Nitrogen Stocks Research Articles

Management intensive grazing on New England dairy farms enhances soil nitrogen stocks and elevates soil nitrous oxide emissions without increasing soil carbon

Management intensive grazing (MIG), also known as rotational grazing or multi-paddock grazing, is purported to sequester carbon (C) in soils compared to other agricultural management systems. Prior research examining the potential for MIG to enhance soil C has been inconclusive, and past investigations have not addressed whether higher nitrous oxide (N2O) emissions may accompany increases in soil C stocks. Here we examined linkages among MIG, soil C accumulation, and N2O emissions in cool-season, organic pastures of the northeastern United States. We found that pastures under MIG increased soil C concentrations by 11% from 0–15 cm depth but that soil C stocks at all sampled depths did not differ between hayed and grazed fields. We observed a divergent response in soil N to MIG, where both N concentrations and stocks significantly increased and the soil C:N ratio significantly decreased in rotationally grazed pastures. Our results also demonstrated that during the second year of the study, N2O emissions were on average 33% higher in grazed fields and compared to hayed fields. These elevated N2O fluxes in MIG fields may have offset any soil C gains achieved under MIG, as demonstrated by similar climate forcing values (as CO2-equivalents) for hayed and grazed pastures over a 100-year time horizon. The significant variation we detected among farms in soil C and N stocks, soil microbial activity, plant biomass production, and soil greenhouse gas emissions demonstrates that MIG does not have uniform effects across the landscape. Overall, our study demonstrates that care should be taken when promoting management practices that may have unintended climate consequences.

Cowpea Crop Response to Mineral and Organic Fertilization in SE Spain

Mineral fertilization is considered to be useful for improving soil fertility and yields. However, its use is linked to global warming and soil and water pollution by its rapid mobilization. On the other hand, organic fertilization is recommended to maintain or improve soil organic carbon and total nitrogen stocks while contributing to climate change mitigation. The main goal of this study was to assess the effect of two different fertilizer types, mineral and organic, during three cowpea crop cycles on the soil’s physicochemical properties, enzyme activities, crop yield, crop quality and nutritional composition when considering two cowpea cultivars (Feijão frade de fio preto (FP) and Feijão frade de fio claro (FC)). The use of mineral fertilizers was seen to contribute to improved soil fertility due to the increase in soil properties, such as recalcitrant carbon, total nitrogen, ammonium content, available K and available Mg. On the other hand, organic fertilizers only increased the nitrate content in the soil. There were no differences in terms of cowpea crop yield, quality and nutritional composition by fertilizer type. Thus, both fertilizer types contributed to the same crop yield and quality, and thus the use of organic fertilizers can result in a sustainable alternative for maintaining cowpea crop yield and quality.

Fate of plastic film residues in agro-ecosystem and its effects on aggregate-associated soil carbon and nitrogen stocks

Biodegradable (Bio) plastic films are widely viewed as promising alternative products of low-density polyethylene (LDPE) films to minimize plastic debris accumulation and pollution in agroecosystems. Yet, this speculation indeed lacks of sufficient evidences. We conducted a landfill investigation on the aging characteristics of Bio and LDPE plastic films in maize field, and the effects on soil aggregate composition and carbon & nitrogen stocks. The degradation rate of Bio film was up to 41.1% while that of LDPE film was zero. Scanning electron microscope (SEM) showed that the crack formation of Bio film had a pronounced domino effect, and FTIR showed that old Bio film displayed an extra wide peak threshold ranging from 3000 to 3500 cm−1. Particularly, the abundance of microplastics was elevated with the increased plastic residues, and the increment mostly resulted from Bio residues. Critically, plastic residues significantly lowered the soil macro-aggregates (>0.25 mm) proportion, while increasing that of micro-aggregates (0.1–0.25 mm) in LDPE, and silt/clay fraction (<0.1 mm) in Bio respectively. They significantly promoted total nitrogen content of the aggregates with the same size, but decreased the organic carbon content, dramatically lowering the C/N. Therefore, we first identified the fate of plastic film residues in agroecosystems and revealed the serious deficiencies of Bio plastic film.

