Long-term Organic Fertilization Research Articles

Soil Organic Matter and Amorphous Oxides Determine the Surface Electrochemical Properties of Purple Soil Under Long-Term Inorganic and Organic Fertilization

Soil Organic Matter and Amorphous Oxides Determine the Surface Electrochemical Properties of Purple Soil Under Long-Term Inorganic and Organic Fertilization

Comparative evaluation of 16S rRNA primer pairs in identifying nitrifying guilds in soils under long-term organic fertilization and water management

Compared with 454 sequencing technology, short-read sequencing (e.g., Illumina) technology generates sequences of high accuracy, but limited length (<500 bp). Such a limitation can prove that studying a target gene using a large amplicon (>500 bp) is challenging. The ammonia monooxygenase subunit A (amoA) gene of ammonia-oxidizing archaea (AOA), which plays a crucial part in the nitrification process, is such a gene. By providing a full overview of the community of a functional microbial guild, 16S ribosomal ribonucleic acid (rRNA) gene sequencing could overcome this problem. However, it remains unclear how 16S rRNA primer selection influences the quantification of relative abundance and the identification of community composition of nitrifiers, especially AOA. In the present study, a comparison was made between the performance of primer pairs 338F-806R, 515F-806R, and 515F-907R to a shotgun metagenome approach. The structure of nitrifier communities subjected to different long-term organic matter amendment and water management protocols was assessed. Overall, we observed higher Chao1 richness diversity of soil total bacteria by using 515F-806R compared to 338F-806R and 515F-907R, while higher Pielou’s evenness diversity was observed by using 515F-806R and 515F-907R compared to 338F-806R. The studied primer pairs revealed different performances on the relative abundance of Thaumarchaeota, AOB, and NOB. The Thaumarchaeota 16S rRNA sequence was rarely detected using 338F-806R, while the relative abundances of Thaumarchaeota detected using 515F-806R were higher than those detected by using 515F-907R. AOB showed higher proportions in the 338F-806R and 515F-907R data, than in 515F-806R data. Different primers pairs showed significant change in relative proportion of NOB. Nonetheless, we found consistent patterns of the phylotype distribution of nitrifiers in different treatments. Nitrosopumilales (NP) and Nitrososphaerales (NS) clades were the dominant members of the AOA community in soils subject to controlled irrigation, whereas Ca. Nitrosotaleales (NT) and NS clades dominated the AOA community in soils subject to flooding irrigation. Nitrospira lineage II was the dominant NOB phylotype in all samples. Overall, ideal 16S rRNA primer pairs were identified for the analysis of nitrifier communities. Moreover, NP and NT clades of AOA might have distinct environmental adaptation strategies under different irrigation treatments.

Soil Acidification Can Be Improved under Different Long-Term Fertilization Regimes in a Sweetpotato-Wheat Rotation System.

Soil acidification is a significant form of agricultural soil degradation, which is accelerated by irrational fertilizer application. Sweetpotato and wheat rotation has emerged as an important rotation system and an effective strategy to optimize nutrient cycling and enhance soil fertility in hilly areas, which is also a good option to improve soil acidification and raise soil quality. Studying the effects of different fertilization regimes on soil acidification provides crucial data for managing it effectively. An eight-year field experiment explored seven fertilizer treatments: without fertilization (CK), phosphorus (P) and potassium (K) fertilization (PK), nitrogen (N) and K fertilization (NK), NP fertilization (NP), NP with K chloride fertilization (NPK1), NP with K sulfate fertilization (NPK2), and NPK combined with organic fertilization (NPKM). This study focused on the soil acidity, buffering capacity, and related indicators. After eight years of continuous fertilization in the sweetpotato-wheat rotation, all the treatments accelerated the soil acidification. Notably, N fertilization reduced the soil pH by 1.30-1.84, whereas N-deficient soil showed minimal change. Organic fertilizer addition resulted in the slowest pH reduction among the N treatments. Both N-deficient (PK) and organic fertilizer addition (NPKM) significantly increased the soil cation exchange capacity (CEC) by 8.83% and 6.55%, respectively, compared to CK. Similar trends were observed for the soil-buffering capacity (pHBC). NPK2 increased the soil K+ content more effectively than NPK1. NPKM reduced the sodium and magnesium content compared to CK, with the highest magnesium content among the treatments at 1.60 cmol·kg-1. Regression tree analysis identified the N input and soil magnesium and calcium content as the primary factors influencing the pHBC changes. Structural equation modeling showed that the soil pH is mainly influenced by the soil ammonium N content and pHBC, with coefficients of -0.28 and 0.29, respectively. Changes in the soil pH in the sweetpotato-wheat rotation were primarily associated with the pHBC and N input, where the CEC content emerged as the main factor, modulated by magnesium and calcium. Long-term organic fertilization enhances the soil pHBC and CEC, slowing the magnesium reduction and mitigating soil acidification in agricultural settings.

