Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR

CQESTR simulates the effect of management practices on soil organic carbon (SOC) stocks. The beta version of the model had been calibrated and validated for temperate regions. Our objective was to evaluate the CQESTR model performance for simulating carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. In the southeast (20.75 S 42.81 W), tillage systems consisted of no tillage (NT); reduced tillage (RT) (one disc plow and one harrow leveling [RT1] or one heavy disc harrow and one harrow leveling [RT2]); and conventional tillage (CT) (two heavy disc harrows followed by one disc plow and two harrow levelings). In the northeast (7.55 S 45.23 W), tillage systems consisted of NT, RT (one chisel plow and one harrow leveling), and CT (one disk plow, two heavy disk harrowings, and two harrow levelings). CQESTR underestimated SOC at both sites, especially under NT systems, indicating that adjustments (e.g., the inclusion of clay mineralogy factor) are necessary for more accurate simulation of SOC in the tropics. In spite of this, measured and simulated values of SOC in the 0–20 cm depth were well correlated (southeast, R² = 0.94, p < 0.01; northeast, R² = 0.88, p < 0.05). With respect to initial conditions (native forest), CQESTR estimated a decrease in SOC stocks in plowed and no-tillage systems. In 2006, in the southeast, SOC stocks were 28.8, 23.7, 23.2, and 22.0 Mg ha^?1 under NT, RT2, RT1, and CT, respectively; in the northeast, stocks were 36.0, 33.8, and 32.5 Mg ha^?1 under NT, RT, and CT, respectively. The model estimated carbon emissions varying from 0.36 (NT) to 1.05 Mg ha^?1 year^?1 (CT) in the southeast and from 0.30 (NT) to 0.82 (CT) Mg ha^?1 year^?1 in the northeast. CQESTR prediction of SOC dynamics illustrates acceptable performance for the two tropical soils of Brazil.     

Soil management alters seedling emergence and subsequent autumn growth and yield in dryland winter wheat–fallow systems in the Central Great Plains on a clay loam soil

Stand establishment and subsequent autumn development and growth are important determinants of winter wheat (Triticum aestivum L.) yield. Soil management practices change soil properties and conditions, which alter seedling emergence, crop development and growth. Pre-plant soil management practices were studied for 6 years in a wheat–fallow rotation in eastern Colorado, USA, to isolate the impacts of pre-plant tillage (PT) and residue level on winter wheat seedling emergence and autumn development and growth. A split plot design was used with PT, using a moldboard plow that incorporated surface residue, and with no-tillage (NT). The tillage systems represented the main plots and three residue levels within each tillage treatment as subplots: no residue (0R), normal residue (1R) and twice-normal residue (2R). Residue amount had little effect on emergence or autumn growth and development. PT resulted in soil water loss from the plow zone. NT plots had more favorable soil water levels in the seeding zone which resulted in faster, more uniform and greater seedling emergence in 4 out of the 6 years. This is especially critical for stand establishment in years with low rainfall after planting. Soil or air temperature did not account for differences among treatments. Earlier and greater seedling emergence in NT treatments resulted in greater autumn development and growth. Shoot biomass, tiller density and leaf numbers were greater in NT, and again residue amount had little effect. At spring green-up, NT treatments had greater soil water in the profile. Grain yield was always equal or greater in NT than in PT, and positively correlated with earlier/greater seedling emergence and autumn growth. NT will enhance soil protection and likely increase snow catch, reduce evaporation and benefit yield in semiarid eastern Colorado.     

Effects of reduced tillage,crop residue management and manure application practices on crop yields and soil carbon sequestration on an Andisol in northern Japan

