To clarify how nitrogen (N) and water regulate the microbe mediated carbon (C) cycle in farmland, a 3-year experiment was conducted in a wheat–maize rotation at Jiaozhou Station, North China. Twelve treatments combined four drip irrigation regimes (T1: no irrigation; T2: 40 mm irrigation at flowering; T3: 40 mm irrigation at the grain filling stage; T4: both, 40 mm each) and three N levels (N0: 0 kgN·hm−2; N1: 92 kgN·hm−2; N2: 184 kgN·hm−2). In this study, we measured wheat yield and biomass, soil organic carbon and nitrogen content, soil respiration, soil microbial community, and C-metabolic genes. The results showed that wheat yield increased with N, peaking at 8949.81 kg·hm−2 in the N2T3 treatment, while irrigation had no significant independent effect on yield but interacted with nitrogen fertilization: under identical nitrogen levels (N1, N2), yields in the T1 and T2 treatments were significantly lower than those in the T3/T4 treatments. The soil organic carbon content in N2 was significantly higher; the soil C/N ratio was highest in N2, and T3 resulted in a significantly higher C/N ratio than T1 under the same N level; total soil respiration in N0 was significant lower, and T4 had higher respiration than T2 under the same N level. N addition increased Actinobacteriota, Chloroflexi, Gemmatimonadetes, and Ascomycota, while decreaing Proteobacteria and Acidobacteriota. No reduction in fungal phylum was observed with nitrogen addition. N application significantly upregulated key enzymes in the pentose phosphate pathway (e.g., transketolase K00615, transaldolase K00616), while irrigation increased phosphoserine aminotransferase (K00831) abundance and decreased methylmalonyl-CoA mutase (K01848) abundance. N2T3 maintains high SOC content while achieving maximum yield, promoting soil fertility retention. Compared to T4, N2T3 also enhances water use efficiency. The N2T3 treatment (high N and grain filling stage irrigation) achieved the optimal balance between high wheat yield and SOC sequestration.

Unraveling the influence of microbes on C content at aggregate scale is pivotal for promoting soil C accumulation. Previous studies were based mainly on the mutual transformation process between aggregates, the links between the microorganisms in initial aggregates and inner C content and aggregate sizes were still unclear. In this study, the classified aggregates (> 5 mm, 2-5 mm, 1-2 mm, 0.25-1 mm, and < 0.25 mm) were individually incubated for 10 months under C-13-labeled maize straw application to analyze the relationship between microbial community structure in independent aggregates and inner C accumulation under straw addition. The results show that the SOC content increased in independent aggregates under straw addition, with higher stable C accumulation in < 0.25 mm than in > 2 mm aggregates. Aggregates of > 5 mm were more capable of improving unstable C accumulation and C derived from straw (C-straw) than smaller aggregates. Fungi and Gram-negative bacteria (G-) were more important to increasing C accumulation in > 2 mm aggregates, whereas Gram-positive (G+) bacteria dominated in < 2 mm aggregates. The results indicate that the contribution of microorganisms within aggregates to inner C accumulation was associated with aggregate sizes.

