Long term tillage,cover crop,and fertilization effects on microbial community structure,activity: Implications for soil quality

Conservation agriculture practices, such as reduced tillage, cover crops and fertilization, are often associated with greater microbial biomass and activity that are linked to improvements in soil quality. This study characterized the impact of long term (31 years) tillage (till and no-till), cover crops (Hairy vetch- Vicia villosa and winter wheat- Triticum aestivum, and a no cover control), and N-rates (0, 34, 67 and 101 kg N ha⁻¹) on soil microbial community structure, activity and resultant soil quality calculated using the soil management assessment framework (SMAF) scoring index under continuous cotton (Gossypium hirsutum) production on a Lexington silt loam in West Tennessee.No-till treatments were characterized by a significantly greater (P < 0.05) abundance of Gram positive bacteria, actinomycetes and mycorrhizae fungi fatty acid methyl ester (FAME) biomarkers compared to till. Saprophytic fungal FAME biomarkers were significantly less abundant (P < 0.05) under no-till treatments resulting in a lower fungi to bacteria (F:B) ratio. Key enzymes associated with C, N & P cycling (β-glucosidase, β-glucosaminidase, and phosphodiesterase) had significantly higher rates under no-till relative to till, corresponding to significantly greater (P < 0.05) soil C and N, extractable nutrients (P, K and Ca) and yields. Mycorrhizae fungi biomarkers significantly decreased (P < 0.05) with increasing N-rate and was significantly less (P < 0.05) under the vetch cover crop compared to wheat and no cover. Treatments under vetch also had significantly higher β-glucosaminidase and basal microbial respiration rates compared to wheat and no cover.Consequently, the total organic carbon (TOC) and β-glucosidase SMAF quality scores were significantly greater under no-till compared to till and under the vetch compared to wheat and no cover treatments, resulting in a significantly greater overall soil quality index (SQI).Our results demonstrate that long-term no-till and use of cover crops under a low biomass monoculture crop production system like cotton results in significant shifts in the microbial community structure, activity, and conditions that favor C, N and P cycling compared to those under conventional tillage practices. These practices also led to increased yields and improved soil quality with no-till having 13% greater yields than till and treatments under vetch having 5% increase in soil quality compared to no cover and wheat.     

Sustaining Soil Quality with Legumes in No‐Tillage Systems

Abstract

Tillage, cropping system, and cover crops have seasonal and long‐term effects on the nitrogen (N) cycle and total soil organic carbon (C), which in turn affects soil quality. This study evaluated the effects of crop, cover crop, and tillage practices on inorganic N levels and total soil N, the timing of inorganic N release from hairy vetch and soybean, and the capacity for C sequestration. Cropping systems included continuous corn (Zea mays L.) and stalk residue, continuous corn and hairy vetch (Vicia villosa Roth), continuous soybeans (Glycine max L.) plus residue, and two corn/soybean rotations in corn alternate years with hairy vetch and ammonium nitrate (0, 85, and 170 kg N ha^?1). Subplot treatments were moldboard plow and no tillage. Legumes coupled with no tillage reduced the N fertilizer requirement of corn, increased plant‐available N, and augmented total soil C and N stores.     

