Effects of additions of organic matter on the penetration resistance of glacial till for the entire water tension range

Hardsetting soil properties are undesirable in agricultural soils because they hamper crop production by limiting seedling emergence and root growth via increased mechanical soil resistance at low moisture contents. The objective of this study was to determine the effect of additions of organic matter on the penetration resistance of a hardsetting soil for the entire water tension range. Investigations were carried out on Saalian glacial till, which is used as a reclamation substrate in post-lignite-mining reclamation. Proportions of 0%, 1%, 2%, 3% and 4% by mass of organic matter (OM) were used. The remoulded samples were saturated under a constant load of 2.4 kPa to achieve bulk densities equivalent to a soil depth of 15–20 cm via water-induced consolidation. Subsequently, the mixtures were adjusted to water tensions between 10⁰ and 10⁷ hPa and penetrated using a small cone penetrometer. Compared to 0% OM, the addition of 1% OM led to a very small but significant (P < 0.01) increase in the bulk density, while between 1% and 4% OM bulk density was seen to decrease in a linear fashion. At moisture contents greater than field capacity, penetration resistance values were consistent with the observed changes in bulk density, leading to an increase in the samples containing 0–1% OM to critical values for root-growth and a decrease for samples containing 2% and more organic matter reaching to values non-critical for roots. At moisture contents smaller than field capacity, penetration resistance values were inversely related to the bulk density, supporting the concept that the type of organic matter added contributed to soil cohesion. Modeling the relation between water tension and penetration resistance using a sigmoidal equation showed a high consistency between the observed data and the model.     

Effect of freezing and thawing processes on some physical properties of saline–sodic soils mixed with sewage sludge or fly ash

Dispersion of saline–sodic soils was rather difficult to leach. Therefore, negative effects of freeze–thaw on soil physical properties should be reduced by inexpensive and practical methods. This study investigates the effect of freeze–thaw cycles (3, 6, and 9) on wet aggregate stability, bulk density, and permeability coefficient in three soils with different electrical conductivity and exchangeable sodium percentage levels (soil I: 5.30 dS m⁻¹, 47.51%; soil II: 42.80 dS m⁻¹, 55.45%; soil III: 36.30 dS m⁻¹, 59.34%) which consist of different proportions of sewage sludge and fly ash by volume (10%, 20%, and 30%). The experiment was conducted under laboratory conditions using disturbed and non-cropped soil samples mixed with sewage sludge and fly ash. Soils mixed with sewage sludge produced higher aggregate stability and permeability coefficients and lower bulk density values as compared to the soils mixed with fly ash. Sewage sludge added with a rate of 30% eliminated the negative effects of freeze–thaw processes on wet aggregate stability. Freeze–thaw processes did not affect the bulk density of the soils II and III, which were mixed with sewage sludge. However, fly ash addition decreased the bulk density of these soils very significantly after nine freeze–thaw cycles. Addition of sewage sludge or fly ash with rates of 20% and 30% significantly increased the permeability coefficients in soil I after nine freeze–thaw cycles. Results indicated that addition of sewage sludge and/or fly ash to saline–sodic soils could be alternative way for reducing negative effects of freezing–thawing on soil wet aggregate stability, bulk density, and permeability coefficient.     

Comparative genetic diversity of <Emphasis Type="Italic">Triticum aestivum–Triticum polonicum</Emphasis> introgression lines with long glume and <Emphasis Type="Italic">Triticum petropavlovskyi</Emphasis> by AFLP-based assessment

