首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 202 毫秒
1.
Submerged rice paddies are a major source of methane (CH4) which is the second most important greenhouse gas after carbon dioxide (CO2). Accelerating rice straw decomposition during the off-rice season could help to reduce CH4 emission from rice paddies during the single rice-growth season in cold temperate regions. For understanding how both temperature and moisture can affect the rate of rice straw decomposition during the off-rice season in the cold temperate region of Tohoku district, Japan, a modeling incubation experiment was carried out in the laboratory. Bulk soil and soil mixed with 2% of δ13C-labeled rice straw with a full factorial combination of four temperature levels (?5 to 5, 5, 15, 25°C) and two moisture levels (60% and 100% WFPS) were incubated for 24 weeks. The daily change from ?5 to 5°C was used to model the freezing–thawing cycles occurring during the winter season. The rates of rice straw decomposition were calculated by (i) CO2 production; (ii) change in the soil organic carbon (SOC) content; and (iii) change in the δ13C value of SOC. The results indicated that both temperature and moisture affected the rate of rice straw decomposition during the 24-week aerobic incubation period. Rates of rice straw decomposition increased not only with high temperature, but also with high moisture conditions. The rates of rice straw decomposition were more accurately calculated by CO2 production compared to those calculated by the change in the SOC content, or in its δ13C value. Under high moisture at 100% WFPS condition, the rates of rice straw decomposition were 14.0, 22.2, 33.5 and 46.2% at ?5 to 5, 5, 15 and 25°C temperature treatments, respectively. While under low moisture at 60% WFPS condition, these rates were 12.7, 18.3, 31.2 and 38.4%, respectively. The Q10 of rice straw decomposition was higher between ?5 to 5 and 5°C than that between 5 and 15°C and that between 15 and 25°C. Daily freezing–thawing cycles (from ?5 to 5°C) did not stimulate rice straw decomposition compared with low temperature at 5°C. This study implies that to reduce CH4 emission from rice paddies during the single rice-growth season in the cold temperate regions, enhancing rice straw decomposition during the high temperature period is very important.  相似文献   

2.
Abstract

Contamination of agricultural soil by fecal pathogenic bacteria poses a potential risk of infection to humans. For the biosafety control of field soil, soil solarization in an upland field was examined to determine the efficiency of solarization on the inactivation of Escherichia coli inoculated into soil as a model microorganism for human pathogenic bacteria. Soil solarization, carried out by sprinkling water and covering the soil surface with thin plastic sheets, greatly increased the soil temperature. The daily average temperature of the solarized soil was 4–10°C higher than that of the non-solarized soil and fluctuated between 31 and 38°C. The daily highest temperature reached more than 40°C for 8 days in total in the solarized soil during the second and third weeks of the experiment. Escherichia coli in the solarized soil became undetectable (< 0.08 c.f.u. g?1 dry soil) within 4 weeks as a result, whereas E. coli survived for more than 6 weeks in the non-solarized soil. Soil solarization, however, had little influence on the total direct count and total viable count of bacteria in the soil. These results indicate that soil solarization would be useful for the biosafety control of soil contaminated by human pathogens via immature compost or animal feces.  相似文献   

3.
ABSTRACT

Variations in the levels of the highly toxic oleandrin molecules were studied during composting of Nerium oleander L. waste mixed with clippings of the grass Pennisetum clandistenum L. The thermophilic phase is characterized by a rise in temperature, which reached 70°C. After 150 days of co-composting, the C/N ratio was 11, the pH was 8, the NO3?/NH4+ ratio was greater than 1 and overall decomposition reached 70%. During the successive stages of co-composting, oleandrin concentrations were monitored by HPLC. The relative abundance of oleadrin was 26.84% at T0 with 10% abatement during the first month and 90% after two months (stabilization phase), reaching 100%, i.e., total removal after 90 days of co-composting (maturation phase). The biodegradation of the toxic substance was largely attributed to the activity of actinomycetes and fungi. The germination index of lettuce and watercress seeds exceeded 50% after 90 days and reached 95% after 150 days, confirming that the final compost was mature, stable, and free from phytotoxicity in spite of the highly poisonous starting material.  相似文献   

