Effects of alternative tillage systems on soil quality and yield of spring cereals on silty clay loam and sandy loam soils in the cool, wet climate of central Norway

Tillage trials were established on a poorly drained silty loam overlying silty clay loam and on a freely drained sandy loam overlying medium sand, in 1988 and 1989, respectively. Autumn and spring ploughing and two ploughless systems were compared for 12–13 years, with three replications at each site. The ploughless treatments comprised deep versus shallow spring harrowing until 1999, and thereafter autumn plus spring harrowing versus spring harrowing only. In 6 years, treatments with and without fungal spraying of the cereal crops were included. In other years, fungicides were not used. Perennial weeds were controlled by herbicides as necessary, on nine occasions up until 2001. Average spring barley (Hordeum vulgare L.) and spring oat (Avena sativa L.) yields were similar with spring ploughing as with autumn ploughing at both sites. In treatments without ploughing, average yields on the silty loam over clay were 93% of those obtained with ploughing, and on the sandy loam over sand they were 81%. Smaller and non-significant yield differences were found between spring harrowing versus deep spring harrowing, and between autumn plus spring harrowing versus spring harrowing only. Fungal spraying increased yields markedly at both sites (25%), but there was no significant interaction between this treatment and tillage system. Oat was compared with barley in 2 years, with oat performing better under ploughless tillage. At both sites increases in penetrometer resistance occurred in the topsoil of unploughed treatments. These were considered particularly limiting on the sandy loam. On the silty loam there was an increase in surface horizon porosity in the absence of ploughing, which was associated with an increase in topsoil organic matter content. On this soil there was also a tendency toward lower penetrometer resistance at >30 cm depth on autumn plus spring harrowed soil than on ploughed soil, indicating that the plough pan may have diminished. This was supported by observations of greater earthworm activity on unploughed soil. Soil chemical analyses revealed that mineral N and plant-available P and K accumulated in the upper horizon under ploughless tillage. The percentage yields obtained in individual years with autumn as opposed to spring ploughing, were positively correlated with air temperature during 0–4 weeks after planting on the silty loam, and with precipitation during 0–12 weeks after planting on the sandy loam. In the case of yields obtained with spring harrowing only, relative to spring ploughing, positive correlations were found with 0–4 week temperature on both soil types, suggesting that low early season temperatures may limit yields under ploughless tillage.     

Microbial biomass and N transformations in two soils cropped with annual and perennial species

A field study was undertaken to determine the effects of different plant species on soil microbial biomass and N transformations in a well drained silty clay loam (Typic Dystrochrept) and a poorly drained clay loam (Typic Humaquept). The crop treatments were faba bean (Vicia faba L.), alfalfa (Medicago sativa L.), timothy (Phleum pratense L.), bromegrass (Bromus inermis L.), reed canarygrass (Phalaris arundinacea L.), and wheat (Triticum aestivum L.). Measurements of microbial biomass C, denitrification capacity, and nitrification capacity were performed periodically in the top 2–10 cm of soil. On most sampling dates, all three parameters were higher under perennial than under annual species. The nitrification capacity was positively affected by the level of N applied to each species (r=0.65^** for the silty clay loam and 0.84^*** for the clay loam) and not directly by the plant. The differences found in microbial biomass C were significantly correlated with the water-soluble organic C present under each plant species (r=0.74^*** for the silty clay loam and 0.90^*** for the clay loam), suggesting differences in C deposition in the soil among plant species. In the silty clay loam, the denitrification capacity was positively related to the amount of organic C found under each plant species, while in the clay loam, it was dependent on the amount of N applied to each species. There was less denitrification activity per unit biomass under legume species than under graminease, suggesting that, depending on their composition, root-derived materials may be used differently by soil microbes.     

Does no-till wheat sowing in a rice-wheat cropping sequence cause surface-soil compaction?

