Soil Organic Matter Input Research Articles

Cropping and soil management systems effects on soil organic matter fractions in diversified agricultural fields in the Cerrado

ABSTRACT Soil organic matter (SOM) dynamics can be significantly influenced by various cultivation practices, particularly under environmental and edaphic conditions that enhance and accelerate the transformations of organic materials such as straw, root biomass, and organic fertilizers. This study aimed to evaluate the impact of different cultivation and soil management systems on SOM fractions in agricultural areas of the Cerrado Goiano region. The research was conducted across three areas with diverse production systems: 1) BV area, including soybean monoculture (SM01), integrated crop-livestock-forest (ICLF01), pasture (PA01), and Cerrado vegetation (NV01); 2) ML area, featured soybean-corn monoculture succession (SMS02), agroforestry (AF02), pasture (PA02), and native Cerrado vegetation (NV02); and 3) IF area, comprised soybean-corn succession (SMS03), integrated livestock-forest (ILF03), pasture (PA03), and native Cerrado vegetation (NV03). Disturbed and undisturbed soil samples were collected from two layers: 0.00-0.05 and 0.05-0.10 m. Samples were analyzed for total organic carbon, carbon storage, and SOM physical (granulometric and densimetric) and chemical (fulvic acid, humic acid, and humin) fractionations of soil organic matter (SOM). Additionally, water-floatable light organic matter (LOM), the carbon management index, and its components were determined. Soil organic matter fractions were similarly influenced by the characteristics of cultivation and management systems. However, there were more pronounced differences between systems in the BV area compared to the ML and IF areas. Among the parameters studied, LOM proved to be the most efficient and effective in distinguishing SOM input across different cultivation and soil management systems, particularly in pasture systems.

Organic Management and Intercropping of Fruit Perennials Increase Soil Microbial Diversity and Activity in Arid Zone Orchard Cropping Systems

Organic farming encourages soil management practices that can improve soil health and fertility by increasing soil organic matter inputs and system sustainability. This study evaluated the effect of three years of continuous organic farming and intercropping orchard treatments on soil microbial diversity, microbial enumeration, respiration, soil fertility and fruit yields. Organic management resulted in higher soil organic matter content, Olsen P, and water holding capacity, but did not affect soil pH, electrical conductivity (EC), K, or Na levels. Growth parameters measured on all fruit trees were not significantly different among treatments. The enumeration of bacteria was significantly higher in organic plots when compared to conventionally managed plots. Soil respiration and substrate-induced respiration were significantly higher in the organic diverse plots in comparison to both conventional systems. The genomic analysis of prokaryotes (16S rRNA) and eukaryotes/fungi (ITS) revealed a significantly higher number of taxa, Shannon H index, and Equitability index in the organic systems for both prokaryotes and eukaryotes, in comparison to conventional farming, all of which are indicators of system sustainability. The relative abundance of Operational Taxonomic Units (OTUs) previously reported as diazotrophs, denitrifiers, or involved in the sulfur cycle, as well as Arbuscular Mychorrizae Fungi (AMF)/glomeromycotan, were highest in the organically managed soils than in the conventional plots. A multivariate correlation network clustering revealed that the microbial communities within the organic and conventional soils had strong dissimilarities regarding soil microbial niches. Our work provides evidence that organic management can be used for increasing soil microbial diversity and soil health, leading to higher levels of sustainability in fruit orchard systems.

Economic optimization of sustainable soil management: a Dutch case study

Soil quality is pivotal for crop productivity and the environmental quality of agricultural ecosystems. Achieving sufficient yearly income and long-term farm continuity are key goals for farmers, making sustainable soil management an economic challenge. Existing bio-economic models often inadequately address soil quality. In this study, we apply the novel FARManalytics model, which integrates chemical, physical, and biological indicators of soil quality indicator, quantitative rules on how these indicators respond to farmers’ production management over time, and an economic calculation framework that accurately calculates the contribution of production management decisions towards farm income. This is the first study applying this model on existing arable farms. FARManalytics optimizes crop rotation design, cover crops, manure and fertilizer application and crop residue management. Nine Dutch arable farms were analyzed with a high variation in farm size, soil type, and cultivated crops. First, we assessed farm differences in soil quality and farm economics. Second, we optimized production management to maximize farm income while meeting soil quality targets using farm-specific scenarios. Third, we explored the impact of recent policy measures to preserve water quality and to increase the contribution of local protein production. The results show that the case farms already perform well regarding soil quality, with 75% of the soil quality indicators above critical levels. The main soil quality bottlenecks are subsoil compaction and soil organic matter input. We show that even in front-runner farms, bio-economic modeling with FARManalytics substantially improves economic performance while increasing soil quality. We found that farm income could be increased by up to €704 ha−1 year−1 while meeting soil quality targets. Additionally, we show that to anticipate on stricter water quality regulation and market shift for protein crops, FARManalytics is able to provide alternative production management strategies that ensure the highest farm income while preserving soil quality for a set of heterogenous farms.

