Soil Nutrient Pools Research Articles

A silver lining for hurricanes

Coastal Ecology Hurricanes are notorious for the havoc that they wreak on coastlines. However, destruction can also be accompanied by an injection of nutrients into ecosystems. Castaneda-Moya et al . report a hitherto underappreciated beneficial effect of high-energy disturbances. In the aftermath of Hurricane Irma, which hit the Florida Everglades in 2017, there was a notable fertilization pulse in mangrove forests as far as 10 kilometers inland. Phosphorus-rich sediments deposited by the hurricane boosted the soil nutrient pool and resulted in increased phosphorus uptake by mangrove species. The potential hurricane-enhanced plant productivity may promote soil stabilization and resilience to future disturbances and sea level rise Proc. Natl. Acad. Sci. U.S.A. 117 , 4831 (2020).

Negative effects of cattle on soil carbon and nutrient pools reversed by megaherbivores

Wild herbivore populations are declining in many African savannas, which is related to replacement by livestock (mainly cattle) and the loss of megaherbivores. Although some livestock management practices may be compatible with the conservation of native savanna biodiversity, the sustainability of these integrated wild herbivore/livestock management practices is unknown. For instance, how will these herbivore mixes influence key processes for the long-term functioning of savanna ecosystems, such as soil carbon, nitrogen and phosphorus pools and cycling? The Kenya Long-term Exclosure Experiment studies the ecosystem consequences of manipulating the presence and absence of wild herbivores and cattle at moderate densities in a ‘black cotton’ savanna. Here we show that after 20 years, cattle presence decreased total soil carbon and nitrogen pools, while the presence of megaherbivores (mainly elephants) increased these pools and even reversed the negative effects of cattle. Our results suggest that a mix of cattle at moderate densities and wild herbivores can be sustainable, provided that the assemblage of wild herbivores includes the largest species. Cattle are replacing wildlife in many African savannas. This field study finds that wild megaherbivores, such as elephants, increased soil carbon and nitrogen, and hence soil fertility, normally lost when only cattle are present.

Hurricanes fertilize mangrove forests in the Gulf of Mexico (Florida Everglades, USA)

Hurricanes are recurring high-energy disturbances in coastal regions that change community structure and function of mangrove wetlands. However, most of the studies assessing hurricane impacts on mangroves have focused on negative effects without considering the positive influence of hurricane-induced sediment deposition and associated nutrient fertilization on mangrove productivity and resilience. Here, we quantified how Hurricane Irma influenced soil nutrient pools, vertical accretion, and plant phosphorus (P) uptake after its passage across the Florida Coastal Everglades in September 2017. Vertical accretion from Irma's deposits was 6.7 to 14.4 times greater than the long-term (100 y) annual accretion rate (0.27 ± 0.04 cm y-1). Storm deposits extended up to 10-km inland from the Gulf of Mexico. Total P (TP) inputs were highest at the mouth of estuaries, with P concentration double that of underlying surface (top 10 cm) soils (0.19 ± 0.02 mg cm-3). This P deposition contributed 49 to 98% to the soil nutrient pool. As a result, all mangrove species showed a significant increase in litter foliar TP and soil porewater inorganic P concentrations in early 2018, 3 mo after Irma's impact, thus underscoring the interspecies differences in nutrient uptake. Mean TP loading rates were five times greater in southwestern (94 ± 13 kg ha-1 d-1) mangrove-dominated estuaries compared to the southeastern region, highlighting the positive role of hurricanes as a natural fertilization mechanism influencing forest productivity. P-rich, mineral sediments deposited by hurricanes create legacies that facilitate rapid forest recovery, stimulation of peat soil development, and resilience to sea-level rise.

