黄土性土壤在连续液流条件下吸附、解吸磷酸根的动力学研究

采用连续液流法研究了黄土性土壤吸附,解吸磷酸根的动力学性质。结果表明：（１）供试土壤对磷酸根的吸附,解吸扫速率可分为快,中,慢三种反应类型;（２）描述吸附,解吸反应的最优模型均为Ｅｌｏｖｉｃｈ方程,最差模型分别为一级反应方程及双常数方程,拟合差的模型对反应速率变化“敏感”,可用于反应类型划分和机理研究;（３）粘粒含量及代换量对吸附速率有著影响,游离铁对吸附速率,ＣａＣＯ３对较低温度下的吸附及较高温     

Quantifying microbial biomass phosphorus in acid soils

 This study aimed to validate the fumigation-extraction method for measuring microbial biomass P in acid soils. Extractions with the Olsen (0.5 M NaHCO₃, pH 8.5) and Bray-1 (0.03 M NH₄F–0.025 M HCl) extractants at two soil:solution ratios (1 : 20 and 1 : 4, w/v) were compared using eight acid soils (pH 3.6–5.9). The data indicated that the flushes (increases following CHCl₃-fumigation) of total P (P_t) and inorganic P (P_i) determined by Olsen extraction provided little useful information for estimating the amount of microbial biomass P in the soils. Using the Bray-1 extractant at a soil:solution ratio of 1 : 4, and analysing P_i instead of P_t, improves the reproducibility (statistical significance and CV) of the P flush in these soils. In all the approaches studied, the P_i flush determined using the Bray-1 extractant at 1 : 4 provided the best estimate of soil microbial biomass P. Furthermore, the recovery of cultured bacterial and fungal biomass P added to the soils and extracted using the Bray-1 extractant at 1 : 4 was relatively constant (24.1–36.7% and 15.7–25.7%, respectively) with only one exception, and showed no relationship with soil pH, indicating that it behaved differently from added P_i (recovery decreased from 86% at pH 4.6 to 13% at pH 3.6). Thus, correcting for the incomplete recovery of biomass P using added P_i is inappropriate for acid soils. Although microbial biomass P in soil is generally estimated using the P_i flush and a conversion factor (k _P) of 0.4, more reliable estimates require that k _P values are best determined independently for each soil. Received: 3 February 2000     

The effectiveness of cover crops during eight years of a UK sandland rotation

Abstract. Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-course crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management systems were imposed on the rotation to test their effects on nitrate loss. The effects of cover crops on nitrate leaching and crop yields were compared with the more conventional practice of over-winter bare fallow before potatoes and sugarbeet.
Cover crop N uptake was variable between years, averaging 25 kg ha⁻¹, which is typical of their performance on sandy soils in the UK. The cover crops usually decreased nitrate leaching but their effectiveness depended on good establishment before the start of drainage. Over 7 years, cover crops decreased the average N concentration in the drainage from 24 to 11 mg l⁻¹. Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c . 8%; this was unlikely to be due to additional N mineralization from the cover crop because the potatoes received 220–250 kg fertilizer N ha⁻¹, and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop.
After 8 years of nitrate-retentive practices, there were no measurable differences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic matter at the end of the experiment.     

武夷山土壤形成特点与系统分类

选取武夷山土壤垂直带中 6个代表性剖面 ,研究了土壤的形成条件和特点 ;按照《中国土壤系统分类 (修订方案 )》 ,鉴定了诊断层和诊断特性 ,检索了土壤系统分类名称 ;随海拔由低到高 ,依次为湿润富铁土—湿润淋溶土—常湿淋溶土—常湿雏形土等亚纲 ;并与发生学分类、美国土壤系统分类 (USST)以及世界土壤资源参比基础 (WRB)等不同分类系统中的土壤类别归属作了参比     

The effect of soil flooding on the transformation of Fe oxides and the adsorption/desorption behavior of phosphate

As repeatedly reported, soil flooding improves the availability of P to rice. This is in contrast with an increased P sorption in paddy soils. The effects of soil flooding on the transformation of Fe oxides and the adsorption/desorption of P of two paddy soils of Zhejiang Province in Southeast‐China were studied in anaerobic incubation experiments (submerging with water in N₂ atmosphere). Soil flooding significantly increased oxalate‐extractable Fe (Fe_ox), mainly at the expense of dithionite‐soluble Fe (Fe_DCB), as well as oxalate‐extractable P (P_ox), but decreased the ratio of P_ox/Fe_ox. Flooding largely increased both, P adsorption and the maximum P adsorption capacity. The majority of newly sorbed P in the soils was P_ox, but also more newly retained P was found to be not extractable by oxalate. Flooding also changed the characteristics of P desorption in the soils. Due to a decrease of the saturation index of the P sorption capacity, P adsorbed by flooded soils was much less desorbable than that from non‐flooded soils. There are obviously significant differences in the nature of both, the Fe_ox and P_ox fractions under non‐flooded and flooded conditions. The degree of the changes in Fe_ox, P_ox, P adsorption and P desorption by flooding depended on the contents of amorphous and total Fe oxides in non‐flooded soils. Our results confirm that the adsorption and desorption behavior of P in paddy soils is largely controlled by the transformation of the Fe oxides. The reasons of the often‐reported improved P availability to rice induced by flooding, in spite of the unfavorable effect on P desorbability, are discussed.     

