Addition Of Organic Amendments Research Articles

Ecological intensification strategies increase abundance of denitrifying functional genes in a greenhouse agricultural soil

Understanding the denitrification process in agriculture is key to preventing nitrogen (N) losses and reducing emissions of the greenhouse gas nitrous oxide (N2O) to the atmosphere. Since the type of fertilization influences this process, in this study we evaluated the comparative effect of conventional (CON) versus ecological intensification (EI) soil management under greenhouse conditions on the abundance and expression of the denitrifying functional genes nitrite reductase (nirK, nirS) and nitrous oxide reductase (nosZ). For this purpose, quantitative PCR (qPCR) was performed in three phenological stages of eggplant (Solanum melongena L var. Telma). The results showed that the addition of organic amendments tripled the copies of nirK DNA, doubled the copies of nosZ DNA and increased the copies of nirS, albeit by 2 %, compared to conventionally managed soils. The abundance of mRNA transcripts also increased for all three genes studied: nirK increased 15-fold, followed by nirS, which tripled its expression, and nosZ, which doubled its expression. Ammonium ion (NH4-N) correlated positively with the three genes analyzed, total organic carbon (TOC) with nirK and nosZ, and pH correlated negatively with nirK and nosZ. Regardless of the type of fertilization (CON or EI), a decreasing trend in gene abundance was observed from the initial growth phase of the crop (t0) until the crop was removed and crop residues incorporated into the soil (t2). The results suggest that the dynamics and composition of the denitrifying community varied in response to the type of fertilization and the phenological stage of the crop. Further studies based on metagenomics and transcriptomics, including N2O flux measurements, are needed to better understand the denitrification process in these soils.

Sulfur dynamics in saline sodic soils: The role of paddy cultivation and organic amendments

The phenomenon of sulfur (S) deficiency in Chinese soil is becoming increasingly severe, especially in the northeastern saline-sodic wasteland (WL). To determine the bioavailability of S in long-term cultivated paddy soil with or without organic amendment addition, the long-term field experiment site was established and incubation experiments were conducted. Compared to WL, soil properties have been continuously improved during the 15-year paddy field (PF) cultivation, ultimately enhancing the content of soil organic carbon (by 242.62 %), total nitrogen (by 126.49 %) and alkali-hydrolyzed nitrogen (by 28.07 %). Additionally, soil salinization has been decreasing, and the stock of total sulfur (TS) and available sulfur (AS) in the 0–60 cm soil layer have increased by 32.09 % and 293.52 % respectively. In contrast, organically-amended soil (OA) manifested superior TS and AS levels vs. PF. Additionally, water-soluble sulfur (WSS) was markedly elevated, registering post-annual increments of 227.31 % and 268.36 % in PF and OA, respectively, relative to WL. The key mechanistic impetus for the application of organic amendments was the enhancement of the soil's adsorptive and mineralization capabilities. As observed in our soil culture experiment, the maximum adsorption of sulfate ions and the cumulative mineralization of sulfur in the soil follow the pattern of OA > PF > WL. The Partial Least Squares Path Model (PLSPM) corroborated that both organic amendments and years of cultivation indirectly influenced total inorganic sulfur fractions. This influence is primarily mediated via structural soil enhancements and salinization amelioration, thereby elevating available quantities of sulfur in saline-sodic soil environments. In conclusion, from the perspective of soil sulfur biogeochemical cycling, we have confirmed that reclaiming saline-sodic wasteland for paddy field could be a beneficial and sustainable approach for soil management. These findings of this study can also provide an in-depth understanding of the bioavailability and influencing mechanism of sulfur in long-term saline-sodic paddy fields.

Rhizoctonia solani disease suppression: addition of keratin-rich soil amendment leads to functional shifts in soil microbial communities.

