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1.
The antifungal activity of onion (Allium cepa L.) on two important dermatophytes, Trichophyton rubrum and Trichophyton mentagrophytes, with special reference to morphological aspects was studied. Growth of both fungi was found to be strongly inhibited by aqueous onion extract (AOE) as a dose-dependent manner. The extract showed fungicidal effect for both fungi at concentrations >3.12% (v/v). The fungus T. mentagrophytes was more affected by the onion as compared to T. rubrum at all concentrations used. Morphological effects of onion exposure were examined in correlation with fungal growth. Corresponding to the growth inhibition, light and electron microscopy observations revealed morphological anomalies in hyphal compartments. The results demonstrated that AOE targets the cell membrane of the fungi as breaking down of both inner and outer membranes with consequent extrution of materials into the surrounding medium. Cytoplasmic membranes and other membranous structures of organelles, such as nuclei and mitochondria, were also disrupted. In correlation to the fungal growth, morphological alterations occurred to a less content for T. rubrum compared with T. mentagrophytes. The hyphae of T. rubrum were found to be mainly affected by converting to resistant forms, i.e., chlamidospores as a consequence of phenotype switching response to AOE. Plasmolysis accompanied by an almost complete depletion and disorganization of cytoplasmic structures were found to be the final event which led to cell death. Ultrastructural evidences obtained from this study strongly support that morphological changes of T. rubrum and T. mentagrophytes caused by AOE are associated with its fungistatic and fungicidal activities. With respect to the morphological results and the preliminary data on fungal biochemistry, a mechanism of action by interacting of AOE with thiol (-SH) groups present in essential compartments of the fungal cells was postulated.  相似文献   
2.
Drought and salinity reduce crop productivity especially in arid and semi‐arid regions, and finding a crop which produces yield under these adverse conditions is therefore very important. Quinoa (Chenopodium quinoa Willd.) is such a crop. Hence, a study was conducted in field lysimeters to investigate the effect of salinity and soil–drying on radiation use efficiency, yield and water productivity of quinoa. Quinoa was exposed to five salinity levels (0, 10, 20, 30 and 40 dS m?1) of irrigation water from flower initiation onwards. During the seed‐filling phase the five salinity levels were divided between two levels of irrigation, either full irrigation (FI; 95 % of field capacity) or non‐irrigated progressive drought (PD). The intercepted photosynthetically active radiation was hardly affected by salinity (8 % decrease at 40 dS m?1) and did not differ significantly between FI and PD. Radiation use efficiency of dry matter was similar between salinity levels and between FI and PD. In line with this, no negative effect of severe salinity and soil–drying on total dry matter could be detected. Salinity levels between 20 and 40 dS m?1 significantly reduced the seed yield by ca. 33 % compared with 0 dS m?1 treatment owing to a 15–30 % reduction in seed number per m2, whereas the seed yield of PD was 8 % less than FI. Consequently, nitrogen harvested in seed was decreased by salinity although the total N‐uptake was increased. Both salinity and drought increased the water productivity of dry matter. Increasing salinity from 20 to 40 dS m?1 did not further decrease the seed number per m2 and seed yield, which shows that quinoa (cv. Titicaca) acclimated to saline conditions when exposed to salinity levels between 20 and 40 dS m?1.  相似文献   
3.
Sandy soils, with low productivity, could be improved by compost application to sustain crop production. This study aimed to examine the effect of three compost types (vegetable, fruit and yard waste compost, garden waste compost, and spent mushroom compost) on basic properties of a loamy sand and greenhouse tomato productivity. Disturbed and intact soil samples were taken from a decade-long compost field experiment on loamy sand with three compost types at application rate of 30 m3 ha?1 yr?1 (7.5 ton ha?1 yr?1). The soils were characterized for chemical and physical properties. Tomato was planted in a greenhouse using soil samples from the field and vegetative and yield parameters (plant height, stem diameter, leaf number, and fruit yield), water productivity, and harvest index were evaluated. All compost types significantly increased soil total carbon, total nitrogen, pH, electrical conductivity and significantly decreased bulk density, with no effect on plant available water compared to the control. Fresh and dry fruit weights were significantly increased after compost addition. Plant height, leaf number, stem diameter, and total biomass did not significantly improve after compost addition. Spent mushroom compost had greater effect in improving tomato productivity. A decade-long application of composts on loamy sand improved basic chemical and physical properties which were reflected in increased fruit yield in tomato. Since no negative effect of compost was observed, we suggest that sandy soils may serve as a safe end use option for these composts and potentially support crop growth.  相似文献   
4.
