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Global warming is accompanied by increasing water stress across much of our planet. We studied soil biological processes and changes in soil organic carbon (SOC) storage in 30 Hungarian oak forest sites in the Carpathian Basin along a climatic gradient (mean annual temperature (MAT) 9.6–12.1 °C, mean annual precipitation (MAP) 545–725 mm) but on similar gently sloped hillsides where the parent materials are loess and weathered dust inputs dating from the end of the ice age. The purpose of this research was to understand how a drying climate, predicted for this region, might regulate long-term SOC sequestration. To examine the effects of decreasing water availability, we compared soil parameters and processes in three categories of forest that represented the moisture extremes along our gradient and that were defined using a broken-stick regression model. Soil biological activity was significantly lower in the driest (“dry”) forests, which had more than double the SOC concentration in the upper 30 cm layer (3.28 g C/100 g soil ± 0.11 SE) compared to soils of the wettest (“humid”) forests (1.32 g C/100 g soil ± 0.09 SE), despite the fact that annual surface litter production in humid forests was ~ 37% higher than in dry forests. A two-pool SOM model constrained to fit radiocarbon data indicates that turnover times for fast and slow pools are about half as long in the humid soil compared to the dry soil, and humid soils transfer C twice as efficiently from fast to slow pools. Enzyme activity and fungal biomass data also imply shorter turnover times associated with faster degradation processes in the soils of humid forests. Thermogravimetry studies suggest that more chemically recalcitrant compounds are accumulating in the soils of dry forests. Taken together, our results suggest that the predicted climate drying in this region might increase SOC storage in Central European mesic deciduous forests even as litter production decreases.

Soil application of fresh organic matter is a way to increase soil organic matter and provide nutrients to trees. The effect of application of organic matter depends on the interaction among soil, root and microbial biomass. The aim of this research was to evaluate the potential release of N for hybrid GF677 (P. persica x P. dulcis) uptake, of 6 neemcakes available on the Italian market compared with fresh leaves of Melia azedarach, an ornamental tree that grows in the area of investigation. The release of N, and consequently root uptake was related to C:N ratio, the lower the ratio the higher the N concentration in plant tissues and plant growth. Using the 15N isotope technique, we found that up to 30% of the N applied with fresh Melia leaves, was accumulated in the tree, however the mineral N concentration in soil and plant and plant growth was not affected by the application of plant derivatives.

Soil properties and the ability to sustain agricultural production are seriously impaired by salinity. The cultivation of halophytes is seen as a solution to cope with the problem. In this framework, a greenhouse pot experiment was set up to assess salinity response in the perennial C4 species Atriplex halimus, and in the following three cultivars of the annual C3 Atriplex hortensis: green, red, and scarlet. The four genotypes were grown for 35 days with water salinity (WS) ranging from 0 to 360 mM NaCl. Plant height and fresh weight (FW) increased at 360 vs. 0 WS. The stomatal conductance (GS) and transpiration rate (E) were more severely affected by salinity in the C4 A. halimus than in the C3 species A. hortensis. This was reflected in a lower leaf water potential indicating stronger osmotic adjustment, and a higher relative water content associated with more turgid leaves, in A. halimus than A. hortensis. In a PCA including all the studied traits, the GS and E negatively correlated to the FW, which, in turn, positively correlated with Na concentration and intrinsic water use efficiency (iWUE), indicating that reduced gas exchange associated with Na accumulation contributed to sustain iWUE under salinity. Finally, FTIR spectroscopy showed a reduced amount of pectin, lignin, and cellulose under salinity, indicating a weakened cell wall structure. Overall, both species were remarkably adapted to salinity: From an agronomic perspective, the opposite strategies of longer vs. faster soil coverage, involved by the perennial A. halimus vs. the annual A. hortensis cv. scarlet, are viable natural remedies for revegetating marginal saline soils and increasing soil organic carbon.

In agriculture, the use of soil biodegradable mulch films could represent an eco-friendly alternative to conventional plastic films. However, soil biodegradable mulch films incorporated into the soil through tillage, being not only a physical but also a biogeochemical input, is expected to influence the soil quality by affecting its functions. Therefore, the eco-compatibility of these biodegradable plastics needs to be evaluated for their impact on different soil functions. To understand the effect of biodegradable plastics on soil quality (i.e. microbial biomass, nitrogen cycle, and activity of soil enzymes involved in the biochemical processes of carbon and nitrogen), we added increasing quantities of biodegradable plastics in two different soils: a loamy (Cambisol) and sandy (Arenosol) soil. The results highlight that the carbon added through the biodegradable plastics influenced the processes linked to carbon and nitrogen cycles. Significant effects were observed mainly with the highest dose of biodegradable plastics added (1%), resulting in a higher growth of microbial biomass, increased carbon mineralisation, and increased immobilisation of available nitrogen. The results also underline the importance of evaluating the impact of biodegradable plastics in different soils because all the processes considered are also influenced also by soil physicochemical characteristics.

