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91.
Quanzhen Wang Yuyan LiuJian Cui Jinhong DuGuo Chen Haitao Liu 《Industrial Crops and Products》2011,34(3):1429-1438
The present study evaluated the herbicidal potential of extracts from chicory (Cichorium intybus L.) roots on the germination of Echinochloa crusgalli L. Beauv and Amaranthus retroflexus L. Eight ultrasonic assisted-extraction (UAE) conditions were optimized, using an orthogonal matrix design. The extract concentrations that would yield the largest allelopathic effects on the plant species were estimated by a modeling analysis. Our results showed that an alcohol solvent extract of chicory root had significant herbicidal activity which depended on the extract concentrations and the target species. The half-inhibitory concentrations of crude extract of chicory root ranged from 0.5 g l−1 to 40.5 g l−1. At a frequency of 40 kHz, the optimum UAE conditions to produce an extract for use as herbicide against E. crusgalli L. included an ethanol content (Ec) of 50% (v/v), a solvent-to-solid ratio (SR) of 16:1, an ultrasound temperature (UT) of 35 °C, an impregnation time (Imt) of 24 h with two rounds of impregnation (Imr), a sonication period (St) of 120 min with two rounds of sonication (Sr) and an ultrasound input power (P) of 200 W. The optimum conditions to produce an extract for use against A. retroflexus L. included an Ec of 100% (v/v), a SR of 16:1, an UT of 20 °C, an Imt of 48 h with two Imr, a St of 30 min with one Sr and a P of 400 W. The extract had the largest inhibitory effects on the germination index and root growth of both E. crusgalli L. and A. retroflexus L. at concentrations ranging from 30.8 to 33.7 g l−1. At a concentration of 4.2 g l−1, the extract significantly enhanced the shoot growth of A. retroflexus L. Overall, chicory root extract has potential for use as a main ingredient in natural herbicides or for development as a novel plant-derived herbicide. 相似文献
92.
Models can play an important role in agricultural planning and management. Thermal time accumulation is a common way of describing phenological development in crop models, but the sensitivity of this concept to water stress is rarely quantified. The effect of pre-anthesis droughts on the timing of anthesis and physiological maturity was assessed for quinoa (Chenopodium quinoa Willd.) var. ‘Santa Maria’, with the help of two field experiments (2005–2006 and 2006–2007) in the central Bolivian Altiplano. Various treatments with different sowing dates and irrigation applications were considered. To evaluate the effect of drought stress on crop development, drought stress during the first 60 days after sowing was assessed with three different stress indicators: the number of days that the soil water content of the root zone was above a threshold, the average relative transpiration, and the sum of daily actual transpiration, standardized for reference evapotranspiration (∑(Ta/ET0)). The best indicator to quantify the effect of pre-anthesis drought stress on phenological development was ∑(Ta/ET0) cumulated until 60 days after sowing. This indicator showed a significant logarithmic relation with the time to anthesis and time to physiological maturity. Correlations of the drought stress indicator with thermal time accumulation were better than with calendar time accumulation. Due to an effect of post-anthesis droughts, the correlations of the drought stress indicator with the time to anthesis were stronger than with the time to physiological maturity. It was also demonstrated that deficit irrigation can contribute to a better agricultural planning due to a better control of the phenological development of quinoa. The proposed relations can be used for modeling phenological development of quinoa in drought prone regions and for efficient deficit irrigation planning. 相似文献
93.
94.
Rice–Wheat rotation system utilizes surface, ground and rain water resources conjunctively. Recent studies have shown increasing
contribution of groundwater for crop irrigation. As the system utilizes water pumped from the underlying aquifer and partly
seeps back, a cycle of recharge and discharge continues. Sustainability of groundwater system for the on-going drought in
the country depends mainly on the recharge of the aquifer. The reported study was, therefore, carried out to measure and assess
the recharge contribution of a distributary of canal in Punjab, Pakistan. Assessment of recharge through distributary was
carried out using a groundwater flow “MODFLOW” model, which utilized the observed watertable, climatic, crop and soil for
a period of about 1 year in addition to hydraulic conductivity, evapotranspiration and aquifer characteristics data. The requisite
primary data for “MODFLOW” were collected from field and secondary data from public sector organizations dealing with water.
Model calibration involved changing input parameters within reasonable limits until acceptable matches were obtained between
the observed and simulated water levels for all observed hydrographs. The external inputs such as, recharge through irrigation,
precipitation, stresses due to evaporation, lateral flow and stream were simulated to calculate the monthly water budget of
aquifer. As concluded, recharge contribution was 16.5% of the inflow rate of the distributary. Using predicted results of
the model a relationship between recharge (R) and discharge (Q) was also developed. Although, the presented results of recharge
contribution were limited to one distributary of canal irrigation system, yet the developed methodology can be extended to
the other canal systems of the Indus Basin. 相似文献
95.