Promoting soil suppressiveness against soil borne pathogens could be a promising strategy to manage crop diseases. One way to increase the suppression potential in agricultural soils is via the addition of organic amendments. This microbe-mediated phenomenon, although not fully understood, prompted our study to explore the microbial taxa and functional properties associated with Rhizoctonia solani disease suppression in sugar beet seedlings after amending soil with a keratin-rich waste stream. Soil samples were analyzed using shotgun metagenomics sequencing. Results showed that both amended soils were enriched in bacterial families found in disease suppressive soils before, indicating that the amendment of keratin-rich material can support the transformation into a suppressive soil. On a functional level, genes encoding keratinolytic enzymes were found to be abundant in the keratin-amended samples. Proteins enriched in amended soils were those potentially involved in the production of secondary metabolites/antibiotics, motility, keratin-degradation, and contractile secretion system proteins. We hypothesize these taxa contribute to the amendment-induced suppression effect due to their genomic potential to produce antibiotics, secrete effectors via the contractile secretion system, and degrade oxalate-a potential virulence factor of R. solani-while simultaneously possessing the ability to metabolize keratin.

Impact of organic amendments addition to sandy clay loam soil and sandy loam soil on leaching process of chlorantraniliprole insecticide and bispyribac-sodium herbicide

The leaching of two pesticides, cholantraniliprole (CAP) and bispyribac-sodium (BPS) in sandy clay loam soil (soil A) and sandy loam soil (soil B) were examined, by soil columns under laboratory conditions. In addition, the effect of adding 5% biochar and wheat straw to the soils on the leaching of CAP and BPS was studied. It is clear from the results that BPS is more leachable than CAP in all soil columns, and more leached to soil B. It was found that the addition of biochar and wheat straw has a significant effect on the movements of these pesticides and can be used to reduce the environmental impact. For CAP, 71 to 97% and 84 to 97% were recovered from the soil A columns and soil B columns, respectively, while for BPS, 94 to 99% were recovered from columns of soil A and soil B.

Interaction of fulvic acid with soil organo-mineral nano-aggregates and corresponding phosphate release

For more insight into the interaction of natural organic matter (NOM) with metal (hydr)oxides and oxyanions, the adsorption of added fulvic acid (FA) and the corresponding release of phosphate (PO4) were studied for a series of agricultural soils (∼0 – 25 cm), strongly varying in soil properties. Interpretation of the data with surface complexation modeling using the NOM-CD model applied in a dual-phase mode shows that the adsorption of added FA, in contrast to PO4, is restricted to the external surfaces of nano-aggregates. The adsorption is relatively weak and pH-independent, due to its competition with the native NOM of the organo-mineral phase. At low pH, the functional groups of both added FA and native NOM shift in the interface towards the soil oxide surfaces, making both a good competitor for adsorbed phosphate, resulting in a higher amount of phosphate being released. With an increase in pH, the competition becomes weaker. As a result, more phosphate is bound and less is released when FA is added. Our surface complexation modeling points to the existence of organo-mineral nano-aggregates with sizes of >∼10 – 270 nm, which depends on the total reactive surface area of the soil. Our findings imply that organic amendments containing FA equilibrate with only a portion of the total reactive surface area. In acidic soils, the addition of such organic amendments will be more effective in solubilizing phosphate, which is beneficial from a plant nutrition perspective, but simultaneously it may also contribute more to environmental eutrophication.

Addition of organic amendments derived from invasive apple snails alleviated soil acidification, improved soil nitrogen and phosphorus effectiveness, microbial growth and maize yield in South China

Pomacea canaliculata (apple snail) is an invasive agricultural pest posing serious threats to aquatic crop production and wetland ecosystem function in Asia. The shell of P. canaliculata is composed of calcium carbonate (CaCO3), while its soft tissue is protein-rich (carbon (C) and nitrogen (N) sources). Thus, P. canaliculata has the potential to be used as a source of organic soil amendments. Here, we evaluated the effectiveness of snail derivatives (powder, including shells and soft tissues of the snails) as organic soil amendments to improve the productivity of an acidic dryland soil in South China. Snail powder (SP) was incorporated into the soil at application rates of 0–50 g kg−1, followed by planting of maize. Our results showed that SP addition significantly increased soil pH (up to 7.25–7.95), alleviated soil acidification. Moreover, SP addition improved soil N, phosphorus (P) effectiveness, and dissolved organic carbon (DOC) content, increasing biomass of actinobacteria and arbuscular mycorrhizal fungi (AMF) to stimulate microbial growth. Notably, SP addition increased height (up to 42.4 %), biomass (up to 117.6 %) and yield (up to 118.9 %) of maize, with 10 g kg−1 SP optimal for plant productivity. However, the optimal application rate and buffer time for field application of SP warrant further study. Our findings demonstrate the potential of SP resource utilization for acidic soil remediation and the invasive snail P. canaliculata control.