Life Cycle Assessment and Soil Nitrogen Balance of Different N Fertilizers for Top Dressing Rye as Energy Crop for Electricity Generation

Nitrogen fertilizers have been identified in energy crops LCAs as the main contributors to global warming, as well as to many other environmental impacts. The distinct production process and application emissions of nitrogen fertilizer types for top dressing produce different GHG savings when energy crops value chains are compared to fossil energy alternatives. In this study, three types of fertilizers (calcium ammonium nitrate, urea and ammonium sulphate) at N top dressing rates of 80 kg N/ha are used to grow rye for electricity generation under the conditions of the Continental Mediterranean climate of central-northern Spain. Complete LCAs for the whole value chain based on real data were performed in conjunction with soil nitrogen balances (SNBs) to assess the accomplishment of European Union (EU) GHG savings sustainability criteria, as well as the sustainability of fertilization practices for soil nitrogen stocks. The results obtained can provide interesting insights for policy making, since calcium ammonium nitrate, the most common fertilizer for rye crops, led to 66% GHG savings, as opposed to the 69% achieved when applying urea and 77% when ammonium sulphate was used. Nevertheless, the three fertilizers produced annual soil deficits greater than 50 kg N/ha. In order to ensure savings above 80%, as required by the EU sustainability criteria, and sustainable SNBs, additional optimization measures should be taken at key points of the value chain.

Impacts of forest harvest removal and fertiliser additions on end of rotation biomass, carbon and nutrient stocks of Pinus radiata

Forest harvesting practices remove tree biomass and the nutrients that they contain. There is uncertainty around the impact of this nutrient removal on the long-term sustainable production of forests over multiple rotations. To explore the impact of harvest management practices on planted forest sustainability, three long-term trials in Pinus radiata D. Don forests were assessed at the end of their second rotation of 26 to 27 years to determine the impact of harvest residue removal and fertiliser additions on sustainable forest productivity. The harvest residue removal treatments were stem only (SO), whole-tree (WT), and whole-tree plus forest floor (FF) removal with and without urea-nitrogen fertiliser additions (cumulative range across three sites 950 – 3200 kg N ha−1) from early rotation out to mid-rotation (last fertiliser application age range across sites 8 – 22 years). The FF removal treatment reduced soil carbon and nitrogen stocks throughout the subsequent rotation, whereas forest floor carbon and nutrient stocks had recovered from the FF removal treatment by the end of the rotation. Forest productivity was reduced at one site with the FF removal treatment, taking 3 years longer for stems to reach 35 cm diameter at breast height than other residue removal treatments. Between WT and SO harvest residue treatments there were very limited impacts on soil carbon and nutrient stocks, no impact on forest floor mass, carbon and nutrient stocks and the sum of the above ground live biomass, carbon and nutrient stocks or tree productivity. Across all harvest removal treatments fertiliser addition increased soil carbon and nitrogen stocks for sites with low initial soil stocks. The increased soil carbon and nitrogen stocks from fertiliser addition were associated with forest productivity gains with the time to reach 35 cm (diameter at breast height) for one site reduced by 3 – 5 years. Fertiliser addition to sites with FF removal was able to mitigate soil carbon and nitrogen stocks only when very large amounts of fertiliser were added (cumulative amounts of 1150 and 3200 kg N ha−1). The end of rotation results from this long-term study demonstrate the importance of harvest residues and forest floor material at low fertility sites for long-term nutrient sustainability in planted forests.

Fine root production, turnover of Reaumuria songarica and soil carbon and nitrogen in Alxa steppe desert of NW China

Variations of fine root production and turnover of the dominant shrubs associated with soil carbon (C) and nutrients are of key importance for evaluating desert ecosystem sustainability. Here we examined fine root production and turnover rate of Reaumuria songarica in Alxa steppe desert of northwestern China through sequential coring, ingrowth cores, and mesh‐bag methods, and then assessed soil C and nitrogen (N) stock and its correlation with fine root and leaf litter input. Results showed that fine root production and turnover rate were closely related to soil water content. Fine root production density and turnover rate of R. songarica were 386.8 g m−2 and 2.4 yr−1, respectively. Annually, fine root and leaf litter of R. songarica input 126.3 g C m−2 and 4.7 g N m−2 to soil. Soil organic C and N under shrub canopies increased substantially, which promoted the heterogeneity of soil properties and is considered as an important mechanism underlying the restoration of degraded sandy lands.