Abstract

Soil carbon sequestration in agricultural lands has been deemed a sustainable option to mitigate rising atmospheric CO₂ levels. In this context, the effects of different tillage and C input management (residue management and manure application) practices on crop yields, residue C and annual changes in total soil organic C (SOC) (0–30 cm depth) were investigated over one cycle of a 4-year crop rotation (2003–2006) on a cropped Andisol in northern Japan. For tillage practices, the effects of reduced tillage (no deep plowing, a single shallow harrowing for seedbed preparation [RT]) and conventional deep moldboard plow tillage (CT) were compared. The combination of RT, residue return and manure application (20 Mg ha^?1 in each year) increased spring wheat and potato yields significantly; however, soybean and sugar beet yields were not influenced by tillage practices. For all crops studied, manure application enhanced the production of above-ground residue C. Thus, manure application served not only as a direct input of C to the soil, but the greater crop biomass production engendered enhanced subsequent C inputs to the soil from residues. The SOC contents in both the 0–5 cm and 5–10 cm layers of the soil profile were greater under RT than under CT treatments because the crop residue and manure were densely incorporated into the shallow soil layers. Comparatively, neither tillage nor C input management practices had significant effects on annual changes in SOC content in either the 10–20 cm or 20–30 cm layers of the soil profile. When soil C sequestration rates, as represented by annual changes in total SOC (0–30 cm), were assessed on a total soil mass basis, an anova showed that tillage practices had no significant effect on total C sequestration, but C input management practices had significant positive effects (P ≤ 0.05). These results indicate that continuous C input to the soil through crop residue return and manure application is a crucial practice for enhancing crop yields and soil C sequestration in the Andisol region of northern Japan.     

不同耕作方式下旱作玉米田土壤呼吸及其影响因素

为揭示不同耕作方式对旱作玉米田土壤呼吸的影响,对比研究深松耕、免耕、旋耕和翻耕4种耕作方式下土壤呼吸速率的动态变化及其与土壤水分、温度、有机质、全氮、pH值等的关系。结果表明,夏玉米生长季,4种耕作方式下土壤呼吸速率随生育时期均呈先增加后降低的趋势,平均土壤呼吸速率为深松耕>翻耕>旋耕>免耕;播种前至拔节期土壤温度为翻耕>深松耕>旋耕>免耕,抽雄期至成熟收获期为免耕>旋耕>深松耕>翻耕;各耕作方式下0～20cm层土壤有机质、全氮均逐渐增加,与免耕比较,翻耕有机质和全氮均降低;生育前期土壤pH值波动明显,抽雄期后趋于平缓,土壤pH值平均值为翻耕>旋耕>免耕>深松耕。各影响因素与土壤呼吸速率相关分析表明,深松耕和翻耕土壤水分、温度与土壤呼吸速率呈显著或极显著正相关;有机质与土壤呼吸速率呈负相关,且与深松耕措施下土壤呼吸速率呈显著负相关;除免耕外,其他耕作方式下土壤全氮、pH值与土壤呼吸呈负相关。该研究可为补充完善土壤呼吸排放机理、评估区域碳收支平衡及制定科学有效的土壤碳调控管理措施提供依据。     

Soil carbon and nitrogen changes as affected by tillage system and crop biomass in a corn–soybean rotation

A wide range of tillage systems have been used by producers in the Corn-Belt in the United States during the past decade due to their economic and environmental benefits. However, changes in soil organic carbon (SOC) and nitrogen (SON) and crop responses to these tillage systems are not well documented in a corn–soybean rotation. Two experiments were conducted to evaluate the effects of different tillage systems on SOC and SON, residue C and N inputs, and corn and soybean yields across Iowa. The first experiment consisted of no-tillage (NT) and chisel plow (CP) treatments, established in 1994 in Clarion–Nicollet–Webster (CNW), Galva–Primghar–Sac (GPS), Kenyon–Floyd–Clyde (KFC), Marshall (M), and Otley–Mahaska–Taintor (OMT) soil associations. The second experiment consisted of NT, strip-tillage (ST), CP, deep rip (DR), and moldboard plow (MP) treatments, established in 1998 in the CNW soil association. Both corn and soybean yields of NT were statistically comparable to those of CP treatment for each soil association in a corn–soybean rotation during the 7 years of tillage practices. The NT, ST, CP, and DR treatments produced similar corn and soybean yields as MP treatment in a corn–soybean rotation during the 3 years of tillage implementation of the second experiment. Significant increases in SOC of 17.3, 19.5, 6.1, and 19.3% with NT over CP treatment were observed at the top 15-cm soil depth in CNW, KFC, M, and OMT soil associations, respectively, except for the GPS soil association in a corn–soybean rotation at the end of 7 years. The NT and ST resulted in significant increases in SOC of 14.7 and 11.4%, respectively, compared with MP treatment after 3 years. Changes in SON due to tillage were similar to those observed with SOC in both experiments. The increases in SOC and SON in NT treatment were not attributed to the vertical stratification of organic C and N in the soil profile or annual C and N inputs from crop residue, but most likely due to the decrease in soil organic matter mineralization in wet and cold soil conditions. It was concluded that NT and ST are superior to CP and MP in increasing SOC and SON in the top 15 cm in the short-term. The adoption of NT or CP can be an effective strategy in increasing SOC and SON in the Corn-Belt soils without significant adverse impact on corn and soybean yields in a corn–soybean rotation.     

