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1.
Chemical fixation of NH3 to soil organic matter was studied in two Swedish soils with different contents of organic matter: a clay soil with 2.3% C and an organic soil with 36.6% C. 15N‐labelled urea was applied at different rates to both sterilized and non‐sterilized soils. After 10 days, the soils were extracted and washed with K2SO4 and determined for total N and atom% 15N excess. Urea N was recovered as non‐extractable N in sterilized soil corresponding to 9.7% of supplied l5N‐labelled urea in the organic soil and 2.2% in the clay soil. Since no biological immobilization is thought to occur in the sterile soil, this non‐extractable N is suggested to be chemically fixed to soil organic matter. Owing to urea hydrolysis in the clay soil, pH increased from 6.3 to 9.3 and in the organic soil from 5.7 to 6.9 and 8.8, respectively, at the low and high urea supply.  相似文献   

2.
Reliable and quick methods for measuring nitrogen (N)–supplying capacities of soils (NSC) are a prerequisite for using N fertilizers. This study was conducted to develop a routine method for estimation of mineralizable N in two calcareous soils (sandy loam and clay soils) treated with municipal waste compost or sheep manure. The methods used were anaerobic biological N mineralization, mineral N released by 2 M potassium chloride (KCl), ammonium (NH4 +) N extracted by 1 N sulfuric acid (H2SO4), NH4 +-N extracted by acid potassium permanganate (KMnO4), and NH4 +-N released by oxidation of soil organic matter using acidified potassium permanganate. The results showed that oxidizable N extracted by acid permanganate, a simple and rapid measure of soil N availability, was correlated with results of the anaerobic method. Oxidative 0.05 N KMnO4 was the best method, accounting for 78.4% of variation in NSC. Also, the amount of mineralized N increased with increasing level of organic materials and was greater in clay soil than sandy loam soil.  相似文献   

3.
Four soils with a range of clay and silt contents were incubated for 5 a with 15N-labelled (NH4)SO4 and 14C-labelled hemicellulose and then fractionated according to particle size by ultrasonic dispersion and sedimentation. The distribution of labelled and native N between clay, silt and sand fractions was determined and elated to previous results on the C distributions. Between 29% and 48% of the added N was found in organic form. The 15N atom percentage excess decreased in the order: clay > whole soil > silt > sand. For both clay and silt, the enrichment factor for labelled and native N decreased with increasing fraction weight. Clay enrichment was higher for labelled than for native N, the converse being true for silt. The distribution of whole soil labelled organic N was: clay 77–91%, silt 4–11%, and sand <0.5%. Corresponding values for native N were 69–74%, 16–22%, and 1–2%, respectively. All soils had higher proportions of labelled than of native N in the clay, the converse was true for the silt. The C/N ratio of the native silt organic matter was higher and that of clay organic matter lower than whole soil C/N ratios. Differences between the C/N ratio distributions of native and labelled organic matter were small. The relative distribution of labelled N and C was very similar confirming that the turnover of C and N in soil organic matter is closely interrelated.  相似文献   

4.
Abstract

A modified selenium (Se) fractionation procedure was used to study Se distribution in three soils (two silt loams and one silty clay). This sequential procedure consisted of: i) 0.2 M potassium sulfate (K2SO4)‐soluble fraction, ii) 0.1 M potassium dihydrogen phosphate (KH2PO4)‐exchangeable fraction, iii) 0.5 M ammonium hydroxide (NH3H2O)‐soluble fraction, iv) 6 M hydrochloric acid (HCl)‐extractable fraction, and v) residual fraction digested with perchloric (HClO4) and sulfuric (H2SO4) acids. The fractionation procedure had high recovery rates (92.5 to 106%). The Se distribution in soil was controlled by soil properties, such as pH, oxide, clay, and calcium carbonate (CaCO3) contents. In the untreated soil samples, residual Se fraction was dominant. In the Se‐enriched soils, the silty clay had significantly more Se in the NH3H2O and residual fractions while in the two silt loams the largest were KH2PO4 and residual fractions. The Se availability in the two silt loams was higher than in the silty clay. The Se availability pattern in the untreated soils was: unavailable (HCl + residual fractions) >> potentially available (KH2PO4 + NH3H2O fractions) > available (K2SO4 fraction), while in the Se‐enriched soils it was potentially available > unavailable > available.  相似文献   

