Humification Coefficient Research Articles

Soil Carbon Stock and Indices in Sandy Soil Affected by Eucalyptus Harvest Residue Management in the South of Brazil

There has been limited research on the effect of eucalyptus harvest residue management on soil organic carbon (SOC) in subtropical environments. This research evaluated the effect on soil C indices of the following eucalyptus harvest residue managements: AR, with all forest remnants left on the soil; NB, where bark was removed; NBr, in which branches were removed; NR, which removed all residues; and NRs, which is same as NR but also used a shade net to prevent the litter from the new plantation from reaching the soil surface. C stocks within the soil depths of 0–20 cm and 0–100 cm increased linearly with the C input from eucalyptus harvest residues. In the layer of 0–20 cm, the lowest soil C retention rate was 0.23 Mg ha−1 year−1, in the NR treatment, while in the AR treatment, the retention rate was 0.68 Mg ha−1 year−1. In the 0–100 cm layer, the highest C retention rate was obtained in the AR (1.47 Mg ha−1 year−1). The residues showed a high humification coefficient (k1 = 0.23) and a high soil organic matter decomposition rate (k2 = 0.10). The carbon management index showed a close relationship with the C input and tree diameter at breast height.

The influence of organic–mineral fertilization system and the structure of crop rotation on the humus condition of leached chernozem

Purpose. To study the influence of organic-mineral fertilization systems and the structure of crop rotation on the transformation of organic matter and the state of humus in leached chernozem.
 Меthods. Long-term field and analytical.
 Results. Research data on the amount of organic matter entering the soil, its humification, and the effect on the humus content in leached chernozem, depending on fertilization systems and the structure of crop rotation, are given. It was established that under the mineral fertilization system, the humus content in the soil was the lowest and demonstrated a negative seasonal dynamic. The stability of the humus content in the soil was ensured by traditional and alternative organic-mineral fertilization systems.
 Conclusions. The content of humus in leached chernozem mainly depended on the fertilization system and slightly depended on the crop rotation structure. Application of N90Ρ90Κ90 + straw + green manure or N48.8Ρ45Κ55 + by-products + green manure per 1 ha of crop rotation under sugar beet during 20 years provided the highest humus content in the soil. The content of humus was 4.04–4.07% in the 0–30 cm soil layer and 3.79–3.81% in the 30–50 cm layer, which was higher compared to mineral fertilizations by 0.18–0.20% and 0.06–0.08%, respectively. The alternative organic-mineral fertilization system stabilized the humus content in the soil at the level of the conventional manure-based fertilization system. In the mineral fertilization system, the humus content in the soil of the crop rotations decreased at the end of the vegetation season compared to the initial indicator by 0.02–0.03%, while in the organic-mineral fertilization system it increased by 0.02–0.04%. The humus content remained stable in the 30–50 cm soil layer. The alternative fertilization system with the application of mineral fertilizers, straw and green manure had the highest stabilization effect on the state of soil humus. The application of N90Ρ90Κ90 + straw + green manure provided the highest amounts of organic matter entering the soil in crop rotations − 3.55–3.57 t/ha accompanied by high humification coefficients: 22 % in a crop rotation with two fields of soybean, 41 % with barley and pea mix as preceding crops, and 44 % with pea, vetch and oat mix as preceding crops. The influence of the structure of crop rotation on the state of humus in leached chernozem was found insignificant.

Microbiological activity of chernozem depending on the use and size of soil aggregates

The results of the studies of changes in biological and enzymatic activity of soils depending on the anthropogenic influence and the size of soil aggregates are presented. The work was carried out in 2015-2021 in the conditions of the south-east of the Central Chernozem region. The soil of the experimental site is ordinary (segregational) medium–sized medium-humus heavy loamy chernozem. The objects of research are long–used arable land and the layland used for haying since 1882. The quantitative change of individual groups of microorganisms, determined by the nature of the impact on the soil cover, is shown. The total number of microorganisms in both arable land and chernozems under natural vegetation was at the same level of 40.0 and 39.3 million CFU, respectively. Significant differences in the biological activity of chernozems by individual groups of microbial cenosis structure were noted. An increase in the number of ammonification bacteria on the arable analogue was revealed by an average of 30.7%; micromycetes by 4.4%; cellulolytics by 46.4%; nitrifiers by 46.9%; calculated humification coefficient by 45.4%. According to other components of microbial cenosis, the advantage of layland steppe soils is noted: actinomycetes by 18.5%; humus mineralizers by 11.8%. An increase in the activity of most groups of microorganisms was shown in the smaller structural units of 1-5 mm. In larger mesoaggregates, CFU numbers tend to decrease. This pattern is most clearly traced in agrogenically altered soils. In the soils occupied by natural vegetation, there is a higher activity of biochemical processes.

