土壤固定态铵的影响因素

本文研究了有机质、全氮、有机氮、粘粒、CEC、溶液中铵浓度、水分、温度等影响土壤固定态铵含量的因素。结果表明,固定态铵与<0.01lmm的粘粒呈显著正相关,但与<0.00lmm的粘粒、有机质、全氮、有机氮、CEC相关性很差。通过拟合Langmuir方程可知河沙泥的最大固铵量为357.2mgN/kg,这与359mgN/kg相近。无论是潮沙泥还是紫泥田,固定态铵含量均有:30oC>20oC,30oC>40oC。除了黄泥田外,紫泥田,河沙泥和潮沙泥三种土壤的固定态铵含量均有:长期淹水>干湿交替8次>长期干燥。     

苏南经济快速发展区土壤Ni的形态分布影响因素——以昆山市为例

以江苏省昆山市为典型区,通过现场采样及室内分析测定,定量研究了几种因素对农田土壤Ni形态分布的影响。结果表明：（1）土壤有效态Ni含量为1.31 mg.kg-1,土壤全Ni含量为40.95 mg.kg-1,土壤Ni的活化率为3.38%。（2）土壤重金属Ni各形态含量相对大小为残渣态（36.20 mg.kg-1）〉有机质结合态（2.80 mg.kg-1）〉铁锰氧化物结合态（1.31 mg.kg-1）〉可交换态（0.54 mg.kg-1）、碳酸盐结合态（0.10 mg.kg-1）,残渣态含量明显高于其他形态,达88.16%。（3）pH值是影响可交换态Ni含量的最主要因素,达极显著负相关水平;全Ni含量是影响碳酸盐结合态Ni含量、铁锰氧化物结合态Ni含量和残渣态Ni含量的最主要因素,达极显著正相关水平;有机质含量是影响有机质结合态Ni含量的最主要因素,呈显著正相关水平。（4）〈0.01 mm粘粒含量是影响可交换态Ni含量的重要因素,有机质含量是碳酸盐结合态Ni含量的重要影响因素,pH值和有机质含量都是影响铁锰氧化物结合态Ni含量的重要因素,〈0.01 mm粘粒含量、pH值都是影响有机质结合态Ni含量的重要因素,pH值是影响残渣态Ni含量的重要因素。     

土壤颗粒组成与固定态铵之间的关系

大量研究表明,固定态铵的含量与土壤质地有关.李生秀等人的研究表明[1],西北地区土壤的固定态铵含量与粘粒含量呈显著正相关,与砂粒含量呈显著负相关;Feigin和Yaalon的测定证明,以色列129种钙质土固定态铵含量与粘粒(＜0.002 mm)含量显著正相关(r=0.63,p＜0.01)[2];施书莲等人[3]报道,棕壤、栗钙土、黑土、棕钙土和红壤带土壤中的固定态铵含量与粘粒、粘粒及细粉砂含量之和的相关均达到0.01显著水准.这些结果说明,固定态铵主要存在于粘粒和粉粒中,而砂粒中几乎没有[4].     

粤东凤凰山茶区土壤铜、铬化学形态分布及茶叶有效性研究

采用连续化学提取法对粤东凤凰山茶区12个大型茶园共60份土壤样品中Cu和Cr的5种化学形态分布和茶叶有效性进行研究。结果发现,土壤中Cu的5种化学形态的分布规律为残渣态〉有机束缚态〉铁锰氧化态〉碳酸盐态〉交换态,而Cr的化学形态分布为残渣态〉有机束缚态〉交换态〉碳酸盐态〉铁锰氧化态。可交换态Cu和有机束缚态Cu含量与土壤有机质呈显著正相关,而土壤pH值与土壤可交换态Cu呈极显著负相关,与碳酸盐态Cu呈极显著正相关,与有机束缚态Cu和铁锰氧化态Cu呈显著正相关。可交换态Cr含量与土壤有机质呈显著正相关,而土壤pH值与土壤可交换态Cr呈极显著负相关,与碳酸盐态Cr呈极显著正相关。凤凰山茶叶Cu含量的范围在41.20～118.93mg·kg^-1之间,平均为52.92mg·kg^-1。茶叶中Cu含量与土壤可交换态Cu、有机束缚态Cu、有机质都有显著的正相关性,而与土壤pH值有显著的负相关性。茶叶Cr含量的范围在2.73～6.29mg·kg^-1之间,平均为4.13mg·kg^-1。茶叶Cr含量与土壤有机质和pH值分布呈显著正相关和显著负相关。     