Wheat planting in rice-harvested fields without land preparation is more economical, but the physical characteristics of the plant root sphere are not well documented. Comparative changes in the soil compaction in parallel fields used for no-till and conventional tillage were measured in replicated field trials for two soil types and in three randomly selected farmers’ fields. Weakly to moderately developed soils on recent to old Pleistocene calcareous alluvium were studied. They differed in their clay content. No-till wheat sowing resulted in a greater soil bulk density and a lower total porosity in the heavy-textured soils compared to the light-textured soil. In the light-textured Jhakkar soil, the no-till regime resulted in a greater infiltration at the saturated state and under most suction levels and a greater macroporosity compared to the conventional tillage. The silty clay Kotly soil had greater macroporosity in the conventional tillage than in the no-till regime. The wheat root growth and penetration seemed to be favored by the relatively low bulk density resulting from the conventional tillage, particularly in the silty clay loam soil. The dense layer restricted root penetration in the silty clay loam soil, while there was less resistance in the sandy loam soil. The study demonstrated the suitability of the no-till regime for specific soil types. Published in Russian in Pochvovedenie, 2008, No. 11, pp. 1362–1370. The text was submitted by the authors in English.     

土壤盐－水动力学: V.土壤剖面盐平衡

Salt balance in simulated soil coulumns was calculated on the basis of a large amount of long term observation data.The results showed that under the climate conditions of semi-arid region of the Huang-Huai-Hai Plain,the soils in the columns were under salt accumulation conditions when the groundwater depth was controlled at less than 2.0m,and under desalinization conditions when at larger than 2.5m.In the soil columns with clay soil and silty loam soil intercalated with a clay layer,the amount of salt accumulated was far less than that in the soil column with silty loam soil throughout the whole profile.Under no irriagtion conditions crop planting may increase groundwater evaporation and hence salt accumulation in soil,making the soil columns under desalinization be under salt accumulation conditions.     

碱化盐土掺砂对土壤理化性状和玉米产量影响的研究

为解决内蒙古河套平原黏性碱化盐土土壤黏重,作物难以正常生长、产量低下等问题,对河套平原黏性碱化盐土进行了土壤耕层(0~20 cm)掺砂的土壤改良试验,研究掺砂对土壤理化性状和玉米产量的影响。结果表明:试验区土壤掺砂可以降低土壤容重,改变土壤机械组成和土壤质地,提高了黏性碱化盐土的通气孔隙度,改善土壤的通气透水性,降低土壤全盐量和碱化度,有效改善玉米生长环境,提高了玉米的产量。掺砂20%处理的土壤容重从1.64 g/cm3(CK)降低到1.49 g/cm3,土壤通气孔隙度从8.57%提高到18.17%,达到正常范围,使土壤砂粒、粉粒、粘粒含量比例趋向适中,土壤质地由壤质黏土转变为黏壤土,土壤全盐量下降了13%,碱化度降低了21%,玉米产量提高了301%。综合分析,掺砂20%处理对当地碱化盐土改良效果较为适宜。     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.     

不同土壤质地和含水率对炭基肥料氮素矿化的影响

为了探究土壤特性对炭基肥料氮素矿化的影响,采用室内培养和大田小区试验,分析了炭基肥在不同土壤质地(砂质壤土、粉砂质壤土、黏土)及含水率(80%、60%、40%田间最大持水量)条件下,氮素矿化动态变化特征。结果表明:在室内培养条件下,对于不同土壤质地,炭基肥在砂质壤土条件下矿化势最高,其次为黏土,最低的为粉砂质壤土;对于不同田间持水量,在粉砂质壤土条件下,炭基肥矿化势最高的为80%田间最大持水量(80%SMC),其次为60%SMC,最低的是40%SMC;在砂质壤土和黏土条件下,炭基肥的矿化势均表现为60%SMC>80%SMC>40%SMC。培养状态下粉砂质壤土、砂质壤土、黏土条件下最大氮素有效性分别是34.12%、56.31%、41.14%,而在大田条件下,炭基肥单季氮素最大矿化率在粉砂质壤土、砂质壤土、黏土3种土壤质地下分别是50.61%、32.27%、34.29%。     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.     