4.
Soil respiration, nitrogen mineralization and humus decomposition of East African soils after drying and remoistening Soil respiration and nitrogen mineralization of 51 East African cultivated, savanna and forest soils were compared after 3 and 21 weeks of air drying. The average soil respiration after 21 weeks of drying was 1.221 ± 0.106 times higher than that after 3 weeks of drying whereas the average nitrogen mineralization was not increased significantly (factor 1.132 ± 0.256). The increase in soil respiration was correlated positively with the water soluble organic matter. During air dryings of 3 days and moist incubations of 4 days at 30°C, which were repeated 20 times in 10 soils, 3–10% of the organic carbon and 8–19% of the organic nitrogen (low humus vertisol 69%) were mineralized. Changes in the amount and the extinction of humic and fulvic acids were considered to be indicative for an increased humification during the drying and remoistening of soils.  相似文献   

5.
This study aims to assess radiation-based models versus the FAO Penman–Monteith (FPM) model to determine the best model using linear regression under different weather conditions. The reference evapotranspiration was estimated using 22 radiation-based methods and was compared with the FPM. The results showed that the Stephens method estimates the reference evapotranspiration better than other methods in the most provinces of Iran (nine provinces). However, the values of R2 were more than 0.9930 for 24 provinces of Iran. The radiation-based methods estimated the reference evapotranspiration near the Caspian Sea better than other regions. The most precise methods were the Berengena–Gavilan, Modified Priestley–Taylor, and Priestley–Taylor methods for the provinces ES (center of Iran), GI and GO (north of Iran) and the Stephens–Stewart method for IL (west of Iran). Finally, a list of the best performance of each method has been presented to use other regions and next research steps according to the values of mean, maximum, and minimum temperature, relative humidity, solar radiation, elevation, sunshine, and wind speed. The best weather conditions to use radiation-based equations are 23.6–24.6 MJ m?2 day?1, 12–20°C, 18–24°C, 5–13°C, and <180 hour month?1 for solar radiation, mean, maximum, and minimum temperature, and sunshine, respectively.  相似文献   

6.
Abstract

Seed dormancy and slow germination often cause poor establishment of Poa pratensis L. in lawns and pastures. This study was conducted to determine whether persistent dormancy occurs and the influence of light and temperature on germination of Poa pratensis L. strains from Northern Norway. Seed from 23 different genotypes and seed lots was germinated in various phytotron chambers during the winters of 1986 and 1990. At 21°C constant temperature, dormancy was evident even after seven years of storage in a dry room at 0–10°C. By contrast, alternating temperatures (21/12°C) elicited 80–100% germination of viable seed of nearly all genotypes and seed lots. Light treatment had no impact on germination after 28 days at 21/12°C, but continuous darkness and continuous fluorescent light were both inferior to 8 h light/16 h dark illumination cycles at 21°C constant temperature. Seed of the commercial cultivar Lavang produced in Southern Norway developed the same long-term, temperature-dependent dormancy as seed produced in Northern Norway. One lot of the cultivar Holt showed a higher ability to germinate at low temperatures than any of the other genotypes.  相似文献   

