DOC) And N Research Articles

Plastic mulching significantly improves soil enzyme and microbial activities without mitigating gaseous N emissions in winter wheat-summer maize rotations

Plastic mulching is an important agricultural practice to increase crop yield by increasing soil temperature and moisture. Plastic mulching can also affect soil greenhouse gas emissions [e.g., N 2 O emissions and NH 3 volatilization] and soil characteristics such as soil enzyme and microbial activities, but the simultaneous effects of plastic mulching on these parameters and the potential links between them are rarely evaluated. Here, we conducted a field study to investigate the concurrent responses of N 2 O emissions, NH 3 volatilization, soil enzyme and microbial activities, soil dissolved organic C (DOC) and N (DON), and crop yield to plastic mulching (mulching) and no mulching (ambient) under consecutive winter wheat–summer maize rotation cycles in China’s Loess Plateau. The mulching treatment significantly increased soil water-filled pore spaces (WFPS) and soil temperature during growing cycle 1 (2018–2019 winter wheat and 2019 summer maize) and cycle 2 (2019–2020 winter wheat and 2020 summer maize). Averaged across both growing cycles, the mulching treatment significantly increased winter wheat yield by 31.8 %, summer maize yield by 36.4 %, soil NO 3 – -N content by 18.2 %, NH 4 + -N content by 27.4 %, cumulative N 2 O emissions by 34.0 % and NH 3 volatilization by 50.6 %, relative to the ambient treatment. Moreover, the mulching treatment significantly enhanced soil alkaline phosphatase, invertase, catalase, and urease activities and soil microbial biomass C and N contents in the 0–10 cm soil layer across both growing cycles. This study revealed a tradeoff, with plastic mulching significantly improving crop yields and soil enzyme and microbial activities but not mitigating N 2 O emissions or NH 3 volatilization. Our results highlight that simultaneously documenting gaseous N emissions and changes in soil properties under plastic mulching can advance the understanding of sustainable agriculture in semi-arid areas. • Soil water-filled pore spaces and soil temperatures differed highly in plastic mulching and no mulching. • Plastic mulching had higher grain yield and soil mineral N content than no mulching. • Plastic mulching significantly improved soil enzyme and microbial activities. • Plastic mulching increased NH 3 volatilization and N 2 O emissions.

Yak dung pat fragmentation affects its carbon and nitrogen leaching in Northern Tibet, China

The dung excreted by yaks (Bos grunniens) into alpine grasslands on the Qinghai-Tibetan Plateau is an important ecological pathway for returning organic matter and nutrients that are closely linked to soil fertility and grassland productivity. However, few previous studies have investigated the dynamics of carbon (C) and nitrogen (N) associated with yak dung pats, particularly with respect to C and N leaching. This study experimentally investigated the effects of yak dung pat fragmentation on its C and N dynamics in Northern Tibet. Four treatments were examined: a full-size dung pat (control, FDP) and respectively splitting the full-size dung pat into four (1/4FDP), eight (1/8FDP), and sixteen (1/16FDP) equal-sized pats, each within an identical leaching device and had three replicates. The results showed that fragmentation did not influence (P > 0.05) dung total organic C (TOC) and N (TN) concentrations, but it did cause a decrease (P < 0.05) in both ammonium-N (NH4+-N) and nitrate-N (NO3−-N) concentrations and also reduced the loss of dry matter (P < 0.05), after 72 days of dung decomposition. Cumulative amounts of dissolved organic C (DOC) and N (DON) leached from the dung were significantly higher in the three fragmentation treatments than in the control (respectively 2.46–3.50 vs. 1.64 g C chamber−1, 0.14–0.16 vs. 0.10 g N chamber−1; P < 0.05). However, fragmentation did not always decrease cumulative dung NH4+-N and NO3−-N leaching, and neither NH4+-N nor NO3−-N leaching (P > 0.05) were affected by the 1/4FDP treatment. The DOC leaching accounted for 1.58–3.36 % of the initial dung TOC input, while the DON, NH4+-N, and NO3−-N leaching respectively accounted for 2.34–3.82 %, 0.68–0.87 %, and 0.19–0.27 % of the initial dung TN input. In conclusion, our findings suggest that yak dung pat fragmentation can increase the leaching of DOC and DON and the heavily fragmenting can decrease the leaching of both NH4+-N and NO3−-N after short-term dung decomposition in Northern Tibet.