覆盖作物－玉米间作对土壤碳氮含量及相关酶活性的影响

  目的  针对东北地区常规农业重用轻养以及玉米连作导致土壤养分不均衡、土壤健康下降等问题,开展覆盖作物－玉米间作对土壤碳氮含量及相关酶活性的影响研究,以期为东北地区保护性利用模式的扩展提供科学依据。  方法  在覆盖作物－玉米间作种植模式下,探讨紫花苜蓿、毛苕子和黑麦草三种覆盖作物对土壤碳氮及酶活性的影响。  结果  不同种植模式和覆盖作物类型显著影响了覆盖作物－玉米间作系统的土壤氮含量及相关酶活性,土壤有机碳含量仅在不同种植模式间有显著差异。在拔节期,与玉米单作相比,紫花苜蓿－玉米间作可以显著增加土壤速效氮含量,其硝态氮和铵态氮含量分别增加了14.94 mg kg?1和2.07 mg kg?1,并且参与氮转化的亮氨酸氨基肽酶活性提高17.9 nmol g?1 h?1。与其他覆盖作物相比,单作毛苕子可以显著提高土壤乙酰氨基葡萄糖苷酶和亮氨酸氨基肽酶的活性。毛苕子间作系统的过氧化氢酶和多酚氧化酶活性显著高于黑麦草间作系统,二者分别提高了12.65%和66.94%。在成熟期,玉米单作和间作的土壤有机碳和全氮含量显著高于覆盖作物单作,土壤碳氮水解酶和氧化酶活性均无显著差异。冗余分析表明,土壤铵态氮含量是影响土壤酶活性的关键环境因子。  结论  玉米与豆科覆盖作物的种植增加了间作玉米土壤速效氮的含量,提高了氮转化相关酶的活性,增强了土壤氮素转化潜能及可利用性。研究区适宜选取紫花苜蓿和毛苕子作为覆盖作物种植。     

Soil properties in organic olive groves compared with that in natural areas in a mountainous landscape in southern Spain

This study evaluates soil properties in organically managed olive groves and natural zones in a mountainous area of Andalusia, Spain. Two soil types (Eutric Regosol and Eutric Cambisol) and the most common soil management methods (tillage and two intensities of grazing) were studied. Both soil types in the groves had values not much lower than those in the natural areas. Average (±SE) values in the groves were 1.58 ± 0.71% for organic carbon, 323 ± 98 g kg^?1 for macroaggregate stability, 1.11 ± 0.16 g cm^?3 for bulk density, 3.5 ± 1.6 mm h^?1 for saturated hydraulic conductivity and 1209 ± 716 mg CO₂ kg^?1 for soil respiration. Overall, these values tended to be lower in the tilled compared with that in the grazed groves. The average phosphorus soil content (5.83 ± 5.22 mg kg^?1) was low for olive production and within adequate ranges for N (0.12 ± 0.05%) and K (142 ± 81 mg kg^?1). Soil erosion was high in the tilled groves (35.5 ± 18.2 t ha^?1 year^?1) with soil loss correlating with indicators of soil degradation such as organic carbon content and water stable macroaggregates. In the grazed groves, soil loss was moderate with no clear indications of soil degradation. Overall, there was significant farm‐to‐farm variability within the same soil and land management systems. Olive production had a moderate effect on soil degradation compared with natural areas and olive cultivation could be sustained in future if cover crop soil management replaced tillage, especially in the most sloping areas.     

Snap bean response to soil tillage management and cover crops

Abstract

Snap beans (Phaseolus vulgaris) were grown using conventional tillage (CT) and no‐tillage (NT) soil management following either hairy vetch (Vicia villosa Roth) or rye (Secale cereale L.) in 1992 and 1993 in the mountain regions of Georgia near Blairsville. Soil bulk density and inorganic nitrogen content as well as crop dry matter production and yield were monitored. Soil bulk density of the surface (0 to 10 cm) layer under NT exceeded that under CT at planting by as much as 0.33 Mg/m³. However, growth‐limiting bulk densities (values>1.45 Mg/m³) did not occur under either tillage regime. Inorganic soil nitrogen to a depth of 30 cm at planting and at five weeks after planting was similar for the two tillage systems. However, soil nitrogen (N) tended to be greater following hairy vetch than following rye. There were no significant effects of tillage or cover crop on plant stand or plant dry weight. Total yields were generally similar regardless of tillage or cover crop. A notable exception was that early yield in 1992 was 62% greater using NT. These results indicate great potential for use of conservation tillage and cover crops in the production of snap beans in the mountain regions of the southeastern United States.     