Fire Affects Asymbiotic Nitrogen Fixation in Southern Amazon Forests

AbstractIn this study, we investigate the biogeochemical consequences of fire in seasonally flooded Amazon forests, where recent declines in forest cover have been linked to increases in fire frequency and severity. Previous studies have hypothesized that a quasi‐permanent state‐shift transition from typical Amazon forests to open savannas can occur when fire results in further depletion of already impoverished soil nutrient pools. Asymbiotic N2 fixation (ANF) is an essential pathway for fire‐affected forests to acquire nitrogen (N) after disturbance, but ANF response to fire has yet to be quantified in Amazonia. Here, we quantify ANF through field sampling and laboratory incubations using 15N‐labeled dinitrogen (15N2) and measurement of 14 biogeochemical parameters in surface (0–10 cm) and subsurface (10–30 cm) soils. Our data represent burned and unburned replicated sampling sites, across five stands, spanning a gradient from infrequent (once in 13 years) to frequent (five times in 13 years) fire occurrences. ANF did not vary with fire frequency but was, on average, 24% lower in burned than in unburned surface soils across all stands. Burned and unburned subsurface soils had similar ANF rates. About 58% of ANF variance was explained by the joint effect of carbon (C):N ratio and available phosphorus (P) in burned and unburned soils. ANF increased linearly with C:N and P availability in unburned soils, but a highly non‐linear relationship was observed in burned soils. Our findings show that fire alters soil C‐to‐nutrient stoichiometry, which resulted in lower N inputs via ANF into burned relative to unburned tropical forest soils.

Soil microbial community structure and function mainly respond to indirect effects in a multifactorial climate manipulation experiment

Future climate change scenarios predict increases in surface temperature as well as atmospheric CO2 concentration. In this study we simultaneously addressed individual and combined effects of these factors on the soil microbial community structure and function. We tested linear as well as non-linear responses in a multifactorial climate manipulation experiment.After two years of climate change manipulations on a pre-Alpine managed grassland, topsoil samples were taken for analysis of functional enzyme activities, as well as microbial community structure. Besides, soil and vegetation parameters were measured to allow evaluation of direct and indirect effects.Pronounced and statistically significant spatial effects were observed on our field site for some variables. It is assumed that the history of site preparation could provide an explanation for the observed differences. Elevation of temperature or atmospheric CO2 did not induce strong shifts of soil fungal or bacterial communities. Only the inclusion of the spatial effects in the response surface regression model allowed the detection of subtle microbial responses to climate change scenarios. Mucor globulifera responded to temperature and CO2 in a pattern similar to soil water content. An increase in the relative abundance of coprophilous white rot fungi was observed upon warming, and this might be attributed to preferences of macrofauna for warmer plots. Specific extracellular enzyme activities were positively correlated with each other, especially within two groups of enzymes, which were involved in C-acquisition and in N-mining. The latter group responded positively to elevated CO2 concentrations. Chitinolytic activity increased with the relative abundance of the nematophagous and entomopathogenic ascomycete Purpureocillium lilacinum.We conclude that the indirect effects of future climate change scenarios prevail over direct effects on soil microbial community composition and function. Soil water content, nutrient pools, atmospheric CO2 and plant root identity were identified as drivers of the observed changes after removal of unintended spatial effects. Application of advanced statistical tools, which take spatial variability into account, was necessary to detect these effects. Minor changes in the fungal community occurred already after a short period of climate manipulation. More pronounced effects of elevated atmospheric CO2 concentration and surface warming on soil microbial community structure and function are expected on the longer-term, but indirect effects will most likely remain the dominant drivers.

Above- and belowground responses to long-term herbivore exclusion

ABSTRACT Herbivores can play an important role in determining arctic ecosystem function with effects determined in part by herbivore identity. We examined the impact of long-term (twenty-two years) small and large mammal herbivore exclusion in two arctic plant communities in northern Alaska: dry heath (DH) and moist acidic tundra (MAT). Our aims were to examine how herbivore exclusion influences (1) plant communities and (2) soil nutrient pools and microbial processes. Though herbivore absence increased moss and decreased evergreen shrub cover in MAT, there were few other significant effects on vegetation in either community. We also observed no influence of exclusion on most soil properties. However, in DH, phosphatase activity was greater in areas where small mammals alone were present, suggesting that they are altering phosphorus (P) availability, perhaps through herbivores’ influence on the plant community and subsequently on competition for P with the microbial community. We conclude that herbivore impacts in the Arctic are dependent on both the plant community and herbivore identity (size). We show the importance of understanding the roles of herbivores in the Arctic and contribute to a growing number of herbivore studies in a biome likely to experience future changes in herbivore communities and ecosystem function.