Soil carbon and nitrogen fractions in response to land use/cover changes

The effects of deforestation and land use/cover changes, i.e. Alnus subcordata and Cupressus sempervirens plantations, rice cultivation, and also deforested areas of Carpinus betulus-Parrotia persica on soil carbon (C) and nitrogen (N) fractions were evaluated in Hyrcanian region, northern Iran. Twelve samples per land use/cover were taken from the top 10 cm soil and characterized with respect to soil physico-chemical and biological properties. The fraction of C and N including microbial respiration (MR), microbial biomass C (MBC) and N (MBN), particulate organic matter C (POM-C) and N (POM-N), dissolved organic C (DOC) and N (DON), and N mineralization were measured. Land use/cover affected soil physico-chemical and biological properties. Higher values of MR were observed under Alnus (0.51 mg CO2-C g soil−1 day−1) whereas the amount of MBC (711.73 mg kg−1), POM-C (3.48 g kg−1) and DOC (82.31 mg kg−1) were significantly higher in Cupressus plantation. Soil N fractions (that is, mineralized N, MBN, POM-N, and DON) were significantly higher and lower under the Alnus and deforested areas (52.18–22.29 mg N kg soil−1, 61.41–18.48 mg kg-1, 0.49–0.22 g kg−1, 33.23–13 mg kg−1), respectively. In conclusion, plantations of A. subcordata and C. sempervirens increased the soil C and N fractions in deforested areas of northern Iran and are recommended for rehabilitation of degraded natural forests in the region.

Co-incorporation of rice straw and leguminous green manure can increase soil available nitrogen (N) and reduce carbon and N losses: An incubation study

Returning rice straw and leguminous green manure alone or in combination to soil is effective in improving soil fertility in South China. Despite the popularity of this practice, our understanding of the underlying processes for straw and manure combined application is relatively poor. In this study, rice straw (carbon (C)/nitrogen (N) ratio of 63), green manure (hairy vetch, C/N ratio of 14), and their mixtures (C/N ratio of 25 and 35) were added into a paddy soil, and their effects on soil N availability and C or N loss under waterlogged conditions were evaluated in a 100-d incubation experiment. All plant residue treatments significantly enhanced CO2 and CH4 emissions, but decreased N2O emission. Dissolved organic C (DOC) and N (DON) and microbial biomass C in soil and water-soluble organic C and N and mineral N in the upper aqueous layer above soil were also enhanced by all the plant residue treatments except the rice straw treatment, and soil microbial biomass N and mineral N were lower in the rice straw treatment than in the other treatments. Changes in plant residue C/N ratio, DOC/DON ratio, and cellulose content significantly affected greenhouse gas emissions and active C and N concentrations in soil. Additionally, the treatment with green manure alone yielded the largest C and N losses, and incorporation of the plant residue mixture with a C/N ratio of 35 caused the largest net global warming potential (nGWP) among the amended treatments. In conclusion, the co-incorporation of rice straw and green manure can alleviate the limitation resulting from only applying rice straw (N immobilization) or the sole application of leguminous green manure (high C and N losses), and the residue mixture with a C/N ratio of 25 is a better option because of lower nGWP.

Carbon and nitrogen dynamics affected by litter and nitrogen addition in a grassland soil: Role of fungi

Fungi are critical for carbon (C) and nitrogen (N) dynamics in forest soils, but much less is known about their activity in grassland soils. Here we examined how fungal activity affected C and N cycling in a grassland soil with and without litter and N addition. Soil from a semi-natural grassland was amended with and without a fungicide (cycloheximide) to manipulate fungal activity, with and without N (20 mg N kg−1 soil as KNO3), and with and without grass litter (27 g litter kg−1 soil). Soil respiration, N2O emission, gross N mineralization, microbial biomass C (MBC) and N (MBN), available NH4+, NO3−, dissolved organic C (DOC) and N (DON) were measured during a 10-day incubation experiment. We observed that the fungicide decreased soil respiration on average by 59% but increased gross N mineralization on average by 59% with litter addition. Fungicide addition decreased N2O emission both with and without litter addition. Furthermore, N addition enhanced fungal activity, but only with litter addition when fungi became limited by N. We conclude that fungi play an important role in decomposing litter and N2O emission in grasslands but that fungal activity is sensitive to external N addition without litter inputs.