【Background and Objective】 The APEX model is a comprehensive watershed-scale model for simulating the effects of management practices on agricultural systems and their impacts on water quality, soil erosion, and nutrient cycling. This paper analyzes the sensitivity of its parameters to water status in soil. 【Method】 The analysis is based on data measured from 2016 to 2019 from an irrigation experiment conducted in Jiaodong in Shandong province. Winter wheat was used as the model plant; the Sobol, Morris, and FAST methods were used to analyze the sensitivities of the APEX model parameters associated with crop growth and water stress. We considered the influences of groundwater depth, rainfall and irrigation. 【Result】 When groundwater depth was 1.25 m, the maximum root depth (RDMX) was the most sensitive parameter affecting evapotranspiration, biomass, and yield, while the maximum potential leaf area index (DMLA) was the most sensitive parameter impacting leaf area index (LAI). When the groundwater depth was increased to 5 m, the sensitive parameters influencing crop evapotranspiration and yield differed, with PARM38 (weight coefficient of water stress calculation) and RWPC1 (proportion of root biomass during germination) becoming the most sensitive parameters. Results calculated from all three methods indicated that as irrigation water increased, the sensitivity of RDMX decreased, while the sensitivities of DMLA, DLAI (peak point in growth season), and WA (potential light energy utilization) increased. The sensitivity of RDMX was significantly higher in dry years than in humid years, as opposed to the sensitivity of DMLA. Uncertainty analysis demonstrated that wheat biomass, yield, and evapotranspiration fell within the 5% to 95% confidence interval of the simulated data. 【Conclusion】 The most sensitive parameters identified by the Sobol, Morris, and FAST methods were consistent, although their sensitivity indexes varied with irrigation treatments, rainfall patterns, and groundwater depth. Considering computational efficiency and accuracy, the Morris method is more suitable for parameter sensitivity analysis of the APEX model. These findings provide valuable insights into the application of the APEX to analyze the impact of environmental conditions on crops.

Increasing soil carbon (C) stock and improving soil structure are critical challenges in semi-arid agroecosystems. Conservation tillage management has been widely applied to promote aggregate stability and enhance soil organic C (SOC) storage, both of which are affected by microbial community composition. However, the relation among soil microbial groups, aggregate stability and SOC under tillage management remains unclear. Here, we conducted a 17-year field experiment located in Loess Plateau of northwest China, with three managements: CT-RR (conventional tillage with residue removal), RT-RI (reduced tillage with residue incorporation) and NT-RM (no-tillage with residue mulching). RT-RI and NT-RM treatments improved the aggregate stability index (ASI) by 11% and 16% relative to CT-RR in the 0–10 cm layer; RT-RI improved ASI by 13% relative to CT-RR in 10–25 cm layer. The RT-RI treatment increased the SOC concentration and SOC stock of macroaggregates (> 250μm), which harbor most of the SOC stock in bulk soil. Both RT-RI and NT-RM increased total microbial biomass and biomass of six microbial groups [i.e. gram-negative bacteria (GN), gram-positive bacteria (GP), total bacteria (B), total fungi (F), arbuscular mycorrhizal fungi (AMF) and saprophytic fungi (SF)] in the 0–10 cm layer, and RT-RI increased the above groups at 10–25 cm. Across a range of microbial community indicators, we found strong relationships between SOC and GN, ASI and AMF in bulk soil. A random forest model indicates that GN and F were the best microbial predictors of SOC concentration and overall aggregate stability, whereas AMF/SF was the best predictor of SOC concentration within aggregates and the stability of individual aggregate size classes. Together, these results demonstrate a strong link between aggregate stability, SOC dynamics and microbial community composition, and suggest that RT-RI increases both soil aggregation and SOC storage in dryland agroecosystems.

为明确胶东半湿润区不同播种密度和株行距对冬小麦产量形成的调控机理,以当地主栽品种'济麦 22 号'为材料,探讨了不同株行距配置和播种密度对冬小麦群体动态、地上生物量、产量及其构成要素等指标的影响.两年试验结果表明:播种密度与基本苗、公顷穗数及籽粒产量呈显著正相关,相关系数分别为 0.97、0.95 和 0.50,与穗粒数呈显著负相关,相关系数为-0.69;在相同播种密度下,窄行宽株距处理明显优于宽行窄株距处理,其增产的关键是穗数的提高.当播种密度降低时,行距变化对冬小麦总分蘖数、公顷穗数和籽粒产量的影响均大于株距变化的影响,而株距变化对单株分蘖的影响大于行距变化的影响;株行距影响籽粒产量的主控因素为穗数,而通过穗粒数和千粒重对产量的调控作用存在较大的年际差异.综上可知,胶东半湿润区播种密度和株行距主要通过穗数调控冬小麦产量,为实现小麦高产,推荐窄行(20 cm)宽株距(1.0 cm)和中高播种密度(500×104 粒/hm2)为最佳播种方法.

