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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.

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.

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.

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.

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.

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.

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.

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.

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.