Agronomic amendments drive a diversity of real and apparent priming responses within a grassland soil

Soil carbon (C) sequestration is often viewed as a nature-based solution to help mitigate climate change. Key to realising this potential is a better understanding of which C inputs promote greater long-term C storage. The priming effect (PE) is the change in rates of microbial soil organic matter (SOM) decomposition caused by the addition of organic or mineral amendments to soil. The apparent PE (changes in CO2 from microbial biomass turnover) of substrates is often studied as a confounding factor, however, the real PE (decomposition of native SOM) is rarely measured due to uncertainties in C pool differentiation. Here, we used a 50-day mesocosm study to compare the effect of various common soil amendments (wood biochar and ash, protein, amino acids, glucose, cellulose, cattle farmyard manure (FYM), cattle slurry, inorganic N fertiliser, and different ratios of wheat straw:shoot mixes) on the real and apparent PEs of soil, using 5-year old quasi-stable 14C-labelled SOM and 14C-labelled active microbial biomass, respectively. Our results show that there are often significant differences in the real and apparent PE, for the same amendment, with variance in magnitude and, in some case, direction. We identified few consistent drivers of PE across the two assays, however, there was a negative relationship between the initial C:N ratio of the treatment and PEs, suggesting that while the nutrient stoichiometry of the C amendment is important, the usability and quality of the substrate for the microbial community are key to determining its priming response. Equally, context is important for interpretation, as treatments that elicit positive priming may still be replenishing or increasing soil C stocks.

Screening of Soil Ameliorants to Enhance the Productivity of Green Gram (Vigna radiata L.) under Sodic Soil in Cauvery Delta Zone of Tamil Nadu

Background: In India, about 6.75 million ha, which is around 2.3% of the country’s geographical area is salt affected of which 3.79 million ha is sodic soil. Total sodic soil area in Tamil Nadu is around 0.36 million ha, accounting for 9.5% of total sodic soil area in India. Reclamation of salt-affected soil using drainage is expensive and leaching with good quality water is uneconomical in shallow water table areas. Addition of organic amendments performs a dual role in these situations by enhancing gypsum solubility and improving soil physico-chemical characteristics. Methods: In this context a field experiment was conducted at Anbil Dharmalingam Agricultural College and Research Institute, Tiruchirappalli during summer season of 2021 and 2022 to study the reclamation potential of ameliorants under sodic soil. The experiments were laid out in split plot design with three replications. The treatments comprised of different soil amendments in main plot and foliar nutrition in sub plot. Result: The results showed that, gypsum @ 50% GR+CSR GROMOR @ 25 kg ha-1 registered significantly higher growth parameters viz., plant height (53.5 and 58.4 cm), no. of branches plant-1 (7.27 and 6.75), DMP (2791 and 2801 kg ha-1), physiological characters viz.,CGR (4.12 and 4.46 g m-2 day-1), SPAD value (27.70 and 29.96), RWC (64.10 and 56.15%) and soluble protein (74.60 and 69.72 mg g-1) at harvest. It also increased grain yield of 834 and 875 kg ha-1 with higher exchangeable Ca and Mg with lower Na content during 2021 and 2022 year of experiments.

Can Plant Nutrient Dynamics and Indian Mustard Yield Be Influenced by Addition of Organic Amendments Under Saline Sodic Soils?

