保护性耕作对黑土微生物群落的影响

耕作方式通过影响土壤微生物群落而影响土壤生态系统过程。本研究以传统耕作玉米连作处理为对照,通过测定土壤微生物量碳及磷脂脂肪酸含量,分析了保护性耕作(包括免耕玉米连作和免耕大豆-玉米轮作)对黑土微生物群落的影响。结果表明,保护性耕作可显著增加土壤表层(0～5cm)全碳、全氮、水溶性有机碳、碱解氮和微生物量碳(P0.05),为微生物代谢提供了丰富的资源。同时,保护性耕作显著提高了土壤表层(0～5cm)总脂肪酸量、真菌和细菌生物量(P0.05),提高了土壤的真菌/细菌值,有利于农田土壤生态系统的稳定性。研究结果对于探讨保护性耕作的内在机制具有重要意义。     

Soil carbon and nitrogen dynamics as affected by long-term tillage and nitrogen fertilization

Quantifying seasonal dynamics of active soil C and N pools is important for understanding how production systems can be better managed to sustain long-term soil productivity especially in warm subhumid climates. Our objectives were to determine seasonal dynamics of inorganic soil N, potential C and N mineralization, soil microbial biomass C (SMBC), and the metabolic quotient of microbial biomass in continuous corn (Zea mays L.) under conventional (CT), moldboard (MB), chisel (CH), minimum tillage (MT), and no-tillage (NT) with low (45kgNha^–1) and high (90kgNha^–1) N fertilization. An Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf) in south Texas, United States, was sampled before corn planting in February, during pollination in May, and following harvest in July. Soil inorganic N, SMBC, and potential C and N mineralization were usually highest in soils under NT, whereas these characteristics were consistently lower throughout the growing season in soils receiving MB tillage. Nitrogen fertilization had little effect on soil inorganic N, SMBC, and potential C and N mineralization. The metabolic quotient of microbial biomass exhibited seasonal patterns inverse to that of SMBC. Seasonal changes in SMBC, inorganic N, and mineralizable C and N indicated the dependence of seasonal C and N dynamics on long-term substrate availability from crop residues. Long-term reduced tillage increased soil organic matter (SOM), SMBC, inorganic N, and labile C and N pools as compared with plowed systems and may be more sustainable over the long term. Seasonal changes in active soil C and N pools were affected more by tillage than by N fertilization in this subhumid climate. Received: 20 September 1996     

Yield and N uptake as affected by soil tillage and catch crop

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.     

The influence of tillage on the proportion of organic carbon and nitrogen in the microbial biomass of medium-textured soils in a humid climate

Summary Microbial biomass C and N respond rapidly to changes in tillage and soil management. The ratio of biomass C to total organic C and the ratio of mineral N flush to total N were determined in the surface layer (0–5 cm) of low-clay (8–10%), fine sandy loam, Podzolic soils subjected to a range of reduced tillage (direct drilling, chisel ploughing, shallow tillage) experiments of 3–5 years' duration. Organic matter dynamics in the tillage experiments were compared to long-term conditions in several grassland sites established on the same soil type for 10–40 years. Microbial biomass C levels in the grassland soils, reduced tillage, and mouldboard ploughing treatments were 561, 250, and 155 g g^-1 soil, respectively. In all the systems, microbial biomass C was related to organic C (r=0.86), while the mineral N flush was related to total N (r=0.84). The average proportion of organic C in the biomass of the reduced tillage soils (1.2) was higher than in the ploughed soils (0.8) but similar to that in the grassland soils (1.3). Reduced tillage increased the average ratio of mineral N flush to total soil N to 1.9, compared to 1.3 in the ploughed soils. The same ratio was 1.8 in the grassland soils. Regression analysis of microbial biomass C and percent organic C in the microbial biomass showed a steeper slope for the tillage soils than the grassland sites, indicating that reduced tillage increased the microbial biomass level per unit soil organic C. The proportion of organic matter in the microbial biomass suggests a shift in organic matter equilibrium in the reduced tillage soils towards a rapid, tillage-induced, accumulation of organic matter in the surface layer.     