Effects of Long-Term Organic Fertilizer Application on Tea Plantation Soil of Its Physical and Chemical Properties and Microbial Communities

Effects of Long-Term Organic Fertilizer Application on Tea Plantation Soil of Its Physical and Chemical Properties and Microbial Communities

Mitigating soil degradation in continuous cropping banana fields through long-term organic fertilization: Insights from soil acidification, ammonia oxidation, and microbial communities

Exploring the potential of organic fertilizers as a mitigating strategy against the negative consequences induced by prolonged use of inorganic fertilizers in high-intensity banana cultivation is critically essential. Ammonia-oxidizer are closely linked to soil acidification, and how they respond to the long term fertilized banana field soil still poorly understood. In this study, soil samples from long-term inorganic (CF), and inorganically plus organically fertilized banana fields (OF) (from 2010 to 2019) were used to investigate the soil acid buffer capacity (pHBC), the potential nitrification rate (PNR), and the community structure of bacteria, fungi, ammonia-oxidizing archaea (AOA), and bacteria (AOB). Compared to the natural soil (CK, unplanted, and unfertilized), the pH and pHBC in the long-term fertilized banana field (both CF and OF) were significantly reduced. However, the pHBC was 1.3 times higher in soil receiving OF treatment than that in CF treatment. Organic matter (OM) and total nitrogen (TN) were significantly increased in the OF treated soil, which were 1.88 and 1.6 times higher compared to the CF-treated ones. The PNR in banana soil was 3.71–4.85 times higher than in the natural soil. High-throughput sequencing results showed that Candidatus Nitrosospharea SCA1170-like AOA and Nitrosospira spp-like AOB were adapted to long-term fertilization in banana field soil. Potentially pathogenic bacteria, Xanthomonadaceae, were enriched in CF-treated soil compared to CK and OF soils. Opposingly, potentially beneficial Streptomyces and Arthrobacter were enriched in natural soil. Meanwhile, the OF-treated soil demonstrated a greater abundance of beneficial Bacillus and Alicyclobacillus. The study reveals that organic fertilizers ameliorate soil acidification, low organic matter content and microbial diversity compared to inorganic fertilizers for banana cultivation.

Biological Interactions Mediate Soil Functions by Altering Rare Microbial Communities.

Soil microbes, the main driving force of terrestrial biogeochemical cycles, facilitate soil organic matter turnover. However, the influence of the soil fauna on microbial communities remains poorly understood. We investigated soil microbiota dynamics by introducing competition and predation among fauna into two soil ecosystems with different fertilization histories. The interactions significantly affected rare microbial communities including bacteria and fungi. Predation enhanced the abundance of C/N cycle-related genes. Rare microbial communities are important drivers of soil functional gene enrichment. Key rare microbial taxa, including SM1A02, Gammaproteobacteria, and HSB_OF53-F07, were identified. Metabolomics analysis suggested that increased functional gene abundance may be due to specific microbial metabolic activity mediated by soil fauna interactions. Predation had a stronger effect on rare microbes, functional genes, and microbial metabolism compared to competition. Long-term organic fertilizer application increased the soil resistance to animal interactions. These findings provide a comprehensive understanding of microbial community dynamics under soil biological interactions, emphasizing the roles of competition and predation among soil fauna in terrestrial ecosystems.