Interpretation of uniaxial,confined compression test data for agricultural topsoils

Traditionally, soil strength is estimated from uniaxial, confined compression tests by procedures adopted from classical soil mechanics. The heterogeneity of agricultural topsoil calls for an alternative approach. Undisturbed soil cores were collected in the plough layer of 14 soils in arable agriculture. Soil texture ranged from coarse sandy to silty loam soils with a maximum of 20% clay. The samples were drained to either of six matric potentials in the range from − 30 to − 300 hPa. Uniaxial, confined compression was applied to ∼800 kPa with strain-controlled stress application (1 mm min⁻¹). Measured strain was fitted to stress by the Morgan-Mercer-Flodin (MMF) model. The model fitted data remarkably well for all samples. Three fitting parameters of the model reflected physical characteristics of soil reaction to stress. The estimates of soil compressibility calculated from the model at 10 kPa (C₁₀) correlated closely and linearly to the C_s index considered to reflect elastic deformation in classical studies of soil compression tests. Soil bulk density and content of soil organic matter decreased C₁₀ as well as compressibility at 100 (C₁₀₀) and 400 kPa (C₄₀₀). A complex pattern in the effects of soil texture and soil moisture on compressibility was revealed. The pattern in strain-stress data is interpreted as a reflection of a gradual transition from elastic to plastic deformation of the mixture of structural units. The MMF model is suggested for interpretation of strain-stress data from uniaxial, confined compression tests. This implies use of stress in a linear scale.     

Influence of subsoiling on the yield of sugar-beets

Root growth and yield of sugar-beets were studied on two Belgian silt loam soils and one alluvial clay soil after subsoiling to a depth of 60 cm. The removal of the plough sole layer, characterized by penetration resistances > 3 MPa, resulted in an increase of the root quantity and a higher availability of water. As a consequence, a mean yield increase of 5 tons/ha for sugar-beets was found on the subsoiled plots in drier years. The yield increase was accompanied by a higher uptake of nutritive elements.     

Harrowing for weed control: Impacts on mineral nitrogen dynamics, soil aggregation and wheat production

Tillage with a spring tine harrow has become a recommended mechanical weeding technique for cereal crops. In this study, the impact of its use on soil mineral N content, soil aggregation and spring wheat (Triticum aestivum L.) production was investigated. The experiment was performed during 2 successive years (2005–2006) on a clay loam and on a silty loam. The two-main plot treatments consisted of a wheat crop subjected or not to intensive harrow use in a weed-free production system. Two N fertilizer treatments (mineral fertilizer and dry granular poultry manure) were also included as subplots within these main treatments and compared to a non-fertilized control. Harrowing had significant and variable effects on soil NO₃⁻ contents in the 0–5 cm soil layer. Slightly higher NO₃⁻ contents (average difference of 3.2 kg NO₃⁻ ha⁻¹) were measured in the harrowed treatments than in the undisturbed plots in the clay loam soil in 2006. However, significantly lower mineral N contents were observed in the harrowed treatments than in the undisturbed plots in the clay loam soil in 2005 and in the silty loam soil in 2006. This apparent N immobilization amounted to 19 kg NO₃⁻ ha⁻¹ in the clay loam soil in 2005 (for both fertilizers) and 30 kg NO₃⁻ ha⁻¹ in the silty loam soil in 2006 (only in mineral fertilizer plots) after the successive harrowing treatments. In all cases, data of the last sampling dates in the fall indicated that residual NO₃⁻ content was not affected by the treatments. Overall harrowing had a minor decreasing and transient effect on the mean weight diameter (MWD) of soil aggregates while the dry poultry manure tended to increase MWD. The harrowing treatment had no significant effect on wheat, grain N uptake and yield. In conclusion, harrow use had variable impacts on soil NO₃⁻ content and a minor decreasing effect on the MWD of soil aggregates. Of note, significant apparent mineral N immobilization was observed on a few sampling dates following the harrow treatments.     