耕作方式对双季稻田土壤有机碳储量的影响

Tillage practices can potentially afect soil organic carbon (SOC) accumulation in agricultural soils. A 4-year experiment was conducted to identify the influence of tillage practices on SOC sequestration in a double-cropped rice (Oryza sativa L.) field in Hunan Province of China. Three tillage treatments, no-till (NT), conventional plow tillage(PT), and rotary tillage(RT), were laid in a randomized complete block design. Concentrations of SOC and bulk density(BD) of the 0-80 cm soil layer were measured, and SOC stocks of the 0-20 and 0-80 cm soil layers were calculated on an equivalent soil mass(ESM) basis and fixed depth (FD) basis.Soil carbon budget(SCB) under diferent tillage systems were assessed on the basis of emissions of methane(CH4) and CO2 and the amount of carbon (C) removed by the rice harvest. After four years of experiment, the NT treatment sequestrated more SOC than the other treatments. The SOC stocks in the 0-80 cm layer under NT (on an ESM basis) was as high as 129.32 Mg C ha 1,significantly higher than those under PT and RT (P < 0.05). The order of SOC stocks in the 0-80 cm soil layer was NT > PT > RT,and the same order was observed for SCB; however, in the 0-20 cm soil layer, the RT treatment had a higher SOC stock than the PT treatment. Therefore, when comparing SOC stocks, only considering the top 20 cm of soil would lead to an incomplete evaluation for the tillage-induced efects on SOC stocks and SOC sequestrated in the subsoil layers should also be taken into consideration. The estimation of SOC stocks using the ESM instead of FD method would better reflect the actual changes in SOC stocks in the paddy filed, as the FD method amplified the tillage efects on SOC stocks. This study also indicated that NT plus straw retention on the soil surface was a viable option to increase SOC stocks in paddy soils.     

川西贡嘎山不同森林生态系统土壤有机碳垂直分布与组成特征

通过野外采样与室内实验相结合的方法,对川西典型亚高山不同海拔处暗针叶林、针阔混交林和常绿-落叶阔叶林3种森林类型表层土壤总有机碳（SOC）和活性有机碳的含量特征进行分析,旨在为亚高山生态系统土壤碳循环研究提供理论和数据支撑。结果表明：3种森林类型土壤中总有机碳含量（SOC）在44.21～179.98g·kg-1,表层（0-15cm）SOC含量大小顺序为针阔混交林＞常绿-落叶阔叶林＞暗针叶林,0-5cm土层SOC含量与活性有机碳含量均高于5-15cm土层,说明土壤有机碳具有土壤表聚现象。3种森林类型间SOC密度差异不显著,但不同森林类型土壤SOC密度沿土层的分布具有差别：与常绿-落叶阔叶林和暗针叶林相比,针阔混交林5-15cm土层SOC密度较高。土壤溶解性有机碳（DOC）、轻组分有机碳（LFOC）和微生物（MBC）含量均以针阔混交林最高,但其相对于SOC的比例则以暗针叶林最高,说明高海拔生态系统土壤活性有机碳有更大的累积,同时也暗示在气候变化背景下,高海拔生态系统可能具有更大的CO2排放风险。     

Soil organic matter quality as influenced by tillage,lime, and phosphorus

In Eastern Canada, cereal yields are often restricted by soil acidity and low fertility. Continuous cereal production can also lead to soil structural degradation. The addition of lime and fertilizers and the adoption of conversation tillage practices are proposed solutions which may have a positive impact on soil quality. The objective of the present work was to assess the impact of 3 years of different tillage practices and P additions, and of a single lime addition on organic C and total N, microbial biomass C, and on N mineralization at the surface layer (0–7.5 cm) of a Courval sandy clay loam (Humic Gleysol). The easily mineralizable N, total amount of N mineralized in 22.1 weeks, the rate of N mineralization, and microbial biomass C were significantly greater in the minimum tillage than in the moldboard plow treatment. Chisel plow treatment showed intermediate values. The ratios of potentially mineralizable N and of easily mineralizable to total soil N were also significantly larger under minimum tillage and chisel plowing than under moldboard plowing. The lime and P treatments had no significant effect on the measured soil quality parameters. The total amount of N mineralized per unit of biomass C decreased as the tillage intensity increased, suggesting a decrease in the efficiency of the biomass in transforming organic N into potentially plant-available forms and thus a loss in soil organic matter quality. The results of this study indicate that conservation tillage practices such as rototilling and chisel plowing are efficient ways of maintaining soil organic matter quality when old pastures are brought back into cultivation.     

