为探讨不同微生物菌群对华北地区中度石油污染土壤的修复效果,在实验室模拟条件下分别进行优势外源石油降解菌群的筛选和优势菌群与植物联合修复试验.结果显示:4种外源石油降解菌群中,PDC-3菌群对中度石油污染土壤总石油烃(TPH,total petroleum hydrocarbons)去除率为84.07％,在各菌群中效果最优;该优势菌群与植物联合修复中度石油污染土壤比单独使用优势菌群修复可获得更好的效果,优势菌群与黑麦草联用及优势菌群与紫花苜蓿联用120 d TPH的去除率分别为91.58％和89.30％,修复后土壤中TPH含量均小于500 mg/kg;同时优势菌群与黑麦草联合修复在90 d即可去除89.32％的土壤TPH,相比选用紫花苜蓿可有效缩短修复周期;优势菌群对土壤TPH的去除起主要作用,其贡献率远高于土著微生物菌群或植物的贡献率;植物对土壤TPH去除的贡献率为4.09％～6.48％,且其作用主要发生在修复过程的中后期;优势菌群单独使用或与植物联合修复中度石油污染土壤120 d均可有效去除C10～C12及C22～C40石油烃组分,去除率为85.14％～100.00％;然而,C13～C21石油烃组分含量表现出阶段性的积累效应;除对土壤石油烃的去除作用外,使用优势菌群进行生物修复存在一定的调节土壤pH、增加土壤肥力,且有利于恢复修复后的土壤功能.

[目的]探究添加秸秆对不同耕作措施下土壤有机碳及其相关因素的影响,为北方旱作农田固碳增产管理提供理论依据.[方法]采集长期进行传统耕作(CT)和免耕(NT)的大田土壤样品进行室内培养试验,共设置4个处理,分别为传统耕作土壤不加秸秆(CT)、免耕土壤不加秸秆(NT)、传统耕作土壤加秸秆(CTS)和免耕土壤加秸秆(NTS),每个处理15次重复.在25℃恒温培养箱中进行通气培养,培养时间共180 d,此间定期取样进行有机碳含量、水稳性团聚体构成、土壤微生物量碳和相关土壤酶活性的测定.[结果](1)添加秸秆显著提高土壤有机碳含量和大团聚体含量.与CT相比,CTS提高土壤有机碳含量15％-46％;与NT相比,NTS提高土壤有机碳含量12％-21％;培养结束时,CTS、NTS处理的有机碳含量较初始分别提高26.8％和7.0％.CTS和NTS处理以2 000-250μm团聚体含量最高,占全部团聚体的41％-50％,CTS较CT提高＞250μm团聚体比例235％-310％,NTS较NT提高＞250μm团聚体比例96％-149％.(2)添加秸秆显著增加土壤有机碳δ13C值,CTS处理为80.93‰-115.22‰,NTS为48.92‰-80.49‰;CTS秸秆来源碳所占比例显著高于NTS,较NTS处理提高13％-66％.(3)添加秸秆显著提高微生物量碳(MBC)含量、β-葡萄糖苷酶(BG)、β-纤维二糖苷酶(CBH)和β-木糖苷酶(BXYL)活性.CTS较CT提高MBC含量239％-623％,提高BG、CBH和BXYL活性58％-170％、52％-337％和117％170％;NTS 较 NT 处理提高 MBC 含量 124％-555％,提高 BG、CBH 和 BXYL 活性28％-181％、4％-304％和 13％-118％.(4)土壤有机碳含量与BG、CBH和BXYL活性、MBC及＞2 000μm、2 000-250μm团聚体比例呈显著正相关关系,与250-53 um、＜53μm团聚体比例呈显著负相关关系;BG、CBH、BXYL 3种酶活性彼此之间表现为极显著正相关关系,且均与MBC、＞2 000μm团聚体、2 000-250μm团聚体显著正相关,与＜53μm团聚体极显著负相关.线性相关分析结果表明水稳性大团聚体(＞250μm)可解释有机碳变化的48％,MBC可解释有机碳变化的45％,BG、CBH和BXYL酶活性分别可解释有机碳变化的66％、44％、53％.[结论]添加秸秆可显著提高土壤有机碳和大团聚体含量,促进微生物数量增加和土壤酶活性增强,且对传统耕作土壤有机碳及其相关因素的影响更大,有机碳在土壤中的固定除了受团聚体物理保护外,还受土壤中微生物作用的调节.