Nitrogen and phosphorus uptake from isotope‐labeled fertilizers by sorghum and soil microorganisms

AbstractOn nutrient‐depleted Lixisols from Burkina Faso, nutrient acquisition by crops and soil microbes mainly relies on the limited amounts of mineral and organic fertilizers applied by small‐scale farmers. The objective of this study was to determine simultaneously the uptake of nitrogen (N) and phosphorus (P) contained in organic and mineral fertilizers by sorghum [Sorghum bicolor (L.) Moench ] and soil microbial biomass. Double 15N and 33P direct and indirect labeling techniques were applied in a pot experiment to determine the contributions of different fertilizers to sorghum N and P uptake during 52 d of growth. In parallel, soil respiration, available, and microbial N and P were tracked in an incubation experiment. Sorghum derived 83–90% of P from fertilizers. Nitrogen from cattle manure was poorly available, contributing only 20% of the N taken up by sorghum. Water‐soluble mineral fertilizers increased soil N and P availability, resulting in the highest total N and P uptake by sorghum from fertilizers and soil among all treatments. The application of cowpea [Vigna unguiculata (L.) Walp.] residues induced microbial N and P immobilization, reducing sorghum N and P uptake to the level of the non‐fertilized treatment. The use of double 15N and 33P labeling elucidated the impact of fertilizers on soil nutrient pools. The low plant N/P ratio suggested N limitation for sorghum in the manure treatment. Cowpea residues were inefficient for sorghum nutrition, but they increased soil microbial nutrient pools. This study gives insights on the potential effects of legume residues used as green manure to build soil fertility.

Base cations in the soil bank: non-exchangeable pools may sustain centuries of net loss to forestry and leaching

Abstract. Accurately quantifying soil base cation pool sizes is essential to interpreting the sustainability of forest harvests from element mass-balance studies. The soil-exchangeable pool is classically viewed as the bank of “available” base cations in the soil, withdrawn upon by plant uptake and leaching and refilled by litter decomposition, atmospheric deposition and mineral weathering. The operational definition of this soil bank as the exchangeable (salt-extractable) pools ignores the potential role of “other” soil nutrient pools, including microbial biomass, clay interlayer absorbed elements, and calcium oxalate. These pools can be large relative to “exchangeable” pools. Thus neglecting these other pools in studies examining the sustainability of biomass extractions, or need for nutrient return, limits our ability to gauge the threat or risk of unsustainable biomass removals. We examine a set of chemical extraction data from a mature Norway spruce forest in central Sweden and compare this dataset to ecosystem flux data gathered from the site in previous research. The 0.2 M HCl extraction released large pools of Ca, K, Mg, and Na, considerably larger than the exchangeable pools. Where net losses of base cations are predicted from biomass harvest, exchangeable pools may not be sufficient to support more than a single 65-year forest rotation, but acid-extractable pools are sufficient to support many rotations of net-ecosystem losses. We examine elemental ratios, soil clay and carbon contents, and pool depth trends to identify the likely origin of the HCl-extractable pool. No single candidate compound class emerges, as very strongly supported by the data, as being the major constituent of the HCl-extractable fraction. A combination of microbial biomass, fine grain, potentially shielded, easily weatherable minerals, and non-structural clay interlayer bound potassium may explain the size and distribution of the acid-extractable base cation pool. Sequential extraction techniques and isotope-exchange measurements should be further developed and, if possible, complemented with spectroscopic techniques to illuminate the identity of and flux rates through these important, and commonly overlooked, nutrient pools.

Base Cation Fluxes from the Stemflow in Three Mixed Plantations in the Rainy Zone of Western China

Base cation transfer from stemflow is an important process for nutrient transfer and plays a key role in maintaining the balance of soil nutrient pools. To research the differences of stemflow chemistry in mixed plantations, we conducted a continuous field experiment in the rainy zone of Western China from December 2016 to November 2017. Three representative mixed plantations, including a conifer–broadleaved mixed plantation, a deciduous broadleaved mixed plantation and a multispecies mixed plantation, were selected to investigate the concentration and flux characteristics of K+, Na+, Ca2+ and Mg2+ in stemflow. The results showed that: (1) the K+, Na+, Ca2+ and Mg2+ fluxes ranged from 1.75 to 2.44 kg ha−1 year−1, 0.14 to 0.24 kg ha−1 year−1, 1.25 to 2.11 kg ha−1 year−1, and 0.40 to 0.60 kg ha−1 year−1 in these mixed plantations during the one-year observation, and the annual or seasonal (i.e., rainy or dry season) base cation fluxes in the stemflow varied slightly with the plantation types; (2) broadleaved trees had a higher average stemflow base cation contribution rate and flux-based enrichment ratio than coniferous trees, and the enrichment ratios showed a decreasing tendency with increasing trunk diameter; (3) the stemflow base cation concentration was higher in the dry season, while flux was observed to be higher in the rainy season. These results suggested that increasing the proportion of broadleaved species in mixed plantations might improve soil nutrient content and benefit material cycling in subtropical forest ecosystems.