Nutrient deficiencies in olives grown on typical Mediterranean soils (Terra rossa,Rendzina, Lithosol)

An important part of agriculture in the European Mediterranean area is olive (Olea europaea L.) production. Characterising the relationships between properties of different soils where olive is grown and nutrient status in olive leaves can enhance our understanding of soil-plant interactions. Three different soils (Terra rossa, Rendzina, Lithosol) were characterized for their physical and chemical characteristics; plant-available nutrients were extracted with ammonium nitrate. Soils, soil extracts and leaf digests were analysed for nutrients and for nitrogen in soils and leaf. A redundancy analysis (RDA) was applied to elucidate relationships between soil properties and leaf nutrients. As revealed by RDA, leaf concentrations of Mg, K, Ca and micronutrients were explained by available Mg, total carbonates and soil organic carbon in topsoil. Leaf concentration of Na was associated with total Na in topsoil. Copper and Mo deficiencies were detected in plants grown in Lithosol, and Mg, P, Mn and Zn deficiencies were noted in all plants. Through appropriate agronomic techniques, Lithosols can be used for olive groves, but they have significant limitation regarding nutrient availability. Our results support the relevance of using soil nutrient variability to provide a basis for optimisation of measures for olive groves.     

Cover crop nitrogen availability to conventional and no‐till corn: Soil mineral nitrogen,corn nitrogen status,and corn yield

Abstract

Understanding seasonal soil nitrogen (N) availability patterns is necessary to assess corn (Zea mays L.) N needs following winter cover cropping. Therefore, a field study was initiated to track N availability for corn in conventional and no‐till systems and to determine the accuracy of several methods for assessing and predicting N availability for corn grown in cover crop systems. The experimental design was a systematic split‐split plot with fallow, hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), wheat (Triticum aestivum L.), rye+hairy vetch, and wheat+hairy vetch established as main plots and managed for conventional till and no‐till corn (split plots) to provide a range of soil N availability. The split‐split plot treatment was sidedressed with fertilizer N to give five N rates ranging from 0–300 kg N ha^‐1 in 75 kg N ha^‐1 increments. Soil and corn were sampled throughout the growing season in the 0 kg N ha^‐1 check plots and corn grain yields were determined in all plots. Plant‐available N was greater following cover crops that contained hairy vetch, but tillage had no consistent affect on N availability. Corn grain yields were higher following hairy vetch with or without supplemental fertilizer N and averaged 11.6 Mg ha^‐1 and 9.9 Mg ha^‐1 following cover crops with and without hairy vetch, respectively. All cover crop by tillage treatment combinations responded to fertilizer N rate both years, but the presence of hairy vetch seldom reduced predicted fertilizer N need. Instead, hairy vetch in monoculture or biculture seemed to add to corn yield potential by an average of about 1.7 Mg ha^‐1 (averaged over fertilizer N rates). Cover crop N contributions to corn varied considerably, likely due to cover crop N content and C:N ratio, residue management, climate, soil type, and the method used to assess and assign an N credit. The pre‐sidedress soil nitrate test (PSNT) accurately predicted fertilizer N responsive and N nonresponsive cover crop‐corn systems, but inorganic soil N concentrations within the PSNT critical inorganic soil N concentration range were not detected in this study.     

Root growth dynamics of spring cereals with discontinuation of mouldboard ploughing

A vigorous root system is essential for efficient use of plant nutrients. This paper focuses on root growth and its response to tillage changes in the most fertile soil horizon, 0–40 cm depth. The field experiment was established in 1995 on clay soil, with 45–50% clay and 5.5% organic matter in the topsoil. Three tillage treatments were mouldboard plough to a depth of 20 cm (conventional), field cultivator to a depth of 8 cm, and no primary tillage (conservation). The field had an oat (Avena sativa L.)–barley (Hordeum vulgare L.) crop rotation. In 1997–1998 and 2000, root distribution during the growing season was evaluated by a non-destructive minirhizotron (MR) and video recording method. Root length density and root diameter were also measured once a season (1997 and 1998) by destructive root sampling and image analysis of washed roots. At shoot elongation, root numbers increased more under conventional than conservation tillage, at soil depth of 10–25 cm. The effect was clear for both barley (1997) and oat (2000) with maximum root numbers of 175 and 210 per 100 cm² by mouldboard ploughing, but 120 and 170 per 100 cm² under unploughed conditions (in the whole 0–0.4 m region). The suboptimal condition of unploughed soil was also indicated by lower shoot nutrient contents at tillering (studied in 1997) and by higher penetrometer resistance (studied in 1998, 2000) and lower macroporosity (studied in 2000) at 10–25 cm soil depth. Root growth dynamics were similar for both plant species. Root diameter was not significantly affected by the tillage treatments. Discontinuation of mouldboard ploughing reduced root growth (P<0.05) within this clay soil 5 years after the tillage change, although conservation tillage preserved more water for plant use. The data show that a clay soil can be too dense for optimal rooting during the 3rd–6th-years after discontinuation of ploughing.     

