Long-term Chemical Fertilization Research Articles

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

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

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.

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.

Long-Term Chemical Fertilization Drove Beneficial Bacteria for Rice Soil to Move from Bulk Soil to the Rhizosphere

Overuse of chemical fertilizer (CF) causes damage to soil and the environment. To reveal the process of the response of crop rhizospheric and bulk soil fertility and the bacterial community to long-term CF conditions, CF application and nonfertilization (CK, control) treatments were used in a long-term (12-year) fertilization experiment. Long-term CF application significantly increased the soil organic matter, total nitrogen, and available phosphorus contents (p &lt; 0.05), increased the available nitrogen (AN) and potassium (AK) contents to varying degrees, and decreased the soil pH in both rice rhizospheric soil and bulk soil. In addition, the bacterial Shannon and Ace indices in rice rhizospheric soil under the CF treatment were all higher than those under the control (CK) treatment, and the bulk soil bacteria showed the opposite trend. The LEfSe results showed that unidentified_Gammaproteobacteria and Geobacter (genera) were significantly enriched in the rhizospheric and bulk soil of rice under the CK treatment, respectively. Gemmatimonadetes (phylum) and Nitrospirae (phylum) + Thiobacillus (genus) were significantly enriched in the rice rhizospheric and bulk soil under the CF treatment. Only AK and AN had strong positive correlations with soil bacteria. Long-term CF application accelerated the migration of soil bacteria from the bulk soil to the rhizosphere, thus improving soil fertility and nutrient cycling.

Chemical Fertilization Alters Soil Carbon in Paddy Soil through the Interaction of Labile Organic Carbon and Phosphorus Fractions

The influence of long-term chemical fertilization in paddy soils is based on the interaction between labile carbon and phosphorus fractions and the manner in which this influences soil organic carbon (SOC). Four soil depths (0–30 cm) were analyzed in this study. Easily oxidized organic carbon components, such as permanganate oxidized carbon (POXC) and dissolved organic carbon (DOC), and other physicochemical soil factors were evaluated. The correlation and principal component analyses were used to examine the relationship between soil depth and the parameter dataset. The results showed that Fe-P concentrations were greater in the 0–5 cm soil layer. DOC, inorganic phosphate fraction, and other soil physiochemical characteristics interacted more strongly with SOC in the 0–5 cm soil layer, compared to interactions in the 10–15 cm layer, influencing soil acidity. An increase in DOC in the 0–5 cm soil layer had a considerable effect on lowering SOC, consistent with P being positively correlated with POXC, but negatively with SOC and water-soluble carbon (WSC). The changes in SOC could be attributed to the relationship between DOC and inorganic phosphate fractions (such as Fe-P) under specific soil pH conditions. An increase in soil DOC could be caused by changes in the P fraction and pH. The DOC:Avai. P ratio could serve as a compromise for the C and P dynamic indicators. The soil depth interval is a critical element that influences these interactions. Agricultural policy and decision-making may be influenced by the P from chemical fertilization practices, considering the yields and environmental effects.

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.

Long-Term Chemical and Organic Fertilization Differently Affect Soil Aggregates and Associated Carbon and Nitrogen in the Loess Plateau of China