Soil Organic Matter Input Promotes Coastal Topsoil Desalinization by Altering the Salt Distribution in the Soil Profile

Organic amendment is an effective method to reclaim salt-affected soil. However, in coastal land with shallow saline groundwater, it is limited known about the mechanism of organic amendment on soil desalinization. Thus, to examine the effect of topsoil organic matter content on soil water/salt transport and distribution, two-year field observations in Bohai coastal land, North China, and soil column experiments simulating salt accumulation and salt leaching were conducted, respectively. There were different organic fertilizer amendment rates in 0–20 cm topsoil, 0% (CK), 50% (OA 0.5), and 100% (OA 1.0) (w/w) for soil column experiments. Field observation showed that after organic amendment (OA), the soil’s physical structure was improved, and less of the increase in topsoil salt content was observed, with more salt accumulated in deep soil layers during the dry season. In addition, OA greatly promoted salt leaching during the rainy seasons. The results of the soil column tests further indicated that OA treatments significantly inhibited soil evaporation, with less salt accumulated in the topsoil. Although there was no difference in soil water distribution between the CK and OA 0.5 treatment, the topsoil EC for the OA 0.5 treatment was significantly lower than that for CK. During soil water infiltration, the OA 0.5 and OA 1.0 treatments significantly increased the infiltration rates, enhanced the wetting front, and promoted salt leaching to deeper soil layers, compared with CK. The improvement of soil organic amounts could make the soil more self-resistant to the coastal salinization. The findings of this study provide some insights into soil water/salt regulation in heterogeneous soil masses and on the permanent management of coastal saline farmland.

FARManalytics – A bio-economic model to optimize the economic value of sustainable soil management on arable farms

Soil quality is an important determinant of agricultural productivity and environmental quality. Despite its importance, few economic models incorporate sustainable soil management. The objective of this study is to develop and illustrate FARManalytics: a bio-economic model to gain quantitative insight in the economic value of sustainable soil management. First, we defined a comprehensive set of chemical, physical and biological soil quality indicators and quantitative rules on how these indicators respond to farmers’ production management over time. Second, we introduce an economic calculation framework that enables accurate calculation of the contribution of different production management decisions towards farm income using Activity-Based-Costing. The set of soil quality indicators and economic calculations serve as the basis for the bio-economic model FARManalytics, which consists of two modules: (1) the PMcalculator, a module that calculates the impact of current production management on soil quality and farm economics and (2) the PMoptimizer, a module that uses Mixed-Integer-Linear-Programming to maximize farm incomewithin predefined soil quality indicator constraints. The decision variables are the crop rotation, cover crops, manure & fertilizer application and crop residue management. We illustrate the added value of the model by applying it to an extensive and intensive farm type, both on clay and sandy soil. These farm types are derived from the Farm Accountancy Data Network (FADN) in the Netherlands. FARManalytics demonstrates that it is possible to increase farm income with up to €940 ha−1 year−1 on clay soil and up to €683 ha−1 year−1 on sandy soil, while meeting all soil quality targets except subsoil compaction vulnerability. The latter was among the most limiting soil quality indicators for the farm types in this study, together with soil organic matter input, wind erosion vulnerability and plant-parasitic nematodes. FARManalytics integrates the impact of production management decisions on soil quality and economics at farm level. Combined with representative farm types, the bio-economic modeling approach of FARManalytics can provide useful information for policy support. FARManalytics can also be tailored to provide decision support for individual farms, based on data that is commonly available on arable farms at low cost.

