石灰性土壤机械分析的良好分散剂——偏磷酸钠

石灰性土壤中含有大量的碳酸钙,碳酸钙有聚结土壤颗粒的作用。土壤中的碳酸钙不除去,机械分析中的土壤悬浊液不易稳定,而常呈絮凝状态。一般石灰性土壤的机械分析操作中,多先用盐酸洗去碳酸钙,但是土壤中的碳酸钙不是和土粒聚结在一起,便是呈单独颗粒状态,如用盐酸洗去后,土壤物理性质将大有变动,同时自然情况的质地也发生差异。另外,在机械分析比重计法中,加上盐酸处理的步骤,增加了繁重的洗涤工作,失去速测的意义。     

蔬菜农药残留速测方法中若干问题的探讨

随着“无公害蔬菜”、“放心菜”工程的开展,蔬菜上农药残留速测技术备受关注,各种速测方法应运而生,作者对常见的几种速测技术的原理与方法进行了评价,对目前速测方法中存在的重现性差、灵敏度低、误差大、实用性差等问题进行了讨论,为防止未成熟产品、伪劣产品流入市场,影响“三绿工程”的正常开展,提出建立多学科协作研究体系,把农药残留速测技术提高到一个新水平。     

快速检测法检测5种有机磷类农药在青白菜中残留量初探

在青白菜上喷施甲胺磷、三唑磷、乐果、氧化乐果、敌敌畏田间试验与定期取样进行气相色谱分析和农残速测检验以及农药标样速测检验,初步得出了不同有机磷农药不同残留量情况下相应的农残速测结果,不同农药的残留时间,以及5种农药速测结果呈阳性的试样浓度。     

土壤速效氮、磷、钾速测方法的改进Ⅰ.新速测方法的建立

本文对国内现行土壤速效养分速测方法进行了改进 ,包括 :饱和浸提液的制备、浸提剂的筛选、测定方法的改进等 .实验结果表明 :新方法与代表性土壤速效养分速测方法比较 ,提高了精度 ,省时 ,成本低 ,适合于基层土肥站和肥料厂开展测土施肥工作 .     

土壤养分的低成本速测技术

本文论述了测土施肥必须遵循经济规律,强调测土施肥必须适合我国国情,提出了以常规分析技术为后盾以速测技术为主体的测土施肥技术路线;文章还论述了土壤养分速测技术,提出了推广速测技术必须解决的观念问题、技术问题和服务体制问题.     

土壤养分的低成本速测技术

本文论述了测土施肥必须遵循经济强调测土施肥必须适合我国国情，提出了以常规分析技术为后盾以速测技术为主体的测土施肥技术路线；文章还论述了土壤养分速测技术，提出了推广速测技术必须解决的观念问题、技术总是和服务体制问题。     

基层蔬菜农残速测体系建设现状及发展建议

基层蔬菜农残速测体系的建设,对农产品的质量安全监督管理起着重要的作用。基于此,以广西玉林市福绵区为例,通过对蔬菜农残速测体系建设现状的梳理,分析了目前存在的问题,从而结合实际,提出了基层蔬菜农残速测体系建设的建议。     

泥沙含量简易测算方法的探讨

根据长期水土流失实验观测经历,通过一系列实验,探讨称重法、比重计法测算泥沙含量的适用性。结果显示,称重法器材要求低、便携、操作简单、效率高、且精度较高,非专业技术人员易掌握。比重计法器材要求低、便携、操作简便、效率高,且免去了取样环节,但精度较差,非专业技术人员掌握稍有困难。当试验条件确实存在困难或宏观研究对数据精度要求不高时,特别是生产建设项目水土保持监测,称重法和比重计法具有较好的适用性,且称重法较比重计法适用性更好。另外,泥沙密度取值不同对测算结果影响较小,一般可取2.7g/cm3。     

浅谈思茅区蔬菜农残速测常见的影响因素及解决方法

做好农产品药物残留检测,是保证农产品质量安全的有效手段,也是绿色无公害农产品生产的一种重要保障。蔬菜农残速测的常用方法是酶抑制法,具有检测速度快、成本低廉、操作简单等优点,但在实际应用中存在许多影响因素,可能导致检测结果不够准确。基于此,从蔬菜农残速测的基本原理出发,以普洱市思茅区为例,对蔬菜农残速测中一些常见的影响因素和解决方法进行了讨论。     