喀斯特边远农区正安县植烟土壤重金属含量及其特征

在喀斯特边远农区典型植烟县采取代表性植烟土壤样品66个,研究县级尺度下植烟土壤重金属含量及其特征。结果表明,Pb,Hg,Cr 3种重金属含量全部符合国家土壤环境质量二级标准,As含量符合国家土壤环境质量二级标准的样点数高达98.5%,4种重金属环境状况良好,无污染。Cd含量符合国家土壤环境质量二级标准样点数占69.7%,且有10.1%的样点含量高于国家土壤环境质量三级标准,部分植烟土壤已受到染污。3种不同植烟土壤类型重金属含量差异较大,石灰土Cd,Hg,As平均含量最高（分别为0.51 m g/kg,0.173 m g/kg,15.45m g/kg）,水稻土Pb,Cr平均含量最高（分别为66.13 m g/kg,55.63 m g/kg）,黄壤居于中间水平。土壤重金属含量与土壤质地密切相关,与土壤粒径具有一定的相关性,粘粒与镉、砷极显著正相关（r=0.333^＊＊,r=0.345^＊＊）,与汞显著正相关（r=0.289^＊）,砂粒与汞、砷显著负相关（r=-0.286^＊,r=-0.245^＊）。喀斯特边远农区植烟土壤重金属环境状况总体良好,但应重视Cd的控制管理。     

湖南省主要稻田土壤的固定态铵含量与最大固铵容量

应用Silva-Bremner法,研究了湖南省7种主要母质发育的稻田土壤的固定态铵含量和最大固铵容量。研究结果表明:①供试耕层土壤固定态铵含量变动在69.2~457.5mg/kg之间,平均为304.7mg/kg±96.7mg/kg,占土壤全N的2.6%~25.7%,平均为14.0%±5.1%,是该地区一项重要的土壤N素资源。7种不同母质发育的稻田耕层土壤固定态铵含量的大小顺序为:湖潮泥>黄泥田>河沙泥>紫泥田>灰泥田>红黄泥>麻沙泥。②在土壤剖面中,土壤固定态铵含量随剖面深度的变化因土壤类型不同而不同,但其相对含量随深度增加而恒增大:表层平均为15.1%±6.6%,亚表层为25.9%±11.7%,表下第3层平均为34.6%±16.3%。③供试耕层土壤的最大固铵容量以湖潮泥最高,达658.7mg/kg,以麻沙泥最低,为97.6mg/kg。④相关分析表明,土壤耕层固定态铵含量与0.01~0.001mm黏粒含量呈极显著正相关(r=0.698**,n=28),与有机质、全N、碱解N、CEC、缓效K和<0.001mm黏粒含量的相关性均不显著。耕层土壤最大固铵容量与固定态铵量呈极显著正相关(r=0.841**,n=32),与0.01~0.001mm黏粒含量呈极显著正相关(r=0.659**,n=28)。     

南京地区水稻土中固定态铵与伊利石的相关性

本文以南京地区长城岗和泉水两个水稻土剖面为研究对象,在利用Silva-Bremner法测定土壤全样和3个粒级(黏粒、粉粒和细砂粒)的固定态铵含量、利用X-射线衍射仪测定矿物成分的基础上,讨论了固定态铵含量与粒级以及矿物种类的关系.结果认为,两个剖面在以下几个方面具有共性:①在黏粒、粉粒和细砂粒3个粒级中,黏粘粒含量与固定态铵含量的关系最为密切,相关系数分别为0.68和0.64;②在黏粒中的伊利石、高岭石和蒙脱石3种主要矿物中,伊利石含量与固定态铵含量相关性最好,相关系数分别为0.50和0.49;⑨对于全样来说,其中的伊利石含量与同定态铵含量呈极显著正相关,相关系数分别为0.68和0.66.这些数据充分说明,伊利石是南京地区水稻土中固定态铵赋存的最主要载体.     

