Can P NMR spectroscopy be used to indicate the origins of soil organic phosphates?

The relationship between organic P status of 4 soils, 20 microorganisms isolated from these soils (2 bacteria and 3 fungi for each soil) and 13 dominant plant species of typical natural ecosystems of these soils was evaluated. The soils used were represented by two pairs with different ratios of monoester and diester P, and of DNA and other diester P. A Dystric Podzoluvisol and an alpine Umbric Leptosol were characterized by a relatively high proportion of diester P including much DNA P, while a Calcic Chernozem and subalpine Umbric Leptosol had lower proportion of diesters containing relatively less DNA P. The proportions of P compounds in bacteria and plants were very similar on average, based on the monoester to diester P ratio and on the proportions of different diesters in alkaline extract, whereas fungi contained considerably higher proportions of monoesters and polyphosphates, and a higher proportion of phospholipids in the diester fraction. The results showed that the P_org composition of NaOH extracts from different soils was more similar to the composition of extracts from different groups of microorganisms. There was no clear correspondence between soil and microbial diester P proportion and composition. A high proportion of polyphosphate P including pyrophosphate P in soil extracts indicates a significant contribution of fungal P compounds in the soil while the monoester to diester P ratio, and DNA to non-DNA P ratio should be used with caution to interpret the origins of soil P_org. The relative contributions of microorganisms and plants to monoester and diester P in soils is only partially understood.     

Mineralisation of <Superscript>15</Superscript>N-labelled sheep manure in soils of different texture and water contents

In order to investigate the effect of soil water and texture on C and N mineralisation of applied organic matter, sheep manure was sandwiched between two halves of intact soil cores and incubated at 20°C. The soils contained 10.8% (L1), 22.4% (L3) and 33.7% (L5) clay, respectively, and were drained to seven different matric potentials in the range -15 to -1,500 hPa. Evolution of CO₂-C was determined during 4 weeks of incubation. Contents of NO₃^--N, ¹⁵N and microbial biomass N were determined at the end of the incubation. The net release of CO₂-C from the manure (estimated as the difference between soils with and without manure) and the total CO₂-C evolution from soils with manure was not related to soil water content. Most CO₂-C evolved from manure-amended soils in the least clayey L1 soil. The manure caused immobilisation of soil NO₃^--N but the soil matric potential had no major effects on the net NO₃^--N production. Less than 1% of the manure ¹⁵N was found as NO₃^--N at the end of the incubation. When unamended, the sandy L1 soil held the least N in microbial biomass but the largest increases in biomass N caused by manure application were found in this soil. Despite the higher increases in microbial biomass N in the L1 soil, the total content of microbial biomass N in soils with manure application peaked in the most clayey soil (L5). The recovery of manure ¹⁵N at the end of the incubation ranged from 89% to 102%. The variation in ¹⁵N recovery was not related to soil clay content nor to soil matric potential. The experimental set-up was designed to mimic field conditions where manure is left as a discrete layer surrounded by structurally intact soil. In this situation the soil clay content and the soil water level appeared to have little influence on the C and N turnover in the manure layer.     

Kinetics of microbial phosphorus uptake in cultivated soils

Knowledge about the role of microorganisms in P cycling at conditions of constant soil respiration rates and constant size of microbially bound P is lacking. To study the kinetics of microbial P uptake and cycling under such conditions, soils differing in biological activity were ³³PO₄ labelled by introducing a carrier-free tracer solution and incubated for 56 days. The ³³PO₄ incorporation into the fraction of microbial P releasable by chloroform treatment (P_chl) was assessed and the isotopic composition [=specific activity (SA); SA=³³PO₄/³¹PO₄] of P_chl and soil solution P compared. Soils were taken from a 20-year-old field experiment including a non-fertilised control (NON), a minerally fertilised conventional (MIN) and two organic farming systems [bio-organic (ORG); bio-dynamic (DYN)]. Tracer P incorporation continuously increased during incubation in DYN, ORG and MIN soils. It decreased in the order DYN>ORG>MIN, with differences in ³³PO₄ uptake between the farming systems being higher than suggested by the differences in the amount of P_chl. In the P-deficient NON soil, the highest initial incorporation of tracer P was found, but no additional uptake could be detected thereafter. In all soils, the SA of P_chl converged to the SA of the soil solution with increasing time. Since P_chl remained almost constant during the experiment, the findings suggest an intensive uptake of P from the soil solution into P_chl and concomitant release of P back to the soil solution and, thus, a rapid cycling through P_chl. Intensive P cycling between P_chl and the soil solution was confirmed in an additional experiment where microbial activity was stimulated by glucose and N additions.     

