Phosphorus availability in different types of open-cast mine spoil and the potential impact of organic matter application

Greenhouse experiments were conducted in order to determine for carboniferous and non-carboniferous mine spoil substrates from the Lusatian lignite mining area (i) the suitable extraction method for plant available P, (ii) the soil capacity for immobilisation of P and (iii) the impact of sewage sludge and compost on P availability. Ca-lactate extraction (DL) and NH₄F-extraction (Bray) were both suited equally well for the determination of plant available P as they extracted similar amounts of P on both spoils, they showed a close correlation with each other (R=0.97 ²) and they showed a close relation with plant P uptake (R²=0.63 and R²=0.66, respectively). Phosphorus recovery from limed carboniferous mine spoil five days after mineral fertiliser application was only 50%, and decreased to 30% after 54 days. As pH was increased from 3.0 to 5.0 the amount of P immobilised decreased only by about 5%. Several pH dependent processes of P immobilisation and release could occur concurrently counteracting each other. One process could be P sorption to newly formed hydroxy-Al-surfaces but P desorption could also take place as pH increases by decreasing surface positive charge. Finally, due to high Ca concentrations in spoil solution formation of Ca-phosphates, even at lower pH values, cannot be excluded as a possible mechanism of P immobilisation. As part of the P is bound in organic matter, application of P with organic matter resulted in a lower P recovery compared to mineral P-fertiliser. However, the amount of P recovered did not differ between carboniferous and non-carboniferous mine spoil, if P was applied in the form of organic matter, indicating that the application of P with organic matter might be a measure to overcome P immobilisation in carboniferous mine spoils. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spoil characteristics and vegetation development of an age series of mine spoils in a dry tropical environment

A series of coal mine spoils (5, 10, 12, 16 and 20-yr old) in a dry tropical environment was sampled to assess the changes with time in spoil characteristics, species composition and plant biomass. Coarse fragments (>2 mm) decreased with age of mine spoil while the proportion of 0.2–0.1 mm particles increased. Total soil N, mineral N, NaHCO₃-extractable Pi, and exchangeable K increased with age of mine spoil and these parameters were lower in mine spoils than native forest soil even after 20 years of succession. Exchangeable Na decreased with age of mine spoil and in 20-yr old spoil it was higher than native forest soil. Plant community composition changed with age. Only a few species participated in community formation. Species richness increased with age, while evenness and species diversity declined from 5-yr old to 16-yr old community with an increase in the 20-yr old community. A reverse trend occurred for concentration of dominance. Area-weighted shoot and root biomass of other species increased with the age of the mine spoil while that of Xanthium strumarium patches declined with age. Data collected on spoil features, microbial C, N and P, and shoot and root biomass when subjected to Discriminant Analysis indicated a continued profound effect of age. 10 and 12-yr old mine spoils were closer to each other, and 5 and 20-yr old spoils were farthest apart.     

Effects of afforestation on phosphorus dynamics and biological properties in a New Zealand grassland soil

Selected chemical, biochemical and biological properties of mineral soil (0–30 cm) were measured under a 19 year old forest stand (mixture of Pinus ponderosa and Pinus nigra) and adjacent unimproved grassland at a site in South Island, New Zealand. The effects of afforestation on soil properties were confined to the 0–10 cm layer, which reflected the distribution of fine roots (< 2 mm) in the soil profile. Concentrations of organic C, total N and P and all organic forms of P were lower under the forest stand, while concentrations of inorganic P were higher under forest compared with grassland, supporting the previously described suggestion that afforestation may promote mineralisation of soil organic matter and organic P. On the other hand, microbial biomass C and P, soil respiration and phosphatase enzyme activity were currently all lower and the metabolic quotient was higher in soil under forest compared with grassland, which is inconsistent with increased mineralisation in the forest soil. Reduced biological fertility by afforestation may be mainly attributed to changes in the quantity, quality and distribution of organic matter, and reduction in pH of the forest soil compared with the grassland soil. We hypothesize that the lower levels of C, N and organic P found in soil under forest are due to enhanced microbial and phosphatase activity during the earlier stages of forest development. Forest floor material (L and F layer) contained large amounts of C, N and P, together with high levels of microbial and phosphatase enzyme activity. Thus, the forest floor may be an important source of nutrients for plant growth and balance the apparent reduction in C, N and P in mineral soil through mineralisation and plant uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparison of methodologies for field measurement of net nitrogen mineralisation in arable soils