ABSTRACT Arid and semi-arid regions are having huge potential for agricultural production but also have limitations of salinity and alkalinity. By mediating rhizospheric environment with the application of organic and inorganic nutrient sources, Indian mustard yield could be enhanced in these areas. For this, a field experiment was conducted to study the effect of organic (FarmYard Manure and vermicompost) and inorganic (urea) amendments with irrigation water of different sodium absorption ratios (SAR; 6, 10, 20 and 30). The experiment was laid out in a split-plot design (SPD) with 24 treatment combinations keeping different SAR in main plots and organic and inorganic nitrogen sources in sub plots. Experiment results revealed that increasing SAR levels reduced the availability of major plant nutrients, i.e. nitrogen, phosphorus and potassium. The soil organic carbon mineralization rate and Indian mustard seed yield were also deceased with increasing levels of SAR. Application of nitrogen through farm yard manure (FYM) and vermicompost decreased the electrical conductivity (EC), pH, and enhanced the cation exchange capacity (CEC) of soil solution. Application of 50% recommended dose of nitrogen (RDN) through urea and 75% through vermicompost produced maximum seed and stover yield of Indian mustard. Thus, supply of recommended dose of nitrogen as inorganic (50%) and organic (75%) sources improved the soil health and Indian mustard yield of arid lands with sodic irrigation water. The use of organic sources in place of sole application of N fertilizer may be a potential management option in sodic groundwater irrigated areas for enhancing mustard crop yield.

Metabolic quotient and specific enzymatic activity in response to the addition of organic amendments to mining tailings

Adding organic amendments to mining tailings to ameliorate extreme conditions that limit plant growth is a common practice in reclamation projects; still, the impact on microbial activity is not commonly considered. This work aimed to explore the use of the metabolic quotient and specific enzymatic activity as indicators of microbial carbon use efficiency in response to adding organic amendments to mining tailings. An experiment in vitro on adding organic amendments: compost, biochar, a mixture of them, and no addition on mining tailing from Taxco, Guerrero, Mexico, was established. Carbon mineralization, microbial biomass, and the enzymatic activity of β-glucosidase, phosphatase, polyphenol oxidase, and dehydrogenase were measured, while specific enzymatic activity and metabolic quotient were calculated. The results showed that microbial activity increased by adding all organic amendments in the following order: compost > mixture > biochar. In the treatment with the addition of compost, we observed a higher carbon mineralization and a greater enzymatic activity. The treatment with adding biochar showed similarities with the control treatment in parameters related to carbon dynamics, such as β-glucosidase, dehydrogenase, and carbon mineralization. This reflects microorganisms’ trade-off between investing energy in searching for resources or using them to improve their biomass clearly to view the specific enzymatic activity and metabolic quotient indicators.

Biochar and Organic Fertilizer Co-Application Enhances Soil Carbon Priming, Increasing CO2 Fluxes in Two Contrasting Arable Soils.

Biochar soil amendments, along with non-tillage agriculture, are often proposed as a strategy for carbon sequestration. It is still questionable how the quality of biochar might influence the priming effect on soil organic matter and whether the addition of unprocessed organic amendments will affect biochar stability. In the study, six different biochars and three exogenous organic matter sources were added to two distinct arable soils. CO2 emission was monitored for 100 days of incubation and CO2 flux was estimated. Results showed that biochar increased soil CO2 fluxes. The highest peaks, up to 162 µg C-CO2 h-1 100 g-1, were recorded in treatments with food waste biochars, suggesting that they serve as a source of easily available carbon to soil microbes. Co-application of raw organic materials (manure and fresh clover biomass) enhanced CO2 emission and carbon losses, especially in sandy soil, where 0.85-1.1% of total carbon was lost in the short-term experiment. Biochar properties and content of labile C can stimulate CO2 emission; however, in a long-term period, this contribution is negligible. The findings of our study showed that more attention should be paid to priming effects caused by the addition of exogenous organic matter when applied to biochar-amended soils.

