Management of Nitrogen Flow in Livestock Waste System Towards an Efficient Circular Economy in Agriculture.

The race is on to achieve high level of efficiency in the attainment of circular economy in Agriculture especially with the aim of sustainable nitrogen management. This cycle in the agricultural sector cuts across livestock farming, agriculture induced waste generation, recycling and utilization, energy generation, crop production, ecosystem protection and environmental management through the mitigation of climate changes. In this work, we access the process and functionalities of livestock waste generated from the piggery farm and the combinations with other by-products such as biochar and ash in comparison with mineral fertilisation (MN) as sources of nitrogen (N) applied in agricultural soil. The experiment was performed in a controlled environment with wheat (Triticum aestivum L.) grown in a neutral and an acidic soil. Pig manure was used as the primary feedstock, fed, and processed to biogas and nutrient rich digestate by anaerobic digestion process. The digestate generated were amended with biochar and ash. In the course of the cultivation period, pig manure digestate with other co-amendments showed a positive influence on mobile potassium and phosphorus contents, biomass yield and nitrogen use efficiency. Greenhouse gas (GHG) emissions in the form of methane, carbon dioxide and nitrous oxide released in both soil types from the amendments were significantly lower when compared to mineral nitrogen treatment. The amendments did not have any significant influence on dehydrogenase activity, especially in the acid soil with the pH negatively influencing the enzymatic activities. The pig manure and pig manure digestate treatments showed positive response in the soil microbial biomass-C in the two soil types when compared to other co-amendments. Application of single use amendment application or in combination with biochar and ash as a means of waste management can enhance the N flow to meet up with crop needs, reduce GHG emissions and reduce potential agriculture’s negative environmental footprint.

Organic Amendments and Elemental Sulfur Stimulate Microbial Biomass and Sulfur Oxidation in Alkaline Subtropical Soils

Sulfur deficiency arising due to intensive cultivation, use of sulfur free fertilizers and reduction in atmospheric sulfur depositions has become a major issue limiting crop production in many parts of the world. Elemental sulfur could be a good source of available S, but its slow oxidation is a problem for its efficient use as a sulfur fertilizer. Main objective of the study was to assess the effect of organic amendments (OA) and elemental sulfur (ES) on microbial activities, sulfur oxidation and availability in soil. A laboratory incubation experiment was carried out for a 56 days period using two sulfur deficient alkaline soils. Organic amendments (OA), i.e., farmyard manure (FYM), poultry litter (PL) and sugarcane filter cake (SF), were applied (1% w/w) with or without elemental sulfur (ES) at 50 mg kg−1. Application of ES alone or in combination with OA significantly increasedCO2-C evolution, microbial biomass, and enzyme activities in the soils, except dehydrogenase activity (DHA) which was not affected by ES application. Combined application of OA and ES had a more pronounced effect on microbial parameters compared to ES or OA applied alone. Ratios of dehydrogenase activity-to-microbial biomass C and arylsulfatase activity-to-microbial biomass C were high in ES+FYM and ES+SF treatments, respectively. Elemental sulfur got sufficiently oxidized resulting in significant improvement in plant available S. Relatively more ES was distributed into C-bonded-S than ester bonded-S. Increase in sulfur availability in ES+OA amended soils was the combined function of sulfur oxidation and mineralization processes through improved microbial activity.

Kinetic Properties of Microbial Exoenzymes Vary With Soil Depth but Have Similar Temperature Sensitivities Through the Soil Profile

Current knowledge of the mechanisms driving soil organic matter (SOM) turnover and responses to warming is mainly limited to surface soils, although over 50% of global soil carbon is contained in subsoils. Deep soils have different physicochemical properties, nutrient inputs, and microbiomes, which may harbor distinct functional traits and lead to different SOM dynamics and temperature responses. We hypothesized that kinetic and thermal properties of soil exoenzymes, which mediate SOM depolymerization, vary with soil depth, reflecting microbial adaptation to distinct substrate and temperature regimes. We determined the Michaelis-Menten (MM) kinetics of three ubiquitous enzymes involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition at six soil depths down to 90 cm at a temperate forest, and their temperature sensitivity based on Arrhenius/Q10 and Macromolecular Rate Theory (MMRT) models over six temperatures between 4–50°C. Maximal enzyme velocity (Vmax) decreased strongly with depth for all enzymes, both on a dry soil mass and a microbial biomass C basis, whereas their affinities increased, indicating adaptation to lower substrate availability. Surprisingly, microbial biomass-specific catalytic efficiencies also decreased with depth, except for the P-acquiring enzyme, indicating distinct nutrient demands at depth relative to microbial abundance. These results suggested that deep soil microbiomes encode enzymes with intrinsically lower turnover and/or produce less enzymes per cell, reflecting distinct life strategies. The relative kinetics between different enzymes also varied with depth, suggesting an increase in relative P demand with depth, or that phosphatases may be involved in C acquisition. Vmax and catalytic efficiency increased consistently with temperature for all enzymes, leading to overall higher SOM-decomposition potential, but enzyme temperature sensitivity was similar at all depths and between enzymes, based on both Arrhenius/Q10 and MMRT models. In a few cases, however, temperature affected differently the kinetic properties of distinct enzymes at discrete depths, suggesting that it may alter the relative depolymerization of different compounds. We show that soil exoenzyme kinetics may reflect intrinsic traits of microbiomes adapted to distinct soil depths, although their temperature sensitivity is remarkably uniform. These results improve our understanding of critical mechanisms underlying SOM dynamics and responses to changing temperatures through the soil profile.

