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1.
Arne Helweg 《Soil biology & biochemistry》1981,13(5):401-407
14C-labelled maleic hydrazide (MH) was added to each of three soils at a concentration of 4 mg kg?1, and its degradation measured by the release of 14CO2 after 2 days. Between 1 and 30°C, at a constant moisture content (full field capacity), the mean degradation rate increased by a factor of 3 for each temperature increment of 10°C (Q10 = 3). The mean activation energy was 78 kJ mol?1. Above 35°C, the degradation rate decreased.At soil moisture contents between wilting point and 80–90% of field capacity, the degradation rate doubled with an increase in moisture content of 50% of field capacity (constant temperature, 25°C). Above field capacity, the degradation rate was either unchanged or decreased. Below wilting point the degradation was very slow, even after 2 months.The rate of decomposition of MH at all temperatures and moisture contents was lowest in the soil with the highest content of organic matter and the lowest clay content. This soil had the highest Freundlich K value, and presumably adsorbed MH the most strongly, although the lower clay content may also play a role in the lower decomposing capacity of this soil. 相似文献
2.
Phosphate extracted by ion-exchange resins in the chloride and sodium forms from a deep river-gravel soil under widely varying conditions is always from the isotopically exchangeable or‘labile’ pool. At any reaction time, a constant fraction of this pool is desorbed by the chloride form of the anion-exchange resin alone, irrespective of the pH and phosphate manuring of the soil. If, however, a sodium: cation exchange resin is included, increasing fractions of the‘labile pool’ are desorbed with decreasing soil acidity. Phosphate desorption by the anion-exchange resin alone and with the cation exchange resin is shown to be‘particle-diffusion’ controlled in the anion exchange resin and neither a‘chemical reaction’ nor a‘film-diffusion’ mechanism. Over the pH range 4·5–8·5, values between 4·8 and 0·9 × 10-9 cm2 sec-1 were calculated for the interdiffusion coefficient of the phosphate: chloride exchange process in the resin. The isotopically exchangeable phosphate in the soils seems to behave like sparingly soluble or weakly dissociating compounds towards ion-exchange resins and its rate of desorption depends on the nature and composition of the resins. 相似文献
3.
The effects of wheat, potato, sunflower, and rape residues and calcite were evaluated in soil that received sodic water. These materials were added to a sandy‐loam soil at a rate of 5%, after which the treated soils were incubated for 1 month at field‐capacity moisture and a temperature of 25°C–30°C. Column leaching experiments using treated soils were then conducted under saturated conditions using water with three sodium‐adsorption ratios (SAR) (0, 10, 40) with a constant ionic strength (50 mmol L–1). The results indicated that the application of plant residues to soils caused an increase in cation‐exchange capacity and exchangeable cations. Leaching experiments indicated that the addition of plant amendments led to increased Na+ leaching and decrease in exchangeable‐sodium percentage (ESP). The ESP of the control soil, after leaching with solutions with an SAR of 10 and 40, increased significantly, but the level of sodification in soils treated with plant residue was lower. Such decreases of soil ESP were greatly affected by the type of plant residues, with the order of: potato‐treated soil > sunflower‐treated soil > rape‐treated soil > wheat‐treated soil > calcite‐treated soil > control soil. 相似文献
4.
The effect of soil ESP on soil moisture retention and volume change of montmorillonitic type clay soil (vertisol) in the 10–58 ESP range showed increase in moisture retention with soil ESP in 10-bar suction range. Soil moisture suction (h) – water content (θ)relationship of the form h = ho(θ/θs)?b, where ‘ho’is air entry suction and ‘b’ is a constant, was obtained at all ESP levels. Soil bulk density at low moisture contents increased considerably with soil ESP due to dispersion and decreased linearly with increase in soil water content because of mineral swelling. The soil water diffusivity and conductivity in the 0.15–0.35 g/g moisture content range followed an exponential increase with soil moisture content recording a sharp decrease at soil ESP 10. The effect of high exchangeable sodium, however, was mitigated, to a large extent, by the increase in electrolyte concentration of permeating water to 5 mmhos/cm or greater. Decrease in water transmission parameters ascribed to exchangeable Na+ in the drier moisture regime was accounted for by dispersion of soil particles at low ESP. Whereas adsorbed Na+ – induced swelling was regarded as the major factor modifying soil water relations at relatively high ESP under wet moisture regime. Soil ESP of 10 may be treated as critical for swelling clay soil from soil and water – management view point. 相似文献
5.