7.
Abstract

The weekly nitrogen (N), phosphorus (P), and potassium (K) release from 17 polymer‐coated controlled‐release fertilizer (CRF) formulations of Nutricote, Apex Gold, Osmocote, and a 9‐month Macrocote were measured at 30.6±0.8°C and 40.0±1.5°C. Five grams of each CRF were placed at a depth of 50 mm in 280x50 mm acid washed then rinsed silica sand columns which were leached with deionized water three times each week until nutrient recovery ceased. The volume of leachate was recorded each week and subsampled for ammonium‐N, nitrate‐N, phosphate‐P, and K analyses. Each CRF treatment was replicated three times at each temperature. Nutrient release profiles were determined. Longevities, measured as weeks to 90% nutrient recovery, were considerably shorter than the nominated release periods for all formulations. Within each CRF product group, the longevity of 9 and 12 month formulations were similar with Apex Gold 12–14 month high nitrate having the longest (38 weeks for N at 30°C) and Osmocote 8–9 month the shortest (23 weeks for N at 30°C). There were consistent trends in the nutrient release periods across all CRFs with P>K>N and with differences of around 10% in duration between nutrients. The P:N release ratio exceeded 0.10 for most CRFs during the early release period indicating an adequate P supply for most plant species. The mean reduction in longevity for Nutricote, Apex Gold, and Osmocote formulations for an increase in incubation temperature from 30°C to 40°C was 19–21 % for N, 13–14% for P, and 14–15% for K. All CRFs released nutrients unevenly with the highest rate occurring during the early part of the release period. This pattern was accentuated at 40°C and by the shorter term release formulations. The nutrient release rates of all CRFs declined steadily after their maxima.  相似文献   

8.
The metabolic rate of three captive manatees was measured at different water and air temperatures. The animals responded metabolically to cold water (15–20°C), but not to cold air (10–20°C). Average metabolic rates in the thermal neutral zone (T1 ? 24°) were 15–22% of predicted weight-specific values, and thermal conductances were 117–229% of predicted levels. Body temperatures averaged 36·4°C. The low heat production and high thermal conductance suggest that manatees are poorly adapted energetically to winter water temperatures in much of Florida. These results support behavioural observations of captive and free-living manatees which suggest that 20°C is the minimum suitable water temperature for manatees. Manatees wintering in colder waters are probably in marginal habitat and are most susceptible to cold-related mortality. Warm water refuges reduce energetic maintenance costs and probably temper the effects of occasional periods of severely cold weather, particularly in northern Florida.  相似文献   

9.
High temperature during grain filling has been identified as a major factor in the end-use properties of bread wheat (Triticum aestivum L.). Our objectives were to assess the effect of high temperature during maturation on the grain characteristics, milling quality, and flour quality of hard red winter wheat. In three separate experiments, plants of wheat cultivar Karl 92 were subjected to regimes (day-night) of 20–20, 25–20, 30–20, and 35–20°C from 10 and 15 days after anthesis (DAA) until ripeness, and 25–20, 30–20, and 35–20°C from 20 DAA until ripeness. In other experiments, plants of wheat cultivars Karl 92 and TAM 107 were dried at 20 and 40°C, and spikes of Karl 92 were dried at different temperature and humidity conditions to asses the effects on quality of high temperature and drying rates during grain ripening. Flour yield correlated positively with kernel weight and diameter, test weight, and proportion of large kernels. Flour yield decreased as temperature increased and correlated negatively with hardness index and proportion of small grains. High growth temperatures and rapid grain desiccation decreased mixing time and tolerance of the flours. The greatest damage occurred when high temperature was maintained continuously from early grain filling until ripeness. Weakening of dough properties by rapid desiccation during ripening suggest that temperature, humidity, and possibly soil moisture all contribute to the final quality of bread wheat.  相似文献   

10.
The browning indicators furosine and color were determined in infant cereals and infant cereals containing powdered milk to evaluate the utility of these parameters for monitoring storage. Studies were made on seven infant cereal samples including both gluten and gluten‐free products. Samples were stored under laboratory conditions at 28°C for four or 16 weeks; or under modified water activity conditions at 25°C or 55°C for one, two, three, or four weeks; or under industrial conditions in air or nitrogen atmospheres at 32°C or 55°C for one, three, six, or 12 months. Furosine levels increased during the storage of infant cereals containing powdered milk under all time, temperature, and water activity (aw) conditions assayed, except drastic conditions (55°C, aw = 0.65). Color values increased in infant cereals with gluten (7‐cereal and 8‐cereal samples), regardless of milk content, when they were stored under drastic conditions (55°C or 25°C with normal or modified water activity). However, the gluten‐free infant cereals (rice‐corn and rice‐corn‐soy samples) that have a characteristic yellow color showed no increase in color during storage. The extent of the Maillard reaction was greatest in the infant cereals that included milk in their formulation.  相似文献   