Active microbial population dynamics and life strategies drive the enhanced carbon use efficiency in high-organic matter soils.

Microbial carbon use efficiency (CUE) is a critical parameter that controls carbon storage in soil, but many uncertainties remain concerning adaptations of microbial communities to long-term fertilization that impact CUE. Based on H218O quantitative stable isotope probing coupled with metagenomic sequencing, we disentangled the roles of active microbial population dynamics and life strategies for CUE in soils after a long-term (35 years) mineral or organic fertilization. We found that the soils rich in organic matter supported high microbial CUE, indicating a more efficient microbial biomass formation and a greater carbon sequestration potential. Organic fertilizers supported active microbial communities characterized by high diversity and a relative increase in net growth rate, as well as an anabolic-biased carbon cycling, which likely explains the observed enhanced CUE. Overall, these results highlight the role of population dynamics and life strategies in understanding and predicting microbial CUE and sequestration in soil.IMPORTANCEMicrobial CUE is a major determinant of global soil organic carbon storage. Understanding the microbial processes underlying CUE can help to maintain soil sustainable productivity and mitigate climate change. Our findings indicated that active microbial communities, adapted to long-term organic fertilization, exhibited a relative increase in net growth rate and a preference for anabolic carbon cycling when compared to those subjected to chemical fertilization. These shifts in population dynamics and life strategies led the active microbes to allocate more carbon to biomass production rather than cellular respiration. Consequently, the more fertile soils may harbor a greater microbially mediated carbon sequestration potential. This finding is of great importance for manipulating microorganisms to increase soil C sequestration.

Long-term organic fertilization combined with deep ploughing enhances carbon sequestration in a rainfed sorghum-maize rotation system

Organic fertilization and deep ploughing are expected to contribute to carbon (C) sequestration in arable soils. This hypothesis was evaluated over 11 years of chemical and organic fertilization under conventional tillage (20 cm) and deep ploughing (40 cm) in a rainfed sorghum-maize rotation system on the Loess Plateau. Soil was collected and analysed to determine the soil organic C (SOC) and total nitrogen (TN) contents in the soil profiles (0–60 cm) or in the macroaggregates, microaggregates and silt and clay fractions (0–20 cm only). The SOC and TN stocks at the 0–60 cm depth displayed a net decrease in the unfertilized control, a marginal increase with chemical fertilizer, a significant increase of 23–45 % and 19–42 %, respectively, with organic amendments and a significant increase of 54 % and 48 %, respectively, when combined with deep ploughing. A critical input amount of 2064 kg C ha−1 yr−1 or 162 kg N ha−1 yr−1 was found to be required to maintain the initial SOC or TN stock. The annual N input was positively correlated with the C sequestration efficiency (P < 0.001). This supports the microbial N mining theory. Organic fertilization increased soil aggregation and the specific activity of N-acetyl-glucosaminidase, which was positively correlated with the specific respiration rate in the whole soil profile (P < 0.001) and aggregates (P < 0.001). This appears to support the stoichiometric decomposition theory. However, deep ploughing decreased the specific activity of N-acetyl-glucosaminidase at the 40–60 cm depth compared with conventional tillage. Collectively, long-term organic fertilization combined with deep ploughing enhances SOC sequestration in three ways: directly through the input of exogenous C, indirectly by alleviating microbial N limitations and increasing the amount and stability of subsoil-associated C, and to a lesser extent by improving soil aggregation.

Long-term application of organic fertilizer prompting the dispersal of antibiotic resistance genes and their health risks in the soil plastisphere

Microplastic (MP) pollution is a rapidly growing global environmental concern that has led to the emergence of a new environmental compartment, the plastisphere, which is a hotspot for the accumulation of antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs). However, studies on the effects of long-term organic fertilizer application on the dispersal of ARGs and virulence factor genes (VFGs) in the plastisphere of farmland soil have been limited. Here, we performed a field culture experiment by burying nylon bags filled with MPs in paddy soil that had been treated with different fertilizers for over 30 years to explore the changes of ARGs and VFGs in soil plastisphere. Our results show that the soil plastisphere amplified the ARG and VFG pollution caused by organic fertilization by 1.5 and 1.4 times, respectively. And it also led to a 2.7-fold increase in the risk of horizontal gene transfer. Meanwhile, the plastisphere tended to promote deterministic process in the community assembly of HBPs, with an increase of 1.4 times. Network analysis found a significant correlation between ARGs, VFGs, and bacteria in plastisphere. Correlation analysis highlight the important role of mobile genetic elements (MGEs) and bacterial communities in shaping the abundance of ARGs and VFGs, respectively. Our findings provide new insights into the health risk associated with the soil plastisphere due ARGs and VFGs derived from organic fertilizers.

