Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro- N -(2-ethoxyethyl)- N -(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.     

Residual phytotoxic activity of pethoxamid in soil and its concentration in soil water under different soil moisture conditions

The relationship between the residual phytotoxic activity of pethoxamid (2-chloro- N -[2-ethoxyethyl]- N- [2-methyl-1-phenyl-1-propenyl] acetamide) on rice ( Oryza sativa cv. Kiyohatamochi) seedlings and its behavior in soil was investigated under different moisture conditions. The phytotoxic activity of pethoxamid on the shoot growth of rice seedlings in soil was higher in 80% soil moisture content than in 70% and 60% soil moisture contents. The phytotoxic activity in soil in 70% and 80% soil moisture conditions decreased with the increasing time after application, but the phytotoxic activity was slight in 50% soil moisture conditions at any given time after application. The residues of pethoxamid in soil water, the amount adsorbed on soil solid, and the amount in total soil was reduced with the time after application in a similar manner among these soil moisture conditions. The residual phytotoxic activity of pethoxamid on the shoot growth of rice seedlings in soil was more highly correlated with the concentration in soil water than with the amounts adsorbed on soil solid and in total soil. The partition coefficients between the amounts of pethoxamid adsorbed on soil solid and its concentration in soil water were similar among the soils with different moisture conditions at each day, and the partition coefficient increased with the time after application. These results suggested that the residual phytotoxic activity of pethoxamid in soil depends on the decreasing concentration of pethoxamid in soil water with time, except in low soil-moisture conditions, which were insufficient for seedling growth.     

黄土丘陵区不同土地利用方式下土壤水分分析

采用定位监测法,对地处黄土丘陵区的延安燕沟不同植被类型下土壤水分状况进行了对比分析。结果表明:农林草地土壤水分剖面(0~4 m)存在显著差异,平均土壤含水量由高到低依次为:旱农坡地>草地>柠条灌丛>果园>黄刺玫灌丛>刺槐,与旱农坡地对照分别相差2.04%、2.27%、4.75%、4.8%和5.68%;刺槐、柠条和黄刺玫的土壤水分垂直分布呈现较一致的趋势,表现为上层水分高于下层且差异显著,水分较明显的分界点在100cm左右,其100 cm以上平均土壤湿度分别为10.12%、13.58%和11.89%,100 cm以下分别为8.79%、12.16%和9.07%;同时,不同植被类型下土壤剖面低湿层不同,乔灌地低湿层深度较农地和草地深;土壤水分剖面形态与分层特征受植被利用影响作用显著。     

长武塬区不同土地利用条件下土壤水分深剖面分布特征比较

通过调查取样的方法对长武塬面不同土地利用条件下(作物地,果园,苜蓿地)土壤水分状况在0～600 cm范围深度内进行对比,结果显示:长武塬区小麦收获期,不同土地利用条件下土壤水分含量总体存在较大差异,其中春玉米地由于上年小麦收获后直到春玉米播种前土地休闲,土壤含水量显著高于其它土地利用方式.其它土地利用条件下土壤平均含水量相对较低,在0～300 cm的范围内含水量分布表现为果园>苜蓿地>小麦地.300 cm以下含水量表现为小麦地>果园>苜蓿地;同时,不同利用条件下土壤水分剖面低湿层的位置深度也不相同,小麦地土壤水分低湿层深度较果园地和多年苜蓿地浅,土壤水分剖面形态与分布特征受利用模式影响显著.     

滴灌棉田不同盐分土壤水分变化规律及其利用效率研究

通过研究滴灌条件下不同盐分含量土壤含水率、日蒸散量和棉花干物质积累量的变化规律,以及棉花的干物质水分利用效率,探讨滴灌棉花的水盐互作效应。设置室内模拟试验,采用称质量法获得棉花蒸散量和干物质积累量,分析不同土壤盐分含量〔0(CK)、0.15%、0.25%、0.35%、0.45%、0.55%、0.65%〕条件下,棉花日蒸散量、干物质积累量以及土壤水分含量变化规律,计算棉花干物质水分利用效率。结果表明:随着棉花生育期的推进,不同盐分含量土壤的水分含量变化和日平均蒸散量均呈现先增大后减小的趋势,蕾铃期土壤日平均蒸散量达到最大;棉花的干物质积累量和生育期耗水量随土壤盐分含量的增大呈减小的趋势。棉花的干物质水分利用效率在T4处理达到最大,与CK、T1、T2、T5处理差异并不显著,说明土壤中适量的含盐量在一定程度上可以有效提高水分利用效率。     