Most studies only measure soil biochemical parameters in the surface soil at one growth stage to uncover how fertilization affects crop yield and soil respiration. A field study was conducted in a wheat (Triticum aestivum L.)-maize (Zea mays L.) rotation system to determine whether correlations among soil biochemical parameters, crop yield, and soil respiration vary with growth stage and soil depth. Annual crop yield, seasonal soil respiration, soil biochemical parameters at different growth stages (i.e., soil enzyme activity and available N content), and soil chemical parameters at different soil depths (i.e., soil organic carbon [SOC] and total nitrogen [TN] content) were measured. Stronger positive relationships between crop yield, soil respiration, and soil biochemical parameters were found at the first growth stage relative to other stages during both the 2013 wheat and 2014 maize growing seasons. In addition, the most significant relationship among soil chemical properties, crop yield, and soil respiration was found at 20-to-40-cm soil depth during the 2013 wheat growing season but was found at 0-to-20-cm soil depth during the 2014 maize growing season. Overall, correlations among soil biochemical parameters, crop yield, and soil respiration vary with growth stage and soil depth under fertilization. Our study indicates that single time-point measurements of only surface soil biochemical parameters are not sufficient to understand fertilization impacts on crop yield and soil respiration.

自2004年开始利用干旱棚,长期定位模拟不同降雨年型对小麦产量及土壤水分的影响.本文以平水年为研究对象,结果表明:在11年间小麦生育期降雨量高于常年降雨量(231.8 mm)有2年占18％,与常年持平的有3年占27％,其他年份均低于常年,且生育期降雨极不均匀,干旱时期也不尽相同,大气候对小麦的生长影响较大.十一年间小麦产量呈下降趋势,2004-2008每年平均以673.5 kg/hm2降低;2009-2014年每年平均以628 kg/hm2降低.小麦成产因素穗数均呈下降趋势,而千粒重呈上升趋势,穗粒数变化比较平稳.小麦播种期土壤水分呈下降趋势,收获期土壤水分比较平稳.产量与穗数和播种期土壤含水量呈极显著相关,与穗粒数显著相关.

To ascertain the effects of long-term conservation tillage and residue retention on soil organic carbon (SOC) content and aggregate distribution in a deep soil (>20-cm depth) in a dryland environment, this paper analyzed the SOC and aggregate distribution in soil, and the aggregate-associated organic carbon (OC) and SOC physical fractions. Conservation tillage (reduced tillage with residue incorporated (RT) and no-tillage with residue mulch (NT)) significantly increased SOC sequestration and soil aggregation in deep soil compared with conventional tillage with residue removal (CT). Compared with CT, RT significantly increased the proportion of small macroaggregates by 23%–81% in the 10–80 cm layer, and the OC content in small macroaggregates by 1%–58% in the 0–80 cm layer. RT significantly increased (by 24%–90%) the OC content in mineral-SOC within small macroaggregates in the 0–60 cm layer, while there was a 23%–80% increase in the 0–40 cm layer with NT. These results indicated that: (1) conservation tillage treatments are beneficial for soil aggregation and SOC sequestration in a deep soil in a dryland environment; and (2) the SOC in mineral-associated OC plays important roles in soil aggregation and SOC sequestration. In conclusion, RT with NT is recommended as an agricultural management tool in dryland soils because of its role in improving soil aggregation and SOC sequestration.