5.
14C-labelled cellulose and 15N-labelled (NH4)2SO4 were added to four soils with clay contents of 4, 11, 18 and 34%, respectively. Labelled cellulose was added to each soil in amounts corresponding to 1, 2 and 4 mg C g?1 soil, respectively, and labelled NH4+ at the rate of 1 mg N per 25 mg labelled C.After the first month of incubation at temperatures of 10, 20 and 30°C, respectively, from 38 to 65% of the labelled C added in cellulose had disappeared from the soils as CO2, and from 60 to nearly 100% of the labelled N added as NH4+ were incorporated into organic forms. The ratio of labelled C remaining in the soils to labelled N in organic forms was close to 25 after 10 days of incubation, decreasing to about 15 after 1 month and about 10 after 4 yr.The retention of total labelled C was largest in the soil with the highest content of clay where after 4 yr it was 25% of that added, compared to 12 in the soil with the lowest content of clay. The incorporation of labelled N in organic forms and its retention in these forms was not directly related to the content of clay in the soils, presumably because the two soils with the high content of clay had a relatively high content of available unlabelled soil-N which was used for synthesis of metabolic material.The proportionate retention of labelled C for a given soil was largely independent of the size of the amendments, whereas the proportionate amount of labelled N incorporated into organic forms increased in the clay-rich soils with increasing size of amendments. Presumably this is because the dilution with unlabelled soil-N was less with the large amendments.From 50 to 70% of the total labelled C remaining in the soils after the first month of incubation was acid hydrolyzable, as compared to 80–100% of the total remaining labelled organic N. This relationship held throughout the incubation and was independent of the size of the amendment and of the temperature of incubation.During the second, third and fourth year of incubation the half-life of labelled amino acid-N in the soils was longer than the half-life of labelled amino acid-C, presumably due to immobilization reactions. Some of the labelled organic N when mineralized was re-incorporated into organic compounds containing increasing proportions of native soil-C. whereas labelled C when mineralized as CO2 disappeared from the soils.In general, native C and native organic N were less acid hydrolyzable and were accounted for less in amino acid form than labelled C and N.The amount of labelled amino acid-C, formed during decomposition of the labelled cellulose, and retained in the soil, was proportional to the clay content. This amount was about three times as large in the soil with the highest content of clay as in the soil with the lowest content. This difference between the soils was established during the first 10 days of incubation when biological activity was most intense, and it held throughout the 4 yr of incubation; proportionally it was independent of the amount of cellulose added and the temperature.In contrast, the labelled amino acid-N content was not directly related to the amount of clay in the soil, presumably because more unlabelled soil-N was available for synthesis of metabolic material in the two clay-rich soils than in those soils with less clay. The wider ratio between labelled amino acid-C and labelled amino acid-N in the two clay-rich soils as compared with those obtained with the soils with less clay indicates this.The effect of clay in increasing the content of organic matter in soil is possibly caused by newly synthesized matter, extracellular metabolites, as well as cellular material, forming biostable complexes and aggregates with clay. The higher the concentration of clay the more readily the interactions take place. The presence of clay may also increase the efficiency of using substrate for synthesis.  相似文献   