长期不同施肥下红壤活性有机质与碳库管理指数变化

对长期不同施肥5a和10a后红壤活性有机质进行了测定，结果表明，耕作10a不施肥或仅施化肥（CK、N、NP、NK、PK、NPK）的土壤活性有机质（LOM）及碳库管理指数（CMI）都明显下降，最大下降（CK）分别为40．5％和48．1；而有机肥或有机肥化肥配合施用（M、MNPK、1．5MNPK），LOM和CMI则显著升高，最大升高（1．5MNPK）分别为183％和195；秸秆还田（SNPK）处理LOM和CMI先下降后增加，5a分别下降25．2％和31，10a又分别上升17．9％和13。说明化肥主要提高非活性有机质，有机肥则显著改善土壤有机质质量，秸秆还田对提高红壤有机质质量比有机肥慢。用33mmol L^-1、167mmol L^-1、333mmol L^-1KMnO4测定的三种活性有机质（本文分别称其为高活性有机质HLOM、中活性有机质MLOM和活性有机质LOM）的含量依次增加，分别占总有机质的5．6％、9．6％和14．5％。三种活性有机质之间呈显著或极显著相关，HLOM与MLOM相关系数为0．478^＊，HLOM与LOM为0．592^＊＊，MLOM与LOM为0．716^＊＊。作物产量只与MLOM和LOM极显著相关，相关系数分别为0．821^＊＊和0．602^＊＊，而和总有机质没有显著的相关性。同时，LOM及CMI与土壤阳离子交换量、交换性钾、交换性钙、盐基总量、微量元素等呈显著或极显著正相关，但总有机质与上述土壤化学指标相关性差。这些结果暗示LOM和CMI比总有机质更能客观反映土壤肥力和土壤质量的变化情况，应该成为描述土壤质量和评价土壤管理的良好指标。     

氮肥施用对土壤固定态铵有效性和剖面变化特征的影响

农田生态系统中肥料氮素施用通过改变土壤中"原有的"固定态铵和肥料来源"新"固定态铵的动态,从而影响固定态铵的有效性以及其剖面变化特征。固定态铵相对含量在垂直剖面的大小顺序为10~20 cm0~10 cm40~60 cm20~40 cm,在多年淋溶渗透作用下,土壤中黏粒和氮素养分不断向下迁移,从而随着深度增加固定态铵含量升高。在连年施肥的条件下,土壤中固定态铵的含量和碱解氮之间呈极显著正相关关系(r=0.756,p0.01),而且肥料来源部分的相关性显著高于土壤中"原有的"固定态铵。固定态铵含量与植株中氮含量呈显著负相关(r=-0.525,p0.05),同时肥料氮素在固定态铵中的残留与植株中15N含量呈显著负相关(r=-0.526,p0.05),表明固定态铵可以通过长期的固定-释放过程持续为植物供给有效氮源。肥料来源固定态铵的有效性高于土壤中原有部分。连年施肥条件下,固定态铵对作物氮素利用的调节作用十分显著。     