[目的]研究玉米秸秆还田对不同耕作处理下旱地土壤团聚体及其有机碳的影响,旨在探究长期传统耕作土壤添加秸秆后团聚体及其有机碳的变化规律,并确定添加秸秆提高土壤有机碳的主要原因,为旱地农田固碳技术提供理论依据.[方法]采集大田长期试验地的传统耕作和免耕小区土样进行室内培养试验,设置4个处理,分别为传统耕作土壤不加秸秆(CT)、免耕土壤不加秸秆(NT)、传统耕作土壤加秸秆(CTS)和免耕土壤加秸秆(NTS),15次重复;秸秆为传统耕作玉米植株地上部分,用量为5％烘干土质量,在25℃恒温培养箱中通气培养180d,定期取样进行团聚体组成和有机碳含量的测定.[结果](1)不加秸秆处理团聚体以250-53 μmm为主,占全部团聚体的52％-66％;添加秸秆处理以2 000-250 μm团聚体为主,占全部团聚体的41％-50％,CTS较CT提高230％-302％,NTS较NT提高92％-134％.(2)添加秸秆处理平均重量直径(MWD)、几何平均直径(GMD)以及＞0.25 mm团聚体百分比(R0.25)显著提高,培养到180 d时,CTS较CT分别提高133％、130％和235％,NTS较NT分别提高53％、75％和87％.(3)培养至180 d时,CTS较CT分别提高250-53μm和＜53μm团聚体有机碳70％和54％;NTS较NT分别提高250-53 μm和＜53μm团聚体有机碳30％和25％.(4)添加秸秆显著提高2 000-250 μm团聚体有机碳对土壤有机碳的贡献率,CTS和NTS分别为49％-61％和50％-60％,且受团聚体组成影响较大.[结论]添加秸秆能够有效提高旱作土壤大团聚体(＞ 250 μm)形成并增强其稳定性,提高大团聚体有机碳对土壤有机碳的贡献率,且对传统耕作处理土壤的促进效果更明显.

Soil respiration (RS), which is the second largest carbon flux between the atmosphere and terrestrial ecosystems, has significant impact on atmospheric CO2 concentration and climatic dynamics. Nitrogen (N) fertilizer has been heavily applied in agroecosystems at the global scale for high crop yields, and plays a major role in regulating RS. Although the respective response of soil biochemical property and RS to N addition has been widely studied, the contributions of soil biochemical parameters especially in the rhizosphere to changes in RS and its components (soil heterotrophic (RH) and autotrophic (RA) respiration) under N application remain poorly understood. The present study aimed to examine whether the rhizosphere effect alters the relationship between soil biochemical properties and RS under N addition in croplands.

The adoption of conservation tillage is promising for soil management system in the Loess Plateau of China; however, how conservation tillage influences the molecular structure contributes and long-term stabilization of soil organic matter (SOM) is still not clear in this area. In this study, experimental plots were continually cultivated with winter wheat (Triticum aestivum L.) and soil samples were collected in September 2009 and September 2015,10 and 16 years after the experiment was initiated, respectively. Four treatments were applied: reduced tillage (RT), no tillage (NT), sub-soiling (SS) and conventional tillage (CT). Soil samples were physically fractionated into five fractions: free light fraction (FLF), occluded light fraction (OLF), coarse sand particulate organic matter (c-POM), fine sand particulate organic matter (f-POM) and mineral associated organic matter + silt + clay (m-SOM). The soil organic carbon (SOC) stocks were analysed in SOM fractions and bulk soil (BS). Solid state C-13 cross polarization/total sideband suppression nuclear magnetic resonance (C-13 CP/TOSS NMR) spectroscopy was applied to determine the abundance of different forms of carbon (C) (carboxyl C, O/N-alkyl C, aromatic C and alkyl C) in the soil physical fractions. The SOC stocks in the 0-30 cm layer were influenced by the tillage systems. Although there were no significant differences in SOC stocks among these four treatments in the 0-10 and 10-20 cm layers in first 10 years, after 16 years, the SOC stocks were highest in the SS and NT treatments in the 0-10 cm layer. As the duration of the experiment increased from 2009 to 2015, the SOC content of m-SOM-C fraction under RT and CT also increased. As determined by C-13 NMR, in the light fractions (FLF to OLF), the abundance of aromatic C increased when the abundance of O/N-alkyl C declined and there was a higher aromatic C/O/N-alkyl C ratio. A gradual increase in the abundance of alkyl C of heavy fractions was accompanied by a decrease in aromatic C, which might be due to the microbial by-products deposited on mineral surface in the soils. In addition, a higher SOM preservation were shown in conservation tillage (NT and SS) by our NMR data. Particular interesting were the results of the light and c-POM fractions, in which conservation tillage showed a higher abundance of O/N-alkyl C and a lower aromatic C/O/N-alkyl C ratio in these two fractions compared with conventional tillage (RT and CT). However, these changes were not evident in the heavy fractions. The changes in the chemical structures of the light and c-POM fractions were possibly due to the retention of crop residues and low levels of soil disturbance. In conclusion, long-term conservation tillage affected the fractions and the chemical functional groups of SOM and could be ideal to preserve SOC in the Loess Plateau.