Slow Recovery of Major Soil Nutrient Pools during Reclamation in a Sub-Alpine Copper Mine Area, Southeastern Edge of the Tibetan Plateau, Sichuan Province, SW China

Improvement of soil nutrients is crucial for the long-term development and stability of restored ecosystems in mine areas. However, knowledge about the variation in soil nutrients and their influencing factors during the reclamation of sub-alpine metal mine soil is still scarce. We assess the status of soil organic carbon (SOC), total nitrogen (TN), N fractions, total phosphorus (TP), and available P in reclaimed soil at a copper mine site (2702 m above sea level) in the southeastern edge of the Tibetan Plateau, southwest China. The mine area had been reclaimed by distributing stockpiled topsoil (~15 cm) in 2008, sowing seeds of ryegrass (Lolium perenne L.) in 2009, and planting seedlings of A. ferdinandi-coburgii and Rosa omeiensis f. pteracantha in 2010. We found that, eight years after the reclamation, although the concentrations of SOC (24.3 g kg−1) and TN (2.21 g kg−1) in the reclaimed soil increased by 25% and 29% compared with the stockpiled topsoil, respectively, they only accounted for about half of the levels in the undisturbed topsoil. In contrast, the concentration of TP (498–570 mg kg−1) did not significantly change between the reclaimed and stockpiled topsoil. The concentrations of NH4-N (30.1 g kg−1), NO3-N (17.2 g kg−1), and available P (11.1 mg kg−1) in the reclaimed soil were 2.2, 1.3, and 1.6 times the levels in stockpiled topsoil, respectively, but still lower than those in undisturbed soil. The concentrations of microbial C, N, and P in the reclaimed soil had a similar variation pattern to the available nutrients. The soil C:P and N:P ratios and microbial biomass C:P and N:P ratios in the reclaimed soil were significantly lower than the levels in the undisturbed forest soil. The average accumulation rates of SOC and TN in the reclaimed soil were 85.3 and 11.4 g m−2 year−1, respectively. The rates are much lower than those of reclaimed mine soils with similar reclaim duration but better climate conditions. Relatively slow development of vegetation and soil microorganisms and leaching due to a freeze–thaw cycle controlled by the sub-alpine climate are likely responsible for the slow recovery of soil SOC and TN.

Effects of six-year biochar amendment on soil aggregation, crop growth, and nitrogen and phosphorus use efficiencies in a rice-wheat rotation

Abstract The effective use of biochar as biomass recycling in agriculture to improve both crop production and environmental performance requires an understanding of its effects on soil nutrients, i.e., nitrogen (N) and phosphorus (P) and soil structure and soil carbon stocks. Thus, crop yield, soil aggregate stability and N and P use efficiencies (NUE and PUE, respectively) were investigated in a rice-wheat rotation field experiment 6 years after biochar amendment (20 and 40 t ha−1). Biochar application increased crop (rice and wheat) root (by 3–19%), straw (by 10–19%) and grain (by 10–16%) biomasses, as well as grain NUE (by 20–53%) and PUE (by 38–230%) compared with N fertilization only, whereas decreases in the N stocks in the root (2–5%), straw (13–17%) and grain (0–2%) occurred after biochar addition in the rice growth stage. No differences were observed between 20 and 40 t ha−1 biochar with respect to root, straw and grain biomasses as well as NUE and PUE. Biochar improved soil organic carbon (by 26–53%), total N (by 14–16%) and P (by 6–19%) compared to N fertilization only and positively affected the 250–2000 μm aggregate class (by 87–93%) and aggregate stability (by 43–48%). Based on structural equation modeling (SEM), this additional carbon affected aggregate stability by improving the aggregate structure, whereas P affected aggregate stability directly in biochar-fertilized soils. Improvement of soil carbon stocks and nutrient pools (i.e., N, P), promoted root growth, uptake of N and P fertilizers and crop production. Thus, biochar application is an effective strategy to increase crop yield, even in the long-term, and is connected not only with the improvement of soil structure and carbon stocks but also with increases in nutrient use efficiency.