Fertilizer sources may have variable effects on soil aggregation, aggregated-associated C and N, and wheat yield. A 34-year field experiment was performed to evaluate the influences of chemical and organic fertilization on soil aggregates and associated carbon and nitrogen under winter wheat in a Cumulic Haplustoll of the Loess Plateau, China. Treatments included unfertilized control (CK), inorganic N fertilizer (NF), inorganic P fertilizer (PF), inorganic N and P fertilizer (NP), organic manure (M), inorganic N fertilizer plus manure (NM), inorganic P fertilizer plus manure (PM), and inorganic N plus P fertilizers plus manure (NPM). Compared to CK, long-term fertilization significantly increased the proportion of soil macro-aggregates, mean weight diameter (MWD), and geometric mean diameter (GMD), but decreased the proportion of micro-aggregates and fractal dimension, especially fertilizer plus manure. Compared to CK, manure treatments (M, NM, PM, and NPM) had a better improvement on soil organic carbon (SOC), soil total nitrogen (STN), particle organic C, and microbial biomass C in all aggregates than the fertilizer alone. The SOC in different aggregates increased with the increased aggregate size, which was because the larger aggregates formed by the binding of the smaller aggregates and organic matter. PON increased in NM and NPM, and MBN was more sensitive to N fertilizer. The C/N ratio in bulk soil and aggregates decreased with fertilization, especially in fertilizer with manure and in macro-aggregates. The improved soil structure was related to the increased SOC and STN, which was proved by the positive correlations among SOC and STN with macro-aggregates and MWD. A correlation analysis also showed that the contribution rate of SOC and STN in macro-aggregates was positively associated with the macro-aggregate and stability. Therefore, the sequestration of C and N in soil was related to aggregate size and was mainly affected by larger aggregates. The results demonstrated that fertilizer with manure improved the soil structure and fertility better than fertilizer alone, thus increasing crop yield.

Long-term chemical fertilization results in a loss of temporal dynamics of diazotrophic communities in the wheat rhizosphere

Diazotrophs are potential bacterial biofertilizers with efficacy for plant nutrition, which convert atmospheric N2 into plant available nitrogen. Although they are known to respond strongly to fertilization, little is known about the temporal dynamics of diazotrophic communities throughout plant developmental under different fertilization regimes. In this study, we investigated diazotrophic communities in the wheat rhizosphere at four developmental stages under three long-term fertilization regimes: no fertilizer (Control), chemical NPK fertilizer only (NPK), and NPK fertilizer plus cow manure (NPKM). Fertilization regime had greater effect (explained of 54.9 %) on diazotrophic community structure than developmental stage (explained of 4.8 %). NPK fertilization decreased the diazotrophic diversity and abundance to one-third of the Control, although this was largely recovered by the addition of manure. Meanwhile, Control treatment resulted in significant variation in diazotrophic abundance, diversity, and community structure (P = 0.001) depending on the developmental stage, while the NPK fertilization resulted in the loss of temporal dynamics of the diazotrophic community (P = 0.330), which could be largely recovered by the addition of manure (P = 0.011). Keystone species identified in this study were quite different among the four developmental stages under Control and NPKM treatment but were similar among stages under NPK treatment. These findings suggest that long-term chemical fertilization not only reduces diazotrophic diversity and abundance, but also results in a loss of temporal dynamics of rhizosphere diazotrophic communities.

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.

Pathways and Drivers of Gross N Transformation in Different Soil Types under Long-Term Chemical Fertilizer Treatments

Microbial-mediated nitrogen (N) dynamics is not only a key process for crop productivity, but also a driver for N losses. Therefore, a better understanding of N dynamics and controlling factors in different soil types is needed to better manage N fertilization in crop fields. To achieve this, a 15N tracing approach was used to quantify simultaneously occurring N transformation rates in four agricultural trials (&gt;20 years chemical fertilizer application) with contrasting climatic and edaphic types (three upland soils and one paddy soil). The results showed that recalcitrant soil organic carbon (SOC) mineralization was the main source of NH4+ at all the sites, with rates ranging from 0.037 in fluvo-aquic soil to 3.096 mg kg−1 day−1 in paddy red soil. Autotrophic nitrification (ONH4) was the predominant NO3− production mechanism in the black and fluvo-aquic soils, whereas it was negligible in the upland and paddy red soils. Nitrification capacity, as an indicator of nitrate leaching risk, was in the order: upland red soil (1%) &lt; paddy red soil (8%) &lt; black soil (235%) &lt; fluvo-aquic soil (485%), implying a high nitrate leaching risk in the last two soils. However, high microbial immobilization (41%) and abiotic adsorption (6%) decreased NO3− leaching in black soil. The partial least squares path modeling (PLS-PM) showed that SOC, temperature and pH were the main factors controlling nitrate immobilization, N mineralization and nitrification. In summary, even under similar chemical fertilization conditions, N transformation dynamics are expected to differ with respect to soil type. Therefore, N management strategies should be adjusted to soil type to control N losses and increase crop yield.

