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1.
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2.
The dominant pools of C and N in the terrestrial biosphere are in soils, and understanding what factors control the rates at which these pools cycle is essential in understanding soil CO2 production and N availability. Many previous studies have examined large scale patterns in decomposition of C and N in plant litter and organic soils, but few have done so in mineral soils, and fewer have looked beyond ecosystem specific, regional, or gradient-specific drivers. In this study, we examined the rates of microbial respiration and net N mineralization in 84 distinct mineral soils in static laboratory incubations. We examined patterns in C and N pool sizes, microbial biomass, and process rates by vegetation type (grassland, shrubland, coniferous forest, and deciduous/broadleaf forest). We also modeled microbial respiration and net N mineralization in relation to soil and site characteristics using structural equation modeling to identify potential process drivers across soils. While we did not explicitly investigate the influence of soil organic matter quality, microbial community composition, or clay mineralogy on microbial process rates in this study, our models allow us to put boundaries on the unique explanatory power these characteristics could potentially provide in predicting respiration and net N mineralization. Mean annual temperature and precipitation, soil C concentration, microbial biomass, and clay content predicted 78% of the variance in microbial respiration, with 61% explained by microbial biomass alone. For net N mineralization, only 33% of the variance was explained, with mean annual precipitation, soil C and N concentration, and clay content as the potential drivers. We suggest that the high R2 for respiration suggests that soil organic matter quality, microbial community composition, and clay mineralogy explain at most 22% of the variance in respiration, while they could explain up to 67% of the variance in net N mineralization.  相似文献   

3.
《Soil biology & biochemistry》1997,29(8):1215-1223
The contribution of soil macroorganic matter N (macro-OM, d < 1.0 g cm−3) to gross rates of N mineralization was examined in two grassland field soils in England using three 15N-labelling techniques, referred to as the difference, mirror image and net recovery methods. The difference method involved measuring gross mineralization rates in soils with or without incorporated unlabelled macro-OM, using isotope dilution of added 15NH4+. The mirror image approach involved measuring the isotopic enrichment of the ammonium pool in soil to which 15N-labelled macro-OM had been incorporated. The net recovery method was a net N mineralization estimate based upon the recovery of label in plants and soil to which 15N-labelled macro-OM had been incororated. The difference method provided the most accurate estimates of N mineralization from the incorporated macro-OM. Estimates made using the direct and net recovery methods were more variable and confounded by movement of the macro-OM away from the original site of incorporation. Approximately 2.4 and 13.7% of the N in the incorporated macro-OM isolated from the different soils was mineralized over the 66 d following incorporation. This represented approximately 3.4 and 2.3% of the cumulative gross N mineralization when corrected for background amounts of soil macro-OM. This low contribution suggests that most of the N mineralized in grazed grasslands is derived from other forms of soil organic matter associated with mineral particles.  相似文献   

4.
In temperate forest soils, N net mineralization has been extensively investigated during the growing season, whereas N cycling during winter was barely addressed. Here, we quantified net ammonification and nitrification during the dormant season by in situ and laboratory incubations in soils of a temperate European beech and a Norway spruce forest. Further, we compared temperature dependency of N net mineralization in in situ field incubations with those from laboratory incubations at controlled temperatures. From November to April, in situ N net mineralization of the organic and upper mineral horizons amounted to 10.9 kg N (ha · 6 months)–1 in the spruce soil and to 44.3 kg N (ha · 6 months)–1 in the beech soil, representing 65% (beech) and 26% (spruce) of the annual above ground litterfall. N net mineralization was largest in the Oi/Oe horizon and lowest in the A and EA horizons. Net nitrification in the beech soil [1.5 kg N (ha · 6 months)–1] was less than in the spruce soil [5.9 kg N (ha · 6 months)–1]. In the range of soil temperatures observed in the field (0–8°C), the temperature dependency of N net mineralization was generally high for both soils and more pronounced in the laboratory incubations than in the in situ incubations. We suggest that homogenization of laboratory samples increased substrate availability and, thus, enhanced the temperature response of N net mineralization. In temperate forest soils, N net mineralization during the dormant season contributes substantially to the annual N cycling, especially in deciduous sites with large amounts of litterfall immediately before the dormant season. High Q10 values of N net mineralization at low temperatures suggest a huge effect of future increasing winter temperature on the N cycle in temperate forests.  相似文献   