6.
Changes in 15N abundance and amounts of biologically active soil nitrogen   总被引：1，自引：0，他引：1  
 Estimation of the capacity of soils to supply N for crop growth requires estimates of the complex interactions among organic and inorganic N components as a function of soil properties. Identification and measurement of active soil N forms could help to quantify estimates of N supply to crops. Isotopic dilution during incubation of soils with added 15NH4 + compounds could identify active N components. Dilution of 15N in KCl extracts of mineral and total N, non-exchangeable NH44 +, and N in K2SO4 extracts of fumigated and non-fumigated soil was measured during 7-week incubation. Samples from four soils varying in clay content from 60 to 710 g kg–1 were used. A constant level of 15N enrichment within KCl and K2SO4 extracted components was found at the end of the incubation period. Total N, microbial biomass C and non-exchangeable NH4 + contents of the soils were positively related to the clay contents. The mineralized N was positively related to the silt plus clay contents. The active soil N (ASN) contained 28–36% mineral N, 29–44% microbial biomass N, 0.3–5% non-exchangeable NH4 + with approximately one third of the ASN unidentified. Assuming that absolute amounts of active N are related to N availability, increasing clay content was related to increased N reserve for crop production but a slower turnover. Received: 7 July 1998  相似文献   

7.
Abstract

The effects of various soil properties on ammonia (NH3) volatilization from soils treated with urea were studied by measuring the NH3 evolved when 20 soils selected to obtain a wide range in properties were incubated at ‐0.034 mPa soil moisture potential and 30°C for 10 days after treatment with urea. The nitrogen (N) volatilized as NH3 from these soils represented from 0 to 65% of the urea‐N applied and averaged 14%. Simple correlation analyses showed that loss of NH3 was negatively correlated (P<0.1%) with cation‐exchange capacity, silt content, and clay content and was positively correlated (P <0.1%) with sand content. Loss of NH3 was also negatively correlated with total nitrogen content (P<1.0%), organic carbon content (P<1.0%), hydrogen ion buffering capacity (P<5.0%), and exchangeable acidity (P<5.0%), and was positively correlated with calcium carbonate equivalent (P <1.0%) and with soil pH after incubation with urea (P<1.0%), but was not significantly correlated with initial soil pH or soil urease activity. Multiple linear regression analyses indicated that the amount of urea N volatilized as NH3 from the 20 soils studied increased with increase in sand content and decreased with increase in cation‐exchange capacity. They also indicated that soil texture and cation‐exchange capacity are better indicators of potential loss of urea N as NH3 from soils fertilized with urea than are hydrogen ion buffering capacity or initial soil pH.  相似文献   

8.
The reactions of methyl nitrite (CH3ONO), a gaseous product of NO?2 decomposition in soils, were studied by exposure of soils in closed vessels to the gas. The N transformations occurring in soils at different soil-water states were assessed by measuring CH3ONO and other gaseous forms of N in the gas space, soil inorganic N (NH4+, NO?2, NO3?) and incorporation of CH3O15NO into the soil organic N fraction. The initial rate of uptake of CH3ONO increased with decreasing soil-water content, but the rate of hydrolysis decreased as soil-water content decreased below – 33kPa matric potential. Uptake was not affected by y-irradiation of soils. Adsorption isotherms conformed to the Langmuir equation in each of 22 oven-dry soils studied. Langmuir adsorption maxima were positively correlated with the clay contents of the soils, and adsorption was reversible to some extent at all soil-water states. Small amounts of added CH3ONO were recovered as N2 and N2O and as 15NH4+ in γ-irradiated soils. From 60 to 72% of added CH3O15NO was recovered by Kjeldahl digestion; this was indicative of a chemical reaction with soil organic matter. The results suggest that the physical process of adsorption of CH3ONO by clay minerals and the chemical fixation of CH3ONO by soil organic matter are key factors controlling the atmospheric concentration of CH3ONO, and that the combined effect of these processes, together with hydrolysis in the soil solution, will inhibit the emission of CH3ONO formed in N-fertilized soils.  相似文献   

