and potato under plastic film mulching (PM) and without mulching (CK) systems on the Loess Plateau for 2020–2100. The result showed that the DNDC model could simulate crop yields and carbon dioxide, nitrous oxide, and methane emissions (adjusted R2 > 0.55, normalized root mean square error (nRMSE) < 0.32). Under multiple emission scenarios, the yields of maize and winter wheat increased linearly with time (p < 0.05), the GWP decreased linearly with time (p < 0.05), and the coefficients of variation of both were lower for the PM than CK, indicating that the impact of future climate change on PM system was small and can achieve synergy between food security and carbon reduction. The results of regional divergence characteristics suggested that areas with precipitation below 400 mm were suitable for maize cultivation, especially the PM system, while areas with precipitation above 400 mm were suitable for winter wheat cultivation – both of which could achieve the goals of high yield and low GHG emissions. This study presents an overview of spatiotemporal changes in production and ecological effects, providing a basis for developing agricultural management practices and cultivation areas to address climate change, and could promote the development of dryland agroecosystems in China in a green and sustainable direction.

Impact of Future Climate Change on the Yield of Spring Maize and the Effect of Resilient Measures on it Under Different Parameters in the Major Agro-Ecosystems in China and Kenya

Impact of Future Climate Change on the Yield of Spring Maize and the Effect of Resilient Measures on it Under Different Parameters in the Major Agro-Ecosystems in China and Kenya

Effect of straw return on soil respiration in dryland agroecosystem of China: A meta-analysis

In agroecosystems, straw return is considered an important agricultural management practice influencing soil respiration. However, the impact of straw return on soil respiration is equivocal and the underlying mechanisms underpinning any responses remain unclear. To address this, we synthesized 86 recently published papers on dryland agroecosystems in China, which comprise approximately 74% of the agricultural land area, using a meta-analysis approach and explored the influence of straw return on soil respiration and the underlying mechanisms involved. Straw return resulted in a 13.5% increase in soil respiration, a 9.4% increase in soil moisture, a 10.4% increase in crop yield, a 18.9% increase in SOC (soil organic carbon), and a 2.6% decrease in soil temperature. Compared to conventional tillage without straw return treatment, the increase in soil respiration in response to straw return was closely related to modifications in soil temperature, soil moisture, SOC, and crop yield (P < 0.05). The contribution of the different drivers to increases in soil respiration in response to straw return showed a trend of crop yield > soil temperature > SOC > soil moisture. In addition, straw mulching, crop planting system, tillage method, and fertilization modified the effect of straw return on soil respiration. The increase in soil respiration was less when straw was used as a mulch (12.9%), compared to when it was incorporated into the soil (18.8%). The cropping system also influenced the effect of straw return on soil respiration and was increased by 21.1% in inter-crops, and by 17.3% and 11.0% in monocultures and rotations treatments, respectively. Our results also showed that the effect of straw return on soil respiration was larger in deep tillage treatments than in shallow tillage treatments (26.9% vs.18.7%). In addition, the effect of straw return on soil respiration was also larger in fertilized treatment compared to unfertilized one (12.7% vs. 0.5%). However, this depended on the amount of nitrogen fertilizer applied rates and was higher (14.8%) with low (<300 kg ha−1) application rates compared to high (≧300 kg ha−1) ones (2.5%). Therefore, in dryland agroecosystems in China, biological factors, especially those related to crop yield, may be a more important factor regulating the effect of straw return on soil respiration. However, straw mulching, crop planting system, tillage method, and fertilization can modify the effect of straw return on soil respiration.