Microbial mechanisms associated with soil organic carbon (SOC) decomposition are poorly understood. We aim to determine the effects of inorganic and organic fertilizers on soil labile carbon (C) pools, microbial community structure and C mineralization rate under an intensive wheat-maize double cropping system in Northern China. Soil samples in 0-10 cm layer were collected from a nine-year field trial involved four treatments: no fertilizer, CK; nitrogen (N) and phosphorus (P) fertilizers, NP; maize straw combined with NP fertilizers, NPS; and manure plus straw and NP fertilizers, NPSM. Soil samples were analyzed to determine labile C pools (including dissolved organic C, DOC; light free organic C, LFOC; and microbial biomass C, MBC), microbial community composition (using phospholipid fatty acid (PLFA) profiles) and SOC mineralization rate (from a 124-day incubation experiment). This study demonstrated that the application of chemical fertilizers (NP) alone did not alter labile C fractions, soil microbial communities and SOC mineralization rate from those observed in the CK treatment. Whereas the use of straw in conjunction with chemical fertilizers (NPS) became an additional labile substrate supply that decreased C limitation, stimulated growth of all PLFA-related microbial communities, and resulted in 53% higher cumulative mineralization of C compared to that of CK. The SOC and its labile fractions explained 78.7% of the variance of microbial community structure. Further addition of manure on the top of straw in the NPSM treatment did not significantly increase microbial community abundances, but it did alter microbial community structure by increasing G+/G- ratio compared to that of NPS. The cumulative mineralization of C was 85% higher under NPSM fertilization compared to that of CK. Particularly, the NPSM treatment increased the mineralization rate of the resistant pool. This has to be carefully taken into account when setting realistic and effective goals for long-term soil C stabilization.

Straw residue has been widely applied in the North China Plain agroecosystems due to their positive roles in soil fertility improvement, sustainable production, and climate change mitigation. However, little is known about how straw application alters soil respiration by influencing soil biochemical properties in this region. This is the first study to evaluate the role of soil enzyme activity and glomalin content in the response of soil respiration to straw application at different growth stages in a wheat-maize rotation system.