Arylamidase and amidohydrolases in soils as affected by liming and tillage systems

This study investigated the long-term effect of lime application and tillage systems (no-till, ridge-till and chisel plow) on the activities of arylamidase and amidohydrolases involved in N cycling in soils at four long-term research sites in Iowa, USA. The activities of the following enzymes were assayed: arylamidase, -asparaginase, -glutaminase, amidase, urease, and -aspartase at their optimal pH values. The activities of the enzymes were significantly (P<0.001) and positively correlated with soil pH, with r values ranging from 0.42^* to 0.99^*** for arylamidase, 0.81^*** to 0.97^*** for -asparaginase, 0.62^*** to 0.97^*** for -glutaminase, 0.61^*** to 0.98^*** for amidase, 0.66^** to 0.96^*** for urease, and 0.80^*** to 0.99^*** for -aspartase. The Δactivity/ΔpH values were calculated to assess the sensitivity of the enzymes to changes in soil pH. The order of the sensitivity of enzymes was as follows: -

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-aspartase. The enzyme activities were greater in the samples of the 0–5 cm depth than those of the 0–15 cm samples under no-till treatment. Most of the enzyme activities were significantly (P<0.001) and positively correlated with microbial biomass C (C_mic) and N (N_mic). Lime application significantly affected the specific activities of the six enzymes studied. Results showed that soil management practices, including liming and type of tillage significantly affect soil biological and biochemical properties, which may lead to changes in nitrogen cycling, including N mineralization in soils.     

In situ and potential CO2 evolution from a Fluventic Ustochrept in southcentral Texas as affected by tillage and cropping intensity

Quality of agricultural soils is largely a function of soil organic matter. Tillage and crop management impact soil organic matter dynamics by modification of the soil environment and quantity and quality of C input. We investigated changes in pools and fluxes of soil organic C (SOC) during the ninth and tenth year of cropping with various intensities under conventional disk-and-bed tillage (CT) and no tillage (NT). Soil organic C to a depth of 0.2 m increased with cropping intensity as a result of greater C input and was 10% to 30% greater under NT than under CT. Sequestration of crop-derived C input into SOC was 22±2% under NT and 9±4% under CT (mean of cropping intensities ± standard deviation of cropping systems). Greater sequestration of SOC under NT was due to a lower rate of in situ soil CO₂ evolution than under CT (0.22±0.03 vs. 0.27±0.06 g CO₂–C g⁻¹ SOC yr⁻¹). Despite a similar labile pool of SOC under NT than under CT (1.1±0.1 vs. 1.0±0.1 g mineralizable C kg⁻¹ SOC d⁻¹), the ratio of in situ to potential CO₂ evolution was less under NT (0.56±0.03) than under CT (0.73±0.08), suggesting strong environmental controls on SOC turnover, such as temperature, moisture, and residue placement. Both increased C sequestration and a greater labile SOC pool were achieved in this low-SOC soil using NT and high-intensity cropping.     

Root growth conditions in the topsoil as affected by tillage intensity

Many studies have reported impeded root growth in topsoil under reduced tillage or direct drilling, but few have quantified the effects on the least limiting water range for root growth. This study explored the effects of tillage intensity on critical soil physical conditions for root growth in the topsoil. Samples were taken from a 7-year tillage experiment on a Danish sandy loam at Foulum, Denmark (56°30′ N, 9°35′ E) in 2008. The main crop was spring barley followed by either dyer's woad (Isatis tinctoria L.) or fodder radish (Raphanus sativus L.) cover crops as subtreatment. The tillage treatments were direct drilling (D), harrowing 8-10 cm (H), and ploughing (P) to 20 cm depth. A chisel coulter drill was used in the H and D treatments and a traditional seed drill in the P treatment. Undisturbed soil cores were collected in November 2008 at soil field moisture capacity from the 4-8 and 12-16 cm depths.We estimated the critical aeration limit from either 10% air-filled porosity (ε_a) or relative gas diffusivity (D/D₀) of 0.005 or 0.02 and found a difference between the two methods. The critical limit of soil aeration was best assessed by measuring gas diffusivity directly. Root growth was limited by a high penetration resistance in the D and H soils (below tillage depth). Poor soil aeration did not appear to be a significant limiting factor for root growth for this sandy loam soil, irrespective of tillage treatment. The soil had a high macroporosity and D/D₀ exceeded 0.02 at field capacity. Fodder radish resulted in more macropores, higher gas diffusivity and lower pore tortuosity compared to dyer's woad. This was especially important for the H treatment where compaction was a significant problem at the lower depths of the arable layer (10-20 cm depth). Our results suggest that fodder radish could be a promising tool in the amelioration of soil compaction.     