黄土高原典型土壤矿物固定态铵变化的南北差异

采集从北向南依次分布的干润砂质新成土(神木)、黄土正常新成土(延安)和土垫旱耕人为土(杨陵)等典型土壤剖面0200.cm土层土样,通过测定土样全氮和矿物固定态铵,以阐明黄土高原典型区域土壤全氮和矿物固定态铵及二者比率随地理位置和土层的变异规律,为全面了解黄土高原土壤相对稳定氮库累积提供科学数据。结果表明,不同地理位置、不同土层全氮和矿物固定态铵含量存在显著差异。从南到北全氮和矿物固定态铵呈下降趋势,但各土壤全氮和矿物固定态铵的分布显著不同,全氮含量在060.cm随土层深度增加下降很明显,60120.cm有一定下降,120.cm以下低而稳定。矿物固定态铵在全剖面上的分布比较均匀,随土层深度的变化差异不显著,不同土层间的差异基本在误差范围内,土垫旱耕人为土、黄土正常新成土和干润砂质新成土表层(010.cm)矿物固定态铵平均含量分别为215.807.45、165.808.73和146.501.83.mg/kg,表层以下(10200.cm)平均含量分别为193.409.67、157.145.75和142.025.47.mg/kg。从地理位置分析,干润砂质新成土、黄土正常新成土和土垫旱耕人为土表层(010.cm)矿物固定态铵占全氮的百分比分别为(39.570.78)%、(32.916.82)%和(29.747.01)%;在表层以下所占比例更高,干润砂质新成土10200.cm土壤矿物固定态铵含量占全氮比例为(89.5213.42)%,黄土正常新成土为(59.5213.86)%,土垫旱耕人为土为(47.269.01)%。供试土壤中矿物固定态铵与0.01.mm物理性粘粒含量存在极显著正相关关系,说明物理性粘粒是矿物固定态铵的主要载体;矿物固定态铵与全氮含量也有极显著正向相关性。以上结果揭示,在黄土高原黄土母质上形成的土壤,全剖面矿物固定态铵相对均匀,而有机氮相差较大,两种氮库的这种地理位置和剖面分布特征,是黄土母质形成的必然结果,也进一步支持了黄土高原黄土母质的风成学说;同时也反映了需要对有机氮占全氮比例及矿物固定态铵在全氮中地位的传统观念予以重新评价。     

Labile organic matter fractions as early‐season nitrogen supply indicators in manure‐amended soils

Soil test indicators are needed to predict the contribution of soil organic N to crop N requirements. Labile organic matter (OM) fractions containing C and N are readily metabolized by soil microorganisms, which leads to N mineralization and contributes to the soil N supply to crops. The objective of this study was to identify labile OM fractions that could be indicators of the soil N supply by evaluating the relationship between the soil N supply, the C and N concentrations, and C/N ratios of water extractable OM, hot‐water extractable OM, particulate OM, microbial biomass, and salt extractable OM. Labile OM fractions were measured before planting spring wheat (Triticum aestivum L.) in fertilized soils and the soil N supply was determined from the wheat N uptake and soil mineral N concentration after 6 weeks. Prior to the study, fertilized sandy loam and silty clay soils received three annual applications of 90 kg available N (ha · y)^?1 from mineral fertilizer, liquid dairy cattle manure, liquid swine manure or solid poultry litter, and there was a zero‐N control. Water extractable organic N was the only labile OM fraction to be affected by fertilization in both soil types (P < 0.01). Across both test soils, the soil N supply was significantly correlated with the particulate OM N (r = 0.87, P < 0.001), the particulate OM C (r = 0.83, P < 0.001), and hot‐water extractable organic N (r = 0.81, P < 0.001). We conclude that pre‐planting concentrations of particulate OM and hot‐water extractable organic N could be early season indicators of the soil N supply in fertilized soils of the Saint Lawrence River Lowlands in Quebec, Canada. The suitability of these pre‐planting indicators to predict the soil N supply under field conditions and in fertilized soils from other regions remains to be determined.     

Soil slaking sensitivity as influenced by soil properties in alluvial and residual humid tropical soils

Purpose

In the humid Caribbean region characterized by high-intensity tropical rainfall, soil aggregate breakdown and pore blocking due to slaking pressures are major land degradation mechanisms. In this research, we investigated the susceptibility of soils to slaking pressures under rapid wetting as influenced by soil properties and the depositional origin from which the soil is formed using water-stable aggregates (WSAr) and percolation stability (PSc) as indices of the strength of aggregate inter-particle cohesion.

