土壤容重对玉米光合特性的影响及调控研究

以耕地棕壤为试验材料,采用盆栽方法,研究不同土壤容重对玉米光合指标(光合速率、气孔导度、胞间二氧化碳浓度)及叶绿素(a、b)的影响,并进一步研究了施用不同有机肥量及模拟不同耕作深度对玉米光合指标的调控效果。结果表明:不同容重处理之间对玉米叶绿素含量的影响拔节期前差异不显著,拔节期后达极显著差异(p<0.01),叶绿素含量在研究的生育期内始终增长。光合速率与容重、胞间二氧化碳浓度呈负相关,与气孔导度呈正相关。高容重土壤有机质调节至40～50 g kg-1即可以获得比较理想的效果;低容重的土壤有机质在研究含量范围内效果始终显著增长,有机质含量在15 g kg-1左右制约玉米生长,有机质含量应至少调节至3%以上。耕层厚度增加能提高所测定生理指标,但耕层厚度处理对叶绿素、光合指标影响不显著,当耕层厚度调节至30～40 cm时,各项指标增加基本达到限值,再增加耕层厚度作用不再明显。     

土壤溶质迁移的指数函数模型

边界层方法是描述土壤溶质迁移的简单方法,通过边界层距离与时间的关系可以估计溶质迁移参数。基于边界层方法,研究了土壤溶质迁移的数学模拟及相应参数估计问题。假定土壤溶质浓度剖面为指数函数,得到了描述溶质浓度分布的指数函数模型。各参数对边界层距离的影响分析表明,应选取较小的孔隙水流速度、短历时推求土壤溶质迁移参数;对不同模型预测土壤溶质分布进行比较,结果表明,在短距离处指数型解与精确解的误差比其它都要小。误差分析表明了指数函数模型的有效性和实用性。     

RESPONSES OF WHEAT PLANTS IN TERMS OF SOIL WATER CONTENT,BULK DENSITY,SALINITY, AND ROOT GROWTH UNDER DIFFERENT PLANTING SYSTEMS AND VARIOUS IRRIGATION FREQUENCIES

The effects of irrigation water rates and seed bed shapes on changes in soil water and salinity status, bulk density, root growth and dry matter (DM) weights of wheat plants (Triticum aestivum L.) were investigated with a split plot design in a field trial in Zahak Agricultural Research Station in Sistan, Iran in 2005. Irrigation intervals after 80 and 160 mm evaporation from class A evaporation pan were used as main plot. Flat surface, single, triple, and six-row beds with a 20 cm row space were used as subplots. Each treatment was replicated four times. Volumetric soil water content and soil electrical conductivity (EC) were measured using Time Domain Reflectometry (TDR) at 0 —20, 20 —40 and 40 —60 cm depths at nine different times during the growing season. Soil water contents were also measured at 0 —10 and 10 —20 cm depths using standard sampling rings at four different times. The three and six-row beds increased the EC of the saturated paste extract with the more frequent irrigation intervals in this coarse textured soil. Soil water content, DM, and root density were always greater with the more frequent irrigations (shorter irrigation intervals). Root density was greatest in 0 —20 cm depth with the single row bed treatment. Grain yield and root density were greatest with single row bed treatment due to the bed shape at the root development stage (possibly due to a reduced mechanical resistance). A greater soil water content by the short irrigation interval increased grain yield and root density via reducing mechanical resistance. With the loamy sand, bulk density and mechanical resistance increased rapidly after cultivation. Bed shape at root development stage might have enhanced root growth and the crop yields. Apparently, mechanical resistance was the most limiting factor with these loamy sand soils than salinity.     

Response of soil properties and yam yield to Chromolaena odorata (Asteraceae) and Tithonia diversifolia (Asteraceae) mulches