Seeds Act as Vectors for Antibiotic Resistance Gene Dissemination in a Soil-Plant Continuum.

Though the evidence for antibiotic resistance spread via plant microbiome is mounting, studies regarding antibiotic resistome in the plant seed, a reproductive organ and important food resource, are still in their infancy. This study investigated the effects of long-term organic fertilization on seed bacterial endophytes, resistome, and their intergenerational transfer in the microcosm. A total of 99 antibiotic resistance genes (ARGs) and 26 mobile genetic elements (MGEs) were detected by high-throughput quantitative PCR. The amount of organic fertilizer applied was positively correlated to the number and relative abundance of seed-associated ARGs and MGEs. Moreover, the transmission of ARGs from the rhizosphere to the seed was mainly mediated by the shared bacteria and MGEs. Notably, the rhizosphere of progeny seedlings derived from seeds harboring abundant ARGs was found to have a higher relative abundance of ARGs. Using structural equation models, we further revealed that seed resistome and MGEs were key factors affecting the ARGs in the progeny rhizosphere, implying the seed was a potential resistome reservoir for rhizosphere soil. This study highlights the overlooked role of seed endophytes in the dissemination of resistome in the soil-plant continuum, and more attention should be paid to plant seeds as vectors of ARGs within the "One-Health" framework.

Long-term fermented organic fertilizer application reduce urea nitrogen-15 loss from plastic shed agricultural soils

Continuous application of fermented organic fertilizer can improve soil quality, while the performance of nitrogen (N) in the improved soils is rarely investigated. To investigate the fate of applied N in the soils with organic management history, the 15NH2CO15NH2 (15N abundance of 19.6 %) was employed as the exogenous N source to conduct an experiment in the Chinese cabbage and tomato rotation system under plastic shed condition. The cultivated soils have received 15-year of effective microorganism (EM) fermented organic fertilizer (EM-OF), N, P, K inorganic fertilizer (NPK-IF) and no fertilizer (NoF). The 15N use by cabbage and tomato, the soil 15N forms, as well as the 15N distribution were observed. Results showed that the 15N use efficiency of cabbage in the EM-OF, NPK-IF and NoF soils were 55.1 %, 37.3 % and 26.6 % respectively, showing significant (p ≤ 0.05) differences. The succeeding crop tomato could take up the soil residual 15N, and the highest 15N reuse efficiency was 7.1 % that detected in the NoF soil. The total 15N loss (6.0 %) from the rotation system was the lowest in the EM-OF soil, compared to that in the NPK-IF and NoF soils. It was concluded that the long-term fermented organic fertilizer applied soils can reduce urea 15N loss from plastic shed agriculture, mainly through improving the in-season crop 15N use efficiency.

Long-term organic fertilization reshapes the communities of bacteria and fungi and enhances the activities of C- and P-cycling enzymes in calcareous alluvial soil