This study evaluated the suitability of a soil core incubation technique (with acetylene added to inhibit loss of N by denitrification; CIT) and a resin-core incubation technique (RCT) for measurement of net N mineralisation under arable cropping conditions. A conventional N balance (BAL) approach to the measurement of N mineralisation was used for comparison. In a sandy soil during winter 1996/97, CIT estimates of net N mineralisation were approximately 3 times greater than RCT and BAL estimates, which were in close agreement. Soil disturbance (with the consequent exposure of physically protected organic matter) did not enhance the rate of net N mineralisation measured by CIT on the sandy, low-organic-matter soil studied, although an increase in soil aeration may have enhanced rates above those measured by RCT and BAL. Overall, RCT was considered to be the more favourable technique for estimation of net N mineralisation. It also provided a measure of nitrate leaching which was comparable to that obtained by porous ceramic water samplers. However, separate estimates of the likely loss of N by denitrification should be obtained with soils which are particularly vulnerable (eg. poor aeration and high clay or water content). Spatial variability was a particular problem with all three techniques which can be overcome by taking a large number of soil cores to increase sample replication. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigations on pyrite oxidation in mine spoils of the Lusatian lignite mining district

The impact of organic waste material and fly ash on microbial and chemical pyrite oxidation was investigated in a field experiment, as well as in column tests under laboratory conditions. For the field experiment, pyritic mine spoil was ameliorated with fly ash and treated either with mineral fertiliser, with sewage sludge or with compost. Independent of treatment, during the 18 months following application, the pyrite-S contents decreased steadily in the top spoil (0–30 cm depth). However, high variations of the pyrite-S content were observed. Compared to other pyrite oxidation studies, the pyrite content of the mine spoil at the experimental site was low. Therefore, a model spoil with a higher pyrite content, derived from Tertiary strata of the overburden sequence in the same open-cast mine, was used for the column experiments. For the first column experiment, the model spoil was mixed with fly ash and mineral fertiliser, reflecting the common reclamation practice in the Lusatian open-cast lignite mining district. Columns with this spoil were either inoculated with different cell numbers of autochthonous acidophilic bacteria, isolated from the model spoil, or with a commercial strain of Thiobacillus ferrooxidans. The ratio of sulphate-S to total S was used as a measure for the degree of pyrite oxidation. The ratio of sulphate-S to total S increased within 28 days of incubation. The increase was related to the inoculated cell numbers of bacteria, but independent of the origin of the bacteria. It can be stated, that autochthonous bacteria from the model spoil oxidised pyrite at a similar rate as did the commercial T. ferrooxidans strain. For the second column test, mineral fertiliser, sewage sludge or compost were applied to the model spoil. The columns were inoculated with autochthonous bacteria, isolated from the model spoil. Application of sewage sludge and compost seemed to promote the weathering of pyrite, as the ratio of sulphate-S to total S increased more rapidly in these treatments compared to control or mineral fertiliser application. Both experiments showed an increase of cell numbers of inoculated bacteria, independent of the ratio of sulphate-S to total S. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Organic matter composition and degree of humification in lignite-rich mine soils under a chronosequence of pine