Plant materials differ in their chemical composition, rate of decomposition and suitability as mulch materials. Experiments were conducted during 2006–2007 and 2007–2008 cropping seasons for early yam cultivation at Owo in the forest–savanna transition zone of southwest Nigeria to study the effect of Chromolaena odorata and Tithonia diversifolia mulches applied at 0.0, 5.0, 7.5, 10.0 and 12.5 t ha^?1 on soil chemical properties, leaf nutrient composition, growth and tuber yield of white yam (Dioscorea rotundata Poir). Both C. odorata and T. diversifolia mulches reduced soil bulk density and temperature; increased concentrations of soil organic matter (SOM), total N, available P, exchangeable K, Ca and Mg, leaf N, P, K, Ca and Mg; enhanced growth and yield of yam compared with control. The values of SOM, total N and available P and leaf N and P concentrations increased with increasing mulch rate. C. odorata mulch and T. diversifolia mulch applied at 10.0 and 7.5 t ha^?1, respectively, was found to be suitable for yam production. T. diversifolia mulch compared with C. odorata mulch produced higher values of soil chemical properties, leaf nutrient concentrations, growth and yield of yam. T. diversifolia mulch produced 19% and 18% higher tuber yield compared with C. odorata mulch during 2006–2007 and 2007–2008 cropping seasons, respectively.     

Yield components,light interception and marker compound accumulation of stevia (Stevia rebaudiana Bertoni) affected by planting material and plant density under western Himalayan conditions

A field experiment was conducted to study the effect of planting material and plant density on stevia (Stevia rebaudiana Bertoni) under western Himalayan conditions during 2011 and 2012. The experiment conducted in a split plot design consisted of two types of planting material (rooted slips and fresh seedlings) in the main plot and five inter- and intra-row spacing in subplots with three replications. Yield attributes and dry leaf biomass yield of stevia were not affected by the type of planting material; however, plant density significantly influenced the yield attributes and leaf and stem dry biomass. Although the wider spacing (60 × 45 cm) gave more leaves, higher leaf area index, higher leaf dry mass per plant as compared to closer spacing, it resulted in lower values of these attributes per unit area. Plants spaced in 30 × 30 cm accumulated 41.2% and 42.8% more total biomass than 60 × 45 cm. Steviol glycoside content did not change due to different planting materials and plant densities; however, closer plant spacing (30 × 30 cm) recorded 114.8% and 70.0% higher steviol glycoside accumulation compared to wider row spacing (60 × 45 cm) in 2011 and 2012, respectively.     

玉米生长后期的根系分布研究

为了研究玉米生长后期根系的生长发育规律,利用中国气象局固城农业气象试验站大型根剖面系统,采用微根管观测系统及方形整段标本法和地下根系室玻璃窗,对‘屯玉46号’玉米根系的生长状况进行了试验研究。结果表明:垂直方向上,方形整段标本法和微根管法测得的根长密度占整层总根长密度比例的变化趋势一致,相关系数分别为0.987和0.717,且两种方法在0~20 cm土层的根长密度比例均为最大。0~60 cm土层为玉米根系生长活跃区,方形整段标本法测得根长密度生长量为其余层的4倍。两种方法测得的根长密度无显著差异,相关系数为0.830,均匀性水平较好。玉米成熟期根系的水平幅度较乳熟期窄,下层根系仍处于生长中,垂直深度增加。玻璃窗与方形整段标本法观测的根深测定结果存在差异,这可能与观测环境条件不一致有关。     

成都典型区轮作与土壤特征类型对有机碳密度影响力比较研究

研究分析轮作制度与土壤特征类型对农田土壤有机碳密度变异的主导作用程度,对提高农田土壤固碳潜力具有重要意义。基于2010年在新都区和郫县采集的土壤样点数据,利用方差分析和逐步回归分析方法研究分析土壤特征类型(土壤质地、土壤亚类、成土母质)和轮作制度对成都平原典型区农田土壤有机碳密度(SOCD)变异的影响,比较土壤特征类型与轮作制度对土壤有机碳密度变异的影响力。结果显示:土壤特征类型和轮作制度均对SOCD的变异具有显著影响,特别是土壤质地类型,其中黏粒含量与各土层的SOCD之间均存在极显著正相关性(P0.01);与轮作制度影响力比较,土壤特征类型对SOCD变异性影响起主导作用,能够分别解释SOCD在0~40、0~20和20~40 cm土层变异性的35.9%、43.0%和16.8%;而轮作制度对SOCD变异性影响表现在0~40和0~20 cm土层,SOCD逐步回归解释能力在土壤特征类型基础上仅增加2.2%和4.5%,轮作制度影响力不足以改变土壤特征类型对区域土壤有机碳密度变异的影响地位。研究和揭示区域农田土壤有机碳密度变异及其驱动力,更应注重土壤特征的影响力,轮作制度影响力可以被忽略。     