Twenty years of tillage research in subarctic Alaska: I. Impact on soil strength, aggregation, roughness, and residue cover

Soil properties and surface characteristics affecting wind erosion can be manipulated through tillage and crop residue management. Little information exists, however, that describes the impact of long term tillage and residue management on soil properties in the subarctic region of the United States. This study examines the impact of 20 years of tillage and residue management on a broad range of physical properties that govern wind erosion processes on a silt loam in interior Alaska. A strip plot experimental design was established in 1983 and included intensive tillage (autumn and spring disk), spring disk, autumn chisel plow, and no tillage with straw either retained on or removed from the soil surface. Soil and residue properties measured after sowing barley (Hordeum vulgare L.) in May 2004 included penetration resistance, soil water content, shear stress, bulk density, random roughness, aggregate size distribution, and residue cover and biomass. No tillage was characterized by larger aggregates, greater soil strength (penetration resistance and shear stress), wetter soil, and greater residue cover compared to all other tillage treatments. Despite crop failures the previous 2 years, crop residue management influenced residue biomass and cover, but not soil properties. Autumn chisel and spring disk appeared to be viable minimum tillage options to intensive tillage in controlling erosion. Autumn chisel and spring disk promoted greater roughness, aggregation, and residue cover as compared with intensive tillage. Although no tillage appeared to be the most effective management strategy for mitigating wind erosion, no tillage was not a sustainable practice due to lack of weed control. No tillage also resulted in the formation of an organic layer on the soil surface over the past 20 years, which has important ramifications for long term crop production in the subarctic where the mean annual temperature is <0 °C.     

Effects of residue management and controlled traffic on carbon dioxide and water loss

Management of crop residues and soil organic matter is of primary importance in maintaining soil fertility and productivity and in minimizing agricultural impact on the environment. Our objective was to determine the effects of traffic and tillage on short-term carbon dioxide (CO₂) and water (H₂O) fluxes from a representative soil in the southeastern Coastal Plain (USA). The study was conducted on a Norfolk loamy sand (FAO classification, Luxic Ferralsols; USDA classification, fine-loamy siliceous, thermic Typic Kandiudults) cropped to a corn (Zea mays L.) — soybean (Glycine max (L.) Merr) rotation with a crimson clover (Trifolium incarnatum L.) winter cover crop for eight years. Experimental variables were with and without traffic under conventional tillage (CT) (disk harrow twice, chisel plow, field cultivator) and no tillage (NT) arranged in a split-plot design with four replicates. A wide-frame tractive vehicle enabled tillage without wheel traffic. Short-term CO₂ and H₂O fluxes were measured with a large portable chamber. Gas exchange measurements were made on both CT and NT at various times associated with tillage and irrigation events. Tillage-induced CO₂ and H₂O fluxes were larger than corresponding fluxes from untilled soil. Irrigation caused the CO₂ fluxes to increase rapidly from both tillage systems, suggesting that soil gas fluxes were initially limited by lack of water. Tillage-induced CO₂ and H₂O fluxes were consistently higher than under NT. Cumulative CO₂ flux from CT at the end of 80 h was nearly three times larger than from NT while the corresponding H₂O loss was 1.6 times larger. Traffic had no significant effects on the magnitude of CO₂ fluxes, possibly reflecting this soil’s natural tendency to reconsolidate. The immediate impact of intensive surface tillage of sandy soils on gaseous carbon loss was larger than traffic effects and suggests a need to develop new management practices for enhanced soil carbon and water management for these sensitive soils.     