In the Lusatian mining district, in the eastern part of the Federal Republic of Germany, organic matter of reclaimed mine soils consists of a mixture of lignite and recently formed soil organic matter (recent carbon). The aim of the study was to investigate the recent carbon accumulation and the degree of humification of a chronosequence of young mine soils under forest. The lignite content of the forest floor, Ai (0–5 cm) and Cv horizons (1 m depth) was determined by ¹⁴CU activity measurements and the structural composition of the organic matter was characterised by ¹³C CPMAS NMR spectroscopy. To obtain a characterisation of the degree of humification, the soil samples were analysed for the content of polysaccharides, proteins, lignin and lipids by wet chemical methods. ¹⁴C activity measurements indicate that at the oldest site, comparable amounts of carbon accumulated in the first few centimetres of the soil profile than in natural forest soils. ¹³C CPMAS NMR spectra of the organic matter in the Ai horizons of the three soil profiles were dominated by aromatic and alkyl carbon species characteristic for lignite, but indicated as well an increasing contribution of carbon species from decomposing plant litter with soil age. When the results from wet chemical analyses were normalised to the total carbon content no changes with age could be noticed. After normalisation of the amount of litter compounds to the recent carbon content, the carbon identified by plant litter compound analysis decreased with increasing depth and increasing age of the soils. After 32 years the values are comparable to those of natural forest soils. These observations were confirmed by increasing degree of lignin alteration with stand age and soil depth. The data of wet chemical analyses complement data obtained by ¹⁴C activity measurements and ¹³C CPMAS NMR spectroscopy and lead to the conclusion that 32 years after reforestation the degree of humification of the soil organic matter is in the same range as those of natural sites. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of gap size and soil properties on microbial biomass in a subtropical humid forest of north-east India

We examined the effects of treefall gap size and soil properties on microbial biomass dynamics in an undisturbed mature-phase humid subtropical broadleaved forest in north-east India. Canopy gaps had low soil moisture and low microbial biomass suggesting that belowground dynamics accompanied changes in light resources after canopy opening. High rainfall in the region causes excessive erosion/leaching of top soil and eventually soil fertility declines in treefall gaps compared to understorey. Soil microbial population was less during periods when temperature and moisture conditions are low, while it peaked during rainy season when the litter decomposition rate is at its peak on the forest floor. Greater demand for nutrients by plants during rainy season (the peak vegetative growth period) limited the availability of nutrients to soil microbes and, therefore, low microbial C, N and P. Weak correlations were also obtained for the relationships between microbial C, N and P and soil physico–chemical properties. Gap size did influence the microbial nutrients and their contribution to soil organic carbon, total Kjeldhal nitrogen and available-P. Contribution of microbial C to soil organic carbon, microbial N to total nitrogen were similar in both treefall gaps and understorey plots, while the contribution of microbial P to soil available-P was lower in gap compared to the understorey. These results indicate that any fluctuation in microbial biomass related nutrient cycling processes in conjunction with the associated microclimate variation may affect the pattern of regeneration of tree seedlings in the gaps and hence be related with their size. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil microcosm experiments to study the effects of waste material application on nitrogen and carbon turnover of lignite mine spoils in Lusatia (Germany)

The lignite and pyrite containing spoil substrates of the Lusatian mining district are marked by very high acidity and salt concentrations due to pyrite oxidation and by a very low content of pedogenic organic matter and nutrients. The effects of fly ash application to neutralize the produced acid and of organic waste material application to improve the ecological soil functions were studied considering the carbon and nitrogen cycling. Nineteen, 38 and 57 t ha⁻¹ sewage sludge and 22, 44 and 66 t ha⁻¹ compost were applied to ameliorated lignite and pyrite containing substrate. An automated soil microcosm system was used to analyse the solid, gaseous and liquid phases. Almost 9% of total N applied with sewage sludge (620, 1240 and 1860 t N ha⁻¹ applied) were lost over a period of 150 days mainly as NO₃-N. The total N losses from compost treatments were three times lower (2.8–3.1% of applied Nt) and occurred in similar quantities as NH4-N and NO₃-N. Only sewage sludge treatments showed slightly increased N₂O emissions at the beginning of the experiment. CO₂ emissions determined the carbon losses of all treatments. The C losses amounted to 3.2–4.7% and 1.5–2.7% of C_t applied with sewage sludge and with compost, respectively. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Impact of application of organic waste materials on microbial and enzyme activities of mine soils in the Lusatian coal mining region