Deforested and drained tropical peatland sites show poorer peat substrate quality and lower microbial biomass and activity than unmanaged swamp forest

Swamp forests on deep tropical peatlands have undergone extensive deforestation and draining for agriculture and plantations, consequently becoming globally significant carbon (C) sources.To study the effects of land-use change on peat as a biological environment, which directly affects decomposition dynamics and greenhouse gas emissions, we sampled peat from four common land-use types representing different management intensities in Central Kalimantan, Indonesia. The near-pristine swamp forest was used to describe unmanaged conditions, and the three other sites in order of increasing management intensity were reforested; degraded; and agricultural. We examined peat substrate quality (total C & nitrogen (N), dissolved organic C (DOC) and N (DON)), organic matter quality characterized by infrared spectroscopy, and microbial biomass and extracellular enzyme activity, to describe both biotic and abiotic conditions in peat.We found that the peat at altered sites was poorer in quality, i.e. decomposability, as demonstrated by the higher intensity of aromatic and aliphatic compounds, and lower intensity of polysaccharides, and concentration of total N, DOC, and DON compared to the peat in the swamp forest. The observed differences in peat properties can be linked to changes in litter input and decomposition conditions altered after deforestation and draining, as well as increased leaching and fires. The quality of the peat substrate was directly related to its biotic properties, with altered sites generally having lower microbial biomass and enzyme activity. However, irrespective of management intensity or substrate quality, enzyme activity was limited primarily to the first 0–3 cm of the peat profile. Some differences between wet and dry seasons were observed in enzyme activity especially in swamp forest, where the most measured enzyme activities were higher in dry season.Reforestation 6 years before our measurements had not yet restored enzyme activity in the peat to the level of the swamp forest, although the topmost peat characteristics in the reforested site already resembled those in the swamp forest. This is likely contributed by the limited capacity of the young tree stand to produce litter to support peat formation and restore the quality and structure of the peat, and the chemical weed control performed at the site. Therefore, we conclude that intensive land management, including deforestation and draining, leads to the surface peat becoming poorer biological environment, and it may take long time to restore the peat properties.

Temporal dynamics of carbon and nitrogen in the surface soil and forest floor under different prescribed burning regimes

Prescribed burning has been widely used in the management of forests for reducing wildfire risk, and can have significant effects on soil carbon (C) and nitrogen (N) pools and their temporal changes. This study aimed to investigate the impacts of different burning frequency regimes on the temporal dynamics of C and N in the topsoil and forest floors. The experimental site was a 39year old wet scherophyll forest prescribed burning trial at Peachester, southeast Queensland, Australia, with treatments of no burning (NB) since 1969, 2 yearly burning (2yrB) and 4 yearly burning (4yrB) since 1972. Each of three burning treatments had four replications and these plots were randomly distributed over an area of the forest with similar vegetation and soil characteristics. Soil (0–10cm) and forest floors were sampled monthly for 6months prior to the next scheduled burning for both burning treatments to minimize the effects of fire recency. Prescribed burning significantly (P<0.01) affected most C and N variables in both soils and forest floors. The 2yrB treatment had significantly lower (P<0.01) soil total C, total C:N ratio, microbial biomass C (MBC) and N (MBN), MBC:MBN ratio, dissolved organic C (DOC) and N (DON), NO3−-N, inorganic N and L layer total N, DON and NO3−-N, compared with the NB and 4yrB treatments. However, there were no overall significant differences in these variables between the NB and 4yrB treatments. Sampling month significantly (P<0.01) affected C and N variable in both soils and forest floors except for soil total C and N and F layer MBC. Temporal dynamics of most of these labile C and N variables were highly related to soil and forest floor moisture content, seven day mean air temperature (MAT) and cumulative rainfall prior to sampling date. However, fire effects were independent of sampling month, as there were no significant interactions between them for most response variables measured. This study has clearly demonstrated that more frequent burning (2yr burning) had negative impact on soil and forest floor C and nutrient pools. Insignificant differences observed in soil C and N and forest floor N pools between less frequent burning (4yrB) and NB treatments highlighted that the prescribed burning at four year interval gave sufficient time for recovery of these soil and forest floor nutrients to pre-burn levels.