To be economically and environmentally sound, the nitrogen (N) supply in orchards needs to be finely tuned according to crop needs. This requires knowledge of the amount and the dynamics of N uptake by roots and of its allocation. This paper reports two experiments, carried out on the same set of trees, in order to: 1) study the uptake dynamics of N derived from fertiliser (N dff ) and its allocation to tree organs and, 2) quantify its N remobilization in spring from storage organs to new growth. The study was carried out using field-grown adult orange trees (cv. Tarocco nucellare grafted on Troyer Citrange), one of the most important fruit tree crops in the Mediterranean area. Nitrogen was supplied as ammonium nitrate in 10 applications with equal doses evenly distributed from March to November 2009. Four groups of 5 trees each received 15 N-enriched N starting from March, July, September, and November, respectively, while they received unlabelled N in the remaining periods. The results show that trees absorbed roughly 30% of the fertiliser N. Fertiliser-N use efficiency (NUE) was generally low in spite of the fact that readily available N sources were regularly supplied and the trees were irrigated; the later the fertiliser N was supplied, the lower was the NUE. Uptake rate was rather constant from April to November, but relatively less N was partitioned to fruits when the fertiliser was supplied later in the season. Remobilization of N from one-year-old leaves provided more than 60% of the N required by shoots in spring. By the end of April, most of the N had already been transferred from storage to growing organs. We estimated that, during the vegetative season, trees absorbed 94 kg N ha −1 from the soil and half of this amount derived from fertiliser. Spring remobilisation of winter stored N contributed for additional 40 kg N ha −1 to the N needs.

The initial online publication contained a typesetting mistake in the author information. The original article has been corrected.

The root-derived carbon (C) input to the soil, whose quantification is often neglected because of methodological difficulties, is considered a crucial C flux for soil C dynamics and net ecosystem productivity (NEP) studies. In the present study two independent methods to quantify this C input to the soil were compared in a young forest plantation in Italy. Specifically, a mass balance approach to the soil C balance and a new dual in-growth core (IGC) isotopic technique that accounts for both root- and non-root-derived C inputs were compared. No statistically significant difference between the results obtained by the two methods was found (3.09 ± 0.50 vs 5.30 ± 2.92 Mg C ha − 1 ). Both estimates matched with the results obtained by other authors for similar ecosystems. The application of this new dual IGC isotopic technique has shown that the traditional IGC isotopic technique can lead to a significant overestimation (60% in the present study) of root C input to the soil as it doesn't take into account changes in the soil C isotopic signature due to factors other than root derived inputs. These include isotopic discrimination that could take place during the decomposition of original soil organic matter (SOM), the contamination due to dissolved organic C (DOC) leaching, or the C input via leaf litter. The proposed dual IGC isotope technique, taking into account the abovementioned non-root derived inputs seems to be a promising and reliable method to estimate root-derived C input to the soil in terrestrial ecosystems

The litter decomposition process depends on the litter chemical composition, especially the ratio between more labile compounds, cellulose, and the recalcitrant lignin and waxes. Their determination is crucial to predict the process, though lignin measurement presents some limitations due to drawbacks of the different methods. Thermal analysis has been successfully applied to several organic materials in order to obtain quali-quantitative information of the chemical structure of the sample. In this work TG-DTA was used in a short-term litter decomposition study of two broadleaf forest stands of contrasting ages, and the results were compared to those obtained with a chemical method (Klason’s method) commonly used to quantify cellulose and lignin. TG-DTA was applied to the litter and to the cell walls (CW) extracted from the litter, whose cellulose and lignin content was determined using the Klason’s method. When applied to litter, thermal analysis showed a weak correlation with the Klason’s method, though it allowed the detection of the dynamics of waxes, that increased during the decomposition and could influence the later stages of the process. Contrastingly, a good correlation between cellulose and lignin determined with the two methods was found when TG-DTA was applied to the CW. In this case TG-DTA, according to NMR data, also highlighted the changes in the CW chemical structure compared with that of the litters, in particular the loss of waxes and the decreased thermostability of aromatic components. Moreover, a new concept of quality of the decomposing litter, based on the balance between the energy stored in the litter and the energy needed to release it obtained by thermal analysis, was recently introduced. Samples of the old forest litter had an initial energetic balance more favorable than those collected in the young stand. At the end of the period, the decrease in litter quality was greater in the young than in the old forest samples, due to the combined effect of the higher degradation of thermolabile substances and the accumulation of more thermostable components. Thermal analysis seems to have a good potential in litter decomposition studies, as it can link structural and energetic changes during the process.

Fractionation of soil organic carbon (SOC) is crucial for mechanistic understanding and modeling of soil organic matter decomposition and stabilization processes. It is often aimed at separating the bulk SOC into fractions with varying turnover rates, but a comprehensive comparison of methods to achieve this is lacking. In this study, a total of 20 different SOC fractionation methods were tested by participating laboratories for their suitability to isolate fractions with varying turnover rates, using agricultural soils from three experimental sites with vegetation change from C3 to C4 22-36 years ago. Enrichment of C4-derived carbon was traced and used as a proxy for turnover rates in the fractions. Methods that apply a combination of physical (density, size) and chemical (oxidation, extraction) fractionation were identified as most effective in separating SOC into fractions with distinct turnover rates. Coarse light SOC separated by density fractionation was the most C4-carbon enriched fraction, while oxidation-resistant SOC left after extraction with NaOCl was the least C4-carbon enriched fraction. Surprisingly, even after 36 years of C4 crop cultivation in a temperate climate, no method was able to isolate a fraction with more than 76% turnover, which challenges the link to the most active plant-derived carbon pools in models. Particles with density > 2.8 g cm(-3) showed similar C4-carbon enrichment as oxidation resistant SOC, highlighting the importance of sesquioxides for SOC stabilization. The importance of clay and silt sized particles (< 50 mu m) for SOC stabilization was also confirmed. Particle size fractionation significantly outperformed aggregate size fractionation, due to the fact that larger aggregates contain smaller aggregates and organic matter particles of various sizes with different turnover rates. An evaluation scheme comprising different criteria was used to identify the most suitable methods for isolating fractions with distinct turnover rates, and potential benefits and trade-offs associated with a specific choice. Our findings can be of great help to select the appropriate method(s) for fractionation of agricultural soils.