A major challenge facing China is to meet the increasing food demand of its growing population in the face of decreasing arable land area, while sustaining or improving soil productivity and avoiding adverse environmental impacts from intensive agriculture. This study uses data from China Statistical Yearbooks to analyze trends in regional soil productivity and grain yields in the major grain-producing regions in North China (NC), Northeast China (NE), East China (EC), Central China (CC), and Southwest China (SW), associated with regional fertilizer use and annual climate variation in rainfall and mean temperature over the 20 years. During 1992-2012, the average fertilizer increase rates (in kg ha(-4) year(-1)) were in the order of regions CC (6.6) > NC (4.8) > EC (2.4) > SW (2.1) > NE (1.3). while yield responses to fertilizer use (with regression model coefficients, in kg kg(-1)) were in the order: SW (-0.9) < CC (1.1) < NC (1.7) < EC (5.7) < NE (9.3), showing higher yield responses to fertilizer use for NE and EC than for other regions. The changes in regional grain yields also showed higher yield responses to soil-based productivity for NC, CC, and SW, or to annual climate variability for CC than for other regions, indicating that other factors (such as inherent soil productivity or annual climate variability could be more important than fertilizer in affecting yields. The strategies for regulating nutrient management are needed considerably based on regional indigenous soil nutrient supply under varying regional climate conditions.

Utilization of flue gas desulfurization (FGD) gypsum in China to improve alkaline soils started in the late 1990s.The FGD gypsum is a kind of desulfurized waste residue from power plant.It is an industrial by-product gypsum obtained by desulfurization and purification of flue gas produced by sulfur bearing fuel (mainly coal).With the increasing of installation of flue gas pollution control system,such as dust removal,desulfurization and denitrification in coal-fired power plants in China,more and more desulfurization by-product gypsum will be produced while reducing SO2 emission and other harmful gases in the process of coal combustion.The utilization of FGD gypsum has attracted more attention for solving the problem with increased disposal of desulfurization residues in power plants.Because the nature of FGD gypsum is similar to that of natural gypsum,some researchers have tried to use it instead of natural gypsum in the improvement of saline alkali land.However,since some enterprises introduced flue gas purification technology and synergistic mercury removal process,several hazardous pollutants in coal would inevitably transfer into FGD by-products (FGD gypsum and fly-ash).The process of FGD and synergistic mercury removal causes the enrichment of several hazardous pollutants in FGD gypsum (mainly Hg,F,Cl,and Se),and in FGD fly-ash (mainly As,Cd,Cr,Cu,Ni,Pb,and Zn).Research results indicated that the enrichment of hazardous pollutants could result in high levels of hazardous pollutants (especially Hg,Se,F and Cl) in some FGD gypsum in China,inordinately beyond the limits of Environmental Quality Standards for Soils and the limits of Environmental Quality Standards for Ground Water.In order to ensure soil health,food safety,and environmental quality,it was suggested that those FGD by-products without any harmless treatment of pollutants should not be allowed to use as for soil remediation or conditioning directly into the farmlands by solid waste disposal methods;especially material source and technology of desulfurization,application rate in farmland and long-term environmental safety risk should be concerted,to prevent hazardous pollutants from entering food chain and harming to human health.

In the Loess Plateau of China, conventional tillage is defined as the tillage without crop residues left on the soil surface and ploughed twice a year. The use of alternative practices is a way to reduce soil erosion. Our objectives were to assess the long-term impacts of different soil tillage systems on soil physical and hydraulic characteristics, emphasizing management practices to improve the soil physical qualities (reduce bulk density and increase stability of aggregate) under the conservation tillage system in the Loess Plateau of China. Conventional tillage (CT), no tillage (NT), and sub-soiling (SS) were applied in this experiment. Soil wet aggregates distribution and stability, soil organic carbon (SOC) content, soil water retention curves and pore size distributions were measured. The results showed that in the 0–10 cm and 10–20 cm depth soil layers, NT and SS treatments showed a significantly higher proportion of wet aggregates >250 μm (macroaggregates) compared to CT. In these two layers, the proportion of wet aggregates <53 μm (microaggregates) was significantly higher in CT with respect to NT and SS. SOC content increased as the aggregate fraction size increased, and was higher within wet aggregates >250 μm than within the 250–53 μm and < 53 μm (silt + clay) fractions at both depths. In addition, the conservation tillage (NT and SS) can result in improved total porosity and reduced soil bulk density compared with CT in the surface layer. Pore size distribution in CT soil was unimodal, with the maximum in the 10–30 μm matrix pores of the surface layer. However, in the surface layer the pore size distributions from NT and SS showed a dual porosity curve, with two peaks in the matrix and structural pore areas. The 10–20 cm layer showed similar pore size distributions in each treatment. After scanning the soils by micro-computed tomography, we visualized the pore characteristics. The images showed that CT reduced the long and connected macropores compared with conservation tillage. Overall, soil aggregate stability and soil macropores are most improved under conservation tillage. Conservation tillage with crop residues should be adopted instead of conventional tillage, as an effort to improve crop yield and control soil erosion in the Loess Plateau of China.

