Long-term Application Of Chemical Fertilizers Research Articles

Comparative growth analysis of Raphanus sativus L. (Radish): effects of vermiwash and vermicompost applications on plant development

Long-term application of chemical fertilizers has negative impacts on soil health, crop productivity, and ecosystems. Hence, organic substrates have been proposed as alternatives for enhancing soil health and plant growth parameters. Among them, vermicompost and vermiwash are widely used in the sustainable agriculture sector to enhance plant growth, yield, and soil fertility. Hence, in this study, we aimed to investigate the effects of vermiwash and vermicompost on the growth of Raphanus sativus L. Pot culture experiments were conducted in four groups which included: group A) control soil (10 kg pot−1), group B) soil (8.5 kg pot−1) + vermicompost (1.5 kg pot−1), group C) soil (10 kg pot−1) + vermiwash (1.5 L pot−1), and group D) soil (8.5 kg pot−1) + vermicompost (1.5 kg pot−1) + vermiwash (1.5 L pot−1), respectively. The results revealed that the plants treated with vermiwash and vermicompost (Group D) had significantly enhanced the growth of the plants with higher germination percentage (100%), number of leaves (32.08%), length of leaves (56.35%), width of leaves (28.05), area of leaves (100.22%), shoot length of plant (78.02%), chlorophyll concentration (42.72%), leaf relative water content (13.30%), fresh weight (65.61%), dry weight of leaves (57.59), and tuber yield (74.96%) when compared to plants under groups A, B, and C. Furthermore, the application of the vermiwash and vermicompost combination improved the soil's physicochemical properties, increased glycine betaine concentrations, and decreased proline accumulation. Hence, this study suggests that vermicompost and vermiwash may be a potential source of plant nutrients for sustainable crop production.

Characteristics of the Soil Microbial Community Structure under Long-Term Chemical Fertilizer Application in Yellow Soil Paddy Fields

To compare the differences in the soil microbial community structure in yellow soil paddy fields after the long-term application of chemical fertilizer, the role and mechanism of chemical fertilizer in maintaining soil microbial diversity were analyzed, and a theoretical basis for fertilization management in farmlands was provided. In this study, long-term experiments were conducted at the Scientific Observation and Experimental Station of the Arable Land Conservation and Agricultural Environment (Guizhou), Ministry of Agriculture and Rural Affairs. Soil samples were collected from five treatments: fertilizer N, P, and K (NPK); fertilizer P and K (PK); fertilizer N and K (NK); fertilizer N and P (NP); and no fertilizer (CK). High-throughput sequencing technology was used to analyze the microbial composition and diversity of the colonies, and the influencing factors are discussed. An analysis of the soil bacterial α diversity indices under the different fertilization treatments revealed that the long-term application of NPK fertilizers had less of an effect on the soil bacterial α diversity indices than did the CK. The long-term application of chemical fertilizers significantly reduced the soil bacterial Chao1, Shannon, and Simpson indices, while there was no significant difference in the bacterial Pielou e index among the treatments. The long-term application of chemical fertilizers significantly increased the soil fungal Chao1 index, but the effects on the other indices were not significant (p < 0.05). An analysis of the bacterial and fungal species under different fertilization treatments showed found that compared with CK, the long-term application of chemical fertilizer increased the relative abundance of Proteobacteria to varying degrees while reducing the relative abundance of Chloroflexi. The impact of other phyla was relatively small, and the difference in the relative abundance of fungi was not significant (p < 0.05). Principal component analysis revealed that, at the genus level, the bacterial and fungal community structures in the CK and NK treatments were relatively independent, while those in the NPK, PK, and NP treatments were similar. Random forest analysis revealed that OM, TP, and TK are the dominant factors that affect soil bacteria α diversity. The dominant factors affecting fungi α diversity are pH, OM, and AK. Redundancy analysis indicated that AK and TP were the main factors affecting bacterial community structure, while AP, AK, and pH were the main factors affecting fungal community structure. The conclusion drawn from this study is that the long-term application of nitrogen, phosphorus, and potassium fertilizer; phosphorus and potassium fertilizer; and nitrogen and phosphorus fertilizer can improve soil fertility, alter the soil environment, enhance microbial diversity, and improve the microbial community structure in yellow soil paddy fields, promoting soil ecosystem stability and health.