INFLUENCE OF OIL POLLUTION ON ACTIVITY OF SOIL ENZYMES OF OXIDOREDUCTASE AND HYDROLASE CLASSES

Soil enzymatic activity is the most important biochemical parameter of soil fertility and it is determined by chemical composition, species and quantitative diversity of soil microbiota and plants, and the set and degree of activity of soil enzymes. The article shows the dynamics of enzymatic activity of the soil contaminated with oil from Vishenskoyedeposit in Melekesskiy district of Ulyanovsk region before and after spring wheatcultivation, as well as using biohumus, zeolite and diatomite sorbents. To assess the biological state of the soil contaminated with oil products, the activity of the main enzymes of the soil pool of the class of oxidoreductases (polyphenol oxidase), peroxidase, catalase) and the class of hydrolases (phosphatase, invertase) was determined. As a result of the studies, it was found that oil pollution reduces activity of oxidoreductase and part of hydrolytic enzymes. The inhibitiondegree correlates with oilconcentration in the soil. A direct dependence of inhibitiondegree of polyphenol oxidase, catalase, phosphatase and invertase on oil concentration was found. It was found that introduction of diatomite increased the activity of peroxidase and invertase, zeolite and biohumus - phosphatase. To assess the state of soil fertility, humus accumulation coefficient (humification coefficient) is used, which is defined as the ratio of polyphenol oxidase activity to peroxidase activity. This coefficient allowsto assess the tendencies of humus formation processes: humification or mineralization. It was determined that the introduction of low doses of oil (2-3%) increases humification coefficient, and high concentrations (8%) reduce it. To diagnose the state of oil-contaminated soils, it is recommended to determine the activity of basic enzymes: polyphenol oxidase, peroxidase, catalase, phosphatase, and invertase.

Сirculation of carbon oxide depending on the energy efficiency of agriculture – regional aspect

Aim. To establish the relationship between energy efficiency of crop production with the balance of carbon monoxide during the period of increasing manure application (1956–1995) and its replacement by by-products as organic fertilizer and to develop a model of carbon monoxide and agrocenosis depending on energy costs in agriculture. AIC of Cherkasy region in the period from 1956 to 2020. Methods. Information-analytical, mathematical-statistical (correlation-regression, factor, method of nonparametric statistics). Results. The increase in energy efficiency in agriculture of the region's agro-industrial complex is associated with a decrease in the formation of humus from organic fertilizers, when the increase in Kee per unit was accompanied by a decrease in humus production of 0.16 million tons and accompanied by an increase in mineralization (Kee per unit was 2.42 million. tons of C-CO2 mineralization). During the period of manure application and supplementation with crop and root residues, the ratio of С-СО2, which passed from manure and crop residues to humus was in the range of 0.7–1.2 to 1, but due to the higher level of humification coefficients of crop and root residues mineralization of manure is a more intense source of C-CO2 emissions compared to the mineralization of crop and root residues, which are a stock factor of C-CO2. With the complete replacement of manure by side phytomass as an organic fertilizer, the emission of C-CO2 from the mineralization of its excess remains lower on average by 2.27 times compared to the period of manure application. Conclusions. With the growth of Kee, the level of mineral processes increases and the sequestration capacity of С-СО2 decreases (according to Ib humus and agrocenosis), agricultural productivity increases, but the fertility of agricultural lands decreases, which is typical for the period of manure application. When manure is replaced by by-products, the Kee, the level of mineralization processes and the increase of sequestration capacity of С-СО2 humus and agrocenosis decrease, which provides conditions for the formation of land fertility against the background of reduced agricultural productivity.