Nutrient Allocation to Different Compartments of Age-Sequence Larch Plantations in China

Increased demand for forest-derived biomass has led to more intensive harvesting practices. However, the export of large nutrient quantities with the harvested biomass may lead to the depletion of soil nutrients. Therefore, improved knowledge concerning macronutrient allocation (N, P, K, Ca, and Mg) to different components in forests along age sequences is crucial for their sustainable management. In this study, we quantified nutrient allocation to different ecosystem components, including trees, understorey, forest floor, and different soil depths within a chronosequence (6-, 15-, 23-, and 35-year-old) of larch plantations in China. We then assessed the danger of significant nutrient losses from whole tree harvesting (WTH). Nutrient amounts in trees increased with stand age due to an increase in biomass. Stems accounted for 59%–72% of tree biomass and contained 40%–50% of total tree nutrients in the 15- to 35-year-old stands. The forest floor’s nutrient quantities increased from the 6- to 23-year-old stands and then decreased in the 35-year-old plantations. Conversely, most soil indicators initially declined from 15- to 23-year-old stands and then increased in the 35-year-old stand. The total nutrient stocks were greatest in the soil (0–40 cm), which accounted for about 93%–99% of total nutrients in the larch ecosystem. These data indicate that WTH causes nutrient losses about 2.0–2.5 times higher than stem-only harvesting, when thinning 15- or clear-cut harvesting 23- and 35-year-old stands. However, nutrient losses by WTH have little effect on the soil nutrient pools. Prolonging the crop cycle of larch plantations may be beneficial to improve nutrient return through litterfall and allow available soil nutrients to recover.

Rapid nitrogen fixation by canopy microbiome in tropical forest determined by both phosphorus and molybdenum.

Biological nitrogen fixation is critical for the nitrogen cycle of tropical forests, yet we know little about the factors that control the microbial nitrogen fixers that colonize the microbiome of leaves and branches that make up a forest canopy. Forest canopies are especially prone to nutrient limitation because they are (1) disconnected from soil nutrient pools and (2) often subject to leaching. Earlier studies have suggested a role of phosphorus and molybdenum in controlling biological N-fixation rates, but experimental confirmation has hitherto been unavailable. Here we present the results of a manipulation of canopy nutrient availability. Our findings demonstrate a primary role of phosphorus in constraining overall N fixation by canopy cyanobacteria, but also a secondary role of molybdenum in determining per-cell fixation rates. A conservative evaluation suggests that canopy fixation can contribute to significant N fluxes at the ecosystem level, especially as bursts following atmospheric inputs of nutrient-rich dust.

Responses of wetland soil carbon and nutrient pools and microbial activities after 7 years of experimental warming in the Yangtze Estuary

Wetlands play an important role in global carbon (C) cycling. However, little is known about the effects of climate warming on wetland C cycling, which may bias our prediction of wetland functioning under global climate change. This study was undertaken to examine the potential changes in soil C, nitrogen (N) and phosphorus (P) pools and the related microbial activities after 7 years of in-situ experimental warming by open-top chambers (OTCs) in a Phragmites wetland in the Yangtze Estuary. The mean soil temperature, moisture, and salinity in both the 0–10 cm and 10–40 cm soil layers were significantly increased by the warming treatment. In the upper 10 cm soil layer, significant increases in total organic C (TOC) and total N (TN) were observed under the warming treatment, while the phenomenon were further clarified by comparing the year-round data in the warming plots between 2008 and 2015; However, the molar C/molar N ratio (C/N) and total phosphorus (TP) were not affected. In both layers, microbial biomass C (MBC) and the molar MBC/molar MBN ratio (MBC/MBN) showed no significant responses, but microbial biomass N (MBN) and microbial biomass P (MBP) were increased by warming. Warming did not affect MBC/TOC, but it significantly increased both MBN/TN and MBP/TP throughout the 0–40 cm soil profile. Invertase activity was not affected in the 0–40 cm soil profile. The acid phosphatase, alkaline phosphatase, and urease activities in the upper 10 cm soil layer were increased by warming. Only alkaline phosphatase activity was increased by warming in the 10–40 cm soil layer. These field-experimental warming results suggested that in temperate P. australis wetlands without tidal impacts, climate warming might increase the soil organic C pools while exerting no effect on microbial C decomposition, whereas the N and P cycling that is mediated by soil microbes might be enhanced by moderate warming.

