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The incorporation of earthworms and straw into cropland soil can greatly affect soil structure and soil organic C (SOC) dynamics. However, information regarding how earthworms affect both carbon (C) in its transition from residue into soil and SOC turnover under conventional tillage (CT) and conservation tillage is limited, and some results are even contradictory. Moreover, most of studies were conducted out based on sieved soil samples. In this study, intact soil samples were used to analyze the effects of earthworms (Eisenia foetida) and both of earthworms and straw addition on SOC fractions and soil CO2 emission in a 30-day incubation experiment with CT and no tillage (NT) treatments. The results showed that CT accelerated the straw decomposition and increased the content of soil active C. In contrast, NT resulted in slower decomposition of the original straw and reduction of the total amount of SOC and soil active C. The earthworms could inhibit the straw from decomposing in CT and stimulate the decomposition of straw in NT. Whatever in NT or CT, earthworms did not affect soil CO2 emission, but straw addition significantly increased soil CO2 emission. The results of this study provide the selection of the appropriate tillage practice as well as the amount of returned straw to fertilize the soil.

Earthworm casts have been recognized as contributing to long-term carbon protection, but few studies have focused on the mechanism by which this is achieved. Most of the literature documenting earthworm casts revolves around the difference between the earthworm cast and natural soil, whereas little attention has been given to deciphering the effects of different tillage systems on earthworm casts. Further, whether or not an earthworm cast, like soil, affects its own organic carbon content through physical structure stability is still somewhat vague, and very little is known. The objective for this study was to determine the effect of tillage on organic carbon and physical structure stability parameters in earthworm casts. Undisturbed soil columns were collected from a 17-year tillage experiment including no tillage (NT), ridge tillage (RT) and mouldboard ploughing (MP) in Northeast China. Each column was seeded with ten earthworms (Eisenia foetida), incubated at 18 °C for 120 days and casts were collected and analysed. Both NT and RT led to significantly greater organic carbon (20.5% and 14.4%), total pore volume (54.6% and 75.6%), total pore area (45.4% and 60.4%), permeability (21.8% and 66.4%), fluid conductivity (26.2% and 31.1%), tensile strength (34.1% and 51.2%) and water resistance index (16.7% and 22.3%) in the casts compared to MP (P

Previous research has shown the varied effect of earthworms on soil carbon dynamics. We carried out a 180-day incubation experiment with earthworms and maize residue additions under conventional tillage (CT) and no tillage (NT) system conditions to quantify the earthworm effect in the black soil of northeastern China. Earthworms did not affect soil CO2 emissions, while residue addition significantly increased such emissions. The effects of earthworms on dissolved organic carbon (DOC) and microbial biomass carbon (MBC) gradually weakened with time in CT with and without residue addition, but gradually increased with time in NT with residue addition. In the CT system, earthworms accelerated the soil organic carbon (SOC) mineralization, and the newly added residue decomposed into SOC. In the NT system, earthworms accelerated the decomposition of native residues increasing the SOC content, this increase in decomposition rates by earthworms was greater than the inhibitory effect imposed by the addition of the new residue. Earthworms and residues combine to play a single role in CT and NT. This result will help in the understanding of the role of earthworms and residue in SOC dynamics, and in the development of management strategies to improve SOC.