A Meta-analysis of No-tillage Effects on Greenhouse Gas Emissions from Wheat-based Rotation Cropping Agroecosystem in China

A Meta-analysis of No-tillage Effects on Greenhouse Gas Emissions from Wheat-based Rotation Cropping Agroecosystem in China

A biophysical model to simulate seasonal variations of soil respiration in agroecosystems in China

Characterizing the seasonal patterns of soil respiration using a biophysical model is crucial for understanding the mechanisms of the terrestrial carbon (C) cycle. We developed a biophysical soil respiration model including four submodels that were associated with the functions of soil temperature, moisture, leaf area index (LAI), and soil organic C, and the model parameters were determined and calibrated. The modeling reproducibility was examined in various crop fields at our study site, and the modeling performance was also validated in twenty-five other agroecosystems in China. The monthly and annual soil respiration was estimated using the model, and the modeling uncertainty was evaluated. The results showed that the soil respiration model had good modeling reproducibility in various crop fields at our site. The measured soil respiration in the different agroecosystems in China validated our model well. The R2, root mean squared error (RMSE), model efficiency (ME), and mean absolute error (MAE) were within the ranges of 0.449‒0.932, 0.526‒1.465 μmol m−2 s−1, 0.176‒0.796, and 0.312‒1.377 μmol m−2 s−1, respectively, across the twelve agroecosystem sites for validation. The measured soil respiration was significantly (P < 0.001) correlated with the modeled soil respiration across all twenty-six validation sites. Adding LAI significantly improved the modeling of soil respiration when the performance of the model (with LAI) vs. that without LAI was compared. The modeled monthly soil respiration was within the range of 0.016 ± 0.001‒0.117 ± 0.006 Pg C mo−1 in 2010 in agroecosystems in China. The black soils in Northeast China are fertile, which resulted in high temperature sensitivity and a clear increasing tendency of soil respiration from winter to summer in 2010 in agroecosystems in Northeast China. The established biophysical soil respiration model was proven to be effective for characterizing the temporal variations of soil respiration in various agroecosystems in China.

Climate Change Impacts on Agroecosystems in China: Processes, Mechanisms and Prospects

Climate Change Impacts on Agroecosystems in China: Processes, Mechanisms and Prospects

Optimizing low-cost sampling of pollinator insects in oilseed rape fields

Insects are key pollinators to ecosystem function, but much work remains to determine the most cost-effective, reliable scheme to monitor them. Pan traps (PT) and flight interception traps (FIT) are two of the most popular insect sampling methods used. However, their relative sampling performance and cost is poorly known for agroecosystems in China. We conducted a study across 18 oilseed rape fields in smallholder farmland in Zhejiang, China using these two traps. Our results showed that a single FIT had a greater sampling efficiency (more individuals and higher species richness) than a single PT, but controlling for cost, four PTs (the cost for four PTs is close to one FIT) showed a greater sampling efficiency than FITs. PTs collected more small-bodied individuals while FITs and PTs did not significantly differ in terms of monitoring pollinator insects with large body size. When exploring whether semi-natural habitat embedded in the agricultural landscape affected these results, results from both trap types shows that semi-natural habitat had a significant positive impact on wild pollinator diversity and rarefied species richness. Future studies that examine the effects of agricultural landscape on the wild pollinator community should combine PTs with netting or other active methods for long-term wild pollinator monitoring strategies.