Direct nitrous oxide emissions from a crop rotation of maize and mung bean after different long-term fertilizer applications in Thailand

Nitrous oxide (N2O) is a greenhouse gas primarily released by fertilizers used in crop cultivation. In Thailand, cropland occupies the majority of the arable land but studies on N2O emissions from cropland remain scarce. The present study aimed to evaluate the N2O emissions, soil characteristics, and crop productivity resulting from different long-term fertilizer applications in a crop rotation of maize and mung bean. A long-term experimental field managed through crop residue incorporation combined with different fertilizer applications over 45 years was utilized in this study. It consisted of four distinct treatments: no fertilizer (CON), 134 kg N ha−1 from organic fertilizer (ORG), 188 kg N ha−1 from chemical fertilizer (CHE), and 322 kg N ha−1 from a combination of organic and chemical fertilizers (OAC). Long-term application of chemical fertilizer induced soil acidification, whereas the use of organic fertilizer maintained soil pH and enhanced soil carbon accumulation. Results showed that the OAC, CHE, and ORG practices significantly (p < 0.05) increased direct N2O emissions from the soil, particularly during the maize cultivation period. Annual cumulative N2O emissions were enhanced on average by 204 % (3.22 kg N2O ha−1) in OAC, 181 % (2.98 kg N2O ha−1) in CHE, and 79.4 % (1.90 kg N2O ha−1) in ORG compared with CON (1.06 kg N2O ha−1), indicating that larger N input rates induced larger N2O emissions. Chemical fertilizer induced significantly (p < 0.05) larger and faster N2O emissions than organic fertilizer. When considering N2O emissions per N application rate in all treatments as the emission factor, the use of N fertilizers combined with crop residues in the soil over two years averaged 0.61 % (± 0.13 %). This value was approximately 39 % lower than the default value recommended by the Intergovernmental Panel on Climate Change, which is currently used in Thailand. The consecutive addition of fertilizers significantly (p < 0.05) increased maize grain yield compared with the CON. However, no significant differences were observed among the various fertilizer treatments. Despite all fertilizer applications induced larger N2O emissions, they also produced greater crop yields. Consequently, this study recommended the practice of ORG as a means to mitigate emissions without compromising crop yield and soil quality.

Effect of Application Rates of N and P Fertilizers on Soil Nematode Community Structure in Mollisols

Long-term application of chemical fertilizer poses an environmental threat to belowground ecosystems. However, the impact of nitrogen (N) or phosphorus (P) fertilizers on soil biodiversity and the conditions of soil food web remains largely unknown. Soil nematodes are the most abundant multicellular soil animals and serve as excellent bioindicators of soil. Here, we investigated soil nematode communities and food web structure in a long-term experiment with different application rates of N and P fertilizers in northeast China. The application of N and P fertilizers increased the abundance of bacterivores but suppressed the abundance of omnivores and predators. The abundance of bacterivores exhibited an increasing trend, while that of omnivores and predators showed a decreasing trend with increasing rates of N and P fertilizers. Plant parasites displayed a decreasing trend in response to N fertilizer, but not to P fertilizer. N and P fertilizers also altered nematode functional guild composition, with N fertilizer increasing the abundance of Ba1, and P fertilizer increasing the abundance of Fu2 and Ba3. Nonmetric multidimensional scaling (NMDS) analysis revealed apparent successions of nematode communities from no fertilizer soils to high rates of N or P fertilizer soils at both the genus and functional guild levels. Furthermore, N and P fertilizers resulted in different nematode communities. In terms of nematode food web indices, N fertilizer increased the enrichment index (EI) but reduced the channel index (CI) and structure index (SI), whereas P fertilizer only reduced the SI value. High rates of N and P fertilizers increased the respired carbon of bacterivores but reduced the respired carbon of predators. Mantel tests revealed significant correlations between soil properties and the community composition of both fungivores and omnivores. Among all soil properties, available phosphorus (AP) had the greatest influence on the community structure of soil nematodes. Our findings indicate that N fertilizer has a powerful effect on nematode food web structure, while P fertilizer exerts a stronger effect on soil nematode community composition.

Plant Growth Promoting Endophytic Microorganisms from Orchids for A Sustainable Agriculture

Conventional agriculture practice has heavily relied on chemical fertilizers to increase crop yield. However, long-term application of chemical fertilizers carries tremendous negative impact on the environment and is unsustainable. Hence, the search for an alternative source of fertilizers is required. Orchids are flowers and can be found in tropical countries. The growth and development of orchids are closely tied to the presence of plant growth promoting endophytic microorganisms (PGPM). PGPM harbours various beneficial traits such as potassium and phosphorus solubilization and indole acetic acid and siderophore production which enhance and support plant growth and development. This review article showed that PGPM isolated from orchids could be utilized in conventional agriculture to reduce dependency on chemical fertilizer.