Decomposition dynamics and driving factors of manure in reclaimed soils in coal mining area

Understanding the decomposition dynamics and driving factors of manure in the soil subjected to different reclaimed years could provide theoretical basis to rational utilization of manure and soil fertility improvement in coal mining area. Cattle manure and pig manure were mixed with soils subjected to different reclaimed years (one year, R1; 10 years, R10; and 30 years, R30) at the ratio of manure carbon to soil mass of 4 to 100, so as to examine manure decomposition characteristics using the nylon mesh bag (15 cm deep of soil buried) in the Shanxi coal mine reclamation area, with no manure addition as control (CK). Soil samples were collected at day 12, 23, 55, 218, 281, and 365 to measure the contents of soil manure residual, soil microbial biomass carbon (MBC), and dissolved organic carbon (DOC). The contributions of soil properties, manure properties, and hydrothermal condition to manure decomposition were quantified. The results showed that the decomposition rates of pig manure were significantly higher than cattle manure. The humification coefficient of pig manure (average 46.3%) was lower than that of cattle manure (average 71.7%). The humification coefficient of pig manure was significantly lower in the 30-year reclaimed soil (44.5%) compared to the 1-year and 10-year reclaimed soil (average 47.2%). There was no significant difference in the humification coefficient of cattle manure among the three reclaimed soils. The proportion and decomposition rate constant of labile carbon pool of pig manure and cattle manure were significantly different, with values of 52% and 26%, and 0.00085 and 0.00074 ℃-1, respectively. The positive effect of pig manure on MBC and DOC in reclaimed soil was significantly higher than that of cattle manure over 0-218 days, but no difference over 281-365 days. The magnitude of the enhancement of MBC and DOC in those three reclaimed soils after manure amendments showed a similar trend of R1 >R10 ≈ R30. Results of variance partitioning analysis showed that manure decomposition was mainly controlled by manure properties (17.9%) when considering soil properties, manure properties, and hydrothermal condition. In conclusion, the decomposition of pig manure but not cattle manure was regulated by reclamation year. Cattle manure, with higher humification coefficient than pig manure, was recommended for reclaimed mining area to improve soil fertility.

The combination of residue quality, residue placement and soil mineral N content drives C and N dynamics by modifying N availability to microbial decomposers

Crop residues are the main source of carbon (C) inputs to soils in cropping systems, and their subsequent decomposition is crucial for nutrient recycling. The interactive effects of residue chemical quality, residue placement and soil mineral nitrogen (N) availability on carbon and N mineralization dynamics were experimentally examined and interpreted using a modelling approach with the deterministic-functional, dynamic decomposition module of the Simulateur mulTIdisciplinaire pour les Cultures Standard (STICS) model. We performed a 120-day incubation at 25 °C to evaluate how the mineralization of C and N from residues would respond to residue type (residues of 10 crop species with C:N ratios varying from 13 to 105), placement (surface or incorporated) and initial soil mineral N content (9 or 77 mg N kg−1 dry soil). A reduced C mineralization rate was associated with N limitation, as observed for high-C:N ratio residues, and shaped by residue placement and initial soil mineral N content. This was not observed for low-C:N ratio residues. Overall, increased net N mineralization corresponded with reduced N availability. Using the optimization procedure in the STICS decomposition module to explain the C and N dynamics of surface-decomposing residues, we estimated that 24% of the total soil mineral N would be accessible to decomposers. The STICS decomposition module reproduced the C and N dynamics for each treatment well after five parameters were optimized. The optimized values of the biomass C:N (CNbio), residue decomposition rate (k), humification coefficient of microbial C (h), and microbial decomposition rate (λ) were significantly correlated with total N availability across all 40 treatments. Under low total N availability, CNbio increased, while k, h and λ decreased compared to their values under high N availability, suggesting functional changes in the microbial community of decomposers. Our results show that an N availability approach could be used to estimate residue C dynamics and net N mineralization in the field in response to crop residue quality and placement and demonstrate the potential to improve decomposition models by considering the effects of N availability on C dynamics.

Effects of additives on physical, chemical, and microbiological properties during green waste composting

Composting is an environmentally friendly and sustainable way to transform Green waste (GW) into a useful product. GW, however, contains substantial quantities of lignocelluloses that extend the composting period unless substances that accelerate composting are added. The objective of this research was to assess the influence of the following additives on GW composting (w/w dry matter contents of the additives were indicated): sugarcane bagasse at 15%; bean dregs at 35%; silage at 45%; flue gas desulfurization gypsum at 5%; maifanite at 4%; and furfural residue at 20%. Based on the composting temperature, compost density, porosity, particle-size distribution, water retention, pH, cation exchange capacity, available nutrient contents, humification coefficient, organic matter loss, microbial populations, and phytotoxicity, the best additives were 45% silage and 5% flue gas desulfurization gypsum. The latter two additives produced a high-quality product in only 35 and 37 days, respectively.