秸秆还田对中国农田土壤节肢动物数量及多样性影响的整合分析

PDF HTML阅读 XML下载 导出引用 引用提醒 秸秆还田对中国农田土壤节肢动物数量及多样性影响的整合分析 DOI: 10.5846/stxb202111053105 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 江苏省自然科学基金项目（BK20200552）；国家自然科学基金项目（32001181）；江苏省博士后基金项目（2020Z201）；南京农业大学中央高校基本业务费项目（KJQN202113） Impacts of straw returning on the number and diversity of soil arthropods in China: A meta-analysis Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:秸秆还田是提高土壤生物数量和多样性的有效手段，但土壤节肢动物对秸秆还田的响应尚未明确。搜集2005到2020年国内有关秸秆还田对农田土壤节肢动物数量及多样性影响的25篇田间试验文献，分别获得230对土壤节肢动物数量数据和112对土壤节肢动物多样性数据，并采用整合分析方法探究不同气候类型、土层深度、种植制度、秸秆还田量、还田方式及还田时间下秸秆还田对农田土壤节肢动物数量及多样性的影响。结果表明，与不还田相比，秸秆还田总体上显著增加了农田土壤节肢动物的数量，但在亚热带季风气候区或还田时间大于5 a时，秸秆还田对节肢动物数量的增加效应则不显著；此外，秸秆还田对土壤节肢动物数量的促进作用还受到节肢动物体型的影响，秸秆还田显著增加土壤中小型节肢动物的数量，特别是蜱螨目类土壤节肢动物，但是对大型土壤节肢动物的促进作用并不显著。秸秆还田总体上也提高了农田土壤节肢动物的多样性，特别是在温带季风气候、年均温小于5℃、年均降水量小于600 mm、秸秆还田量大于10000 kg/hm2、轮作以及还田时间大于5 a这些条件下，秸秆还田能显著提高土壤节肢动物的多样性。回归分析结果显示随着秸秆还田时间的增加，土壤节肢动物数量的增加率显著降低，而随着秸秆还田量的增加，节肢动物数量的增加率则显著升高；节肢动物多样性的增加率随着年均降水量的增加显著降低，而随着秸秆还田时间和还田量的增加显著升高。以上结果表明，秸秆还田有助于提高农田土壤节肢动物的数量和多样性，但此效应会受到气候因子及农田管理方式的影响。 Abstract:Straw returning is an effective way to enhance the number and diversity of soil organisms, but the responses of soil arthropods to straw returning are still unclear. In this study, we conducted a meta-analysis involving 230 comparisons of soil arthropod number and 112 comparisons of soil arthropod diversity collected from 25 related literatures during 2005-2020. The objectives of this study are to assess the effects of straw returning on the number and diversity of soil arthropods in agroecosystems of China, as well as the variation of these effects under different climates, soil depths, cropping systems, straw returning amounts, straw returning methods and time. The results showed that straw returning significantly increased the number of soil arthropods compared with no straw returning, except the studies conducted at subtropical monsoon climate regions, or the time of straw returning was more than 5 a. In addition, the promotional effect of straw returning on soil arthropod number was also affected by the size of arthropods, with straw returning significantly increasing the number of small and medium-sized soil arthropods, especially acari, rather than large soil arthropods. Straw returning also had a tendency to increase the diversity of soil arthropods, and this effect was significant under the conditions of temperate monsoon climates, mean annual temperature less than 5℃, mean annual precipitation less than 600 mm, rotation cropping, amount of straw returning more than 10000 kg/hm2 and straw returning time more than 5 a. The regression analysis showed that the increased rate of soil arthropod number under straw returning significantly decreased with straw returning time, but it significantly increased with straw returning amount; the increased rate of soil arthropod diversity under straw returning decreased significantly with mean annual precipitation, but it significantly increased with straw returning amount and time. Together, these results indicated that straw returning could improve the number and diversity of soil arthropods, which could be affected by climate factors and agricultural managements. 参考文献 相似文献 引证文献

Genetic Relationships of Puccinia striiformis f. sp. tritici in Southwestern and Northwestern China.

ABSTRACTWheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a crucial disease for wheat worldwide and constantly threatens wheat production in southwestern and northwestern China, where the environment is a good fit for Pst oversummering and overwintering. However, the underlying genetic dynamics of spring epidemic Pst populations across large areas of continuous planting in the southwestern and northwestern regions are poorly understood. A total of 2,103 Pst isolates were sampled in the spring of 2019 from the two agroecosystems and grouped into three horizontal spatial scales (countywide, provincial, and regional subpopulations) and two vertical spatial scales that consisted of elevational and geomorphic subpopulations. A total of 776 multilocus genotypes were identified, with the highest genetic diversity found in the northern and Sichuan populations, particularly in the Ningxia and Sichuan Basins, while the lowest genetic diversity was found in the Yunnan and Guizhou populations. Multivariate discriminant analysis of principal components (DAPC) and STRUCTURE (STRUCTURE 2.3.4) analyses revealed variation in the genotypic compositions of the molecular groups on horizontal and vertical dimensions from north to south or vice versa and from low to high or vice versa, respectively. The regional neighbor-joining tree revealed three large spatial structures consisting of the southwestern, the northwestern, and the Xinjiang regions, while the Tibetan population connected the southwestern and northwestern regions. The isolates of the Sichuan Basin were scattered over the four quartiles by principal coordinate analysis, which indicated frequent genotype interchange with others. Greater genetic differentiation was observed between the southwestern and northwestern regions. Linkage equilibrium (P ≥ 0.05) was detected on different spatial scales, suggesting that Pst populations are using sexual reproduction or mixed reproduction (sexual and clonal reproduction) in southwestern and northwestern China.IMPORTANCE Understanding the epidemiology and population genetics of plant pathogens is crucial to formulate efficient predictions of disease outbreaks and achieve sustainable integrated disease management, especially for pathogens with migratory capability. Here, this study covers the genetic homogeneity and heterogeneity of different geographical Pst populations on broad to fine spatial scales from the key epidemic regions of the two agroecosystems in China, where wheat stripe rust occurs annually. We provide knowledge of the population genetics of Pst and reveal that, for instance, there is greater genetic diversity in northwestern China, there are close genetic relationships between Yunnan and Guizhou and between Gansu-Ningxia and Qinghai, and there are effects of altitude on genetic compositions, etc. All of these findings clarify the genetic relationships and expand the insights into the population dynamics and evolutionary mechanisms of Pst in southwestern and northwestern China, providing a theoretical basis for achieving sustainable control of wheat stripe rust in key epidemic regions.