红壤坡耕地耕层土壤质量特征及障碍因素研究

为探究红壤坡耕地耕层质量特征及其障碍因素,通过野外调查、资料查阅及室内土壤理化性质分析等综合性研究手段,对江西红壤坡耕地耕层土壤质量统计特征、演变特征及主要障碍因素进行分析。结果表明:(1)红壤坡耕地田面坡度主要分布在2~16°之间,耕层平均厚度13.40 cm,有效土层厚度平均88.30 cm,土壤容重平均为1.17 g/cm~3;耕层土壤有机质平均含量19.37 g/kg,土壤pH值平均5.36。(2)红壤坡耕地耕层质量近20年有明显提高,田面坡度从6°降至4°,耕层厚度从13.68 cm增至16.42 cm;耕层土壤有机质含量24.63 g/kg,提高33.93%,全氮、有效磷和速效钾含量分别增加10.53%、230.98%、44.18%。(3)红壤坡耕地低产耕层土壤质量的主要障碍因素是土壤养分贫瘠化、粘重化和酸化;花生和木薯低产耕层的土壤容重和粘粒含量均大于高产耕层,而土壤孔隙度、田间持水量、有机质含量及pH值均小于高产耕层,表明高产坡耕地耕层土壤质量优于低产坡耕地。研究结果可为江西红壤坡耕地耕层质量改善和合理耕层构建提供科学参考。     

Evaluation of pedotransfer functions for estimating the soil water retention points

Direct measurement of soil moisture has been often expensive and time-consuming. The aim of this study was determining the best method to estimate the soil moisture using the pedotransfer functions in the soil par2 model. Soil samples selected from the database UNSODA in three textures include sandy loam, silty loam and clay. In clay soil, the Campbell model indicated better results at field capacity (FC) and wilting point (WP) with RMSE = (0.06, 0.09) and d = (0.65, 0.55) respectively. In silty loam soil, the Epic model had accurate estimation with MBE = 0.00 at FC and Campbell model had the acceptable result of WP with RMSE = 0.03 and d = 0.77. In sandy loam, Hutson and Campbell models had a better result to estimation the FC and WP than others. Also Hutson model had an acceptable result to estimation the TAW (Total Available Water) with RMSE = (0.03, 0.04, 0.04) and MBE = (0.02, 0.01, 0.01) for clay, sandy loam and silty loam, respectively. These models demonstrate the moisture points had the internal linkage with the soil textures. Results indicated that the PTFs models simulate the agreement results with the experimental observations.     

Verdichtung und Regeneration des Gefüges eines schluffigen Tonbodens (Tschernosem): Bodenphysikalische,computertomographische und rasterelektronenmikroskopische Untersuchungen

Compaction and recovery of soil structure in a silty clay soil (Chernozem): physical, computer tomographic, and scanning electron microscopic investigations In spring of 1995 a field experiment was started on a loess-derived Chernozem, managed by deep (22 cm) and shallow (12 cm) inversion tillage by spade plough, to test the effect of stepwise mechanical loading on the structure of a silty clay soil (30% clay) and its recovery during subsequent years. Beside an unwheeled control tillage systems were compacted track by track at a water content near field capacity using the following loading treatments: light (2 × 2.5 t; number of wheel passes times wheel load); medium (2 × 5 t) and high (6 × 5 t). Soil physical investigations, density distribution, and spatial visualizations of macropores based on computed tomography (CT) and scanning electron microscopy of aggregate surfaces indicate that increasing loading leads to a progressive homogenization of soil structure. Different stages of this process include the compression of aerated macropores or interaggregate pore space, respectively, by light loading and the deformation of aggregates to a coherent soil mass by high loading. Accord-ingly, the intraaggregate structure is characterized by an increase of parallel arrangement of clay particles, causing an extension of the range of normal shrinkage by elimination of structural shrinkage and displace-ment of residual shrinkage to lower moisture contents. Soil homogenization caused by kneading and supported by positive pore water pressure is the dominant harmful process of structure deterioration of the silty clay, when compacted with high loads at high soil water content. As a consequence of 12 cm shallow tillage over years the lower part of the topsoil has been preconsolidated. Therefore, the deformation resistance is slightly higher compared to 22 cm deep tillage. The stronger the deformation and homogenization of soil structure by loading, the stronger is the contraction of the soil matrix associated with a reheterogenization during three years after loading. Cracking by shrinkage induces a reaggregation of structure, having been obtained before by medium and high loading. Thereby the density of the soil matrix between cracks increases. As a consequence of this heterogenization by densification and cracking aggregates are preferentially remoistened via crack walls, inducing a partial but not a complete reswelling as shown by CT-images. Therefore the spatial position of the crack pattern does not change. On the other hand, at the end of investigation period, the light loaded treatment was not longer different to the unloaded control. Reaggregation by wetting and drying cycles is a key process in silty clays in initiating a restoration of the degraded structure. The formation of biopores is less significant. However, the mechanism of ”︁structure repair” by physical processes does not lead to a reproduction of unloaded structure.     