In ‘Trebbiano Romagnolo’ grapevines basal bud fertility is usually low and can be related to bud N status. The aim of the present investigation was to evaluate the effect of foliar N application on bud fertility in a mature vineyard subjected to two levels of soil N (39 and 78 kg N ha−1) fertility induced by application of urea. Both the vines at low and high N soil availability were sprayed once with 2.5 kg 15 N ha−1 in pre-bloom and in post-bloom 15N-enriched-ammonium nitrate. Nitrogen soil application increased soil mineral N significantly from June to October, however, with the exception of main shoot axes, the N concentration in the canopy organs (leaves, buds, and bunches) did not respond to the increase of soil fertility. Foliar N applied in June promoted the percentage of NDFF in apical and basal bud and bunch as well, compared with the application made in July. A linear correlation between leaf and basal bud N concentration in 2014 and basal bud fertility (number of inflorescences per shoot) in 2015 was observed indicating a positive effect of sprayed N on bud fruitfulness even when soil N availability is not limiting.

The fruit size of early ripening pear varieties is one of the most important attributes for its quality. In pear (Pyrus communis L.) the thinning effect of urea is controversial, even if urea sprays increase in general the average fruit size. We therefore tested the hypothesis that foliar-applied urea at bloom also plays an important nutritional role. Trials were carried out in two orchards of the experimental farm of the INTA Alto Valle research station, in the province of Rio Negro, Argentina on mature trees of the cv. “Williams Bon chretien” on seedling. Urea (5%, w/v) application at full bloom had a slight effect of fruit thinning of fruitlets, but increased fruit size and the number of cells per fruit. Sprayed spurs showed larger fruit weight before a significant difference in fruit number per spur was observed. The uptake of N from urea, measured by the aid 15N techniques, enhanced N concentration and contents of flowers and spur leaves by about 10%. Although we cannot exclude that the thinning effect of urea has contributed to the enhancing of the fruit size and the number of cells per fruits, our data indicated that before the thinning effect of urea occurred, the fruit size already benefited from the foliar N supply due to an enhanced leaf and flower N concentration. Due to the both the thinning and the nutritional effects, the supply of urea early of the season is therefore a powerful and relatively inexpensive tool for enhancing fruit size in pear trees.

Many studies on soil organic carbon (SOC) sequestration in perennial biomass crops are available for Atlantic and continental environments of North Central Europe, while there is insufficient information for Southern Europe. Therefore, we assessed SOC turnover under Mediterranean climate, after a 9-year-old conversion from two annual crop systems, continuous wheat and maize/wheat rotation, to Miscanthus (Miscanthus sinensis × giganteus) and giant reed (Arundo donax), respectively. The naturally occurring 13C signature down to 0.60 m was used to evaluate the total amount of SOC in annual vs perennial species and to determine the portion of SOC derived from perennial species. Soil organic C was significantly higher under perennial (average, 91 Mg C ha−1) than annual species (average, 56 Mg C ha−1), with a stronger accumulation in the topsoil (0–0.15 m). This difference was consistent with reduced soil disturbance associated with perennial crop management. After 9 years of Miscanthus plantation, the amount of C4-derived C was 18.7 Mg ha−1, mostly stored at 0–0.15 m, whereas the amount of C3-derived C under giant reed was 34.7 Mg ha−1 and was more evenly distributed through soil depths, probably due to its deeper root apparatus. It is suggested that both Miscanthus and giant reed have a remarkable potential for SOC sequestration also under Mediterranean conditions, while supporting the growing bioenergy sector with biomass supply.

none 6 no In this study, we assessed the carbon (C) distribution within soil aggregates, macroaggregates (Macro), microaggregates (micro), and silt and clay (s + c) through three soil depths (0– 0.15, 0.15–0.30, and 0.30– 0.60 m) and af ter 9 years of land conversion from two annual crops continuous wheat and maize/wheat rotation to Miscanthus and giant reed, respectively. The 13 C natural abundance analysis wa s combined with physical fractionation to trace the fate of the new C that wa s derived from Miscanthus and giant reed in aggregate fractions. Macro always represented the highest proportion of the soil and the highest amount of C. In Miscanthus, the amount of C decreased from the 0–0.15 to the 0.30–0.60 m soil layer, whereas the C storage capacity of micro and s + c increased with depth. In giant reed, the distribution of the soil fractions and the associated C were more uniform in all of the layers. The new C derived from the perennial species wa s mainly concentrated in the upper layer in the Macro under Miscanthus , whereas it wa s more evenly distributed in the three layers and the fractions under giant reed. Irrespective of the fractions, in the Miscanthus plantation, the great C accumulation wa s derived from both the new C directly entering the soil and the old C that wa s preserved from mineralization. Conversely, in the giant reed plantation, C accumulation wa s only derived from the new C component. These patterns reflect the different structure of the root apparatus of the two perennial species, which were mainly concentrated in the upper layer of Miscanthus and were more evenly distributed in soil profile of the giant reed. It is likely that this is responsible for the different mechanisms of C storage and turnover. mixed Gioacchini, Paola; Cattaneo, Francesca; Barbanti, Lorenzo; Montecchio, Daniela; Ciavatta, Claudio; Marzadori, Claudio Gioacchini, Paola; Cattaneo, Francesca; Barbanti, Lorenzo; Montecchio, Daniela; Ciavatta, Claudio; Marzadori, Claudio