Excess of Organic Carbon in Mountain Spruce Forest Soils after Bark Beetle Outbreak Altered Microbial N Transformations and Mitigated N-Saturation.

Mountain forests in National park Bohemian Forest (Czech Republic) were affected by bark beetle attack and windthrows in 2004–2008, followed by an extensive tree dieback. We evaluated changes in the biochemistry of the uppermost soil horizons with the emphasis on carbon (C) and nitrogen (N) cycling in a near-natural spruce (Picea abies) mountain forest after the forest dieback, and compared it with an undisturbed control plot of similar age, climate, elevation, deposition, N-saturation level, and land use history. We hypothesised that the high litter input after forest dieback at the disturbed plot and its consequent decomposition might influence the availability of C for microorganisms, and consequently, N transformations in the soil. The concentrations of dissolved organic C (DOC) and N (DON) in soil water extracts rapidly increased at the disturbed plot for 3 yeas and then continually decreased. Net ammonification exhibited a similar trend as DOC and DON, indicating elevated mineralization. Despite the high ammonium concentrations found after the forest dieback (an increase from 0.5 mmol kg-1 to 2–3 mmol kg-1), net nitrification was stable and low during these 3 years. After the DOC depletion and decrease in microbial biomass 5 years after the forest dieback, net nitrification started to rise, and nitrate concentrations increased from 0.2–1 mmol kg-1 to 2–3 mmol kg-1. Our results emphasize the key role of the availability of organic C in microbial N transformations, which probably promoted microbial heterotrophic activity at the expense of slow-growing nitrifiers.

Soil microbial community structure and function are significantly affected by long-term organic and mineral fertilization regimes in the North China Plain

An improved understanding of the complex interactions and relationships in the soil ecosystem is essential to predict the impact of farming practices on soil quality and its capacity for agricultural production. This study aims to improve our understanding of the impacts of fertilization strategy on key indicators of soil biological and chemical quality. We studied soils from a winter wheat-summer maize rotational experiment in the North China Plain with six different fertility treatments: no amendments (CK); standard mineral fertilizer treatment (SMF) or standard organic manure treatment (SMA) reflecting local farmer practice; mixed treatment with fertilizer and manure at half the rates for the SMF and SMA treatments (1/2 SMF+1/2 SMA); double mineral fertilizer treatment (DMF); and double organic manure treatment (DMA). Soil organic C (SOC), total N (TN), total P (TP), pH, and dissolved organic C (DOC) and N (DON) and microbial biomass C (Cmic) and N (Nmic) were determined using standard methods. Soil bacterial community structure was assessed by denaturing gradient gel electrophoresis (DGGE), and activities for 10 extracellular enzymes (EEAs) were measured as indicators of soil function. Repeated application of either organic manure or mineral fertilizer increased SOC, TN, TP, DOC, DON, Cmic and Nmic, and decreased soil pH. Higher rates of organic manure fertilization significantly affected soil chemical properties compared to the lower rate. Soil bacterial community structure was significantly altered by the long-term fertilization regimes and diversity was significantly higher in the double manure rate treatment relative to mineral fertilizer. The higher urease, α-glycosidase, N-acetyl-β-glucosaminidase, l-leucine aminopeptidase (involved in N cycling), β-glucosidase, β-xylosidase and β-cellobiosidase (involved in C cycling), and alkaline phosphatase (involved in P cycling) activities for organic manure fertilized soils reflected a higher nutrient cycling capacity compared to mineral fertilized and control plots. Soil bacterial community diversities increased with Cmic and variations in EEAs were strongly correlated with soil DOC availability. Our study has demonstrated that a long-term fertilization strategy can be used to improve soil quality. Clearly, the use of organic fertilizers where available, is a win–win strategy for maintaining soil quality and crop productivity, while ensuring the delivery of soil ecosystem services into the future.