Heterogeneity of soil bacterial and bacteriophage communities in three rice agroecosystems and potential impacts of bacteriophage on nutrient cycling

BackgroundAs genetic entities infecting and replicating only in bacteria, bacteriophages can regulate the community structure and functions of their host bacteria. The ecological roles of bacteriophages in aquatic and forest environments have been widely explored, but those in agroecosystems remains limited. Here, we used metagenomic sequencing to analyze the diversity and interactions of bacteriophages and their host bacteria in soils from three typical rice agroecosystems in China: double cropping in Guangzhou, southern China, rice–wheat rotation cropping in Nanjing, eastern China and early maturing single cropping in Jiamusi, northeastern China. Enterobacter phage-NJ was isolated and its functions on soil nitrogen cycling and effect on soil bacterial community structure were verified in pot inoculation experiments and 16S rRNA gene sequencing.ResultsSoil bacterial and viral diversity and predicted functions varied among the three agroecosystems. Genes detected in communities from the three agroecosystems were associated with typical functions: soil bacteria in Jiamusi were significantly enriched in genes related to carbohydrate metabolism, in Nanjing with xenobiotics biodegradation and metabolism, and in Guangzhou with virulence factors and scarce in secondary metabolite biosynthesis, which might lead to a significant occurrence of rice bacterial diseases. The virus community structure varies significantly among the three ecosystems, only 13.39% of the total viral species were shared by the three rice agroecosystems, 59.56% of the viral species were specific to one agroecosystem. Notably, over-represented auxiliary carbohydrate-active enzyme (CAZyme) genes were identified in the viruses, which might assist host bacteria in metabolizing carbon, and 67.43% of these genes were present in Jiamusi. In bacteriophage isolation and inoculation experiments, Enterobacter bacteriophage-NJ reduced the nitrogen fixation capacity of soil by lysing N-fixing host bacteria and changed the soil bacterial diversity and community structure.ConclusionOur results showed that diversity and function predicted of paddy soil bacteria and viruses varied in the three agroecosystems. Soil bacteriophages can affect nutrient cycling by boosting host metabolism through the carried auxiliary metabolic genes (AMGs) and lysing the host bacteria that are involved in biogeochemical cycles. These findings form a basis for better understanding bacterial and bacteriophage diversity in different rice agroecosystems, laying a solid foundation for further studies of soil microbial communities that support ecofriendly production of healthy rice.