Impacts of irrigation on soil C and N stocks in grazed grasslands depends on aridity and irrigation duration

Irrigation has been used for millennia to increase the quantity and reliability of food and fibre production in areas where lack of precipitation limits plant growth. Despite the importance of irrigation, our understanding of the impact of irrigation on soil carbon (C) and nitrogen (N) stocks is still limited, particularly for grazed grasslands. In this study, we analysed soil profile C and N data collected to 0.6 m depth from 124 paired irrigated and unirrigated grassland sites across different regions and soils in New Zealand. Averaged across all sites, soil C and N stocks were significantly lower in irrigated than adjacent unirrigated soils. Cumulative differences increased with depth in the profile to a maximum at 0.5 m, where irrigated soils had 5.21 Mg ha−1 less C (P < 0.001) and 0.3 Mg ha−1 less N (P < 0.05). The C:N ratio was also consistently lower (P < 0.001) in irrigated soils. There was no evidence for an overall effect of soil order or region on the irrigation effect on C and N, but there was a significant negative relationship between the irrigation effect on soil C and aridity. There was no irrigation effect on soil C at the most arid sites, but as aridity decreased (precipitation >575 mm or aridity index >0.85) there were increasingly significant C losses from irrigated soils relative to adjacent unirrigated soils. There was evidence that the effect of irrigation increased with irrigation duration – from no significant effect at any depth for sites irrigated for <6–12 years, to a difference of 8.2 Mg C ha−1 in the top 0.5 m for sites irrigated for more than 12 years. There was no compelling evidence for continued long-term loss of C, which suggests that a new equilibrium may be reached with soil C stocks 5–10 Mg ha−1 lower under irrigated than unirrigated grasslands. Lower C stocks in irrigated than unirrigated soils do not agree with current IPCC recommended default values and this discrepancy needs to be addressed.

Comparing carbon and nitrogen stocks in paddy and upland soils: Accumulation, stabilization mechanisms, and environmental drivers

Paddy soils, a type of Hydragric Anthrosol, have much greater soil organic C (SOC) and total N (TN) contents than that in upland soils. However, this fact has never been generalized or mechanistically explained. We conducted a global meta-analysis on the organic C and total N contents and their stocks in continuous paddy soils (578 sites) and compared them with those in adjacent upland soils. Average C stocks up to depths of 35 cm in upland and paddy soils were 31 and 47 Mg C ha−1, respectively. The N stocks in upland and paddy soils were 2.2 and 3.2 Mg N ha−1, respectively. The combined effects of mean annual temperature and precipitation showed that C and N stocks in paddy and upland soils are generally the largest under cool and humid conditions and the smallest in warm and dry climates. Quantitative analysis of climatic, and soil physical and chemical factors showed that 1) climate effects are weakened by management such as puddling and flooding, thereby increasing the importance of soil physico-chemical properties, which control soil organic matter (SOM) stabilization, and 2) climate (e.g., mean annual precipitation) mainly affects C and N stocks in upland soils; the chemical properties (such as pH), on the other hand, primarily affect C and N stocks in paddy soils. Greater C and N stocks in paddy soils are the result of 1) a larger input of organic C by rice than by most upland cereals, 2) slower decomposition of plant residues and SOM under anoxic conditions, and 3) a greater importance of sesquioxides in the biochemical stabilization of SOM. We conclude that these man-made paddy soils store more organic C and N than their upland neighbors despite long-term and intensive management.

Carbon and nitrogen stocks and microbiological attributes of soil under eucalyptus cultivation in the Pampa biome of southern Brazil

In the south of Brazil, the intensification of eucalyptus planting can impact the local biome, characterized by grasslands that extends to Uruguay and Argentina. Thus, the objective of the study was to evaluate changes in soil carbon, nitrogen and their labile fractions and soil microbiological attributes due to the introduction of eucalyptus cultivation in the Pampa biome. The soils evaluated were Eutric Regosol (RG), Haplic Lixisol (LX), Dystric Leptosol (LP) and Pellic Vertisol (VR). For this, areas of homogeneous cultivation of Eucalyptus saligna (7 years old) and areas of grassland (native vegetation) were selected. Physical granulometric fractionation of soil organic matter (SOM) was performed in the 0–5, 5–10 and 10–15 cm soil layers, quantifying levels, stocks and distribution of total organic carbon (TOC) and total nitrogen (TN) in the labile and associated with minerals fractions, and the carbon management index (CMI) was calculated. In the 0–5 and 5–10 cm soil layers, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), basal soil respiration, metabolic coefficient, MBC / TOC, MBN / TN, MBC / MBN ratios were also evaluated. Eucalyptus cultivation increased the TOC and POC carbon stocks by 8.7 and 21.7%, respectively (0-15 cm) in compared to grassland. It was also observed that the cultivation of eucalyptus increased 6.7% and 26.0% the stocks of TN and PN, respectively, compared to grassland in the pampa biome. Carbon stocks associated with minerals were not affected by eucalyptus cultivation. The cultivation of eucalyptus increased the basal respiration and the microbial biomass carbon in relation to grassland and there is a reduction of microbial biomass nitrogen in the soil. Thus, the cultivation of eucalyptus in the Pampa biome in southern Brazil demonstrates that it is a forest crop that can contribute to the increase in total and labile carbon stocks and also the biomass and microbial activity of the soil, which are important indicators of assessment of soil quality.