滴灌技术结合节水灌溉制度可显著提高作物水分利用效率,但针对滴灌条件下冬小麦节水灌溉制度的优化研究相对较少,利用作物模型优化节水灌溉制度可以弥补田间试验的不足,对于作物精确灌溉具有重要的指导意义.本研究利用胶东冬小麦滴灌节水试验数据(2016—2019年)评价了根区水质模型(RZWQM-CERES)的适应性,并模拟评价了不同节水滴灌制度对冬小麦产量和水分利用效率的影响,以筛选最佳节水滴灌制度.结果表明RZWQM-CERES可以较好地模拟土壤水分、冬小麦生长和产量对不同滴灌处理和季节的响应,其中模拟0～90 cm土壤贮水量的均方根误差(RMSE)为22.7～32.3 mm、相对均方根误差(NRMSE)为11.9％～16.3％、决定系数(R2)为0.52～0.69,模拟收获期生物量的RMSE为1184～1904 kg hm-2、NRMSE为9.9％～16.8％、R2为0.67,模拟产量的RMSE为361～491 kg hm–2、NRMSE为5.7％～7.8％、R2为0.75.长期模拟结果表明该地区冬小麦需水关键期为孕穗期(丰水年和平水年)或拔节期(枯水年).针对不同降水年型冬小麦产量和水分利用效率对灌溉量的响应差异,筛选滴灌条件下冬小麦最佳灌溉制度为:丰水年在拔节期和开花期各灌水45 mm;平水年(或枯水年)在拔节期、孕穗期及开花期各灌水35 mm(或45 mm).本研究结果扩展了RZWQM-CERES优化冬小麦滴灌制度的应用潜力,为实施冬小麦精确灌溉提供了重要的技术支持.

Categorization of soil organic carbon (SOC) into different functional subpools according to their recalcitrance and protective mechanisms helps better understand ecosystems organic carbon (OC) dynamics, and various attempts have been made to explore the suitable experimental fractionation method for such purpose. However, most previous studies neglected the influences of environmental factors on the effectiveness of varying fractionation methods. Density fractionation has shown great promise in elucidating SOC immobilization mechanisms. Here, we compared three varying types of density fractionation methods (density, density + dispersion, and density + other procedures) for categorizing the SOC into three functional pools, that is, active OC (OCactive), moderately stable OC (OCm-stable), and stable OC, (OCstable) using global data compiled for 95 sites in 31 published studies, and examined the influences of climate (mean annual temperature [MAT] and annual precipitation), vegetation type, and soil properties (soil depth, clay content, and soil type) on SOC fractions determined by the three density fractionation methods. The percentage of OCm-stable fraction was found to be highest using the density method and lowest using the density + dispersion method, due to differential density ranges between the two methods. At a global scale, the contents of total SOC and its OC fractions decreased with temperature. Precipitation had no apparent influences on the subdivided SOC fractions using either the density + dispersion method or the method of density + other procedures, whereas soil type constrained the effect of precipitation on SOC fractions using the density method. The percentage of OCm-stable determined by the density + dispersion method was more responsive to MAT and vegetation type than that by the other two methods. The percentage of OCstable determined by the method of density + other procedures was significantly and positively related to the clay content as the OCstable based on this method included small particles. For all the three methods of fractionation, soil type had a greater influence than the clay content on the SOC fractions, especially the OCm-stable and the OCstable. For soil type characterized by rich metal oxides, both the density method and the method of density + other procedures could be used for SOC fractionation. For soil type rich in nutrients, the density + dispersion method would have higher sensitivity for distinguishing the OCm-stable.