Soil properties and microbial functional attributes drive the response of soil multifunctionality to long-term fertilization management

Fertilization is a vital management practice to improve soil fertility and promote agricultural production. However, there is limited knowledge about the interactive effects between soil abiotic and biotic factors and soil multifunctionality after long-term fertilization. There has been little research on determining whether the application of organic fertilizers can improve the functional potential of microorganisms to maintain multifunctional stability. In this study, we integrated soil physicochemical properties, extracellular enzyme activities, bacterial community characteristics, and the abundance of functional genes related to carbon (C) and nitrogen (N) cycling to evaluate the mechanism of soil functional potential response to 13 years of fertilization management. Four treatments were compared, including no fertilizer (CK), conventional fertilization (CF), formulated fertilization by soil testing (SF), SF with organic fertilizer (SFO). The addition of organic fertilizer enhanced the soil electrical conductivity, N-cycling enzyme activities, contents of macroaggregate and associated C, and soil nutrients, while decreasing the content of microaggregates compared with other treatments. The co-application of chemical and organic fertilizer led to significant increases in soil multifunctionality and the bacterial Shannon index compared with the CK and CF treatments. Soil abiotic factors are the key predictors for shaping soil multifunctionality. The addition of organic fertilizer could increase the abundance of functional genes related to C- and N-cycling mediated by the contents of nutrients and the aggregates associated with nutrients. Additionally, treatment with organic fertilizer can mitigate the decrease in genes for C-cycling function caused by the long-term application of chemical fertilizer (SF). In addition, the structural equation models revealed that the fertilization positively affected soil multifunctionality indirectly by changing the bacterial diversity and community composition, as well as the functional potential related to N-cycling. Overall, soil properties and microbial functional attributes jointly drive the response of soil multifunctionality to long-term fertilization management. These results suggest that the combination of organic and chemical fertilizer is worth popularizing to improve multifunctionality and its stability to maintain agricultural sustainability.

Effects of Long-Term Straw Returning and Nitrogen Fertilizer Reduction on Soil Microbial Diversity in Black Soil in Northeast China

Returning straw to the field, coupled with fertilizer application, is an effective means to improve the fertility of black soil in Northeast China. Previous studies have mainly focused on the physical and chemical properties of soil structure and fertility. However, few efforts have been made to study the impact of straw returning on the microbial community of black soil in Northeast China. Here, we studied the typical northeast black soil in Heilongjiang Province to characterize the effects of long-term chemical fertilizer application and straw returning on its bacterial community structure. High-throughput sequencing was conducted to characterize the bacterial community of northeast black soil under different agricultural fertilization treatments, and the main factors affecting the bacterial community of northeast black soil were revealed through bioinformatic analyses. The results of high-throughput sequencing analyses demonstrated that the main bacterial phyla in the black soil in Northeast China were Actinomycetes, Proteobacteria, Acidobacteria, Chloroflexus, and Bacteroidetes. Long-term application of chemical fertilizers significantly increased the fertility and crop yield of black soil in Northeast China but led to significant changes in bacterial community structure and a significant decrease in diversity. Although straw returning improved soil fertility, it did not alleviate the adverse effects of the long-term application of chemical fertilizers on soil bacterial communities. Furthermore, our results demonstrated that changes in soil pH were the main factor leading to variations in soil bacterial communities. Returning straw to the field based on fertilizer application can improve black soil fertility in Northeast China but fails to alleviate the adverse effects of fertilizer-induced soil acidification on the composition and diversity of soil bacterial communities. This suggests that returning straw to the field may not have a significant beneficial impact on the microbial ecology of the black soil of Northeast China. Therefore, further research is needed to establish new straw return strategies to maximize agricultural yields while minimizing ecological impacts.

Influence of long-term fertilization on soil aggregates stability and organic carbon occurrence characteristics in karst yellow soil of Southwest China.

Current research has long focused on soil organic carbon and soil aggregates stability. However, the effects of different long-term fertilization on the composition of yellow soil aggregates and the characteristics of the occurrence of organic carbon in the karst region of Southwest China are still unclear. Based on a 25-year long-term located experiment on yellow soil, soil samples from the 0-20 cm soil layer were collected and treated with different fertilizers (CK: unfertilized control; NPK: chemical fertilizer; 1/4 M + 3/4 NP: 25% chemical fertilizer replaced by 25% organic fertilizer; 1/2 M + 1/2 NP: 50% chemical fertilizer replaced by organic fertilizer; and M: organic fertilizer). In water-stable aggregates, soil aggregates stability, total organic carbon (TOC), easily oxidized organic carbon (EOC), carbon preservation capacity (CPC), and carbon pool management index (CPMI) were analyzed. The findings demonstrated that the order of the average weight diameter (MWD), geometric mean diameter (GWD), and macro-aggregate content (R0.25) of stable water aggregates was M > CK > 1/2M +1/2NP > 1/4M +3/4NP> NPK. The MWD, GWD, and R0.25 of NPK treatment significantly decreased by 32.6%, 43.2%, and 7.0 percentage points, respectively, compared to CK treatment. The order of TOC and EOC content in aggregates of different particle sizes was M > 1/2M +1/2NP > 1/4M +3/4NP> CK > NPK, and it increased as the rate of organic fertilizer increased. In macro-aggregates and bulk soil, the CPC of TOC (TOPC) and EOC (EOPC), as well as CPMI, were arranged as M > 1/2M +1/2NP > 1/4M +3/4NP> CK > NPK, but the opposite was true for micro-aggregates. In bulk soil treated with organic fertilizer, the TOPC, EOPC, and CPMI significantly increased by 27.4%-53.8%, 29.7%-78.1%, 29.7-82.2 percentage points, respectively, compared to NPK treatment. Redundancy analysis and stepwise regression analysis show that TOC was the main physical and chemical factor affecting the aggregates stability, and the TOPC in micro-aggregates has the most direct impact. In conclusion, the primary cause of the decrease in SOC caused by the long-term application of chemical fertilizer was the loss of organic carbon in macro-aggregates. An essential method to increase soil nutrient supply and improve yellow soil productivity was to apply an organic fertilizer to increase aggregates stability, storage and activity of SOC in macro-aggregates.