The objective of the present work was to study the short-term stimulation of microbial and enzyme activity in mine soils by application of organic waste materials in lysimeter and mesocosm studies. The mine soils derived from tertiary and quaternary deposits were ameliorated with brown coal filter ash (tertiary deposits) and lime (quaternary deposits). At the beginning of recultivation the soils were treated with varying amounts of sewage sludge, coal sludge, composted sewage sludge and compost to a depth of 30 cm. In the first 2 years after application of organic waste materials we found a very low level of microbial properties especially in the sandy materials from quaternary deposits but a significant increase in microbial respiration, substrate induced respiration and enzyme activities like invertase and alkaline phosphatase with increasing application rates of sewage sludge, compost and sewage sludge mixed with coal sludge. This can be explained by an increase in organic matter and nutrient content of the soils and an improvement of soil physical properties such as water and nutrient retention capacity. Additionally it can be assumed, that constituents of the coal admixtures of tertiary deposits can be mineralised or converted by the soil microorganisms. In the tertiary materials ameliorated with brown coal ash the highest amounts of microbial and enzyme activities were measured after application of nitrogen-rich sewage sludge or very high amounts of mature compost mainly consisting of green waste. Compared with sewage sludge the stimulating effects of composted sewage sludge were quite lower because of organic matter fragmentation and a reduced energy and nutrient supply to soil microorganisms. This revised version was published online in June 2006 with corrections to the Cover Date.     

Simulation of C and N mineralisation during crop residue decomposition: A simple dynamic model based on the C:N ratio of the residues

C and N mineralisation kinetics obtained in laboratory incubations during decomposition of crop residues under non-limiting nitrogen conditions were simulated using a simple dynamic model. This model includes three compartments: the residues, microbial biomass and humified organic matter. Seven parameters are used to describe the C and N fluxes. The decomposed C is either mineralised as CO₂ or assimilated by the soil microflora, microbial decay producing both C humification and secondary C mineralisation. The N dynamics are governed by the C rates and the C:N ratio of the compartments which remain constant in the absence of nitrogen limitation. The model was parameterised using apparent C and N mineralisation kinetics obtained for 27 different residues (organs of oilseed rape plants) that exhibited very wide variations in chemical composition and nitrogen content. Except for the C:N ratio of the residues and the soil organic matter, the other five parameters of the model were obtained by non-linear fitting and by minimising the differences between observed and simulated values of CO₂ and mineral N. Three parameters, namely the decomposition rate constant of the residues, the biomass C:N ratio and humification rate, were strongly correlated with the residues C:N ratio. Hyperbolic relationships were established between these parameters and the residues C:N ratio. In contrast, the other two parameters, i.e. the decay rate of the microbial biomass and the assimilation yield of residue-C by the microbial biomass, were not correlated to the residues C:N ratio and were, therefore, fixed in the model. The model thus parameterised against the residue C:N ratio as a unique criterion, was then evaluated on a set of 48 residues. An independent validation was obtained by taking into account 21 residues which had not been used for the parameterisation. The kinetics of apparent C and N mineralisation were reasonably well simulated by the model. The model tended to over-estimate carbon mineralisation which could limit its use for C predictions, but the kinetics of N immobilisation or mineralisation due to decomposition of residues in soil were well predicted. The model indicated that the C:N ratio of decomposers increased with the residue C:N ratio. Higher humification was predicted for substrates with lower C:N ratios. This simple dynamic model effectively predicts N evolution during crop residue decomposition in soil.     

