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 thenylchlor concentration in soil water and its phytotoxic activity in soil

The phytotoxic activity of soil-applied thenylchlor (2-chloro- N -[3-methoxy-2-thenyl]-2',6'-dimethylacetanilide) on the growth of rice seedlings and its behavior in two different types of soil, Ryugasaki soil and Tsukuba soil, after application was investigated with emphasis on the concentration in the soil water. The greatest inhibition of thenylchlor on the growth of rice seedlings was found immediately after application to both the Ryugasaki and Tsukuba soils. The phytotoxic activity decreased with time in both soils. However, the rate of decrease in phytotoxic activity was slower in the Ryugasaki soil than in the Tsukuba soil. The concentration of thenylchlor in soil water, the amount adsorbed on the soil solid, and the amount in the total soil reduced with time after application to both soils. The amount of thenylchlor adsorbed on the soil solid phase was more persistent than that in the soil water in both soils and the concentration in the soil water was higher in the Ryugasaki soil than in the Tsukuba soil at any given time. The residual phytotoxic activity of thenylchlor on the growth of the rice seedlings in the soil was highly correlated with its concentration in the soil water but not with the amount in the total soil. These results suggested that the residual phytotoxic activity of thenylchlor in the soil is determined by its concentration in the soil water after application.     

Phytotoxic activity of clomeprop in soil and concentration of its hydrolysed metabolite DMPA in soil water

The relationship between the fate of clomeprop in soil and its phytotoxic activity on the growth of radish (Raphanus sativus) seedlings was investigated in the laboratory. The phytotoxic activity of clomeprop in sea sand was much higher than in non-autoclaved soil, and the phytotoxic activity in non-autoclaved soil was higher than in autoclaved soil. The phytotoxic activity of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolysed metabolite of clomeprop, was higher than that of the latter under both soil conditions. Clomeprop was adsorbed on soil to a greater extent than DMPA. The concentration of clomeprop in soil water of non-autoclaved soil decreased with increase of the DMPA concentration in the soil water in a time-dependent manner. It is suggested that the phytotoxic activity of clomeprop applied to soil is induced mostly by the DMPA concentration in soil water after hydrolytic degradation by soil microbes. © 1999 Society of Chemical Industry     

Residual activity of clomeprop and its downward movement under laboratory conditions

The relationship between the behavior of clomeprop ([ RS ]-2-[2,4-dichloro- m -tolyloxy]propionanilide) and its residual phytotoxic activity in the soil was investigated in the laboratory with special emphasis on the concentration in the soil water. The phytotoxic activity of clomeprop on radish seedlings ( Raphanus sativus L. var. radicula cv. Akamaruhatsukadaikon), as the test plant, became greater with time after application but the inhibition was different between the two soils, which had different properties. The amount of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolyzed and active metabolite of clomeprop, in the soil water and total soil increased with time, corresponding to the decrease in the amount of clomeprop under non-water leakage conditions. The residual phytotoxic activity of clomeprop in the soil was more highly correlated with the concentration of DMPA in the soil water than with the amount of DMPA in the total soil. In addition, a leaching column test was conducted with clomeprop and DMPA. The DMPA easily moved downward and the concentration in the soil water in the upper layer decreased with time after application. It is supposed that the downward movement of DMPA was one of the factors influencing the lasting effect of clomeprop in the field.     

Behavior of pyriftalid in soil and its phytotoxic activity on Echinochloa oryzoides seedlings emerging from various soil depths

The phytotoxic activity of pyriftalid ([RS]‐7‐[4,6‐dimethoxypyrimidin‐2‐ylthio]‐3‐methyl‐2‐benzofuran‐1[3H]‐one) on barnyard grass (Echinochloa oryzoides) seedlings emerging from various depths in the soil was investigated in relation to its behavior in the soil. The growth of the barnyard grass seedlings in the soil mixed with pyriftalid was inhibited, depending on the concentration of the herbicide in the soil water but not on the amount in the total soil. A topmost pyriftalid‐treated layer was formed by applying the herbicide to the soil surface under water‐leakage conditions. The concentration of pyriftalid in the soil water and the amount that was adsorbed on the soil solid decreased with time, but the decrease was more marked in the pyriftalid concentration in the soil water than in the amount that was adsorbed on the soil solid. The emergence time of barnyard grass in the soil was faster in the seeds that were located in the shallower soil layer, compared to the deeper soil layer. The growth inhibition of the barnyard grass seedlings emerging from the shallower soil layer was greater than that of the barnyard grass seedlings emerging from the deeper soil layer after the soil surface application of pyriftalid. It is suggested that the emergence timing from the different soil depths is an important factor affecting the herbicidal activity of pyriftalid when it is applied to the soil surface under paddy field conditions.     