The cropping system conversion, from rice to vegetable, showed various influences on the greenhouse gases (GHG) emission with conversion time and fertilizer/irrigation management. In this study, we evaluated the DeNitrification-DeComposition (DNDC) model for predicting carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) emissions and crop yields as rice converted to vegetable cropping system under conventional or no fertilization from 2012 to 2014. Then, we quantified the long-term (40 years) impacts of rice-vegetable cropping system conversions and fertilization levels (0, 50, 100 and 150% conventional fertilization rate) on GHGs emissions and global warming potentials (GWP) using the calibrated model. The DNDC model-simulated daily GHG emission dynamics were generally consistent with the measured data and showed good predictions of the seasonal CH4 emissions (coefficient of determination (R2) = 0.96), CO2 emissions (R2 = 0.75), N2O emissions (R2 = 0.75) and crop yields (R2 = 0.89) in response to the different cropping systems and fertilization levels across the two years. The overall model performance was better for rice than for vegetable cropping systems. Both simulated and measured two-year data showed higher CH4 and CO2 emissions and lower N2O emissions for rice than for vegetable cropping systems and showed positive responses of the CO2 and N2O emissions to fertilizations. The lowest GWP for vegetable without fertilization and highest the GWP for rice with fertilization were obtained. These results were consistent with the long-term simulation results. In contrast to the two-year experimental data, the simulated long-term CH4 emissions increased with fertilization for the rice-dominant cropping systems. The reasonable cropping systems and fertilization levels were recommended for the region.

Soil microbial metabolism is critically important for regulating soil carbon (C) sequestration. However, how soil organic C (SOC) stock responds to the changes in microbial resource limitation and microbial C use efficiency (CUE) under long-term tillage system remains uncertain. Soil samples were randomly collected from a long-term (19 years) tillage experiment growing winter wheat with three treatments [i.e., moldboard-plough without straw retention (MPN), no-tillage with straw retention (NTS), and subsoiling with straw retention (SSS)] and an adjacent natural grassland (GRL) in 2018. We analyzed microbial resource limitation and CUE based on ecoenzyme stoichiometry. Results revealed that the reduction of soil bulk density and total dissolved nitrogen (N) resulted in an increased vector angle. Higher total dissolved N and lower vector length jointly led to higher CUE under long-term conservation tillage practices (i.e., NTS and SSS). Notably, the higher CUE and soil available phosphorus as well as the lower N limitation both directly contributed explaining the increase in SOC stock under conservation tillage practices. Overall, long-term conservation tillage practices could alleviate microbial resource limitation by enhancing available nutrients to promote SOC sequestration. Our study provides new knowledge to enhance the understanding of SOC stock regulated by microbial resource limitations and microbial C use efficiency.

Conservation tillage practices may stimulate soil organic carbon (SOC) storage in croplands by reducing soil disturbance and increasing inputs of crop residue. Although the effect of tillage practices on soil C dynamics is mediated by soil microbes, the relation between microbial community traits and SOC accumulation rate (SAR) remains unclear. In this study, we investigated the effect of tillage management on soil properties and microbial community traits (i.e. diversity, composition and keystone taxa) in a long-term (17 years) field experiment. Our experiment was located in a spring maize field with a sandy loam soil (Calcaric-Fluvic Cambisol) in northwest China and included three tillage practices: 1) CT-RR, conventional tillage with residue removed; 2) RT-RI, reduced tillage with residue incorporated; and 3) NT-RM, no-tillage with residue mulched. We sampled soil at 0-10 cm and 10-25 cm to assess the relation between bacterial and fungal community traits and SAR. We found that the initial and current of average SOC stocks was 19 and 28 Mg ha-1 at 0-25 cm, respectively. RT-RI and NTRM increased SOC accumulation at 0-10 cm by 116% and 131% compared with CT-RR, respectively, and RT-RI increased SOC accumulation at 10-25 cm by 159%. Changes in co-occurrence network analysis revealed that NTRM resulted in a stable bacterial network, whereas both RT-RI and NT-RM produced a stable fungal network relative to CT-RR. Microbial diversity and keystone taxa correlated positively with SAR under conservation tillage practices. Using a Zi-Pi plot, we identified several keystone OTUs, five of which (i.e. Cytophagales, JG30KF-CM45, Sphingobacteriales, Thelephorales and Pleosporales) showed a positive correlation with SAR. Our results suggest a strong link between microbial community traits and SOC accumulation rate under conservation tillage practices, and provide insights into the contribution of microbial traits to the sustainability of agroecosystems.