Among Meliaceae derivatives, neem cake is usually used as a fertilizer; however its origin and industrial processing are often unknown, so that its effect on soil fertility is not predictable. In this study, the effect of soil incorporation of 6 commercial neem cakes and leaves of Melia azedarach L. on nitrogen (N) and carbon (C) dynamics was investigated in a 118-day laboratory incubation experiment. Neem cake at a rate of 8 g/kg of soil and melia leaves at16 g/kg were incorporated into the soil and their net N and C mineralisation were evaluated 2 h after application and at day 1, 2, 6, 12, 26, 54 and 118, by analysing a 50-g soil sample placed in 250 glass jars. The apparent net N mineralisation was well predicted by N concentration and C/N ratio of derivatives. The derivatives with a C/N ratio < 24 caused a net N mineralisation, whereas those with a C/N ratio ≥ 24 caused net N immobilisation. C mineralisation ranged between 15% and 25% and was not related to chemical composition of the derivative. Neem cake with a C/N ratio < 24 can be used to add N, while neem cake with a C/N ratio > 24 can be used to reduce soil mineral N. © 2016, Czech Academy of Agricultural Sciences. All rights reserved.

The fate of nitrogen (N) derived from soil incorporating 15N-labeled apple (Malus domestica) leaves and wood from pruning (hereafter referred to as “pruning wood”) was studied in an 8-month pot experiment. The net mineralization of N was measured as 15N recovery in perennial ryegrass (Lolium perenne) that was allowed to grow in soils amended with residues

Each year, significant fractions of nutrients absorbed by trees and orchard grasses, return to the soil by abscised leaves and mowed biomass. Using litter bag technique and labelled ( 15 N) litter, we assessed the decay dynamics and the related nutrient releases in a mature, drip irrigated, apple ( Malus domestica ) orchard located in the Eastern Po Valley (Italy) on a silty clay loam soil. Litter bags containing abscised apple leaves were placed in December 2001 on the soil surface and collected over a 2-year period, while the decomposition of perennial ryegrass was studied over a 6-month period from May 2002. The dynamics of mass and C losses from decomposing apple leaves fitted to a single exponential decay model. At 1 year from their placement, about 50% of original mass was lost, while and additional 20% was not recovered in the second year. Initial C losses were not accompanied by degradation of cellulose which started only in the spring of the year after their placement on the soil. Along with the decomposition process, the remaining litter was progressively enriched in lignin-like compounds. Net N and S immobilization occurred during the winter–spring period and net release of these nutrients occurred only in the second year. Ryegrass lost about half their mass and original N content after 6 weeks and most of sward derived N was recovered in the underneath soil volume. Both apple and ryegrass released most their initial K content during the period of decomposition. The knowledge of the dynamics of nutrient release on the orchard floor will be useful for predicting nutrient availability for tree uptake and therefore for managing amounts and dynamics of nutrient supply.

Olive pulp (OP), the residual material of a two-phase olive oil extraction system, and effluents from hydrogen (EH2) and methane (ECH4) production, have been evaluated as soil amendments particularly for their impact on soil mineral nitrogen (N) dynamics, gross N mineralization, and soil microbial biomass N (Nmic). Both N transformation and microbial growth were mainly influenced by the amount and quality of added organic carbon (C). Both OP and EH2, which contain more carbohydrates and lipids than polyphenolic compounds, stimulated NO3 − immobilization during the early incubation period and increased Nmic, saprophytic fungi, and N mineralization. On the contrary, soil amended with ECH4, which is characterized by the lowest C content but the highest content of polyphenolic compounds, behaved as the control; neither NO3 − immobilization nor microbial growth were observed and gross N mineralization was stimulated only at the beginning of the incubation period. Bacterial plate count was significantly correlated with direct bacterial count and fungal count was correlated with Nmic. Therefore, it is suggested that both bacterial and fungal plate counts may be used as indicators of the overall bacterial and fungal populations inhabiting soil, respectively. The knowledge of the impact of these materials on soil N dynamics is crucial for their correct use in agriculture because it has been shown that NO3 − availability can be strongly influenced by the addition of different amounts and quality of organic amendment.

In the current study, total organic carbon (TOC) analysis and spectroscopic characterization (IRMS, DRIFT, and SERS) are applied to investigate the molecular changes in humic acids (HA) extracted from soil samples amended for more than 30 years with cattle manure (CM), cow slurries (CS), and crop residues (CR). All samples are compared to the unamended (T) sample. A variation in soil TOC percentage occurs in all samples, but a significant (P

Thermal analyses (TG-DTA), elemental composition and isotope analyses (13C and 15N) were performed on humic acids (HA) from peats, leonardites and lignites, in order to investigate their structure and the changes taking place during the humification process. Thermal analyses showed structural differences between HA samples in relation to their coalification rank. In particular the lignite HA were characterized by a more stable chemical composition at high temperatures. The δ13C and δ15N values can provide information on the biogeochemical processes involved in HA formation. In particular, peat HA were linked to anoxic environments that enable plant residues to persist in their structure. In contrast, leonardite and lignite HA formation seems to be governed by different biogeochemical processes from those responsible for peat diagenesis. However, the isotopic analyses did not provide any distinction between leonardite and lignite HA. On the basis of the data presented in this study, it may be concluded that TG-DTA and isotope ratio measurements are powerful tools for investigating the formation pathway of humic substances from coals. © 2004 Elsevier Ltd. All rights reserved.