Selecting appropriate soil management practices (e.g. tillage treatments) provides an opportunity to sequester soil carbon (C), improve soil health, and achieve ample food production in an agricultural system. The responses of soil CO2 emission, soil microbial community, and crop yield to precipitation are crucial for assessing sustainability of conservation tillage. Soil CO2 flux, soil microbial phospholipid fatty acid (PLFA) contents and crop yield were measured in a long-term (15 years) tillage study in the Northeast of China under a normal year in 2013 and natural drought year in 2015. The results showed in a normal year with precipitation similar to the 30-year mean, soil temperatures at 5, 10 and 20 cm in June under mouldboard plough (MP) were higher by 0.9, 1.0 and 1.1 °C, respectively, than under no-tillage (NT); soil water content in the top 22 cm under MP was significantly lower than that under NT in 04 June and 31 July; and MP significantly increased maize (Zea mays L.) yield and C emission efficiency (the ratio of yield to annual soil CO2 emission) by 22% and 25%, respectively. In a dry year (2015), soil temperatures at 5, 10, and 20 cm in June and July under MP were higher by 2.0, 1.8 and 1.7 °C than under NT, respectively; soil water content in the top 22 cm under MP was significantly lower than under NT by 28% in July; moreover, MP significantly decreased maize yield and C emission efficiency by 47% and 63%, respectively. However, there were no significant differences in annual soil CO2 emission between NT and MP in the normal and dry years. Compared with MP, NT significantly increased soil microbial PLFA contents in pre-planting (April) and late segments of the growing season (August-September) of a normal year, but significantly increased soil microbial PLFAs content in pre-planting and all of early, mid and late segments of the growing season in a dry year. Structural equation modelling (SEM) revealed that soil water content, temperature, bacteria and fungi directly contributed to C emission efficiency. Tillage was indirectly associated with C emission efficiency through soil water content, temperature, soil fungi and bacteria. These results suggested that the higher maize yield and C emission efficiency under NT compared to CT were related to improved soil water content and soil microbial PLFA contents and the lower soil temperature in a dry year. Our results suggested that NT (a subset of conservation tillage) might be a positive adaptation strategy to cope with drought under monoculture maize in northeast China.

Our understanding of seasonal dynamics of fungal communities under different agricultural management practices remains limited. In this study, phospholipid fatty acid (PLFA) analysis and Illumina MiSeq high-throughput sequencing targeting fungal ITS1 region were combined to assess the responses of soil fungal communities to different tillage practices and cropping systems during the crop growing season. Bulk soils were collected from two long-term tillage practices (conventional tillage, CT and no-tillage, NT) under two cropping systems (maize (Zea mays L.)-soybean (Glycine max Merr.) rotation and continuous maize) in April, June and August of 2015 at 0–5 cm and 5–15 cm depths. Our results clearly highlighted the importance of cropping system and tillage for soil fungi; seasonal effect, by contrast, was weaker. The fungal PLFA content, used as an indicator of fungal biomass, appeared higher under continuous maize system than maize-soybean rotation system at depths of 0–5 cm and 5–15 cm, and higher in NT than CT at 0–5 cm depth, irrespective of sampling time. DNA-based sequencing results showed that soil fungal diversity (i.e. Shannon) and evenness (i.e. Pielou) indices were higher under rotation cropping system than continuous maize system at both soil depths. Soil fungal richness (i.e. Chao1) index was higher in NT than in CT at 0–5 cm depth. None of these three α diversity indices were significantly affected by sampling time. Cropping system and tillage played the most important roles in shaping soil fungal community at both soil depths. At 0–5 cm depth, there was an obvious consistent trend of enrichment from Ascomycota in maize-soybean rotation system to Basidiomycota in continuous maize system over the growing season. At 5–15 cm depth, there was an obvious consistent trend of enrichment from Tausonia and Chaetomidium in CT to Leptodontidium, Ceratobasidium in NT over the crop growing season. Notably NT favored symbiotrophs throughout the growing season, irrespective of cropping system and soil depth.

Soil structure plays a key role in soil organic carbon (SOC) dynamics. To determine how soil structure and aggregate affects SOC, we collected undisturbed soil cores of 0-5 cm layer (Typic Hapludoll) at an experimental site in Northeast China. The site had been under continuous tillage treatments of conventional tillage (CT) and no tillage (NT) for 17 years. We measured SOC by elemental analysis, aggregate size distribution by wet sieving, and soil pore parameters of pore size distribution, pore average diameter, pore numbers, pore connectivity, pore anisotropy, and pore fractal dimension by X-ray computer tomography. SOC content was significantly correlated with aggregate-associated SOC and soil water-stable aggregate content. CT with residue removal and annual plowing and cultivation increased53 μm and 53-250 μm aggregates. CT decreased total SOC of 0-5 cm soil layer but increased aggregate-associated SOC of53 μm. NT with greater residue input increased total SOC of 0-5 cm soil layer by 26.0% and aggregate mean weight diameter by 111.8% and increased aggregates of 250-1000 μm and1000 μm. Soil under NT had a greater total number of micropores and greater connectivity whereas CT had a greater total number of macropores, average macropore diameter, anisotropy, and fractal dimension. Structural equation modeling showed that CT can decrease SOC of 0-5 cm soil layer by different paths, including increased anisotropy and macropore porosity, and NT can increase SOC of 0-5 cm soil layer by different paths, including increased mean weight diameter and connectivity. These results enhance our understanding of the relationship between soil structure and SOC, and could guide tillage management decisions to increase SOC.