Effects of crude oil on the biological activity of chernozem soils

The article investigates the effect of crude oil on soil microorganisms and the enzymatic activity of chernozem soils. Experiments were carried out on podzolized medium loamy chernozem in the Samara region using high-sulphur crude oil of medium density. Per 1 kg of soil, 10.00 g (1%), 30.00 g (3%) and 50.00 g (5%) of oil were applied. According to the obtained results, the native soil microbiota contains a wide variety of microorganisms capable of oxidizing both individual hydrocarbons and crude oil in general. Bacteria of the Acinetobacter, Bacillus, Mycobacterium, Pseudomonas and Streptomyces genera, filamentous fungi of the Aspergillus and Penicillium genera, as well as Candida yeast showed the greatest activity in the degradation of both individual hydrocarbons and crude oil in general. The soils freshly polluted with oil demonstrated an increase in the number of bacteria that consume organic forms of nitrogen, actinomycetes, fungi and hydro-carbon-oxidizing microorganisms. In addition, a growing trend in the number of autochthonous microorganisms participating in the mineralization of humic substances was observed. Following 3 months of experiments, a decrease in the number of bacteria consuming organic forms of nitrogen and actinomycetes was revealed. The number of fungi showed the most pronounced decrease upon addition of 3 and 5% of oil, while the number of autochthonous microorganisms participating in the mineralization of humic substances and hydrocarbon-oxidizing microorganisms grew with an increase in the degree of oil pollution. Inhibition of various microorganisms by means of physical or toxic action of hydrocarbons contained in crude oil can cause a decrease in the activity of enzymes present in chernozem soils. Oil hydrocarbons inhibit the activity of polyphenol oxidase, catalase, invertase, phosphatase and lipase present in chernozem soils, although slightly stimulating the peroxidase activity. A decrease in the soil humification coefficient indicates that the oxidation of humic substances prevail over the decomposition of organic aromatic compounds into soil humus components, as well as a decrease in soil fertility as a result of its contamination with crude oil hydrocarbons.

Contribution of above- versus belowground C inputs of maize to soil organic carbon: Conclusions from a 13C/12C-resolved resampling campaign of Belgian croplands after two decades

The few available studies on maize biomass in soil of field experiments have shown that belowground maize biomass resides more than twice as long as aboveground residues. Our principal objective was to investigate the effect of maize crop residue incorporation on the long-term dynamics of soil organic carbon (SOC) for a selection of croplands with sandy to sandy loam texture in Flanders, Belgium. After a period of more than 20 years, we resampled 31 and 29 parcels that had either silage maize (MS, only belowground biomass input) or grain maize (MG, both above- and belowground biomass input) dominated crop rotations. Changes in maize-derived SOC (Cmaize) of MS and MG systems between 1993 and 2018 were evaluated by detecting SOC content and its δ13C value. In addition, a 140-day incubation experiment (at 20.5 °C) was carried out to compare the stability of Cmaize and the related nitrogen (N) mineralization between the MG and MS fields. After two decades, δ13C raised 2.4 and 2.6‰, while Cmaize increased 1.6 and 2.2 g kg−1 in MS and MG systems, respectively. The estimated average humification coefficient over this period of maize-C was 0.11 for the MS system, about twice as that of the MG system (0.06). This reconfirms findings of stronger contribution of belowground biomass versus aboveground residues to stabilized SOC pools over the medium to long term. By the end of the incubation, on average 10.4% and 11.6% of Cmaize had been decomposed in the MS and MG soils, respectively. These Cmaize mineralization rates were statistically equal for the two systems, which indicates that mainly belowground biomass remained in the soils. Also, net N mineralization was indifferent to the crop rotations (MS: 58.8 mg N kg−1 and MG: 52.6 mg N kg−1). To reconcile the two main observations in this study, we hypothesize that the lower preservation of shoot-C could be manifested on a shorter term. Detailed research is needed to determine the time scale of increased stabilization of root-C versus shoot-C under field conditions.