Soil structural improvements with the addition of Lantana camara biomass in rice-wheat cropping

Abstract. A long-term field experiment was initiated in June 1988 in a silty clay loam soil to investigate the potential of Lantana camara, an obnoxious weed, for improving structural properties and productivity of soil in rice-wheat cropping. Lantana was incorporated into the soil 10–15 days before puddling at 10, 20 and 30 t/ha (fresh weight). At the end of the sixth cropping season, Lantana additions increased the organic carbon (OC) of the 0–15 cm soil layer by 11–24%, and of water-stable aggregates (WSA, 0.50–8.0 mm diameter) by 10–21%; OC of WSA <0.50 mm diameter remained unaffected. About 17–25% of the applied OC was retained in the soil. The OC increase resulted in a decrease in bulk density of the plough layer (0–15 cm) by 7%, a decrease in aggregates of 2–8 mm diameter and of clods by 4% and 6%, respectively. There was an increase in water-stable aggregates and aggregate porosity, and a decrease in clod-breaking strength from 420 to 216 kPa. Soil cracking at the surface changed from wide, deep cracks in hexagonal pattern to a close-spaced network of fine cracks. Lantana additions increased <5mm wide cracks at the expense of 10–20 mm wide cracks; 5–10 mm wide cracks remained unchanged. Total volume of cracks decreased by 36% and surface area of cracks by 55% compared with the control plots.     