Effects of Combined Application of Chemical Fertilizer and Biochar on Soil Physio-Biochemical Properties and Maize Yield

Excessive, long-term chemical fertilizer application adversely affects soil quality and maize yield. The combined application of biochar with chemical fertilizer can increase maize yield and improve soil fertility. A four-year field experiment was conducted to determine soil physio-biochemical properties and maize yield under a soybean–maize rotation in the black soils of Northeast China. There were five treatments, including no fertilization (CK), fertilizer (NPK), fertilizer + biochar (15.75 t·hm−2, BC1), fertilizer + biochar (31.50 t·hm−2, BC2), and fertilizer + biochar (47.25 t·hm−2, BC3). Compared with CK, the number of macroaggregates and the average weight diameter of soil aggregates in BC2 treatment increased significantly by 10.3% and 24.5%, respectively. The soil pH in the study area was 7.03, and it increased in all treatments except for BC1. The highest pH of 7.17 was recorded in NPK and BC2 treatments, which was around the optimal soil pH. In contrast to the CK and NPK treatments, the biochar application increased soil organic carbon (SOC) and total nitrogen (TN) content. The BC2 treatment improved soil C/N and increased the copy number of soil bacteria by 25.6% compared to CK. The combined application of chemical fertilizer and biochar was better than NPK treatment alone, and improved soil mechanical composition and fine soil particle contents (powder and clay). Mixed biochar with chemical fertilizer application also significantly increased maize yield and the weight of 100 grains increased from 9.5% to 10.9% compared to CK. The maize yield of the three fertilizer and biochar treatments was higher than treatments with applied chemical fertilizer alone, in the order of BC2 &gt; BC3 &gt; BC1 &gt; NPK &gt; CK (BC2 treatment increased by 34.8%). Additionally, the maize yield was significantly and positively correlated with soil aggregates, organic carbon and total nitrogen (p &lt; 0.05) as well as the 100-grain weight (p &lt; 0.01). The application of 31.50 t·hm−2 (BC2 treatment) of biochar can enhance soil physicochemical properties and improve maize yield.

Effects of long-term organic fertilizer substitutions on soil nitrous oxide emissions and nitrogen cycling gene abundance in a greenhouse vegetable field

Intensive vegetable fields, characterized by extremely high nitrogen (N) application rates, emit a large amount of the potent greenhouse gas nitrous oxide (N2O). Short-term substitution of organic fertilizers for chemical fertilizers may mitigate N2O emissions from vegetable fields. However, the long-term impacts, particularly on soil background N2O emissions (excluding effects caused by newly applied fertilizers) in vegetable fields, remain poorly elucidated. Thus, we conducted an 11-year experiment to investigate the long-term fertilization effects on soil background N2O emissions and the abundance of N-cycling genes in a greenhouse vegetable field. The soil capacity for potential denitrification activity (PDA) was further measured to evaluate denitrification potential. The field experiment comprised of four treatments: no fertilization (control, CK), only chemical N fertilizers (CF), 50 % of chemical N fertilizers substituted by organic fertilizers (OL), and 87.5 % of chemical fertilizers substituted by organic fertilizers (OH). The long-term application of chemical fertilizers alone (CF) and organic fertilizer substitutions (OL and OH) increased soil background N2O emissions 30-fold and 10-fold, respectively, with average N2O fluxes of 1.2 ± 3.8, 33.8 ± 5.1, 9.4 ± 2.3 and 10.2 ± 2.7 μg N2O-N m−2 h−1 in the CK, CF, OL and OH treatment, respectively. The CF treatment significantly decreased the abundance of AOA amoA, nirS and nosZ genes, while both the OL and OH treatments increased the abundance of AOB amoA, and the OH treatment also increased nosZ gene abundance. Soil pH was a key determinant of the contrasting responses of N-cycling genes to different fertilizer types. Compared with low fertilizer substitutions (OL), high organic fertilizer substitutions (OH) did not result in more soil background N2O emissions, despite higher potential denitrification activities and soil total N contents. This was due to increased abundance of nosZ gene and likely enhanced N2O consumption activities. Soil NO3−-N concentrations, soil pH, and the abundance of nosZ gene were three main factors in controlling the responses of soil background N2O emissions to long-term fertilization. Overall, this study suggests that in the long-term perspective organic fertilizer substitution is a beneficial practice to mitigate N2O emissions from intensive greenhouse vegetable cropping systems.