Effects of Long-Term Chemical and Organic Fertilizer Application on Soil Phosphorus Fractions in Lei Bamboo Plantations

Phosphorus (P) is a key nutrient in forest ecosystems in subtropical regions. However, the effects of the long-term application of organic amendments on P availability are poorly understood. Here, we compared the soil P fractions and associated soil properties in southern Chinese Lei bamboo plantations using both an intensive management system (IMS) and a traditional management system (TMS). The results show that the IMS significantly (p &lt; 0.05) increased the soil total organic carbon (C), soil ammonium N (NH4-N), total P, and available potassium content; microbial biomass C and P content; P activation coefficient, and soil C:P ratios, while significantly (p &lt; 0.05) decreasing pH and microbial C:P. The labile-P-to-total-phosphorus-content ratio increased significantly in the IMS (46%) compared with that in the TMS (32%). The selected soil properties (except nitrate [NO3−N]) were significantly related to soil P fractions (except for concentrated HCl-extracted organic P). The IMS had a higher C:P ratio and labile P content than the TMS, suggesting that the IMS could promote soil P transformation and availability. Overall, the IMS increased soil P availability and supply capacity, and the changes in P forms could be a risk factor for P loss.

Ammonia oxidizing bacteria dominate soil nitrification under different fertilization regimes in black soils of northeast China

Although autotrophic ammonia oxidizing archaea (AOA) and bacteria (AOB) and comammox coexist in soils, their abundances and contributions to nitrification are not well addressed, especially in arable black soils. In this study, using the nitrification inhibitors acetylene and octyne, the contributions to nitrification potential provided by different ammonia oxidizers and heterotrophic nitrifiers in four long-term fertilization treatments, i.e., no fertilization (NoF), manure fertilization (M), chemical fertilization (CF), and chemical fertilization plus manure (CFM), were investigated in samples collected from the northern, middle and southern black soil regions of northeast China. The amoA gene abundances of AOA, AOB, comammox Clade A and comammox Clade B in these soils were quantified by qPCR. The results showed that the amoA gene abundances of the three ammonia oxidizers tended to increase from the northern to southern sites, while the opposite trend was observed in the ratios of AOA/AOB and comammox Clade B/Clade A; the different fertilization treatments significantly influenced the amoA abundances, and the effects varied with the ammonia oxidizers and across the sites. Autotrophic ammonia oxidizers accounted for 62%–100% of the gross soil nitrification potential across all soils. Among them, AOB dominated soil autotrophic nitrification in the fertilized soils, while no fertilization may have increased the nitrification potential provided by AOA plus comammox. Pairwise analysis showed that the amoA gene abundances of AOA and AOB were significantly and positively correlated with their respective nitrification-driven potentials. Correlation heatmaps indicated that soil pH and inorganic nitrogen content were the main soil factors related to nitrification activities and the abundances of the ammonia oxidizers. Our findings highlight that AOB are the dominant ammonia oxidizers contributing to nitrification in arable fertilized black soils, although AOA and comammox are highly abundant.