Factors affecting phytotoxic activity of allelochemicals in soil

Allelopathy is the inhibitory or stimulatory effect of a plant (donor) on other plants (receivers) through the chemicals released from the donor plant to the environment, mostly into the soil. These chemicals may reach the receiver plants in various ways, including leaching from plant foliage, exudation from the roots, and decomposition of dead residue of the donor plants. However, allelopathy in soil is a complicated phenomenon that is affected by soil condition, growth condition of the donor and receiver plants and climatic condition. Allelochemicals in soil are adsorbed on soil solids, and metabolized by chemical and biological reactions during the movement in soil. This behavior is affected by various soil factors, such as soil texture, organic and inorganic matter, moisture and organisms, which affect the phytotoxic activity in soil. If an allelochemical can directly affect the growth of receiver plants in soil, then the allelochemical might be present in the soil water so that it is directly available for absorption by the plant. Thus, it is suggested the concentration of an allelochemical in soil water is a dominant factor directly determining the phytotoxic activity in soil, and the concentration is controlled by soil factors that affect the behavior of adsorption, desorption and degradation in soil.     

Allelopathic activity of Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray] in soil under natural field conditions and different moisture conditions

The allelopathic activity of Mexican sunflower [ Tithonia diversifolia (Hemsl.) A. Gray] in soil under natural field conditions and the effect of water stress on the growth and allelopathic activity of this plant were investigated. Seed germination, shoot growth and root growth of tested plant species in soil collected from a field where Mexican sunflower had been grown for 5 years were less than those in soil from an area without the plant. Growth of young leaves, mature leaves, senescent leaves, stem and roots of Mexican sunflower was reduced with decrease in soil moisture level. The allelopathic activity of water extracts (per dry weight of starting material) from each part of the plants grown at low soil moisture levels was greater than that of the water extracts from the same part of the plants grown at high soil moisture levels. The allelopathic activity was found in the soil from the pots previously planted with Mexican sunflower to a similar extent (per plant) at different soil moisture levels. These results suggested that, in the field, under water stress conditions, the growth of Mexican sunflower was reduced but the plants contained a greater amount of allelopathic substance(s) per dry weight than in the absence of water stress. It was considered that allelopathic activity of Mexican sunflower in soil was maintained to a similar extent under various soil moisture conditions in natural fields.     

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.     

长安少陵塬近5年麦地土壤水分变化与土壤水资源研究

通过对2003.3-2007.4西安市南郊长安区四府村麦地0-6 m土壤含水量的测定,分析了长安区四府村麦地土壤水分变化特点及与降水量之间的关系,同时对土壤水资源量对冬小麦生长的影响进行了研究。结果表明:西安市长安区大贫水年翌年春季冬小麦地0-6m土壤水分主要为中效水,土壤供水明显不足,平水年及丰水年翌年春季主要为极易效水和渗透重力水,水分供应充足。大贫水年的翌年春季冬小麦生长期内土壤水分不能正常下渗补给地下水,形成大气-土壤水分循环模式;平水年及丰水年的翌年春季冬小麦地入渗降水能正常补给地下水,形成大气-土壤-地下水循环模式。平水年和丰水年的翌年春季冬小麦地0-1m根系层水资源量变化主要受地表蒸发和作物耗水的影响,1-2m、2-4m层位水资源量变化主要受前一年降水量的影响,4-6 m层位水资源量主要与前一年土壤原有水资源量有关。经历连续两个贫水年之后的2003年春季冬小麦生长受到水分的严重限制,若要达到正常产量,春季需灌溉水量约300 mm。长安区近13年来干旱年和丰水年交替变化,总体来说降水对地下水的补给状况基本正常,通过采取有效的集水保墒措施,干旱年冬小麦也会获得较高产量。     

晋北黄土丘陵区不同林草措施的蓄水保土和土壤水分效应研究

以设在山西省阳高县的大型径流观测场为依托,以2005-2009年的野外实测数据为依据,研究了晋北黄土丘陵区人工植被与鱼鳞坑配合的蓄水保土及土壤水分效应,并与荒坡、苜蓿地进行了对比。结果表明:在观测的5年内,柠条、沙棘、油松的蓄水保土能力随种植年限延长无明显增加趋势,但鱼鳞坑的蓄水能力和保土能力分别高达84.7%～96.0%和95.2%～99.7%;荒坡和苜蓿(Medicago sativa)第一年和第二年的蓄水保土能力较差,第三年和第四年随植被盖度增加能力急剧增强,第四年蓄水能力分别达82.8%和91.2%,保土能力达97.0%和98.0%;土壤水份分析结果表明:不同小区4～9月土壤水分变异系数为7.0%～19.1%,油松区变异系数最大,其次为沙棘、苜蓿和柠条区,荒坡区和裸坡区变异较小,不同小区土壤水分亏缺率为23.98%～52.66%,亏缺顺序为柠条区>苜蓿区>油松区>沙棘区>荒坡区>裸坡区;林草植被有效地减少了水土流失,亦增加了土壤水分的变异及亏缺程度,应注意林草植被的合理选择和配置。     