Adaptive multi-paddock grazing enhances soil carbon and nitrogen stocks and stabilization through mineral association in southeastern U.S. grazing lands

Grassland soils are a large reservoir of soil carbon (C) at risk of loss due to overgrazing in conventional grazing systems. By promoting regenerative grazing management practices that aim to increase soil C storage and soil health, grasslands have the potential to help alleviate rising atmospheric CO2 as well as sustain grass productivity across a vast area of land. Previous research has shown that rotational grazing, specifically adaptive multi-paddock (AMP) grazing that utilizes short-duration rotational grazing at high stocking densities, can increase soil C stocks in grassland ecosystems, but the extent and mechanisms are unknown. We conducted a large-scale on-farm study on five “across the fence” pairs of AMP and conventional grazing (CG) grasslands covering a spectrum of southeast United States grazing lands. We quantified soil C and nitrogen (N) stocks, their isotopic and Fourier-transform infrared spectroscopy signatures as well as their distribution among soil organic matter (SOM) physical fractions characterized by contrasting mechanisms of formation and persistence in soils. Our findings show that the AMP grazing sites had on average 13% (i.e., 9 Mg C ha−1) more soil C and 9% (i.e., 1 Mg N ha−1) more soil N compared to the CG sites over a 1 m depth. Additionally, the stocks’ difference was mostly in the mineral-associated organic matter fraction in the A-horizon, suggesting long-term persistence of soil C in AMP grazing farms. The higher N stocks and lower 15N abundance of AMP soils also point to higher N retention in these systems. These findings provide evidence that AMP grazing is a management strategy to sequester C in the soil and retain N in the system, thus contributing to climate change mitigation.

Nitrogen Stocks in Soil Classes Under Different Land Uses in the Brazilian Semiarid Region

Estimates of soil nitrogen (N) stocks are important for assessing potential nitrogen oxide emissions due to land-use changes and agricultural practices. No comprehensive data set exists for N stocks for the 850,000 km2 of the semiarid Brazilian northeastern region, according to land use and soil classes. Changes in N stocks due to the conversion of caatinga to pasture or agriculture, in different soil classes, were quantified in 201 soil profiles down to 1 m deep, except in shallower soils (Leptosols, 50 cm; Luvisols, and Planosols, 80 cm). Acrisols, Arenosols, and Regosols had the larger N stocks (8.07 to 9.72 Mg ha−1) than Ferralsols (6.10 Mg ha−1), whose stocks were similar to those of the shallower soils (5.87 to 6.72 Mg ha−1). The conversion of dense caatinga to agricultural fields caused reductions in 23% in N stocks. The soils of the semiarid Brazilian region accumulate 612 Tg of N in the top 1 m in the different classes of soils and land uses, being 226.8 Tg under dense caatinga, 145 Tg under open caatinga, 168 Tg under pastures, and 70 Tg under crop fields. This study contributes to elucidating N dynamics in different soil classes and land uses, and it is the most complete cover of soil N stocks in the semiarid region of Brazil. The results highlight the importance of preserving native vegetation and the need to identify and foster the adoption of agricultural management practices to maintain and restore soil N stocks.