Soil Organic Carbon Sequestration under Long-Term Chemical and Manure Fertilization in a Cinnamon Soil, Northern China

To mitigate climate change and improve food security, it is essential to understand how fertilizer strategies impact the dynamics of soil organic carbon and its fractions. The soil organic carbon (SOC), light fraction organic carbon (LFOC), and particulate organic carbon (POC) were investigated every five years in a corn (Zea mays L.) cropping system with chemical fertilization and manuring over twenty-four years (1992–2016) in a semiarid area of northern China. There were four treatments with chemical fertilizer (i.e., N1P1, N2P2, N3P3, N4P4), three treatments with chemical fertilizer plus manure (i.e., N2P1M1, N3P2M3, N4P2M2), and one treatment with manure alone (i.e., M6), and an unfertilized treatment (control). The carbon sequestration rate (CSR) and efficiency (CSE) of SOC, POC, and LFOC were identified. The results revealed that the fertilization treatments (N2P2, N3P3, N2P1M1, N3P2M3, N4P2M2, and M6) promoted SOC sequestration, with a sequestration rate of 0.19~1.29 Mg ha−1 y−1. The excess application of chemical fertilizer caused a reduction in POC, whereas the application of NP, NPM or manure resulted in greater POC sequestration in soil, with a carbon sequestration rate of 0.04~0.24 Mg ha−1 y−1. The LFOC stocks were 1.43~2.24 Mg ha−1 under the NP treatments, 2.47~6.68 Mg ha−1 under the NPM treatments and 8.12 Mg ha−1 under the M treatment; these stocks were all higher than that of the control treatment. Different fertilization strategies affected the pools of SOC with different sequestration rates. We found the carbon sequestration rates of SOC and LFOC were logarithmically correlated with the annual carbon input. When the annual C input is approximately 1.39 Mg ha−1 y−1, the SOC level will be maintained; when the annual C input is higher than 0.8 Mg ha−1 y−1, the LFOC level increases. This study describes the relationship between carbon inputs and the SOC(LFOC) sequestration rates under continuous fertilization in arid cropland. The results further evidence that the long-term fertilization of NPM and M increases the potential for SOC sequestration and quantifies the amount of exogenous carbon input required for soil organic matter enhancement.

Metagenomics reveals divergent functional profiles of soil carbon and nitrogen cycling under long-term addition of chemical and organic fertilizers in the black soil region

The long-term effects of different fertilization regimes on the microbial functional potential of soils involving nutrient cycling remain largely unknown. Here, metagenomic sequencing was applied to investigate the influences of long-term chemical and organic fertilization on soil microbial C and N cycling across southern, middle and northern sites of black soil region in Northeast China. The results showed that biogeographic distance induced the most influential on the microbial functional profiles of soil C and N cycling, and significant effects of manure fertilization were detected across three experimental sites. Organic fertilization enriched the relative abundances of Proteobacteria and Planctomycetes that carry C and N cycling genes, while inhibited the growth of oligotrophic groups such as Verrucomicrobia. Chemical fertilization increased the gene abundances involved in methane oxidation, but had little effect on soil C degradation and fixation. Contrarily, manure fertilization, particularly the combination of chemical and organic fertilizers (CFM), significantly decreased the abundance of cooC (reductive acetyl-CoA pathway) and coxS (CO oxidation) while enhanced the abundance of icd (rTCA cycle), which are involved in C fixation. Additionally, chemical fertilization enriched the gene abundance that involved in soil N degradation, nitrification and anammox, whereas manure fertilization was beneficial for the functional potentials of assimilatory and dissimilatory nitrate reductions across the black soils. However, CFM significantly promoted the soil denitrification potential, possibly due to excess N input, which might result in soil N loss via the emission of nitrogenous gas in this region. Furthermore, the substantial enhancement in soil P contents induced by manure addition predominantly affected the C and N cycling profiles, abundance of functional genes and microbial taxa. Moreover, diverse correlations between C and N cycling genes suggested the synergetic or antagonistic interactions of C and N metabolic potentials in the black soils. Overall, this study provided in-depth insights into distinct microbial functional potentials under long-term chemical and organic fertilization that may have predictable consequences for soil nutrient cycling in agroecosystems of black soil region.