A Modified Version of RothC to Model the Direct and Indirect Effects of Rice Straw Mulching on Soil Carbon Dynamics, Calibrated in Two Valencian Citrus Orchards

The mulching of agricultural soils has been identified as a viable solution to sequester carbon into the soil, increase soil health, and fight desertification. This is why it is a promising solution for carbon farming in Mediterranean areas. Models are used to project the effects of agricultural practices on soil organic carbon in the future for various soil and climatic conditions, and to help policy makers and farmers assess the best way to implement carbon farming strategies. Here, we modified the widely used RothC model to include mulching practices and their direct and indirect effects on soil organic matter input, soil temperature changes, and soil hydraulic balance. We then calibrated and tested our modified RothC (RothC_MM) using the dataset collected in two field mulching experiments, and we used the tested RothC_MM to estimate the expected soil carbon sequestration due to mulching by the year 2050 for the Valencian Community (Spain). Our results show that RothC_MM improved the fit with the experimental data with respect to basic RothC; RothC_MM was able to model the effects of mulch on soil temperature and soil water content and to predict soil organic carbon (SOC) and CO2 observations taken in the field.

Conversion of forest to cinnamon plantation depletes soil carbon stocks in the top metre of the tropical highlands of Kerinci Regency, Jambi Province, Indonesia

AbstractThis study aimed to investigate the effect of conversion from natural forest to cinnamon plantation on the top 1 m soil carbon stocks and soil characteristics. The project was conducted on Andosols of Kerinci Regency, Sumatera, Indonesia, sampling the soil profile under natural forests and a chronosequence of cinnamon plantations of different ages (1, 5 and 10 years). SOC stocks were quantified alongside physical properties (bulk density) and chemical properties (carbon, nitrogen, C/N ratio) to investigate the impact of land conversion. SOC stocks increased 1 year after conversion to cinnamon plantations, but then tended to decrease as the plantations got older. The initial increase was observed alongside decreasing bulk density 1 year after forest conversion to cinnamon plantation, likely as a result of the fresh input of (less dense) pyrogenic soil organic matter as a result of slash and burn practices and transport down the soil profile owing to leaching. In older plantations SOC stocks were lower, probably because organic matter had been decomposed or leached out of the profile. The free particulate organic matter (fPOM) was isolated from selected topsoil and subsoil layers and analysed for carbon, nitrogen, and FTIR analysis. FTIR analysis revealed that topsoil fPOM contained more aromatic functional groups than subsoils and had a higher degree of decomposition. Aromatic and carbohydrate functional groups were initially lower in recently converted cinnamon plantation, but the trend was reversed 10 years after conversion. The initial flush of fresh organic matter into soils after slash and burn provides fPOM with a lower degree of decomposition but is short‐lived and fPOM becomes more microbially processed as the cinnamon plantation ages. We conclude that, after a short term increase brought about by slash and burn, forest conversion to cinnamon plantation in Kerinci Regency depletes SOC stocks both in topsoils and subsoils.

Melanization slows the rapid movement of fungal necromass carbon and nitrogen into both bacterial and fungal decomposer communities and soils.

Microbial necromass contributes significantly to both soil carbon (C) persistence and ecosystem nitrogen (N) availability, but quantitative estimates of C and N movement from necromass into soils and decomposer communities are lacking. Additionally, while melanin is known to slow fungal necromass decomposition, how it influences microbial C and N acquisition as well as elemental release into soils remains unclear. Here, we tracked decomposition of isotopically labeled low and high melanin fungal necromass and measured 13C and 15N accumulation in surrounding soils and microbial communities over 77 d in a temperate forest in Minnesota, USA. Mass loss was significantly higher from low melanin necromass, corresponding with greater 13C and 15N soil inputs. A taxonomically and functionally diverse array of bacteria and fungi was enriched in 13C and/or 15N at all sampling points, with enrichment being consistently higher on low melanin necromass and earlier in decomposition. Similar patterns of preferential C and N enrichment of many bacterial and fungal genera early in decomposition suggest that both microbial groups co-contribute to the rapid assimilation of resource-rich soil organic matter inputs. While overall richness of taxa enriched in C was higher than in N for both bacteria and fungi, there was a significant positive relationship between C and N in co-enriched taxa. Collectively, our results demonstrate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate but also necromass C and N release and that both elements are rapidly co-utilized by diverse bacterial and fungal decomposers in natural settings. IMPORTANCE Recent studies indicate that microbial dead cells, particularly those of fungi, play an important role in long-term carbon persistence in soils. Despite this growing recognition, how the resources within dead fungal cells (also known as fungal necromass) move into decomposer communities and soils are poorly quantified, particularly in studies based in natural environments. In this study, we found that the contribution of fungal necromass to soil carbon and nitrogen availability was slowed by the amount of melanin present in fungal cell walls. Further, despite the overall rapid acquisition of carbon and nitrogen from necromass by a diverse range of both bacteria and fungi, melanization also slowed microbial uptake of both elements. Collectively, our results indicate that melanization acts as a key ecological trait mediating not only fungal necromass decomposition rate, but also necromass carbon and nitrogen release into soil as well as microbial resource acquisition.