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。     

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。     

滴灌棉田土壤水分测点最优布设研究

为寻求滴灌棉田土壤剖面水分测点的最优布设方案,2009年在棉花生育期内采用取土烘干法对膜下滴灌棉田不同位置、不同深度土壤质量含水率进行连续监测。利用监测数据分析了膜下滴灌棉田土壤剖面内不同观测点垂直方向上各层次土壤含水率之间的相关关系,并利用R型谱系聚类法对剖面内各观测点8个土壤层次的土壤含水率变量进行分类,筛选出适合膜下滴灌棉田墒情观测的土壤水分测点布设方案。最后利用2007年试验数据对提出的水分测点布设方案进行验证,结果表明,水平方向上距滴灌带0 cm、32.5 cm和50 cm处3个观测点,各观测点垂直方向上0~10 cm、20~30 cm、40~50 cm和60~80 cm深处4个层次12个测点的土壤含水率能较好地反映整个剖面的土壤水分信息,可作为膜下滴灌棉田土壤水分探头的布设点。     

不同秸秆还田模式冬麦田土壤水分特征比较

在陕西杨凌区布设田间试验,在冬小麦发育期间观测5种不同玉米秸秆覆盖与耕作方式相结合模式的土壤水分特征。结果表明5种覆盖耕作模式的土壤水分垂直变异系数大小排列为传统翻耕(0.1376)>浅旋覆盖(0.1360)>传统覆盖(0.1309)>深翻覆盖(0.1265)>免耕留茬(0.1167);免耕覆盖土壤水分贮存量(342 mm)最高,以浅旋覆盖(289 mm)、传统翻耕(287 mm)土壤水分贮存量相对为低,深翻覆盖(307 mm)、传统覆盖(300 mm)土壤水分贮存量相对居中。     

不同土壤水分条件下夏玉米蒸发蒸腾特征研究

以郑单958为材料,在防雨测坑模拟试验条件下,研究了不同土壤水分条件下夏玉米蒸发蒸腾特性.试验结果表明:夏玉米在不同土壤水分条件下,土壤蒸发与土壤水分含量有关,干旱条件下土壤蒸发日变化低于适宜土壤水分条件,充足水分条件下土壤蒸发量高于适宜水分处理.蒸腾速率日变化则是适宜水分75%最高,单叶瞬时蒸鹰速率比干旱处理和充足水分处理分别高11.8%、4.3%.茎流量日变化蜂值随水分含量的增高而增高,其峰值比蒸腾峰值要延迟约2 h.     

孙家岔流域坡面不同土地利用的土壤水分变化分析

以甘肃省兰州市孙家岔流域为研究对象,采用1982—1983年和2011年土壤水分实测资料,分析该流域坡面防护区不同土地利用土壤水分的年内、年际变化特征。结果表明,在黄土丘陵区小流域内,农坡和荒坡土壤水分的年内动态变化具有相同的规律,但农坡年内平均含水量要高于荒地。流域内降雨量的多少以及时空分配是土壤水分变化趋势的主要影响因子。土壤水分的变异程度随降雨量和土层深度的增加而减小,土壤深度在1.20~1.40 m内含水量受季节气候动态变化影响显著,土壤深度超过1.60 m内含水量在相同年度具有一定的时间稳定性。土质较好的荒地,选择适宜的农作物(如洋芋),可提高缓坡区(5°~15°)降水资源的有效利用率。     

华北平原不同灌水条件下两冬麦品种土壤水分动态与产量差异

采用LSD法对华北平原不同灌水条件下(设4个水分处理:0水、1水、2水和3水)两品种(科麦一号和石家庄8号)冬小麦田土壤水分动态变化进行了观测,并对产量、产量构成要素及其生态指标进行了定量分析,以探讨品种间的差异.研究发现:所有灌水处理0～140 cm土层土壤水分变化较大,而0水处理的0～40 cm和80～140 cm土层含水量变化比较活跃,其幅度低于灌水处理.品种间相同水分处理的土壤含水量变化趋势一致,除1水处理科麦一号变幅较大外,其他3个处理均以石家庄8号变幅较大.科麦一号与石家庄8号均以3水处理的产量最高,比0水处理分别增产44.44%、42.88%,但由于该处理灌水充足,小麦相对晚熟耗水量大,致使收获前土壤含水率急剧下降.在各水分处理中,产量构成要素穗数皆以3水最高;穗粒重皆以1水最高(两个品种穗粒重1水与2水差异不显著);千粒重皆以0水最高.穗粒数以1水最高.收获指数皆以0水最高.科麦一号对水分较为敏感,但耗水量明显小于石家庄8号.要达到经济高产的目标,科麦一号灌2水较为合适,石家庄8号需灌3水.