Partial substitution of chemical fertilizers with manure alters soil phosphorus fractions and optimizes vegetable production in alkaline soil

ABSTRACT Maintaining phosphorus (P) supply for plants or reducing P mobility is critical to sustainable agricultural production and the environment. However, substituting long-term chemical fertilizer with a fraction of (i.e. partial substitution) manure and its effect on soil P surplus and P fractionation have not been widely studied. An eight-year protected field study with no fertilization (NF), chemical fertilizer substituted with no manure (NS), partial manure (40%, PS), and total manure (100%, TS) combined with multiple P characterization methods were conducted to examine P pools and stability in alkaline soil. NS, PS, and TS have the same input amount of nutrients. It showed that PS treatment lowered the annual P surplus by 6.21% and 11.2% compared with NS and TS, respectively, maintaining optimal P input–output balance and vegetable yields. TS decreased total Po by 31.9% and stable Ca-associated P by 21.1%, while increased labile organic P, compared with NS. The labile P in PS was at a moderate level compared with NS and TS treatments, which not only maintained the soil labile P pools but also reduced P leaching risk. Therefore, partial substitution of chemical fertilizer with manure leads to an optimal level of nutrients for vegetable production.

Influence of different fertilization and chemical recruitment systems on the phosphorus regime of gray forest soil

Phosphorus is extremely important in agriculture. This is due to the fact that without its participation in the plant body does not undergo any biochemical reaction, because it is part of the ATP molecule, which provides energy. It is an essential element of nucleic acids, phospholipids and the others is actively involved in the regulation of enzymatic reactions. It is part of human, animal, plant and bacterial cells. The research was conducted on the basis of a stationary experiment conducted in 1992 on gray forest coarsegrained light loam soil, studied the effect of long-term chemical reclamation and various fertilization systems (mineral, organic, organic-mineral) on the transformation of Optimal phosphorus nutrition promotes the development of the root system, which improves the supply of plants with moisture and nutrients, increases the share of marketable products in the organic crop, increases the starch content in potatoes, sugar in roots, vegetables and fruits, oilseeds, oilseeds the output of a long fiber, its strength increases. That is why the management of phosphorus nutrition of plants is one of the key issues. Changes in various forms of phosphorus (gross, mobile, water-soluble) under the influence of the above factors are analyzed. For a more objective assessment of these factors on the phosphate regime of the soil on the variant results of the analysis were compared not only with absolute control, but also tied to baseline (age of fallow 28 years), located next to the experimental field. It was found that the content of gross phosphorus, which characterizes the genetic characteristics of the soil, depends almost entirely on the total humus reserves and clearly repeats the parameters of the profile accumulation of carbon, taking into account the depth and thickness of humus horizons. The particle size distribution is of great importance in the processes of gross phosphorus accumulation, as defects are quite easily adsorbed on the surface of soil structures. Evaluation of the results of the analysis shows a large gap in the gross forms of phosphorus and low concentration of its mobile forms, the content of which is 4.7% of the total. According to our data, water-soluble salts of phosphoric acid in gray forest soil are generally found in very small quantities (0.62 mg / kg in the horizon NOT with a gradual decline down the profile), which often becomes a limiting factor in phosphorus nutrition of crops. Lime, by reducing the activity of one and a half oxides, weakens the adsorption bonds of phosphorus and increases the relative amounts of calcium phosphates. The application of mineral fertilizers replenished the pool of gross phosphorus (by 0.08% of the control dock), but mobile forms of phosphorus (according to Kirsanov) increased by only 23 mg/kg, which was second only to liming. In general, the effect of liming significantly increases the use of soil phosphates and fertilizers.