Summary In the Netherlands, the dung beetleTyphaeus typhoeus (Col., Geotrupidae) is confined to sandy and loamy sandy soils. Experiments were carried out in the laboratory and in the field to ascertain the effects of soil bulk density and soil moisture on various aspects of the reproductive behaviour and development of this dung beetle. Some of the results were validated under natural field conditions. The nesting burrows were shown not to penetrate beyond the upper level of the soil moisture saturation zone. The depth of the burrows was not influenced by the bulk density in moist and free-drained sandy soils. Lower bulk densities of the soil were shown to result in fewer dung sausages being made, even when sufficient dung was availabe to provide for the larvae. This phenomenon was attributed to a behavioural response from the dung beetles. The critical bulk density in the field appeared to be approximately 1.40 × 103 kg/m3. The survival rate of eggs and larvae was shown to be adversely affected by conditions of high soil moisture (> 20% by volume) at the depths where the larvae develop. Evidence is given for a low survival rate of larvae at conditions of low soil moisture (pF > 2.7) at these depths. The impact of certain other soil factors is discussed.Communication no. 280 of the Biological Station, Wijster, The Netherlands 相似文献
6.
Laboratory studies were conducted to evaluate the effect of soil pH, temperature and water content on the rate of nitrification and on the amount of N2O evolved from samples of Plano silt loam soil. The rate of nitrification of added NH4+-N increased with increasing soil pH (4.7, 5.1 and 6.7), temperature (10, 20 and 30°C) and water content (0.1, 0.2 and 0.3 m3 m?3). At soil water contents of 0.1 and 0.2 m3 m?3, corresponding to 18 and 36% water-filled pore space, respectively, N2O evolution was proportional to NO3? production. Approximately 0.1–0.2% of the nitrified N was evolved as N2O-N. At 0.3 m3 m?3 water content (54% water-filled pore space) and 20 and 30°C, the ratio of N2O-N evolved to N nitrified was significantly higher (range of 0.3–1.1%).An additional experiment was conducted using diurnally fluctuating temperatures (10–30°C). The pattern of N2O evolution was markedly different when the system was sampled at 10 and 30°C than at 20°C. The apparent N2O emission rates were approximately equal for 12-h periods during which the temperature increased from 10 to 30°C or decreased from 30 to 10°C. In contrast, the apparent N2O emission rates were significantly lower for the 12-h period when the incubation flasks were sampled at 20°C following the daily minimum temperature compared to the 12-h period when the samplings were at 20°C following the daily maximum temperature. This provides additional evidence that temperature fluctuation in the surface soil is a factor in-observed diurnal variations in N2O emissions under field conditions.Our findings indicate that an interaction of three factors (soil pH, temperature and water content) affects the amount of N2O evolved during nitrification in soils. In relatively dry soils, estimated N2O production of ca. 0.1–0.3% of the N nitrified may be sufficiently accurate. Much higher N2O output can be expected following rainfall or irrigation. Diurnal variability in N2O fluxes from soils due to fluctuating temperature is an additional uncertainty in quantifying N2O production in field soils. 相似文献
7.