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。     

Transport of labile carbon in runoff as affected by land use and rainfall characteristics

The mobilization of organic carbon (C) by water erosion could impact the terrestrial C budget, but the magnitude and direction of that impact remain uncertain due to a lack of data regarding the fates and quality of eroded C. A study was conducted to monitor total organic C and mineralizable C (MinC) in eroded materials from watersheds under no till (NT), chisel till (CT), disk till low input (DT-LI), pasture and forest. The DT-LI treatment relies on manure application and legume cover crops to partly supply the N needed when corn is grown, and on cultivation to reduce the use of herbicides. Each watershed was instrumented with a flume and a Coshocton wheel sampler for runoff measurement. Carbon dioxide (CO₂) evolved during incubation (115 days) of runoff samples was fitted to a first-order decomposition model to derive MinC. Annual soil (6.2 Mg ha⁻¹) and organic C (113.8 kg C ha⁻¹) losses were twice as much in the DT-LI than in the other watersheds (<2.7 Mg soil ha⁻¹, <60 kg C ha⁻¹). More than management practices, rainfall class (based on intensity and energy) was a better controller of sediment C concentration and biodegradability. Sediment collected during the low-intensity (fall/winter) storms contained more organic C (37 g C kg⁻¹) and MinC (30–40% of sediment C) than materials displaced during the high-intensity summer storms (22.1 g C kg⁻¹ and 13%, respectively). These results suggest a more selective detachment and sorting of labile C fractions during low-intensity storms. However, despite the control of low-intensity storm on sediment C concentration and quality, increased soil loss with high-energy rainfall suggests that a few infrequent but high-energy storms could determine the overall impact of erosional events on terrestrial C cycling.     

Short-term temporal changes of soil carbon losses after tillage described by a first-order decay model

Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions, and thus favoring microbial decomposition. In addition, soil aggregate disruption by tillage exposes once protected organic matter to decomposition. We propose a model to explain carbon dioxide (CO₂) emission after tillage as a function of the no-till emission plus a correction due to the tillage disturbance. The model assumes that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as: dC_sail(t)/dt = −kC_soil(t) and that soil C-CO₂ emission is proportional to the C decay rate in soil, where C_soil(t) is the available labile soil C (g m⁻²) at any time (t). Emissions are modeled in terms soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between no-till (F_NT) and tilled (F_T) fluxes, which is: F_T=a₁F_NT e^−a₂t, where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient (R²), index of agreement and model efficiency, with R² as high as 0.97. The two parameters included in the model are related to the difference between the decay constant (k factor) of tilled and no-till plots (a₂) and also to the amount of labile carbon added to the readily decomposable soil organic matter due to tillage (a₁). These two parameters were estimated in the model ranging from 1.27 and 2.60 (a₁) and −1.52 × 10⁻² and 2.2 × 10⁻² day⁻¹ (a₂). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the no-till emission plus an exponential term modulated by tillage and environmentally dependent parameters.     

Soil organic carbon and nitrogen in a Mollisol in central Ohio as affected by tillage and land use

Minimum tillage practices are known for increasing soil organic carbon (SOC). However, not all environmental situations may manifest this potential change. The SOC and N stocks were assessed on a Mollisol in central Ohio in an 8-year-old tillage experiment as well as under two relatively undisturbed land uses; a secondary forest and a pasture on the same soil type. Cropped systems had 51±4 (equiv. mass) Mg ha⁻¹ lower SOC and lower 3.5±0.3 (equiv. mass) Mg ha⁻¹ N in the top 30 cm soil layer than under forest. Being a secondary forest, the loss in SOC and N stocks by cultivation may have been even more than these reported herein. No differences among systems were detected below this depth. The SOC stock in the pasture treatment was 29±3 Mg ha⁻¹ greater in the top 10 cm layer than in cultivated soils, but was similar to those under forest and no-till (NT). Among tillage practices (plow, chisel and NT) only the 0–5 cm soil layer under NT exhibited higher SOC and N concentrations. An analysis of the literature of NT effect on SOC stocks, using meta-analysis, suggested that NT would have an overall positive effect on SOC sequestration rate but with a greater variability of what was previously reported. The average sequestration rate of NT was 330 kg SOC ha⁻¹ year⁻¹ with a 95% confidence interval ranging from 47 to 620 kg SOC ha⁻¹ year⁻¹. There was no effect of soil texture or crop rotation on the SOC sequestration rate that could explain this variability. The conversion factor for SOC stock changes from plow to NT was equal to 1.04. This suggests that the complex mechanisms and pathways of SOC accrual warrant a cautious approach when generalizing the beneficial changes of NT on SOC stocks.     