Tillage practice can alter the content and distribution of soil organic matter by burying crop residue and soil disturbance, which would impact soil microbial properties. The objective of the present study was to evaluate the effects of tillage practices (no tillage, NT; ridge tillage, RT; mouldboard plow, MP) and sampling date (April, June, September) on soil microbial properties at different soil depths. Soil core samples were taken at 0–5, 5–10 and 10–20 cm depths from a long-term tillage experiment site (initiated in 2001) in black soils in northeast China. Microbial biomass and extractable organic C were determined using by chloroform-fumigation-extraction method. Microbial abundance and community structure were determined using the phospholipid fatty acid (PLFA) method. Principal response curve (PRC) analysis revealed the magnitude of the effect of sampling date on the PLFA relative abundance decreased with depth within the tilled layer, whereas increased with depth for tillage practice. Microbial biomass carbon, abundance and the F/B ratio varied with the variation in available substrates at the 0–5 cm depths. NT and RT improved microbial abundance (total, fungal and bacterial abundance) in the 0–5 cm depth soil, but they did not contribute to a higher F/B ratio in the 0–5 cm depth soil, and had a lower F/B ratio than MP in the deeper soils below 5 cm depth. These results demonstrated that long-term conservation tillage practice has potential for improving microbial properties in surface soil, but may not cause a shift of microbial community structure in Northeast China.

Soil microbial community can vary with different agricultural managements, which in turn can affect soil quality. The objective of this work was to evaluate the effects of long-term tillage practice (no tillage (NT) and conventional tillage (CT)) and crop rotation (maize-soybean (MS) rotation and monoculture maize (MM)) on soil microbial community composition and metabolic capacity in different soil layers. Long-term NT increased the soil organic carbon (SOC) and total nitrogen (TN) mainly at the 0-5 cm depth which was accompanied with a greater microbial abundance. The greater fungi-to-bacteria (F/B) ratio was found in NTMS at the 0-5 cm depth. Both tillage and crop rotation had a significant effect on the metabolic activity, with the greatest average well color development (AWCD) value in NTMS soil at all three soil depths. Redundancy analysis (RDA) showed that the shift in microbial community composition was accompanied with the changes in capacity of utilizing different carbon substrates. Therefore, no tillage combined with crop rotation could improve soil biological quality and make agricultural systems more sustainable.

The severe soil deterioration and the accompanying decline in maize yield are the main factors jeopardizing the sustainability of agricultural production in the black soil region of Northeast China. Conservation tillage practices have been proposed as new practices to enhance soil fertility and to produce food from a dwindling land resource in this region, but wide adoption of these practices can occur only when the practices demonstrate a steady increase in agricultural production. To compare the effects of tillage on corn yield, the structural equation modeling (SEM) was used in analyzing the relationships between maize growth/yield and soil properties (physical and chemical characteristics) based on a long-term (12 years) tillage study that included no tillage (NT), ridge tillage (RT) and conventional tillage (CT) practices. Compared with CT, NT and RT had higher maize grain yield, soil carbon/nitrogen ratio and soil moisture, and lower soil temperature and seedling emergence rate. The advantages of NT and RT in maize yield were primarily ascribed to the favorable soil nutrients and soil water content, which could increase plant size at the later growing season and ultimately yield more maize grain. The lower soil temperature and subsequently lower emergence rates in NT and RT at early stages (sowing to emergence) of maize growth did not exert negative effects on maize yield. These adverse effects of low soil temperature and low emergence rates could be offset by postponing sowing date without compromising the maize yield. Our study indicated that both NT and RT practices could offer a potentially significant improvement over the current conventional tillage practice in the black soil region of Northeast China.