Simple models describing nitrogen processes are required both to estimate nitrogen mineralization in field conditions and to predict nitrate leaching at large scales. We have evaluated such a model called LIXIM, which allows calculation of nitrogen mineralization and leaching from bare soils, assuming that these are the dominant processes affecting N in bare soil. LIXIM is a layered, functional model, with a 1-day time step. Input data consist of frequent measurements of water and mineral N contents in soil cores, standard meteorological data and simple soil characteristics. The nitrate transport is simulated using the ‘mixing-cells’ approach. The variations in N mineralization with temperature and moisture are accounted for, providing calculation of the ‘normalized time’. An optimization routine is used to estimate the actual evaporation and the N mineralization rates that provide the best fit between observed and simulated values of water and nitrate contents in all measured soil layers. The model was evaluated in two field experiments (on loamy and chalky soils) including treatments, lasting 9–20 months. The water and nitrate contents in soil were satisfactorily simulated in both sites, and all treatments, including a 15N tracer experiment performed in the loamy soil. In the chalky soil, the calculated water balance agreed well with drainage results obtained in lysimeters and independent estimates of evaporation. At both sites, N mineralization was reduced by the incorporation of crop residues (wheat or oilseed rape straw); the amounts of nitrogen immobilized varied between 20 and 35 kg N ha?1. In the treatments without crop residues, the mineralization rate followed first-order kinetics (against normalized time) in the loamy soil, and zero-order kinetics in the chalky soil. In the latter soil, the mineralization kinetics calculated in situ were close to the kinetics measured in laboratory conditions when both were expressed against normalized time. 相似文献
8.
The rice‐wheat annual double cropping system occupies some 0.5 million ha in the Himalayan foothills of Nepal. Alternating soil drying and wetting cycles characterize the 6–10 weeks long dry‐to‐wet season transition period (DWT) after wheat harvesting and before wetland rice transplanting. Mineral fertilizer use in the predominant smallholder agriculture is low and crops rely largely on native soil N for their nutrition. Changes in soil aeration status during DWT are likely to stimulate soil N losses. The effect of management options that avoid the nitrate build‐up in soils during DWT by N immobilization in plant or microbial biomass was studied under controlled conditions in a greenhouse (2001/2002) and validated under field conditions in Nepal in 2002. In potted soil in the greenhouse, the gradual increase in soil moisture resulted in a nitrate N peak of 20 mg (kg soil)–1 that rapidly declined as soil moisture levels exceeded 40 % water‐filled pore space (equiv. 75 % field capacity). Similarly, the maximum soil nitrate build‐up of 40 kg N ha–1 under field conditions was followed by its near complete disappearance with soil moisture levels exceeding 46 % water‐filled pore space at the onset of the monsoon rains. Incorporation of wheat straw and/or N uptake by green manure crops reduced nitrate accumulation in the soil to < 5 mg N kg–1 in pots and < 30 kg N ha–1 in the field (temporary N immobilization), thus reducing the risk for N losses to occur. This “saved” N benefited the subsequent crop of lowland rice with increases in N accumulation from 130 mg pot–1 (bare soil) to 185 mg pot–1 (green manure plus wheat straw) and corresponding grain yield increases from 1.7 Mg ha–1 to 3.6 Mg ha–1 in the field. While benefits from improved soil N management on lowland rice are obvious, possible carry‐over effects on wheat and the feasibility of proposed options at the farm level require further studies. 相似文献
9.
Yang Wang Manfred Bölter Qingrui Chang Rainer Duttmann Annette Scheltz James F. Petersen 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(7):589-604
Investigations of diurnal and seasonal variations in soil respiration support modeling of regional CO2 budgets and therefore in estimating their potential contribution to greenhouse gases. This study quantifies temporal changes in soil respiration and their driving factors in grassland and arable soils located in Northern Germany. Field measurements at an arable site showed diurnal mean soil respiration rates between 67 and 99 mg CO2 m–2 h–1 with a hysteresis effect following changes in mean soil temperatures. Field soil respiration peaked in April at 5767 mg CO2 m–2 day–1, while values below 300 mg CO2 m–2 day–1 were measured in wintertime. Laboratory incubations were carried out in dark open flow chambers at temperatures from 5°C to 40°C, with 5°C intervals, and soil moisture was controlled at 30%, 50%, and 70% of full water holding capacity. Respiration rates were higher in grassland soils than in arable soils when the incubating temperature exceeded 15°C. The respiration rate difference between them rose with increasing temperature. Monthly median values of incubated soil respiration rates ranged from 0 to 26.12 and 0 to 7.84 µg CO2 g–1 dry weight h–1, respectively, in grassland and arable land. A shortage of available substrate leads to a temporal decline in soil respiration rates, as indicated by a decrease in dissolved organic carbon. Temporal Q10 values decreased from about 4.0 to below 1.5 as temperatures increased in the field. Moreover, the results of our laboratory experiments confirmed that soil temperature is the main controlling factor for the Q10 values. Within the temperature interval between 20°C and 30°C, Q10 values were around 2 while the Q10 values of arable soils were slightly lower compared to that of grassland soils. Thus, laboratory studies may underestimate temperature sensitivity of soil respiration, awareness for transforming laboratory data to field conditions must therefore be taken into account. 相似文献
10.