Impact of drying/rewetting cycles on the bioavailability of dissolved organic matter molecular-weight fractions in a Mediterranean stream

AbstractMediterranean fluvial systems are subject to severe drought/rewetting cycles. These extreme periods modify the direction and magnitude of the water fluxes between the stream surface water and the riparian ground water, enabling exploration of the abrupt changes affecting dissolved organic matter (DOM). We investigated the variability in DOM concentration and composition over a drying and rewetting period in a stream–riparian groundwater system. We analyzed dissolved organic C (DOC) and N (DON), and bioavailable DOC (BDOC) in whole water and 3 molecular-weight (MW) fractions (high [HMW]: >10 KDa, medium: 1–10 KDa, low [LMW]: 6 mg/L) and DON (>0.4 mg/L) in stream water. Asynchronous inputs of DOC and DON were detected in stream water during rewett...

Response of Soil C and N, Dissolved Organic C and N, and Inorganic N to Short-Term Experimental Warming in an Alpine Meadow on the Tibetan Plateau

Although alpine meadows of Tibet are expected to be strongly affected by climatic warming, it remains unclear how soil organic C (SOC), total N (TN), ammonium N (NH4 +-N) , nitrate N (NO3 +-N), and dissolved organic C (DOC) and N (DON) respond to warming. This study aims to investigate the responses of these C and N pools to short-term experimental warming in an alpine meadow of Tibet. A warming experiment using open top chambers was conducted in an alpine meadow at three elevations (i.e., a low (4313 m), mid-(4513 m), and high (4693 m) elevation) in May 2010. Topsoil (0–20 cm depth) samples were collected in July–September 2011. Experimental warming increased soil temperature by ~1–1.4°C but decreased soil moisture by ~0.04 m3 m−3. Experimental warming had little effects on SOC, TN, DOC, and DON, which may be related to lower warming magnitude, the short period of warming treatment, and experimental warming-induced soil drying by decreasing soil microbial activity. Experimental warming decreased significantly inorganic N at the two lower elevations,but had negligible effect at the high elevation. Our findings suggested that the effects of short-term experimental warming on SOC, TN and dissolved organic matter were insignificant, only affecting inorganic forms.

Temperature sensitivity of soil carbon and nitrogen mineralization: impacts of nitrogen species and land use type

Background and aims Climate warming, nitrogen (N) deposition and land use change are some of the drivers affecting ecosystem processes such as soil carbon (C) and N dynamics, yet the interactive effects of those drivers on ecosystem processes are poorly understood. This study aimed to understand mechanisms of interactive effects of temperature, form of N deposition and land use type on soil C and N mineralization. Methods We studied, in a laboratory incubation experiment, the effects of temperature (15 vs. 25 °C) and species of N deposition (NH4 + -N vs. NO3 � -N) on soil CO2 efflux, dissolved organic C (DOC) and N (DON), NH4 + -N, and NO3 � -N concentrations using intact soil columns collected from adjacent forest and grassland ecosystems in north-central Alberta. Results Temperature and land use type interacted to affect soil CO2 efflux, concentrations of DON, NH4 + N and NO3 � -N in most measurement times, with the higher incubation temperature resulted in the higher CO2 efflux and NH4 + -N concentrations in forest soils and higher DON and NO3 � -N concentrations in grassland soils. Temperature and land use type affected the cumulative soil CO2 efflux, and DOC, DON, NH4 + -N and NO3 � -N concentrations. The form of N added or its interaction with the other two factors did not affect any of the C and N cycling parameters. Conclusions Temperature and land use type were dominant factors affecting soil C loss, with the soil C in grassland soils more stable and resistant to temperature changes. The lack of short-term effects of the deposition of different N species on soil C and N mineralization suggest that maybe there was a threshold for the N effect to kick in and long-term experiments should be conducted to further elucidate the species of N deposition effects on soil C and N cycling in the studied systems.