Response of Soil Microbial Community Structure and Function to Different Altitudes in Arid Valley in Panzhihua, China

Background: Altitude affects biodiversity and physic-chemical properties of soil, providing natural sites for studying species distribution and the response of biota to environmental changes. We sampled soil at three altitudes in an arid valley, determined the physic-chemical characteristics and microbial community composition in the soils, identified differentially abundant taxa and the relationships between community composition and environmental factors. Results: The low, medium and high altitudes were roughly separated based on the physic-chemical characteristics and clearly separated based on the microbial community composition. The differences in community composition were associated with differences in all measured factors except pH. The contents of organic and microbial biomass C, total and available N and available P, and the richness and diversity of the microbial communities were lowest in the medium altitude. The relative abundances of phyla Proteobacteria, Gemmatimonadetes, Actinobacteria and Acidobacteria were high at all altitudes. The differentially abundant ASVs were mostly assigned to Proteobacteria and Acidobacteria. The highest number of ASVs characterizing altitude were detected in the high altitude. However, the predicted functions of the communities were overlapping, suggesting that the contribution of the communities to soil processes changed relatively little along the altitude gradient. Conclusions: The composition of microbial community at different altitudes was related to the differences of all measuring factors except pH in arid valley in Panzhihua, China.

Long Term Resource Conservation Technologies Sustained Yield, Microbial Activities and Soil Physico-chemical Properties in Rice-green Gram Cropping System

PurposeMicrobial communities in rhizospheric soil play a significant role in sustaining the soil quality and also recognized as key ecological indicators to assess the soil health. MethodsWe studied the long-term effects of resource conservation technologies on functional microbial diversity and their interactions with soil biochemical properties and enzymatic activities in tropical rice-green gram cropping system. The experiment included conventional practice (CC), brown manuring (BM), green manuring (GM), wet direct drum sowing (WDS), zero tillage (ZT), green manuring-customized leaf colour chart based-N application (GM-CLCC N) and biochar (BC) treatments. ResultsThe result revealed that microbial biomass nitrogen (N), carbon (C) and phosphorus (P) in GM practice increased by 23.3, 37.7 and 35.1%, respectively over CC. The Shannon index and McIntosh index were higher by 86.9% and 29.2% in GM as compared to conventional practice and significantly correlated with microbial biomass (C & P) and soil microbial populations whereas, Shannon index was positively correlated with the microbial biomass (C, N & P) and soil enzyme activities. Principal component analysis showed a significant separate cluster among the treatments amended with and without biomass addition. ConclusionsMoreover, dominance of carbon utilizing microbes in biomass amended treatments indicated that these could supply good amount of labile carbon sources on real time basis for microbial activity. Which may protect the stable carbon fraction in soil, hence could support higher build-up of carbon in long run and could offer sustainable yield under rice-green gram soil.

Strong Interactive Effects of Warming and Insect Herbivory on Soil Carbon and Nitrogen Dynamics at Subarctic Tree Line

Warming will likely stimulate Arctic primary production, but also soil C and N mineralization, and it remains uncertain whether the Arctic will become a sink or a source for CO2. Increasing insect herbivory may also dampen the positive response of plant production and soil C input to warming. We conducted an open-air warming experiment with Subarctic field layer vegetation in North Finland to explore the effects of warming (+3°C) and reduced insect herbivory (67% reduction in leaf damage using an insecticide) on soil C and N dynamics. We found that plant root growth, soil C and N concentrations, microbial biomass C, microbial activity, and soil NH4+ availability were increased by both warming and reduced herbivory when applied alone, but not when combined. Soil NO3– availability increased by warming only and in-situ soil respiration by reduced herbivory only. Our results suggest that increasing C input from vegetation under climate warming increases soil C concentration, but also stimulates soil C turnover. On the other hand, it appears that insect herbivores can significantly reduce plant growth. If their abundance increases with warming as predicted, they may curtail the positive effect of warming on soil C concentration. Moreover, our results suggest that temperature and herbivory effects on root growth and soil variables interact strongly, which probably arises from a combination of N demand increasing under lower herbivory and soil mineral N supply increasing under higher temperature. This may further complicate the effects of rising temperatures on Subarctic soil C dynamics.