Long-term combined organic manure and chemical fertilizer application enhances aggregate-associated C and N storage in an agricultural Udalfs soil.

Little information is known on whether carbon (C) and nitrogen (N) immobilization is synchronized in different sizes of aggregates under different agricultural management practices. Carbon and N concentrations and the C/N ratios in different sizes of aggregates down to 40 cm depth were determined after long-term application of chemical fertilizers combined with manure or without manure in a wheat-rice cropping system. Manure application usually produced significantly (P < 0.05) higher C and N concentrations and lower C/N ratios in bulk soil and in different sizes of aggregates down to 20 cm depth than the other treatments, and the 1.5 MNPK treatment at 0-10 cm depth had the highest SOC concentration of 26.3 g/kg. The C and N concentrations in bulk soil and all aggregate fractions decreased markedly with increasing soil depth. Among water stable aggregates in all soil depths, the highest C (48.2-66.4%) and N (47.8-68.3%) concentrations as a percentage of SOC were found in the small macroaggregates (2000-250 μm, SM). Manure application significantly (P < 0.05) increased the mass and C and N concentrations of SM and SM fractions down to 20 depth. The mean C/N ratios of silt-clay within large and small macroaggregates (inter-SC) were 1.57 and 1.46 units lower than those of silt-clay particles, respectively, indicating that inter-SC had relative high N availability. Moreover, the C and N content of SM down to 40 cm depth tended to saturation with increasing C input rate. Overall, manure application effectively improved soil structure, SM were the dominant particles involved in soil C and N storage, and inter-SC were the main particles responsible for N availability.

The Use of Raw Poultry Waste as Soil Amendment Under Field Conditions Caused a Loss of Bacterial Genetic Diversity Together with an Increment of Eutrophic Risk and Phytotoxic Effects.

Poultry waste has been used as fertilizer to avoid soil degradation caused by the long-term application of chemical fertilizer. However, few studies have evaluated field conditions where livestock wastes have been used for extended periods of time. In this study, physicochemical parameters, metabarcoding of the 16S rRNA gene, and ecotoxicity indexes were used for the characterization of chicken manure and poultry litter to examine the effect of their application to agricultural soils for 10years. Poultry wastes showed high concentrations of nutrients and increased electrical conductivity leading to phytotoxic effects on seeds. The bacterial communities were dominated by typical members of the gastrointestinal tract, noting the presence of pathogenic bacteria. Soils subjected to poultry manure applications showed statistically higher values of total and extractable phosphorous, increasing the risk of eutrophication. Moreover, while the soil bacterial community remained dominated by the ones related to the biogeochemical cycles of nutrients and plant growth promotion, losses of alpha diversity were observed on treated soils. Altogether, our work would contribute to understand the effects of common local agricultural practices and support the adoption of the waste treatment process in compliance with environmental sustainability guidelines.

Effects of Chlorella extracts on growth of Capsicum annuum L. seedlings

The long-term application of chemical fertilizers has caused to the farmland soil compaction, water pollution, and reduced the quality of vegetable to some extent. So, its become a trend in agriculture to find new bio-fertilizers. Chlorella extract is rich in amino acids, peptides, nucleic acids, growth hormones, potassium, calcium, magnesium, iron, zinc ions, vitamin E, B1, B2, C, B6, folic acid, free biotin and chlorophyll. Chlorella extract can promote biological growth, mainly by stimulating the speed of cell division, thereby accelerating the proliferation rate of cells and playing a role in promoting plant growth. Whether Chlorella extract can be used to improve the growth of pepper (Capsicum annuum), needs to be verified. In current study, a pepper variety 'Chao Tian Jiao' was used as experiment material, by determining the changes of the related characteristics after spraying the seedlings with Chlorella extract, and its effect on growth of Capsicum annuum plants was investigated. The results showed that the Chlorella extract significantly increased plant height of pepper seedlings (treatment: 32.2 ± 0.3 cm; control: 24.2 ± 0.2 cm), stem diameter (treatment: 0.57 ± 0.02 cm; control: 0.41 ± 0.03 cm) and leaf area (treatment: 189.6 ± 3.2 cm2; control: 145.8 ± 2.5 cm2). Particularly, the pepper seedlings treated with Chlorella extract, developed the root system in better way, significantly increased the chlorophyll a, and the activities of SOD, POD and CAT enzymes were also improved significantly. Based on our results, we can speculate that it is possible to improve the growth of Capsicum annuum seedlings and reduce the application of chemical fertilizers in pepper production by using Chlorella extract.