荒漠土壤有机质含量高光谱估算模型

为解决荒漠土壤有机质含量高光谱估算存在的困难,提高土壤有机质含量估算的精准性,该文对准噶尔盆地东部荒漠土壤进行采样、化验分析和光谱测量、处理,分析土壤光谱与有机质含量的相关性,确定敏感光谱波段,建立荒漠土壤有机质含量多种高光谱估算模型,旨在通过模型精度的比较,确定最优模型。结果表明：反射率、倒数对数光谱与荒漠土壤有机质含量相关性低,而经过一阶微分、二阶微分变换后,相关系数有所提高,部分波段的相关系数通过0.01显著水平的检验,可以用来荒漠土壤有机质含量的估算;一元线性回归建立的估算模型的精度低,不适用荒漠土壤有机质含量高光谱的估算。荒漠土壤有机质多元逐步回归模型的二阶微分、倒数对数二阶微分修正决定系数得到了较大提高,分别提高了0.22和0.31,均方根误差下降了0.66和0.80,建模精度高于一元线性回归模型。荒漠土壤有机质一阶微分、二阶微分光谱的最小偏二乘回归模型的决定系数比其多元逐步回归模型提高了0.07、0.04,一阶微分、二阶微分均方根误差都下降了0.11,二阶微分偏最小二乘法回归模型是该研究所建12个模型的最优估算模型。在多元逐步、偏最小二乘回归模型中,最优估算模型是二阶微分模型,因而用偏最小二乘法回归估算荒漠土壤有机质含量是个可行的方法。该研究的成果为荒漠土壤有机质高光谱遥感分析提供了支撑,实现荒漠土壤有机质监测的时效性、准确性,为区域生态环境的修复提供依据。     

不同种植方式对红壤旱地土壤水分及抗旱能力的影响

通过3年田间小区试验,研究不同种植方式对红壤旱地土壤水分及抗旱能力的影响.结果表明：1）与种植花生相比,种植苎麻可显著提高土壤有机质质量分数（28.44％）、田间持水量（10.06％）和总孔隙度（5.65％）,土壤密度则显著降低7.20％;2）监测期内,花生地各层土壤以及整个0～ 100 cm土体水分变异系数普遍高于苎麻地,苎麻地0 ～ 100 cm土体水分的时间稳定性和空间协调性优于花生地;3）苎麻地0～ 40 cm土壤较花生地延长抗旱时间7d以上,但随着土层的加深,差异越来越小;4）红壤坡耕地种植苎麻有利于提高红壤旱地土壤抗旱能力,特别是中、上层土壤.从扩充土壤水库的角度考虑,红壤旱地种植苎麻优于种植花生,该研究结果可为挖掘红壤区深层土壤水分提供参考.     

体积置换法直接测量土壤质量含水率及土壤容重

土壤含水率直接测量是相关研究和应用的基础,在土壤力学、作物栽培、农田灌溉、生态环境等研究和实践中十分重要。该文提出了一种与传统烘干称质量法相当的体积置换法直接测量土壤质量含水率及土壤容重。该方法在假设一定土壤颗粒密度的前提下,用一定体积的标准取样环刀取得土样后,通过向待测量土体补充水分使土壤达到饱和,用一定体积的水置换土壤中的充气空隙,直到土样达到饱和状态;再通过测量得到的初始/原始土样质量、饱和后土壤的质量以及已知土壤颗粒密度和水密度,计算得到被置换的充气空隙的体积,进而由此计算得到土壤质量含水率和土壤容重。采用3种不同土壤,即陕西杨凌黏黄土、北京粉壤土和江西黏红土,分别预配制成7种不同初始土壤体积含水率,含水率约为:风干土(含水率2%～3%)、5%、10%、15%、25%、30%和饱和含水率,以及3种不同土壤容重:1.25、1.35和1.45g/cm3进行室内试验。用类似的土样,采用传统方法烘干土样8、12、24、48h后,测量确定土壤的质量含水率,通过延长烘干时间测得数据表明,传统方法烘干8h所测得的质量含水率仍有1%～3.2%的含水率误差。最终试验结果表明体积置换方法测得的土壤含水率比传统烘干土样8h所测得的结果大2%～3%,比烘干土样48h所测得的结果大1%左右。体积置换方法测量操作过程简单,耗时较少,节约能源,测量结果具有较高精度。