Organic matter extracted with 0.01 M CaCl2 or with 0.01 M NaHCO3 as indices of N mineralisation and microbial biomass

A pot experiment was carried out with three soils at ambient temperature in which temporal changes in fractions of soil organic matter that were extractable with either 0.01 M CaCl₂ or 0.01 M NaHCO₃ were compared with changes in N mineralisation and microbial biomass C. UV spectral analysis of soil extracts was also carried out on sub-samples taken at the beginning of the experiment. The objective was to quantify the fractions of extractable soil organic matter and determine whether these could be used to estimate the mineralisable organic N content of the soils. The results suggested that part of the NaHCO₃-extractable organic matter originated in the microbial biomass but that non-biomass material was also present. The non-biomass material was not identified directly, but was composed of compounds with high UV absorbance. In the case of CaCl₂, the results suggested that extracellular proteins were contained in the extract and that some material released from the actively growing microbial biomass may also have been present. A supplementary study with 16 soils was carried out to determine the ability of the organic matter solubilised by either extractant to predict soil N uptake by barley seedlings. A significant relationship (P<0.01) was found between N uptake and CaCl₂-extractable material only.     

Decomposition of carbon-14-labelled wheat straw in repeatedly fumigated and non-fumigated soils with different levels of heavy metal contamination

We analysed the decomposition of ¹⁴C-labelled straw at five different levels of heavy metal contamination (100-20,000 µg total Zn g^-1 soil) in non-fumigated and repeatedly fumigated soils. The soils were not spiked with Zn, but were taken from sites containing different heavy metal concentrations. Zn was only used as a reference and the effects observed are most likely due to this metal. Microbial biomass decreased with increasing heavy metal content of soils, paralleled generally by the decreasing amount of wheat straw ¹⁴C incorporated into the microbial biomass. In addition, the newly synthesised microbial biomass declined more rapidly as the incubation proceeded. In the repeatedly fumigated soils, microbial biomass ¹⁴C corresponded to roughly 50% of the maximum ¹⁴C incorporation of the non-fumigated soil. The relative decline during incubation was similar to that of the non-fumigated soil at the respective contamination level. These results reveal clearly that heavy metal effects on straw decomposition do not depend on the ratio of substrate C to microbial biomass C. In contrast to microbial biomass C, the mineralisation of the wheat straw was not seriously affected by heavy metal contamination. The same was true for all of the repeatedly fumigated treatments, where a much smaller microbial biomass mineralised nearly the same amount of straw as in the non-fumigated soils. However, repeated fumigation caused a strong reduction in the decomposition of soil organic matter. The ratio of CO₂-¹⁴C to microbial biomass ¹⁴C after 60 days was linearly related to the Zn concentration in both non-fumigated and repeatedly fumigated samples, clearly indicating that an additional energy cost is required by soil microorganisms with increasing heavy metal concentrations.     

Phosphorus fractions and phosphorus delivery potential of a luvisol derived from loess amended with organic materials

In a long-term field experiment, started in 1962, the fate of P applied with different organic materials [farmyard manure (FYM), compost and sewage sludge] in comparison to mineral fertilizer was investigated. Soil samples were collected after 38 years' continuous addition of these amendments to a luvisol derived from loess and cultivated to a cereal-root crop sequence. The total P (P_t) content of all treatments increased compared with the original soil; NaOH-inorganic P (NaOH-P_i) representing Fe- and Al-bound P was the dominant inorganic fraction. At the beginning of the experiment the various P pools could be quantitatively ranked in the following order: NaOH-P_i>residual P~NaHCO₃-P_i>H₂O-P>HCl-P. The order changed as follows: NaOH-P_i>NaHCO₃-P_i>residual P~H₂O-P>HCl-P, with transformations of non-labile residual P to the labile NaHCO₃-P_i pool with continued P fertilization and cropping. In addition, the content of organic P (P_o) forms (NaOH-P_o and NaHCO₃-P_o) increased. P_t delivery potential (desorbable P pool) increased between 35% and 185% compared to the P delivery potential in 1962. Compared to mineral fertilizer application, the application of organics resulted in a significantly higher, and FYM in a lower, P adsorption capacity of soils. The calcium lactate-extractable P (plant-available P) increased from 43.1 mg kg^-1 soil in 1962 to 175.9 mg kg^-1 soil in the treatment with 49 t compost ha^-1. The increase in the citrate-dithionate Fe-O ranged between 44% and 154% in the different treatments compared to the Fe-O content in 1962. In a pot experiment with soil from the field experiment, P removal by ryegrass was in the following sequence: FYM>compost=sewage sludge>mineral fertilizer.     