Fe‐modified biochar improved the stability of soil aggregates and organic carbon: Evidence from enzymatic activity and microbial composition

AbstractBiochar modifications are used to improve soil organic carbon (SOC) content, while its effects on soil structure stability and carbon (C) mineralization are less known especially in saline–alkaline soils. A 5 years field experiment was arranged with organic amendments addition in the Yellow River Delta, including (i) NPK, only 255, 56, and 190 kg ha−1 N, P, and K each year, (ii) RS, NPK + rice straw, (iii) BC, NPK + straw‐derived biochar, and (iv) FeBC, NPK + biochar modified with ferric chloride. Relative to NPK treatment, the mean weight diameter was significantly increased with organic amendments addition, which was the highest in FeBC treatment. Meanwhile, SOC content in the soil added with organic amendment was increased by 2%–18%. Compared with the RS and BC, FeBC addition increased the content of stable humin (HU), crystalline Fe oxides (Fed), and amorphous Fe oxides (Feo). There was a positive correlation between HU and Feo/Fed, indicating HU and Fe oxides might form organic mineral complexes to limit SOC biodegradation. While the mineralization rate of SOC in FeBC treatment was decreased by more than 30.4% than that in BC treatment. This might be due to the decrease of soil β‐glucosidase and cellobiohydrolase activities, as well as the abundance of Gammaproteobacteria and Actinobacteria. These results were the mechanism of soil enzyme activity and bacterial community regulating C stability. Therefore, Fe‐modified biochar is a better organic amendment to improve the stability of aggregates structure and SOC in saline–alkaline paddy soil.

Organic amendment-mediated reclamation and build-up of soil microbial diversity in salt-affected soils: fostering soil biota for shaping rhizosphere to enhance soil health and crop productivity.

Soil salinization is a serious environmental problem that affects agricultural productivity and sustainability worldwide. Organic amendments have been considered a practical approach for reclaiming salt-affected soils. In addition to improving soil physical and chemical properties, organic amendments have been found to promote the build-up of new halotolerant bacterial species and microbial diversity, which plays a critical role in maintaining soil health, carbon dynamics, crop productivity, and ecosystem functioning. Many reported studies have indicated the development of soil microbial diversity in organic amendments amended soil. But they have reported only the development of microbial diversity and their identification. This review article provides a comprehensive summary of the current knowledge on the use of different organic amendments for the reclamation of salt-affected soils, focusing on their effects on soil properties, microbial processes and species, development of soil microbial diversity, and microbial processes to tolerate salinity levels and their strategies to cope with it. It also discusses the factors affecting the microbial species developments, adaptation and survival, and carbon dynamics. This review is based on the concept of whether addition of specific organic amendment can promote specific halotolerant microbe species, and if it is, then which amendment is responsible for each microbial species' development and factors responsible for their survival in saline environments.

Biochar with Organic and Inorganic Fertilizers Improves Defenses, Nitrogen Use Efficiency, and Yield of Maize Plants Subjected to Water Deficit in an Alkaline Soil

Nutrient management practices, such as optimum fertilizer addition rate and co-addition of inorganic fertilizers and organic amendments (compost and biochar), were investigated to enhance crop production and nitrogen (N) use efficiency. However, how these practices improve the defense system, N use efficiency, yield quantity and quality, and physio-biochemical constituents of maize (Zea mays L.) plants grown on an alkaline soil under different irrigation levels (well-watered conditions, mild drought, and severe drought) remains unclear. A two-year field trial was carried out in a split–split plot with a randomized complete block design with three irrigation levels (100% evapotranspiration (ET), 80% ET, and 60% ET) as the main plots, two amendments (5 Mg ha–1 biochar or compost) as subplots, and three regimes of inorganic fertilization (119-16-69, 179-24-99, and 238-31-138 kg N-phosphorus (P)-potassium (K) ha−1) as sub-subplots. We found that maize yield, oil, starch, protein, carbohydrates, and NPK uptake significantly decreased with increasing drought levels, but catalase, peroxidase, superoxide dismutase, and proline contents significantly increased. The addition of organic amendments (compost or biochar) with inorganic fertilizers was more effective in enhancing the above attributes than inorganic fertilizers alone, but these attributes were positively related to inorganic fertilizer rates. The treatment of compost or biochar plus 238-31-138 kg N-P-K ha−1 was the best treatment. The agronomic efficiency of applied fertilizer N (NAE) significantly decreased with increasing drought levels by 28.4–34.7%. The addition of biochar with inorganic fertilizers significantly enhanced NAE by 11.6% compared to inorganic fertilizers alone. Comparing the effect of inorganic fertilizer rates across all irrigation levels, the treatment of 119-16-69 kg N-P-K ha−1 gave the highest NAE. Thus, the addition of optimum NPK fertilizer rate with biochar or compost is suitable to enhance the yield quantity and quality of maize plants grown on alkaline soils by improving its defensive system and N use efficiency, especially under the expected increase in aridity response to climate change.