Preservation of organic carbon promoted by iron redox transformation in a rice-wheat cropping system

Mineral protection regulates long-term global preservation of soil organic carbon (SOC), but little research has been conducted on the iron (Fe) oxide availability for carbon binding regulated by seasonal variation of wetting and drying and fertilization in paddy soils. The objective of this study was to explore the effects of five-year rice-wheat rotation and organic fertilization on the production of short-range-ordered (SRO) Fe oxides and SOC sequestration. Five fertilization treatments were examined: (1) no fertilizer control (CK), (2) chemical nitrogen, phosphorus and potassium (NPK), (3) 50% NPK plus manure (NPKM), (4) 100% NPK plus straw (NPKS), and (5) 30% NPK plus manure organic-inorganic compound fertilizer (NPKMOI). Soil samples were collected from 2013 to 2015 after each wheat and rice harvest. A split-plot analysis of variation was used to investigate the respective role of fertilizer treatments (main-plot) and crop seasons (sub-plot) in the transformation of SRO-Fe oxides. Variation partitioning analysis was used to quantify the contribution of SRO-Fe oxides to the accumulation of SOC. Five-year rice-wheat rotation without any fertilization (CK) increased the oxalate extractable Fe oxides (Feo) by 55.06% compared with the initial soil. The Feo concentration was higher (P < 0.05) in the NPKM, NPKS and NPKMOI treatments than in the NPK and CK treatments, and was higher after the rice harvest than after the wheat harvest. Furthermore, the Feo concentration was positively (P < 0.001) correlated with the SOC content and negatively correlated with the specific carbon mineralization rate (SCMR, rate per unit SOC). Moreover, the Feo could explain 52.57% and 40.5% of the variation in the SOC content and the SCMR, respectively. In addition, the partial humification coefficient (PHC, the percentage of SOC change per unit of exogenous carbon input) of the crop straw was 12.92% but amounted to 41.45% to 46.35% for different types of compost. These results indicate that the reductive dissolution and subsequent oxidative precipitation of Fe oxides induced by seasonal alternation of wetting and drying can be further promoted via organic fertilization possibly by forming organo-Fe complexes, which contribute to the accumulation of SRO-Fe oxides and the preservation of organic carbon in paddy soils.

Increased microbial anabolism contributes to soil carbon sequestration by mineral fertilization in temperate grasslands

Ecosystem responses to nitrogen (N) additions are manifold and complex, and also affect the carbon (C) cycle. It has been suggested that increased microbial carbon use efficiency (CUE), i.e. growth per C uptake, due to higher N availability potentially increases the stabilization rates of organic inputs to the soil. However, evidence for a direct link between altered microbial anabolism and soil organic C (SOC) stocks is lacking. In this study, unfertilized (control) and NPK-fertilized (NPK) treatments of seven temperate grassland experiments were used to test the hypothesis that fertilizer-induced differences in SOC stocks (ΔSOC) cannot be explained by differences in C input alone, but that microbial anabolism plays an important role in C sequestration. At two experimental sites, microbial CUE and related metabolic parameters was determined using an 18O labeling approach at two different incubation temperatures (10 °C and 20 °C). Fertilization effects on the abundance of Bacteria, Archaea and Fungi were also determined using quantitative PCR targeting the respective rRNA genes. Due to the availability of yield and belowground biomass data, the introductory carbon balance model (ICBM) could be used for all seven sites to estimate the contribution of C input to ΔSOC. A significantly higher microbial growth (+102 ± 6%), lower specific respiration (−16 ± 7%) and thus significantly higher CUE (+53 ± 21%) was found for the NPK treatments, which was consistent across experiments and incubation temperatures and correlated with measured root C:N ratios. Growth (+49 ± 5%) and respiration (+70 ± 9%) were increased by a higher incubation temperature, but this was not the case for CUE. The fungi to bacteria ratio changed significantly from 0.18 ± 0.02 (control) to 0.09 ± 0.02 (NPK). On average, only 77% (51% when excluding one extreme site) of observed ΔSOC was explained by C inputs. The optimized humification coefficient h of the model used to fit the observed ΔSOC was strongly correlated to differences in the root C:N ratio between the control and NPK treatments (R2 = 0.71), thus confirming a link between microbial anabolism and substrate C:N ratio. Furthermore, varying h directly by observed differences in CUE improved the model fit at the two sites investigated. This study provides direct evidence that CUE of soil microbial communities is relevant for SOC sequestration, and its dependency on soil N availability or substrate C:N ratio might allow for its inclusion in models without explicit microbial C pools.