Afforestation inhibited soil microbial activities along the riparian zone of the upper Yangtze River of China

Afforestation strongly influences soil microbial traits, especially microbial biomass and enzyme activity. However, the magnitude and direction of soil microbial traits and their controls following afforestation remain unclear. Here, we examined microbial carbon (C), nitrogen (N), and phosphorus (P) biomass and activities of the most common enzymes involved in C (α-1,4-glucosidase, β-1,4-glucosidase, β-D-1,4-cellobiohydrolase, and β-1,4-xylosidase), N (β-1,4-N-acetyl-glucosaminidase and l-leucine aminopeptidase), and P (alkaline phosphatase) cycling under a 15-year-old forest stands (Morus alba, Salix bablyonica, and a mix of the two species) and adjacent croplands along the riparian zone of the upper Yangtze River of China. Unexpectedly, we found that the 15-year afforestation significantly lowered the contents of total C and N, available P, and NO3– compared to the adjacent cropland soils. The microbial biomass C, N, and P contents were also approximately 14–60%, 34–88%, and 9–89% lower, respectively, in the afforested soils than in the adjacent cropland soils across afforestation types and soil depths. Correspondingly, enzymatic C and N activities were 71–90% and 54–75% lower, respectively, under the S. bablyonica stands across soil depths, whereas enzymatic P activity was 39–72% lower in the afforested soils than in the adjacent cropland soils across afforestation types and depths. Reduced microbial biomass and enzymatic activities after afforestation were attributed to the decreased total C and nutrients in the afforested soils than in the adjacent cropland soils, likely due to high plant uptake nutrients and low soil organic matter inputs during the early stages of forest development. Overall, afforestation with plantations of Morus alba or Salix bablyonica species may reduce soil functions such as C storage and N fertility, suggesting that large-scale afforestation using these species should not be prioritized to restore soil functions within a short period.

Root litter decomposition rates and impacts of drought are regulated by ecosystem legacy

In grassland ecosystems, about two-thirds of productivity is in roots, and therefore roots constitute a major soil organic matter input. However, influences on the rate of root litter decomposition remain unresolved, especially in the context of land-use conversion and climate change. Ecosystem legacy can affect root decomposition rates via impacts on substrate chemistry and soil environments, and this may manifest in responses of decomposition to changing temperature and moisture. Here we investigate the impacts of anthropogenic legacy effects and moderate drought on root litter decomposition rates in five “Land Use History Types”: crop fields, cow pastures, remnant tallgrass prairie, and prairie restored from crop fields and pastures. We measured root losses of mass, carbon, and nitrogen over 11 months. Soil bulk density was unimportant for decomposition, but soil moisture content and temperature were relevant for decomposition rates while time since disturbance predicted decomposition initiation times. Furthermore, soil moisture and temperature dynamics alone could not explain the responses of decomposition rates to drought, which were positively correlated to time since disturbance. Our findings suggest that anthropogenic legacy impacts decomposition rates in grasslands, especially when soil moisture and temperature dynamics are substantially altered, and mediates soil community responses to drought.