Switchgrass (Panicum virgatum L.) is a perennial biofuel crop with a high production potential and suitable for growth on marginal land. This study investigates the long-term planting effect of switchgrass on the dynamics of soil moisture, pH, organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO3–-N) and ammonium nitrogen (NH4+-N) for soils to a depth of 90-cm in a sandy wasteland, Inner Mongolia, China. After crop harvesting in 2015, soil samples were collected from under switchgrass stands established in 2006, 2008, and 2009, native mixture, and a control that was virgin sand. Averaged across six layers, soil moisture and pH was significantly higher under the native mixture than switchgrass or virgin sand. However, SOC and TN were significantly higher under the 2006 switchgrass stand when compared with all other vegetation treatments and the control. The SOC and TN increased from 2.37 and 0.26 g kg?1, respectively, for 2009 switchgrass stand, and to 3.21 and 0.42 g kg?1, respectively, for 2006 switchgrass stand. Meanwhile, SOC and TN contents were 2.51 and 0.27 g kg?1, respectively, under the native mixture. The soil beneath switchgrass and native mixture showed the highest NO3–-N and NH4+-N, respectively. The soil moisture increased with depth while SOC, TN, and NO3–-N decreased. An obvious trend of increasing moisture, SOC, TN, and mineral N was observed with increasing switchgrass stand age. Thus, growing switchgrass on sandy soils can enhance SOC and TN, improve the availability of mineral N, and generate more appropriate pH conditions for this energy cropping system. 相似文献
11.
《Soil biology & biochemistry》2012,44(12):2432-2440
Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO2 emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q10 values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ13C analyses) subject to decomposition, changed depending on depth in the peat profile. 相似文献
12.
J. H. A. MAIDA 《European Journal of Soil Science》1980,31(3):595-606
Twenty surface soils from four main Soil Groups in Malawi and their sub-soils were divided into three groups based on cation exchange capacity (group I, CEC < 50; group II, 50–100; and group III > 100μeq g–1). In each soil group the maximum amounts of K removed by successive extraction with 0.005 M CaCl2 solution were well related to the potassium potential pK–0.5p(Ca + Mg), exchangeable K, ‘step K’, and the quotient ‘step K’/CR.K, where CR.K is ‘constant-rate’potassium. In Group III soils only, ‘step K’/CR.K values were significantly correlated with pH, clay, and CEC, and this suggested that the soils were relatively rich in K+ specific binding sites. In 27 soils from an NPK factorial experiment on tea, the rate of depletion of extractable K reserve increased with ammonium sulphate treatment, whereas K fertilizers tended to off-set significantly (P= 0.001) the depletion of K reserve. The values for the change in free energy ΔG =RT In aK/ (a(Ca+Mg)) ½, ranged from –12 to –16 kJ mol–1, and field observations showed that tea plants growing on soils having ΔG values less than –15 kJ mol–1 responded to K fertilizers. The investigation has indicated that heavily cropped soils are likely to show crop responses if the intensive cropping system does not include supplementation of K. 相似文献
13.