Twenty years of tillage research in subarctic Alaska: I. Impact on soil strength,aggregation, roughness,and residue cover

Soil properties and surface characteristics affecting wind erosion can be manipulated through tillage and crop residue management. Little information exists, however, that describes the impact of long term tillage and residue management on soil properties in the subarctic region of the United States. This study examines the impact of 20 years of tillage and residue management on a broad range of physical properties that govern wind erosion processes on a silt loam in interior Alaska. A strip plot experimental design was established in 1983 and included intensive tillage (autumn and spring disk), spring disk, autumn chisel plow, and no tillage with straw either retained on or removed from the soil surface. Soil and residue properties measured after sowing barley (Hordeum vulgare L.) in May 2004 included penetration resistance, soil water content, shear stress, bulk density, random roughness, aggregate size distribution, and residue cover and biomass. No tillage was characterized by larger aggregates, greater soil strength (penetration resistance and shear stress), wetter soil, and greater residue cover compared to all other tillage treatments. Despite crop failures the previous 2 years, crop residue management influenced residue biomass and cover, but not soil properties. Autumn chisel and spring disk appeared to be viable minimum tillage options to intensive tillage in controlling erosion. Autumn chisel and spring disk promoted greater roughness, aggregation, and residue cover as compared with intensive tillage. Although no tillage appeared to be the most effective management strategy for mitigating wind erosion, no tillage was not a sustainable practice due to lack of weed control. No tillage also resulted in the formation of an organic layer on the soil surface over the past 20 years, which has important ramifications for long term crop production in the subarctic where the mean annual temperature is <0 °C.     

Influence of tillage and plant residue management on respiration of a Florida Everglades Histosol

Subsidence of drained, high organic matter Histosols in the Everglades Agricultural Area (EAA) is a concern for the sustainability of crop production in southern Florida. Histosol subsidence is primarily due to oxidation of organic matter by aerobic microorganisms, but far less is known about the influence of agricultural practices. The use of shallow tillage, as opposed to deep tillage, combined with proper plant residue management, may help to reduce the present rate of subsidence and soil CO₂ emissions. The present study was conducted on a Lauderhill soil (euic, hyperthermic, Lithic Haplosaprist) previously cropped in sugarcane (Saccharum spp.). The objectives were to (1) determine the effects of tillage depth on short-term CO₂ losses in a herbicide-killed weedy residue covered field and another field kept fallow without residue cover, and (2) compare soil respiration measurements made with two different dynamic closed-system portable chamber techniques. Four tillage practices common to the EAA were used to produce soil disturbance ranging in depth from approximately 20 to 300 mm. These practices included switch plowing, disk harrowing, and single and multiple tine cultivation. Twenty-four hours after tillage, cumulative CO₂ loss from the deepest tillage treatment (switch plow; 300 mm deep) was as much as 33 times greater than that from the no-till (control) treatment. Cumulative CO₂ loss following intermediate tillage (disk harrow; 78–145 mm deep) was as much as 2.3-fold greater than the no-till treatment, but shallower tillage (tine cultivation; 20–41 mm deep) was generally not different. Short-term tillage-induced CO₂ loss was primarily related to soil moisture content and soil porosity. Soil respiration measurements made with the two chamber techniques agreed well with each other except for the deepest tillage treatment, where the larger chamber measured CO₂ flux that was approximately 10 times greater than for the smaller chamber. Results indicate that minimum or no-tillage may reduce short-term tillage-induced CO₂ emissions on organic soils, thus minimizing soil subsidence.     