11.
To assess emergence time of shoots from roots of the perennial weed Sonchus arvensis as a function of root weight and soil temperature, we performed an experiment to which linear models were fitted. Root parts of three distinct initial weight classes were grown in pots in the dark at constant temperatures of 4, 8 and 18°C, respectively. During five harvest occasions, prior to or at shoot emergence, below-ground shoot length was measured. Root planting depth (3, 10 and 17 cm) did not influence shoot elongation rate. The below-ground shoot elongation rate for a given initial root-weight class was estimated from the observations to be constant with time, but to increase with temperature and initial root weight. By expressing shoot length for a given day as a linear function of the number of days from planting date, and elongation rate as a linear function of temperature, we calculated (1) the accumulated temperature-sum requirement for emergence, (2) emergence time for variable temperature conditions in a clay soil using soil temperature recordings at 5-cm depth for seven seasons in central Sweden and (3) the emergence time at three elevated temperature levels and initial root-weight classes. The accumulated temperature-sum requirements for below-ground shoots of S. arvensis to reach soil surface are independent of temperature regime for roots of a given initial weight but lower for heavier than lighter roots. The temperature limit for below-ground shoot elongation to occur is about 2.0–2.5°C. Between-year variations in temperature under field conditions cause larger variation to emergence time than initial root-weight differences. An average temperature increase of 3°C would cause an earlier emergence time, in the same range (about 2 weeks) as the difference between the earliest and latest year in the current weather conditions.  相似文献   

12.
Mesta (Hibiscus sabdariffa) is an important fibre crop in the north coastal zone of Andhra Pradesh which accounts for 59% of India's total production of mesta. The area under this crop has reduced dramatically in recent years and in order to understand the contribution of weather to this decline, long-term experimental data (14 years) on mesta cv. AMV-4 and regional crop yields were analysed. Crop yields decreased in seasons when rainfall exceeded 900 mm and maximum temperature remained below 32.0°C during 10–16 weeks after sowing (WAS), which coincided with the active vegetative stage. The average yields of the region were high when seasonal rainfall ranged between 600 and 725 mm. Increased fibre yields were observed when increasing seasonal rainfall coincided with maximum temperatures exceeding 33.5°C. Fibre yields from a long-term experiment showed strong positive correlations with maximum temperature during 6–16 WAS (r = 0.79) and with mean diurnal temperature range (8.6–10.7°C) during 11–19 WAS (r = 0.66). Step-wise regression showed that maximum variability in fibre yield was explained by maximum temperature which could be used to develop models to predict yield at least one month in advance with acceptable accuracy. This prediction could then be used as an input for crop planning and market intelligence.  相似文献   

13.
Abstract

Mean monthly weather data values from 1968 – 2000 for 12 major rainfed wheat production areas in north-west and western Iran were used with a climate model, United Kingdom Meteorological Organization (UKMO), to predict the impact of climate change on rainfed wheat production for years 2025 and 2050. The crop simulation model, World Food Study (WOFOST, v 7.1), at CO2 concentrations of 425 and 500 ppm and rising air temperature of 2.7 – 4.7°C, projected a significant rainfed wheat yield reduction in 2025 and 2050. Average yield reduction was 18 and 24% for 2025 and 2050, respectively. The yield reduction was related to a rainfall deficit (8.3 – 17.7%) and shortening of the wheat growth period (8 – 36 d). Cultivated land used for rainfed wheat production under the climate change scenarios may be reduced by 15 – 40%. Potential improvements in wheat adaptation for climate change in Iran may include breeding new cultivars and changing agronomic practices like sowing dates.  相似文献   