Influence of reduced tillage on earthworm and microbial communities under organic arable farming

Although reduced tillage is an agricultural practice reported to decrease soil erosion and external inputs while enhancing soil fertility, it has still rarely been adopted by European organic farmers. The objective of this study was to assess the long-term interactive effects of tillage (conventional (CT) vs. reduced (RT)) and fertilization (slurry (S) vs. composted manure/slurry (MCS)) on earthworms and microbial communities in a clay soil under spelt in an organic 6-year crop rotation. Earthworm populations (species, density and biomass, cocoons) were investigated by handsorting the soil nine years after initial implementation of the treatments. Soil microbial carbon (C_mic) and nitrogen (N_mic) were measured by chloroform-fumigation extraction and a simplified phospholipid fatty acid (PLFA) analysis was used to separate for populations of bacteria, fungi and protozoa. Significantly increased total earthworm density in RT plots was mainly attributed to increased numbers of juveniles. Moreover, we found five times more cocoons with RT. Species richness was not affected by the treatments, but tillage treatments had differentially affected populations at the species-level. In addition, cluster analysis at the community level revealed two distinct groups of plots in relation to tillage treatments. In RT plots C_mic increased in the 0–10 cm and 10–20 cm soil layers, while PLFA concentrations indicative of Gram-negative bacteria, fungi and protozoa only increased in the topsoil. Lower bacteria-to-fungi ratios in the upper soil layer of RT plots indicated a shift to fungal-based decomposition of organic matter whereas a higher C_mic-to-C_org ratio pointed towards enhanced substrate availability. Slurry application decreased microbial biomass and enhanced density of juvenile anecic earthworms but overall fertilization effect was weak and no interactions with tillage were found. In conclusion, tillage is a major driver in altering communities of earthworms and microorganisms in arable soils. The use of reduced tillage provides an approach for eco-intensification by enhancing inherent soil biota functions under organic arable farming.     

Labile, recalcitrant, and microbial carbon and nitrogen pools of a tallgrass prairie soil in the US Great Plains subjected to experimental warming and clipping

Carbon (C) and nitrogen (N) fluxes are largely controlled by the small but highly bio-reactive, labile pools of these elements in terrestrial soils, while long-term C and N storage is determined by the long-lived recalcitrant fractions. Changes in the size of these pools and redistribution among them in response to global warming may considerably affect the long-term terrestrial C and N storage. However, such changes have not been carefully examined in field warming experiments. This study used sulfuric acid hydrolysis to quantify changes in labile and recalcitrant C and N fractions of soil in a tallgrass prairie ecosystem that had been continuously warmed with or without clipping for about 2.5 years. Warming significantly increased labile C and N fractions in the unclipped plots, resulting in increments of 373 mg C kg⁻¹ dry soil and 15 mg N kg⁻¹ dry soil, over this period whilst clipping significantly decreased such concentrations in the warmed plots. Warming also significantly increased soil microbial biomass C and N in the unclipped plots, and increased ratios of soil microbial/labile C and N, indicating an increase in microbial C- and N-use efficiency. Recalcitrant and total C and N contents were not significantly affected by warming. For all measured pools, only labile and microbial biomass C fractions showed significant interactions between warming and clipping, indicating the dependence of the warming effects on clipping. Our results suggest that increased soil labile and microbial C and N fractions likely resulted indirectly from warming increases in plant biomass input, which may be larger than warming-enhanced decomposition of labile organic compounds.     

Physical and mechanical properties of a clayey soil as affected by tillage systems for wheat growth

Abstract

The effect of tillage systems on soil physical properties of a clayey soil was studied. Tillage systems consisting of conventional tillage I (CT₁), conventional tillage II (CT₂), reduced conventional tillage (RCT), reduced tillage (RT) and no tillage (NT) were carried out in autumn after harvest of sugar beet. Significant differences between tillage systems were recorded on the measured properties, apart from moisture content, at 15–30 cm soil layer. The CT₁, CT₂ and RCT systems resulted in similar penetration resistance and bulk density values below the 15 cm soil depth, while the RT and NT systems resulted in higher but similar values. The mean penetration resistance values were less than 1 MPa in the CT₁, CT₂ and RCT systems at the 0–15 cm depth, while they were 1.41, 1.84 MPa in RT and NT, respectively. The mean total porosity increased with tillage from 8.2 to 28% when compared with NT. The CT₁, CT₂ and RCT systems resulted in lower moisture content at the 0–15 cm depth. The lowest moisture content occurred in RCT (24.4%) and the highest in NT (30.9%), while it was 30.3% in RT system. The lowest and highest mean weight diameter values were reported for the RT (1.36 mm) and NT (2.37 mm) systems, respectively. The lowest wheat grain yield was obtained in NT (4.14) and the highest in CT₁ (5.24 Mg ha^?1). A significant difference occurred between only NT and the other systems. When both grain yield and advantages of reduced tillage are considered, the RT system is recommended.     