免耕秸秆还田和传统耕作方式下东北黑土氨基糖态碳的积累特征

以吉林德惠市中层黑土进行7年田间定位试验的小区土壤为研究对象,对免耕(NT)和传统耕作下(CT)耕层(0～20 cm)氨基糖态碳含量的变化特征进行了分析。结果表明,与传统耕作相比,实施免耕7年后整个耕层土壤中氨基糖态碳含量显著增加(p<0.05),以表层(0～5 cm)增加幅度最大,高达94.7%。说明在研究地区,免耕措施有利于微生物代谢物如细胞壁物质等作为潜在的碳源逐渐积累在土壤中。免耕土壤中不同微生物来源氨基糖态碳的含量均较传统耕作有显著增加,但是变化特征有所不同,其中免耕条件下真菌来源的氨基葡萄糖的积累量较传统耕作高出1倍多,而且氨基葡萄糖与细菌来源的胞壁酸的比值(6.9～7.3)显著高于传统耕作(4.7～5.4),暗示实施免耕秸秆还田7年后土壤中真菌已逐渐转为优势群体,而真菌占优势的农田生态系统具有更大的固碳潜力。     

Spatial distributions of soil chemical and physical properties prior to planting soybean in soil under ridge‐, no‐ and conventional‐tillage in a maize–soybean rotation

Detailed information on the profile distributions of agronomically important soil properties in the planting season can be used as criteria to select the best soil tillage practices. Soil cores (0–60 cm) were collected in May, 2012 (before soybean planting), from soil transects on a 30‐yr tillage experiment, including no‐tillage (NT), ridge tillage (RT) and mouldboard plough (MP) on a Brookston clay loam soil (mesic Typic Argiaquoll). Soil cores were taken every 19 cm across three corn rows and these were used to investigate the lateral and vertical profile characteristics of soil organic carbon (SOC), pH, electrical conductivity (EC), soil volumetric water content (SWC), bulk density (BD), and penetration resistance (PR). Compared to NT and MP, the RT system resulted in greater spatial heterogeneity of soil properties across the transect. Average SOC concentrations in the top 10 cm layer were significantly greater in RT than in NT and MP (P = 0.05). NT soil contained between 0.8 and 2.5% (vol/vol) more water in the top 0–30 cm than RT and MP, respectively. MP soil had lower PR and BD in the plough layer compared to NT and RT soils, with both soil properties increasing sharply with depth in MP. The RT had lower PR relative to NT in the upper 35 cm of soil on the crop rows. Overall, RT was a superior conservation tillage option than NT in this clay loam soil; however, MP had the most favourable soil conditions in upper soil layers for early crop development across all treatments.     

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

Soil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P < 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths >10 cm. All parameters were positively correlated (P < 0.01); linear regressions exhibited similar patterns (P < 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.     

Influence of wheat residue management on irrigated corn grain production in a reduced tillage system

Management of wheat (Triticum aestivum L.) residues for corn (Zea mays L.) planting is an important issue in southern parts of Iran where these two irrigated crops are consecutively grown. Concerns have been raised in recent years over the burning of the crop residues by farmers in these areas. A 2-year (2001–2002) field experiment was conducted as a randomized complete block design with three replications. The treatments consisted of irrigated corn planted, after burning wheat residues followed by conventional tillage (CT), after residue removal followed by CT, after soil incorporation of 0, 25, 50, 75, and 100% of residue followed by chisel plow, disk harrow, and row crop planter equipped with row cleaner. The CT operations consisted of mollboard plowing followed by two times disk harrowing. Treatments had significant effects on corn grain yield, biological yield, and leaf area index. The highest grain yield (15.73 t ha⁻¹) and grains per ear (709.3) were obtained when 25–50% of wheat residues were soil incorporated and the seeds were sown with planter equipped with row cleaner in both years as compared with conventional tillage practices. It is recommended that complete residue removal or burning should be avoided; hence for successful corn production after wheat, residue management techniques that reduce residue level in the row area should be implemented.     