Organic amendment effects on cropland soil organic carbon and its implications: A global synthesis

Increasing soil organic carbon (SOC) content can promote soil health and crop yield. Organic amendment application is a common practice to accelerate soil carbon sequestration in cropland. The effects of different organic amendments (e.g., compost, slurry) on SOC are uncertain. Previous studies have investigated SOC response to environmental factors but not well addressed the effect of organic amendment characteristics (e.g., source, liquid/solid form, pH). Depending on 1,972 comparisons from 424 articles, we undertook a meta-analysis approach to explore organic amendment effects on SOC content and the related influence factors. The results show that organic amendment addition increased SOC by an average of 26.9% (or 5.1 Mg C ha−1). Specifically, organic amendments can enhance SOC over the long term (>20 years) or within 1.0 m depth. Organic-residue inputs increased more SOC in regions with an arid climate, alkaline soils, or no-mineral nitrogen application soils than the humid climate regions, acidic soils, and nitrogen application soils, respectively. Sewage sludge and municipal solid waste as organic amendments led to high SOC. The organic amendments' pH and liquid/solid form caused significant differences in SOC accumulation. Amendments with a relatively low carbon content or rich nitrogen content have great potential to increase SOC storage. Our results illustrate the importance of amendment characteristics when estimating the potential of organic amendment addition to soil carbon accumulation. This study highlights that amendment application might be a sustainable strategy to increase soil carbon storage while promoting organic waste utilization.

Invertebrate communities (Collembola and Acari) in soil cover treatments for mine tailings in a long‐term field experiment

AbstractAssessment of mine rehabilitation strategies including soil cover treatments rely mainly on soil physico‐chemical properties or plant performance indices, while much less is known about the response of biological soil properties. This field study evaluated the response of soil mesofauna (Collembola and Acari) in soil cover treatments (mainly subsoil and subsoil) on mine tailings, with or without organic amendments. The field experiment was conducted in large (1 m3) units rehabilitated in 2014, and mesofauna in soil cores was assessed 7 years later. The richness of Collembola and Acari as well as the density of Acari increased with organic amendments. Collembola community composition changed with the addition of soil cover and organic amendments. The density and community composition of Acari were strongly positively associated with organic carbon. The density of Euedaphic Collembola decreased, whereas Hemiedaphic and Epedaphic forms increased with soil cover. The contribution of generalist and metal‐tolerant species explained the high density of Euedaphic life forms in tailings. Species‐specific traits for Collembola and Acari could play an essential role in explaining the response of populations to treatments, such as affinity for C‐enriched habitats, food preferences, and sensitivity to heavy metals. Overall, it is recommended to use a multiple diversity indices approach, to collect data on the density and assemblage of mesofauna species to investigate the response of mesofauna communities to soil cover treatments. Mine tailings rehabilitation strategies should focus on improving the nutrient content of soil covers, since it benefits diversity and density of soil fauna.