Jeffrey W. White Gerrit Hoogenboom Bruce A. KimballGerard W. Wall 《Field Crops Research》2011,124(3):357-368
Ecophysiological models are widely used to forecast potential impacts of climate change on future agricultural productivity and to examine options for adaptation by local stakeholders and policy makers. However, protocols followed in such assessments vary to such an extent that they constrain cross-study syntheses and increase the potential for bias in projected impacts. We reviewed 221 peer-reviewed papers that used crop simulation models to examine diverse aspects of how climate change might affect agricultural systems. Six subject areas were examined: target crops and regions; the crop model(s) used and their characteristics; sources and application of data on [CO2] and climate; impact parameters evaluated; assessment of variability or risk; and adaptation strategies. Wheat, maize, soybean and rice were considered in approximately 170 papers. The USA (55 papers) and Europe (64 papers) were the dominant regions studied. The most frequent approach used to simulate response to CO2 involved adjusting daily radiation use efficiency (RUE) and transpiration, precluding consideration of the interacting effects of CO2, stomatal conductance and canopy temperature, which are expected to exacerbate effects of global warming. The assumed baseline [CO2] typically corresponded to conditions 10-30 years earlier than the date the paper was accepted, exaggerating the relative impacts of increased [CO2]. Due in part to the diverse scenarios for increases in greenhouse gas emissions, assumed future [CO2] also varied greatly, further complicating comparisons among studies. Papers considering adaptation predominantly examined changes in planting dates and cultivars; only 20 papers tested different tillage practices or crop rotations. Risk was quantified in over half the papers, mainly in relation to variability in yield or effects of water deficits, but the limited consideration of other factors affecting risk beside climate change per se suggests that impacts of climate change were overestimated relative to background variability. A coordinated crop, climate and soil data resource would allow researchers to focus on underlying science. More extensive model intercomparison, facilitated by modular software, should strengthen the biological realism of predictions and clarify the limits of our ability to forecast agricultural impacts of climate change on crop production and associated food security as well as to evaluate potential for adaptation. 相似文献
96.
97.
98.
采用反距离加权法、径向基函数插值法、克里格法、回归模型法,以云南省昭阳区农田土壤养分采样数据为对象,对全区土壤交换性镁含量进行模拟。结果表明,由于中量元素分布的复杂性,不同模拟方法得到的预测精度不同;反距离加权法强调空间距离权重的影响,未能较好的反应分布规律;径向基函数插值法由于采样点数据具有很大的不确定性,故效果也不理想;克里格法误差最小,精度最高;回归模型法误差较大,但最能反应农田土壤交换性镁分布的地域特征和立体变化特征。 相似文献
99.
Lefebvre HP Jeunesse E Laroute V Toutain PL 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2006,20(3):499-507
Ramipril, an angiotensin-converting enzyme (ACE) inhibitor for use in dogs, is converted in vivo to its active form, ramiprilat, which is eliminated in the bile and urine in the dog. The objective of this study was to assess the effect of renal impairment on the pharmacokinetics (PKs) and pharmacodynamics (PDs) of ramipril and ramiprilat. Ten adult Beagle dogs were used. PK/PD studies were performed before and after the induction of subclinical renal impairment. Ramiprilat was given at 0.25 mg/kg by a single IV bolus. After a 2-week washout period, ramipril was administered PO at 0.25 mg/kg once daily for 8 days. Ramipril and ramiprilat PKs were studied by using a physiologically based model. The relationship between free plasma ramiprilat concentration and ACE activity was described by using the fractional Hill model. Glomerular filtration rate was decreased by 58%. No biologically relevant changes in usual plasma variables were observed between the 1st and the 8th day of oral treatment with ramipril under either condition. After an IV bolus of ramiprilat, the only changes in renal-impaired dogs were a 14 and 49% decrease in clearance of the free fraction of ramiprilat (P < .01) and free plasma concentration required to produce 50% of the maximal effect (P < .05), respectively. After repeated PO administration of ramipril, there were no alterations in any of the PK and PD parameters in healthy or renal-impaired dogs. No adjustment of the recommended PO dosage of ramipril is needed in dogs with moderate renal impairment. 相似文献
100.
本文在对丝绸服装面料和款式等特征阐述的基础上,通过其平面与立体结构设计以及制作工艺中的准备、裁剪、缝制、整理、装饰等方面对丝绸服装造型设计中的工艺技法进行了浅析,以期对丝绸服装设计提供相关工艺理论参考。 相似文献