PENGARUH PERBANDINGAN DOSIS PUPUK KANDANG TERNAK AYAM DAN SAPI TERHADAP BIOMASSA JAGUNG DAN DINAMIKA KATION TANAH

Soil nutrient deficiency is a problem aftermath of reduction caused by metals and leaching due to low soil organic matter and high input of synthetic chemical fertilizers. The decline in the corn harvest index is a decrease in soil fertility. Hence, local organic materials have urgently needed as a Ultisol ameliorant. This study aims to determine the right combination of chicken manure and cow manure to produce the best increase in plant height and increase the plant dry weight, soil pH, and CEC. The research has conducted at the Hasnur Polytechnic, South Kalimantan, from April 2022 to August 2022 and used a completely randomized design with 200 g of manure divided into three combinations of P0 (control), P1 (30% chicken manure versus 70% cow manure), P2 (50% chicken manure versus 50% cow manure), P3 (70% chicken manure versus 30% cow manure). The results showed that the P2 treatment increased plant height, dry weight, and optimal soil pH, while P3 showed significant soil CEC because chicken manure had varied and balanced nutrient content compared to cow manure.

Phosphorus extractability in relation to soil properties in different fields of fruit orchards under similar ecological conditions of Pakistan

Productivity of an orchard generally depends upon the fertility of the soil and the nutrient requirements of the fruit trees. Phosphorus (P) extractability from soils influences the P sorption, release patterns, and P bioavailability. A study was carried out to investigate P extractability via seven extraction methods in relation to soil properties in three fruit orchards. In total, 10 soil samples were collected from each fruit orchard, namely, citrus (Citrus sinensis L.), loquat (Eriobotrya japonica L.), and guava (Psidium guajava L.), located in similar ecological conditions to the Haripur district of Pakistan. Available P in the soil was extracted using deionized H2O, CaCl2, Mehlich 1, Bray 1, Olsen, HCl, and DTPA methods. Selected soil properties [pH, electrical conductivity (EC), soil organic matter (SOM)], texture, cation exchange capacity (CEC), macronutrients, and micronutrients were also determined. Soils sampled from orchards indicated significant differences in soil properties. Orchards have sequestered more amount of C stock in soil than without an orchard. The extractability of P from soils was profoundly affected by P extraction methods. The average amount of extractable P was relatively higher in those soils where the total amount of P was also higher. These methods extracted different pools of soil P with varying P concentrations regulated by the soil properties. Phosphorus amounts extracted were varied in the order of HCl > DTPA > Mehlich 1 > Bray 1 > Olsen > CaCl2 > water. Among orchards, a higher amount of P was found in soils of loquat followed by citrus and guava orchards. Regardless of the method, subsurface soil got a lower concentration of extractable P than surface soil in all orchards. The extractable P was highly associated with soil properties. DTPA extractable P was related to SOM soil clay content and CEC by R2 values of 0.83, 0.87, and 0.78, respectively. Most of the extraction methods were positively correlated with each other. This study indicated that SOM inputs and turnover associated with orchard trees exhibited a substantial quantity of extractable P in soils. Predicting available P in relation to its bioavailability using these methods in contrasting soils is required.

The conversion of monoculture sugarcane to a tree-based agroforestry system increases total carbon sequestration and soil macrofauna population

Vegetations accumulate carbon (C) from the atmosphere in the form of tree biomass, producing litter which then becomes the main input of soil organic matter. The accumulation of soil organic matter provides food and energy for soil macrofauna to help maintain soil fertility. Total C accumulation is affected by land use changes which can then reduce soil ecosystem and ecological functioning. This study examined the impact of land use conversion from monoculture sugarcane to a tree-based agroforestry system. The results showed that the land use changes affected soil texture, bulk density, soil organic matter, and total C sequestration. The total C sequestration under 5 years old sengon <em>(Paraserianthes moluccana)</em> agroforestry system was almost double that of total C sequestration 2 times or even 5 times ratooned monoculture sugarcane <em>(Saccharum officinarum)</em>. The lowest IVI of soil macrofauna was detected under 1-year-old sengon agroforestry system before it was getting lowered under a longer period of cultivation, whilst the highest population was detected under 5 years old Sengon. Multivariate analysis, which was employed to detect the impact of land use changes, could cluster and group the effect of treatments based on selected variables such as soil physical, chemicals, and soil macrofauna structure and diversity, which accounted for 97.75% of the total variance. There was a strong relationship between the abundance of <em>Formicidae </em>sp. and <em>Carabidae </em>sp.<em></em>