Soil microorganisms are actively involved in many processes of the soil N cycle and are strong competitors with plants for soil N. Therefore, microbial dynamics are important factors in controlling forest productivity. Nevertheless, they are poorly studied especially in relation to forest age, which can produce strong effects on the microbial community by affecting the forest floor environment. In the present study, seasonal variations of soil microbial N (Nmic) were monitored in an old floodplain hardwood forest (270 years) and in a young hardwood plantation (19 years) in two soil horizons (0–15 and 15–30 cm). Although the differences according to time of sampling and soil horizon were statistically significant, Nmic was significantly higher in old than in young forest, especially for the deeper soil layer. However, the highest percentage of total N (Ntot) immobilised in microbial biomass was found in the surface soil layer of the young plantation. Soil organic C (Corg) explained 23% of the spatial–temporal variation of Nmic over all sampling periods in the old forest, whereas the linear combination of Ntot, total extractable soil N (Ntotex) and the C/N ratio explained 59% of variation in Nmic when considering only the growing season. In contrast, Corg and Ntotex explained 59% of variation in Nmic in the young stand when considering all sampling periods and 75% when the analysis was limited to growing season. Soil moisture did not show any significant correlation with Nmic in either site. The sensitivity of Nmic to variation in Corg and Ntot seems to be affected by forest age, being higher in young than in old forest. Finally our results indicate that during the growing season, when the Ntotex availability is low, the dynamics of Nmic and Ntotex are temporally interdependent, suggesting the existence of a reciprocal control whose mechanisms deserve to be elucidated.

Nitrogen (N) storage capacity of cherry (Prunus avium L.) trees grown in sand culture was preconditioned by applying contrasting N supplies for one year. During the spring of the following year, a constant amount of 15N was supplied and the dynamics of N remobilization and root uptake were characterized as a function of internal N status of the trees. To calculate the flux of N through xylem, both xylem sap N concentration and whole-tree transpiration rates were measured. By comparing the cumulative flux of N through the xylem with the amount of N recovered in the new above ground growth, we indirectly evaluated the recycling of N in the xylem, i.e., the amount of N derived from shoot-root translocation that was subsequently reloaded into the xylem. The contrasting N storage capacities imposed during the first year affected both N remobilization and uptake from roots in the following year. Recycling of N in the xylem apparently did not occur during the remobilization of internal reserves (i.e., during the first 6-8 weeks after bud burst). However, when remobilization declined, measurement of the cumulative flux of N through the xylem overestimated the amount of N recovered in the new biomass, allowing the extent of N recycling to be evaluated. The amount of N recycling in the xylem was greater in high-N trees, which also took up less N through their roots than trees preconditioned to have a lower internal N status. This suggests that recycling of N in the xylem is a mechanism by which plants regulate N uptake by roots.

In agricultural calcareous soils, hydroxyapatite (APA) may well represent an important support for urease immobilisation and could be present in both mineral and organo-mineral complexes. In this paper we studied the formation of APA-urease-humic acid (HA) complexes after the addition of urease either before or after HAs. We then proceeded to evaluate the role of HAs on the activity and stability of the complexes as compared to the APA-urease complexes and free urease. When increasing amounts of HAs were added after urease, they did not affect the activity of the enzymes that had already adsorbed onto the complexes. On the contrary, adding the same amount of HA before the enzyme caused a significant reduction in the amount of enzyme adsorbed. However, when urease adsorption onto the APA-HA complexes was carried out in the presence of NaCl, the enzyme activity of the complexes increased sharply to 86% of the initial activity. The immobilisation of the enzyme on the support increased urease stability against pronase treatment as well as directly in soil over time. The inhibition of urease activity by Cu2+ was reduced by urease immobilisation. However, the presence of HA did not alter the stabilisation capability of APA when alone.

The aim of this study was to evaluate how the N losses through volatilization and leaching from soils fertilized with urea can be affected by the application of a urease inhibitor or a urease plus a nitrification inhibitor. The experiment was carried out using lysimeters with 15N-labelled urea and N-(n-butyl) thiophosphoric triamide (NBPT) as urease inhibitor and dicyandiamide (DCD) as nitrification inhibitor, comparing three different treatments: urea alone (U), urea + NBPT (UN) and urea + NBPT + DCD (UND). Both volatilization and leaching were significantly different in the soils used, according to their physico-chemical characteristics. However, the pattern of the loss was similar: the volatilization was significantly reduced by NBPT (UN), but the presence of DCD (UND) significantly increased the loss, with respect to UN. Considering leaching, the highest amount of NO3 – was lost with UND, the lowest with U. The greatest amount of N lost by leaching was soil-derived N produced by the N mineralization-immobilization turnover. We suggest that, by maintaining the NH4 + in the soils, the inhibitors, in particular DCD, caused a priming effect with a subsequent increase in the rate of soil organic matter mineralization and an extra release of soil organic N. The priming effect was real in the sandy loam (SL) soil where a net N release was observed, whereas in the clay loam (CL) soil the effect of the inhibitors was less pronounced and an apparent priming effect was observed; however, a real priming effect also cannot be excluded in this soil.