Soil food webs are important in maintaining agricultural productivity and ecosystem health. However, our understanding is still limited with respect to the influences of tillage transitions on soil food webs. The present study aimed to quantify the response of microflora and microfauna, and their linkage to different tillage treatments: no tillage (NT), ridge tillage (RT) and conventional tillage (CT). Soil samples were collected from 0 to 20 cm depth in April of 2011 after 10 years of conservation tillage. The abundance and richness of bacteria and arbuscular mycorrhizal fungi were greater in NT and RT than in CT. In case of microfauna also, similar patterns were observed with greater protozoa, bacterivores and omnivores–carnivores in NT and RT compared to CT. The connectance of the bacterial and predator–prey pathways was greater in NT and RT than in CT and that of fungal pathway was greatest in RT. The trophic relationship of the bacterial and predator–prey pathways was strengthened due to the higher water content of soil and the lower NO 3 – -N after the conversion of CT to NT and RT. Our study suggested that 10 years of conservation tillage can effectively enhance the structure and function of soil food webs through bottom–up effects in the black soil region of Northeast China.

Soil management is aimed at the maintenance of optimal soil physical quality for crop production. In order to explore the effects of tillage practices on soil physical properties, a study was conducted to compare the effects of no tillage (NT), moldboard plow (MP) and ridge tillage (RT) on soil bulk density (BD), soil penetration resistance (SPR), soil water content (SWC), soil macroporosity (MAC) and soil air-filled porosity (AFP) in Northeast China. Results showed that both NT and RT led to significant BD increment than MP at 0–20 cm ( P < 0.05). Compared with MP, NT and RT increased SPR at the depths of 2.5–17.5 cm (P < 0.05). SWC of 0–10 cm layer was significantly higher in NT and RT than MP soils (P < 0.05). NT showed a significantly lower MAC than MP and RT at 0–20 cm soil depths (P < 0.05). All AFP values were above the limit of 0.10 cm 3 /cm 3 under all tillage treatments. RT improved the soil physical quality as evidenced by decreased BD and SPR, and increased SWC, MAC and AFP relative to NT.

Limited information is available for understanding the spatial variation of soil penetration resistance (SPR) and water content induced by different tillage methods and crop rotations in a black soil of Northeast China. A 11-year tillage experiment in Dehui County, Jilin Province, Northeast China was conducted to evaluate the effects of tillage treatments [no tillage (NT), moldboard plow (MP), and ridge tillage (RT)] and crop rotations (corn-soybean rotation and continuous corn) on SPR and water content in relation to horizontal and vertical variations. Effect of NT, MP, and RT differed on the spatial distributions of SPR and water content among the rows, shoulders, and inter-rows. Compared with MP, NT, and RT treatments increased SPR in row and inter-row positions at the depth of 2.5–17.5 and 2.5–15 cm, respectively (p < 0.05). NT and RT led to significant decrement of soil water content than MP treatment in the rows and inter-rows of 0–15 cm layer (p < 0.05). Greater variability of SPR and water content...

[1] Winter soil CO2 emission is a very important component of the annual carbon budgets, however, almost no information on winter CO2 emission is available from the cropland soil in northeast China. In this study, soil CO2flux was measured for a 2-year period from an ongoing tillage trial on Black soil in northeast China to quantify seasonal patterns in soil CO2 flux rate and wintertime contribution to annual soil respiration. Average soil CO2 flux rates in the winter (November to March) were between 0.64 to 1.22 g CO2 m−2 d−1, in the non-growing season (October and April) were 2.09–3.56 g CO2 m−2 d−1, whereas in the growing season (May to September) they were between 10.9 to 12.7 g CO2 m−2 d−1, with no significant differences among tillage treatments. Total winter, non-growing and growing season soil CO2 emissions were 0.28–0.45 Mg C ha−1, 0.36–0.53 Mg C ha−1, and 4.52–5.55 Mg C ha−1, respectively, among tillage treatments. The contributions of winter soil respiration to annual soil CO2emission ranged from 5.1 to 7.1%, and the non-growing season emission ranged from 11.4 to 15.2% among tillage treatments. Our results indicate that in northeast China, cropland Black soil continuously emits CO2throughout the non-growing season, and the wintertime soil respiration plays a significant role in annual soil carbon budgets. Hence winter soil CO2 emission must be taken into consideration when the role of the soil ecosystem is assessed as either a sink or source of CO2 to the atmosphere.