Effect of Land-Use History on Soil Carbon and Nitrogen in a Mediterranean Catchment

The impact of land use on soil organic matter was investigated. Five land cover types (pine forest, olive groves, wheat, wheat/maize cultivation systems, and a shrub pasture) belonging to three land-use categories from the same catchment in the island of Lesvos, Greece, were used. The soils developed under similar pedogenetic processes and accepted similar agricultural practices for at least 30 years. The results showed that the land-use and cover types ranged according to their total soil carbon (C) content as follows: forest > double cultivation > wheat > olive > pasture. Crop plantations contained 31 to 40% less C at their upper 0- to 45-cm layer than forest. Pasture had shallow soils with a small C accumulation but high C concentration, whereas olive groves had the lowest concentrations of both soil C and nitrogen (N). Olive grove soils were the most prone to degradation but possessed the greatest potential for C sequestration.     

Plant Cover and Control of Diffuse Pollution from P in Olive Groves

Plant cover modifies the physicochemical properties of the soil surface, which results in an enrichment in organic matter and a greater infiltration. So, this study was conducted to determine if its establishment in olive groves was effective, compared to conventional tillage, for the reduction in pollution by soluble phosphorus (P). Surface runoff, soluble P and Olsen P losses in sediment were analyzed in three experiment fields of ecological olive trees in the province of Córdoba (Spain), from 1 June 2003 to 1 June 2005. The cover system reduced the total losses of both variables in the three plots (between 7.6% and 36.5% the dissolved P loss and between 16.3% and 56.4% that of the runoff), with a certain parallelism being observed in the time distribution of the losses in both soil management systems, with significant Spearman coefficients of correlation, ranging between 0.60 and 0.98. Over half the losses of the runoff and dissolved P were produced in two or three events for the two management systems. The establishment of plant cover altered the relative composition in the Olsen P loss (raising the proportion of soluble P) and usually increased the dissolved P rate. Finally, and although it is a positive technique and highly recommendable in the area’s olive groves, it was not completely effective in controlling water pollution in relation to the soluble P concentration, since this was over 0.11 mg l^?1 in all the cases with a cover.     

Determinants of Woody Plant Species Richness in Abandoned Olive Grove Ecosystems and Maquis of Central Greece

The present study aimed to compare the woody plant species richness and cover (%) of five abandoned olive groves and five maquis ecosystems in central Greece and to describe the relationship between woody plant species richness and a set of environmental variables [soil pH, nitrogen (N), phosphorus (P), potassium (K), and organic matter; air temperature and humidity; altitude; slope; type of ecosystem; and presence of leaf litter]. Although woody plants are abundant in the abandoned olive groves, the number of species and amount of cover (%) are significantly greater in maquis. According to principal component analysis, woody plant species richness was positively correlated with soil organic matter, plant litter, and soil P and K in maquis. Also, woody plant species richness was positively correlated with slope in the abandoned olive groves. Olive grove ecosystems abandoned for at least 12 years have developed species compositions similar to the corresponding features of neighboring maquis, although the number of species and amount of cover (%) are significantly greater in maquis.     