Nitrogen losses in desert oasis agroecosystem in China estimated using a nitrogen balance approach

ABSTRACT Agriculture depends on nitrogen (N) fertilizer, but its continuous application also causes several serious ecological and environmental problems. In desert oasis farmlands, environmental issues caused by N loss from excessive chemical N application have been previously reported. However, assessed N loss from desert oasis farmland ecosystems in northwestern China is lacking. Here, we assess the effects of cropping system and fertilizer rates on N loss rate in a desert oasis farmland, based on the 5-year monitoring data of N input and output. Maize/wheat yield and biomass N showed strong interannual variations and strongly related to N fertilizer rate. Soil total N and available N in the surface soil (0–20 cm) increased slightly, and N stock in 0–100 cm exhibited an increasing trend during the experiment period in all four cropping systems. 20.1–55.1% of input N were estimated to be lost to the environment, and sandy texture in new farmlands tends to promote N loss. New reclaimed farmland with sandy texture tends to increase N loss, but maize/wheat intercropping with alfalfa can alleviate it. We concluded that the maize/wheat intercropping with alfalfa could be an effective management practice to reduce N loss and improve N fertilizer use effectivity. However, avoided land transition from desert to farmland, and thus reduced the area of new oasis farmland could be the most essential strategy to reduce N loss in the desert oasis farmland ecosystems in northwestern China.

How plastic mulching affects net primary productivity, soil C fluxes and organic carbon balance in dry agroecosystems in China

Agricultural soil management has a great potential to reduce the anthropogenic emissions of carbon (C), mainly via increasing soil organic carbon (SOC) sequestration. The global use of agricultural plastic mulches has emerged as a widespread soil management practice due to its apparent economic benefits, especially in the dry croplands of China. However, the integrated effects of plastic mulching in China’s drylands on net primary productivity (NPP) of staple crops (i.e. maize, wheat, and potato), SOC stocks, and C emissions have rarely been assessed quantitatively. We conducted a meta‒analysis of nationwide dataset and found that compared with traditional non‒mulching farming, plastic mulching on average increased national aboveground NPP by 1.41 Mg C ha−1 y−1, while it led to rising soil CO2 emissions (437 kg C ha−1 y−1 higher than non‒mulching) because of stimulated microbial metabolism, such as higher microbial biomass C and extracellular enzyme activities. Critically, plastic mulching not only enhanced crop‒sourced C inputs into the soil by 0.24 Mg C ha−1 y−1 through improving belowground NPP, but also facilitated soil CH4 absorption by 0.25 kg C ha−1 y−1 across the entire dataset. As a result, a significant increase in SOC storage under plastic mulching was estimated as 0.012 Mg C ha−1 y−1, and crop types, N input, and precipitation seems to be the strongest predictors explaining variability in mulching‒driven SOC sequestration. These results suggest that plastic mulching in dry agroecosystems can have a distinct potential to curtail the anthropogenic emissions of C through significant increases in both SOC sequestration and crop C fixation.

Accumulation and translocation of phenanthrene, anthracene and pyrene in winter wheat affected by soil water content

Polycyclic aromatic hydrocarbons (PAHs) are universal organic pollutants in the agro ecosystems in China, therefore, it is important to understand the uptake and accumulation of PAHs in crops growing on PAHs contaminated soils for human health risk assessments. Water management is a common practice to maintain high grain yields during wheat production. However, the effects of soil water content on the accumulation and translocation of PAHs in wheat are still not clear. The main objectives of the present study were to investigate the effects of soil water content on the accumulation of three selected PAHs (Σ3PAHs, phenanthrene, anthracene and pyrene) in wheat during whole plant growth stage and on translocation or remobilization of Σ3PAHs from vegetative tissues to wheat grains. Winter wheat (Triticum aestivum cv. Xiaoyan22) were grown on Σ3PAHs spiked soils maintaining 80%, 60% or 40% water-holding capacity during the whole plant growth stage. Plant samplings were performed at jointing, anthesis or maturity stage, respectively. The present study showed that grain yield and biomass of the crop increased with soil water content increasing. Transpiration rate of wheat leaf under 80% and 60% water-holding capacity treatments was significantly (p < 0.05) higher than that under 40% water-holding capacity treatment at both anthesis and filling stage. Soil water content and plant growth stage had significant (p < 0.0001) effects on concentrations of phenanthrene, anthracene and pyrene in winter wheat. When exposed to 0, 15, 60, and 150 mg kg−1 Σ3PAHs in soils, Σ3PAHs concentrations in the grains under 60% water-holding capacity treatment were 46.6%, 69.9%, 89.5% and 81.7% of those under 80% water-holding capacity treatment, respectively. The highest concentrations of Σ3PAHs in the crop were recorded at anthesis stage. The distribution of PAHs in different tissues of wheat varied among different soil water treatments and plant growth stages. The present study indicated that optimizing soil water content during winter wheat production could apparently reduce concentrations of Σ3PAHs in grains via influence root uptake of Σ3PAHs and translocation of Σ3PAHs from stem or leaf into grain, suggesting the potential of water management to cope with PAHs contamination in crops growing on PAHs contaminated soils.