江西省旱地土壤质地与土壤化学性状的相关性研究

通过研究江西省旱地土壤质地及其与化学性状的相关性,为江西省旱地土壤质地的改良提供理论依据。采用比重计速测法和常规化学指标分析方法测定了江西省不同地区的159个旱地土壤样品质地和氮、磷、钾、有机质含量、pH值和阳离子交换量指标,着重分析土壤中物理性粘粒含量及其他各级土粒含量与化学性状的相关性。结果表明:(1)江西省旱地土壤质地以壤土占绝对优势,高达93.71%,而在壤土中中壤土占比为51.57%;(2)土壤物理性粘粒含量与土壤中全氮、碱解氮、有机质含量、阳离子交换量呈显著正相关,与全钾含量呈显著负相关,即土壤颗粒越细,土壤全氮、碱解氮、有机质含量、阳离子交换量越高,土壤全钾含量越低;随着土壤颗粒变细,土壤pH值呈先升高后降低的趋势;土壤有效磷、速效钾、全磷含量与土壤各级土粒含量之间相关性不显著。     

DISPERSION OF SOIL PARTICLES BY SONIC VIBRATION1

Dispersion of soil particles is achieved without use of oxidants, acids, or peptizing reagents, by subjecting an aqueous suspension of the soil sample (10 g soil, 25 ml water) to sonic vibration at 13 to 15°C using a Raytheon (9 kc, 50 w) vibrator. Studies using soils of widely different textures and organic matter contents showed that the dispersion caused by sonic vibration for 30 min, as evaluated by pipette analysis for < 2 μ material, was similar to that obtained by chemical methods currently used for dispersion of soils. The dispersion effected by ultrasonic vibration of soil-water suspensions using a probe-type vibrator (18–20 kc, 60 w) is comparable to that achieved by sonic vibration. The vibration method of dispersing soil particles yields stable suspensions and is effective with highly calcareous soils and with soils containing large amounts of montmorillonite and organic matter. It permits dispersion of soil particles without dissolution of more than trace amounts of organic or inorganic material and does not significantly affect the pH or conductivity of the soil suspension.     

Chemical fixation of ammonia to soil organic matter after application of urea

Chemical fixation of NH₃ to soil organic matter was studied in two Swedish soils with different contents of organic matter: a clay soil with 2.3% C and an organic soil with 36.6% C. ¹⁵N‐labelled urea was applied at different rates to both sterilized and non‐sterilized soils. After 10 days, the soils were extracted and washed with K₂SO₄ and determined for total N and atom% ¹⁵N excess. Urea N was recovered as non‐extractable N in sterilized soil corresponding to 9.7% of supplied ^l5N‐labelled urea in the organic soil and 2.2% in the clay soil. Since no biological immobilization is thought to occur in the sterile soil, this non‐extractable N is suggested to be chemically fixed to soil organic matter. Owing to urea hydrolysis in the clay soil, pH increased from 6.3 to 9.3 and in the organic soil from 5.7 to 6.9 and 8.8, respectively, at the low and high urea supply.     

土壤紧实度与土块分配对水稻生长的影响及耕作方法的调节

本文就苏南地区二种粘质水稻土的土壤紧实度和土块组成对水稻生长的影响进行了研究,并对不同方法耕作后耕层土块的组成状况进行了观测,结果指出:土壤紧实度和土块/细土比例的不同对水稻生长有明显的影响,土壤紧实度对水稻生长的影响是通过土壤对根的机械阻力,抑制土壤养分的转化及水分物理特性的改变所致;而土块组成的影响可能主要是影响土壤养分的转化。研磨细了的土壤转化成NH₄-N的量最高,土块大于1厘米者对NH₄-N的产生受到严重抑制,因此认为,春耕后耕层中小于1厘米的土块是评定春耕质量的一个重要指标,耕层土块大于8厘米时妨碍栽秧操作,8-4厘米者影响次之,1-4厘米者对栽秧无影响。对于要获得较小土块组成的耕作质量,旋转耕作效果最好,机耙最差,但土壤经过充分晒垡后,各种耕作方法均可获得较好的相同效果,这时,对合适机具的选择主要可从经济效益考虑。渍水条件下土垡经过挤压受损后,可使土块膨软,这或对土壤养分的释放有利,故一般用于春耕机具,只考虑其切割效果而不同时考虑挤压作用是不足的。     

Solubility relationships of silica in soils

Abstract

Twenty‐one mineral soils of different physicochemical properties were used in this study. Soil suspensions, 30 grams of soil in 150 ml of distilled water, were shaken for 96 hours at 200 rpm and 25±1°C.