Ecological assessment of soils in high-mountain landscapes of northeastern part of the Greater Caucasus (Azerbaijan)

The current state of soils and bioproductivity of high-mountain pastures and hayfields in the northeastern part of Great Caucasus within Azerbaijan were studied, and the quality assessment of soils was performed. The ecological evaluation of soils was based on special assessment scales and soil bonitet scores. The soils suitable for the development of meadow vegetation were identified. The highest score (89 points) was given to mountainous meadow chernozemlike soils (Eutric Mollic Leptosols); these soils are most suitable for pasturing. Mountainous meadow soddy soils (Dystric Umbric Leptosols) ranked second (76 points). Mountainous meadow-steppe soils (Eutric Mollic Leptosols) were estimated at 72 points; these soils are suitable for plant communities of subalpine meadows. Mountainous meadow soddy–peaty soils (Brunic Umbric Leptosols) had the lowest score of 68 points mostly because of the excessive precipitation against the background of relatively low mean annual temperature limiting the biological productivity of alpine meadows.     

Influence of soil parameters on the effect of 3,4-dimethylpyrazole-phosphate as a nitrification inhibitor

Nitrification inhibitors specifically retard the oxidation of NH₄⁺ to NO₂^- during the nitrification process in soil. In this study, the influence of soil properties on the nitrification-inhibiting effect of 3,4-dimethylpyrazole-phosphate (DMPP), a newly developed nitrification inhibitor, has been investigated. Based on short-term incubation experiments, where the degradation of DMPP could be largely disregarded, the oxidation of the applied NH₄⁺ was more inhibited in sandy soils compared with loamy soils. The influence of soil parameters on the relative NO₂^- formation could be described by a multiple regression model including the sand fraction, soil H⁺ concentration and soil catalase activity (R²=0.62). Adsorption studies showed that the binding behaviour of DMPP was influenced markedly by soil textural properties, viz. the clay fraction (r²=0.61). The adsorption of DMPP was found to be an important factor for the inhibitory effect on NH₄⁺ oxidation in a short-term incubation (r²=0.57). It is concluded that the evaluated soil properties can be used to predict the short-term inhibitory effect of DMPP in different soils. The significance of these results for long-term experiments under laboratory and field conditions needs further investigation.     

Amitrole degradation in vineyard soils in relation to pedo-climatic conditions

The fate of [¹⁴C]-amitrole herbicide was studied in eight soils having different capacities for amitrole mineralisation. Laboratory incubations were run combining different experimental conditions: temperature (4, 28 and 50°C), soil moisture (50, 100 and 150% of soil water holding capacity) and microbial activity (sterile and non-sterile conditions). During incubation, samples of the soils were periodically extracted with 0.5 M NH₄OH and extracts were analysed by HPLC. The lengths of time needed for 50% dissipation of amitrole (DT50) in soils ranged from less than 1 day to more than 70 days. Amitrole mineralisation occurred only in non-sterile soils, showing that it is a biological process. Mineralisation was lower in soils with a coarse texture than in soils with a fine texture. Soil water content had little influence on the total amount of amitrole mineralised at the end of incubation. Temperature had a greater influence on mineralisation, although rates were still high at low and high temperatures. In non-sterile as in sterile soils, the major product detected in the extracts was amitrole. Additional non-identified radioactivity was occasionally extracted. However, it never represented more than 10% of initially applied amitrole. Non-extractable residues represented less than 15% of applied radioactivity in acidic soils and about 30% of applied radioactivity in alkaline and neutral soils. The amount of non-extractable radioactivity formed was enhanced in sterile as compared to non-sterile soils. Furthermore, in sterile soils, high temperature induced an increase of non-extractable residues, showing that amitrole is chemically quite reactive.     