Soil microbial communities and extracellular enzymes are pivotal in governing the dynamics of soil carbon (C) and phosphorus (P) cycling. Nevertheless, comprehending the underlying regulatory factors and intricate interactions among these vital indicators remains an inadequately explored aspect, especially within the scenario of long-term fertilization. Long-term fertilization experiments were conducted on calcareous alluvial soil. The five fertilization regimes selected were as follows: without fertilization treatment (CK); inorganic NK fertilization treatment (NK); inorganic NPK fertilization treatment (NPK); organic fertilization treatment (M); and combined inorganic NPK with organic fertilization treatment (NPKM). The soil physicochemical properties, β-glucosidase (BG), and alkaline phosphomonoesterase (ALP) activities were determined, together with microbial (bacterial and fungal) community DNA sequences and subsequent bioinformatics analysis after 38 years of different fertilization. The results showed that the content of soil organic carbon (SOC) and available P and the activities of BG and ALP were the highest after M and NPKM treatments, which were 79–104 %, 26–36 times, 161–171 %, and 75–91 % higher than CK, respectively. Hierarchical clustering analysis showed that the bacterial and fungal community structures in M and NPKM treatments were similar, but the community structures in non-organic fertilization treatments (CK, NK, and NPK) were significantly different from those in organic fertilization treatments. The indicator species and correlation analysis combined revealed that most indicator species in organic fertilizer treatments were significantly positively correlated with soil BG and ALP, while most indicator species in non-organic fertilizer (CK and NK) treatments were significantly negatively correlated with soil BG and ALP. Organic fertilization treatments favored the growth of the bacterial genus Lysobacter and the fungal genera Acremonium and Mortierella and were significantly positively correlated with BG and ALP activities. Redundancy analysis revealed that SOC is the most important factor in shaping microbial community structure. Co-occurrence network analysis showed organic fertilization had higher network complexity, more keystone taxa, and more associations among microbial taxa compared with non-organic fertilization (CK + NK). Structural equation models revealed that microbial community structure is the direct driving factor of BG and ALP activities and their interactions, and SOC modulated the relationship between microbial community structure and BG and ALP activities. This study highlights how the application of organic fertilizer enhanced the C- and P-cycling enzyme activities, reshaped the soil microbial communities, and regulated these crucial indicators and their interactions by SOC.

Meta-Analysis of Organic Fertilization Effects on Soil Bacterial Diversity and Community Composition in Agroecosystems.

Application of organic fertilizers or their combination with chemical fertilizers is a feasible practice for improving soil fertility and reducing soil degradation in agroecosystems, and these regulations are mainly mediated though soil microbial communities. Despite bacteria ranking among the most abundant and diverse groups of soil microorganisms, the effects of long-term organic fertilization (OF) and chemical-organic fertilization (COF) on soil bacterial diversity and community composition remain unclear. In this study, we conducted a meta-analysis and demonstrated that OF had no significant effect on bacterial alpha diversity. Application of chemical fertilizer and crop residue significantly decreased bacterial Richness index. Both OF and COF significantly altered bacterial community structure, with these changes being predominately attributed to shifts in soil pH. For bacterial phyla, both OF and COF significantly increased the relative abundance of Proteobacteria and Bacteroidetes, suggesting that OF and COF may cause the enrichment of copiotrophic taxa. In addition, COF significantly increased the relative abundance of Gammaproteobacteria but decreased the relative abundance of Acidobacteria. Overall, our results suggest that organic and chemical-organic fertilization can effectively maintain bacterial diversity and enhance soil fertility in agroecosystems, and the alteration of soil bacterial community structure is closely intertwined with soil pH.

Does a decade of soil organic fertilization promote copper and zinc phytoavailability? Evidence from a laboratory biotest with field-collected soil samples

Despite chronic contamination, long-term organic fertilization tends to decrease copper (Cu) and zinc (Zn) availability in agricultural soils. Root activities of crop plants can also induce substantial changes in rhizosphere chemistry and consequently in the Cu and Zn availability in the rhizosphere. The balance between these two drivers and the overall effect of organic fertilization on Cu and Zn bioavailability to plants (i.e., phytoavailability) remains a matter of debate. We assessed the effect of a decade of agronomically realistic organic fertilization on Cu and Zn availability in the rhizosphere and their phytoavailability. Using a laboratory biotest, Festuca arundinacea was exposed to 34 soil samples collected from three agricultural field trials that had received no, mineral, or organic fertilization for a decade. Dissolved organic matter (DOM) properties (i.e., concentration, aromaticity, and binding properties toward Cu), pH, and Cu and Zn availability (i.e., total dissolved concentration and free ionic activity) were determined in the rhizosphere solutions. Cu and Zn phytoavailability was measured as the plant uptake flux. Contrary to bulk soils, organic fertilization induced very few changes in the chemistry and Cu and Zn availability in the rhizosphere solutions compared to no and mineral fertilization. Consistently, Cu and Zn phytoavailability did not increase with organic fertilization, but it was mostly driven by soil properties rather than by fertilization. Despite increasing soil Cu and Zn contamination, a decade of soil organic fertilization did not increase Cu and Zn phytoavailability, presumably due to the root-mediated levelling of Cu and Zn availability in the rhizosphere.