G.C. Papavizas 《Soil biology & biochemistry》1977,9(5):337-341
At least 75% of the sclerotia of Macrophomina phaseolina survived for 1 yr in most natural soils kept at 26°C and at 50–55% of the soil moisture holding capacity (m.h.c.). Although survivability was reduced in a very acid soil (pH 4.5) collected under a pine stand, 33% of the sclerotia survived for 1 yr. Soil pH had very little or no effect on sclerotial survivability. Of three organic amendments tested (alfalfa hay, chitin, pine needles) only ground alfalfa hay at 0.8% (w/w) reduced survivability of sclerotia in soil by about 75% in a year. Alfalfa hay at 0.4% reduced survivability by 36%. Various N sources added at 200 μg Ng?1 soil had no effect on survival. Of 13 fungicides tested, only benomyl and captan at 20 μg a.i. g?1 soil appreciably reduced populations of sclerotia in soil.Soil temperature and moisture content were the two most important factors affecting survivability of sclerotia. At ?5 or 5°C the biggest drop in sclerotial survivability occurred when the soil was incubated moist (at 50% m.h.c. or more). At 26°C the biggest drop occurred in air-dried soil (2–3% m.h.c.) and survivability was decreased to some extent at 15 and 30% m.h.c. Survivability also dropped rapidly in moist soil (50–55% m.h.c.) exposed to four cycles each having 3-week freezing (?5°C) and 1 week thawing (26°C). Sclerotia in air-dried soil (2–3% m.h.c.) continuously kept at ?5°C maintained nearly complete survivability after 16 weeks. Sclerotia survived almost 80–90% in moist soil (50–55% m.h.c.) kept for 16 weeks at 26°C or in moist soil exposed to four cycles each having 3-week thawing (26°C) and 1-week freezing (?5°C). 相似文献
14.
Effect of water tension on ethylene production and consumption in montane and lowland soils in Austria 总被引：8，自引：0，他引：8
The trace gas ethylene affects plant growth and atmospheric chemistry and it interferes with soil restoration. In soil ethylene is simultaneously produced and consumed by different microorganisms. The effects of land use and soil moisture conditions on processes leading to an accumulation of ethylene are still unclear. We measured the rates at which montane and lowland soils from Austria produced and consumed ethylene over a range of water tensions and oxygen supply. Complete anaerobiosis (waterlogging, zero tension) favoured ethylene production, whereas ethylene degradation rates were greatest in soils at 30 kPa water tension. Soils from the lowland region of eastern Austria produced ethylene at rates of up to 12 pmol C2H4 g–1 h–1 under anaerobic conditions, and they consumed ethylene at rates reaching 231 pmol C2H4 g–1 h–1, after addition of 20 μl l–1 ethylene. Deciduous forest soils consumed ethylene fastest. Ethylene formed rapidly and was also consumed rapidly in soils rich in humus and total nitrogen. Soils taken from the mountains both produced and consumed ethylene more rapidly than lowland soils did. Production rates reached 146 pmol C2H4 g–1 h–1 under anaerobic conditions. Spruce forest soils produced significantly more ethylene than pastures. Ethylene formation was negatively correlated with soil pH. In montane soils ethylene production was related to the availability of simple carbon sources, expressed by the amount of extractable glucose equivalents. Maximum ethylene degradation amounted to 895 pmol g–1 h–1. Most of the soils were net sinks for ethylene at a water tension of 30 kPa and drier. 相似文献
15.
Permissible erosion rate also known as soil loss tolerance (‘T’ value) is defined as maximum erosion that can take place on a given soil without degrading its long‐term productivity. In India, default ‘T’ value of 11·2 Mg ha−1 y−1 is used for devising land restoration strategies for different types of soils. However, ability of soil to resist degradation varies with soil type, depth and physico‐chemical characteristics. Therefore, the present investigation was undertaken to determine ‘T’ value of different landforms of Delhi State by taking into account the soil saturated hydraulic conductivity (SHC), bulk density (BD), organic carbon, erodibility and soil pH. Soil state was defined by a quantitative model and scaling functions were used to convert soil parameters to a 0–1 scale. The normalised values were multiplied by appropriate weighting factors based on relative importance and sensitivity analysis of each indicator. Categorical rankings of I, II or III were assigned to soil groups based on overall aggregate score. ‘T’ value of different landforms of Delhi State was computed using the guideline of USDA‐Natural Resource Conservation Services. Majority of landforms of Delhi had ‘T’ value of 12·5 Mg ha−1 y−1, except for the soils of hill terrain, dissected hill, pediment and piedmont plain, where ‘T’ value ranged from 5 to 10 Mg ha−1 y−1. These ‘T’ values could be used for conservation planning and will help the planners in devising suitable land restoration strategies. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
16.