Transformation and bioavailability of specifically sorbed phosphate on variable-charge minerals in soils

Crop production on red soils in China is largely limited by the low availability of phosphorus, which is frequently attributed to the adsorption of phosphate by variable-charge minerals including Fe and Al oxides and kaolinite. Isotopic tracing analysis and soil incubation were carried out to investigate the desorption and microbial transformation of applied specifically sorbed P in two pH-contrasting light-textured soils. A rapid release of P from the added mineral-P surface complex in the two tested soils was observed. Most of the released P was recovered in a 0.5MNaHCO₃ extract and in soil microbial biomass. Microbial biomass-³²P was detected at early stages of incubation and reached up to 10–30% of the added ³²P. Approximately 50–70% of the added complex ³²P, varying between minerals and soils, was extractable in the 0.5MNaHCO₃ at 75 days after incubation for the acid soil but up to 120 days for the neutral soil. Microbial biomass-P plus 0.5MNaHCO₃-extractable ³²P accounted for more than 60–80% of total added complex-³²P, implying high desorption and transformation of the specifically sorbed P in the two soils. There was more inorganic ³²P than organic ³²P in the NaHCO₃ extract, suggesting that chemical release of specifically sorbed P was dominant. Ligand exchange and chemical desorption due to a change in environmental conditions such as pH and ionic strength are likely the major mechanisms responsible for the chemical release of specifically sorbed ³²P in the tested soils. Received: 29 September 1996     

Effects of temperature, soil water status, and soil type on swine slurry nitrogen transformations

Manure N dynamics are affected by manure characteristics, soil factors, and environmental conditions. An incubation experiment was conducted to assess the relationship of these factors. The effects of temperature (11, 18, and 25°C), soil texture (three soils, silt loam to sandy loam), and soil water status (constant at 60% water filled pore space, WFPS, and fluctuating between 30% and 60% WFPS) on net mineralization and nitrification of swine manure N were assessed. Swine manure was applied at an equivalent rate of 350 kg total N ha^-1 to 250 g air-dry soil in 2-l canning jars. Subsamples were taken from each jar for NO₃^- and NH₄⁺ determination when fluctuating moisture treatment dried to 30% WFPS, with sampling continuing through four wet-dry cycles at each temperature. Manure NH₄⁺ was rapidly nitrified to NO₃^-. The relationship between NO₃^- accumulation and degree days after application (DDAA, 0°C base) could be described across temperatures using a single pool exponential model for each soil. More NO₃^- accumulated in coarser-textured soils (150-200 mg N kg^-1 soil), compared to 130 mg N kg^-1 soil in the silt loam soil. Fluctuating soil water status did not alter estimates of rate and extent of NO₃^- accumulation, but slowed NH₄⁺ disappearance somewhat.     

Effects of nitrogen fertilization on soil nitrogen pools and microbial properties in a hoop pine (Araucaria cunninghamii) plantation in southeast Queensland, Australia

A field study was conducted to investigate the effects of N fertilization on soil N pools and associated microbial properties in a 13-year-old hoop pine (Araucaria cunninghamii) plantation of southeast Queensland, Australia. The treatments included: (1) control (without N application); (2) 300 kg N ha^-1 applied as NH₄NO₃; and (3) 600 kg N ha^-1 as NH₄NO₃. The experiment employed a randomized complete block design with four replicates. Soil samples were taken approximately 5 years after the N application. The results showed that application of 600 kg N ha^-1 significantly increased concentrations of NH₄⁺-N in 0-10 cm soil compared with the control and application of 300 kg N ha^-1. Concentrations of NO₃^--N in soil (both 0-10 cm and 10-20 cm) with an application rate of 600 kg N ha^-1 were significantly higher compared with the control. Application of 600 kg N ha^-1 significantly increased gross N mineralization and immobilization rates (0-10 cm soil) determined by ¹⁵N isotope dilution techniques under anaerobic incubation, compared with the control. However, N application did not significantly affect the concentrations of soil total C and total N. N application appeared to decrease microbial biomass C and N and respiration, and to increase the metabolic quotient (qCO₂) in 0-10 cm soil, but these effects were not statistically significant. The lack of statistical significance in these microbial properties between the treatments might have been associated with large spatial variability between the replicate plots at this experimental site. Spatial variability in soil microbial biomass C and N was found to relate to soil moisture, total C and total N.     

Nitrification and denitrification as sources of atmospheric nitrous oxide – role of oxidizable carbon and applied nitrogen

Laboratory incubation experiments were conducted to study the influence of easily oxidizable C (glucose) and mineral N (NH₄⁺ and NO₃^-) on N₂O emission, evolution of CO₂ and consumption of O₂. A flush of N₂O was always observed during the first few hours after the start of soil incubation, which was significantly higher with NH₄⁺ compared to NO₃^- applications. The increase in N₂O emission was attributed mainly to enhanced soil respiration and subsequent O₂ limitation at the microsite level. Application of NH₄⁺ helped to develop denitrifying populations since subsequent additions of NO₃^- and a C source significantly enhanced N₂O emissions. In soils treated with NH₄⁺, N₂O emissions declined rapidly, which was related to decreasing concentrations of easily oxidizable C. Addition of glucose in different amounts and pre-incubation of soil for different lengths of time (to create variation in the amount of easily oxidizable C) changed the pattern of N₂O emissions, which was ascribed to changes in soil respiration.     