Energy analysis and economic assessment of a rice-turtle-fish co-culture system

ABSTRACTRice-fish system is the first globally important agricultural heritage system (GIAHS) and could be a potential option to improve modern rice production. This paper investigates energy flows and economic profits of two rice production agroecosystems in China. Results suggest that total energy input in rice-turtle-fish co-culture (RTF) was 18,889.63 MJ ha−1, less than that of rice monoculture (RM) (20,289.44 MJ ha−1). Total energy output in RTF was 82,836.57 MJ ha−1, higher than that of RM (77,221.21 MJ ha−1). The product safety index (PSI) in RTF and RM were −0.23 and −0.77, respectively, which indicated the products safety potential in RTF was higher than that of RM. The energy sustainable development index (ESI) in RTF and RM were 9.03 and 0.66, respectively, which illustrated RTF has abundant developmental potential, while RM is more of a consuming-type ecosystem. The output/input, gross profits, and net profits in RTF were 5.17, 99,531.30 CNY, and 98,729.96 CNY, respectively, all higher than that of RM (4.58, 11,335.67 CNY and 11,034.33 CNY, respectively). Consequently, RTF has greater potential to reduce agro-chemicals, improve energy use efficiency, and increase economic profits compared to RM.

Linkage between soil organic carbon and the utilization of soil microbial carbon under plastic film mulching in a semi-arid agroecosystem in China

ABSTRACTStudying changes in soil organic carbon (SOC) pools and soil microbial C substrate utilization under plastic mulching in different seasons is of great significance for improving soil fertility and sustainable agricultural development. Based on a 2-year plastic film mulching experiment in northeastern China, we investigated the SOC, labile SOC fractions under three treatments: non-mulching (NM), autumn mulching (AM) and spring mulching (SM). The results showed that SOC decreased with soil depth under the AM and SM treatments compared with the NM treatment. The microbial biomass carbon (MBC) and dissolved organic carbon (DOC) under the AM treatment increased significantly in the 0–10 cm soil layer, by 31.2% and 27.2% (p < 0.05), respectively. The AM treatment significantly increased the utilization of amino acids and carbohydrate C sources. Redundancy analysis (RDA) indicated that MBC was the main factor influencing microbial metabolic functional diversity and accounted for the largest variation in the 0–10 cm layer. Pearson’s correlation analysis illustrated that MBC was strongly correlated with the utilization of the microbial C substrate. We suggest that AM may be an effective and sustainable management practice for improving soil quality and maintaining microbial functional diversity in semi-arid agroecosystems in this area.

Effects of long-term fertilisation on aggregates and dynamics of soil organic carbon in a semi-arid agro-ecosystem in China.

BackgroundLong-term fertilisation has a large influence on soil physical and chemical properties in agro-ecosystems. The effects on the distribution of aggregates, however, are not fully understood. We determined the dynamic change of the distribution of aggregates and soil organic carbon (SOC) content over time in a long-term field experiment established in 1998 on the Loess Plateau of China and illustrated the relationship between them.MethodsWe determined SOC content and the distribution of aggregates in nine fertiliser treatments: manure (M); nitrogen (N); phosphorus (P); M and N; M, N, and P; M and P; N and P; bare land; and an unfertilised control. These parameters were then used for a path analysis and to analyse the fractal dimension (Dv).ResultsThe organic fertiliser increased SOC content. The proportions of 0.1–0.25 mm microaggregates and 0.25–0.5 mm macroaggregates were higher and the proportion of the 0.01–0.05 mm size class of the silt + clay fraction was lower in the treatments receiving organic fertiliser (M, MN, MNP, and MP) than that in the control, indicating that the addition of organic fertiliser promoted aggregation. The distribution of aggregates characterised by their fractal dimension (Dv), however, did not differ among the treatments.DiscussionDv was strongly correlated with the proportion of the <0.002 mm size class of the silt + clay fraction that did not differ significantly among the treatments. The change in the distribution of aggregates was strongly correlated with SOC content, which could produce organic polymer binding agents to increase the proportion of larger particles. Long-term application of organic fertiliser is thus necessary for the improvement and maintenance of soil quality in semi-arid agricultural land when residues are removed.