The activity of H₄SiO₄°, maintained in soil suspensions after shaking for 96 hours, was higher than quartz, cristobalite, and tridymite suggesting that comparatively more soluble forms of silica may be present in soils. All the soils, except Soil P and Soil Q, used in this study supported lower activity of Si than amorphous SiO₂. The average activity of H₄SiO₄° was 10^?3.08 M. It may be reasonable, for general purposes, to assume soil Si level as 10^?3.1 M. The activity of H₄SiO₄° found in soil suspensions was independent of soil pH. None of the selected physicochemical properties of soils was significantly correlated (at 5% significance level) to the activity of H₄SiO₄° in soil suspensions.     

The Impact of Agriculture on Soil Texture Due to Wind Erosion

Wind erosion produces textural changes on topsoil of semiarid and arid environments; however, the selection of particles on different textured soils is unclear. Our objectives were to evaluate textural changes induced by wind erosion on cultivated soils of different granulometry and to asses if textural changes produced by wind erosion are linked to aggregation of granulometric particles into different sizes of aggregates formed in contrasting textured soils. Considering this, we studied the particle size distribution (PSD) with full dispersion (PSD_F) of 14 cultivated (CULT) and uncultivated (UNCULT) paired soils and, on selected sites, the PSD with minimum dispersion (PSD_MIN) and the quotient PSD_MIN/F. Results showed that the content of silt plus clay was lower in CULT than in UNCULT in most of the sites. The highest removal of silt was produced in soils with low sand and high silt content; meanwhile, the highest removal of clay was observed in soils with medium sand content. According to PSD_MIN, particles of 250–2,000 μm predominated in the sandy soil, in the loamy soil particles between 50 and 250 μm and in the silty loam soil particles between 2 and 50 μm. For clay sized particles, PSD_MIN/F was lower than 1 in all soils and managements, but this quotient was higher in CULT compared with UNCULT only in the loamy soil. This means a decrease of clay accumulation in aggregates of larger sizes produced by agriculture, which indicates an increase in the risk of removal of these particles by wind in loamy soils. Copyright © 2014 John Wiley & Sons, Ltd.     

Soluble organic matter and microbial biomass C and N in soils under pasture and arable management and the leaching of organic C,N and nitrate in a lysimeter study

Soluble organic N and C were extracted from soils under long-term kikuyu grass pasture, annual ryegrass pasture and annual maize production using water, 0.5 M K₂SO₄ and 2 M KCl. Quantities extracted with K₂SO₄ were more than double those extracted with water while those extracted with KCl exceeded those using K₂SO₄. Differences in soluble organic C and N between land uses were much more obvious when water rather than salt solutions were used. It was suggested that water extracts give more realistic values than salt solutions. Regardless of the extractant used, the proportion of total N present as soluble N was considerably greater than the equivalent proportion of organic C present as soluble C. While the percentage of soil organic C and total N present in the light fraction and microbial biomass was lower in the kikuyu than ryegrass and maize soils, the equivalent values for water soluble C and N were, in fact, greatest in the kikuyu soil.The leaching of organic C, N and NO₃⁻ from these soils was also measured over a 6-month period in a greenhouse lysimeter study. The soils were either left undisturbed or were disturbed (broken into clods <50 mm diameter) to simulate tillage and stimulate microbial activity. Quantities of organic C and N leached were greater from the kikuyu than other treatments and tended to be greatest from the disturbed kikuyu soil. The percentage of total soil N leached as organic N was considerably greater than that of total organic C leached as soluble C. Leaching of NO₃⁻ was greatest from the disturbed kikuyu soil and least from the undisturbed kikuyu soil. The mean percentage of total soluble N present in organic form in leachates ranged from 17 to 32% confirming the importance of this form of N to leaching losses of N from agricultural soils.     

冬小麦-夏玉米轮作体系中不同施氮水平对玉米生长及其根际土壤氮的影响

在河北衡水潮土上进行田间试验,以当地习惯高氮用量(小麦季施N 300 kg/hm2,玉米季施N 240 kg/hm2)为对照,研究冬小麦-夏玉米轮作体系中减少氮肥用量对玉米季植株生长、氮素吸收及根际土壤中无机氮与微生物量氮的影响。结果表明,两季作物氮肥施用量减少25%和40%,对玉米产量、生物量及植株体内氮累积量未产生明显影响,氮肥利用率提高。不同氮肥施用量对根际和非根际土壤铵态氮含量的影响不显著;减少氮肥施用量,对玉米根际土壤硝态氮含量也没有明显影响。在玉米苗期、抽雄期和成熟期,习惯高施氮量处理的非根际土壤硝态氮含量较高,其中抽雄期,非根际土壤硝态氮含量较氮肥减施40%用量处理高出近一倍,但非根际土壤微生物量氮水平含量明显降低。氮肥减施未影响根际土壤微生物量碳、氮含量,反而增加了非根际土壤微生物量碳、氮水平。在高肥力的潮土上,冬小麦/夏玉米轮作体系中适当减施氮肥并未影响玉米根际土壤氮素水平,可保证玉米稳产,实现减氮增效。     

