Populations of methanogenic bacteria in paddy field soil under double cropping conditions (rice-wheat)

The methanogenic populations able to use H₂–CO₂, methanol, and acetate were investigated in paddy field soil in situ under double cropping conditions [rice (Oryza sativa L.) as a summer crop under flooded conditions and wheat (Triticum aestivum L.) as an upland winter crop] over 2 years approximately bimonthly by the most probable number method. Three fields, one without fertilizer, one treated with inorganic fertilizer (mixed fertilizer including urea, ammonium phosphate, and potassium sulfate), and one treated with wheat straw plus inorganic fertilizer, were examined. The population of H₂–CO₂, methanol, and acetate utilizers in the paddy field soil at a depth of 1–6 cm was 10³–10⁴, 10⁴–10⁵, and 10⁴–10⁵ g^-1 dry soil, respectively. These values were almost constant during the 2 years irrespective of moisture regime (flooded or nonflooded), crop (rice or wheat), fertilizer treatment, and soil depth (0–1, 1–10, and 10–20 cm).     

武夷山黄山松群落物种多样性与种群空问格局的研究

对武夷山黄山松群落物种多样性和种群空间格局的研究结果表明 ,低海拔地区由于受人为干扰影响较大而物种多样性与种群空间分布格局未表现出明显规律性 ,高海拔地区群落物种多样性指数、丰富度和均匀度均有不同程度下降 ,黄山松种群空间格局均呈集群分布 ,且随海拔高度升高而黄山松种群生长受到一定抑制     

磷肥在潮褐土中动态转化及其影响因素的研究

利用培养及微区试验研究P肥施用潮褐土后的动态转化及其影响因素表明,施肥初期土壤中除难溶性Ca10-P外,各无机P组分均有不同程度地提高,随着时间的延续各组分间的相互转化呈一定规律。种植作物直接影响P肥动态转化的方向。     

Fungal abundance and distribution as influenced by clearing and land use in a vertic soil of Argentina

The influence of native vegetation clearing and different further soil managements on fungal propagule population diversity was studied in the present work. In each of the 3 years (1998, 1999, and 2000), soil samples were collected at the depth of 0–7.5 cm from sites under native vegetation (V0); naturalized prairie, cleared in 1982 (P16); conventional tillage, cleared in 1972 (T26); and direct drilling, cleared in 1958 (D40). Fungal population size and relative abundance of fungal genera were studied by plate counts and further identification of isolates on potato dextrose agar. The undisturbed site and the other sites with increasing time elapsed since native vegetation clearing and different management history showed a distinctive distribution of fungal genera. There were significant differences (p<0.05) among the sites in the abundance of fungal genera analyzed in all the 3 years. Principal component analysis based on relative fungal genus abundance differentiated the sites with 75% variance explained by the first and second components. Diversity and abundance of isolated fungal genera were increased as density of Penicillium spp. decreased, suggesting a competitive effect of this fungal genus. The largest diversity was found in the site under no-till management. The different distribution and relative abundance of the fungal genera studied seemed to be influenced strongly by the management and the presence of surface residue in the no-tilled site.     

Effect of selection under cultivation on morphological traits and yield of Ladino white clover landraces

One reason for the relatively low genetic advance realized in forage legumes may be the possible selection, under the severe intraspecific competition occurring naturally during cultivation, of a few high-yielding genotypes that would be of similar value in a broadly-based landrace or old cultivar and a narrowly-based, modern variety. The effect of selection under cultivation was assessed in two Ladino white clover farm landraces. Genotypes collected from each farm after a three-year crop cycle (survivor populations), or obtained from the seed used to establish each meadow (original populations), were multiplied clonally and evaluated in isolation and monoculture conditions for one year. The occurrence of directional selection was observed only in the landrace featured by greater intra-population variation in favour of genotypes with longer petioles (+11%), larger leaf size (+13%), less stolons (–14%) and lower production of heads (–16%). Selection for the first two traits would imply an increase of competitive ability, whilst that for the fourth trait appeared mainly as a correlated response. The trade-off between leaf gigantism and head production could act as a buffering mechanism against rapid change in genotype frequencies following random mating. A slight trend towards directional selection for higher yield (+6%) in the same landrace was not statistically significant. No disruptive or stabilizing selection was observed for any trait in either landrace.     