9.
The role of aluminium on humus accumulation in acid forest soils The impact of soil-borne aluminum on humus accumulation was investigated in a forest soil of the chestnut zone (Castanea sativa) in southern Switzerland (Ticino). Soil samples of two soils formed on bedrocks which differ mainly in their aluminum content were extracted with HNO3, NH4Ac.-EDTA, NH4Cl, KCl, and NH4F-HCl and analyzed for the most abundant elements. On gneiss which contains up to about 10% of total aluminum the common soil type in this area is a Cryptopodzol. This soil is similar to the nonallophanic Udands. It is rich in wellhumified organic matter and shows dark-colored Ah-, A(E)- and Bh-horizons. The soil samples of these horizons are extremely rich in nonexchangeable aluminum which is, however, extractable with NH4Ac.-EDTA. It is assumed that this Al is intimately bound to the organic matter. The soil samples of these horizons contain large amounts of HNO3-extractable phosphorus. Up to 90% of this P appears in the organic fraction. The content of NH4F-HCl-extractable P is only 0.7 to 3.4 mg/kg. It is concluded that due to excessive Al in the organic matter the humus mineralization is inhibited compared to the Haplumbrepts of the region.  相似文献   

10.
The influence of selected factors on Cd levels in soils and in grain of oats and winter wheat was investigated. Soil and grain were sampled at sites randomly distributed over Sweden. Organic soils generally had higher Cd contents and lower pH levels than mineral soils, and plants growing in organic soils tended to have higher Cd contents than plants growing in mineral soils. In mineral soils the amount of soil Cd extractable in 2M HNO3 was positively correlated with the pH and the contents of organic matter and clay. The studied variable best correlated with the Cd content of oat grain grown on mineral soils was the pH (negative correlation). Soil contents of organic matter, clay, HNO3-extractable Cd and Zn were also found to be significantly related to the Cd content in a stepwise regression analysis. In winter wheat grain, Cd content was best correlated with the HNO3-extractable Cd (positive correlation). Additional significant factors were pH, grain yield and contents of organic matter, clay and HNO3-extractable Zn. In winter wheat the presence of Zn reduced Cd uptake, and vice versa; no such mutually antagonistic relationship was apparent in oats. In oats, but not in wheat, it was possible to predict most of the differences in grain Cd content, caused by the factors described above, based on the variation in CaCl2-extractable soil Cd. Analysis of samples from field trials indicated that there were differences in Cd content between varieties of both crops. Variation in factors described generally explained most of the differences in soil- and grain Cd levels between regions.  相似文献   

11.
Abstract

Soil pot culture experiment was conducted on 22 soils of Balewal‐Phaguwala‐Narike (BPN) and 24 soils of Isri‐Langrian‐Narike (ILN) associations using rice (PR 106) as test crop at 0 and 7.5 ppm Zn levels. Chelating extractants 0.005M DTPA, 0.01M EDTA‐(NH4)2CO3 and 0.05M EDTA, extracted more soil Zn than double‐acid and were significantly correlated with each other as well as with soil pH and clay in BPN and only with clay in ILN soil association. Soil CaCO3 governed the double‐acid extractable Zn in these soils. Dry matter yield and Zn uptake by rice significantly increased with 7.5 ppm Zn application. The response was higher in ILN than BPN soil association, The DTPA method gave the highest correlation with Bray's yield and Zn uptake (r =0.72 and 0.55) followed by 0.05M EDTA (r ‐ 0.75 and 0.61) or EDTA‐(NH4)2CO3 (r =0.70 and 0.61). The predictability of rice yield improved from 18–27 to 27–35, 32–43, 34–44 and 51–55 percent as a result of stepwise inclusion of pH, CaCO3, organic carbon (OC) and clay respectively in the regression equation alongwith Zn extracted by chelating agents.