Tillage practices can influence soil microbial carbon use efficiency (CUE), which is critical for carbon cycling in terrestrial ecosystems. The effect of tillage practices could also be regulated by nitrogen (N) addition. However, the soil microbial mechanism about N fertilizer effect on microbial CUE under no-tillage is still unclear. We investigated how N fertilizer regulates the effect of tillage management on microbial CUE through changing microbial properties and further assessed the impact of microbial CUE on particulate (POC) and mineral-associated organic matter carbon (MAOC) using a 16-yr field experiment with no-tillage (NT) and conventional tillage (CT), both of which combined with 105 (N1), 180 (N2), and 210 kg N ha (N3) N application. We found that microbial CUE increased with increasing N application rate. NT increased microbial CUE compared with CT under N1. The bacterial and fungal diversities of NT was higher than CT and N application decreased their diversities in the 0-10 cm layer. The partial least squares path model showed that bacteria diversity, fungal diversity, and fungal community structure played more critical roles in increasing microbial CUE. Furthermore, POC and MAOC under NT were higher than CT and they also increased with increasing N application rate. This could be explained by the finding that increasing microbial CUE induced by N application had the potential to increase POC and MAOC. Overall, N addition is an important pathway to influence microbial CUE, which is mainly regulated by bacterial and fungal diversities rather than their biomass under no-tillage.

[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.

[目的]耕作措施对土壤有机碳(SOC)和全氮(TN)具有重要影响.本研究利用团聚体和密度联合分级方法,旨在揭示长期耕作对表层土壤团聚体内密度颗粒组分SOC及TN的影响,为深入理解黄土高原农田土壤碳氮提升机理提供依据.[方法]长期试验位于黄土高原东部边缘地区,开始于1999年,共设4个处理:少耕无覆盖(RT)、免耕覆盖(NT)、深松覆盖(SM)和传统翻耕(CT).于2013年7月采集0—10 cm土层样品,首先通过干筛法筛分>2、1—2、0.25—1和<0.25 mm粒级团聚体,之后利用颗粒密度分组,将团聚体有机质分为轻组有机质(LF)、粗颗粒有机质(cPOM)、细颗粒有机质(fPOM)和矿质结合有机质(m-SOM).[结果](1)15年保护性耕作(包括NT和SM处理)显著提高了0—10 cm土层的SOC和TN含量,与CT相比,NT和SM处理的SOC含量分别提高了22.9％和21.8％,TN含量分别提高了35.2％和42.3％.不进行秸秆覆盖的少耕处理(RT)对SOC和TN无显著影响.(2)不同耕作措施改变了团聚体质量组成及其内部SOC和TN含量.NT和SM处理显著提高了1—2 mm和0.25—1 mm粒级的干筛大团聚体含量,相对地,降低了>2 mm和<0.25 mm粒级团聚体的含量.NT和SM处理不同程度提高了团聚体的SOC和TN含量,与CT相比,团聚体SOC平均提高了8.5％和9.5％,尤其对>1 mm粒级团聚体SOC含量提高幅度最大;团聚体TN平均提高了12.2％和24.1％,尤其对<0.25 mm微团聚体TN含量提高幅度最大.(3)fPOM和m-SOM组分对团聚体SOC和TN的贡献最大,对SOC的贡献率分别为27.3％—45.1％和25.0％—52.6％;对TN的贡献率分别为23.5％—34.7％和42.2％—64.3％.不同有机质组分对耕作的响应不同,cPOM和fPOM组分最为敏感.与CT相比,NT和SM处理显著提高了土壤所有粒级团聚体的cPOM和fPOM的SOC和TN含量,尤其对>2 mm团聚体cPOM和<2 mm团聚体fPOM的SOC和TN含量提升幅度最大.[结论]长期免耕和深松提高了团聚体中有机碳及全氮含量,尤其提高了团聚体中颗粒有机质的碳氮含量,有利于土壤碳氮的长效累积,是黄土高原坡耕地区值得推荐的耕作管理方式.