黄土不同湿度状态下动、静变形特性关系的探讨

从实用角度出发,对西安、兰州和太原3个典型黄土地区的原状黄土在不同湿度状态下所取得的动三轴振陷资料以及常规侧限压缩、湿陷试验的资料进行了统计分析,给出了黄土动、静力变形特性参数之间的相关关系,探讨了用常规的静力特性参数评估动力特性的可能性。     

土壤脲酶活性对稻田田面水氮素转化的影响

以浙江省嘉兴市双桥农场的青紫泥水稻田为研究对象，采用大田小区的研究方法，对不同供肥水平下水稻追施尿素后田面水中氮素主要形态的浓度变化进行了动态监测，并从土壤酶学的角度探讨了其氮素转化的深层机制。研究发现．土壤脲酶在稻田田面水氮素转化中起着关键作用，施尿素后3天内田面水中总氮、氨氮的浓度及氨氮／总氮比值达到峰值．且第二次追肥较第一次追肥后峰值低．随后急剧下降。5天后维持在较低的水平，说明施肥后前5天是氮素大量且快速流失的关键时期，其流失以氨氮为主；土壤脲酶活性在第一次追肥后3～5天也出现了明显的增长趋势，第二次追肥后脲酶活性增强幅度远小于第一次追肥．N270处理初期甚至出现了负增长；线性相关分析表明田面水中氨氮／总氮的比值与土壤脲酶活性之间存在显著的正相关关系．说明土壤脲酶在水土界面氮素迁移转化过程中发挥着关键作用，因此，抑制脲酶活性可能是降低稻田氮素流失的主要途径之一。     

农业用水及其生态社会效应的研究

研究建立了农业用水水资源城市人口非线性动力学模型,并探讨了农业用水的生态效应和有关稳定性问题。研究结果表明水资源城市人口 农业用水三者之间关系是非常复杂的非线性关系,盲目、超规模的农业用水将使城市城镇化抑或城镇农村化;稳定的城市人口与农作物生物总量成线性关系,低灌溉效率下农业用水的增加非但不能使农业增产,还将导致农作物生物总量的减少和城市规模的减小;为达到增加农业用水时既可使农业增产,又支持城市扩大的目的,惟一途径是提高农业灌溉效率     

考虑动态吸收率的玻璃温室覆盖层温度预测模型

覆盖层温度是影响温室热环境的重要因素之一。为了实现温室覆盖层温度预测,该研究以玻璃温室覆盖层为研究对象,综合考虑太阳辐射吸收、对流换热等能量传递形式,建立温室覆盖层温度预测模型。为提高模型精度,该研究进一步提出温室覆盖层动态吸收率计算方法,并使用该方法将覆盖层太阳辐射吸收率分为直射辐射吸收率、散射辐射吸收率与地表反射辐射吸收率分别计算,进而精确计算覆盖层吸收太阳辐射。为验证模型正确性及其精度,在山东省泰安市选择3个时段开展相关验证试验并得出如下结论,温室覆盖层温度预测值与测量值变化趋势较为一致,模型计算值与覆盖层温度测量值的决定系数R^2最小为0.92,均方根误差RMSE最大为2.05℃,通过与相关模型对比得出该研究提出的模型能够精确预测覆盖层温度。     

A nitrogen dynamic hydroponic culture on performance and quality of water spinach (Ipomoea aquatica)

Abstract

In view of the unreasonable application of chemical fertilizers in agriculture and the groundwater pollution caused by nitrogen (N) leaching, a nitrogen dynamic hydroponic culture was used to simulate the dynamics variation of ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) in the leaching loss soil. Solutions with different ratio of NO₃-N and NH₄-N (100:0, 70:30, 50:50, 30:70 and 0:100) were prepared as well as the same solutions that not containing NO₃-N .Water spinach was chosen to culture in the two solutions that differ from NO₃-N every two (E2) or five days (E5) to observe the growth, quality and nutrient solution uptake. In terms of the growth, uptake of N source, N use efficiency and the chemical indicators, plants grown in the balanced solution all showed the best results. The nitrogen dynamic hydroponic culture showed some differences between E2 and E5 in some aspects. Under the same N source level, plants in E2 showed a better growth and higher NO₃-N uptake than E5. On the other hand, the uptake of NH₄-N seemed to be affected significantly by the interchanged frequency, which showed the same variations of glutamine synthetase activity. The activity of nitrate reductase and glutamine synthetase showed the coexist of NO₃-N and NH₄-N could play synergistic effect. It is not recommended to supplement NO₃-N frequently in the case of N leaching loss, which has little impact on the growth and may lead to the hard taste and groundwater pollution.