Long-term bioorganic and organic fertilization improved soil quality and multifunctionality under continuous cropping in watermelon

Continuous cropping has can majorly damage the soil ecosystem, leading to an increased prevalence of pathogenic microorganisms and severe yield losses for watermelons. Multiple prevention strategies have been adopted to overcome this obstacle, among which the application of bioorganic fertilizer can improve microbiome deterioration. However, the response of soil ecosystem multifunctionality and soil quality to fertilizer regimes under continuous cropping remains poorly understood. In this study, based on an 8-year field experiment, we evaluated soil health and ecosystem multifunctionality under different fertilization treatments. Long-term bio-organic fertilization preserved soil electrical conductivity and increased total Cu, Zn, Fe, Mn, Ca, and Mg, total and available nutrients, and enzyme activities compared with those in unfertilized control (CK) and chemical fertilizer treatments. Enzyme activities and yield rapidly changed, indicating their sensitivity to these management practices. Conversely, soil pH, biodiversity, medium/trace elements, and total NPK content were more resistant to change than enzyme activities, suggesting higher stability over time. The area of soil quality index under bio-organic fertilization was 1.2–2.9 times larger than that under CK treatment. Applying biological organic fertilizer and a mixture of chemical and organic fertilizers improved the multifunctionality decline caused by continuous cropping by 1.1–1.4 times, whereas the effect of the chemical fertilizer was weak. Soil health was positively correlated with ecosystem multifunctionality. These findings suggest that long-term bioorganic and organic fertilization is an effective strategy for improving soil quality and multifunctionality in continuous watermelon crops while also contributing toward a more sustainable agricultural system.

Effects of the combined application of organic and chemical nitrogen fertilizer on soil aggregate carbon and nitrogen: A 30-year study

To understand the long-term effects of combined organic and chemical nitrogen fertilization on soil organic C (SOC) and total N (TN), we conducted a 30-year field experiment with a wheat–maize rotation system on the Huang-Huai-Hai Plain during 1990–2019. The experimental treatments consisted of five fertilizer regimes: no fertilizer (control), chemical fertilizer only (NPK), chemical fertilizer with straw (NPKS), chemical fertilizer with manure (NPKM), and 1.5 times the rate of NPKM (1.5NPKM). The NPK, NPKS, and NPKM treatments had equal N inputs. The crop yields were measured over the whole experimental duration. Soil samples were collected from the topsoil (0–10 and 10–20 cm) and subsoil (20–40 cm) layers for assessing soil aggregates and taking SOC and TN measurements. Compared with the NPK treatment, the SOC and TN contents increased significantly in both the topsoil (24.1–44.4% for SOC and 22.8–47.7% for TN) and subsoil layers (22.0–47.9% for SOC and 19.8–41.8% for TN) for the organically amended treatments (NPKS, NPKM and 1.5NPKM) after 30 years, while no significant differences were found for the average annual crop yields over the 30 years of the experiment. The 0–10 cm layer of the NPKS treatment and the 20–40 cm layer of the NPKM treatment had significantly higher macroaggregate fraction mass proportions (19.8 and 27.0%) than the NPK treatment. However, the 0–10 and 20–40 cm layers of the 1.5NPKM treatment had significantly lower macroaggregate fraction mass proportions (–19.2 and –29.1%) than the control. The analysis showed that the higher SOC and TN in the soil of organically amended treatments compared to the NPK treatment were related to the increases in SOC and TN protected in the stable fractions (i.e., free microaggregates and microaggregates within macroaggregates), in which the contributions of the stable fractions were 81.1–91.7% of the increase in SOC and 83.3–94.0% of the increase in TN, respectively. The relationships between average C inputs and both stable SOC and TN stocks were significantly positive with R2 values of 0.74 and 0.72 (P<0.01) for the whole 40 cm soil profile, which indicates the importance of N for soil C storage. The results of our study provide key evidence that long-term combined organic and chemical nitrogen fertilization, while maintaining reasonable total N inputs, benefited soil C and N storage in both the topsoil and subsoil layers.