Soluble organic nitrogen in temperate forest soils

Very few studies have been related to soluble organic nitrogen (SON) in forest soils. However, this nitrogen pool could be a sensitive indicator to evaluate the soil nitrogen status. The current study was conducted in temperate forests of Thuringia, Germany, where soils had SON (extracted in 0.5 M K₂SO₄) varying from 0.3 to 2.2% of total N, which was about one-third of the soil microbial biomass N by CFE. SON in study soils were positively correlated to microbial biomass N and soil total N. Multiple regression analysis also showed that mineral N negatively affected SON pool. The dynamics of the SON was significantly affected by mineralization and immobilization. During the 2 months of aerobic incubation, the SON were significantly correlated with net N mineralization and microbial biomass N. SON extracted by two different salt solution (i.e. 1 M KCl and 0.5 M K₂SO₄₎ were highly correlated. In mineral soil, SON concentrations extracted by 1 M KCl and 0.5 M K₂SO₄ solutions were similar. In contrast, in organic soil layer the amount of KCl-extractable SON was about 1.2-1.4 times higher than the K₂SO₄-extractable SON. Further studies such as the differences of organic N form and pool size between SON and dissolved organic N (DON) are recommended.     

Impact of addition of different rates of rice-residue biochar on C and N dynamics in texturally diverse soils

Impacts of crop residue biochar on soil C and N dynamics have been found to be subtly inconsistent in diverse soils. In the present study, three soils differing in texture (loamy sand, sandy clay loam and clay) were amended with different rates (0%, 0.5%, 1%, 2% and 4%) of rice-residue biochar and incubated at 25°C for 60 days. Soil respiration was measured throughout the incubation period whereas, microbial biomass C (MBC), dissolved organic C (DOC), NH₄⁺-N and NO₃^–N were analysed after 2, 7, 14, 28 and 60 days of incubation. Carbon mineralization differed significantly between the soils with loamy sand evolving the greatest CO₂ followed by sandy clay loam and clay. Likewise, irrespective of the sampling period, MBC, DOC, NH₄⁺-N and NO₃^–N increased significantly with increasing rate of biochar addition, with consistently higher values in loamy sand than the other two soils. Furthermore, regardless of the biochar rates, NO₃^–-N concentration increased significantly with increasing period of incubation, but in contrast, NH₄⁺-N temporarily increased and thereafter, decreased until day 60 in all soils. It is concluded that C and N mineralization in the biochar amended soils varied with the texture and native organic C status of the soils.     

Chloroform fumigation and the release of soil nitrogen: The effects of fumigation time and temperature

Fumigation with CHC1₃ (24 h, 25°C) increased the amount of NH₄-N and total N extracted by 0.5 M K₂SO₄ from two soils (one arable, one grassland). The amount of N released by CHC1₃ increased with the duration of fumigation up to 5 days, when it levelled off. Between about 10–34% of the total N released by CHC1₃ was in the form of NH₄-N, the proportion increasing with duration of exposure.When a grassland soil that had received a field application of ¹⁵N-labelled fertilizer 1 yr previously was fumigated, the N released by CHC1₃ was 4 times more heavily labelled than the soil N as a whole. Prolonging the exposure of this soil to CHC1₃ increased the amount of total N released, but hardly altered the proportion of labelled N in the CHC1₃-released N, suggesting that N is being released from a single soil fraction. The most likely soil fraction is the soil microbial biomass. It is suggested that CHC1₃ does not alter the K₂SO₄-extractability of soil-N fractions other than microbial N and that the extra N released by CHC1₃ and extracted by K₂SO₄ gives a direct measure of soil microbial biomass N.In contrast to fumigation done at lower temperatures, less total N was released by soil fumigated at 60°C, or above, than was released from unfumigated soil held at the same temperature. The greater release of N in the non-fumigated soils above 60°C could have been due to soil enzymic processes which were inhibited by CHC1₃ in the fumigated soil.