Long-term fertilization altered microbial community structure in an aeolian sandy soil in northeast China.

Soil microorganisms play crucial roles in nutrient cycling and determining soil quality and fertility; thus, they are important for agricultural production. However, the impacts of long-term fertilization on soil microbial community remain ambiguous due to inconsistent results from different studies. The objective of this study was to characterize changes in bacterial and fungal diversity and community structures after 12 years of different fertilization in aeolian sandy soil by analyzing 16S rRNA and ITS rRNA gene sequences and the soil properties to discover the driving factors. Eight different fertilizer treatments have been set up since 2009: no fertilizer (CK), chemical N fertilizer (N), chemical N and P fertilizer (NP), chemical N, P and K fertilizer (NPK), pig manure only (M), pig manure plus chemical N fertilizer (MN), pig manure plus chemical N and P fertilizer (MNP), pig manure plus chemical N, P, and K fertilizer (MNPK). The results indicated that the long-term application of chemical fertilizer reduced soil pH, whereas the addition of pig manure alleviated a decrease in soil pH value. Chemical fertilizer plus pig manure significantly improved soil available nutrients and soil organic carbon. Long-term MNPK fertilization resulted in changes in bacterial diversity due to effects on specific bacterial species; by contrast, all fertilization treatments resulted in changes in fungal diversity due to changes in soil properties. Principal component analysis indicated that fertilization had a significant effect on soil microbial community structure, and the effect of chemical fertilizer combined with pig manure was greater than that of chemical fertilizer alone. Soil available phosphorus, total phosphorus, and pH were the most important factors that influenced bacterial taxa, whereas soil pH, total phosphorus, organic carbon, ammonium nitrogen and nitrate nitrogen were the most important factors influencing fungal taxa after 12 years of fertilization in aeolian sandy soil.

Short-term application of chicken manure under different nitrogen rates alters structure and co-occurrence pattern but not diversity of soil microbial community in wheat field.

Manure application is an effective way to improve the utilization efficiency of organic resources and alleviate the adverse effects of long-term application of chemical fertilizers. However, the impact of applying manure under different nitrogen rates on soil microbial community in wheat field remains unclear. Treatments with and without chicken manure application under three nitrogen rates (N 135, 180 and 225 kg⋅hm–2) were set in wheat field. Soil organic carbon, available nutrients, and abundance, diversity, structure and co-occurrence pattern of soil microbial community at wheat maturity were investigated. Compared with no manure application, chicken manure application increased the soil organic carbon and available phosphorus, while the effects on soil mineral nitrogen and available potassium varied with different nitrogen rates. Chicken manure application significantly increased soil bacterial abundance under the nitrogen fertilization of 135 and 225 kg⋅hm–2, increased soil fungal abundance under the nitrogen fertilization of 135 kg⋅hm–2, but decreased soil fungal abundance under the nitrogen fertilization of 180 and 225 kg⋅hm–2 (P < 0.05). There was no significant difference in alpha diversity indices of soil microbial communities between treatments with and without chicken manure application under different nitrogen rates (P > 0.05). Chicken manure application and its interaction with nitrogen rate significantly changed soil bacterial and fungal community structures (P < 0.05). There were significantly different taxa of soil microbial communities between treatments with and without chicken manure application. Chicken manure application reduced the ecological network complexity of soil bacterial community and increased that of soil fungal community. In summary, the responses of soil available nutrients and microbial abundance to applying chicken manure varied with different nitrogen rates. One growing season application of chicken manure was sufficient to alter the soil microbial community structure, composition and co-occurrence pattern, whereas not significantly affected soil microbial community diversity.

Root-Derived Endophytic Diazotrophic Bacteria Pantoea cypripedii AF1 and Kosakonia arachidis EF1 Promote Nitrogen Assimilation and Growth in Sugarcane.