5.
N mineralization capacity and its main controlling factors were studied in a large variety (n=112) of native (forest, bush) and agricultural (pasture, cultivated) soils from several climatic zones in Spain. The available inorganic N content, net N mineralization, and net N mineralization rate were determined after 6 weeks of aerobic incubation. NH inf4 sup+ –N largely predominated over NO inf3 sup- -N (ratio near 10:1) except in some agricultural soils. Net N mineralization predominated (83% of soils) over net N immobilization, which was more frequent in agricultural soils (25%) than in native soils (9%). In forest soils, both net N mineralization and the net N mineralization rate were significantly higher than in the other soil groups. The net N mineralization rate of pasture and cultivated soils was similar to that of bush soils, but available inorganic N was lower. The net N mineralization rate decreased in the order: soils over acid rocks>soils over sediments>soils over basic rocks or limestone; moreover, the highest net N mineralization and available inorganic N were found in soils over acid rocks. The highest N mineralization was found in soils with low C and N contents, particularly in the native soils, in which N mineralization increased as the C:N ratio increased. N mineralization was higher in soils with a low pH and base saturation than in soils with high pH and base saturation values, which sometimes favoured N immobilization. Soils with an Al gel content of >1% showed lower net N mineralization rates than soils with Al gel contents of <1%, although net N mineralization and available inorganic N did not differ between these groups. The net N mineralization rate in silty soils was significantly lower than in sandy and clayey soils, although soil texture only explained a low proportion of the differences in N mineralization between soils.  相似文献   

6.
A comparative study was conducted to determine the NH4^＋ and NO3^- concentrations in soil profiles and to examine the net nitrogen （N） mineralization and nitrification in adjacent forest, grassland, and cropland soils on the Tibetan Plateau. Cropland soil showed significantly higher inorganic N concentrations in soil profiles compared with forest and grassland soils. NO3^- -N accounted for 70%-90^ of inorganic N in cropland soil, while NH4^＋ -N was the main form of inorganic N in forest and grassland soils. The average net N mineralization rate at 0 20 cm depth was approximately twice in cropland soil （1.48 mg kg^-1 d^-1） as high as in forest （0.83 mg kg^-1 d^-1） or grassland soil （0.72 mg kg^-1 d^-1）. Cropland showed strong net nitrification, with the net rate almost equal to the total net N mineralization. Urea addition stimulated soil respiration, particularly in forest soil. Most urea-N, however, remained as NH4^＋ in forest and grassland soils, while NO3^- was the main form of inorganic N to increase in cropland soil. Higher rates of net nitrification in cropland soils suggest that land use change on the Tibetan Plateau may lead to high N losses through nitrate leaching.  相似文献   

7.
In south-western Australia, plantations of Eucalyptus globulus are being established on land that has previously been used for conventional agriculture. Sustaining the productivity of these tree plantations in second and subsequent rotations will depend partly on maintenance of soil fertility, especially soil nitrogen (N) supply rates. We compared soil N status and supply rates between adjacent pasture and 6-11 year old first-rotation eucalypt plantations at 31 paired sites in south-western Australia. Total soil N varied widely among sites (0.07-0.68% in the fraction <2 mm of the 0-10 cm soil layer), but concentrations averaged over all sites did not differ between land-use types. However, measurements of the indices of mineralization (mineral N produced during incubation of intact cores), potentially available N (from short-term anaerobic incubation) and model-predicted mineralization rates during 28-day aerobic incubations were generally lower in afforested soils than in pasture soils. This finding was supported by in situ field estimates of N mineralization over a full year at two contrasting paired pasture-plantation sites. At each site there was a marked reduction (2-3-fold) in net annual mineral N flux rates in soils under eucalypt plantations. Reduced N mineralization associated with tree plantations was due to both changes in soil organic matter quality and the generally lower soil moisture content under trees in comparison with pasture. These results suggest that N supply rates of pasture soils are likely to decline when the land is planted to successive crops of eucalypts. Eucalypt plantation managers will need to take account of this and implement management strategies to maintain adequate N nutrition to sustain tree growth in future rotations.  相似文献   