Short-Term Effect of Nitrogen Fertilization on Carbon Mineralization during Corn Residue Decomposition in Soil

The effect of N fertilization on residue decomposition has been studied extensively; however, contrasting results reflect differences in residue quality, the form of N applied, and the type of soil studied. A 60 d laboratory incubation experiment was conducted to ascertain the effect of synthetic N addition on the decomposition of two corn (Zea mays L.) stover mixtures differing in C:N ratio by continuous monitoring of CO2 emissions and periodic measurement of microbial biomass and enzyme activities involved in C and N cycling. Cumulative CO2 production was greater for the high than low N residue treatment, and was significantly increased by the addition of exogenous N. The latter effect was prominent during the first month of incubation, whereas N-treated soils produced less CO2 in the second month, as would be expected due to more rapid substrate depletion from microbial C utilization previously enhanced by greater N availability. The stimulatory effect of exogenous N was verified with respect to active biomass, microbial biomass C and N, and cellulase and protease activities, all of which were significantly correlated with cumulative CO2 production. Intensive N fertilization in modern corn production increases the input of residues but is not conducive to soil C sequestration.

Soil microbial respiration, biomass carbon and community composition data induced by substrate quality from an agricultural grassland

The data presented here are related to the research article entitled ‘Effects ofsubstrate quality on carbon partitioning and microbial community composition in soil from an agricultural grassland’ [1]. Data illustrate cumulative CO2 efflux, microbial biomass C (Cmic), priming effect expressed as priming index (PI) and total phospholipid fatty acid (PLFA) profiles. The data were measured during four soil laboratory incubations using a silty clay loam soil under permanent grassland from May until August 2015. The soil was treated with carbohydrates of different complexity (glucose, glucose-6-phosphate (G6P) or cellulose) alone or in conjunction with livestock slurry amended or non-amended with a biological additive. Our data may be of great significance for further studies on microbial respiration and biosynthesis, and microbial community structure following slurry application to soil, alongside the potential beneficial effects of the addition of slurry amended with biological additives.

Application of Livestock Slurry Significantly Influences Microbial Biosynthesis and Cumulative Respiration in Agricultural Grassland Soil

The long-term application of livestock slurry to intensive grassland soils may lead to positive effects, including an increase in soil organic matter and plant nutrient supply to soils. Further, there is increasing interest in the potential of biological slurry additives (mixtures of selected living or latent microorganisms added to slurry) to enhance soil fertility through mobilisation of key elements in slurry and soil. However, significant uncertainties remain surrounding the potential impacts of slurry amended with biological additives on carbon (C) partitioning within three pools: respired CO2, microbial biomass C (Cmic) and C retained in the soil, as well as composition of the microbial community in temperate grassland soils. We examined how slurry that has received a biological additive ultimately affects the partitioning of C within these pools and the composition of the soil microbial community, based on phospholipid fatty acid (PLFA) analysis. Four short-term incubations in which soil collected from a grassland field that has received livestock slurry treated with a commercial biological additive, alongside 14C-labelled carbohydrates of different complexity (14C-glucose, 14C-glucose 6-phosphate (G6P), and 14C-cellulose) were undertaken. Our results indicate that the addition of slurry to soil alongside carbohydrate compounds led to lower 14C biomass uptake and cumulative respiration of carbohydrate compounds, as well as greater residual 14C activities in soil, compared to the treatments in which slurry was not applied. A dominance of bacteria over fungi characterised soil microbial community composition in all treatments through time, with a prevalence of gram-negative over gram-positive bacteria. Our results also indicate that the addition of biological additives during slurry storage increased 14C biomass uptake following application of slurry to agricultural grasslands. Therefore, biological additives have the potential to create a favourable environment for maintaining and increasing soil fertility through modification of the microbial community associated with the slurry and influence of the soil microflora.

Changes in Soil Labile Organic Matter as Affected by 50 Years of Fertilization with Increasing Amounts of Nitrogen

Microbially mediated soil organic matter is an extremely sensitive pool that indicates subtle changes in the quality parameters responsible for the soil’s ecological and productive functions. Fifty years of mineral fertilization of a wheat-corn cropping system has a strong impact on soil quality parameters. The goal of the research was to study the dynamics and quality of soil biological parameters affected by increasing amounts of mineral nitrogen. Soil respiration, potentially mineralizable C and N, microbial biomass C and N and light-fraction OM on Cambisol were analyzed in the following treatments: (1) Control (without fertilization); (2) NPK (60/51/67); (3) NPK (90/51/67); (4) NPK (120/51/67); (5) NPK (150/51/67 kg ha−1). The parameters studied were significantly affected by the long-term application of mineral fertilizer compared with both the control and the adjacent native soil. The highest amounts of nitrogen (N150) did not significantly differ from N120 and N90 for most of the parameters studied. Potentially mineralizable C represented the largest labile carbon pool, while microbial biomass N was the largest labile nitrogen pool. The mineralization rates for C and N were oppositely distributed over the seasons. The sensitivity index correlated with the amount of light-fraction OM. The results give a deeper insight into the behavior and distribution of different pools of labile SOM in the agro-landscapes and can serve as a reliable basis for further research focused on zero soil degradation.