不同质地土壤玉米出苗适宜墒情研究

通过室内盆栽试验,研究不同质地土壤、不同底墒(即初始含水量,下同)、不同底墒增加量下玉米的出苗率,分别就砂土、壤土和黏土三种质地给出了底墒、底墒增加量和出苗率之间的回归方程,并通过方程计算得出三种质地土壤在不同底墒的条件下,达到80%的出苗率所需的底墒增加量。     

Allelopathic potential of itchgrass (Rottboellia exaltata L. f.) powder incorporated into soil

Itchgrass ( Rottboellia exaltata L. f.) is a widespread weed in northern Thailand. The farmers in this area have been using itchgrass as a mulching material in order to control other weeds in vegetable fields. Laboratory experiments were undertaken to investigate the phytotoxic activity of itchgrass powder incorporated into soil in order to evaluate the allelopathic activity in the field. The phytotoxic activity on the growth of radish seedlings ( Raphanus sativa L. var. radicula ), used as a test plant, was more pronounced in the root than in the shoot growth. The phytotoxic activity was found to be similar for the soils incorporated with the shoot or the root powder of itchgrass. The growth of the radish seedlings grown in sea sand and watered with soil water obtained from the soil previously incorporated with itchgrass powder showed a similar inhibition to those planted in the treated soil. The phytotoxic activity on the growth of the radish seedlings in the soil incorporated with the powder decreased over time. It is suggested that itchgrass releases phytotoxic compound(s) into soil water and the concentration of the active compound(s) in the soil water decreases over time.     

Degradation of atrazine and isoproturon in surface and sub-surface soil materials undergoing different moisture and aeration conditions

The influence of different moisture and aeration conditions on the degradation of atrazine and isoproturon was investigated in environmental samples aseptically collected from surface and sub-surface zones of agricultural land. The materials were maintained at two moisture contents corresponding to just above field capacity or 90% of field capacity. Another two groups of samples were adjusted with water to above field capacity, and, at zero time, exposed to drying-rewetting cycles. Atrazine was more persistent (t(1/2) = 22-35 days) than isoproturon (t(1/2) = 5-17 days) in samples maintained at constant moisture conditions. The rate of degradation for both herbicides was higher in samples maintained at a moisture content of 90% of field capacity than in samples with higher moisture contents. The reduction in moisture content in samples undergoing desiccation from above field capacity to much lower than field capacity enhanced the degradation of isoproturon (t(1/2) = 9-12 days) but reduced the rate of atrazine degradation (t(1/2) = 23-35 days). This demonstrates the variability between different micro-organisms in their susceptibility to desiccation. Under anaerobic conditions generated in anaerobic jars, atrazine degraded much more rapidly than isoproturon in materials taken from three soil profiles (0-250 cm depth). It is suggested that some specific micro-organisms are able to survive and degrade herbicide under severe conditions of desiccation.     

不同保墒措施对陕北山地枣园土壤温湿度及生长的影响

针对陕北地区水资源日趋紧张,雨水、灌溉水利用效率低下的现状,在陕西省米脂县孟岔试验示范区通过定位观测实验,研究了秸秆覆盖(J1、J2、J3)、地膜覆盖(D)及施用保水剂(B16、B12、B8)不同处理对陕北山地枣园土壤温、湿度及生长的动态规.结果表明:覆盖有调节土壤温度的作用,秸秆覆盖与对照温差的幅度为-5.5℃～0....     

不同耕作方式下旱作玉米田土壤CO2排放量及其与土壤水热的关系

为探讨不同耕作方式对旱作玉米田土壤CO_2排放量的影响,设置深松耕(DT)、翻耕(PT)和免耕(NT)3个处理,分析3种耕作方式下土壤CO_2排放量的动态变化及其与土壤温度和土壤水分间的关系。结果显示:2010-2011年夏玉米生长季,3种耕作方式下土壤CO_2排放量均呈先增后降的变化趋势,表现为DTPTNT,且不同处理间差异显著(P0.05);耕作方式可显著影响夏玉米生育前期土壤温度,且土壤CO_2排放量对不同耕作方式下土壤温度的敏感性不同,土壤温度分别可以解释PT、DT和NT处理土壤CO_2排放量季节变化的50.72%~53.90%、48.10%~59.63%和13.31%~19.90%;土壤水分和温度共同分别可以解释旱作夏玉米田DT和PT处理下土壤CO_2排放量季节变化的57.61%~76.83%和56.62%~67.12%。土壤温度和水分是影响旱作农田DT和PT处理下土壤CO_2排放量的关键因素。     