We investigated the topsoil from some mountain Regosols for their nutrient status and loss of fertility due to aggregate breakdown, establishing also the relationship between the nutrient losses, the soil characteristics and the aggregates stability. The aggregate stability varied from 57 to 80%. The nutrient losses differed among elements and varied from 20 to 96%. The availability of nutrients directly influenced the quality of nutrient losses, but did not influence the quantity of nutrients lost. K, Mg and Ca were the most susceptible element to the water abrasion (>85% of their total loss was due to water abrasion). Instead for C, N, and partly P, important loss occurred because of the water saturation alone and their losses were related to the aggregates ruptures due to fast wetting (r=0.98, 0.99 and 0.81, respectively). These findings suggest a high vulnerability to soil fertility losses, and that a great depletion can occur even because of rainfall of low intensity, but sufficient to water saturated the topsoil. We investigated the topsoil from some mountain Regosols for their nutrient status and loss of fertility due to aggregate breakdown, establishing also the relationship between the nutrient losses, the soil characteristics and the aggregates stability. The aggregate stability varied from 57 to 80%. The nutrient losses differed among elements and varied from 20 to 96%. The availability of nutrients directly influenced the quality of nutrient losses, but did not influence the quantity of nutrients lost. K, Mg and Ca were the most susceptible element to the water abrasion (>85% of their total loss was due to water abrasion). Instead for C, N, and partly P, important loss occurred because of the water saturation alone and their losses were related to the aggregates ruptures due to fast wetting (r=0.98, 0.99 and 0.81, respectively). These findings suggest a high vulnerability to soil fertility losses, and that a great depletion can occur even because of rainfall of low intensity, but sufficient to water saturated the topsoil., EQA - International Journal of Environmental Quality, Vol 11 (2013)

A laboratory experiment evaluated the rate of urea hydrolysis and ammonia volatilization from urea (U) mixed in organo‐mineral (O‐M) fertilizers. These fertilizers were incubated in soil in the presence or absence of N‐(n‐butyl)thiophosphoric triamide (NBPT) as a urease inhibitor. Two organic matrices, leather (L) and peat (P), were used to prepare the O‐M fertilizers. In the absence of NBPT, the highest ammonia losses and the fastest rate of urea hydrolysis were in the soil treated with the fertilizer containing leather (UL50). Significantly lower ammonia losses occurred with peat‐based fertilizers. Although the fertilizer containing peat (UP50) stimulated the rate of urea hydrolysis with respect to the urea alone, no increase in ammonia volatilization was detected. NBPT‐containing fertilizers were stored for different times (0,7, 30, and 60 days) and temperatures (25°C and 40°C), and the NBPT recovery was monitored by extraction and analysis by HPLC. The NBPT recovery decreased by increasing ei...

The amount of interlayer NH 4 + -N and net mineralization of organic N were measured at periodic intervals, over a period of 10 months, in soil samples collected from a peach orchard which had been subjected to different rates of N fertilizer application. Two different groups of soil samples, designated sampling 1 and sampling 2 were collected. Soils of sampling 1 were collected from sites where the soil was heavily penetrated by tree roots and those of sampling 2 were collected from sites where the soil remained free from tree roots. In sampling 1, during the 10-month period, the concentration of interlayer NH 4 + -N showed significant variations, while in sampling 2 no significant variation was found. In sampling 1 the amount of NH 4 + -N released from the interlayers of the clay minerals were not influenced by the N fertilizer application rate. Changes in the interlayer NH 4 + -N concentrations were related to variation in net N mineralization and immobilization rates as well as to plant uptake N. It is concluded that, in our experiment, the dynamics of interlayer NH 4 + -N in soil were influenced by the spatial distribution of the tree roots and organic N mineralization, while N application influenced seasonal variation but not the total interlayer NH 4 + -N released during the experiment.

Laboratory incubation experiments were conducted to study the influence of increasing concentrations of N-(n-butyl)phosphorothioic triamide (NBPT) on NH3 volatilization and rate of urea hydrolysis and evolution of mineral N in Ozzano, Rimini and Carpi soils with different physicochemical characteristics. Low concentrations of NBPT reduced NH3 losses due to volatilization after urea fertilization and the effectiveness of the inhibitor was related to the soil characteristics (e.g. high concentrations of organic C and sand). After 15 days of incubation, no significant reductions of losses were found for any of the NBPT concentrations employed in Rimini soil. The application of NBPT led to a considerable reduction of the formation of nitrite. This process was completely annulled with the highest dose of NBPT (0.5% w/wurea) in the Carpi soil after 15 days. In Rimini soil, however, the use of NBPT was less effective in influencing nitrite formation. The use of NBPT favoured accumulation of nitrate proportional to the NBPT concentration employed while it had no influence on the NH inf4 sup+ fixation by 2:1 layer silicates. The data obtained support previous evidence that NBPT is effective in reducing the problems encountered in using urea as fertilizer. However, environmental conditions and soil physicochemical characteristics may have an important influence on the effectiveness of NBPT.

In organic farming winter cereals, as cover crops, provide nutrients, when they return to soil as crop residues. The fate of N deriving from two decomposing 15N-labelled winter cereals, with or without the supply of an organic N fertiliser, was studied in a field experiment. The stabilisation of residues N in soil aggregates and the portion lost from the system were also evaluated. Barley or triticale residues were incubated alone or with hydrolysed leather (L) in mesocosms over one year. The residues derived N was measured in soil and in soil aggregate size fractions >250 μm (macroaggregates, macro); 53–250 μm (microaggregates, micro)

Tannery land plaster (TLP) is a byproduct of lime hydrolysis of leather shavings. Its use in agriculture (organic C ≈ 17%, N ≈ 6% dm) could represent an alternative to landfill or incineration, but the high Cr(III) content (≈5% dm) makes it necessary to evaluate the effect on soil biochemical properties. TLP was therefore added at the rates of 220 and 440 kg of N ha−1to 2 agricultural soils and incubated for 56 days under controlled conditions. Extractable NH4 +-N and NO3 −-N, CO2-C evolution, microbial biomass-N, protease activity, and extractable Cr were monitored. The organic N was readily mineralized (>50% in the first week) and a significant increase in microbial activity was measured, regardless of soil type and addition rate. Extractable Cr(III) quickly decreased during the incubation. The absence of a negative impact on soil biochemical properties seems to support the use of TLP in agriculture, although further investigations in long-term field experiments are suggested.