Soil biochemical/microbial indices as ecological indicators of land use change in mangrove forests

The objective of the study was to examine the long-term changes in biochemical/microbial indicators of soil quality due to clear felling of mangroves for establishment of plantations. The biochemical/microbial parameters included dissolved organic-C (DOC) and -N (DON), soil microbial biomass-C (SMBC), -N (SMBN) and -P (SMBP), soil respiration (SR), metabolic quotient (qCO2), adenylates (ATP, AMP and ADP), adenylate energy charge (AEC), ergosterol and their ratios. Results revealed that the undisturbed mangroves possessed considerably greater amounts of soil organic C, DOC and DON. Consequently, SMBC, SMBN and SMBP showed marked reductions in the plantations suggesting an average loss of 66%, 49% and 75%, respectively due to changed land use. Likewise, SR decreased by 46.4% in the plantations. Enhanced qCO2 levels in the plantations indicated a microbial community under stress with a high maintenance carbon demand, while lower qCO2 levels in the mangroves indicated an efficient microbial community and a better use of available organic substrates. The levels of ATP, AMP and ADP followed a trend identical to that of SMB and SR. Greater ergosterol concentration led to greater ergosterol/SMBC ratio suggesting a shift in the microbial community structure from a primarily fungi dominated SMB in the mangroves to a fungi recessive SMB in the plantations.

Fluxes of dissolved organic carbon and nitrogen in cropland and adjacent forests in a clay-rich Ultisol of Thailand and a sandy Ultisol of Indonesia

In the humid tropics, conversion of forests into croplands has the potential to alter the flux of dissolved organic matter (DOM) and influence C balance and N availability in soil. Sites located on a clay-rich Ultisol in Thailand and a highly acidic and sandy Ultisol in Indonesia were used to quantitatively evaluate effects of land use change on fluxes of dissolved organic C (DOC) and N (DON) in cropland and adjacent forest. The DOC flux from surface soil horizons was lower in cropland (poultry manure-amended) than in the forest on the sandy Ultisol (Indonesia), while DON flux increased in cropland due to release of DOM enriched in N from the decomposed SOM and manure. In contrast, DOC and DON fluxes in cropland (non-fertilized) and forest on the clay-rich Ultisol (Thailand) were consistently low due to high adsorption of DOM and rapid DON mineralization. Total dissolved N (TDN) in soil solution was dominated by nitrate for both cropland soils; DON represented a major fraction of TDN in the sandy cropland soil due to lower DOM adsorption capacity and slower DON mineralization. The conversion of forests to croplands could enhance SOM decomposition and produce DOM enriched in N, but leaching losses of DOC and DON were small under low-input agriculture in tropical region. The effects of agricultural use on DOC and DON fluxes could vary depending on application rates of manure and adsorption and mineralization capacities of soils.

Urban Soils of Texas: Relating Irrigation Sodicity to Water‐Extractable Carbon and Nutrients

Effective management of urban soils and their impact on surface water requires an understanding of the mechanisms controlling soil variability within and among cities. To gain a better understanding of soil variability among the cities of Texas, where the use of irrigation is common, we investigated the relationship between irrigation water chemistry and water‐extractable soil dissolved organic C (DOC) and N (DON), NH4–N, NO3–N, and orthophosphate P in 33 irrigated soil samples under turfgrass from 26 cities. Quantified in a 1:10 soil/ distilled water extraction, DOC and nutrients were compared with the chemistry of the water used for irrigation (Na+ and Ca2+ concentrations, Na adsorption ratio [SAR], Na charge percentage [%Na(+)], alkalinity, and electrical conductivity) and several soil properties (silt+clay percentage, total soil C, and total soil N). Utilizing multiple regression analyses, SAR and total soil N explained 71% of the variability in extractable soil DOC, and SAR and alkalinity explained 72% of soil DON. The %Na (+) explained 43% of NH4–N variability and 56% of orthophosphate P variability observed among cities across Texas. Total soil N was the best predictor of water‐extractable soil NO3–N (64%). Our results showed that when irrigation water SAR was &gt;5, there was a two‐ to threefold increase in the solubility of DOC and nutrients from urban soils of Texas, which may contributing to nonpoint sources of C and nutrients in surface waters.