Chemical characteristics and potential source of fulvic acids leached from the plow layer of paddy soil

To understand better the chemical characteristics and source of dissolved organic matter (DOM) leached from the plow layer of rice paddies, a lysimeter study was conducted, which simulated submerged paddy topsoil during rice growth. The fulvic acid (FA) fraction in the percolation water from the lysimeter was collected by adsorption onto insoluble polyvinylpyrrolidone (PVP), and the temporal variations in its elemental composition, molecular size distribution, IR spectra, ¹³C CPMAS NMR spectra, and δ¹³C values were investigated. The proportion of the FA fraction to bulk DOM varied greatly, but the chemical characteristics of the FA fraction did not change appreciably during the experimental period. Thus, it is considered that the changes in the DOM composition in percolation water were mainly due to the differing contributions of the FA fraction. Further, to investigate the source of the FA fraction in the leachate, the chemical characteristics of the FA fraction in the leachate were compared with those extracted from the plow layer soil. A sequential extraction of the FA fraction was conducted using a sequence of water, 0.25 M Na₂SO₄, 0.1 M Na₄P₂O₇ (pH 7.0), 0.1 M Na₄P₂O₇ (pH 10.5), and NaBH₄+0.1 M Na₄P₂O₇ (pH 10.5). It was found that the water- and 0.25 M Na₂SO₄-extractable fractions, which were most mobile, were not the only source of the FA fraction in the leachate. The small molecular size sub-fraction of the NaBH₄+0.1 M Na₄P₂O₇ (pH 10.5)-extractable FAs, most of which are probably bound mainly to iron oxides, are considered to be another source of the FA fraction leached from the plow layer of paddy fields.     

土壤矿物钾的释放及其在植物营养中的意义

本文对土壤钾的形态、矿物钾释放的影响因素及钾的固定、土壤含钾矿物与土壤供钾能力间关系、矿物钾的植物有效性进行了综述 ,表明土壤钾素从有效性的角度进行划分时 ,不能仅把速效性钾和1mol/L热硝酸提取的缓效性钾列为作物吸钾的主要来源 ,而忽视矿物钾的作用 .     

Dynamic of organic matter in the heavy fraction after abandonment of cultivated wetlands

The abandonment of cultivated wetland soil increased the contents of light fraction organic matter (LFOM), heavy fraction organic matter (HFOM) and soil organic matter (SOM). The LFOM and HFOM content increased to 13.3 g kg⁻¹ and 62.4 g kg⁻¹ after 5 years whereas they were 8.4 and 47.9 g kg⁻¹ after 9 years of cropping, respectively. Fourteen years after abandonment, HFOM content increased to 104.3 g kg⁻¹. LFOM was positively correlated with HFOM (p < 0.001). A Langmuir equation was used to calculate the highest HFOM value. The value for the natural wetland soil was closed to this theoretical value (140.8 g kg⁻¹). After 14 years of abandonment, the HFOM maximum (HFOM_Max) value was lower than the equilibrium value suggesting that a further increase in HFOM can occur after abandonment. Assuming a linear accumulation (3.87 Mg C ha⁻¹yr⁻¹), it would take approximately 24 years after the abandonment to reach the HFOM_Max value.     

Influence of water potential on nitrification and structure of nitrifying bacterial communities in semiarid soils

The objective of this study was to examine the relationship between soil water potential, nitrifier community structure and nitrification activity in semiarid soils. Soils were collected after a 5-month dry period (end of summer) and subsequently rewetted to specific water potentials and incubated for 7 days prior to analysis of nitrification activity and nitrifier community structure. The approach used in this study targeted a 491bp segment of the amoA gene which encodes the active site of the ammonia monooxygenase enzyme, which is the key enzyme for all aerobic ammonia oxidisers. amoA serves as a useful target for environmental studies since it is both specific and universal for all ammonia oxidisers and reflects the phylogeny of the ammonia oxidisers. Our results suggest that in semiarid soils water potential plays a key role in determining the structure of ammonia oxidising bacteria (AOB), and that additionally AOB community structure is correlated to potential nitrification rate in these soils.     

不同利用年限红壤水稻土有机碳和养分含量的粒级分布变化

通过田间采样结合沉降法分级提取,研究了不同利用年限红壤水稻土有机碳和养分含量的粒级分布变化特征。结果表明,红壤水稻土有机碳和养分含量随土壤颗粒粒径的增大而下降,但在各粒级中的分布比例存在显著差异。<0.002mm、0.002～0.02mm、0.02～0.05mm、>0.05mm粒级的有机碳占全土有机碳的比例分别是29.2%、30.7%、11.9%、15.4%,氮的相应数值为36.7%、31.9%、10.2%、14.0%,磷为49.2%、26.5%、11.1%、12.4%,钾为36.9%、33.4%、12.9%、20.0%。总体来说,黏粒和粉粒中有机碳和养分的分布比例较高。红壤水稻土有机碳和养分含量及分布比例还随利用年限而有明显变化。开垦利用不到10a的水田土壤,有机碳和养分含量较低且主要集中在<0.002mm粒级中;而利用超过10a的水稻土,有机碳和养分在粉粒中(0.002～0.05mm)的比例大于50%。各利用年限的红壤水稻土多以0.02～0.05mm粒级的C/N为最高,并随利用年限延长而下降。红壤水稻土各粒级有机碳和养分含量及分布状况随利用年限的变化反映了土壤肥力熟化和养分有效性的提高过程。