Fractal features of soil particle size distribution and the implication for indicating desertification

Some of the effects of land desertification on soil properties are manifested by the coarsening of the soil particlesize distribution (PSD) and the losses in organic C and nutrients. The changes and characteristics of PSD and selected chemical properties in soils at the 0-15 cm plough layer from different degrees of desertified croplands are analyzed in the semiarid Horqin Sandy Land, northern China. The fractal dimension of the PSD is emanated to characterize the patterns of PSD. The relationships between the fractal dimension of the PSD and selected soil properties are discussed. The results show that: (1) in the transformation from potential desertified cropland to extremely desertified cropland, the sand content at the 0-15 cm soil increased from 69% to 93%, organic C and total N contents decreased by 65% and 69%, respectively; (2) the fractal dimension of PSD ranged from 2.179 to 2.611, the more the contents of sand, the lower the fractal dimension and the higher the desertified degree of farmland. In the desertification process within the studied area, the mean fractal dimension decreased from 2.555 for the potential desertified soils to 2.298 for extremely desertified soils; (3) there existed considerable linear relationships between fractal dimension and soil properties. It was shown that fractal dimensions of PSD are useful parameters able to monitor soil degradation and to estimate the degree of soil desertification.     

Validating the use of Cs measurements to estimate rates of soil redistribution by wind

Wind erosion has degraded over one-half billion hectares of land worldwide. ¹³⁷Cesium (¹³⁷Cs) has been used as a tracer to study long-term rates of soil redistribution by water and, to a lesser extent, by wind. Early studies assumed that the decline in ¹³⁷Cs activity for a potentially eroded soil relative to that for an uneroded soil was linearly proportional to soil loss. More recently, models have emerged that consider the effects of soil cultivation and the particle surface area-dependent partitioning of ¹³⁷Cs on soils. We investigated the partitioning of ¹³⁷Cs in wind-eroded sediments and with soil surface samples sieved into contiguous ranges of particle sizes. We also compared the ¹³⁷Cs activities and stratification of several adjacent soils with known wind erosion and deposition histories. Finally, we tested ¹³⁷Cs-based soil loss models with measured data from sites with documented histories. ¹³⁷Cs activities and mean particle diameters of aeolian samples agreed well with the ¹³⁷Cs activities and respective mean diameters of the sieved surface soil samples. Good agreement between model estimations and measured data indicated that ¹³⁷Cs models developed to estimate soil redistribution by water were also applicable to soil redistribution by wind provided that the models contained an appropriate particle size correction parameter.     

Relationship between molecular characteristics of soil humic fractions and glycolytic pathway and krebs cycle in maize seedlings

A humic acid (HA) isolated from a volcanic soil was separated in three fractions of decreasing molecular size (I, II and III) by preparative high performance size exclusion chromatography (HPSEC). The molecular content of the bulk soil HA and its size fractions was characterized by pyrolysis-GC-MS (thermochemolysis with tetramethylammonium hydroxide) and NMR spectroscopy. All soil humic materials were used to evaluate their effects on the enzymatic activities involved in glycolytic and respiratory processes of Zea mays (L.) seedlings. The elementary analyses and NMR spectra of the humic fractions indicated that the content of polar carbons (mainly carbohydrates) increased with decreasing molecular size of separated fractions. The products evolved by on-line thermochemolysis showed that the smallest size fraction (Fraction III) with the least rigid molecular conformation among the humic samples had the lowest content of lignin moieties and the largest amount of other non-lignin aromatic compounds. The bulk HA and the three humic fractions affected the enzyme activities related to glycolysis and tricarboxylic acid cycle (TCA) in different ways depending on molecular size, molecular characteristics and concentrations. The overall effectiveness of the four fractions in promoting the metabolic pathways was in the order: III>HA>II>I. The largest effect of Fraction III, either alone or incorporated into the bulk HA, was attributed to a flexible conformational structure that promoted a more efficient diffusion of bioactive humic components to maize cells. A better knowledge of the relationship between molecular structure of soil humic matter and plant activity may be of practical interest in increasing carbon fixation in plants and redirect atmospheric CO₂ into bio-fuel resources.     

西安草滩渭河古河漫滩沉积与洪水变化

根据野外调查、历史文献记录和106个样品的粒度分析,对草滩渭河沉积剖面的洪水变化进行了研究。结果表明,渭河300年来洪水沉积分层明显,对洪水的发生和短期降水量变化反映清楚,分辨率高,能够作为很好地指示洪水和降水量变化的指标。CT剖面厚度约4.5 m,为古洪水沉积层,剖面随深度变化具有明显的粗细变化节律。共分为21个沉积层,指示了21次较大规模的洪水。CT剖面反映的21个阶段的洪水深度和规模由大到小的变化顺序为:第13阶段>第5阶段>第17阶段>第14阶段>第12阶段>第6阶段>第2阶段>第1阶段>第18阶段>第4阶段>第3阶段>第10阶段>第11阶段>第8阶段>第21阶段>第9阶段>第15阶段>第20阶段>第19阶段>第16阶段>第7阶段,其中第13,5,17,14,12,6,2,1阶段为特大洪水阶段,第18,4,3,10,11,8,21,9,15,20,19,16,7阶段为大洪水阶段。CT剖面粒度成分显著大于120年来的洪水沉积,反映了草滩剖面洪水发生时,水动力强,流量大,指示当时降水量应当较多。西安草滩CT剖面第1,2,5,6,12,13,14,17层沉积时,高出河床之上的洪水深度大于6.5 m,其余15个阶段的洪水深度等于或小于6.5 m。     