Phosphorus Stock Depletion and Soil C:N:P Stoichiometry Under Annual Crop Rotations and Grassland Management Systems Over 13 Years

Phosphorus (P) nutrition is essential to both plant yield and soil organic matter (SOM) input. However, continuous extraction of P by plants and biomass harvesting can lead to soil P stock depletion, a reduction in crop yields and ultimately a reduction in organic matter input to the soil. In this work, we analysed P, C and N stock trends in the 0-30 cm topsoil layer cultivated with permanent cropland (CC) and mowed permanent grassland (GG) for 13 years. In addition, we characterized the changes in P organic forms by using 31P-NMR. The results showed that the amount of P exported within 13 years was 10% greater in GG than in CC (295 and 268 kg ha-1, respectively). The total P stocks decreased under both the CC and GG management systems (0.30 and 0.25 Mg ha-1, respectively). This depletion was mainly observed in total Pi forms, which recorded reductions of 0.75 and 0.29 Mg ha-1 in GG and CC, respectively. The total Po stock increased by 42.6% in GG; these results were consistent with the increase in C and N stocks in GG (2.6 and 0.19 Mg ha-1, respectively) and their reduction in CC (-4.2 and -0.38 Mg ha-1, respectively). Although P depletion mainly affected the P pool presenting the highest lability (labile P), this depletion did not have a negative effect on plant yield after 13 years due to the buffering capacity of P pools presenting less lability (moderately labile P). Mowing permanent grasslands led to a change in the pool of labile P from inorganic to organic forms and an increase in soil C and N stocks. Based on the 31P-NMR technique, permanent grasslands significantly reduced α-glycerophosphate and increased myo-IHP and adenosine monophosphate more than the permanent cropland. Although there was no significant decrease in productivity, the depletion of available P should be monitored over time, especially in mown permanent grassland crops, to prevent potential nutrient stress.

Controls of Initial Wood Decomposition on and in Forest Soils Using Standard Material

Forest ecosystems sequester approximately half of the world’s organic carbon (C), most of it in the soil. The amount of soil C stored depends on the input and decomposition rate of soil organic matter (OM), which is controlled by the abundance and composition of the microbial and invertebrate communities, soil physico-chemical properties, and (micro)-climatic conditions. Although many studies have assessed how these site-specific climatic and soil properties affect the decomposition of fresh OM, differences in the type and quality of the OM substrate used, make it difficult to compare and extrapolate results across larger scales. Here, we used standard wood stakes made from aspen (Populus tremuloidesMichx.) and loblolly pine (Pinus taedaL.) to explore how climate and abiotic soil properties affect wood decomposition across 44 unharvested forest stands located across the northern hemisphere. Stakes were placed in three locations: (i) on top of the surface organic horizons (surface), (ii) at the interface between the surface organic horizons and mineral soil (interface), and (iii) into the mineral soil (mineral). Decomposition rates of both wood species was greatest for mineral stakes and lowest for stakes placed on the surface organic horizons, but aspen stakes decomposed faster than pine stakes. Our models explained 44 and 36% of the total variation in decomposition for aspen surface and interface stakes, but only 0.1% (surface), 12% (interface), 7% (mineral) for pine, and 7% for mineral aspen stakes. Generally, air temperature was positively, precipitation negatively related to wood stake decomposition. Climatic variables were stronger predictors of decomposition than soil properties (surface C:nitrogen ratio, mineral C concentration, and pH), regardless of stake location or wood species. However, climate-only models failed in explaining wood decomposition, pointing toward the importance of including local-site properties when predicting wood decomposition. The difficulties we had in explaining the variability in wood decomposition, especially for pine and mineral soil stakes, highlight the need to continue assessing drivers of decomposition across large global scales to better understand and estimate surface and belowground C cycling, and understand the drivers and mechanisms that affect C pools, CO2emissions, and nutrient cycles.

Temperature and pH mediate stoichiometric constraints of organically derived soil nutrients.