Long-term organic fertilization enhances potassium uptake and yield of sweet potato by expanding soil aggregates-associated potassium stocks

Crop straw return and organic manure application are effective and environmentally friendly methods used by farmers to improve soil structure, fertility and agricultural productivity. Sweet potato is a typical “potassium (K)-favoring” food crop and widely grown throughout the world. However, the regulation effects of long-term organic fertilization on soil aggregates-associated K stocks and K uptake by sweet potato are less understood. Herein, a long-term fertilization experiment since 2007 including chemical fertilizer (NPK), NPK combined with commercial manure (NPK+CM), NPK combined with pig manure (NPK+PM), and NPK combined with rice straw (NPK+RS) treatments under peanut-sweet potato crop rotation was employed. Long-term fertilizer application contributed to higher yield, yield stability, and K uptake of sweet potato. NPK+PM and NPK+RS treatments both showed the best promoting effect on plant growth. NPK+PM and NPK+RS treatments showed remarkable increasement of aggregate-associated exchangeable potassium (EK) and non-exchangeable potassium (NEK) stocks, particularly for small-macroaggregates (0.25–2 mm) and large-macroaggregates (> 2 mm). Total potassium (TK), EK and NEK stocks in large and small-macroaggregates displayed positive effects on K uptake and yield for sweet potato. Pearson's correlation and random forest model analysis revealed that EK and NEK stock in large-macroaggregate were the most key factors for K uptake and yield of sweet potato under long-term fertilization. Overall, our study highlights the prominent advantage of long-term organic fertilization.

Effects of long-term organic and inorganic fertilization on greenhouse gas emissions and soil nutrient stoichiometry in a rice–rice–fallow cropping system

Long-term use of organic and inorganic fertilizers can have a negative impact on greenhouse gas (GHG) emissions and nutrient stoichiometry in paddy soil. However, production of sufficient crops to meet food and feed demands globally requires the use of fertilizer in crop production. In the present study, we assessed the environmental impacts of five fertilizer treatments in a rice–rice–fallow cropping system: no fertilizer (CK); inorganic nitrogen, phosphorus, and potassium fertilizers (NPK); manure (M); inorganic phosphorus and potassium fertilizers with manure (PKM); and inorganic nitrogen, phosphorus, and potassium fertilizers with manure (NPKM). Soil parameters were analyzed to examine the relationships between GHG emissions, net ecosystem carbon budgets (NECBs), and soil nutrient stoichiometric ratios. Both the PKM and NPKM treatments increased grain yield and the soil carbon–nitrogen (C:N), carbon–phosphorus (C:P), and nitrogen–phosphorus (N:P) ratios compared to the CK treatment; they also decreased the nitrogen–potassium (N:K) ratio. In the combined fertilization treatments, the fallow season accounted for 9–13% of annual methane (CH4) emissions, whereas early rice accounted for 55–62 % and late rice contributed 38–45 %. Compared to the CK, PKM and NPKM fertilization increased the annual nitrous oxide (N2O) emissions by 52–73 % and 103–115 %, respectively, in both the rice and fallow seasons. In early rice, the C:P ratio and GHG intensity (GHGI) were negatively correlated with CH4 and N2O emissions, whereas both yield and CH4 emissions had strong positive associations with global warming potential (GWP). In the late rice season, GHGI was negatively correlated with carbon dioxide (CO2) and CH4 emissions, and N2O had strong positive associations with GWP. CO2 and N2O emission levels were greater from late rice than from early rice, although CH4 emissions from early rice contributed more to the annual GWP, resulting in higher carbon equivalent emissions but a lower carbon efficiency ratio in early rice output. A Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) optimization analysis suggested that PKM was the best fertilization method to improve yield while minimizing negative environmental impacts, followed in descending order by the NPKM, NPK, and M treatments.