Excessive, long-term application of chemical fertilizers in sugarcane crops disrupts soil microbial flora and causes environmental pollution and yield decline. The role of endophytic bacteria in improving crop production is now well-documented. In this study, we have isolated and identified several endophytic bacterial strains from the root tissues of five sugarcane species. Among them, eleven Gram-negative isolates were selected and screened for plant growth-promoting characteristics, i.e., production of siderophores, indole-3-acetic acid (IAA), ammonia, hydrogen cyanide (HCN), and hydrolytic enzymes, phosphorus solubilization, antifungal activity against plant pathogens, nitrogen-fixation, 1-aminocyclopropane-1-carboxylic acid deaminase activity, and improving tolerance to different abiotic stresses. These isolates had nifH (11 isolates), acdS (8 isolates), and HCN (11 isolates) genes involved in N-fixation, stress tolerance, and pathogen biocontrol, respectively. Two isolates Pantoea cypripedii AF1and Kosakonia arachidis EF1 were the most potent strains and they colonized and grew in sugarcane plants. Both strains readily colonized the leading Chinese sugarcane variety GT42 and significantly increased the activity of nitrogen assimilation enzymes (glutamine synthetase, NADH glutamate dehydrogenase, and nitrate reductase), chitinase, and endo-glucanase and the content of phytohormones gibberellic acid, indole-3-acetic acid, and abscisic acid. The gene expression analysis of GT42 inoculated with isolates of P. cypripedii AF1 or K. arachidis EF1 showed increased activity of nifH and nitrogen assimilation genes. Also, the inoculated diazotrophs significantly increased plant nitrogen content, which was corroborated by the 15N isotope dilution analysis. Collectively, these findings suggest that P. cypripedii and K. arachidis are beneficial endophytes that could be used as a biofertilizer to improve plant nitrogen nutrition and growth of sugarcane. To the best of our knowledge, this is the first report of sugarcane growth enhancement and nitrogen fixation by Gram-negative sugarcane root-associated endophytic bacteria P. cypripedii and K. arachidis. These strains have the potential to be utilized as sugarcane biofertilizers, thus reducing nitrogen fertilizer use and improving disease management.

Green manure incorporation accelerates enzyme activity, plant growth, and changes in the fungal community of soil.

Green manure can sustain agricultural production, preserve biodiversity, and mitigate soil degradation caused by long-term application of chemical fertilizers. Moreover, the application of green manure can improve soil health through increased soil biological activities. Nevertheless, little attention has been paid to the effects of leguminous and non-leguminous plants on phosphorus- and carbon-related enzyme activities and fungal community composition in soil. In this study, a pot experiment was carried out to elucidate the effects of two green manures on plant growth promoting potential, phosphorus- and carbon-related enzyme activities, and soil fungal community composition. Two green manure treatments (Brassica juncea and hairy vetch), poultry compost and control (no amendment) were applied and soil samples were collected after incorporation of green manure and after plant harvest. The results revealed that plant growth with hairy vetch was significantly higher than that with B. juncea and poultry compost, and soil enzyme activities were markedly higher with hairy vetch than with B. juncea. Both green manure amendments altered the soil fungal community composition. It is possible that the incorporation of green manure into soil and their mineralization and decomposition were controlled by the carbon: nitrogen ratio of the manures and that these manures were easily degradable by soil fungi. In particular, the incorporation of leguminous (hairy vetch) green manure with a low carbon: nitrogen ratio resulted in better plant growth through fast mineralization. Our findings suggest that green manure incorporation is an effective practice and provides substantial benefits to the soil-plant system.

Mitigation of soil acidification in orchards: A case study to alleviate early defoliation in pear (Pyrus pyrifolia) trees

Long-term application of chemical fertilizers has aggravated red soil acidification and caused severe early defoliation in pear-growing region of southern China. To investigate the effects of BIO and HA on the growth and activity of fine roots, and in turn the effect on leaf nutrient status and early defoliation of pear trees, we conducted a 2-year pot experiment (2018–2019) using 1-year-old pear (Pyrus pyrifolia) seedlings in a pear orchard in southern China. Four fertilization treatments were included: chemical fertilizer as control (CF), CF with humic acid (CF-HA), BIO, and BIO mixed with HA (BIO-HA). Results showed that BIO and BIO-HA treatments significantly decreased the early defoliation rate of pear trees about 18%–27% compared with CF and CF-HA treatments. For the growth status of the aboveground, the relative growth rate of pear trees treated by BIO and BIO-HA was 1.2 times higher than the CF treatment at 180 days after budding, and it was accompanied by an increase of leaf thickness, microelements content (e.g. calcium, manganese, iron and zinc), and a decrease of leaf temperature. Compared with CF treatment, BIO or BIO-HA significantly improved soil pH value by 0.9–1.1 units, and increased soil exchangeable calcium content by 50%–83%. BIO and BIO-HA treatments also significantly increased total lateral root number, length and root activity, which were negatively correlated with the early defoliation rate by the network analysis. Furthermore, structural equation model showed that root traits were the core factor to alleviate the early defoliation rate, which was directly or indirectly driven by the application of bioorganic fertilizer. In conclusion, BIO or BIO combined with HA can alleviate the early defoliation rate of pear trees by mitigating soil acidification to stimulate the lateral root growth and activity, and in turn increase leaf micronutrients content and aboveground growth. Our study shows that measuring root traits are at the core of plant responses to soil nutrient status and pH.