针对胶东地区冬小麦生育期内降雨和灌溉水资源明显不足问题,通过研究滴灌条件下灌溉制度对土壤水分、冬小麦生长及水分利用的影响,探究该地区冬小麦最优灌溉模式.试验实施从2016到2019年,共3季冬小麦,灌溉方式为滴灌,共设置4种处理:T1:不灌水;T2:拔节期灌水40 mm;T3:开花期灌水40 mm;T4:拔节期和开花期分别灌水40 mm.结果 表明:(1)拔节期灌溉(T2和T4)在0～30、30～60、60～90 cm土壤体积含水量分别为16.0％、25.5％、25.1％,比不灌水处理(T1)分别提高25.9％、5.5％、4.7％,贮水量为204.9 mm,比不灌水处理(T1)提高6.5％,叶面积指数为2.9,比不灌水处理(T1)提高26.3％,生物量为6124.8 kg/hm2,比不灌水处理(T1)提高29.0％.(2)开花期灌溉(T3和T4)在0～30、30～60、60～90 cm土壤体积含水量分别为12.8％、22.7％、22.8％,与不灌水处理(T1)相比分别提高36.6％、11.2％、6.7％,贮水量为188.7mm,比不灌水处理(T1)提高12.8％,叶面积指数为2.2,比不灌水处理(T1)提高24.3％,生物量为10781.0 kg/hm2,比不灌水处理(T1)提高24.2％;(3)与不灌水处理(T1)相比,3年的试验结果表明拔节期灌溉(T2)可提高产量16.5％,耗水量增加13.0％,水分利用效率增加2.7％,开花期灌溉(T3)产量增加26.4％,耗水量增加13.3％,水分利用效率增加11.0％,两次灌溉(T4)产量增加22.7％,耗水量增加23.9％,但是水分利用效率降低2.0％.不同灌水处理(T2、T3和T4)3年结果相比较,T3比T2的叶面积指数增加5.8％,生物量增加5.7％,产量增加9.0％,耗水量之间无显著差异,水分利用效率增加8.7％,灌溉水利用效率增加138.5％.与T4处理相比,T3处理的生物量和产量接近,耗水量降低8.7％,但是水分利用效率增加13.4％,灌溉水利用效率平均增加160.4％.综合考虑不同灌溉制度对冬小麦生长发育、产量及水分利用的影响,滴灌条件下在开花期灌水(T3处理)可作为胶东半岛砂姜黑土区冬小麦最优灌溉制度.

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.

Tillage management is a key factor driving changes in soil physical properties (SPP) and crop yield around the world. However, there is a lack of knowledge about the relationships between SPP and crop yield. The dynamic of SPP during the growth period is also seldom taken into account to understand suitable soil physical environment for crop growth. Moreover, the crop growth process cannot be explained by an individual SPP substantially. The least limiting water range (LLWR), which integrates soil penetration resistance, air porosity, and soil water potential, may provide a better understanding of soil-crop relationship, especially in regions with limited precipitation. Our objective was to explain how dynamic SPP affected grain yield during the growth period. A long-term field experiment was established in 2003, with continuous spring maize, on sandy loam soil. Seasonal changes of SPP (i.e. bulk density, penetration resistance, porosity, mean weight diameter, LLWR, and plant available water) were determined under reduced tillage with residue incorporated (RT-RI), conventional tillage with residue removal (CT), and no-tillage with residue mulch (NT-RM). The results showed that these SPP were affected by both tillage management and growth stage. Bulk density, porosity, S index, and mean weight diameter were not effective indicators to explain the changes of grain yield under the three tillage managements. The range of LLWR was narrower than plant available water (PAW) during the growth period and more sensitive to assess soil water availability under RT-RI, CT, and NT-RM. NT-RM significantly increased the lower limit of LLWR, which made it more difficult for root water uptake. Hence, RT-RI presented higher corn yield compared to NT-RM, even if the water content remained lower. Redundancy analysis further indicated that maize yield was mainly driven by lower limit of LLWR and penetration resistance. Overall, LLWR was an aggregative indicator including not only soil penetration resistance but also air porosity and soil water potential, which can better explain the change of grain yield under the long-term tillage management in semi-arid region.