Compost,Manure and Synthetic Fertilizer Influences Crop Yields,Soil Properties,Nitrate Leaching and Crop Nutrient Content

From 1993 to 2001, a maize-vegetable-wheat rotation was compared using either 1) composts, 2) manure, or 3) synthetic fertilizer for nitrogen nutrient input. From 1993 to 1998, red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) were used as an annual winter legume cover crop prior to maize production. From 1999 to 2001, hairy vetch (Vicia villosa Roth.) served as the legume green manure nitrogen (N) source for maize. In this rotation, wheat depended entirely on residual N that remained in the soil after maize and vegetable (pepper and potato) production. Vegetables received either compost, manure, or fertilizer N inputs. Raw dairy manure stimulated the highest overall maize yields of 7,395 kg/ha (approximately 140 bushels per acre). This exceeded the Berks County mean yield of about 107 bushels per acre from 1994 to 2001. When hairy vetch replaced clover as the winter green manure cover crop, maize yields rose in three of the four treatments (approximately 500-1,300 kg/ha, or 10-24 bu/a). Hairy vetch cover cropping also resulted in a 9-25 % increase in wheat yields in the compost treatments compared to clover cover cropping. Hairy vetch cover crops increased both maize and wheat grain protein contents about 16 to 20% compared to the clover cover crop. Compost was superior to conventional synthetic fertilizer and raw dairy manure in 1) building soil nutrient levels, 2) providing residual nutrient support to wheat production, and 3) reducing nutrient losses to ground and surface waters. After 9 years, soil carbon (C) and soil N remained unchanged or declined slightly in the synthetic fertilizer treatment, but increased with use of compost amendments by 16-27% for C and by 13-16% for N. However, with hairy vetch cover crops, N leaching increased 4 times when compared to clover cover crops. September was the highest month for nitrate leaching, combining high rainfall with a lack of active cash crop or cover crop growth to use residual N. Broiler litter leaf compost (BLLC) showed the lowest nitrate leaching of all the nutrient amendments tested (P= 0.05).     

Factors affecting soil microbial community structure in tomato cropping systems

Soil and rhizosphere microbial communities in agroecosystems may be affected by soil, climate, plant species, and management. The management and environmental factors controlling microbial biomass and community structure were identified in a three-year field experiment. The experiment consisted of a tomato production agroecosystem with the following nine treatments: bare soil, black polyethylene mulch, white polyethylene mulch, vetch cover crop, vetch roots only, vetch shoots only, rye cover crop, rye roots only, and rye shoots only. The following hypotheses were tested: (1) Temperature and moisture differences between polyethylene-covered and cover-cropped treatments are partly responsible for treatment effects on soil microbial community composition, and (2) Different species of cover crops have unique root and shoot effects on soil microbial community composition. Microbial biomass and community composition were measured by phospholipid fatty acid analysis. Microbial biomass was increased by all cover crop treatments, including root only and shoot only. Cover cropping increased the absolute amount of all microbial groups, but Gram-positive bacteria decreased in proportion under cover crops. We attribute this decrease to increased readily available carbon under cover-cropped treatments, which favored other groups over Gram-positive bacteria. Higher soil temperatures under certain treatments also increased the proportion of Gram-positive bacteria. Vetch shoots increased the amount and proportion of Gram-negative bacteria, fungi, and arbuscular mycorrhizal fungi in the rhizosphere of tomato plants. The imposed treatments were much more significant than soil temperature, moisture, pH, and texture in controlling microbial biomass and community structure.     

耕作管理措施对残茬覆盖及其分解的影响

The effects of tillage methods on percent surface residue cover remaining and decomposition rates of crop residues were evaluated in this study. The line transect method was used to measure residue cover percentage on continuous corn (Zea mays L.) plots under no tillage (NT), conventional tillage (CT), chisel plow (CH), and disk tillage (DT). Samples of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) were used for residue decomposition study. Results showed that the percentage of residue cover remaining was significantly higher for NT than for CH and DT and that for CT was the lowest (< 10%). For the same tillage system, the percent residue cover remaining was significantly higher in the higher fertilizer N rate treatments relative to the lower fertilizer N treatments. Weight losses of rye and vetch residues followed a similar pattern under CT and DT, and they were significantly faster in CT and DT than in NT system. Also, the amounts of residue N remaining during the first 16 weeks were always higher under NT than under CT and DT.     