Long-term application of low C:N residues enhances maize yield and soil nutrient pools across Kenya

Declines in soil fertility and limited access to inorganic nitrogen (N) fertilizer constrain crop production in Sub-Saharan Africa. The incorporation of organic residues could increase nutrient mineralization and replenish soil carbon (C), however, the effect that long-term residue management (10+ years) has on maize (Zea mays L.) yields and soil nutrient pools (C and N) is largely unknown. In four identical long-term trials in Kenya that differ by soil type and climate, we compared maize yield and soil C (0–0.15 m) across four treatments comparing organic inputs of contrasting C:N ratios: tithonia [Tithonia diversifolia (Hemsl.) A. Gray] + N (120 kg N ha−1); tithonia − N (0 kg N ha−1); maize stover + N (120 kg N ha−1); maize stover − N (0 kg N ha−1). On average, maize yields were 92% greater under tithonia compared to maize stover at the sandy sites and in general followed this trend: tithonia + N > tithonia − N = stover + N > stover − N. The continuous application of tithonia also increased soil C and N pools; for instance, mineralizable C was up to 57% greater than that of maize stover at the sandy sites. Increases in yield and nutrient pools under tithonia were less apparent at the clay sites. When exploring the relationship between soil C and maize yield, we found that both mineralizable and processed pools were related to agronomic performance. Our findings demonstrate that low C:N residues could significantly benefit crop production and enhance soil organic matter at sandy sites across Kenya.

Effect of tillage on macronutrients in soil and wheat of a long-term dryland wheat-pea rotation

Tillage is known to significantly affect crop residue decomposition and soil nutrient dynamics, but the impacts of tillage on soil and plant macronutrients concentration with time have not been reported. This study was conducted (i) to assess the influence of tillage timing and intensity on soil and wheat (Triticum aestivum L.) macronutrient concentration of a winter wheat-dry pea (Pisum sativum L.) rotation (WW-P) under a dryland cropping system, and (ii) to compare macronutrients in the tillage treatments with a nearby long-term grass pasture (GP). The tillage treatments were fall tillage (FT), spring tillage (ST), no-tillage (NT) and disk/chisel tillage (DT/CT). Soil samples from 1995, 2005, and 2015 were analyzed to determine the concentration of soil organic carbon (SOC), total N and S, Mehlich III extractable P, K, Ca, and Mg, and soil pH. The impact of tillage on soil macronutrient concentration was evident after 52 years of WW-P. As a result, greater concentration of SOC, total S, and extractable P, and K were observed under NT than under FT or ST. The WW-P plots lost 28, 46, and 67% of SOC, Mg, and S, respectively, in the top 10 cm of soil compared with the GP plots, whereas the NT plots were the only plots in WW-P to maintain a P concentration (99 mg P kg−1) comparable with GP plots (102 mg P kg−1) at the same depth. The results indicated that NT could be beneficial to recharge the soil nutrient pool over time compared to FT or ST.

Climate-driven reduction of genetic variation in plant phenology alters soil communities and nutrient pools.

We examined the hypothesis that climate-driven evolution of plant traits will influence associated soil microbiomes and ecosystem function across the landscape. Using a foundation tree species, Populus angustifolia, observational and common garden approaches, and a base population genetic collection that spans 17 river systems in the western United States, from AZ to MT, we show that (a) as mean annual temperature (MAT) increases, genetic and phenotypic variation for bud break phenology decline; (b) soil microbiomes, soil nitrogen (N), and soil carbon (C) vary in response to MAT and conditioning by trees; and (c) with losses of genetic variation due to warming, population-level regulation of community and ecosystem functions strengthen. These results demonstrate a relationship between the potential evolutionary response of populations and subsequent shifts in ecosystem function along a large temperature gradient.