[目的]探讨免耕条件下施用有机肥对冬小麦土壤酶活性及活性有机碳含量的影响,明确免耕条件下的科学施肥方法,为提升土壤生物学活性和改善土壤质量提供理论依据.[方法]基于山西运城长期定位试验,选取免耕(NT)和免耕增施有机肥(NTM)两个处理,在冬小麦不同生育时期测定与碳转化相关土壤酶的活性(β葡萄糖苷酶、β木聚糖酶、纤维二糖苷酶、α葡萄糖苷酶)、土壤温度、土壤含水量和土壤呼吸速率以及成熟期土壤总有机碳(TOC)和活性有机碳组分(可溶性有机碳,DOC;易氧化有机碳,EOC;微生物量碳,MBC)等关键指标.[结果](1)在冬小麦生育期,两个处理不同土壤酶活性具有明显的季节性交化特征.其中β木聚糖酶与α葡萄糖苷酶的活性在拔节期和灌浆期表现出升高趋势;但β-葡萄糖苷酶与纤维二糖苷酶的活性随季节变化波动较小.不同生育时期β木聚糖酶和α葡萄糖苷酶的活性的变化趋势与土壤呼吸速率变化趋势基本一致.此外,主成分分析结果表明,不同生育时期土壤酶活性主要受土壤含水量和土壤呼吸速率的影响.(2)与NT相比,NTM显著提高不同生育时期土壤β木聚糖酶的活性(越冬期:17.6％;抽穗期:8.5％;灌浆期:14.1％和成熟期:1 0.0％);在越冬期和拔节期土壤α葡萄糖苷酶的活性分别提高16.7％和10.2％.同时,主成分分析结果表明,不同处理间酶活性主要受土壤温度和土壤呼吸速率的影响.(3)与NT相比,NTM显著提升冬小麦生长季TOC、DOC、EOC和MBC含量(TOC:16.9％;DOC:27.7％;EOC:38.4％和MBC:50.7％).(4)冬小麦生长季土壤生物学指标相关分析表明,β木聚糖酶与α葡萄糖苷酶的活性与总有机碳及其活性组分呈显著相关关系(相关系数均大于0.850).[结论]免耕增施有机肥通过影响生育期土壤含水量和土壤温度,进而提升β木聚糖酶与α葡萄糖苷酶的活性;同时,秸秆还田基础上增加有机肥碳投入可进一步提高土壤总有机碳和活性有机碳组分的含量,有利于土壤酶等生物学活性和土壤质量的提升.

为了探明晋南地区冬小麦-夏玉米轮作区适宜的节水减氮管理模式,采用田间试验,研究分析了5个水氮组合模式对夏玉米氮素积累特征、籽粒产量、品质和氮肥利用率的影响.结果表明,与大水漫灌、传统撒施肥料(CK)相比,微喷水肥一体化处理的夏玉米籽粒产量提高12.05％～45.4％,其中以微喷灌4次(出苗水+小喇叭口水+大喇叭口水+抽雄水),施纯氮227.5 kg/hm2,氮肥后移、追氮2次处理(WN3)的籽粒产量和蛋白质含量最高,籽粒氮素积累量、总氮素积累量分别较施纯氮227.5 kg/hm2,追氮1次处理(WN2)提高6.8％、14.26％,且与微喷灌、施纯氮300 kg/hm2(WN1)和WN2相比,WN3处理的氮肥利用率分别提高41.81％、23.14％,氮肥农学利用效率分别提高47.45％、49.01％.综上所述,晋南冬小麦-夏玉米一年两熟区,采用微喷水肥一体化可替代漫灌实现节水减氮高产栽培,推荐微喷灌溉4次、氮肥后移处理(基肥45.5 kg/hm2+小喇叭口期追肥136.5 kg/hm2+抽雄期追肥45.5 kg/hm2)作为晋南地区夏玉米灌水施氮适宜的运筹方式,该模式相比CK减少灌水量50％、减施氮肥24.16％,提高氮肥利用效率的效果最好,实现了节水减氮的效果.

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.