Long-Term Organic Fertilization Strengthens the Soil Phosphorus Cycle and Phosphorus Availability by Regulating the pqqC- and phoD-Harboring Bacterial Communities.

The pqqC and phoD genes encode pyrroloquinoline quinone synthase and alkaline phosphomonoesterase (ALP), respectively. These genes play a crucial role in regulating the solubilization of inorganic phosphorus (Pi) and the mineralization of organic phosphorus (Po), making them valuable markers for P-mobilizing bacterial. However, there is limited understanding of how the interplay between soil P-mobilizing bacterial communities and abiotic factors influences P transformation and availability in the context of long-term fertilization scenarios. We used real-time polymerase chain reaction and high-throughput sequencing to explore the characteristics of soil P-mobilizing bacterial communities and their relationships with key physicochemical properties and P fractions under long-term fertilization scenarios. In a 38-year fertilization experiment, six fertilization treatments were selected. These treatments were sorted into three groups: the non-P-amended group, including no fertilization and mineral NK fertilizer; the sole mineral-P-amended group, including mineral NP and NPK fertilizer; and the organically amended group, including sole organic fertilizer and organic fertilizer plus mineral NPK fertilizer. The organically amended group significantly increased soil labile P (Ca2-P and enzyme-P) and Olsen-P content and proportion but decreased non-labile P (Ca10-P) proportion compared with the sole mineral-P-amended group, indicating enhanced P availability in the soil. Meanwhile, the organically amended group significantly increased soil ALP activity and pqqC and phoD gene abundances, indicating that organic fertilization promotes the activity and abundance of microorganisms involved in P mobilization processes. Interestingly, the organically amended group dramatically reshaped the community structure of P-mobilizing bacteria and increased the relative abundance of Acidiphilium, Panacagrimonas, Hansschlegelia, and Beijerinckia. These changes had a greater positive impact on ALP activity, labile P, and Olsen-P content compared to the abundance of P-mobilizing genes alone, indicating their importance in driving P mobilization processes. Structural equation modeling indicated that soil organic carbon and Po modulated the relationship between P-mobilizing bacterial communities and labile P and Olsen-P, highlighting the influence of SOC and Po on the functioning of P-mobilizing bacteria and their impact on P availability. Overall, our study demonstrates that organic fertilization has the potential to reshape the structure of P-mobilizing bacterial communities, leading to increased P mobilization and availability in the soil. These findings contribute to our understanding of the mechanisms underlying P cycling in agricultural systems and provide valuable insights for enhancing microbial P mobilization through organic fertilization.

Response of Soil Absolute and Specific Enzyme Activities to Long-Term Application of Organic Fertilizer to Solonetz in Northeast China

Soil organic carbon (SOC) and microbial biomass carbon (MBC) are highly correlated with enzyme activities. Specific enzyme activities can exclude the autocorrelation between enzyme activity and SOC and MBC. However, the responses of absolute and specific enzyme activities to saline–alkali properties remains unclear. In this study, the absolute and specific enzyme activities of cellobiose hydrolase, β-glucosidase, arylsulfatase, alkaline phosphatase, and urease were measured in soils with 10, 15, 18, 21, and 26 years of organic fertilizer application in contrast to soils without organic fertilizer application. The results showed that long-term organic fertilizer application led to significantly increased in the absolute and specific enzyme activity and decrease in pH, electrical conductivity (EC), exchangeable sodium percentage (ESP), as well as sodium adsorption ratio (SAR5:1). In the structural equation model (SEM), the EC extremely limited the geometric mean of specific enzyme activity per unit of MBC (MBC-GMSEA) (path coefficient, −0.84, p &lt; 0.001). Pearson’s correlation analysis showed that the correlations between EA/MBC and pH, EC, ESP, and SAR5:1 were higher than between the absolute soil enzyme activity and pH, EC, ESP, and SAR5:1. Of the parameters tested, EA/MBC was a more sensitive index to reflect the improvement effect of organic fertilizer on soils and evaluate the saline–alkali barrier.