Gross nitrogen transformations and ammonia oxidizers affected by nitrification inhibitors and/or organic amendments in a calcareous soil: A 15N tracing study

Nitrification inhibitors (NIs) combined with organic amendments are considered effective strategies for improving soil nitrogen availability and reducing nitrogen loss. However, these effects might depend on the types of organic amendments and nitrification inhibitors, and whether their combined application could generate a synergistic effect on nitrogen transformation rate has not been well investigated. In this study, a 15N aerobic incubation experiment was conducted to investigate the effects of nitrification inhibitors (3,4-dimethylpyrazole phosphate [DMPP, 1 % of applied NH4+-N] or methyl 3-(4-hydroxyphenyl) propionate [MHPP, 5 % of applied NH4+-N]) and/or organic amendments (straw [1 %, w/w] or straw-derived biochar [1 %, w/w]) on the gross nitrification rates of mineralization, nitrification, and immobilization in calcareous soil. Our findings revealed that compared with the control treatment, biochar, straw, and MHPP_straw boosted gross mineralization rates by 1.19–2.69 times. The addition of nitrification inhibitors and/or organic amendments inhibited the gross nitrification rates by 15.8 %–89.7 %, which ranged from 0.85 mg N kg−1 day−1 to 8.28 mg N kg−1 day−1 across treatments. DMPP_straw showed the greatest inhibiting effect, whereas 5 % MHPP treatment had the least effect. Gross NH4+ immobilization rates increased by 4.12–18.18 times, where NO3− immobilization rates were only stimulated with the treatments of straw, DMPP_straw, and MHPP_straw. DMPP was more efficient in inhibiting nitrification than MHPP, but it also significantly enhanced ammonia (NH3) volatilization, which rose by 2.77 times over that in MHPP. The high C/N ratio and inorganic-N adsorption of straw and biochar might play prominent roles in affecting NH4+ content by stimulating mineralization and inorganic immobilization. The decrease in the abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) can be partially explained by the inhibitory effects of DMPP and MHPP. Changes in the community of AOB were more sensitive to management measures than those of AOA. In conclusion, our study demonstrates that treatments with DMPP_straw and MHPP_straw efficiently promote inorganic nitrogen immobilization, mitigate NH3 volatilization, inhibit nitrification to the greatest extent, and thus yield the most positive synergistic effects on soil nitrogen retention.

Response of rice yield to organic amendments was regulated by soil chemical properties, microbial functional genes and bacterial community rather than fungal community

Integrated fertilization using mineral fertilizer and organic amendments is common practices for sustainable crop production. However, the impacts of different organic amendments on soil chemical properties, function genes, and microbial community, as well as their contribution to rice yield have not been well illustrated. In this study, soil chemical properties, microbial diversity, community structure and stability, and functional genes were evaluated after 10 years of fertilization. Compared with the mineral fertilizer regime, the integrated addition of mineral fertilizer and organic amendments improved soil fertility and increased the grain yield by 0.32 %–11.45 %, in terms of five-year average yield. Bacterial diversity and microbial community stability were significantly improved by organic amendments (p < 0.05). Additionally, organic amendments significantly reshaped the microbial community and increased the relative abundance of beneficial bacteria and fungi, as well as suppressed the growth of plant pathogenic fungi (p < 0.05). Besides, multiple functional genes were upregulated by organic amendments, and had significant relationships with grain yield. Soil chemical properties explained most of the variation in grain yield. PLS-PM result further revealed that functional genes and bacterial community (diversity, composition, and stability), rather than fungal community, which were positively affected by fertilization and soil chemical properties, had a strong influence on grain yield. Overall, organic amendments strongly improved soil chemical properties and function and regulated bacterial community, thus enhancing rice yield.