不同施磷量对蔬菜地土壤硝态氮淋失的影响

【目的】在两种蔬菜地土壤上研究不同磷肥施用量对土壤硝态氮淋失的影响,为武汉城郊蔬菜合理施用磷肥和安全生产提供理论依据。【方法】利用大型原状土柱渗漏装置,2种实验土壤(粉质粘土和粉质粘壤土)均为武汉城郊典型蔬菜土壤,分别采自华中农业大学校内蔬菜基地和湖北新洲。试验期间共种植了四种蔬菜(小白菜、 辣椒、 苋菜及萝卜)。试验设置了4个P2O5水平处理(0、 125、 250、 375 kg/hm2),氮肥施用量均为N 750 kg/hm2,钾肥施用量均为K2O 500 kg/hm2。试验期间年降雨量为1043.0 mm,各土柱总灌溉量为120.1 L。秋冬季每15天、 春夏季每10天收集一次淋洗液,另外根据天气和降雨情况适当调节,每次收集淋洗液时记录淋洗液体积并测定淋洗液硝态氮浓度。在每季蔬菜生长成熟后将蔬菜收获称重,烘干后测定蔬菜中氮素含量。【结果】1)与不施磷肥相比,施用磷肥显著增加了两种土壤上小白菜、 苋菜、 萝卜产量以及四季蔬菜总产量,其产量随磷肥施用量增加而增加或显著增加,在磷肥施用量最大时产量达到最大值。粉质粘土上的产量显著低于粉质粘壤土上的产量,粉质粘壤土总产量约是粉质粘土总产量的1.63~2.36倍。2)施用磷肥显著增加了小白菜、 苋菜氮素吸收累积量以及四季蔬菜总吸收累积量,且两种土壤上总氮素吸收累积量均在磷肥施用量最大时达到最大值。粉质粘壤土上氮素总吸收累计量显著高于粉质粘土上氮素总吸收累积量。3)磷肥水平对土壤总渗漏液体积并无显著影响(粉质粘壤土P2O5 125 kg/hm2处理除外),粉质粘土渗漏水量显著大于粉质粘壤土。4)施用磷肥降低或显著降低土壤淋失液硝态氮浓度(粉质粘土苋菜季除外),随着磷肥施用量的增加硝态氮淋失浓度不断降低,4季蔬菜平均淋失浓度最大降低了38.6%(粉质粘土)和28.8%(粉质粘壤土)。5)磷肥施用显著降低了两种土壤上硝态氮淋失量(苋菜季除外),且在粉质粘土上随着磷肥施用量的增加硝态氮淋失量不断降低,而在粉质粘壤土上硝态氮淋失量先降低后上升。粉质粘土硝态氮淋失量显著大于粉质粘壤土,磷肥施用降低硝态氮淋失量分别达到达26.4%~33.7%和23.5%~39.9%。【结论】磷肥施用增加了蔬菜产量和作物氮素吸收累积量,从而显著降低了两种土壤上硝态氮的淋失; 土壤质地对硝态氮淋失有较大影响,质地较轻的粉质粘壤土硝态氮淋失显著小于质地较重的粉质粘土; 粉质粘壤土上施用P2O5量为250 kg/hm2时能提高产量同时减少硝态氮淋失,而粉质粘土上施用P2O5量为375 kg/hm2时能获得较大产量和较少硝态氮淋失量。     

Tillage effects on the accumulation of polychlorinated biphenyls in biosolid‐amended soils

Soil tillage along with the application of organic waste probably affects the concentrations of organic carbon and the enrichment of introduced polychlorinated biphenyls (PCBs). In a three‐year experiment the PCB status of soils from three different field sites (silty clay loam, silt loam, sandy loam) which were long‐term differently tilled (NT = no‐tillage, CT = conventional plough tillage) and amended with two different organic wastes such as sewage sludge and compost (biosolids) was examined. No significant alteration in soil‐PCB quality and quantity with biosolid application could be proven within the course of the experiments. This indicates soil‐air exchange of PCBs dominates their concentrations in soil. Organic carbon in soil was significantly tillage‐dependent and determined the fate of PCBs resulting in a generally elevated PCB‐level in the non tilled soils. Linear regression of PCB load and organic matter content of all investigated untreated soils was highly significant (R² = 0.73). Due to already elevated PCB levels in non tilled soils with a maximum of 65 μg kg^—1 in the superficial layer of the silt loam control plot, any additional potential input, i. e. through the amendment with organic wastes, should therefore be avoided.     

Plant‐available soil phosphorus. Part I: the response of winter wheat and spring barley to Olsen P on a silty clay loam

Increasing fertilizer costs have prompted farmers to ask whether soils could be maintained at lower levels of plant‐available phosphorus (Olsen P) than currently recommended without losing yield. To help answer this question, we assessed the response to Olsen P by spring barley grown from 1986 to 1991, followed by winter wheat from 1992 to 2008, on a silty clay loam soil. Each year the curve relating grain yield to Olsen P was fitted statistically to determine the asymptotic yield and the Olsen P associated with 98% of that yield, that is, the critical level of Olsen P. The variance accounted for by the relationship ranged between 83 and 97% in all but two years, suggesting that the availability of soil P was the major soil factor affecting yield and that Olsen P was a reliable measure of plant‐available P in soil. Asymptotic annual yield of spring barley ranged from 2.34 to 7.12 t/ha and of winter wheat from 3.87 to 10.36 t/ha. In part, this range in yields was because of changes in the cultivar grown while the range of yields for any one cultivar was probably due to differences in weather, principally rainfall, between years. Critical Olsen P ranged from 7 to 18 mg/kg for both cereal crops (with one outlier at 26 mg/kg for winter wheat) most probably due to seedbed and soil structure conditions affecting root growth, and thus acquisition of available soil P, and the way these soil factors were affected by weather. Thus, a general recommendation for cereals grown on this silty clay loam, which is comparatively easy to cultivate, would be to maintain Olsen P at about 20 mg/kg in the plough layer to minimize the risk of losing yield in some years. This value, 20 mg/kg, equivalent to 20 mg/L, is the midpoint of P Index 2, the recommended P Index given in the Fertiliser Manual (RB209) (Defra 2010) for soils growing arable crops and grass in England, Wales and Northern Ireland.     