We studied the turnover of interlayer NHinf4sup+in three soils cropped with sugar beet. The three soils chosen for this study (Carpi, Cadriano, and Ozzano) are typical of the soils in the Po Valley where sugar beet is grown. The variation in interlayer NHinf4sup+content during the growing season was significant and very similar for the Carpi and Cadriano soils, while there was no significant variation in the NHinf4sup+content in the Ozzano soil during the same period. The turnover of interlayer NHinf4sup+in the Carpi and Cadriano soils was high, and appeared to cover a substantial amount of the N requirement of the crop. The turnover in these two soils showed a significant decrease during the initial phase followed by a period during which the pool of interlayer NHinf4sup+was replenished and reached the initial levels again. The spatial distribution of the root system, the pattern of N uptake by the sugar beet crop, and the processes of immobilization-mineralization of organic N all have an influence on the mechanisms of adsorption and release of interlayer NHinf4sup+. The release of interlayer NHinf4sup+, and thus its availability for plant uptake, was greater at the beginning of the growing season. The physicochemical characteristics of the soils, the K concentration, and the types of clay minerals present were found to be important in determining the dynamics of interlayer NHinf4sup+turnover of soils.

Although acid soils are common in forest ecosystems, and there is documented evidence of pH influencing transformations of organic matter in soil, there are surprisingly few studies on the influence of soil pH on the chemical structure of physically fractionated soil organic matter (SOM). The aim of this study was to characterize the influence of pH on the chemical and physical processes involved in SOM stabilization. Forest soils of different pH (4.4 and 7.8) sampled from two long-term experiments at Rothamsted Research (UK) were physically fractionated. The free light fraction (FLF), the intra-aggregate light fraction and the fine silt and clay (S + C

Rhizodeposition plays an important role in nitrogen (N) cycling within ecosystems, but it is understudied in agroecosystems, especially in orchards. In this study, we quantified N flux from peach root to soil in two soils with different texture. Seedlings were grown for 1 year in sand and fertilized with 15N-enriched ammonium nitrate. Trees were then transplanted into pots filled with a coarse-textured (CT) or a fine-textured (FT) soil with natural 15N abundance. The isotopic mass balance technique was applied to quantify the uptake and the release of N by roots. At the end of the experimental year tree growth was 431 g tree−1 in CT soil and 188 g tree−1 in FT soil, and root N concentration was 0.98% in CT soil and 0.73% in FT soil. Leaf chlorophyll was always higher in trees grown in CT than in FT soil. Nitrogen uptake in CT soil was more than double that in FT soil (4471 mg tree−1 vs. 2106 mg tree−1), but its allocation was not affected by soil texture (57% aboveground and 43% belowground). Nitrogen flux from roots to soil was 453 and 412 mg N tree−1 year−1 for trees in CT and in FT soil, respectively, 70% of which transferred in the winter. Our data suggest that root mortality is more important than root exudation in N transfer from roots to soil. Rhizodeposition was similar for both soils but tree growth was greater in CT soil than in FT soil. As a consequence, trees in FT soil allocated belowground (root biomass and rhizodeposition) a higher proportion of the absorbed N compared to trees in CT soil. Data also indicate that rhizodeposition can account for a major fraction (25–41%) of the photosynthate flux to the root system and therefore it should be considered to accurately estimate BNPP. A deeper knowledge of the belowground orchard processes is necessary to understand a balanced tree nutrient uptake. Rhizodeposition can also contribute to nutrient mobilization, heavy metal detoxification, root exploitation of soil, and drought tolerance. This work can thus provide information enabling horticulturists to develop management practices to optimise tree growth.

Humic acid extracted from the A horizon of a Chernozem soil and their different molecular size (MS) fractions obtained by SEC–PAGE were investigated using thermal (TG–DTA), spectroscopic (DRIFT) and isotopic (δ13C) analyses. Moreover, the molecular structure of the high temperature stable fraction (residues above 400 °C) was studied by DRIFT spectroscopy. The lowest MS fraction (C + D) was characterized by the highest content of aromatic compounds and by the lowest content of aliphatic and carboxyl groups, carbohydrates and amino acids with respect to the other fractions. Nevertheless, the aromatic structure of A and B fractions seems to be more complex. The δ13C values which indicated the presence of urea traces in the lowest MS fractions (B and C + D) may be due to the purification process.