Medium-Term Effect of Organic Amendments on the Chemical Properties of a Soil Used for Vegetable Cultivation with Cereal and Legume Rotation in a Semiarid Climate

The response of a Petrocalcic Palexeroll dedicated to the cultivation of vegetables (Apium graveolens L.) with a rotation of a mixture of cereals and legumes when organic amendments are added has been studied; specifically, three fertilization treatments were experimented with: two organic (LSM and COA) and one with chemical fertilizers (I). The LSM and COA plots were managed according to the regulations governing organic production, while in I, conventional agricultural production practices were used. Over a three-year period, monthly samples were taken from the topsoil and analyzed for organic carbon (OC), total nitrogen (TN), C/N ratio, total P (P), electrical conductivity of the saturation extract (ECext) and extract ions, pH in water (pHw) and 1 M KCl (pHKCl), cation exchange capacity (CEC), exchangeable bases (Mg2+, K+, Na+), and assimilable elements (Fe, Cu, Mn, Zn). The results obtained indicated significant differences between the treatments for the OC, TN, C/N, and P; specifically, in the case of OC the mean concentrations were 22.2 &gt; 20.1 &gt; 17.5 g kg−1 for the LSM, COA, and I, respectively. The addition of organic amendments also improved the soil function for food production, evidenced by the higher concentrations of K, Mg, and micronutrients. The ECext and extracted ions were also sensitive to the treatments such that the sequence of ECext in the third year was COA = LSM &gt; I, with values of 5.0, 4.8, and 3.3 dSm−1, which forced a rethink of the doses of the amendments applied. These results suggest that the LSM-based agronomic model had a beneficial effect on the soil properties and contributed to its function as a C sink.

Long-term impact of organic and conventional farming on soil physical properties under rice (Oryza sativa)-wheat (Triticum aestivum) cropping system in north-western Indo-Gangetic plains

Long-term (13 years) impact of organic and conventional farming on soil physical properties was evaluated under a rice (Oryza sativa L.) – wheat (Triticum aestivum L.) cropping system in a sandy clay loam soil at New Delhi. The treatments included unfertilized control (T1), conventionally managed (T2) and five organic treatments (T3: FYM @ 10 t/ha to rice and wheat, T4: SGM for rice and LGLM for wheat, T5: SGM + BGA for rice and LGLM + Azotobacter for wheat, T6: SGM + FYM for rice and LGLM + FYM for wheat, and T7: SGM + FYM + BGA for rice and LGLM + FYM + Azotobacter for wheat). The application of organic amendments had positive influence on soil physical properties such as saturated hydraulic conductivity (Ks), field capacity (FC) and permanent wilting point (PWP), plant-available water capacity (PAWC), water holding capacity (WHC), distribution of aggregate size fractions, bulk density (Db), and porosity in the 0-15 and 15-30 cm soil layer. A favourable effect of organic amendments was also found on soil strength (at depth 0-70 cm). Even, values related to these properties were significantly affected by the kinds of organic amendments. But, T1 and T2 had no improvement in soil physical properties over the organic ones. Value of Ks decreased with increase in soil depths. T7 and T3 were superior in Ks to other treatments for 0-15 and 15-30 cm soil depths. Volumetric moisture content at FC (θFC) and PWP (θWP) increased with addition of organic amendments and got varying response due to the kinds of organic amendments or their combinations. θFC and θWP were decreased substantially under T1 and T2, because of no addition of organic inputs. As a result of θFC and θWP, PAWC had also signified an improvement under the influence of different organic amendments over T1 and T2. Generally (for both depths), PAWC of T3, T6 and T7 were 17-26% more than T1, T2, T4 and T5. WHC of upper soil layer (0-15 cm) was greater for organic amended plots than plots devoid of organic inputs and lower values were recorded for 15-30 cm soil layer. WHC of T3, T7 and T6 was highest in comparison to plots amended only with (without FYM) green manure, BGA or Azotobacter as well as T1 and T2 for both depths (0-15 and 15-30 cm). A better soil aggregation was observed under organic amended plots for large and small macro-aggregates (LM - &gt;2 and SM-0.25-2 mm) in both soil depths. Lowest value of Db with highest percentage of pore space was noted under T7 than other treatments in both soil layers. Soil strength was significantly lower in organic amended plots than T1 and T2. This study clearly indicated that application of organic inputs especially FYM, improved the soil physical properties, which resulted in better soil aggregation, porosity and soil moisture retention.