Effect of cadmium contamination with sewage sludge and phosphate fertiliser amendments on soil enzyme activities, microbial structure and available cadmium

The effect of Cd pollution (50 mg kg^-1), with and without sewage sludge (Sw) and PO₄^3- fertiliser (P) addition, on soil biochemical activity and available Cd was assessed in a 112-day soil incubation experiment. The availability of Cd decreased with incubation time and was reduced by the Sw and P additions resulting in the following order of treatments: Cd>P+Cd>Sw+Cd. With the exception of urease and N-acetylglucosaminidase activities, all enzyme activities were negatively correlated with available Cd. The total culturable bacterial population was significantly higher with the addition of Sw alone than in the control during the incubation period (P<0.05). The number of fluorescent pseudomonads decreased with time, but was significantly increased by the addition of Sw. The total fungal populations decreased with time in all treatments, whilst the addition of Sw and PO₄^3- fertilisers relatively increased the fungal population. Addition of Sw in the presence of Cd increased the fungal populations in relation to the addition of Cd alone. The results support the view that Cd contamination has a large detrimental effect on nutrient cycling and microbial activity and that the effects of Cd are reduced by P and Sw additions.     

Mitigation of N2O emission from an alluvial soil by application of karanjin

An incubation experiment was conducted to study N₂O emissions from a Typic Ustochrept, alluvial soil, fertilized with urea and urea combined with different levels of two nitrification inhibitors, viz karanjin and dicyandiamide (DCD). Karanjin [a furano-flavonoid, obtained from karanja (Pongamia glabra Vent.) seeds] and DCD were incorporated at rates of 5, 10, 15, 20 and 25% of applied urea-N (100 mg kg^-1 soil), to the soil adjusted to field capacity moisture content. The highest N₂O flux (366 µg N₂O-N kg^-1 soil day^-1) was obtained on day 1 after incubation from soil fertilized with urea without any inhibitor. The presence of the inhibitors appreciably reduced the mean N₂O flux from the urea-treated soils. The application of karanjin resulted in a higher mitigation of total N₂O-N emission (92-96%) compared to DCD (60-71%). Rates of N₂O flux ranged from 0.9 to 140 µg N₂O-N kg^-1 soil day^-1 from urea combined with different levels of the two inhibitors (coefficient of variation=24-272%). Karanjin (62-75%) was also more effective than DCD (9-42%) in inhibiting nitrification during the 30-day incubation period.     

Effects of earthworms on Zn fractionation in soils

Laboratory incubation experiments were conducted to examine the effect of earthworm (Pheretima sp.) activity on soil pH, zinc (Zn) fractionation and N mineralization in three soils. No Zn uptake by earthworms was observed. Zinc addition decreased pH of red soil (soil 1) and hydragric paddy soil (soil 3) by 0.5 and 0.2 unit, respectively, but had no effect on alluvial soil (soil 2). The effect of Zn on soil pH was possibly due to a specific adsorption mechanism between Zn and oxides. Earthworm activity significantly decreased the pH of the red soil, a key factor affecting Zn solubility, but not of the other two soils. Earthworm activity significantly increased DTPA-Zn (DTPA-extractable) and OxFe-Zn (NH₂OH-HCl-extractable) in the red soil, but had little effect on other fractions. In the alluvial soil, earthworm activity significantly increased OxFe-Zn but decreased organic-Zn (organic-associated Zn). In the hydragric paddy soil, earthworm activity significantly increased MgCl₂-Zn (MgCl₂-extractable) and organic-Zn. The level of CaCl₂-extractable Zn in all three soils was not affected by earthworm activity. Nitrogen mineralized as a result of earthworm activity was equivalent to 110, 120 and 30 kg N ha^-1 in soils 1, 2 and 3, respectively. Zinc added at rates less than 400 mg Zn kg^-1 did not seem to affect the activity of N-mineralizing microorganisms. The present results indicated the possibility of increasing the metal bioavailability of relatively low level metal-contaminated soils, with a higher organic matter content, by earthworm inoculation.     