The critical levels of DTPA, EDTA‐(NH4)2CO3 and EDTA extractable Zn significantly differed in the two associations and were 0.69, 0.82 and 1.24 ppm in BPN and O.BC, 1.09 and 1.42 ppm in ILN soil association. Soil properties further affected the critical levels. This for DTPA available Zn was 0.80 and 1.03 ppm in soil containing less and greater than 2% CaCO3, 1.03 and 0.80 ppm in soils containing less and greater than 0.25% OC. These values for EDTA‐(NH4)2CO3 available Zn were 1.09 and 0.91 ppm Zn in soils containing less and greater than 15% clay suggesting that critical levels of Zn for each category of soil properties should be considered while making recommendations of Zn fertilization of crops.,  相似文献   

12.
集约化大棚蔬菜种植条件下土壤硒有效性的影响因子分析   总被引：2，自引：0，他引：2  
Soil properties dramatically change after long-term greenhouse vegetable cultivation, which further affects soil selenium (Se) nutritional status and plant Se uptake. An evaluation of Se availability after long-term greenhouse vegetable cultivation (GVC) can help in better understanding its influential factors under GVC conditions and will also facilitate further regulation of soil Se nutrition in GVC systems. Two typical GVC bases were chosen: one with clayey and acidic soil in Nanjing, southern China, and the other with sandy alkaline soil in Shouguang, northern China. Twenty-seven surface soil samples at the Nanjing base and 61 surface soil samples at the Shouguang base were collected according to cultivation duration and cultivation intensity. Soil properties including soil available Se (PO43--Se) and total Se (T-Se) were analyzed. The results showed that soil PO43--Se was significantly and negatively correlated with soil Olsen-P, available K (A-K), and electrical conductivity (EC) at the Nanjing base. At the Shouguang base, however, no significant correlation was found between soil PO43--Se and Olsen-P and EC, and soil PO43--Se increased with increasing soil organic matter (OM). Intensively utilized greenhouse vegetable cultivation caused significant changes in soil properties and further affected soil Se availability. Due to different management practices, the dominant factors affecting Se availability varied between the two GVC bases. At the Nanjing base, the dominant influential factor on soil Se availability was soil nutritional status, especially Olsen-P and A-K status. At the Shouguang base, where organic fertilizers were applied at high rates, soil OM was the dominant influential factor.  相似文献   

13.
Laboratory incubation experiments were conducted to study the effects of soil chemical and physical properties on CH4 emission and entrapment in 16 selected soils with a pH range of 4.7–8.1, organic matter content of 0.72–2.38%, and soil texture from silt to clay. There was no significant correlation with CH4 emission for most of the important soil properties, including soil aerobic pH (measured before anaerobic incubation), total Kjeldahl N, cation exchange capacity, especially soil organic matter, and soil water-soluble C, which were considered to be critical controlling factors of CH4 emission. A lower CH4 emission was observed in some soils with a higher organic matter content. Differences in soil Fe and Mn contents and their chemical forms contributed to the this observation. A significant correlation between the CH4 emission and the soil organic C content was observed only after stratifying soils into subgroups according to the level of CH4 emission in soils not amended with organic matter. The results also showed that the soil redox potential (Eh), anaerobic pH, anerobic pH, and biologically reducible Fe and Mn affected CH4 emission significantly. Urea fertilization promoted CH4 emission in some soils and inhibited it in others. This result appeared to be related to the original soil pH. CH4 entrapment was positively correlated with soil clay content, indicating the importance of soil physical characteristics in reducing CH4 emissions to the atmosphere.  相似文献   

14.
Short-term incubation studies of non-symbiotic nitrogen fixation using acetylene as the substrate for nitrogenase were carried out on six soil samples collected from various locations in the Western State of Nigeria, and on one soil sample collected from Wisconsin, U.S.A. Unamended soils reduced a very small amount of acetylene but with added organic materials (5% organic matter, 2% glucose or sucrose) acetylene reduction became substantial and in one case was more than 30,000 times that in the unamended soil. In general, more acetylene was reduced in anaerobic than in aerobic soils. Two of the soils were tested for suppression of acetylene reduction by NH4+-N. With the addition of up to 100 ppm nitrogen as (NH4)2SO4 to the soils incubated with sucrose, no depression of acetylene reduction was observed in one soil while it was reduced by about half in the other.  相似文献   