中国是世界马铃薯生产大国,多年以来马铃薯产量和种植面积一直居世界首位,但单产不及世界平均水平,还有提高的潜力.当前,国家加大了对马铃薯产业发展的政策扶持力度,同时与三大主要粮食作物相比,马铃薯在面积、单产和生产效益方面的优势明显,这均为马铃薯产业的发展奠定了坚实的基础.以联合国粮食及农业组织(FAO)数据等为基础,分析了中国马铃薯产业的发展现状及产业发展优势,并提出了相关发展建议.

BACKGROUNDThis study aimed to assess longer-term (1993-2009) effects of combined applications of fertiliser, maize stover, and cattle manure on maize yields, partial nitrogen (N) and carbon (C) balances, and water and N-use efficiencies, to guide N and C input recommendations for rain-fed maize production in northern China.RESULTSThe field trial, with three factors at five levels and 12 treatments, was conducted at Shouyang Dryland-Farming Experimental Station, Shanxi, China. Data analysis revealed higher N balances but lower C balances significantly occurred in a dry year than in a wet year. Positive N balances related to higher N inputs resulted in higher soil available N, even downward to deep layers with increasing N inputs, while positive C balances due to higher C inputs could be benefit to increase soil organic C. Based on partial N balances and grain yields, N and C inputs at ranges of 100 kg N ha-1 and 1.9-2.9 Mg C ha-1 could be recommended for target yields of 6.7-7.2 Mg ha-1 in rain-fed maize production.CONCLUSIONThe study suggests that N balances close to neutral be given priority to improving N-use efficiency, and more positive C balances also be important for sustaining target yields and soil fertility levels. © 2017 Society of Chemical Industry.

中国是马铃薯生产大国但不是马铃薯贸易大国,马铃薯及其制品的进出口贸易额不足全球的2%,中国马铃薯以出口初级产品和进口冷冻加工品为主,且进出口贸易伙伴分布相对集中.利用显示性比较优势指数和贸易竞争力指数分析中国马铃薯国际贸易竞争力.结果表明,21世纪以来,中国马铃薯的显示性比较优势指数总体处于持续上升的状态,国际竞争力在不断增强,由10年前的竞争优势较弱发展为中度竞争优势.利用贸易竞争力指数分析表明,2001年以前中国马铃薯处于国际竞争劣势,2002年起中国马铃薯已具有较强的竞争优势.

The ecological conservation development area in Beijing is an important ecological barrier and water source protected area, where is the guarantee for the sustainable development of Beijing and the important founda-tion for building the livable city. How to coordinate the relationships and contradictions between the industrial de-velopment and ecological environment protection has become one of the key issues for the sustainable development of ecological conservation development area. Taking Baoshan town, Huairou district, Beijing, as an example, this study discussed the suitable ecological sightseeing leisure agriculture mode in this area, analyzed the current situa-tion of sightseeing leisure agriculture and development potential in Baoshan, and pointed out some problems inclu-ding that its infrastructure was not perfect, the service level was not high, the publicity was not enough, and so on. Finally, it put forward some countermeasures and suggestions for the development of the industry, such as enhan-cing the regional planning, digging the new growth point, innovating the tourism projects, perfecting the preferen-tial policies, strengthening personnel training, and so on, so as to provide a reference for the agricultural industry development in the same type region.