It remains unclear how warming will affect resource flows during soil organic matter (SOM) decomposition, in part due to uncertainty in how exoenzymes produced by microbes and roots will function. Rising temperatures can enhance the activity of most exoenzymes, but soil pH can impose limitations on their catalytic efficiency. The effects of temperature and pH on enzyme activity are often examined in environmental samples, but purified enzyme kinetics reveal fundamental attributes of enzymes’ intrinsic temperature responses and how relative release of decay‐liberated resources (their flow ratios) can change with environmental conditions. In this paper, we illuminate the principle that fundamental, biochemical limitations on SOM release of C, N, and P during decay, and differential exoenzymes’ responses to the environment, can exert biosphere‐scale significance on the stoichiometry of bioavailable soil resources. To that end, we combined previously published intrinsic temperature sensitivities of two hydrolytic enzymes that release C and N during decay with a novel data set characterizing the kinetics of a P‐releasing enzyme (acid phosphatase) across an ecologically relevant pH gradient. We use these data to estimate potential change in the flow ratios derived from these three enzymes’ activities (C:N, C:P, and N:P) at the global scale by the end of the century, based on temperature projections and soil pH distribution. Our results highlight how the temperature sensitivity of these hydrolytic enzymes and the influence of pH on that sensitivity can govern the relative availability of bioavailable resources derived from these enzymes. The work illuminates the utility of weaving well‐defined kinetic constraints of microbes’ exoenzymes into models that incorporate changing SOM inputs and composition, nutrient availability, and microbial functioning into their efforts to project terrestrial ecosystem functioning in a changing climate.

Signatures of natural to anthropogenic transition in lake sediments from the Central Himalaya using stable isotopes

Stable isotopic compositions of carbon (C) and nitrogen (N) in lake sediments have the potential to decipher natural and anthropogenic influences in a region, which has undergone significant cultural changes in the recent past. In this study, using carbon (δ13C) and nitrogen (δ15N) isotopic compositions of organic matter along with C isotopic ratio of black carbon (δ13CBC) in sediments collected from a lake in the Lesser Himalaya, an attempt has been made to decipher the biogeochemical changes in the lake under natural and anthropogenic stresses along with fire history of the region. The sediment core, dated using 210Pb and 137Cs, went back to 1949 AD, where isotopic compositions and elemental ratios (TOC/TN) suggested that the lake biogeochemistry was largely controlled by in-lake primary productivity. A noticeable change in isotopic compositions and elemental ratios was observed in the early 1970s, possibly due to increased input of soil organic matter from the catchment, which coincided with the urbanization and other human interventions in the region. At the same time, a consistent increase in differences between the measured and Suess effect corrected δ13C of organic matter from the early 1970s to 2016 AD indicated towards the increased utilization of fossil fuel-induced atmospheric CO2 by the lake biota. Also, a sudden shift in δ13CBC in the early 1970s showed an increase in fossil fuel-induced black C in the region during that time. Overall, a comparison of the current study with other lakes in the region revealed the effect of land use change and population growth on the lake biogeochemistry, which was clearly recorded in elemental contents and stable isotopic composition of different components of lake sediments. However, the response of each lake depended on the location (i.e., distance from the city) and size of the catchment. The larger lakes in the region appeared to have suffered the anthropogenic stress through both atmospheric and terrestrial routes, whereas the smaller and secluded lake, as in the present study, was largely influenced via atmospheric factors.

Inherent and dynamic effects on the structural stability of Brazilian Oxisols

We assessed long-term cultivation effects on several structural stability indicators within the 0- to 5- and 10- to 15-cm depth increments of different Oxisols. Comparisons were made between native and cultivated soils managed using no-till (NT) practices for 12+ years. Overall, conversion significantly decreased structure stability due to machinery traffic, high fertilizer and lime applications, soil organic matter (SOM) depletion, and reduced input of organic material (roots and crop residues). The magnitude of change varied depending on inherent (mineralogy) and dynamic (cropping system) factors, as well as soil depth. Kaolinitic Oxisols were much more susceptible to degradation than Gibbsitic Oxisols. Combining more diversified cropping systems with NT can mitigate the negative effects of cultivation by increasing living vegetation and crop residue additions throughout the entire year. Increased quantity and quality of SOM input improves soil biological activity and improves topsoil structural stability. Those changes also reduce eluviation of dispersed clay (primarily kaolinite) with percolating water and prevent concentration of the clay at the 10 to 15 cm depth, which further degrades the soil by contributing to formation of the dense subsurface layers beneath either NT or conventional production systems.