Genetic diversity of a set of introgression lines of Triticum aestivum L./T. polonicum L. with long glume and T. petropavlovskyi Udacz. et Migusch. were analyzed by Amplified Fragments Length Polymorphism (AFLP). Small-scale bulk breeding method was applied throughout until F₆ generation to develop the introgression lines. Thirty-eight hexapolid F₇ plants with long glume phenotype and their parents were subjected to AFLP analysis by four primer combinations. A total of 47 polymorphic loci were detected between the parents, 15 of them were introgressed across the 38 lines. It was hypothesized that approximately 50% of A or B genomes associated polymorphic loci were introgressed. The variation of introgression lines was limited within the diversity between their parents, T. aestivum L. cv. Novosibirskaya 67 (N67) and T. polonicum L. cv. IC12196. N67 was closer to 38 introgression lines than that of IC12196. The UPGMA cluster and principal coordinate analysis (PCO) grouping showed 0.84 to 0.98 similarity values between N67 and the introgression lines. Eleven T. petropavlovskyi accessions were distinguished from introgression lines with UPGMA clusters and PCO groupings, and T. petropavlovskyi was located between the introgressions lines and IC12196. Several introgression lines resembled with T. petropavlovskyi for awning and glume length. The genetic variation among 38 introgression lines was much wider than that of T. petropavlovskyi. We concluded that T. petropavlovskyi was established by intensive selection of hybrid between T. aestivum/T. polonicum.     

Record keeping,genetic selection,educational experience and farm management effects on average milk yield per cow,milk fat percentage,bacterial score and bulk tank somatic cell count of dairy farms in the Central region of Thailand

A study was conducted to estimate the record keeping, genetic selection, educational, and farm management effects on average milk yield per cow (AYC), milk fat percentage, bacterial score, and bulk tank somatic cell count (BTSCC) of dairy farms in the central region of Thailand. Farms were located in the provinces of Saraburi and Nakhon Ratchisima and were members of the Muaklek dairy cooperative. Records from individual animals were unavailable. Thus, farm records of milk yield, milk fat percentage, bacterial score, and BTCCC were collected from July 1, 2003 through June 30, 2006. Additional record keeping, genetic selection, education, and farm management information was collected through a questionnaire in May of 2006. Data from the Muaklek dairy cooperative and the questionnaire were then merged by a farm identification number. A single trait mixed model was used to analyze AYC, milk fat percentage, and BTSCC, while a log linear model was used to analyze bacterial score. Results showed that farms that kept records on individual animals had higher (P < 0.05) milk fat percentages and lower bacterial scores than farms that did not. Farms that used genetic information (EBV) and phenotypes when selecting sires were higher (P < 0.05) for milk fat percentage than farms that used only phenotypes and personal opinion. Farms milking cows with a single unit milking machine and by hand, had higher (P < 0.05) bacterial scores and BTSCC than farms using only a single or multi unit machine. Overall farms that kept individual animal records, used EBV when selecting sires, used a single method for collecting milk, and used family labor achieved higher performance from their herds than farms that did not.     

A simplified method for estimating soil compaction

We describe a simplified model that allows users to explore some of the main aspects of soil compaction. It is intended for use by non-experts, such as students, and is written as an easy-to-use spreadsheet. It estimates soil bulk density under the centre-line of a wheel track from readily available tyre details. The model uses an analytical method to estimate the propagation of stress in the soil. It contains compactibility data for contrasting soils and it accounts for both rebound and recompression realistically. We present examples that show the potential of the model in selecting tyres and wheel systems to minimise compaction.     

Soil physical quality of a Brazilian Oxisol under two tillage systems using the least limiting water range approach

Plant growth is directly affected by soil water, soil aeration, and soil resistance to root penetration. The least limiting water range (LLWR) is defined as the range in soil water content within which limitations to plant growth associated with water potential, aeration and soil resistance to root penetration are minimal. The LLWR has not been evaluated in tropical soils. Thus, the objective of the present study was to evaluate the LLWR in a Brazilian clay Oxisol (Typic Hapludox) cropped with maize (Zea mays L. cv. Cargil 701) under no-tillage and conventional tillage. Ninety-six undisturbed soil samples were obtained from maize rows and between rows and used to determine the water retention curve, the soil resistance curve and bulk density. The results demonstrated that LLWR was higher in conventional tillage than in no-tillage and was negatively correlated with bulk density for values above 1.02 g cm⁻³. The range of LLWR variation was 0–0.1184 cm³ cm⁻³ in both systems, with mean values of 0.0785 cm³ cm⁻³ for no-tillage and 0.0964 cm³ cm⁻³ for conventional tillage. Soil resistance to root penetration determined the lower limit of LLWR in 89% of the samples in no-tillage and in 46% of the samples in conventional tillage. Additional evaluations of LLWR are needed under different texture and management conditions in tropical soils.     