15.
低硒土壤中75Se的形态转化   总被引：2，自引：0，他引：2  
李书鼎  张少兰 《土壤学报》1990,27(3):280-285
用75SeO2水溶液分别按0.131ppm和1.631ppm比例处理暗棕色森林土。用这种土壤盆栽的小麦含Se分别为0.023ppm和0.493ppm。小麦收获之后,对土壤残留的75Se用不同的提取剂连续进行化学分级,75Se的各种形态按其占土壤总Se的百分比大小排序为:同位素交换态Se>NH4OH可提态Se>HNO3可提态Se>HCl可提态硒>水溶态Se>K2SO4可提态硒。土壤残留75Se主要以NaHSeO3同位素交换态存在,其量占土壤总硒28%,NH4OH可提态Se次之,占20%;水溶态Se较少,仅6-7%。以SeO3-2形式加入土壤的75Se被土壤紧密吸附。  相似文献   

16.
Abstract

The extractant Mehlich‐1 is routinely used in Brazil for determination of soil nutrients, whereas Mehlich‐3 has been suggested as a promising extractor for soil fertility evaluation. Both were used for extraction of molybdenum (Mo) in Brazilian soils with Mo dosage by the KI+H2O2 method. The Langmuir and Freundlich isotherms were used to study soil Mo adsorption. Mehlich‐1 extracted more Mo than Mehlich‐3 in soils with high contents of organic matter, clay, and iron (Fe) oxides. Mehlich‐3 and Mehlich‐1 extractions correlated positively and significantly with amorphous Fe oxides, crystalline Fe oxides, and organic matter. Molybdenum recovering rates correlated to crystalline Fe oxides and clay contents but not to organic matter, pH, and Mo adsorption capacity. Amorphous and crystalline Fe oxides, clay, and organic matter were responsible for most of the Mo adsorption. The Langmuir isotherm described better the Mo adsorption to soil amorphous Fe oxides and organic matter than the Freundlich isotherm.  相似文献   

17.
Two soils, one a sandy loam and the other of relatively high clay content, were incubated with [14C(U)]gtucose and [15N](NH4)2SO4 for 101 days, either under continuously moist conditions, or with intermittent drying of soils. Rates of evolution of 14CO2, decline in residual organic 14C, and net immobilization and mineralization of N and 15N in the sandy loam soil were more rapid than in the clay soil. First order decay rates for the decomposition of residual 14C, after 10 days, were consistently twice as fast in the sandy loam soil. By contrast, the efficiency with which glucose was utilized within the first few days, and the amounts of C, 14C, N and 15N present as soil biomass throughout the incubation, were greater in the clay soil than in the sandy loam. Biomass 14C as a percentage of residual organic 14C, was consistently 1.5 times greater in the clay soil. Compared with soils held continuously moist, soils which were intermittently dried and remoistened contained smaller amounts of isotope-labelled biomass C and N, but overall similar amounts of total residual organic 14C and 15N. Remoistening of dried soils caused a temporary (4 days) flush in C and N mineralization rates.A simulation model describes C and N behaviour in the two soils. Three features of the model are proposed to expain short-term differences between soils in the rates of C and N turnover, viz. the clay soil (a) has a greater capacity to preserve biomass C and N (b) holds a higher proportion of microbial decay products in the near vicinity of surviving cells, and, to a lesser extent, (c) utilizes glucose and metabolic products more efficiently for biosynthetic reactions.  相似文献   