Modelling the effect of active roots on soil organic matter turnover

The aim of this experiment was to study the effect of living roots on soil carbon metabolism at different decomposition stages during a long-term incubation. Plant material labelled with ¹⁴C and ¹⁵N was incubated in two contrasting soils under controlled laboratory conditions, over two years. Half the samples were cropped with wheat (Triticum aestivum) 11 times in succession. At earing time the wheat was harvested, the roots were extracted from the soil and a new crop was started. Thus the soils were continuously occupied by active root systems. The other half of the samples was maintained bare, without plants under the same conditions. Over the 2 years, pairs of cropped and bare soils were analysed at eight sampling occasions (total-, plant debris-, and microbial biomass-C and -¹⁴C). A five compartment (labile and recalcitrant plant residues, labile microbial metabolites, microbial biomass and stabilised humified compounds) decomposition model was fitted to the labelled and soil native organic matter data of the bare and cropped soils. Two different phases in the decomposition processes showed a different plant effect. (1) During the initial fast decomposition stage, labile ¹⁴C-material stimulated microbial activities and N immobilisation, increasing the ¹⁴C-microbial biomass. In the presence of living roots, competition between micro-organisms and plants for inorganic N weakly lowered the measured and predicted total-¹⁴C mineralisation and resulted in a lower plant productivity compared to subsequent growths. (2) In contrast, beyond 3–6 months, when the labile material was exhausted, during the slow decomposition stage, the presence of living roots stimulated the mineralisation of the recalcitrant plant residue-¹⁴C in the sandy soil and of the humified-¹⁴C in the clay soil. In the sandy soil, the presence of roots also substantially stimulated decomposition of old soil native humus compounds. During this slow decomposition stage, the measured and predicted plant induced decrease in total-¹⁴C and -C was essentially explained by the predicted decrease in humus-¹⁴C and -C. The ¹⁴C-microbial biomass (MB) partly decayed or became inactive in the bare soils, whereas in the rooted soils, the labelled MB turnover was accelerated: the MB-¹⁴C was replaced by unlabelled-C from C derived from living roots. At the end of experiment, the MB-C in the cropped soils was 2.5–3 times higher than in the bare soils. To sustain this biomass and activity, the model predicted a daily root derived C input (rhizodeposition), amounting to 5.4 and 3.2% of the plant biomass-C or estimated at 46 and 41% of the daily net assimilated C (shoot + root + rhizodeposition C) in the clay and sandy soil, respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth response of native shrubs to acid mine spoil and to proposed soil amendments

Successful reclamation of acid mine sites may be enhanced by revegetating with species that are tolerant to acid mine spoil conditions. This study was conducted to assess the response of four native shrub species, Amelanchier alnifolia Nutt., Symphoricarpos albus (L.) Blake, Berberis repens Lindl., and Ceanothus sanguineus Pursh, to 1) pyritic acid mine spoil amended with various levels of lime and composted sewage sludge with added ammonium nitrate (CSS+N) and 2) acidified granitic spoil, with and without CSS+N. Species responded to soil acidity and nutrient supply similarly in both spoil materials. Berberis and Amelanchier exhibited acid soil tolerance, Symphoricarpos grew poorly in acidic soils but had low mortality, and Ceanothus responded to low pH with very poor growth, high mortality, or both. Amelanchier was conservative in growth and did not respond to either soil pH or nutrient supply with significant differences in biomass accumulation. Symphoricarpos varied in response to CSS+N but was most productive at neutral or higher pH. Berberis responded to nutrient availability with substantial increases in biomass production, including significant growth in strongly acidic spoil. Ceanothus responded to nutrient availability with large increases in biomass and was most productive with added CSS+N at neutral or higher pH. Nitrogen fixing nodules developed on the roots of Ceanothus plants grown in granitic spoil without CSS+N. The results indicated that these species differ significantly in acid soil tolerance and in their potential for growth, stress tolerance, and resource acquisition.     

Effects of N-enriched rock powder on soil chemistry,organic matter formation and plant nutrition in lignite-poor sandy mine spoil in the forest reclamation practice

The effects of a slow-release N-enriched rock powder on soil chemistry, on the development of the soil vegetation (field layer vegetation), on the nutritional status of pine seedlings (Pinus sylvestris L.), and on decomposition rates of cellulose in lignite-poor mine spoils were studied. In the initial phase after afforestation fertilization caused a significant increase in NO₃ ⁻-N concentrations in the soil solution of the top-soil (0–60 cm). Subsequently, NO₃ ⁻-N concentrations of all N fertilized treatments decreased with the exception of the highest N application area (500 kg N ha⁻¹). This decrease of NO₃ ⁻-N concentrations was related to the establishment of a field layer vegetation, which developed according to the amount of N applied. In the above-ground phytomass of the field layer vegetation a maximum N accumulation amount of 22 kg ha⁻¹ was measured. Cellulose decomposition increased with higher N application rates. In the second year after N-fertilization, the pine needles indicated insufficient supply for almost all nutrients except for N. The deficiency symptoms were most pronounced at the plots that had received the highest amounts of nitrogen. This phenomenon appears to be related to the competition by the field layer vegetation. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil microfloral and microfaunal response to Salicornia bigelovii planting density and soil residue amendment