不同耕作年限对耕地土壤质地和有机碳垂直分布的影响

研究不同耕作年限新疆玛纳斯县耕地的土壤颗粒组成、不同土壤颗粒有机碳含量变化特征以及二者的相关关系。选取4种不同耕作年限耕地为研究对象,采集土层0—300cm的土壤样品,采用激光法获取土壤颗粒组成,探讨长期耕作对土壤颗粒组成以及不同土壤颗粒有机碳含量的影响。结果表明:研究区域土壤剖面颗粒组成主要以砂粒(约占21.0%~35.4%)和粉粒(约占46.0%~50.0%)为主,砂粒含量下部明显高于上部,而粉粒含量中部明显低于上部和下部;随着耕作年限增加,剖面上部(0—60cm)土壤质地由粉砂质粘壤土转变为壤土,60—100cm土层土壤质地由粉砂壤土转化为壤土,中部和下部(100—300cm)土壤质地变化较小;土壤有机碳含量随着开垦年限的增加呈现先增加后降低的趋势,增幅达到71.8%,耕作年限越长有机碳增加值趋于平缓;土壤粉粒、砂粒与有机碳含量相关性不高,而粘粒与有机碳含量呈现显著正相关关系,未耕作(Y0)、耕作20a(Y20)、耕作30a(Y30)和耕作50a(Y50)的土壤粘粒与有机碳含量的相关系数(r)范围在0.67*~0.75*,均达到显著性差异(P0.05)。耕作对土壤颗粒组成以及有机碳含量产生一定影响,科学合理的耕作能够提高土壤的固碳能力,对土壤碳循环系统起到良好的保护作用。     

Soil physical properties and soybean (Glycine max, Merrill) root abundance in conventionally- and zero-tilled soils in the humid Pampas of Argentina

In the humid Pampas of Argentina soybean is cultivated in different soil types, which were changed from conventional- to zero tillage systems in the last decade. Little is known about the response of soybean roots to these different soil physical environments. Pasture, and conventionally- and zero-tilled field lots cropped to soybean (R1 and R2 ontogenic stages) were sampled in February–March 2001 in a sandy clay loam and two silty clay loam Mollisols, and in a clayey Vertisol. In the 0–0.05 m layer of conventionally- and zero-tilled lots soil organic carbon represented 53–72% of that in pasture lots, and showed an incipient recovery after 4–11 years of continuous zero tillage. Soil aggregate stability was 10.1–46.8% lower in conventionally-tilled than in pasture lots, and recovered completely in zero-tilled lots. Soil relative compaction ranged 60.8–83.6%, which was below the threshold limit for crop yields (>90%). In change, soil porosity >50 μm ranged 0.91–5.09% soil volume, well below the minimum critical limit for root aeration and elongation (>10%, v/v). The threshold of soil resistance (about 2–3 MPa) was only over passed in an induced plough pan in the conventionally-tilled Bragado soil (5.9 MPa), and in the conventionally- and zero-tilled Ramallo soils (3.7–4.2 MPa, respectively). However, neither the low macroporosity nor the high soil resistances impeded soybean roots growth in any site. According to a fitted polynomial function, root abundance was negatively related to clay content in the subsoil (R² = 0.84, P < 0.001). Soybean roots were only abundant in the subsoil of the sandy clay loam Mollisol, which had <350 g kg⁻¹ clay. Results show that subsoil properties, and not tillage systems, were the primary effect of root growth of soybean.