Impact of land use type and altitudinal gradient on topsoil organic carbon and nitrogen stocks in the semi-arid watershed of northern Ethiopia

Understanding the role of soils in the soil organic carbon (SOC) and total nitrogen (TN) cycle is essential, assumed that these parameters are among the key soil quality indicators in a given landscape. Nothing but their status is in a state of continual flux due to land-use, soil management practices, and nature of topographic features. Thus, this study has evaluated the effect of land-use types and altitudinal gradient on SOC and TN concentrations and stocks at a watershed scale in northern Ethiopia. A total of 450 topsoil samples (0–30 cm depth) were collected from four different land-use types (Fig.3) across three elevational categories (Fig.1(b)), and their SOC and TN distributions were studied using descriptive statistics and geostatistical methods. Results revealed significant (p < 0.05) differences in SOC and TN concentrations and stocks by land-use type, elevation, and their interactions. The highest SOC stock was recorded at the lower elevation in GL (7.24 Mg C ha−1), followed by PF (4.65 Mg C ha−1) in the middle and GL (4.61 Mg C ha−1) in the upper elevations, respectively. On the other hand, the lowest SOC stock was observed in the BL areas of the upper (2.34 Mg C ha−1) and middle (2.75 Mg C ha−1) elevations. Spatially, the mean SOC stocks of the different land-uses were in the following order: GL > PF > CL > BL in upper elevation, PF > GL > CL > BL in middle elevation, and GL˃CL in lower elevation, respectively. The estimated total SOC and TN stocks of the study watershed were about 46,868.66 ± 7747.38 Mg C and 7,008.02 ± 441.25 Mg N, respectively. The notable difference is attributable to lack of vegetation cover, unsustainable land-use system, and land degradation via water erosion. Hence, these physical landscape disturbances result in disruption of SOC and TN's storage and stability. The SOC and TN stocks have shown a significant (p < 0.05) negative correlation with soil bulk density in the study watershed. The study concludes that variations in the land-use along topographic gradients drive the soils' SOC and TN storage. Therefore, land suitability planning, soil and water conservation measures, and reforestation practices are needed and practical worth increasing SOC and TN storage in the watershed.

Impacts of species mixture on soil nitrogen stocks in the Loess Plateau of China

Nitrogen (N) is one of the primary limiting elements in terrestrial ecosystems, and vegetation restoration has been regarded as an effective way to increase soil total nitrogen (STN) stocks. Despite compelling evidence indicating that mixed plantations can demonstrate higher vegetation productivity and carbon (C) sequestration capacity than monocultures, the effects of mixed plantations on STN stocks remain unclear. Therefore, we conducted a meta-analysis of 128 observations from 49 peer-reviewed articles across the Loess Plateau of China to evaluate the impact of different afforestation models (i.e., mixed plantations and monocultures) on the dynamics of STN stocks in mineral soil (0–30 cm). The results showed that, compared with monocultures, mixed plantations significantly increased STN stocks by 19.3%. For different mixed types, tree-shrub mixed plantations increased more STN stocks than tree-tree mixed plantations. However, the positive effect of mixed plantations on STN stocks was significant > 20 years after stand establishment. Moreover, for areas with steeper slope (>25°), lower elevation (<1200 m), and climate restricted (MAT < 8℃, MAP < 500 mm), mixed plantations had more advantages in increasing STN stocks than monocultures. Additionally, the response ratio of STN stocks was negatively correlated with the initial STN stocks, response ratios of soil pH, and bulk density (BD) but positively correlated with the response ratio of soil organic carbon (SOC) stocks. Our results demonstrate that increasing tree species richness is an important strategy to increase STN stocks.

Variable root:shoot ratios and plant nitrogen concentrations discourage using just aboveground biomass to select legume service crops

Comparing different winter legume species by plant traits that determine their contributions to ecosystems as service crops. Since root biomass determines soil organic matter formation and biological nitrogen fixation (BNF) increases soil organic nitrogen stock, those plant traits are more suitable than shoot biomass to select service crops. We evaluated shoot and root biomass and BNF (using 15N natural abundance method) of 10 winter legume service crop species under field conditions, in two consecutive years. The legumes significantly varied in shoot (3.4 to 9.1 Mg ha−1 year−1) and root biomass (0.8 to 1.3 Mg ha−1 year−1) and in the proportion and the amount of biologically fixed nitrogen (36–61% and 43–121 kg of N ha−1, respectively). Whereas shoot biomass varied between years, root and BNF were rather constant determining a low correlation between the variables. Among the evaluated species, Trifolium pratense and T. alexandrinum were the top-ranked species for the evaluated conditions, showing the largest amount of root biomass (~ 1.3 Mg ha−1 year−1) and BNF (~ 112 kg of N ha−1 year−1). Selecting service crops species aimed to increase soil organic matter based only on shoot biomass may be insufficient. As a consequence, we highlight the importance of performing breeding programs aimed to increase, in addition to crop yield or shoot biomass production, other plant traits such as root biomass or biological nitrogen fixation that provide key regulating and supporting ecosystem services.