Effect of long-term fertiliser use on acid and alkaline phosphomonoesterase and phosphodiesterase activities in managed grassland

Soil phosphatase activities play an important role in the mineralisation of soil phosphorus (P). In this study acid and alkaline phosphomonoesterase and phosphodiesterase activities of soils under long-term fertiliser management (ca. 100 years) were measured to determine the effects of fertiliser inputs on the cycling and availability of P. Enzyme activities were compared with microbial biomass P, determined by fumigation-extraction, and with extractable P using NH₄F-HCl. Experimental plots were divided into three groups: those receiving farm-yard manure (FYM), those receiving mineral P and those receiving no P amendment. Plots receiving FYM had the highest extractable P values and the greatest enzyme activities. There was no obvious relationship between extractable P and microbial biomass P except in those plots where no P was added (r²=0.778), emphasising the importance of fertiliser management in P dynamics in soils. Acid phosphomonoesterase activity was high in all plots, including those where microbial biomass P levels were low. This supports the findings of previous studies suggesting that acid phosphomonoesterase activity in soils is primarily of root origin. All phosphatase enzyme activities were significantly correlated with extractable P in plots receiving mineral P. This relationship was negative for acid phosphomonoesterase activity (r²=-0.947), suggesting that acid phosphomonoesterase activity is suppressed by extractable P in managed grasslands receiving mineral P fertilisers.     

元素硫和双氰胺对菜地土壤铵态氮硝化抑制协同效应研究

采用好气培养法,研究了双氰胺（DCD）、元素硫（S0）和元素硫分解中间物（S2O32-）及其组合对蔬菜地土壤氮素硝化抑制作用。结果表明,在培养试验72 d内,DCD+S0、DCD、DCD+ Na2S2O3处理土壤NH4+-N总量分别是N处理的5. 8、5.1、5.9倍;S0、Na2S2O3处理分别是N处理的1.8、1.4倍;而所有硝化抑制剂（DCD、S0、S2O32-）处理土壤NO3--N含量显著低于N处理,表明DCD、S0和S2O32-均能抑制菜地土壤铵态氮硝化。培养试验开始8 d后,Na2S2O3和DCD对铵态氮硝化抑制产生协同效应,16 d后S0和DCD对铵态氮硝化抑制也产生协同效应,这可能是由于S0 氧化中间体S2O32-、S4O62-具有抑制DCD降解作用,延长了DCD硝化抑制作用时间。建议蔬菜生产上推荐使用DCD+S0组合,以提高氮素利用率。     

Organic phosphorus species in humic acids of mountain soils along a toposequence in the Northern Caucasus

Organic P was investigated in humic acids extracted from mountain soils developed in the subalpine, upper subalpine and alpine zones of the Northern Caucasus. P contents of humic acids varied between 3.4 and 14.2 g P kg^?1, depending on P contents of the parent vegetation and on site conditions. Organic P was accumulated at sites where microbial activity is restrained due to soil acidity, low soil temperature and hydromorphy.³¹ P NMR spectroscopy revealed that orthophosphate monoesters were the dominent P species (72–85% of extract- able P), orthophosphate diesters amounted to 12–21%, and phospho- nates ranged between 0 and 9%. Humic acids of soils under cold and wet climatic conditions showed highest concentrations in phospho- nates and orthophosphate diesters. Hence, the accumulation of organo-P in the Caucasian mountain soils was partly due to increasing proportions of potentially available organic P species.     

施用不同种类氮肥对日光温室土壤溶液离子组成的影响

采用土培模拟试验研究了施用不同量的尿素[CO(NH2)2]、碳酸氢铵（NH4HCO3）、硫酸铵[(NH4)2SO4]对培养期间日光温室土壤溶液电导率（EC）和不同离子组成及比例的影响。结果表明,不同氮肥种类对土壤溶液电导率（EC）的影响主要表现在培养的前一周左右,之后不同品种间无明显差异。土壤溶液中NO3--N含量随施氮量和培养时间呈明显的上升趋势,不同氮肥种类NO3--N含量无明显差异;不同氮肥种类处理土壤溶液中NH4+-N含量在培养的前7 d有所差异,之后亦无差异。随着氮肥施用量的增加,日光温室土壤溶液的EC及K+、Na+、Ca2+、Mg2+离子的浓度升高;增施氮肥同时提高了土壤溶液中Ca/K、Mg/K的比值,而对土壤溶液钾的活度比（ARK）无显著影响。说明氮肥施用量是影响土－液界面离子交换的重要因素;由此带来的日光温室土壤盐分累积以及K+、Na+、Ca2+和Mg2+离子的淋失等问题值得关注。