黑河流域土壤含水量遥感反演及不同地类土壤水分效应分析

利用NASA提供的MOD IS数据产品和黑河流域的野外实测数据,在充分考虑研究区的下垫面特征、数据的时间特性和遥感反演土壤含水量的模型与算法的基础上,采用了热惯量法,计算了表观热惯量,并与实测数据进行回归分析建模,反演了整个黑河流域的土壤含水量。随后构建了三个区域土壤水分效应评价指标:土壤水分单元权重指数、区域土壤水分单元权重指数和土壤水分效应贡献度,结合黑河流域的土地利用状况,定量评价了不同土地利用类型的土壤水分效应。研究表明:利用MOD IS数据产品,反演参量获取简单,可降低反演土壤含水量的复杂性,有利于大、中尺度的实际应用;利用当地积累的季节标准日变化曲线将温差修正到最大值,使反演的表观热惯量更接近真实,可提高模型精度;用多个地面采样点的土壤含水量均值与一个像元对应建模,能改善因MOD IS数据空间分辨率低而存在大量混合像元致使反演精度降低的问题;在黑河流域,中覆盖度草地、有林地、高覆盖度草地、水田等用地类型的土壤水分效应最为明显,贡献最大。     

生物炭用量对模拟土柱氮素淋失和田间土壤水分参数的影响

利用土柱模拟试验和田间试验,把由果树废枝干制备的生物炭以0,20,40,60 t·hm^-2和80 t·hm^-2的用量施入土壤,以探明不同用量的生物炭对土壤硝铵态氮素淋失和土壤水分的影响。结果表明,施用生物炭可降低土壤NH₄⁺-N和NO₃^--N累积淋溶量,其中用量为80 t·hm^-2处理较对照分别降低了41%和18.6%（P＜0.05）;NO₃^--N淋溶主要集中在前三次,其淋溶量占总量的97.3%～98.8%,生物炭能增加NO₃^--N在土壤中的滞留时间,延缓淋失;在整个淋洗过程中,氮素主要以NO₃^--N的形式淋失,其累积淋溶量占NO₃^--N、NH₄⁺-N淋溶总量的97.3%～98.14%;施用生物炭种植春玉米后,土壤含水率和总孔隙度增加不显著。     

农田土壤墒情预报研究现状及不同预报方法的对比分析

土壤墒情预报是实施农田土壤水分有效调控的基础和前提。回顾总结了国内外土壤墒情预报研究发展的历史和现状,并对几种预报模型进行了重点对比分析。在此基础上,对现有研究中存在的问题及发展趋势和今后研究的重点进行了展望。     

天水旱作区土壤水分变化规律及其与冬小麦产量关系研究

运用天水农业气象基本观测站试验田土壤湿度资料(1980~2005年)及冬小麦产量资料,分析了该地0~100 cm土壤水分运行、变化规律及土壤水分变化对冬小麦产量的影响,分时段对其影响程度进行了定量评述。结果显示:土壤贮水量的年变化呈二次曲线,贮水量最低值出现在6月中旬;累计耗水量的年际变化呈logister曲线;贮水量与冬小麦产量相关最显著的时段在起身到孕穗阶段,4~5月0~100 cm土壤含水量每增加10 mm,产量增加180 kg/hm2。     

黑龙江省南部玉米田间土壤湿度长期时空变化特征及与产量的关系

应用黑龙江省南部1983—2009年15个农业气象观测站玉米生长季的土壤湿度资料,采用气候倾向率统计方法,利用GIS空间分析模块,分析了黑龙江省玉米生长季不同生育期土壤相对湿度的时空变化特征及与产量的关系。结果表明:近27年来黑龙江省南部玉米生长季不同生育期土壤相对湿度均呈下降趋势,与降水量呈极显著正相关;土壤相对湿度的空间分布存在明显差异,黑龙江省玉米产区松嫩平原中东大部及三江平原土壤相对湿度正常或偏高,松嫩平原西部土壤相对湿度偏低。土壤相对湿度年变化倾向率空间分布特征为松嫩平原中东大部、牡丹江大部呈下降趋势,仅少数地区呈增加趋势。松嫩平原西部偏旱地区的青冈、泰来玉米实际单产与生长季各生育期的土壤相对湿度均呈显著的正相关,土壤偏干或偏湿对玉米的产量形成均存在不利的影响。     