Short-term effects of nutrient management regimes on biochemical and microbial properties in soils under rainfed ginger (Zingiber officinale Rosc.)

The aim of the study was to determine the short-term effects of contrasting nutrient management regimes on sensitive soil biochemical and microbial parameters under an annual rainfed crop (ginger, Zingiber officinale Rosc.) grown in raised beds. The nutrient management regimes employed in the study were organic nutrient management (ONM), chemical nutrient management (CNM) and integrated nutrient management (INM). ONM involved organic manures (farmyard manure (FYM), vermicompost, neem cake, ash) and biofertilizers (Azospirillum lipoferum and Bacillus phosphaticum var megaterium), CNM involved exclusive use of chemical sources of NPK and INM involved a combination of chemical sources of NPK+FYM. The study also included a control where no fertilizers, whatsoever, were applied. The variables studied were soil organic carbon (SOC), dissolved organic-C (DOC) and -N (DON), microbial biomass-C (CMIC), -N (NMIC) and -P (PMIC), net N mineralized (NMIN), soil respiration (SR) and activities of dehydrogenase (DHA), acid phosphatase (Ac-P), β-glucosidase (βG), urease (UR) and arylsulphatase (AS). Various ratios of these biochemical/microbial indices viz., DOC:DON, CMIC:SOC (QMIC), CMIC:NMIC, SR:CMIC (metabolic quotient, qCO2) were also examined.The influence of nutrient management regimes was most evident on SOC, DOC, DON, soil microbial and biochemical properties. The levels of SOC and DOC were significantly greater in ONM and INM compared to CNM and control. Conversely, DON level was markedly higher under CNM compared to ONM and INM. CNM also positively influenced NMIC but decreased CMIC, PMIC and SR levels. NMIN followed an identical trend as microbial biomass and SR; being greatest in INM and ONM. Likewise, the DOC:DON, CMIC:SOC (QMIC) and CMIC:NMIC ratios were greatest in ONM and least in CNM. Contrarily, higher qCO2 in CNM and control suggested microbial communities which are energetically less efficient with high maintenance C requirement. Results on enzyme activities revealed that not all the treatments affected the enzyme activities to the same degree. The activities of DH, Ac-P and βG were in the order ONM>INM>CNM, while the activities of UR and AS were in the order CNM>INM>ONM. The strong effects of nutrient management regimes implied that soil biochemical/microbial parameters are sensitive enough to detect changes in soil quality even in the short-term.

Biochar-mediated changes in soil quality and plant growth in a three year field trial

While many laboratory studies have focused on the short term effects of biochar addition to soil), there have been comparatively few tracing its longer term effects in the field. This study investigated the multiyear impact of biochar on crop performance and soil quality with specific emphasis on carbon (C) and nitrogen (N) cycling over a 3 y period. Biochar was added to an agricultural field at 0, 25 and 50tha−1 and planted with maize (year 1) and grass (years 2 and 3). Biochar addition affected plant performance in the grass crop with significant increases in foliar N (year 2) and above-ground biomass (year 3). Below-ground, biochar increased soil respiration, fungal and bacterial growth rate and turnover in year 2. This change coincided with a shift toward a bacterial dominated decomposer community, suggesting a decrease in the potential for microbially mediated C sequestration. Biochar did not affect dissolved organic C (DOC) and N (DON), NO3− or NH4+ pool sizes. Similarly, biochar addition had limited effects on the turnover of 14C-labelled SOC (plant litter), DOC (sugars and organic acids) and DON (amino acids) and no long term effect on N mineralization, NH3 volatilization, denitrification and NH4+ sorption. After 3 years in the field, the alkalinity associated with the biochar had been fully neutralized and biochar lost most of its cations (K, Na, Ca) but had built up an associated microbial community. We conclude that biochar addition to soil causes small and potentially transient changes in a temperate agroecosystem functioning. Importantly, many of the short-term effects of biochar on plant growth and soil behavior reported from laboratory studies were not observed in the field emphasizing the need for long term field trials to help inform agronomic management decisions involving biochar.