Distribution of earthworm communities in agroecosystems with forested riparian buffer strips: A multiscale study

Knowledge is lacking on the factors controlling the structure and spatial distribution of earthworm communities within agroecosystems. We first hypothesized that forested riparian buffer strips (FRBS) within agricultural landscapes would be a refuge for earthworms, as we predicted higher soil moisture and organic matter inputs in FRBS than in adjacent agricultural fields (treatments = FRBS vs. Field). We further hypothesized that earthworms would be most abundant where the chemical quality of above- and belowground plant litter is high, or where soil disturbance is low. We conducted a field survey to quantify earthworm species abundances in FRBS and adjacent agricultural fields in two bioregions, namely Eastern Canada and Central Europe. At each of 77 sites, we collected and identified earthworms from three plots within FRBS and within adjacent agricultural fields. In each plot, we identified the tree species, understory vegetation, soil drainage class, agricultural crop as well as five soil physicochemical properties. In each bioregion and treatment, we found proportionately more endogeic than anecic or epigeic earthworm species. In Eastern Canada, there were proportionately fewer anecic and more epigeic individuals in FRBS than in fields; in Central Europe there were fewer endogeic and more anecic earthworms in FRBS than in fields. We found significant bioregion × treatment interactions on earthworm abundance and soil moisture. More specifically, in Eastern Canada we found higher earthworm abundance and soil moisture in FRBS, whereas in Central Europe we found higher earthworm abundance in fields and no treatment effect on soil moisture. In both bioregions, we found higher organic matter in FRBS than in fields. In Eastern Canada, earthworm abundance in deciduous and mixedwood stands were higher than in coniferous stands; in Central Europe, earthworm abundance was highest in deciduous stands only. Within FRBS in Eastern Canada, the abundance of the prominent endogeic species, Apporectodea rosea, was correlated with herbaceous plants, notably ferns and graminoids. Conditional regression tree analysis revealed positive relationships between earthworms and soil clay content, pH, moisture and organic matter. Our results suggest that local and landscape patterns in earthworm diversity can be predicted by soil and vegetation attributes, however the relative importance of these factors changes across continental scales due to differences in precipitation patterns and soil moisture availability. Comparing the distributions of earthworms across different scales provides insights into the potential of different species to spread into new habitats with climate change.

ПРОДУКТИВНОСТЬ СИДЕРАЛЬНЫХ КУЛЬТУР В РАЗЛИЧНЫХ ГИДРОТЕРМИЧЕСКИХ УСЛОВИЯХ

Green manuring can increase biological activity of the soil, enrich it with organic matter, nutrients and improve its agrophysical and agrochemical properties. The aim of the research was to establish the influence of green manure crops species composition on the productivity of agrophytocenoses and the input of soil organic matter under various hydrothermal conditions. The studies were conducted in 2016–2019 on the experimental fields of the Research Institute of Agriculture of Crimea. Soil – chernozems southern low-humus. Average daily air temperature was: in 2016 – 11.8 °С; in 2017 – 12.7 °С; in 2018 – 12.5 °С; in 2019 – 12.6 °С (average long-term values – 10.8 °С). The amount of precipitation over the years was at the level of 162, 67, 129, 108 % of the norm. The experiments were laid according to B. A. Dospekhov “Methods of field research”. Position of the variants is systematic, triple replication. Fields square – 720 m2. The research subject is green manure crops agrocenoses. The object of the research is the process of forming the productivity of green manure crops. On average, over the years of research, the highest yield of green mass was formed by sweet clover and sainfoin (29.1 and 27.1 t/ha, respectively), winter triticale (24.5 t/ha) and winter rye (25.8 t/ha). T. pratense and P. tanacetifolia were low-yielding. The largest amount of accumulated soil organic matter was detected when rye, triticale, sainfoin and sweet clover were used as green manure; it was 5.88, 5.72, 5.56 and 5.52 t/ha, respectively. We established an average correlation (at 5 % significance level) between the amount of precipitation for the period “sowing – ripeness” in 2016–2017 and the yield of green mass of green manure crops (r = 0.52), as well as dry matter yield (r = 0.59). A negative correlation of average strength was also established between the average daily temperature of the period “sowing – ripeness” in 2017–2018 and yield of green mass (r = –0.66), as well as organic matter yield (r = –0.64).