Effect of tillage intensity on N mineralization of different crop residues in a temperate climate

To evaluate the effect of tillage intensity on the N mineralization pattern of winter wheat residues, sugar beet residues, Italian ryegrass and maize residues undisturbed soil samples were taken from six sites under different tillage management. Site NT_K had been managed for 10 years under reduced tillage (RT), whereby the last 4 years the crops were sown using direct seeding (NT). Site RT_CSE had been managed for 20 years under reduced tillage (RT) and site RT_H for 3 years. For each site under RT a nearby site under conventional tillage (CT) was selected (CT_K, CT_CSE and CT_H). On site NT_K and site RT_CSE a significantly higher amount of SOC in the 0–10 cm was accumulated compared to the respective CT sites. Between site RT_H and site CT_H no such significant difference was found. However, the content of microbial biomass C (MB-C) and the β-glucosidase and urease activities were higher on all RT sites compared to the respective CT sites. This indicates that these microbiological and biochemical parameters seem to be very sensitive for alterations in management intensity. After 98 days, more N was immobilized under NT_K than under CT_K by adding winter wheat residues (expressed as kg ha⁻¹ and as % of total added N). This higher immobilization potential can be explained by a higher microbial activity and a change in microbial population. Under RT_CSE and RT_H net N immobilization of the winter wheat residues was found, but the pattern was less pronounced than for NT_K. However, when expressed as % of total N added, N immobilization of winter wheat residues was higher under CT than under RT, which indicates that high C:N residues when incorporated, decompose more slowly under RT than under CT. Similar results were found comparing the N mineralization pattern of maize residues under RT_H and CT_H. The residues of sugar beet and Italian ryegrass at site CT_H released N more rapidly and to a higher extent, 74.1% and 66.2%, respectively (expressed as % of total N added) than under RT_H at the end of the incubation. The slower mineralization of N rich crop residues under RT compared to CT means that there is less potential risk for nitrate leaching to occur, which may result in a higher N efficiency in RT compared to CT.     

不同保护性耕作措施对麦-豆轮作土壤有机碳库的影响

通过设置在甘肃省定西市李家堡镇的不同保护性耕作试验,对春小麦、豌豆两种轮作次序下的土壤总有机碳、活性有机碳、微生物量碳含量进行了测定,并计算了各处理土壤碳库管理指数.结果表明:经过5年的轮作后,与传统耕作相比,两种轮作次序下免耕秸秆覆盖和传统耕作结合秸秆还田处理均能不同程度地提高土壤总有机碳、活性有机碳、微生物量碳含量及土壤碳库管理指数,而免耕不覆盖处理除在0～5 cm提高了土壤有机碳库管理指数外,其他各层次均降低了土壤有机碳库管理指数,说明仅依靠免耕而不结合秸秆覆盖或还田对于土壤有机碳库的管理来讲是不可持续的.     

Soil respiration from winter wheat-based cropping systems in the US Southern Great Plains as influenced by tillage managements

This study compared soil respiration (SR) fluxes from winter wheat-based cropping systems in the US Southern Great Plains (SGP) under reduced and conventional tillage. The study consisted of four sets of paired paddocks assigned to conventional or reduced tillage with a four-year crop rotation applied over time. During the 2016–2017 study year, four sets of paired paddocks were planted to: winter wheat managed for grazing, dual-purpose (grazing and grain production), and grain-only systems of production, and winter canola. Heterotrophic SR fluxes were measured using a plant and root exclusion method on eight permanently deployed PVC cores per paddock. Fluxes from the cores were measured manually using a closed chamber connected to an infrared gas analyser on 12–13 dates during the winter wheat growing season (October through May). There were strong seasonal patterns of SR flux, with lower rates during dry and cold periods, and higher rates during warm and wet periods. Large rainfall induced pulses of SR flux were observed for both tillage systems. There was no consistent large-scale difference in SR flux between tillage treatments applied to paired paddocks. Results from this study indicate SR fluxes from winter wheat-based cropping systems are controlled more by soil environmental conditions than form of tillage.