BIOPREPARATIONS FOR DECOMPOSITION OF PLANT RESIDUES IN AGROECOSYSTEMS

The article reviews the main results of scientific research in the country and abroad on the evaluation of microbiological preparations-destructors of post-harvest plant residues in agroecjsistems. It is shown that plant remains are the most important resource for reproduction of arable soils fertility. The most environmentally feasible and cost-effective way to recycle them is to enclose in the soil as a fertilizer, providing a return to the agrobiological circulation of nutrients and organic matter. One way to accelerate the decomposition and increase of the humification coefficient of post-harvest residues, which has become widespread in recent years in the practice of the agro-industrial complex, can be inoculation with microbiological destructive preparations before being embedded in the soil. The data of many authors confirm that the use of biopreparations promotes the acceleration of decomposition of high-carbon plant residues and a decrease in their negative effect, an increase in soil biogenicity, and an increase in the yield of subsequent crops. The most active biopreparations "work" in the initial terms of decomposition, in conditions of humidity and temperature optimal for the microbiota. The effectiveness of biopreparations increases in combination with compensating doses of nitrogen. Along with positive results, in scientific publications there are data on the lack of influence of biological products on the rate of straw decomposition. It is concluded that biologics-destructors can be used in agricultural practice to treat stubble and straw before it is application in the soil in order to accelerate the decomposition, increase the yield of subsequent crops. For a better understanding of mechanisms action of biologics, preparation of recommendations for their practical use, further experimental studies are needed in field and laboratory conditions.

Assessment of environmental stability of agroserous soil according to indicator of energy potential of organic substances

Studies of the group and fractional composition of humus have determineded that the long-term use of soil (for 20 years) without the use of fertilizers (control) leads to a decrease in the content of humic acids and fulvic acids relative to the initial soil, which indicates an increase in mineralization of the soil humus. Under the influence of a long application of high doses of mineral fertilizers, the content of mobile fractions of humic and fulvic acids in the field rotation increases in the humus content. In systems of agriculture that are not balanced by organic matter, which are predominant in most farms of the Republic of Tatarstan, the use of very high doses of potassium fertilizers is not justified energetically. To compensate for losses of humus and its energy potential in calculating organic fertilizers on backgrounds with high doses of mineral fertilizers, the humification coefficients of organic residues should be increased by 30-40% during the rotational period of 5-6 years, which will reduce the loss of energy reserves and thereby improve the ecological stability of soils and the stability of agricultural landscapes

A historical perspective on soil organic carbon in Mediterranean cropland (Spain, 1900–2008)

Soil organic carbon (SOC) management is key for soil fertility and for mitigation and adaptation to climate change, particularly in desertification-prone areas such as Mediterranean croplands. Industrialization and global change processes affect SOC dynamics in multiple, often opposing, ways. Here we present a detailed SOC balance in Spanish cropland from 1900 to 2008, as a model of a Mediterranean, industrialized agriculture. Net Primary Productivity (NPP) and soil C inputs were estimated based on yield and management data. Changes in SOC stocks were modeled using HSOC, a simple model with one inert and two active C pools, which combines RothC model parameters with humification coefficients. Crop yields increased by 227% during the studied period, but total C exported from the agroecosystem only increased by 73%, total NPP by 30%, and soil C inputs by 20%. There was a continued decline in SOC during the 20th century, and cropland SOC levels in 2008 were 17% below their 1933 peak. SOC trends were driven by historical changes in land uses, management practices and climate. Cropland expansion was the main driver of SOC loss until mid-20th century, followed by the decline in soil C inputs during the fast agricultural industrialization starting in the 1950s, which reduced harvest indices and weed biomass production, particularly in woody cropping systems. C inputs started recovering in the 1980s, mainly through increasing crop residue return. The upward trend in SOC mineralization rates was an increasingly important driver of SOC losses, triggered by irrigation expansion, soil cover loss and climate change-driven temperature rise.

Effects of straw incorporated to different locations in soil profile on straw humification coefficient and maize yield.