Organic manure rather than phosphorus fertilization primarily determined asymbiotic nitrogen fixation rate and the stability of diazotrophic community in an upland red soil

Biological nitrogen fixation (BNF) plays a vital role in nitrogen supply in agricultural ecosystem but is generally impaired by agricultural fertilization. Understanding the trade-off between fertilization and BNF, and the underlying mechanisms are essential to optimize fertilization management for sustainable agriculture production. In this study, we examined the potential rate of asymbiotic N2 fixation, nifH gene abundance, the composition and co-occurrence network of diazotrophic community in an acidic red soil received different organic and inorganic fertilization regimes for more than 40 years. Our results showed that long-term chemical fertilizer application drastically decreased soil microbial biomass, nitrogenase activity and nifH gene abundance in comparison to the unfertilized control. Organic manure application showed significantly positive effect on soil nitrogenase activity and crop yield via regulating soil pH and the key ecological cluster of diazotrophic community (module #2 which was mainly represented by Bradyrhizobium, Pseudacidovorax and Azospirillum), while phosphorus fertilization showed no obvious promotion effect. Organic manure amendment significantly increased the diversity of diazotrophs and enriched some diazotrophic taxa, particularly Pseudacidovorax and Rhodopseudomonas which were likely responsible for the high N2-fixation potential. The control and organic manure amendment treatments possessed a more complex and stable diazotrophic network than the chemical fertilizer treatments did, which greatly facilitated the resistance of diazotrophic community to environmental stress and thus sustained a high N2 fixation potential. Together, our study demonstrated that organic manure application can effectively alleviate the inhibitory effect of nitrogen fertilization on N2 fixation via regulating soil property and shaping a more stable diazotrophic network.

Effects of Long-Term Application of Chemical Fertilizers and Organic Fertilizers on Heavy Metals and Their Availability in Reddish Paddy Soil

To investigate the effects of long-term fertilization on the accumulation and availability of heavy metals in reddish paddy soil and to analyze the major influencing factors, soil samples were collected after the later rice was harvested in 2018 from a long-term fertilization field experiment that began in 1984. Six treatments were selected, namely CK (control without fertilization), PK (P and K fertilizer), and NPK (N, P, and K fertilizer), and different proportions of organic fertilizer plus chemical fertilizer (M1NPK: 30%M+70%NPK; M2NPK: 50%M+50%NPK; and M3NPK: 70%M+30%NPK), soil chemical properties, total and available heavy metal contents, and the relationships between the available forms of heavy metals and soil chemical parameters and total heavy metals (THM) were analyzed. The results showed that ① long-term fertilization changed the soil chemical properties; compared with those of CK, PK significantly increased the contents of soil available phosphorus (AP) and available potassium (AK), NPK significantly increased the soil organic matter (SOM), cation exchange capacity (CEC), AP, and AK, and the organic fertilizer treatments significantly increased the contents of SOM, CEC, AP, AK, and nitrate (NO3--N). ② There were slight variations in the THM contents under the chemical fertilizer treatments (PK and NPK), whereas the organic fertilizer treatments significantly increased the total contents of Cu, Zn, and Cd. ③ The chemical fertilizer treatments significantly increased the available Cr and As, whereas the organic fertilizer treatments significantly increased the available Cu, Zn, Cr, Cd, As, and Fe. ④ There were significant positive correlations between the available Cu, Zn, Cr, Cd, As, and Fe and the SOM, CEC, AP, and NO3--N. In addition, the available Zn and Cd were significantly positively correlated with the soil pH, whereas the available Pb was significantly negatively correlated with soil pH, SOM, CEC, and NO3--N. ⑤ There were significant positive correlations between the available and total contents of Cu, Zn, and Cd, whereas there were significant negative correlations between the available and total contents of Cr and Fe. ⑥ Redundancy analysis showed that SOM and pH accounted for 80.7% and 5.5% of the variation in THM, whereas the soil CEC, AP, and pH accounted for 81.1%, 4.9%, and 3.3% of the variation in the available heavy metals, respectively. ⑦ The partial least squares path model analysis showed that the path coefficients of the THM, CEC, and AP on the available state of heavy metals were 0.459, 0.417, and 0.293, respectively. Long-term application of organic manure, such as pig manure, significantly improved the soil chemical properties and affected the availability of heavy metals, and soil CEC and AP may play key roles in regulation.