Earthworm dynamics and soil physical properties in the first three years of no-till management

Earthworms are often referred to as ecosystem engineers due to their ability to alter the soil environment. Since earthworms influence a wide range of critical chemical and physical soil properties it is important to understand how their populations are impacted by soil management. Earthworms were sampled during the spring and summer of 2001, 2002, and 2003 from conventional tillage (CT) and no-till (NT) plots established in 2000. Although there was a strong trend for higher earthworm density in NT plots in 2001 (p = 0.08) and 2002 (p = 0.19), statistically significant differences were not detected between tillage treatments until 2003 (p = 0.04) when mean earthworm density was 37.7 individuals m⁻² in CT and 149.9 individuals m⁻² in NT during spring and 17.1 individuals m⁻² in CT and 58.4 individuals m⁻² in NT in summer. A high mortality rate between spring and summer, combined with greater cocoon production under NT suggests that the earthworm population turns over rapidly in NT plots. Data also suggest that adverse soil environmental conditions will limit earthworm density in these dryland agroecosystems. Despite significantly higher earthworm density after three years of NT management, soil bulk density, saturated hydraulic conductivity, and aggregate stability of the 0.5- to 1-mm size fraction were not different between the two tillage treatments. The apparent lack of impact of reduced disturbance and increased earthworm density on soil physical properties may be due to the short time this soil has been under NT management, limited seasonal earthworm activity due to environmental conditions, or differences in the scale at which soil physical properties have been affected after three years of NT management and the scale at which our measurements were made.     

不同耕作方式对中国东北黑土有机碳的短期影响

A tillage experiment, consisting of moldboard plow （MP）, ridge tillage （RT）, and no-tillage （NT）, was performed in a randomized complete block design with four replicates to study the effect of 3-year tillage management on SOC content and its distribution in surface layer （30 cm） of a clay loam soil in northeast China. NT did not lead to significant increase of SOC in topsoil （0-5 cm） compared with MP and RT; however, the SOC content in NT soil was remarkably reduced at a depth of 5-20 cm. Accordingly, short-term （3-year） NT management tended to stratify SOC concentration, but not necessarily increase its storage in the plow layer for the soil.     

Twenty years of conservation tillage research in subarctic Alaska: II. Impact on soil hydraulic properties

Soil management practices are needed in the subarctic that stabilize the soil against the forces of wind and water as well as conserve soil water for crop production. There is a paucity of information, however, regarding the long-term effects of conservation tillage on soil hydraulic properties in subarctic Alaska. The objective of this study was therefore to characterize infiltration, water retention, and saturated hydraulic conductivity of a soil 20 years after establishing tillage and straw management treatments in interior Alaska. The strip plot experimental design, established on a silt loam and maintained in continuous barley (Hordeum vulgare L.), included tillage as the main treatment and straw management as the secondary treatment. Tillage treatments included no tillage, autumn chisel plow, spring disk, and intensive tillage (autumn and spring disk) while straw treatments included retaining or removing stubble and loose straw from the soil surface after harvest. Soil properties were measured after sowing in spring 2004; saturated hydraulic conductivity was measured by the falling-head method, infiltration was measured using a double-ring infiltrometer, and water retention was assessed by measuring the temporal variation in in-situ soil water content. No tillage resulted in greater saturated hydraulic conductivity and generally retained more water against gravitational and matric forces than other tillage treatments. Infiltration was greater in autumn chisel plow than other tillage treatments and was presumably suppressed in no tillage by an organic layer overlying mineral soil. Infiltration was also enhanced by retaining straw on rather than removing straw from the soil surface after harvest. No tillage is not yet a sustainable management practice in this region due to lack of weed control strategies. In addition, the formation of an organic layer in no tillage has important ramifications for the soil hydrological and thermal environment. Therefore, minimum tillage (i.e., autumn chisel plow or spring disk) appears to be a viable management option for maximizing infiltration in interior Alaska.     