Regional Variability of Agriculturally-Derived Nitrate-Nitrogen in Shallow Groundwater in China, 2004–2014

Increasing diffuse nitrate loading of groundwater has long been a major environmental and health concern in China, but little is known about the spatial and temporal variability of nitrate concentrations in groundwater at regional scales. The aim of this study was to assess the spatial distribution and variation of nitrate-nitrogen (NO3−-N) concentrations in groundwater. We used groundwater quality monitoring data and soil physical characteristics from 21 agro-ecosystems in China for years 2004 to 2014. The results indicated that NO3−-N concentrations were highly variable in shallow groundwater across the landscape. Over the study period, most of the NO3−-N concentrations were below the World Health Organization permissible limit for drinking water (&lt;10 mg N·L). NO3−-N concentrations in groundwater neither significantly increased nor decreased in most agro-ecosystems, but fluctuated with seasons. In addition, groundwater NO3−-N under purple soil (6.81 mg·L−1) and Aeolian sandy soil (6.02 mg·L−1) were significantly higher (p &lt; 0.05) than that under other soil types, and it was medium-high (4.49 mg·L−1) under aquic cinnamon soil. Elevated nitrate concentrations occurred mainly in oasis agricultural areas of northwestern China, where farmlands with coarse-textured soils use flood irrigation. Therefore, arid and semi-arid areas are expected to sustain high NO3−-N concentrations in groundwater. Mitigation strategies can prevent this problem, and include control of N fertilizer input, balanced fertilization, proper rotation system, adoption of improved irrigation methods, and establishment of environmental policies.

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.

Interactive effects of planting models with limited irrigation on soil water, temperature, respiration and winter wheat production under simulated rainfall conditions

The development of effective water-saving farming practices have been vitally important for increasing wheat productivity in semi-arid regions of China. Ridge-furrow (RF) rainfall harvesting is a technique for efficient consumption of precipitation that increases water accessibility to crops at critical growth stages. However, this system has not yet been characterized under simulated rainfall conditions with limited irrigation. A two-year field study was carried out from Oct 2015 to May 2017 to investigate the potential role of two planting models: (1) the RF system and (2) traditional flat planting (TF) under three levels of simulated precipitation (1:275 mm, 2: 200 mm, 3:125 mm), with two limited irrigation levels (150 mm or 75 mm). The topsoil (from 5 to 25 cm) temperature and ET were significantly higher under TF planting than in the RF system, which increased both soil moisture between (0–200 cm) and soil respiration rate during different growth stages. The RF system also regulated soil temperature and respiration rate, reduced ET (46%), and prolonged the period of water accessibility which led to exhibited fast and stable seedling establishment. The average grain yield increased by 10.6% and 12.6% for RF1150 and RF175, compared to TF1150 and TF175, and increased by 18.9% and 22.5% for RF2150 and RF275 as compared to TF2150 and TF275, while RF3150 and RF375 treatments significantly increased by 14.3% and 8.9% as compared to TF3150 and TF375, respectively. Average WUE significantly improved by (P < 0.05) in RF1150, RF175, RF2150, RF275, RF3150, and RF375 were 53.3%, 56.4%, 75.8%, 85.1%, 68.2% and 75.3% compared to TF planting, respectively. As precipitation increased from 200 to 275 mm there were no significant increases in moisture contents, soil respiration rate, ET, WUE, and grain yield under both planting models. Therefore, we concluded that the RF2150 treatment is suitable as a water-saving technology to achieve higher wheat production and WUE in semi-arid agro-ecosystems of China.