Seawater-irrigated halophyte systems have been proposed as sites for carbon storage, and therefore the fate of halophyte-derived carbon in the soil needs to be determined. To evaluate the role of the microfloral and microfaunal communities in soil carbon cycling of a halophyte agroecosystem, the response to various agronomic practices was investigated. Biomass and activity of the soil microflora and the abundance and trophic composition of the soil microfauna were determined under three planting densities of the halophyte Salicornia bigelovii (Chenopodiaceae) in plots with and without incorporated post-harvest halophyte residues. Microbial biomass and activity, as well as the abundance of nematode grazers, increased in response to the amendment of soil with halophyte residues. The microbial response to the density and presence of halophyte plants was, however, limited. Microbial activity increased in response to the presence of plants only after Salicornia had entered senescence, a result suggesting that in the mineral soil where halophytes were cropped, only dead root material provided a significant amount of microbially available organic matter. Success of halophyte agroecosystems in storing plant-derived carbon will depend primarily on the management of post-harvest residues and secondarily on the growing practices used prior to plant senescence. This revised version was published online in June 2006 with corrections to the Cover Date.     

长期施肥下农田土壤-有机质-微生物的碳氮磷化学计量学特征

探讨外源养分的输入对土壤系统内碳、氮、磷化学计量特征的影响,对于深刻认识农田土壤有机碳(C)和养分循环及其相互作用过程具有重要意义。以26年的农田长期定位施肥试验为平台,分析长期不同施肥条件下土壤、有机态及微生物生物量碳、氮、磷含量及其化学计量学特征,并根据内稳性模型y=c x~(1/H)计算其化学计量内稳性指数H。结果表明:与长期撂荒处理(CK_0)相比,种植作物条件下26年化肥配施有机肥处理(MNPK和1.5MNPK)显著降低微生物生物量氮含量,但显著提高了微生物生物量磷的含量。相对于撂荒处理,即使长期配施化肥磷处理(NP、PK、NPK),其土壤有机磷降低显著。对于C∶N比而言,化肥配施有机物料处理(秸秆或有机肥)的土壤C∶N比、有机质C∶N及微生物生物量C∶N比均显著低于化肥处理(N、NP、PK和NPK)。对于C∶P比而言,相对于撂荒处理,26年施用磷肥(化肥磷或有机磷)显著降低了土壤C∶P比和微生物生物量C∶P比,而CK和偏施化肥处理(N、NP和PK)显著降低了土壤有机质C∶P比。对于土壤N∶P比而言,撂荒处理土壤N∶P比显著高于其他处理,而撂荒处理土壤有机质N∶P比显著高于CK和化肥处理,表明不施肥或化肥条件下作物种植加剧了土壤有机质中氮素的消耗。微生物生物量C∶N、C∶P、N∶P比的内稳性指数H分别为0.24、0.75、0.64,不具有内稳性特征。微生物生物量C∶N、C∶P、N∶P比分别与土壤C∶N、C∶P、N∶P比呈显著正相关关系,但与土壤有机质碳氮磷化学计量比之间无显著相关性。表明土壤碳、氮、磷元素的改变会直接导致微生物生物量碳、氮、磷化学计量比的改变,但微生物生物量碳氮磷化学计量比对土壤有机质碳氮磷化学计量比无显著影响,土壤有机质的碳氮磷计量比可能更多是受到作物和施肥等养分管理措施的影响。     

Dynamics of mineral N availability in grassland ecosystems under increased [CO2]: hypotheses evaluated using the Hurley Pasture Model