不同覆盖模式对樱桃园土壤团聚体及碳氮的影响

为探究不同覆盖模式对土壤团聚体及其碳氮的影响,以新津县樱桃园土壤为研究对象,采用定位试验,设置清耕(CK)、自然生草覆盖(NGC)、野豌豆覆盖(VC)和地布覆盖(GCM)4个处理,对土壤团聚体分布、大团聚体含量(R_0.25)、平均重量直径(MWD)、几何平均直径(GMD)、团聚体破坏率(PAD)和不稳定团粒指数(E_lt)及水稳性团聚体有机碳、全氮进行了测定与分析。结果表明:自然生草覆盖、野豌豆覆盖、地布覆盖和清耕在0—10 cm和10—20 cm土层的机械稳定性团聚体分布均以>5 mm团聚体含量最高,而水稳性团聚体分布以>5 mm和5～2 mm含量较高。在两个土层中,自然生草覆盖、野豌豆覆盖和地布覆盖与清耕相比,均提高了R_0.25,MWD,GMD,降低了PAD和E_lt,同时提高了水稳性团聚体有机碳、全氮含量。有机碳提升效果以自然生草覆盖处理最好,而全氮提升效果以野豌豆覆盖处理最好。综上,覆盖处理能够提高土壤团聚体稳定性以及水稳性团聚体有机碳、全氮含量,改善土壤质量。     

Soil tillage and herbicide applications in pea: arbuscular mycorrhizal fungi,plant growth and nutrient concentration respond differently

ABSTRACT

We conducted a field- and pot experiment with peas to investigate the impact of soil tillage and herbicide applications on arbuscular mycorrhizal fungi (AMF), plant growth, phosphorus concentrations, C:N ratio in plants and yield. The field study was carried out in a long-term soil tillage experiment where four tillage treatments have been compared. Field soil from the experimental plots were used for the pot experiment. AMF were not affected by herbicide (MCPB) application, neither in the field nor in the pot experiments. However, AMF root colonization was enhanced by reduced tillage, minimum tillage and no-tillage practices, compared to conventional tillage. In the pot experiment, plant growth and nodulation of pea roots was negatively affected by the high herbicide dosage. In the field experiment neither tillage nor herbicide treatment exert specific effects on root growth parameters, phosphorus concentrations, C:N ratio and plant dry matter. This work demonstrates that an appropriate herbicide usage coupled with conservation soil tillage techniques can favour AMF root colonization and benefit plant growth.

Abbreviations: AMF: arbuscular mycorrhizal fungi; CT: conventional tillage; RT: reduced tillage; MT: minimum tillage; NT: no tillage; P: Phosphorus; C:N ratio: carbon:nitrogen ratio     

秸秆和紫云英协同覆盖对西南旱地土壤养分、酶活性及小麦产量的影响

研究秸秆覆盖、紫云英覆盖及两者协同覆盖对西南旱地土壤养分、酶活性以及小麦产量的影响,对于维持农田土壤养分平衡、优化西南旱地保护性耕作措施具有重要的理论和指导意义。以“小麦/玉米/大豆”旱三熟种植模式下的小麦农田为研究对象开展田间试验,共设置4个处理:玉米秸秆覆盖（S）、紫云英覆盖（A）、玉米秸秆 + 和紫云英协同覆盖（S + A）、对照（CK）。结果表明,与CK处理相比,S、S + A处理对土壤有机碳、全氮、全磷、速效钾、缓效钾含量均有显著促进作用;A处理对土壤有机碳、全氮、碱解氮影响明显,但是对磷、钾的促进效果不明显。S +土壤酶活性与土壤养分之间存在密切关系, A处理能够显著提高根际和非根际土壤的蔗糖酶、蛋白酶、脲酶、淀粉酶和酸性磷酸酶活性,S处理和A处理对土壤酶活性的促进效果不如S + A处理。与CK处理相比,S、A、S + A处理的小麦增产率分别为5.14%、8.79%、13.34%,其中,S + A处理的小麦增产率最高。秸秆和紫云英协同覆盖能够显著提高土壤养分含量和酶活性、促进小麦增产,有利于在保护农田生态环境的同时提高农业生产效益,可以作为有效的西南旱地保护性耕作措施推广使用。     

Hydraulic conductivity and porosity under conventional and no-tillage and the effect of three species of cover crop in northern France