Materials and methods

Wet sieving and percolation stability analyses were employed to investigate WSAr and pore blocking, respectively. The combined effect of soil properties of clay, organic matter (OM), cation exchange capacity (CEC), and exchangeable sodium percentage (ESP) was used to determine the slaking sensitivity score (SSc) of 14 physiogeographically important soils in Trinidad, comprising of nine alluvial and five residual soils.

Results and discussion

Results showed that irrespective of alluvial or residual depositional nature of the parent material, samples had high SSc with an average WSAr of 37.8% and PSc of 6.0 mm/10 min. The linear relationships between SSc with WSAr (r²?=???0.12) and SSc with PSc (r²?=???0.012) of all the 14 soils although negative were weak. Clay content accounted for 94.0% of the variation in CEC in alluvial soils and had strong negative relationships with WSAr (r²?=???0.74) and PSc (r²?=???0.79) in residual soils. Additionally, OM with WSAr (r²?=?0.52) and PSc (r²?=?0.24), and CEC with WSAr (r²?=?0.46) and PSc (r²?=?0.39) showed significant positive linear relationships in residual soil.

Conclusions

The predominantly micaceous and kaolinitic clay mineralogy of these soils, coupled with the low OM contents, increases the proneness of the soils to slaking. This suggests that clay mineralogy is responsible for the high slaking sensitivity rather than clay content or just the depositional origin of the soils. As CEC increases, an accompanying increase in OM is required to increase inter-particle cohesion and to impart partial hydrophobicity, which in turn decreases mineralogically induced susceptibility of individual aggregates to slaking.

     

Soil penetrating quality in cultivated and forested coastal plain sands of Southern Nigeria

Conversion of natural forest to intensive cultivation makes to soil susceptible to flooding, declining fertility and loss of organic matter (OM) and reduced water movement into and within the soil. We studied infiltration rates and related soil penetrating indicators of forested and cultivated soils in humid tropical coastal plain sands in Southern Nigeria. Results showed that mean-weight diameter (MWD) and water stability of aggregates were higher in forested than cultivated soils. Stable aggregates > 1.00 mm were 16.5% and 31.1% respectively, for cultivated and forested soils at 0–15 cm depth, indicating formation of more macro-aggregates in forested soil. Soil disturbance through cultivation decreased hydraulic conductivity and increased bulk density of the soil. Infiltration rate attained after 2 hours was higher in forested soil. Temporary infiltration rate of 178 mm hr^?1 at initial time in cultivated soil was followed by very low infiltration rate of 7 mm hr^?1 after 2 hours. Soil organic matter (SOM), saturated hydraulic conductivity, MWD and total sand correlated positively with infiltration rates are r = 0.76, 0.61, 0.57 and 0.51 respectively. Changes in these parameters are dependent on surface soil disturbance by cultivation. Cultivation of forest decreased infiltration rates and water transmission properties of the soil.     

集约水稻系统下施肥对土壤有机氮形态及供氮的影响

Changes of soil organic nitrogen forms and soil nitrogen supply under continuous rice cropping system were investigated in a long-term fertilization experiment in Jinhua, Zhejiang Province, China. The fertilizer treatments included combination of P-K, N-K, N-P, and N-P-K as well as the control. After six years of continuous double-rice cropping, total soil N and hydrolysable N contents remained stable in plots with N treatments, while the hydrolysable N contents were substantially reduced in those plots without N application. Compared to the unbalanced fertilization treatments, P and K increased the percentage of hydrolysable ammonium N in the total soil N with the balanced application of N, and also maintained higher rice grain yields and nitrogen uptake. Grain yield was positively correlated with total N uptake （r = 0.875^＊＊）, hydrolysable N （r = 0.608^＊＊）, hydrolysable ammonium N （r = 0.560^＊＊） and the hydrolysable unknown N （r = 0.417^＊＊）. Total N uptake was positively correlated with hydrolysable N （r = 0.608^＊＊）, hydrolysable ammonium N （r = 0.440^＊＊） and hydro, lysable unknown N （r = 0.431^＊＊）. Soil nutrient depletion and/or unbalanced fertilization to rice crop reduced N content in soil microbial biomass, and therefore increased C/N ratio, suggesting a negative effect on the total microbial biomass in the soil.     