Better irrigation and nitrogen (N) scheduling and more efficient management of crop production require modeling of plant growth and crop yield. Models become more applicable if they are simple and require less and accessible inputs. The objective of this study was to use simple equations of soil water budget, evapotranspiration (ET), leaf area index (LAI), yield, and harvest index (HI)–transpiration function to develop a model for the prediction of growth and yield of maize under various water and N rates. The model was calibrated based on given data under sprinkler irrigation and verified based on independent data under furrow irrigation. The comparison between predicted and measured values of different crop parameters did not show any significant difference and the model was able to estimate LAI, ET, soil water content, HI, dry matter, and grain yield properly. Furthermore, an equation was presented to predict daily dry matter accumulation by a logistic curve for different water and N applications. It was concluded that the presented simple model was able to predict crop yield quite well and hence could be used for farm irrigation and N scheduling and management of both. Furthermore, the relationship between LAI and ET may be different in various environmental conditions that should be considered in using the model.  相似文献   
5.
Drought and salinity are the two major factors limiting crop growth and production in arid and semi‐arid regions. The separate and combined effects of salinity and progressive drought in quinoa (Chenopodium quinoa Willd.) were studied in a greenhouse experiment. Stomatal conductance (gs), leaf water potential (Ψl), shoot and root abscisic acid concentration ([ABA]) and transpiration rate were measured in full irrigation (FI; around 95 % of water holding capacity (WHC)) and progressive drought (PD) treatments using the irrigation water with five salinity levels (0, 10, 20, 30 and 40 dS m?1); the treatments are referred to as FI0, FI10, FI20, FI30, FI40; PD0, PD10, PD20, PD30, PD40, respectively. The measurements were carried out over 9 days of continuous drought. The results showed that increasing salinity levels decreased the total soil water potential (ΨT) and consequently decreased gs and Ψl values in both FI and PD. During the drought period, the xylem [ABA] extracted from the shoots increased faster than that extracted from the roots. A reduction in ΨT, caused by salinity and soil drying, reduced transpiration and increased apparent root resistance (R) to water uptake, especially in PD0 and PD40 during the last days of the drought period. The reasons for the increase in apparent root resistance are discussed. At the end of the drought period, the minimum value of relative available soil water (RAW) was reached in PD0. Under non‐saline conditions, Ψl decreased sharply when RAW reached 0.42 or lower, but under the saline conditions of PD10 and PD20, the threshold values of RAW were 0.67 and 0.96, respectively. In conclusion, due to the additive effect of osmotic and matric potential during soil drying on soil water availability, quinoa should be re‐irrigated at higher RAW in salt‐affected soils, i.e. before the soil water content reaches the critical threshold level causing the drop in Ψl resulting in stomatal closure.  相似文献   
6.
Journal of Soils and Sediments - Deforestation is one of the ecosystem disservices associated with accelerated loss of soil organic carbon (SOC) and nitrogen (TN). The objective of our study was to...  相似文献   
7.
Soil structure formation is essential to all soil ecosystem functions and services. This study aims to quantify changes in soil structure and microbial activity during and after field incubation and examine the effect of carbon, organic amendment and clay on aggregate characteristics. Five soils dominated by illites, one kaolinitic soil and one smectitic soil were sieved to 2 mm, and each soil was divided into two parts and one part amended with ground rape shoots (7.5 t ha?1) as an organic amendment. Samples were incubated in the field for 20 months with periodic sampling to measure water‐dispersible clay (WDC) and fluorescein diacetate activity (FDA). After incubation, WDC and FDA were measured on air‐dried 1–2‐mm aggregates. Tensile strength was measured on four aggregate classes (1–2, 1–4, 4–8 and 8–16 mm) and results used to assess soil friability and workability. Intact cores were also sampled to determine compressive strength. During incubation, the amount of WDC depended on soil carbon content while the trends correlated with moisture content. Organic amendment only yielded modest decreases (mean of 14% across all sampling times and soils) in WDC, but it was sufficient to stimulate the microbial community (65–100% increase in FDA). Incubation led to significant macroaggregate formation (>2 mm) for all soils. Friability and strength of newly‐formed aggregates were negatively correlated with clay content and carbon content, respectively. Soil workability was best for the kaolinite‐rich soil and poorest for the smectite‐rich soil; for illitic soils, workability increased with increasing organic carbon content. Organic amendment decreased the compression susceptibility of intact, incubated samples at smaller stress values (<200 kPa).  相似文献   
8.