We studied soil hydraulic conductivity (K) and porosity in five combinations of soil tillage and cover crop management systems. Treatments were winter wheat (Triticum aestivum L.) grown on a conventionally tilled soil (CT), on a no‐till soil (NT), and on an NT with three different cover crops: red fescue (Festuca rubra L.; Fr), bird's‐foot‐trefoil (Lotus corniculatus L.; Lc) and alfalfa (Medicago sativa L.; Ms). Measurements were made on a loamy soil in Grignon, France, in November 2004, May 2005 and October 2005. K and mean size of hydraulically active pores were measured in situ at three water potentials (?0.6, ?0.2 and ?0.05 kPa) at the soil surface and at 10 cm depth. In November 2004 and May 2005, pore space was described using 2D image analysis of pores on undisturbed soil samples in the 0–10 cm layer and in the 10–20 cm layer. The major differences were caused by soil tillage that created two heterogeneous soil layers and increased K in the 0–10 cm layer relative to NT. The effects of cover crop on K and porosity were not affected by the root type: there were no major differences between the grass cover crop (fibrous‐root type) and the leguminous ones (tap‐root type). However, we recorded larger functional pores and more tubules in the no‐till treatments with a cover crop, compared with the no‐till treatment without cover crop; this was probably the result of root activity. Although these changes generally did not result in larger values of K, they participated in the maintenance of soil structure and K over time.     

Arbuscular mycorrhizal development,glomalin‐related soil protein (GRSP) content,and rhizospheric phosphatase activitiy in citrus orchards under different types of soil management

The arbuscular mycorrhizal (AM) status with respect to colonization of different AM structures in the citrus roots, spore density and hyphal length density, GRSP content, and phosphatase activity in the citrus rhizosphere were investigated in the orchards at Zigui county of the Three Gorges Region, S China. Four soil managements, no‐tillage and natural grass (NN), no‐tillage and sod culture (NS), half‐tillage and film mulching (HT), and clean‐tillage (CT) were employed in those citrus orchards. Our survey showed heavy AM colonization (36%–89%), indicating a high AM dependency of citrus in our experimental orchards. The colonization of different AM structures, spore density, hyphal length density, GRSP content, and phosphatase activity varied greatly between the no‐tillage and tillage citrus orchards. The highest colonization of different AM structures except the ratio of root length with vesicles (RLV), spore density, hyphal length density, GRSP content, and phosphatase activity was observed in the no‐tillage orchards, and the lowest was found in the tillage orchards. A cluster analysis based on the similarity in AM status, GRSP content, and phosphatase activity showed similarities between the NS citrus orchards and the NN citrus orchards. The data presented here demonstrate that tillage reduced the total AM colonization (RLT), spore density, hyphal length density, GRSP content, and phosphatase activity, while those were recovered in the no‐tillage citrus orchards. So, we propose that no‐tillage and planting grass is an effective way for citrus production and improvement of soil quality in orchards of the study area.     

Sensitivity of Cirsium arvense to simulated tillage and competition

Abstract

Single and combined effects were studied of root length, burial depth, cutting and competition from a seasonal green manure crop on the growth and development of C. arvense from roots found in the upper soil layer. The experiment was performed under field conditions and partly repeated in a green house. The green manure consisted of a mixture of phacelia, common vetch, red clover and Italian ryegrass. Root fragments of 5 and 10 cm length were buried at 5 and 15 cm soil depth, simulating soil tillage. Use of green manure alone reduced growth of C. arvense more than any other single factor (81–99%), while root length and burial depth were more variable in their effect (0–96% reduction). Combined treatments involving both green manure, deep root burial (15 cm) and short root length (5 cm) reduced growth of C. arvense consistently by 95–100%. At the minimum regenerative capacity of C. arvense the number of leaves was 3–7 in plots with no green manure, at which time cutting had the greatest effect on regrowth the following year. The level for minimum regenerative capacity was not possible to decide for C. arvense growing in competition with green manure. Combined multiple treatments in spring, including use of green manure and mechanical operations in the upper soil layers, appear to be a potential means of reducing C. arvense infestations.