Seasonal dynamics of soil aggregates and associated C and N stocks in different fertilizer managements

ABSTRACT Soil aggregates and associated carbon (C) and nitrogen (N) stocks are important for soil organic matter (SOM) consequences and quality. The study is meant to understand the mechanisms of how fertilization management affects Cand Nstocks. Tobacco monocropping systems with four fertilizer treatments (0, 75, and 112kg Nha−1, and 60kg Nha−1 + manure) were established in 1998. After 19 years, crop monocrop and fertilization management redetermined soil aggregates and related indicators. The results showed the large aggregates proportion (LMP) and small macroaggregates proportion (SMP) varied inversely with changing season. The LMP gradually rose after the implementation of tillage while microaggregates gradually declined. By manure fertilizer, LMP and SMP were significantly higher than those in inorganic fertilizer treatments, while microaggregates proportion (MIP) and silt and clay proportion (SCP) were lower than in inorganic fertilizer treatments. Soil water-stable aggregate and their associated soil organic stocks are changed with growing season, and tillage practices would have potentially affected these indicators, while the proportion and soil organic stocks more quickly recovered in large aggregates by manure application. Therefore, the proper application of manure combined with chemical fertilizer would maintain soil quality in tobacco cultivation.

Land‐use change alters the stocks of carbon, nitrogen, and phosphorus in a Haplic Cambisol in the Brazilian semi‐arid region

AbstractLand‐use change (LUC) can impact soil quality. In semi‐arid areas of Brazil, impacts of LUC need to be understood for better soil management. This study evaluated the impact of LUC on soil organic carbon (SOC), nitrogen (N), and phosphorus (P) distributions through the soil profile and stocks of a Haplic‐Cambisol in the Brazilian Semi‐arid region. Three land‐use systems (LUS) were investigated: agricultural management (30 years), regeneration under controlled grazing (25 years) after 5 years arable management, and native dry forest. Soil contents of P, total C, total N, and N fractions were used to calculate stocks and their stoichiometric ratios for layers 0–5, 5–10, 10–20, and 20–40 cm. Data from these LUS were compared using Kruskal–Wallis non‐parametric tests. Changes to soil microbial biomass reflected the substantially reduced SOC concentration and stock in managed soils compared with that of the natural dry forest area. Total N stock was not affected by LUC, although increases in nitrate and ammonium offset a significantly reduced organic N fraction in the agricultural area. The largest P stock was found in agricultural land, followed by the grazed fallow regeneration site. LUC significantly influenced the stoichiometric ratio of C, N, and P, with the change from Caatinga to agriculture affecting the equilibrium between organic residues’ input and mineralization. LUC resulted in significant changes to C, N, and P stocks, which did not recover to the original values, even after 25 years of regeneration under controlled grazing.

Root presence modifies the long‐term decomposition dynamics of fungal necromass and the associated microbial communities in a boreal forest

Recent studies have highlighted that dead fungal mycelium represents an important fraction of soil carbon (C) and nitrogen (N) inputs and stocks. Consequently, identifying the microbial communities and the ecological factors that govern the decomposition of fungal necromass will provide critical insight into how fungal organic matter (OM) affects forest soil C and nutrient cycles. Here, we examined the microbial communities colonising fungal necromass during a multiyear decomposition experiment in a boreal forest, which included incubation bags with different mesh sizes to manipulate both plant root and microbial decomposer group access. Necromass-associated bacterial and fungal communities were taxonomically and functionally rich throughout the 30months of incubation, with increasing abundances of oligotrophic bacteria and root-associated fungi (i.e., ectomycorrhizal, ericoid mycorrhizal and endophytic fungi) in the late stages of decomposition in the mesh bags to which they had access. Necromass-associated β-glucosidase activity was highest at 6months, while leucine aminopeptidase peptidase was highest at 18months. Based on an asymptotic decomposition model, root presence was associated with an initial faster rate of fungal necromass decomposition, but resulted in higher amounts of fungal necromass retained at later sampling times. Collectively, these results indicate that microbial community composition and enzyme activities on decomposing fungal necromass remain dynamic years after initial input, and that roots and their associated fungal symbionts result in the slowing of microbial necromass turnover with time.