8.
The aim of this study was to evaluate experimentally derived temperature functions for the rate coefficients of net N mineralization in sandy arable soils from NW Germany via field measurements. In part I of this paper (Heumann and Böttcher, 2004), different temperature functions for the rate coefficients of a two‐pool first‐order kinetic equation were derived by long‐term laboratory incubations at 3°C to 35°C. In this paper, field net N mineralization during winter of 25 plots was measured in undisturbed soil columns with a diameter of 20 cm to the depth of the Ap horizon. Mean simulated net N mineralization with the most adequate multiple functions corresponded also best with the mean of the measured values despite of an overestimation of about 10%. Distinctly larger deviations under use of other temperature functions (Arrhenius, Q10) were directly related to their deviations from mean, experimentally derived rate coefficients. Simulated net N mineralization in the soil columns was significantly correlated with measured values, regardless of the temperature functions. Yet the goodness of fit was generally relatively low due to the spatial variability of measured net N mineralization within replicate soil columns, although the mean CV (38%) was by far not extraordinary. The pool of slowly mineralizable N contributed considerably to net N mineralization during four to five winter months, on an average 10.0 kg N ha–1, about one third of total simulated N mineralization. Sometimes, it contributed even 21.3 kg N ha–1, which is almost sufficient to reach the EU drinking‐water limit for nitrate in these soils. Simulations with widely used functions that were once derived from loess soils overestimated mineralization from pool Nslow in the studied sandy arable soils by a factor of two.  相似文献   

9.
Apparent net N mineralization (mineralization minus immobilization) in fertilized and unfertilized treatments was determined in 133 fertilizer trials with cereals and sugar beet over 3 years (1988-90). Apparent net mineralization was defined as follows: Apparent net N mineralization = (crop N at harvest - crop N in spring) - (Nmin in spring - Nmin at harvest) - N fertilizer applied. Results can be summarised as follows:
  • 1 For both crop species, apparent net N mineralization decreased in the following order: unfertilized > optimally fertilized > overfertilized.
  • 2 The decrease in apparent net mineralization of N with increasing rate of N fertilizer was attributed to immobilization. This was confirmed by measurements of increased remineralization during the following autumn, winter and during the growing season in the following year.
  • 3 Both the soil Nmin at harvest and fertilizer N which was immobilized and remineralized during autumn and winter, is at risk of being leached. At optimal fertilizer doses 30 kg N/ha and 74 kg N/ha were leached on average over winter from loamy and sandy soils respectively.
  • 4 Apparent net mineralization was not important for optimally fertilized cereals and therefore does not need to be considered for fertilizer recommendations for winter cereals. This does not apply to land receiving slurry applications before or during the growth period.
  • 5 In contrast to cereals, apparent net mineralization contributed considerably to the nutrition of sugar beet. Approximately 140 kg N/ha were mineralized at the optimum rate of N fertilizer application. However, the EUF- and CaCl2-methods were unable to predict N mineralization and were therefore unable to improve the prediction of fertilizer requirement even in combination with the NO3 soil N fraction.
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10.
Changes of land-use type (LUT) can affect soil nutrient pools and cycling processes that relate long-term sustainability of ecosystem, and can also affect atmospheric CO2 concentrations and global warming through soil respiration. We conducted a comparative study to determine NH4+ and NO3− concentrations in soil profiles (0–200 cm) and examined the net nitrogen (N) mineralization and net nitrification in soil surface (0–20 cm) of adjacent naturally regenerated secondary forests (NSF), man-made forests (MMF), grasslands and cropland soils from the windy arid and semi-arid Hebei plateau, the sandstorm and water source area of Beijing, China. Cropland and grassland soils showed significantly higher inorganic N concentrations than forest soils. NO3−-N accounted for 50–90% of inorganic N in cropland and grassland soils, while NH4+-N was the main form of inorganic N in NSF and MMF soils. Average net N-mineralization rates (mg kg−1 d−1) were much higher in native ecosystems (1.51 for NSF soils and 1.24 for grassland soils) than in human disturbed LUT (0.15 for cropland soils and 0.85 for MMF soils). Net ammonification was low in all the LUT while net nitrification was the major process of net N mineralization. For more insight in urea transformation, the increase in NH4+ and, NO3− concentrations as well as C mineralization after urea addition was analyzed on whole soils. Urea application stimulated the net soil C mineralization and urea transformation pattern was consistent with net soil N mineralization, except that the rate was slightly slower. Land-use conversion from NSF to MMF, or from grassland to cropland decreased soil net N mineralization, but increased net nitrification after 40 years or 70 years, respectively. The observed higher rates of net nitrification suggested that land-use conversions in the Hebei plateau might lead to N losses in the form of nitrate.  相似文献   