The following arguments are outlined and then illustrated by the response of the Hurley Pasture Model to [CO₂] doubling in the climate of southern Britain. 1. The growth of N-limited vegetation is determined by the concentration of N in the soil mineral N pools and high turnover rates of these pools (i.e., large input and output fluxes) contribute positively to growth. 2. The size and turnover rates of the soil mineral N pools are determined overwhelmingly by N cycling into all forms of organic matter (plants, animals, soil biomass and soil organic matter — `immobilisation' in a broad sense) and back again by mineralisation. Annual system N gains (by N₂ fixation and atmospheric deposition) and losses (by leaching, volatilisation, nitrification and denitrification) are small by comparison. 3. Elevated [CO₂] enriches the organic matter in plants and soils with C, which leads directly to increased removal of N from the soil mineral N pools into plant biomass, soil biomass and soil organic matter (SOM). ‘Immobilisation’ in the broad sense then exceeds mineralisation. This is a transient state and as long as it exists the soil mineral N pools are depleted, N gaseous and leaching losses are reduced and the ecosystem gains N. Thus, net immobilisation gradually increases the N status of the ecosystem. 4. At the same time, elevated [CO₂] increases symbiotic and non-symbiotic N₂ fixation. Thus, more N is gained each year as well as less lost. Effectively, the extra C fixed in elevated [CO₂] is used to capture and retain more N and so the N cycle tracks the C cycle. 5. However, the amount of extra N fixed and retained by the ecosystem each year will always be small (ca. 5–10 kg N ha^-1 yr^-1) compared with amount of N in the immobilisation-mineralisation cycle (ca. 1000 kg N ha^-1 yr^-1). Consequently, the ecosystem can take decades to centuries to gear up to a new equilibrium higher-N state. 6. The extent and timescale of the depletion of the mineral N pools in elevated [CO₂] depends on the N status of the system and the magnitude of the overall system N gains and losses. Small changes in the large immobilisation—mineralisation cycle have large effects on the small mineral N pools. Consequently, it is possible to obtain a variety of growth responses within 1–10 year experiments. Ironically, ecosystem models — artificial constructs — may be the best or only way of determining what is happening in the real world. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization of soil organic matter from a sandy soil in relation to management practice using FT-IR spectroscopy

Previous results from differently fertilized long-term field experiments on a sandy soil suggested that the chemical composition of soil organic matter (SOM) is affected by fertilization. The objective of this paper is to confirm this finding for a site with higher soil-clay contents. Four combinations of different fertilizer treatments at long-term field experiment located at a sandy loam were selected: liquid manure (LM), liquid manure+N (LM+N), straw+N (S+N) and mineral nitrogen only (N). Soil organic matter was extracted using sodium pyrophosphate solution at pH of 10 and hot water. The extracts were analyzed using Fourier-Transform infrared spectroscopy. The results indicate that the composition of SOM from the hot water extracts did not show significant differences while the sodium pyrophosphate extracted SOM is affected by the type of fertilization. Soil samples fertilized with LM+N and S+N show the highest intensity of the carboxyl band. This can be explained by the fact that the combination of S+N fertilization with green manure leads to an enrichment of carboxyl groups in SOM. Differences between the band intensities of the treatments for the SOM samples are, however, not as distinct as for the sandy soil samples. This is possibly a result of the higher clay content and lower age of the long-term experiment at the sandy loam site. The intensity of the carboxyl band of the SOM is correlated with the cation exchange capacity of the soil samples. The composition of SOM may, in addition to the SOM content, be used for studying quantitative effects of different management practices or even land use changes on soil properties. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

The simulation of soil organic matter and nitrogen accumulation in Scots pine plantations on bare parent material using the combined forest model EFIMOD

The individual-based combined forest model EFIMOD including the soil-sub model SOMM has been used for the simulation of Scots pine stand growth and soil organic matter (SOM) accumulation on a humus-free bare mineral surface. The growth of Scots pine plantation, with an initial density of 10 000 trees ha⁻¹ and average tree biomass of 0.01 kg was simulated for 50 yr under Central European climatic conditions (i) with varying atmospheric nitrogen inputs and (ii) different rates of initial application of raw undecomposed organic material or compost, on humus-free parent material. The accumulation of typical raw humus was simulated in all cases. The accumulation was most intensive in the simulation of high atmospheric nitrogen input. The humus pool in the mineral topsoil was small but achieved its maximum value with compost application. SOM nitrogen accumulation was scant in all cases, except the compost applications with low atmospheric nitrogen input. No statistically significant differences of SOM and stand parameters were found between variants without organic matter and those with low input of organic manure. However, the maximum relative rate of SOM and nitrogen accumulation was found in the scenario without organic manure, under slowly growing unstable Scots pine plantation. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

A weighing method to identify the microbial growth phases in solid-state fermentation tests

A general equation correlating the variation rate of the fermenting medium weight (dry matter) and the cell biomass growth rate in solid-state fermentation tests is proposed with the main purpose of identifying the microbial growth phases. This revised version was published online in July 2006 with corrections to the Cover Date.