Comprehensive review on production and utilization of biochar

The on-farm burning of crop residues and biomass results in numerous environmental issues and affects human beings. Crop residues have considerable energy potential if utilized appropriately. Crop residues can be converted into biochar through thermo-chemical routes; conversion helps in the managing and handling of biomass. Biochar reactors usually operate at temperatures between 400 and 600 °C with fixed carbon contents ranging from 60 to 85%. The application of this biochar to soil improves the physiochemical characteristics of soil because biochar is rich in organic carbon content, which makes the soil more fertile and acts as a carbon sequestration agent over the long term. Biochar itself is considered a source nutrient and can alter the soil nutrient pools and availability. Biochar applied up to 10 cm depth of soil may decrease the denitrification potential and lower N2O emission, greatly controlling leaching of mobile nutrients such as potassium, thus improving water use efficiency, nutrient availability and plant growth. Furthermore, it reduces the leaching of nitrogen into the groundwater and increases the water retention and cation-exchange capacity while moderating the soil’s acidity, resulting in improved soil fertility. This article discusses different biochar production processes and various feedstocks and characteristics of biochar. The factors affecting biochar production and advantages of the utilization of biochar in soil are also reviewed.

Composite low thinning and slash burning treatment enhances initial Spanish black pine seedling recruitment

Global change threatens the persistence of native forest ecosystems mainly by limiting the conditions for natural regeneration but also inducing tree mortality and increasing the risk of large wildfires. In this context, understanding the biotic and biotic factors that ultimately determine tree recruitment is of pivotal importance to implement adaptive forest management strategies. In this study we assess how multipurpose management strategies, including combinations of thinning intensities and prescribed burning, affect the seed emergence and seedling survival of Pinus nigra Arn. subsp. salzmannii in two different forest sites in NE Spain. We tested four overstorey and fuel treatments that combined heavy and light intensity thinnings from below with understorey clearing and two different treatments of the resulting slash: prescribed burning and lop and scatter. The results showed: (1) a lack of regeneration in control units, probably caused by the high density of canopy and understorey; (2) greater seedling recruitment in units treated with slash burning than in units treated with slash lop and scatter, probably due to the effects of prescribed burning on the herbaceous layer, soil organic layer, nutrient pools, and understorey; and (3) a different regeneration response between sites for treatments that included prescribed burning, probably due to microclimatic conditions during the experiment and differences in the characteristics of the prescribed burns. These findings indicate the potential effectiveness of combined treatments of thinning and slash burning in the context of the implementation of multipurpose management actions in endangered ecosystems adapted to low intensity fires.

Conversion from temperate secondary forests into plantations (Larix spp.): Impact on belowground carbon and nutrient pools in northeastern China

AbstractConversions from natural broad‐leaved forests into conifer plantations have been increasing over the past half century worldwide, especially in China. However, the impacts of plantation afforestation on macronutrient and micronutrient pools combined with litter, soil, and roots have not been well quantified. We compared macronutrient and micronutrient pools in litter, fine roots, and at 0‐ to 80‐cm soil depths of paired secondary forests and larch plantations. The results showed that compared with natural forest soils, plantation soils exhibited lower concentrations and stocks of C, as well as lower fine root biomass at 0‐ to 10‐cm depth. In contrast, the K, Fe, Mn, and Cu pools in the larch plantations were greater by 27–44% for the 20‐ to 40‐cm depth. Furthermore, soil N, P, Ca, and Mg pools and stoichiometry of C/N/P in litter, soil, and fine roots did not differ significantly in the larch plantation relative to secondary forests. These results suggest that the conversion from secondary forests to larch plantations only decreases soil C pools but does not lead to reductions in other nutrient pools. Our results also showed that there were less C and nutrients in roots and more C and nutrients accumulated in litter of larch plantations compared with secondary forests. In conclusion, converting secondary forests to larch plantations changed the vertical distribution of C and nutrient pools in litter, soil, and root. The results suggest that C and nutrient pools in soils should be considered at levels below 40 cm in depth when evaluating C and nutrient change with afforestation.