不同风沙土壤颗粒的分形特征

应用土壤颗粒的重量与粒径分布原理来描述了古尔班通古特沙漠地风沙土壤颗粒的分形特征。通过对10种样品颗粒的机械组成进行分析,分别计算出了它们的分形维数(D=2.3237～2.9347),并分析了其与流动风沙土、半固定风沙土和固定风沙土之间的关系。分析结果表明,风沙土壤结构具有明显的分形特征,其粒径分布分形维数为2～3。土粒表面分形维数与2～0.2mm间的土粒含量存在显著的负相关;而与0.02～0.002mm和<0.002mm的颗粒含量存在显著的正相关,表现为随着土壤质地从流动风沙土、半固定风沙土到固定风沙土的变化,其土粒表面的平均分形维数呈依次增高。土粒表面分形维数与三种典型风沙土壤有机质含量为极显著正相关,而与其硬度为显著负相关。     

基于Meta分析和气象因子驱动的苏豫皖小麦籽粒蛋白质含量地理空间分布特征

为明确苏豫皖地区小麦籽粒蛋白质含量空间分布规律,收集该区域1999-2019年间与小麦籽粒蛋白质含量相关的研究文献及相应地点的气象数据,运用Meta分析方法建立基于气象因子驱动的小麦籽粒蛋白质含量模型,用ArcGIS反距离插值创建预测图,并利用2019年在江苏实际取样测定的小麦籽粒蛋白质数据予以模型验证;最后根据国家小麦品质标准进行小麦品质区划。结果表明,籽粒蛋白质含量随灌浆中期的总日照时数升高而升高,随播种-孕穗、灌浆前中期的总降水量增加而降低。在苏豫皖各地处于同一气象等级条件时,小麦籽粒蛋白质含量整体上从西向东呈降低趋势。采用2019年多点抽样获得的小麦籽粒蛋白质含量进行验证,发现分省拟合模型的效果较好,相对误差在-10%～0之间。苏豫皖三省中,中筋小麦主要分布在江苏省的中北部、安徽省中部少部分地区;中强筋小麦主要分布在江苏省的北部、安徽省的北部、中西部和西南部、河南省的东北部;强筋小麦主要分布在河南省东部、西北部和西南部;江苏省的南部和中部、安徽省的东南部最适宜弱筋小麦的种植。     

核桃五个主栽品种对Botryosphaeria溃疡病的抗性测定

为测定陕西、川北地区核桃主栽品种对溃疡病的抗性差异,本文通过和针刺接种法,对11个核桃良种栽培品种1年生枝条进行了抗Botryosphaeria的初步评估;在此基础上,对其中抗性较强的5个品种,采用打孔法接种2年生枝条进一步进行了抗性测定和评估。结果表明“清香”和“香玲”对溃疡病的抗病性强,“鲁光”、“西林3号”和“西洛”对溃疡病的抗病性弱。核桃品种抗病性差异与接种方式和时间有关,但抗病品种清香和香玲抗性表现稳定。该研究结果为核桃引种栽培提供了依据。     

紫色土光谱特征及其碱解氮的预测研究

文章分析探索了应用可见近红外光谱技术快速、高效、便捷测定土壤营养参数的可能性。采集蓬莱镇组紫色土样本,比对分析了不同肥力水平、土壤厚度和土壤粒径条件下采集土壤光谱对可见近红外光谱特征的影响,筛选出不同厚度、粒径土壤条件下的碱解氮含量预测模型。研究结果表明,土壤样本厚度为30mm时具有最大的光谱反射率,建立的氮含量预测模型效果最佳,校正集和验证集的相关系数分别为0.84和0.83,均方根误差分别为1.79和1.87。土样粒径在0.25-0.85mm时氮含量的预测效果最佳,校正集和验证集的相关系数均超过0.8,且均方根误差较小;但当土样粒径<0.25mm时,氮含量预测模型效果明显下降。采用20目（<0.85mm）过筛、30mm厚度土壤样本采集可见近红外光谱和偏最小二乘法（PLS）模型预测,可以实现对蓬莱镇组紫色土碱解氮含量的较好光谱预测。     

优质脆李新品种‘中李5号’的选育

‘中李5号’李是以‘青脆李’为母本经自然实生选育而成。该品种生长势较强,树姿半开张;在河南省郑州市观察,3月上旬进入初花期,3月中旬进入盛花期,花期持续约10 d;果实发育期约120 d,于7月中旬成熟;果实近圆形,果顶扁平,缝合线浅,平均单果重46.8 g,果皮呈黄绿色,不着红色,果面有明显果粉层;果肉呈浅黄色,肉质细腻、硬脆,汁液多,纤维少,风味酸甜,无香气;果实可溶性固形物含量15.8%,维生素C含量6.82 mg/100 g,可溶性糖含量9.62%,可滴定酸含量0.82%,可食率97.9%;该品种5年生树的株产可达32 kg以上,丰产能力较强,在河南及周边省市李树适生区均可栽植。     

中晚熟粒用高粱不同组合杂交种的筛选

为选育优质中晚熟粒用高粱新材料,本试验采用单因素随机区组设计,以4份不同杂交组合高粱亲本为试验材料,分析不同组合杂交种的生育期、农艺性状及产量性状的差异,筛选最佳的中晚熟粒用高粱组合.高粱组合杂交种的生育期存在差异,但相差不大,生育期最长的高粱组合23A×014-52,生育期为134天,生育期最短的高粱组合147A×0...