18.
Twenty-four soils were sampled from northwestern China to study the relations of fixed or nonexchangeable ammonium (NH4) determined by the widely used Silva–Bremner method and the simplest ignition Mogilevkina method with organic matter (OM), total nitrogen (N), and soil particle composition. Results showed that the averaged values of 24 soils determined by the Silva–Bremner method were 10.7% greater than those using the Mogilevkina method, and the standard deviations of the Mogilevkina method were larger than those of the Silva–Bremner method. There was a close correlation in the fixed NH4 between the two methods (R2?=?0.7831, n?=?24). The low values obtained by the Mogilevkina method were not due to the heat treatment because there was almost no difference in results between heating for 44 and 72 h. Soil OM had no correlation with the fixed NH4 amounts determined by the two methods due to self-correlations, but total N had significantly weak correlations. The soils sampled from northwestern China were dominant in the 2:1 type of clay minerals, and significant correlations were found for the fixed NH4 amounts determined by the two methods with clay as well as with clay plus silt contents. Correlations (R2) of the fixed NH4 by the Silva–Bremner method were 0.4545 and 0.3145 with clay and clay plus silt contents, respectively, for the initial soils and 0.4765 and 0.446, respectively, for soils after ryegrass planting, which were much greater than those of the Mogilevkina method. Based on the definition of fixed NH4 and the problem that occurred during its determination, two criteria were proposed for evaluation of the methods: (1) the relationship between clay content or clay plus silt contents and fixed NH4 and (2) the correlation of OM content with fixed NH4. By these criteria, the Silva–Bremner method was superior to the Mogilevkina method in terms of reliability and accuracy.  相似文献   

19.
Very few studies have been related to soluble organic nitrogen (SON) in forest soils. However, this nitrogen pool could be a sensitive indicator to evaluate the soil nitrogen status. The current study was conducted in temperate forests of Thuringia, Germany, where soils had SON (extracted in 0.5 M K2SO4) varying from 0.3 to 2.2% of total N, which was about one-third of the soil microbial biomass N by CFE. SON in study soils were positively correlated to microbial biomass N and soil total N. Multiple regression analysis also showed that mineral N negatively affected SON pool. The dynamics of the SON was significantly affected by mineralization and immobilization. During the 2 months of aerobic incubation, the SON were significantly correlated with net N mineralization and microbial biomass N. SON extracted by two different salt solution (i.e. 1 M KCl and 0.5 M K2SO4) were highly correlated. In mineral soil, SON concentrations extracted by 1 M KCl and 0.5 M K2SO4 solutions were similar. In contrast, in organic soil layer the amount of KCl-extractable SON was about 1.2-1.4 times higher than the K2SO4-extractable SON. Further studies such as the differences of organic N form and pool size between SON and dissolved organic N (DON) are recommended.  相似文献   

20.
Summary The dynamics of basally applied 15N-labeled ammonium sulfate in inorganic and organic soil fractions of five wetland rice soils of the Philippines was studied in a greenhouse experiment. Soil and plant samples were collected and analyzed for 15N at various growth stages. Exchangeable NH4 + depletion continued after 40 days after transplanting (DAT) and corresponded with increased nitrogen uptake by rice plants. Part of the applied fertilizer was fixed by 2:1 clay minerals, especially in Maligaya silty clay loam, which contained beidellite as the dominant clay mineral. After the initial fixation, nonexchangeable 15N was released from 20 DAT in Maligaya silty clay loam, but fixation delayed fertilizer N uptake from the soil. Part of the applied N was immobilized into the organic fraction. In Guadalupe clay and Maligaya silty clay loam, immobilization increased with time while the three other soils showed significant release of fertilizer N from the organic fraction during crop growth. Most of the immobilized fertilizer N was recovered in the nondistillable acid soluble (alpha-amino acid + hydrolyzable unknown-N) fraction at crop maturity. Between 61% and 66% of applied N was recovered from the plant in four soils while 52% of fertilizer N was recovered from the plant in Maligaya silty loam. Only 20% – 30% of the total N uptake at maturity was derived from fertilizer N. Nmin (mineral N) content of the soil before transplanting significantly correlated with N uptake. Twenty-two to 34% of applied N was unaccounted for possibly due to denitrification and ammonia volatilization.  相似文献   

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