11.
原状土就地培养取样法定位研究田间土壤氮动态变化   总被引：8，自引：0，他引：8  
本文介绍了原状土就地培养取样技术的原理及方法应用,并对森林破坏后的次生演替、人工林种植和农业耕作等不同方式下氮素营养在时间进程及空间结构上的动态变化过程进行定位监测研究。结果表明,原状土就地培养取样法结构简单,方便易行,对土壤几乎没有扰动,也没有区域土壤类型的限制,弥补了其他方法的不足和研究的单一性,可定量化监测不同利用类型土壤氮库动态变化中的氮释放与固定、吸收和淋失等氮素营养随时间和季节变化的整个过程以及人为活动干扰后土壤氮营养的空间变异,为田间条件下土壤氮库动态变化定位研究的有效方法。  相似文献   

12.
Data on the dynamics of the net N mineralization rate in four soils of catenas in the western Kraichgau region (Germany) were processed using time series analysis, including Census I decomposition. It was shown that the annual cycle of the net N mineralization rate in the Calcaric Regosols is significantly related to the annual cycle of the soil temperature, and its long-term trend is similar to that of the soil moisture. The risk of mineral nitrogen leaching beyond the soil profile is rather high in Calcaric Regosols because of the seasonal dynamics.  相似文献   

13.
A critical review of some approaches to modelling nitrogen mineralization   总被引：2，自引：0，他引：2  
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14.
The uptake of labelled and unlabelled N by wheat was measured in pot and field experiments with 15N-labelled fertilizer. Soils from two sites on the same series were used in the pot experiment; one had been bare-fallowed for 22 years and contained 1.6% organic C, the other had been under grass for many years and contained 3.8% organic C. Fertilizer N increased the uptake of unlabelled soil N in both soils, i.e. there was a positive ‘added nitrogen interaction’ (ANI). There was no ANI in the field experiment. A simulation model is used to show how positive ANIs can arise as a result of ‘pool substitution’—labelled inorganic fertilizer N standing proxy for unlabelled inorganic soil N that would otherwise have been immobilized. In the low-organic fallow soil, pool substitution accounted for the whole of the observed ANI and fertilizer N did not enhance either gross or net mineralization of soil N. Pool substitution also operated in the high organic grassland soil, but here net mineralization of soil N increased with increasing additions of fertilizer, giving rise to a ‘real’ ANI in addition to the larger ‘apparent’ ANI caused by pool substitution. This increase in net mineralization is probably caused by a decrease in immobilization of N as fertilizer N additions increase, not by an increase in gross mineralization of soil N. For pool substitution to operate, fertilizer N and soil inorganic N must occupy the same pool. This occurred in the pot experiment but not in the field experiment, where fertilizer and soil inorganic N remained separate and there was no ANI. When pool substitution occurs, fertilizer use efficiency is predictably lower as measured by the isotopic method than as measured by the conventional non-isotopic procedure.  相似文献   

15.
Grape marc is a common waste product of the wine production industry. When partially composted and applied to soil it may contain enough N to affect vine growth and hence wine quality. Yet little is known about the quantity and timing of N release from composted grape marc. A laboratory incubation was conducted where composted grape marc amended and non-amended soils were periodically sampled over 148 days at 15 °C for gross N mineralization rates, C mineralization and microbial biomass-C. Gross N mineralization rates were determined by 15N pool dilution using both analytical equations and the numerical model FLUAZ (Mary, B., Recous, S., Robin, D., 1998. A model for calculating nitrogen fluxes in soil using 15N tracing. Soil Biology & Biochemistry 30, 1963-1979.). Both analytical and FLUAZ determined gross N mineralization rates were in close agreement in the control soil. However, in composted grape marc amended soils there was a discrepancy between the two solutions. Findings indicate that composted grape marc caused a net immobilization of N for the first 50-days of incubation, after which enough N was released to require consideration in fertilizer-N strategies.  相似文献   