Effects of Landscape Age on Soil Organic Matter Processing in Northern Alaska

Much of the previous research on arctic soil biogeochemistry has focused largely on the effects of climate, organisms, and relief rather than on geologic factors. However, a few studies of limited scope suggest that biogeochemical cycling in tundra soils may be significantly affected by variation in glacial history. To determine if variation in landscape age-related differences in geochemistry influence rates of organic matter decomposition in tundra soils, we conducted soil analyses and a 5-mo soil incubation study across a chronosequence of landscape ages in northern Alaska. Our results indicate that there were landscape-age related controls on microbial activity, with higher microbial biomass, rates of respiration, and production of dissolved organic C (DOC) and N (DON) in soils from the older landscape ages than in soils from younger, less weathered landscapes. This biological boundary corresponded to a chemical boundary, as older soils had lower pH (4.5–5 vs. 6.5) and exchangeable cation concentrations than the youngest soils. There were no differences among landscape ages in total C stocks in organic soils; however, total N stocks in the organic soil decreased with increasing landscape age. Differences among landscape ages in microbial activity due to geochemical variation may have important consequences for tundra C budgets because differences in soil pH and cation content exist throughout the circumpolar region.

Body size and population dynamics of enchytraeids with different disturbance histories and nutrient dynamics

The population dynamics of the enchytraeid Cognettia sphagnetorum originating from an unmanaged forest (FP), a clear-cut area (CCP) or a plot treated with birch ash (APP) and the effects of population origin on labile C and N dynamics were investigated. Twenty individuals of C. sphagnetorum were introduced in microcosms containing humus from the unmanaged forest devoid of enchytraeids and amended with sucrose, and incubated for 14 weeks. Triplicate microcosms from FP, CCP and APP treatments were destructively sampled every second week and enchytraeid population density, individual length, nematode abundance and trophic structure, humus properties and dissolved organic C (DOC) and N (DON), and NH4–N in soil were determined. The enchytraeid body size was initially smaller in CCP and APP than in FP. The enchytraeid propagation rate was lower and individual size less variable in APP than in FP or CCP, and although enchytraeid size increased in all treatments, exponential population models indicated that APP was less stable. Nematode community was dominated by bacterial-feeders especially in the microcosms with APP. N mineralization rate was lower and DOC decomposition rate greater in APP systems. The results show that C. sphagnetorum is more sensitive to wood ash than clear-cutting, and its altered body size distribution has the potential to affect the dynamics of soluble nutrients.

Initial soil responses to experimental warming in two contrasting forest ecosystems, Eastern Tibetan Plateau, China: Nutrient availabilities, microbial properties and enzyme activities

In order to understand the effects of projected global warming on soils in different land-use types, we compared the impacts of warming on soils in two contrasting forest ecosystems (a dragon spruce plantation and a natural forest) using the open-top chamber (OTC) method in the Eastern Tibetan Plateau of China. The OTC on average enhanced daily mean soil temperatures by 0.61 °C (plantation) and by 0.55 °C (natural forest) throughout the growing season, respectively. Conversely, soil volumetric moisture declined by 4.10% in the plantation and by 2.55% in the natural forest, respectively. Warming did not affect dissolved organic C (DOC) and N (DON) in the plantation but significantly increased them in the natural forest. Elevated temperature significantly increased net N mineralization rates and extractable inorganic N pools in both sites. Warming had no effects on microbial biomass C (MBC) and N (MBN) and their ratios (MBC/MBN) in the plantation and significantly increased MBC and MBN only late in the growing season in the natural forest. Warming did not affect basal respiration in the plantation but significantly increased it in the natural forest. No clear change was observed in metabolic quotient between warming regimes for both forest types. Experimental warming tended to increase invertase and urease in both forest soils. Measured pools related to N turnover generally showed significant interactions in warming, forest type and sampling date. Taken together, our results indicate that responses of soils to experimental warming depend strongly on forest managements and seasons.