Copper and lead adsorption as influenced by organic matter in soils from a tropical toposequence with different chemical and mineralogical attributes

The aim of this work was to investigate the influence of the organic matter on copper and lead adsorption in soils with different physiochemical and mineralogical attributes. Suspensions (pH 6.0) of a Latosol, a Neosol and a Vertisol containing increasing amounts of copper or lead were used to obtain sorption isotherms while identical experiments were carried out with the soils previously treated with H₂O₂ to remove organic matter (OM). For the undisturbed soils, L-type and H-type isotherms were predominant for copper and lead respectively, showing that lead interacts more strongly with adsorption sites. For both metals, the non-linear Freundlich adsorption model revealed higher concentration of adsorption sites for Vertisol due to 2:1 clays. For the OM-removed soils, C-type isotherms were observed for copper with the permanence of less stable and more homogeneous sites. For this metal, a high correlation (R² = 0.997) was observed between the decrease of adsorbent sites and the loss of organic carbon, evidencing the central role of organic matter on copper complexation, while lead may be able to interact efficiently with both organic matter and soil minerals.     

Physicochemical properties of the soils associated with shifting cultivation in Northern Thailand with special reference to factors determining soil fertility

Abstract

Recently agricultural activity in the mountainous area of northern Thailand has increased and problems relating to soil fertility have arisen. In order to gain basic information about the soil properties associated with shifting cultivation, physicochemical properties of the surface soils (0–10 cm) and subsoils (30–40 cm) were investigated in selected villages in the area. The physicochemical properties of the soils studied are summarized as follows: 1) The soils were rich in organic matter, content of which ranged from 11.4 to 63.3 g C kg^?1 in the surface soil. 2) The pH(H₂O) of the soils mostly ranged from 5 to 7 and soil acidity was more pronounced in the deeper horizons. In the surface soils, exchangeable Ca and Mg were generally dominant, whereas exchangeable Al was often predominant in the subsoils. 3) Most of the soils showed a medium to fine texture with more than 30% clay. The clay mineral composition was characterized by various degrees of mixture of kaolin minerals and clay mica with, in some cases, a certain amount of 2:1-2:1:1 intergrades. 4) According to the ion adsorption curves, most of the B horizon soils were characterized by the predominance of permanent negative charges. On the other hand, organic matter contributed to the increase of variable negative charges in the surface soils. The content of organic matter and the percentage of the clay fraction were essential for determining the CEC of the soils of the surface 10 and 30–40 cm depths, respectively. Under the field conditions, the composition of exchangeable cations largely reflected the soil acidity. In addition, the content of organic matter also showed a significant correlation with that of available N in the surface soils. Thus, soil acidity both in the surface soils and subsoils, organic matter content in the surface soils, and clay content in the subsoils were considered to be the main factors that affected soil chemical fertility in the area.     

Soil organic matter fractionation as a tool for predicting nitrogen mineralization in silty arable soils