Changes in soil organic carbon and its chemical fractions under different tillage practices on loess soils of the Guanzhong Plain in north‐west China

Over the past 20 years, conservation tillage has been used on the loess plateau of north‐west China to improve the sustainability of local agriculture. There had been particular concern about loss of soil organic matter associated with traditional tillage. We examined the influence of four tillage treatments: conventional tillage (CT), subsoiling tillage (SST), rotary tillage (RT) and no‐tillage (NT), with two straw residue management treatments (return and removal) on the distribution with soil depth (0–20 cm, 20–40 cm) of total organic carbon, labile organic carbon (KMnO₄‐C) and bound organic carbon. The study was carried out on a Loutu soil (Earth‐cumuli‐Orthic Anthrosol) over seven consecutive years of a winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) crop rotation. By the end of this period, conservation tillage (SST, RT and NT) led to greater storage of soil organic carbon (SOC) (22.7, 14.9 and 16.3% with straw return in contrast to 21.4, 15.8 and 12.3% with no straw return, respectively) compared with CT in the surface soil (0–20 cm). The reduced tillage treatments (SST and RT) both increased significantly the highly labile organic carbon (HLOC) content of the surface soil (50% in both SST and RT) and mildly labile organic matter (MLOC) (49.4 in SST and 53.5% in RT) when straw was removed. The largest pool of bound carbon was observed in the Humin‐C pool, and the smallest in the free humic acids C (FHA‐C) in each tillage treatment. Conservation tillage led to an increased content of FHA‐C and CHA‐C. Results from correlation analyses indicate that SOC enrichment might have resulted from the increase in HLOC, MLOC, FHA‐C and CHA‐C over a short period. Labile organic carbon was associated with the organic carbon that was more loosely combined with clay (FHA‐C and CHA‐C). We conclude that both SST and RT are effective in maintaining or restoring organic matter in Loutu soils in this region, and the effect is greater when they are used in combination with straw return.     

Tillage effects on soil properties and wheat cultivars traits

Information regarding the evaluation of tillage effects on soil properties and rainfed wheat (Triticum aestivum L.) cultivars of Iranian fields is not available. Therefore, this research was conducted in Sanandaj (west of Iran) using a randomized complete block design in a split-plot arrangement. Three types of tillage including conventional tillage (moldboard plow to soil depth of 30 cm plus disk harrow twice), minimum tillage (chisel plow to soil depth of 15 cm plus disk harrow once) and no-tillage are assigned to the main plots. Wheat cultivars (Sardari and Azar2) were randomly distributed within the subplots in each tillage system. Results showed that the greatest bulk density and cone index were found in the minimum tillage and no tillage systems. The highest rate of grain yield was obtained in the minimum tillage system. The grain yield of Sardari cultivar (1624.1 kg ha^?1) was significantly greater than that of Azar2 (1572 kg ha^?1). Minimum tillage improved soil physical properties and wheat growth compared with the other tillage systems. No tillage increased microbial biomass carbon and bacteria number in soil compared with the other tillage systems. We conclude that using minimum tillage for Sardari cultivar will be more effective compared with other treatments.     

Soil organic carbon and nitrogen in a Minnesota soil as related to tillage, residue and nitrogen management

Soil organic carbon (SOC) and nitrogen (N) are directly influenced by tillage, residue return and N fertilization management practices. Soil samples for SOC and N analyses, obtained from a 23-year field experiment, provided an assessment of near-equilibrium SOC and N conditions. Crops included corn (Zea mays L.) and soybean [Glycine max L. (Merrill)]. Treatments of conventional and conservation tillage, residue stover (returned or harvested) and two N fertilization rates were imposed on a Waukegan silt loam (fine-silty over skeletal, mixed, superactive, mesic Typic Hapludoll) at Rosemount, MN. The surface (0–20 cm) soils with no-tillage (NT) had greater than 30% more SOC and N than moldboard plow (MB) and chisel plow (CH) tillage treatments. The trend was reversed at 20–25 cm soil depths, where significantly more SOC and N were found in MB treatments (26 and 1.5 Mg SOC and N ha⁻¹, respectively) than with NT (13 and 1.2 Mg SOC and N ha⁻¹, respectively), possibly due to residues buried by inversion. The summation of soil SOC over depth to 50 cm did not vary among tillage treatments; N by summation was higher in NT than MB treatments. Returned residue plots generally stored more SOC and N than in plots where residue was harvested. Nitrogen fertilization generally did not influence SOC or N at most soil depths. These results have significant implications on how specific management practices maximize SOC storage and minimize potential N losses. Our results further suggest different sampling protocols may lead to different and confusing conclusions regarding the impact of tillage systems on C sequestration.