《Communications in Soil Science and Plant Analysis》2012,43(6):768-782
The mountainous region of the Himalayas is covered with forest, grassland, and arable land, but the variation in ecosystem functions has not been fully explored because of the lack of available data. This study appraises the changes in soil properties over the course of a year (spring, summer, autumn, winter) for forest, grassland, and arable soils in a typical hilly and mountainous region of Azad Jammu and Kashmir, Pakistan. Soil samples were collected from major land-cover types in the mountain region: natural forest, grassland, and cultivated land (arable). The natural forest served as a control against which changes in soil properties resulting from removal of natural vegetation and cultivation of soil were assessed. Soil samples were collected from depths of 0–15 and 15–30 cm six times during the year and examined for changes in temperature, moisture, electrical conductivity (EC), micronutrients [iron, manganese, copper, and zinc (Fe, Mn, Cu, Zn, respectively)], and microbial population. Significant differences were found in soil temperature, soil moisture, Fe, Mn, Cu, Zn, and number of bacteria, actinomycetes, and fungi among the three land-cover types. Soil under cultivation had 4–5 °C higher temperature and 3–6% lower moisture than the adjacent soils under grassland and forest. Electrical conductivity (EC) values of forest, grassland, and arable soil were 0.36, 0.30, and 0.31 dS m?1, indicating that soil collected from the forest had 18–20% more EC than the adjacent arable and grassland soils. On average, amounts of Fe, Mn, Cu, and Zn in the soil collected from the arable site were 6.6, 5.7, 1.7, and 0.8 mg kg?1, compared with 24.0, 12.1, 3.5, and 1.2 mg kg?1 soil in the forest soil, showing that arable had two to four times less micronutrients than grassland and forest. Populations of bacteria, actinomycetes, and fungi in the forest were 22.3 (105), 8.2 (105), and 2.5 (103), respectively, while arable land exhibited 8.2 (105), 3.2 (105), and 0.87 (103). Season (temperature) and depth showed significant effects on microbial activity and nutrient concentration, and both decreased significantly in winter and in the subsurface layer of 15?30 cm. Different contents of the parameters among arable, grassland, and forest soils indicated an extractive effect of cultivation and agricultural practices on soil. Natural vegetation appeared to be a main contributor to soil quality as it maintained the moisture content and increased the nutrient status and microbial growth of soil. Therefore, it is important to sustain high-altitude ecosystems and reinstate the degraded lands in the mountain region. 相似文献
17.
POTASSIUM-ALUMINIUM EXCHANGE IN ACID SOILS I. KINETICS 总被引：1，自引：0，他引：1
A kinetic method is described and investigated for determining exchangeable Al in acid soils using M NH4Cl solutions the pH and leaching rate of which was critical for obtaining accurate and reproducible values. Molar concentrations of ammonium acetate displaced at least part of the Al chelated to functional groups in the soil organic matter. The adsorption kinetics of K and Al from 10?3 M chloride solutions on the NH4-saturated forms at the original soil pH of these, under leaching conditions similar to the ‘extraction’ method, showed that, when the atom ratio K/A1 > 1 in the equilibrating solution, initially more K was adsorbed than at equilibrium, although Al did not ‘over-equilibrate’ when K/A1 < 1. At least 24 h were required for attaining equilibrium in K :A1 equilibria work with soils and clays. The kinetics of desorption (extraction method) and adsorption of K and Al obeyed the first-order and parabolic rate respectively. This is attributed to the large difference in anion concentrations in the two methods. 相似文献
18.