After decades of searching for a practical method to estimate the N mineralization capacity of soil, there is still no consistent methodology. Indeed it is important to have practical methods to estimate soil nitrogen release for plant uptake and that should be appropriate, less time consuming, and cost effective for farmers. We fractionated soil organic matter (SOM) to assess different fractions of SOM as predictors for net N mineralization measured from repacked (disturbed) and intact (undisturbed) soil cores in 14 weeks of laboratory incubations. A soil set consisting of surface soil from 18 cereal and root‐cropped arable fields was physically fractionated into coarse and fine free particulate OM (coarse fPOM and fine fPOM), intra‐microaggregate particulate OM (iPOM) and silt and clay sized OM. The silt and clay sized OM was further chemically fractionated by oxidation with 6% NaOCl to isolate an oxidation‐resistant OM fraction, followed by extraction of mineral bound OM with 10% HF (HF‐res OM). Stepwise multiple linear regression yielded a significant relationship between the annual N mineralization (kg N/ha) from undisturbed soil and coarse fPOM N (kg N/ha), silt and clay N (kg N/ha) and its C:N ratio (R² = 0.80; P < 0.01). The relative annual N mineralization (% of soil N) from disturbed soils was related to coarse fPOM N, HF‐res OC (% of soil organic carbon) and its C:N ratio (R² = 0.83; P < 0.01). Physical fractions of SOM were thus found to be the most useful predictors for estimating the annual N mineralization rate of undisturbed soils. However, the bioavailability of physical fractions was changed due to the disturbance of soil. For disturbed soils, a presumed stable chemical SOM fraction was found to be a relevant predictor indicating that this fraction still contains bio‐available N. The latter prompted a revision in our reasoning behind selective oxidation and extraction as tools for characterizing soil organic N quality with respect to N availability. Nonetheless, the present study also underscores the potential of a combined physical and chemical fractionation procedure for isolating and quantifying N fractions which preferentially contribute to bulk soil N mineralization. The N content or C:N ratio of such fractions may be used to predict N mineralization in arable soils.     

旱地土壤的供氮潜力

对潮土、黄褐土、黄棕壤和红壤旱地的供氮潜力进行研究的结果表明,矿化势(No)变化于60340mgkg-1之间,矿化速率常数(K)0.00556-0,01280d-1,矿化势(No)、矿化速率常数(K)和矿化量(Nt)与土壤供氮量均呈显著相关,说明No、Nt和K是土壤供氮潜力的重要参数。这些参数与土壤全氮、有机质、有机氮、易分解有机质、C/N等土壤组成性质密切相关。测定表明,供试土壤粘土矿物多以2:1型为主,土壤固定态铵多在100mgkg-1以上,有部分可重新释放出来,是研究土壤供氮潜力时不容忽视的因素。     

Erodibility in relation to water‐dispersible clay for some soils of eastern Nigeria

Water dispersible clay (WDC) can influence soil erosion by water. Therefore, in highly erodible soils such as the ones in eastern Nigeria, there is a need to monitor the clay dispersion characteristics to direct and modify soil conservation strategies. Twenty‐five soil samples (0–20 cm in depth) varying in texture, chemical properties and mineralogy were collected from various locations in central eastern Nigeria. The objective was to determine the WDC of the soils and relate this to selected soil physical and chemical attributes. The soils were analysed for their total clay (TC), water‐dispersible clay (WDC), clay dispersion ratio (CDR), dispersion ratio (DR), dithionite extractable iron (Fed), soil organic matter (SOM), exchangeable cations, exhangeable sodium percentage (ESP) and sodium adsorption ratio (SAR). Total clay contents of the soil varied from 80–560 g kg⁻¹. The USLE erodibility K ranges from 0·02 to 0·1 Mg h MJ⁻¹ mm and WEPP K fall between 1·2 × 10⁻⁶–1·7 × 10⁻⁶ kg s m⁻⁴. The RUSLE erodibility K correlated significantly with CDR and DR (r = 0·44; 0·39). Also, a positive significant correlation (r = 0·71) existed between WEPP K and RUSLE K. Soils with high clay dispersion ratio (CDR) are highly erodibile and positively correlates (p < 0·51) with Fed, CEC and SOM. Also, DR positively correlates with Mg²⁺ and SOM and negatively correlate with ESP and SAR. Principal component analysis showed that SAR, Na⁺ and percent base saturation play significant role in the clay dispersion of these soils. The implication of this result is that these elements may pose potential problem to these soils if not properly managed. Copyright © 2005 John Wiley & Sons, Ltd.     

Molecular composition and structure of organic matter in density fractions of soils amended with corn straw for five years

Corn straw is an important source of carbon (C),and when applied to soil,it alters the accumulation and distribution of organic C.However,the mechanistic pathways by which newly added C is stored and stabilized in soil remain a subject of interest and debate among scholars.In this study,we investigated the chemistry of organic matter in different density fractions of Haplic Cambisol (sandy clay loam) in a field experiment with corn straw at8 900 kg ha^-1year^-1under no tillag...