14.
Thin-layer drying data was collected for rough rice from 108 treatments. Four thin-layer equations were derived by regression analysis to predict the drying behavior for deep-bed drying of rough rice. The proposed equations consider the effects of drying air temperature, drying air absolute humidity, drying time interval, and tempering time interval. Drying air temperature range was 35–65°C, drying air absolute humidity range was 10–26 g/kg of dry air, drying time interval was 5–15 min, and tempering time interval was 40–120 min. In addition, the variations of moisture content with tempering time intervals and drying time intervals were considered. Within the tempering time interval range of 40–120 min and drying time interval of 5–15 min, a shorter drying time interval and a longer tempering time interval are preferable in a recirculating type rice dryer.  相似文献   

15.
Initial colonization of cotton stems by microarthropods proceeded more rapidly while buried in soil under laboratory conditions (20–23°C) than while buried in the field during the winter months when soil temperatures ranged from 5–10°C in the study area in the San Joaquin Valley of California. While 15 species were found frequently in cotton stems held in the laboratory for 20 weeks, only seven species were found in field buried stems. Arthropods found under both conditions were a species of pyemotid mite; an astigmatid mite, Tyrophagus dimidiatus; two collembolans, Proisotoma minuta and Tullbergia sp.; and a sciarid fly larval stage, Bradysia impatiens. Even though the soils at teh field sites possessed a number of microarthropods in common, the stem colonization at each site was restricted to a single group which differed from each of the other sites. Microenvironments affect stem colonization patterns by microarthropods but microarthropods did not appear to have a significant influence on early cotton stem decomposition rates nor was there evidence that their activities reduced Verticillium microsclerotia populations.  相似文献   

16.
An hypothesis about the different temperature dependences of the decomposition of the labile and stable organic carbon pools has been tested using an agrochernozem sampled from an experimental plot of 42-year-old continuous corn in Voronezh oblast. The partitioning of the CO2 loss during the decomposition of the labile and stable soil organic matter (SOM) at 2, 12, and 22°C in a long-term incubation experiment was performed using the method of 13C natural abundance by C3–C4 transition. On the basis of the determined decomposition constants, the SOM pools have been arranged in an order according to their increasing stability: plant residues < new (C4) SOM < old (C3) SOM. The tested hypothesis has been found valid only for a limited temperature interval. The temperature coefficient Q 10 increases in the stability order from 1.2 to 4.3 in the interval of 12–22°C. At low temperatures (2–12°C), the values of Q 10 insignificantly vary among the SOM pools and lie in the range of 2.2–2.8. Along with the decomposition constants of the SOM, the new-to-old carbon ratio in the CO2 efflux from the soil and the magnitude of the negative priming effect for the old SOM caused by the input of new organic matter depend on the temperature. In the soil under continuous corn fertilized with NPK, the increased decomposition of C3 SOM is observed compared to the unfertilized control; the temperature dependences of the SOM decomposition are similar in both agrochernozem treatments.  相似文献   

17.
The behavior of the herbicide 2.4.5-T in german soils under arable land and forest Sorption, degradation and movement of trichlorphenoxy acetic acid (2.4.5-T) were investigated in 10 german soils with very different climatic and edaphic conditions in field and laboratory experiments. Under field conditions 50% of the applied herbicide were liminated in 8 to 46 days during summer time (13-18°C mean temperature), but in 40 to 220 days during (and after) winter time (4-7°C in the first weeks). Beside microbial decomposition losses due to volatility were observed. Uptake by plants (Lolium perenne) was lower than 1%. Sometimes 10% of 2.4.5-T moved downward more then 30cm during summer time but more then 50cm during winter time. Translocation in the profile was reduced by high contents of organic matter in the A horizon but not by high clay contents. Correlations between behaviour in the field and laboratory experiments were found so that the first could be predicted by the latter.  相似文献   