The emission of CO2 from Galician (NW Spain) forest, grassland and cropped soils was studied in a laboratory experiment, at different temperatures (10-35 °C) and at moisture contents of 100% and 160% of the field capacity (FC) of each soil (the latter value corresponds to saturated conditions, and represents between 120% and 140% of the water holding capacity, depending on the soil). In the forest soil, respiration in the flooded samples at all temperatures was lower than that at 100% field capacity. In the agricultural (grassland and cropped) soils the emission was higher (particularly at the highest incubation temperatures) in the soils wetted to 160% of the field capacity than in those wetted to 100% of the field capacity. In all cases the emission followed first order kinetics and the mineralization constants increased exponentially with temperature. In the forest soil, the Q10 values were almost the same in the soils incubated at the two moisture contents. The grassland and cropped soils displayed different responses, as the Q10 values were higher in the soils at 160% than in those at 100% of field capacity. In addition, and particularly at the highest temperatures, the rate of respiration increased sharply 9 and 17 days after the start of the incubation in the grassland and in the cropped soil, respectively. The above-mentioned anomalous response of the grassland and cropped soils under flooding conditions may be related to the agricultural use of the soils and possibly to the intense use of organic fertilizers in these soils (more than 150 kg N ha−1 year−1 added as cattle slurry or manure, respectively, in the grassland and cropped soils). The observed increase in respiration may either be related to the development of thermophilic facultative anaerobic microbes or to the formation during the incubation period of a readily metabolizable substrate, possibly originating from the remains of organic fertilizers, made accessible by physicochemical processes that occurred during incubation under conditions of high moisture. 相似文献
19.
Nitrogen mineralization and immobilization were investigated in two soils incubated with ammonium sulphate or pig slurry over a range of temperatures and moisture contents. A reduction in the mineralization of soil organic N was observed in soils incubated with 100 μg NH4+-Ng?1 soil as ammonium sulphate at 30°C but not at lower temperatures. Addition of 100 μg NH4+-N g?1 soil as pig slurry resulted in a period of nett immobilization lasting up to 30 days at 5°C. Although the length of the immobilization phase was shorter at higher temperatures the total N immobilized was similar. The subsequent rate of mineralization in slurry-treated soils was not significantly greater (P = 0.05) than in untreated soils. There was no evidence of any subsequent increased mineralization arising from the immobilized N or slurry organic N for up to 175 days. The rate of immobilization was found to increase with increasing moisture content, though the period of nett immobilization was shorter, so that the amount of N immobilized was similar over a range of moisture contents from 10 to 40%. Approximately 40% of the NH4+-N in the slurry was immobilized under the incubation conditions used. 相似文献
20.
Effect of ph on amount of phosphorus extracted by 10 mm calcium chloride from three Rothamsted soils
《Communications in Soil Science and Plant Analysis》2012,43(17-18):2917-2923
Abstract Three silty clay loams from the classical field experiments at Rothamsted Experimental Station (UK) with low phosphorus (P) status were treated with phosphate fertilizer and incubated for 15 days at field capacity with added acid [hydrochloric acid (HCl)] or base [sodium hydroxide (NaOH)] to give pH ranges measured in 1:5 suspensions of soil in 10 mM calcium chloride (CaCl2) of 6.3–8.7 (Hoosfield A, pH 8.2), 3.8–8.2 (Hoosfield B, pH 6.3), and 2.8–7.1 (Geescroft, pH 5.3). Extractable ? was measured by the 10 mM CaCl2 extraction procedure. For the Hoosfield ? and Geescroft soils without added phosphate fertilizer, extractable ? was decreased at both ‘low’ and ‘high’ pH values, the maximum being at about 5.4 in both soils. In the calcareous Hoosfield soil, extractable ? decreased with increasing pH over the range studied. These changes in extractable ? were magnified in soils treated with phosphate fertilizer but the maxima and trends were unaltered. The results indicate that native soil ? appears to be changed by pH in the same way as added ? to the soil. In the calcareous Hoosfield A soil, added acid did not reduce soil pH to less than 6.4 (because of its high buffer capacity) and so the pH level for maximum ? solubility was not found. 相似文献