16.
In this study nutrient supply along transects from farmland to calcareous grasslands was investigated. The aim was to assess a gradient in nutrient supply parallel to the change in species composition. Net nitrogen mineralization was measured under field conditions and in a laboratory incubation experiment. The seasonal course of net N mineralization was determined by the increase of soil temperature in spring and changes in soil moisture during summer. In the farmland soils fertilization was also an important factor. Annual net N mineralization was highest in the moderately acid soils of the Rosenberg on the Lower Devonian schist. It was lowest in the soils of the transect near Erdorf on limestone. Two transects on dolomite took an intermediate position. At all study sites net N mineralization and the mineral nitrogen contents were higher in the peripheral zones of the calcareous grasslands than in the centre of the grasslands. In the base-rich soils of the three transects on limestone and dolomite annual net N mineralization varied in the calcareous grasslands between 4.6 and 61 mg/kg, in the peripheral zones between 35 and 190 mg/kg and in the farmland between 117 and 350 mg/kg. In the base-poor soils of the transect on Rosenberg it was 96 mg/kg in the calcareous grassland, 115–130 mg/kg in the boundary zone and 165 mg/kg in the meadow. It is presumed that the increase in nitrogen supply was caused by nutrient input from the adjacent farmland.  相似文献   

17.
Intact soil cores from three adjacent sites (Site A: grazed, Site B: fenced for 4 years, and Site C: fenced for 24 years) were incubated in the laboratory to examine effects of temperature, soil moisture, and their interactions on net nitrification and N mineralization rates in the Inner Mongolia grassland of Northern China. Incubation temperature significantly influenced net nitrification and N mineralization rates in all the three grassland sites. There were no differences in net nitrification or N mineralization rates at lower temperatures (−10, 0, and 5 °C) whereas significant differences were found at higher temperatures (15, 25, and 35 °C). Soil moisture profoundly impacted net nitrification and N mineralization rates in all the three sites. Interactions of temperature and moisture significantly affected net nitrification and mineralization rates in Site B and C, but not in Site A. Temperature sensitivity of net nitrification and N mineralization varied with soil moisture and grassland site. Our results showed greater net N mineralization rates and lower concentrations of inorganic N in the grazed site than those in the fenced sites, suggesting negative impacts of grazing on soil N pools and net primary productivity.  相似文献   

18.
The rate of mineralization of organic nitrogen (N) in soils depends on environmental factors, specially temperature and water content. In this paper, different models that describe temperature and water content effects on mineralization are examined and the values of the factors used in the different models are compared. The results of mineralization simulations, using the different models at different levels of water content and temperature, are compared with experimental field data from the literature. The results show that the principal differences are found at temperatures greater than 25°C and at water content levels near saturation and near permanent wilting point. The different models were used for an estimation of net mineralized N under field conditions in a soil with ryegrass by using a deterministic model of water and N transport in the soil. The results confirm the differences of moisture and temperature effects on mineralization when the soil became very dry and wet during the rainy months.  相似文献   

19.
Progress in studies of nitrate leaching from grassland soils   总被引：2，自引：0，他引：2  
Abstract. The large input of research effort on aspects of nitrate leaching over the last two decades has produced many innovative scientific and practical results. The MAFF Nitrate Programme has enabled considerable progress to be made in unravelling much of the complexity of the grassland nitrogen (N) cycle, and identifying gaps as essential first stages in providing improved managements for N in grassland systems. From a practical standpoint, there have been key outputs which have allowed the identification of options for policy, and which should allow grassland farmers to increase the efficiency of N use throughout their farming system and thereby improve the sustainability of their enterprises. As well as quantifying N transformations, transfers and losses, other important outcomes have been the development of user-friendly models of N cycling (NCYCLE and variants) and an easy to use field kit to determine mineral N in pasture soils. The use of modelling to produce fertilizer recommendations with a Decision Support System and of new approaches developed within the Programme, in particular system synthesis desk studies, and 'farmlet' investigations to determine the consequences of modifying N flows and losses, have allowed us to produce solutions to satisfy the dual aims of meeting environmental and economic production targets.  相似文献   

20.
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   

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