Tillage and straw incorporation are important agricultural practices that can break plough layer and improve black soil fertility. The effects of tillage and straw incorporation on straw humification coefficient, soil organic carbon (SOC), and maize yield were investigated in a field experiment. Subsoil combined with straw incorporation in 20-35 cm soil layer (ST+S) could break plough layer and decrease the bulk density by 5.7%, 3.3% and 5.7% compared with traditional til-lage (TT), subsoil (ST) and traditional tillage combined with straw incorporation (TT+S) in six experimental years, respectively, and the best effects were observed in ST and ST+S treatments in the first expe-rimental year. The rate of straw decomposition was higher in 0-20 cm (72.0%) than in 20-35 cm (59.2%), and the straw humification coefficient in 0-20 cm and 20-35 cm soil la-yers reached the peak in first experimental year with 15.9% and 12.7%, respectively. Compared with initial soil sample, SOC and light fraction organic carbon (LFOC) of TT, ST and ST+S treatments in 0-20 cm soil layer was decreased in experimental years, but was increased by 2.9% and 12.4% within TT+S, respectively. SOC and light fraction organic carbon (LFOC) of ST+S in 20-35 cm soil layer was increased by 9.2% and 9.9%, respectively. The effect of field treatments on maize yield showed in a decreasing trend of ST+S>TT+S>ST>TT, effects of tillage and straw incorporation on maize yield could continue 3 and 6 years, respectively, indicating that tillage and straw incorporation had time effect. Therefore, straw incorporated into 20-35 cm soil layer based on tillage was an effective, sustainable agricultural practice of improving black soil quality.

A Model–Data Fusion Approach for Predicting Cover Crop Nitrogen Supply to Corn

One potential benefit of cover crops (CCs) is that N mineralization from decomposing CC residues may reduce the N fertilizer requirement of a subsequent crop, but predicting this credit remains a significant challenge. This study used a model–data fusion approach to calibrate a model of CC residue N mineralization and pre‐emptive competition for soil NO3− that occurs during CC growth to predict the yield response of an unfertilized corn (Zea mays L.) crop. The model was calibrated with a data set of 199 observations from four CC experiments in central Pennsylvania. The most parsimonious model explained 82% of the variation in corn yield response. Parameters representing the C humification coefficients for decomposed residues from winterkilled (εwk = 0.00) and winter‐hardy (εwh = 0.40) CCs suggest that all winterkilled CCs resulted in net N mineralization, probably due to the longer period of time for decomposition of winterkilled residues. However, the yield response per unit of potentially mineralized N was greater for winter‐hardy CCs (αwh = 0.034 with tillage, αwh = 0.020 with no‐till) than for winterkilled CCs (αwk = 0.0084), probably due to the improved synchrony between corn N demand and the decomposition of winter‐hardy CC residues relative to winterkilled residues. Pre‐emptive competition for soil NO3− led to a reduction in the corn yield response. Because the model is based on ecological processes and can be calibrated with data sets from simple field experiments, the model–data fusion approach could be widely used to guide adaptive management of CCs and N fertilizer applications in a subsequent corn crop.Core Ideas A simple model predicts how cover crops affect N availability to the next corn crop. The model highlights the ecological controls on N supply from cover crops. Site‐specific cover crop measurements can guide adaptive N management using the model. Regional model calibration could be achieved with easily collected data.

Changes in organic part of the soil and acid-base balance depending on green manure fertilization in podzolized chernozem