不同轮作方式和秸秆还田对麦田土壤CO2排放与水热碳氮状况和产量的影响

为探讨免耕条件下不同轮作方式秸秆还田对土壤CO₂排放的影响,本研究通过长期定位试验,采用GXH-3010E1型便携式红外线分析器测量土壤CO₂排放速率,对比研究冬小麦-夏闲、冬小麦-夏玉米和冬小麦-夏大豆在秸秆还田条件下土壤CO₂排放的动态变化及其与土壤温度、水分之间的回归关系,并分析比较土壤有机碳和碱解氮含量的变化。结果表明：三种轮作方式秸秆还田条件下冬小麦土壤CO₂排放具有明显的季节变化规律,平均CO₂排放通量表现为冬小麦-夏玉米全量还田>冬小麦-夏玉米不还田>冬小麦-夏大豆全量还田>冬小麦-夏大豆不还田>冬小麦-夏闲全量还田>冬小麦-夏闲不还田。所有处理土壤CO₂排 放通量与土壤含水率和土壤温度均呈极显著正相关,秸秆未还田处理地温与CO₂排放通量的模拟模型要好于秸秆还田处理。各处理冬小麦收获后土壤有机碳和碱解氮含量均比播种前高,FA、FN处理有机碳增加最大,SA、SN碱解氮增加最大。     

青海湖区天然草地和农田土壤水分变化特征

对环青海湖地区天然草地和农田土壤重量含水率年际、年代际和年内动态变化进行气候趋势系数法、气候倾向率法和变异系数法等分析,结果表明：环青海湖地区天然草地与农田同期土壤含水率年际变化趋势相反。1997年以来,0～50 cm土壤含水率年际变化农田呈显著或极显著增大趋势,增大幅度3.062%·10a^-1～10.848%·10a^-1;天然草地土壤含水率均呈减少趋势,减少速率中间土层快上下慢,但趋势不显著;20世纪末本世纪初和2004—2010年两个时段农田土壤含水率增大,天然草地土壤含水率减少趋势极显著体现在前一阶段,而近 年来增减趋势不显著,各层次土壤含水率平均值均大于前一阶段,但牧草生长高峰期夏季变小。农田和草地土壤含水率年内变化相同,春季土壤含水率相对较高,其后极显著下滑,农田由于耕作性失墒等影响,土壤含水率下滑幅度大于草地。     

延安碾庄沟流域梯田与坝地土壤水分对比分析

以延安碾庄沟小流域为研究对象,对该小流域内梯田地与坝地的土壤水分特征进行分析.结果表明,梯田地与坝地的土壤水分垂直分布有着相似的特点,梯田地和坝地土壤水分的垂直变化可以分为4个层次:土壤水分剧变层;土壤水分活跃层;土壤水分次活跃层;土壤水分相对稳定层.坝地的土壤含水量高于梯田地,且不同的作物类型可以引起土壤水分的变化,说明作物类型与土壤水分状况有一定的关系.     

黄土高原坡耕地不同耕作措施对土壤温度和水分的作用效应

利用定位实时监测和数学模拟的方法,在中国北方典型的土壤水蚀风蚀区神木县选择试点,对免耕、秸秆覆盖、地膜覆盖等6种不同耕作措施下不同耕作层的地温和土壤含水量进行了连续测定.结果表明:起垄地膜覆盖提高地温的效果最好,在特定时间不同深度或同一深度不同时间的土壤温度都以起垄地膜覆盖最高,其在观测期内的总积温比对照高10% ;而秸秆覆盖在各个测定深度上的地温都低于对照,其在观测期内的总积温比对照低2.3%.     

Impacts of soil moisture level and organic matter content on growth of two Juncus species and Poa pratensis grown under acid soil conditions

The abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) has increased in coastal grasslands in Norway over recent decades, and their spread has coincided with increased precipitation in the region. Especially in water‐saturated, peaty soils, it appears from field observations that productive grasses cannot compete effectively with such rapidly growing rush plants. In autumn–winters of 2012–2013 and 2013–2014, a four‐factor, randomised block greenhouse experiment was performed to investigate the effect of different soil moisture regimes and organic matter contents on competition between these rush species and smooth meadow‐grass (Poa pratensis). The rush species were grown in monoculture and in competition with the meadow‐grass, using the equivalent of full and half the recommended seed rate for the latter. After about three months, above‐ and below‐ground dry matter was measured. J. effusus had more vigorous growth, producing on average 23–40% greater biomass in both fractions than J. conglomeratus. The competitive ability of both rush species declined with decreasing soil moisture; at the lowest levels of soil moisture, growth reductions were up to 93% in J. conglomeratus and 74% in J. effusus. Increasing water level in peat–sand mixture decreased competivitiveness of meadow‐grass, while pure peat, when moist, completely impeded its below‐ground development. These results show that control of rush plants through management may only be achieved if basic soil limitations have been resolved.