18.
The 14C-labelled herbicidal active ingredients methabenzthiazuron, isocarbamid and metamitron were subjected to decomposition for 10 to 12 weeks in a degraded loess soil at 65% of maximum water holding capacity. To simulate the field situation, the standardised soil temperature of 0, 10 and 20°C were increased several times by 5 or 10°C, either daily or weekly. The rates of 14CO2 evolution clearly showed the delay in degradation as a consequence of lowering the temperature or of the retarded microbial activity. For all 3 herbicidal compounds, a strongly reduced degradation was readily observed at 10°C, and at 0°C degradation stopped almost entirely. Daily temperature increases had only a weak stimulating influence. At the standardised temperature of 20°C, however, daily temperature increases, or temperature increases lasting for a longer period, by 5 or 10°C effected a marked increase in the rates of 14CO2-evolution. On the other hand, the higher temperatures led to lower extractability of residual herbicide in the soil. In the case of isocarbamid and metamitron, about 90% of the extracted radioactivity still represented the unchanged active ingredient, whilst, in the case of methabenz-thiazuron, this fraction was between 97 and 100%.  相似文献   

19.
The mineralization and humification of leaf litter collected in a mixed forest of the Prioksko-Terrasny Reserve depending on temperature (2, 12, and 22°C) and moisture (15, 30, 70, 100, and 150% of water holding capacity ( WHC)) has been studied in long-term incubation experiments. Mineralization is the most sensitive to temperature changes at the early stage of decomposition; the Q 10 value at the beginning of the experiment (1.5–2.7) is higher than at the later decomposition stages (0.3–1.3). Carbon losses usually exceed nitrogen losses during decomposition. Intensive nitrogen losses are observed only at the high temperature and moisture of litter (22°C and 100% WHC). Humification determined from the accumulation of humic substances in the end of incubation decreases from 34 to 9% with increasing moisture and temperature. The degree of humification CHA/CFA is maximum (1.14) at 12°C and 15% WHC; therefore, these temperature and moisture conditions are considered optimal for humification. Humification calculated from the limit value of litter mineralization is almost independent of temperature, but it significantly decreases from 70 to 3% with increasing moisture. A possible reason for the difference between the humification values measured by two methods is the conservation of a significant part of hemicelluloses, cellulose, and lignin during the transformation of litter and the formation of a complex of humic substances with plant residues, where HSs fulfill a protectoral role and decrease the decomposition rate of plant biopolymers.  相似文献   

20.
Understanding the temperature sensitivity of soil organic matter (SOM) decomposition is important to predict the response of soil carbon (C) dynamics to projected global warming. There is no consensus, however, as to whether or not the decomposition of recalcitrant soil C is as sensitive to temperature as is that of labile soil C. Soil C is stabilized by three mechanisms: chemical recalcitrance, mineral interaction and physical accessibility. We used artificial soils with controlled compositions to assess the effects of chemical recalcitrance (cellulose compared with lignin) and clay‐mineral composition with montmorillonite (M) or kaolinite (K) on the decomposition of model organic compounds at 2, 12, 22 and 32°C. When only substrate composition was varied, the presence of cellulose enhanced the decomposition rate of lignin. Treatments with relatively large amounts of cellulose were very sensitive to temperature only at low temperatures (2–12°C), whereas treatments with relatively large amounts of lignin had similar temperature sensitivities at all temperatures. When only clay‐mineral composition was varied, CO2 production rates were greatest in soils containing kaolinite‐montmorillonite mixtures (10% K:20% M) and least in soils containing kaolinite only at temperatures ≥12°C. Clay mixtures and pure montmorillonite treatments had their greatest temperature sensitivities at 2–12°C, whereas pure kaolinite treatments had the greatest temperature sensitivities at 12–22°C. Temperature sensitivities at the highest temperatures (22–32°C) were all small (Q10 < 1.1 on days 30 and 140). Artificial soils with controlled but flexible compositions may serve as simple and useful models for evaluating SOM dynamics with a minimum of confounding factors.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号