PSB菌剂在淡水养殖中的研究现状分析

PSB菌剂 (即光合细菌制剂 )是一种营养丰富的环保型饲料添加剂 ,具有可净化水质 ,防治鱼病 ,维持生态平衡 ,减少二次污染等优点 ,颇受养殖业者的欢迎。合理使用该菌剂 ,将在水产养殖中发挥巨大作用。     

Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting

Soil compaction and soil moisture are important factors influencing denitrification and N₂O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N₂O, N₂ and CO₂ from undisturbed soil cores fertilized with (150 kg N ha⁻¹) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρ_D=1.03 g cm⁻³), the interrow area (ρ_D=1.24 g cm⁻³), and the tractor compacted interrow area (ρ_D=1.64 g cm⁻³), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N₂O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N₂ production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N₂O-N emission in most cases. There was no soil moisture effect on CO₂ emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N₂O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O₂ consumption induced by soil drying and rewetting for the emissions of N₂O.     

HEC固化剂对日光温室戈壁土墙体固化性能试验

【目的】测试新疆三种典型日光温室戈壁土墙体土样进行固化性能,分析戈壁土固化前后的力学性能和硫酸盐侵蚀后的强度的变化规律,为新疆非耕地墙体固化方案提供理论依据。【方法】依据《土工试验方法标准》GB 50123-1999、《土力学实验》和《土工试验规程》SL 237-1999的测试要求^[1-3],采用颗粒分析试验、击实试验测定土体的颗粒级配、类别和击实性能,研究戈壁土固化前的物理性能,测定固化土的抗压强度、硫酸盐侵蚀后的强度。【结果】(1)三种戈壁土土样均为圆砾,根据特征粒径得出土样的不均匀系数Cu和曲率系数Cc表明2号土样的级配最好,其次为3号土样,1号土样的级配最差。(2)掺入15%的土壤固化料,与原状土相比,1号土样的最大干密度ρ_d和最优含水率w_op增加最为显著,分别为0.046%、0.017%。(3)戈壁土随固化剂掺量的增加,胶凝材料越多,固化土越密实,抗压强度越大。(4)90 d侵蚀试验中,固化土随侵蚀周期的增长,抗压强度越大。【结论】HEC固化剂对新疆常用的日光温室墙体建材具有显著的固化效果,其抗压强度和抗硫酸盐效果满足土墙温室墙体建造要求,固化后的墙体坚固耐腐蚀,降低了温室的维护成本,有效延长了温室的使用寿命。     

湖南烟区烤烟散叶烟箱烘烤过程中的生理生化研究

为了解散叶烟箱烘烤的效果,降低烟叶烘烤成本,对比分析了烟夹和散叶烟箱2种装烟方式烘烤过程中烟叶水分含量、色素含量、酶活性的变化以及烤后烟叶质量。结果表明:散叶烟箱烘烤过程中烟叶的失水速率低于烟夹烘烤,而叶绿素降解则快于烟夹烘烤;2种装烟方式烘烤过程中烟叶类胡萝卜素含量呈现先增后减再增的趋势,但散叶烟箱烘烤的降解幅度小于烟夹烘烤;散叶烟箱烘烤烟叶PPO活性在42℃结束高于烟夹烘烤,其余温度点均低于烟夹烘烤,而淀粉酶、SOD与POD活性48℃结束之后高于烟夹烘烤;散叶烟箱烘烤烤后烟叶组织致密,油分略显不足,色度较弱。在烟叶烘烤过程中需依据烟叶酶活性变化来调整布局方式,以提高散叶烟箱烘烤质量。