Aim. To study the changes in the content and stock of organic substances as well as the reaction of the soil en- vironment depending on the impact of different types of fertilization of green-manured fallows. Methods. Field studies were conducted on podzolized heavy loamy chernozem, on loess, in conditions of Right-Bank Forest- Steppe of Ukraine. Experimental design included: sweet clover with the seeding rate of 20 kg/ha, white mustard – 20, oilseed radish – 20, spring vetch – 150, and buckwheat – 150 kg/ha with the following fertilization variants: no fertilizers – control; N 40 ; P 40 K 40 ; N 40 K 40 ; N 40 P 40 ; N 40 P 40 K 40 ; N 80 P 40 K 40 . The content of total carbon and nitrogen were defi ned using Anstett’s method, modifi ed by Ponomariova and Nikolaeva; the content of total humus in the soil prior to sowing winter wheat (the impact of green manure for a year) – according to DSTU 4289:2004, pH of the water extract – according to DSTU ISO 10390:2007. Results. Nitrogen-carbon ratio was in the range from 11.1 to 11.8 in the biomass of leguminous crops and from 18.8 to 20.7 – in root remains, and its highest value was observed in root remains of Brassicaceae crops – from 28.8 to 34.5 depending on doses and types of mineral fertilizers. Compared to bare fallow, green manure fertilization promotes humus preservation in the soil. The de- crease in the level of humus intension of the soil by 0.01–0.04 % was registered both in the surface and subsurface layers in conditions of bare fallow compared to green-manured fallow. 1.67 t/ha of humus is mineralized in the soil of bare fallow. The transformation of green manure biomass allows accumulating 1.15–2.05 t/ha of humus depending on doses and types of mineral fertilizers. When the Cruciferae family (white mustard and oilseed rad- ish) are used as green manure, the isohumus index is 1.52–1.55, 1.67–1.69 – for the Leguminosae (annual sweet clover and spring vetch), and 1.52–1.60 – for buckwheat, depending on fertilization. The humifi cation coeffi cient for vegetative biomass of oilseed radish is 0.023, for spring vetch – 0.027, for buckwheat – 0.033, for white mustard – 0.035, and for annual sweet clover – 0.036. The administration of different doses and types of mineral fertilizers conditions the decrease in the coeffi cient of green manure fertilization. Conclusions. The application of green manure both with and without fertilizers compared to bare fallow promotes the preservation of humus content in the soil. The transfer of calcium from lower layers to the arable soil layer, performed by the plant root system in green-manured fallow, decreases active acidity of the soil.

Organic input quality is more important than its quantity: C turnover coefficients in different cropping systems

Abstract Annual C input to soil is a major factor affecting soil organic carbon (SOC) dynamics. However different types of C-sources can have different behaviour, in relation to their chemical characteristics and how they interact with soil. Root-derived C, in particular, should be more efficient than other organic materials as a result of the physicochemical and biological characteristics of the surrounding environment, leading to a reduction in the C decomposition rate. To test this hypothesis, we considered a long-term experiment underway in Northern Italy since 1962, comparing permanent meadow and 6 different crop rotations over a wide range of nutrient inputs, in both organic and inorganic forms. C inputs from amendments were measured and those from crops were calculated using allometric functions and crop and residues yields. The time evolution of SOC was studied through a single-pool, first-order kinetic model, allowing the estimation of humification coefficients for residues, roots, farmyard manure and cattle slurries. The highest value of the humification coefficient was estimated for farmyard manure, which confirmed its high efficiency in stabilising SOC content. Root C presented a humification coefficient 1.9 times higher than above-ground plant materials while slurries were intermediate, with a humification coefficient roughly half that of farmyard manure and even lower that of roots. The quality of C input thus seems of fundamental importance for evaluating the sustainability of different cropping systems in terms of SOC dynamics.

Effect of perennial ryegrass cover crop on soil organic carbon stocks in southern Sweden

Soil organic carbon (SOC) is an important ecosystem property and a potential sink for atmospheric CO2. Many agricultural soils are depleted in SOC and thus have the need and potential to sequester carbon. Cover crops used to prevent nitrate leaching in agroecosystems might be an additional cost-effective and multi-beneficial carbon input, but little is known about their effect on SOC stocks. This study examined the effect of an ryegrass cover crop on SOC stocks in three Swedish long-term experiments (16–24years) and compared it with that at a North American site (Sultan, Washington). Growth was temperature- and light-limited in Sweden and thus the ryegrass was undersown, while it was sown after harvest of the main crop at the Sultan site. In total, seven pairs of cover crop/no cover crop treatments were investigated. The introductory carbon balance model (ICBM) was used to calculate humification coefficients for ryegrass at each site as a measure of carbon sequestration efficiency. Mean aboveground biomass of ryegrass ranged from 550–1050kgDMha−1yr−1 in the Swedish experiments and was 4650kgDMha−1yr−1 at the Sultan site. Yield of the main crop was not significantly affected by the cover crop. Cover crop incorporation increased SOC stocks, with a significant mean carbon sequestration rate (0.32±0.28MgCha−1yr−1) at the Sultan site and all Swedish sites except one. Mean humification coefficient of the ryegrass cover crop was 0.33±0.27, which is comparable to that of highly efficient organic amendments such as farmyard manure and sewage sludge. This was attributed to high belowground productivity of ryegrass, although that was the most uncertain model input variable. A ryegrass cover crop is thus an effective, multi-beneficial measure to increase SOC stocks, even when undersown at northerly latitudes (55–58°N).