Combining perennial grass–legume forages and liquid dairy manure contributes to nitrogen accumulation in a clayey soil

Repeated applications of liquid dairy manure (LDM) and perennial crops generally favor nitrogen (N) stocks in soils, but in ways that may differ with soil type and other management practices. The objective of this study was to assess the long-term (21 yr) changes in soil N stocks (0–50 cm) of a silty clay soil, in a cool humid climate, in response to mineral fertilization (MIN) or LDM, combined with two tillage practices [chisel plow (CP), or moldboard plow (MP)], and two crop rotations [cereal monoculture (monoculture) or cereal–perennial forage rotation (forage-based rotation)]. The forage-based rotation favoured a greater accumulation of N in the first 20 cm of soil (+50 kg N·ha−1·yr−1) when compared with the monoculture. Tillage practices did not impact N stocks in the whole soil profile, but influenced its vertical distribution, with greater accumulation at the surface with CP, and at depth with MP. Annual input of LDM increased N stocks at the surface (0–20 cm) compared with MIN, especially when combined with the forage-based rotation. After 21 yr, soil N stocks (0–50 cm) with LDM were 32% (+2 t N·ha−1) higher in the forage-based rotation than in the monoculture, suggesting better retention and more efficient use of manure-N with perennial forages than cereals. Comparisons between the N mass balance computed for each cropping system, and the changes in soil N stocks indicated that accumulation of N under the forage-based rotation was largely due to symbiotic fixation by legumes in the forage mixture.

English

Tobacco stalks the main agricultural waste after tobacco harvest, are generally discarded directly or returned to the field after burning. They are rarely processed into biochar, a product that could benefit soil properties. To explore the effects of applying tobacco stalk biochar on soil fertility and tobacco production, tobacco was grown at six biochar application levels (0, 3,000, 4,500, 6,000, 9,000 and 12,000 kg ha-1) in three different sites (Jianchuan, Midu and Eryuan) in Dali County, Yunnan Province. Biochar decreased soil bulk density, increased large and small soil aggregate proportion, and increased soil organic carbon and nitrogen stocks. Biochar also improved the yield and quality of tobacco leaves at all sites. Biochar rates of 3,000, 4,500 and 6,000 kg ha-1 linearly improved soil fertility and agronomic traits while application rate of biochar exceeding 9,000 kg ha-1reduced plant growth. Moreover, the optimum biochar application rates for better plant height, stem diameter, maximum leaf length and leaf width, yield, and average price differed by site. These rates were: 6,000 kg ha-1(Midu), 3,000 kg ha-1(Eryuan) and4,500 kg ha-1(Jianchuan), respectively. In conclusion, appropriate application of biochar could improve soil nutrients and contribute to tobacco growth in different soil nutrient conditions.© 2021 Friends Science Publishers

Bentonite clay combined with organic amendments to enhance soil fertility in oasis agrosystem

Soils in arid and semi-arid lands are vulnerable to climate change, erosion, and mismanagement practices that contribute to organic matter depletion and nutrients imbalances. Oasis agrosystems are considered one of the major farming systems in some parts of these lands in the Middle East and North Africa region. However, oases soils are inherently low in organic carbon due to their sandy texture which retains little water and binds low organic matter contents, and the accelerated decomposition rates of organic matter under high temperature, which makes its accumulation difficult. Traditional farming practices in oasis agrosystems have always integrated organic matter derived from livestock to enhance organic carbon (OC) and total nitrogen (TN) stocks in the soil. This study is aimed to examine the potential effects of a new mixture of organic amendments and bentonite clay on organic carbon and total nitrogen stock accumulation in the soil. Five amendments were applied including sand and compost (SC), sand and manure (SM), sand, bentonite, and compost (SBC), sand, bentonite, and manure (SBM), and sand mixed with bentonite (SB). These treatments were compared to untreated soil (U). The results showed that OC and TN stocks increased significantly (p<0.05) in all three depths of the five treatments compared to the untreated soil. Higher organic carbon stocks (2862±3.4 g m−2) were detected in SBM treatment. The combined organic and mineral amendment retarded OC and TN decomposition. After two years of the amendments’ application, 30% of OC remained in the soil for SBC treatment. In conclusion, the mixed mineral and organic amendment is a better choice to preserve OC and, thus, maintain oasis soil fertility.