The mass transfer from root to soil by means of rhizodeposition has been studied in grasses and forest trees, but its role in fruit trees is still unknown. In this study, N fluxes from roots to soil were estimated by applying a 15N mass balance technique to the soil–tree system. Apple (Malus domestica) trees were pre-labelled with 15N and then grown outdoors in 40 L pots for one vegetative season in (1) a coarse-textured, low organic matter soil, (2) a coarse-textured, high organic matter soil, and (3) a fine-textured, high organic matter soil. At tree harvest the 15N abundance of the soils was higher than at transplanting, but the total amount of 15N present in the tree–soil system was similar at transplanting and tree harvest. The soils had a strong effect on N fluxes from and to the soil. In the fine-textured soil, 11% of the total plant-derived nitrogen was transferred to the soil, compared with 2–5% in the two coarse-textured soils. Rhizodeposition was higher in the fine soil (18% of the primary production) than in the coarse-textured soils, whereas higher soil organic matter depressed rhizodeposition. Nitrogen uptake was almost double in the coarse-textured, high organic matter soil versus the other soils. Our results indicate that belowground primary productivity is significantly underestimated if based on root production data only. Rhizodeposition represents a major process, whose role should not be underestimated in carbon and nitrogen cycles in orchard ecosystems.

The purpose of the present study is to investigate, by means of thermogravimetric analysis (TG) and differential thermal analysis (DTA), diffuse reflectance infrared Fourier transform (DRIFT) and 2D nuclear magnetic resonance (NMR) spectroscopies, the structural features of the humic-like fraction (HLF) from olive pulp (OP), its effluents originated from the fermentation processes for hydrogen (EH2) and methane production (ECH4) and humic acid (HA) from soil amended with each of these materials. A considerable structural modification emerged between the HLF, in particular from the ECH4 effluent, which was characterised by a high content of polyphenolic and polypeptidic substances. The short-term amendment trial with OP and EH2 indicated that no chemical or structural changes in soil HA appeared. In contrast, the amendment with ECH4 substantially influenced the chemical and structural composition of soil HA. The structural interpretation performed by 2D NMR indicated the presence of aliphatic and aromatic protons while the sugar-like content and O-CH3 groups decreased with respect to the soil control HA. It emerges from this study that olive wastes contain stabilised humic-like material that may be recycled as an amendment in areas where olive trees are cultivated.

In the present study, rates of litter decomposition and microbial biomass nitrogen were monitored over an 8-month period in a young broadleaf plantation (18 y) and in an old floodplain forest. Moreover, delta13C and delta15N temporal variations within soil profiles were evaluated at both sites. Rates of litter decomposition were higher in spring and autumn than in summer, in both forests. At the end of the observation period the percentage of original litter remaining was not statistically different between the young and the old forest and accounted for 60-70% of the original amount. Microbial biomass nitrogen in the remaining litter and the percentage of litter mass lost during decomposition were positively correlated. The difference in litter quality affected the decomposition rate and also the changes in carbon isotopic composition during the decomposition process. In contrast, 15N isotopic signatures showed a similar trend in the litter of the two forests irrespective of the litter quality. Although delta13Csoil and delta15Nsoil showed considerable temporal variation they increased with depth in the soils of both sites but their seasonal changes did not reflect those of the decomposing litter. Within the same soil horizon, both delta13C and delta15N showed similar seasonal trends in the soils of the two forests, suggesting the involvement of environmental factors acting at regional level, such as soil temperature and rainfall variations, in regulating seasonal delta13C and delta15N soil variations.

In this study, five different slow-release fertilizers were incubated in two soils and their N dynamics was followed for four months. Four of the fertilizers used were organic: two were hydrolyzed fur, one was made by hydrolyzed fur, farmyard manure, horn and hoofs (Endurance), and one contained synthetic organic N (isobutylidendiurea, IBDU). The fifth, on the contrary, was a mineral fertilizer (Entec 26) containing both NO3- and NH4+ and a nitrification inhibitor (3,4 DMPP). The two soils used were a sandy loam (SL) and a clay loam (CL). The fertilizer-N release was conditioned by both the fertilizers and the soil characteristics. The highest accumulation of mineral N as NO3- was observed in the SL soil for all the treatments. The lowest net N release was observed in both soils with End. which was found to be the most resistant to microbial attack and degradation. The two fur-based fertilizers released similar amount of N which was higher in the SL soil than in the CL soil. The highest accumulation of fertilizer-derived N in the CL soil resulted from IBDU, however, the net accumulation of N in the SL soil with this fertilizer, was even higher than the amount of N initially added. This fact was attributed to an increase in mineralization of the soil’s native organic N. A real positive "priming effect" was also observed in the SL soil with E26. On the contrary, E26 caused a low level of N accumulation in the CL soil.

Resumption of growth in deciduous fruit trees in spring depends largely on the re-mobilisation of nitrogen (N) from reserves in perennial organs. Root nitrogen uptake starts before re-mobilisation is finished. Uptake may take place as either nitrate or ammonium. As uptake rates may differ significantly between both sources, we assessed uptake and partitioning of N labelled with 15N. A part of the trees was girdled to test the hypothesis that root N uptake depends on availability at root level of phloem transported carbohydrates.

Potentially mineralizable nitrogen and interlayer ammonium-nitrogen pools of the soil were determined. The mineralization process has an influence on fixation and release of interlayer ammonium. During long-term incubation for determining of the potentially mineralizable nitrogen of soil, the mineralized nitrogen could be affected by the realease of inorganic nitrogen from the other pools, particularly from the interlayer ammonium-nitrogen pool.

Energy crops are designed for biomass production to generate bioenergy. Their recent introduction in the Po Valley (North Italy) is connected to the mitigation of environmental effects of the intensive management. Intensive management has a dramatic impact on the soil ecosystem of the area, reducing soil organic matter, degrading soil structure and altering nutrient cycles by reducing microbial biomass, and thus compromising soil productivity. Soil organic carbon (SOC) content in the Emilia-Romagna region is the lowest in the Po Valley (