In this study, four different methods for reference crop evapotranspiration (ET0) were calibrated and validated for estimation of daily to mean monthly ET0 by weighing lysimeter data during 2005–2006 and 2004–2005, respectively, in a semi-arid region. The value of the constant in the Hargreaves–Samani method changed from 0.0023 to 0.0026 for daily to mean monthly ET0, and can be used in stations with only air temperature data. The constant of the aerodynamic resistance equation in the FAO-56 Penman–Monteith method (208.0) changed to 85.0. The value of coefficient a in the FAO-24-Radiation method was between ?0.5 and ?0.67. Further, the empirical equations were modified to estimate the value of b in the FAO-24-Radiation method and C in the FAO-24 corrected Penman method. The results showed that the modified FAO-56, corrected Penman–Monteith and FAO-24-Radiation methods are the most appropriate for estimating daily to mean monthly ET0. Furthermore, the modified FAO-24 corrected Penman method was ranked in fourth place and its accuracy was lower than that of the other methods. However, it is appropriate for estimating mean monthly ET0. Smoothing the daily data decreased the fluctuation in measured daily weather data and ET0 measured by lysimeter, and consequently resulted in a higher accuracy in the estimation of daily ET0.  相似文献   
9.
Coarse sandy soils have poor water retention capacity, which may constrain crop growth during drought. We investigated the effect of biochar amendment to subsoil on crop physiological processes and maize yield, comparing irrigated and drought conditions. A two‐year greenhouse experiment was conducted with one‐time application of straw biochar at concentrations of 0%, 1%, 2% and 3% (B0, B1, B2 and B3). Maize was planted twice in the same large pots one week and again 12 months after biochar application. Plants were fully irrigated until flowering; thereafter, half of them were subjected to drought. Our results indicate B2 and B3 increased soil water content at field capacity. Leaf water potential, stomatal conductance, photosynthesis and transpiration were maintained in B2 and B3 during the drying cycle in year one and in all biochar levels in year two. In the first year, B3 induced negative root geotropism and significantly reduced vegetative biomass under both irrigation schemes. Cob biomass was significantly reduced by B1 under full irrigation. In year two, B3 significantly increased cob biomass under drought. Nitrogen uptake was significantly reduced by B2 in year one, but increased significantly in B3 in year two. In both years, P uptake was significantly increased by B2 and B3. Furthermore, K uptake was significantly increased in B2 in year one and in all biochar treatments in year two. Overall, biochar improved water content of coarse sandy soil due to decreased bulk density and increased porosity after biochar amendment, consequently, improving crop physiological processes including transpiration and photosynthesis. Significant effects on yields tended to be more negative in the first year, and neutral to positive in the second year suggesting the enhancement of biochar effects with ageing. The positive effect in the second year shows biochar's potential for improving agriculture productivity in drought‐prone regions.  相似文献   
10.
Iran has been faced to drought during last decades, and one way to overcome this phenomenon is to improve the water productivity by introducing new crops tolerant to water stresses such as quinoa. Two-year field experiment was performed to find out the response of quinoa (cv. Titicaca) to deficit irrigation imposed at different growing stages. Hence, the effect of full irrigation (100% irrigation water requirement) and deficit irrigation (50% full irrigation) on physiological parameters, yield, irrigation water productivity and root density of quinoa was investigated during 2016 and 2017 growing seasons. The result showed that there was a significant difference between all variables in two years. Higher average air temperature in 2017 (2.0°C) resulted in a reduction of seed yield and water productivity (55% and 40% of that obtained in 2016, respectively). Application of deficit irrigation during different growing stages reduced crop height, stomatal conductance and seed yield, while it increased the root length density in both years. In conclusion, flowering stage of quinoa was very sensitive to deficit irrigation, and irrigation at grain filling stage would not help to recover the seed yield. Furthermore, the seed yield was lower than that obtained in other studies performed in other countries using same quinoa cultivar, which could be due to higher amount of applied irrigation water and different phenology under different climatic conditions. A decision on cultivating this crop under semi-arid conditions has to be made considering limited water resources.  相似文献   
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