A field experiment was conducted on fluvo-aquic soil in the North China Plain to study the effects of nitrogen application rate on soil nitrogen contents and enzyme activities in rhizosphere and non-rhizosphere of summer maize. The results showed that the soil enzyme activities under different nitrogen application rates showed similar seasonal patterns. In comparison to no nitrogen ferti-lizer treatment, all nitrogen application treatments significantly increased NO3--N contents in rhizosphere and non-rhizosphere soils, NH4+-N content in rhizosphere soil and the activities of β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase and Cellobiohyrolase. During the whole summer maize growing season, the NO3--N content in non-rhizosphere soil was significantly higher than that in rhizosphere soil. The NH4+-N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm-2 but decreased significantly when the rate was higher than 180 kg·hm-2. Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.

Tillage is a common agricultural practice affecting soil structure and biogeochemistry. Pore network geometries are crucial to oxygen concentration, gas diffusivity, water location and water movement. Soil aggregates, 4-6 mm in diameter and collected from silty loam in Belgium and sandy loam in China, were scanned using a micro-computed tomography scanner. Images with a pixel size of 6.9 mu m were then processed with Image) software for pore network analysis. The treatments were no tillage (C-NT) and conventional tillage (C-CT) in China, and shallow tillage (G-ST) and conventional tillage (G-CT) in Belgium. The results showed that aggregates in conservational tillage (G-ST and C-NT) had numerous connected pores compared with conventional tillage (G-CT and C-CT). The Euler number (Ev) was significantly lower and visible total porosity and surface area (SA) were significantly higher in conservational tillage (G-ST and C-NT) than in conventional tillage (G-CT and C-CT) in both studied locations.The predominant size of pores was significantly higher in conservational tillage (G-ST and C-NT) than in conventional tillage (G-CT and C-CT) (>150 mu m vs 90-120 mu m). Pore location within the aggregates also showed differences, with porosity being evenly distributed in the aggregates under conventional tillage ('G-CT and C-CT). Under conservational tillage (G-ST and C-NT), the aggregates were heterogeneous, showing higher porosity at the center of the aggregates. There was a higher soil organic carbon (SOC) content in the external layer than in the internal layer in conservational tillage in Belgium (G-ST). In no tillage in China (C-NT), the SOC in the external and internal layers, however, showed similar results.Overall, conventional tillage (G-CT andC-CT) reduced the proportion of the largest pores within soil aggregates, whereas there was no significant relationship between pore morphologies and SOC content. Further investigation is required to measure the active and slow carbon pool distribution in the different layers and under different tillage practices. (C) 2016 Elsevier B.V. All rights reserved.

Crop production in the dryland farming areas of northern China is constrained by low and variable rainfall. This article presents the analysis of the relationships between variations in rainfall and yields of winter wheat and spring maize. The analysis is based on data from both several short-term and our ongoing long-term field experiments in dryland farming research projects in Tunliu, Linfen, Shouyang, and Luoyang. Grain yields of wheat and maize ranged from 1,548 to 5,169 and from 2,612 to 8,789kg ha(-1) respectively, with differences up to above 200% (between dry and wet years). Wheat yields are sensitive to growing season rainfall but also correlated to water use (ET), whereas maize yields are sensitive to the critical time of water supply (especially June rainfall) but not correlated to ET. The ratio of grain yields to soil water at sowing is an important indicator, showing close relationships between yields and soil water-related ratio within the rainfed crops site. Comparison between the indices of water use efficiency (WUE) and precipitation use efficiency (PUE) suggests that the index WUE is more grain-related indicator than the PUE used for assessing rainfed crop water use by both maize and wheat. The index PUE should be used in caution, especially for wheat crops in dry years. Our results indicate that options to alleviate crop moisture stress must be tailored to the rainfall pattern. This holds especially for conservation tillage with response nutrient management practices that aim at enhancing water use efficiency.