PH and ammonium concentration are dominant predictors of the abundance and community composition of comammox bacteria in long-term fertilized Mollisol

The newly-discovered complete ammonia-oxidizing bacteria (comammox) doubts our inherent understanding of nitrification. Herein, we study communities of comammox, ammonia-oxidizing bacteria (AOB) and archaea (AOA) in Mollisol after a 30-year fertilization history with four treatments: chemical nitrogen (N) and potassium (K) fertilizers (NK); chemical N, phosphorus (P), and K fertilizers (NPK); chemical NPK fertilizers plus organic manure (NPKM); and a control without fertilizers (CK). Compared with CK, chemical fertilizer treatments (NK and NPK) significantly reduced AOA amoA gene abundance and increased AOB and comammox amoA gene abundances. The highest values of AOA and AOB amoA gene abundances were found in the NPKM treatment and the highest value of comammox amoA gene abundance was observed in the NK treatment. The application of combined NPK and organic manure (NPKM) significantly increased AOA, AOB, and comammox amoA gene abundances compared to CK. Long-term chemical fertilization decreased the diversity of comammox community; whereas, the application of combined NPK with organic manure (NPKM) restored it to levels comparable to CK. Long-term fertilization management altered the community structure of comammox based on principal coordinate analysis (PCoA). Soil pH and NH4+-N concentration were the key factors affecting soil abundance and community structure of comammox. This study demonstrates the different responses of comammox community and canonical ammonia oxidizers to long-term fertilization practices in Mollisol.

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.

Agricultural management practices influence the soil enzyme activity and bacterial community structure in tea plantations

BackgroundThe soil quality and health of the tea plantations are dependent on agriculture management practices, and long-term chemical fertilizer use is implicated in soil decline. Hence, several sustainable practices are used to improve and maintain the soil quality. Here, in this study, changes in soil properties, enzymatic activity, and dysbiosis in bacterial community composition were compared using three agricultural management practices, namely conventional (CA), sustainable (SA), and transformational agriculture (TA) in the tea plantation during 2016 and 2017 period. Soil samples at two-months intervals were collected and analyzed.ResultsThe results of the enzyme activities revealed that acid phosphatase, arylsulfatase, β-glucosidase, and urease activities differed considerably among the soils representing the three management practices. Combining the redundancy and multiple regression analysis, the change in the arylsulfatase activity was explained by soil pH as a significant predictor in the SA soils. The soil bacterial community was predominated by the phyla Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Bacteroidetes in the soil throughout the sampling period. Higher Alpha diversity scores indicated increased bacterial abundance and diversity in the SA soils. A significant relationship between bacterial richness indices (SOBS, Chao and ACE) and soil pH, K and, P was observed in the SA soils. The diversity indices namely Shannon and Simpson also showed variations, suggesting the shift in the diversity of less abundant and more common species. Furthermore, the agricultural management practices, soil pH fluctuation, and the extractable elements had a greater influence on bacterial structure than that of temporal change.ConclusionsBased on the cross-over analysis of the bacterial composition, enzymatic activity, and soil properties, the relationship between bacterial composition and biologically-driven ecological processes can be identified as indicators of sustainability for the tea plantation.

Changes of acid and alkaline phosphatase activities in long-term chemical fertilization are driven by the similar soil properties and associated microbial community composition in acidic soil

Acid and alkaline phosphatase (ACP and ALP), encoded separately by the bacterial phoC and phoD genes, participate in the mineralization of organic phosphorus (P) to inorganic P. However, the influence of chemical fertilization on soil phosphatase activities and associated bacterial communities in acidic soils remains unclear. Here, we conducted a 27 year continuous chemical fertilization experiment consisting of the no-fertilizer control (CK), N and P fertilizer (NP), N and K fertilizer (NK), P and K fertilizer (PK), and N, P and K fertilizer (NPK) treatments, in order to investigate phosphatase activities and phoC- and phoD-harboring bacterial communities. Results demonstrated that ACP and ALP activities increased significantly in the NP (198.70 and 35.46 μg pNP g−1 soil h−1, respectively) and NPK treatments (199.62 and 36.51 μg pNP g−1 soil h−1, respectively) compared to CK (143.81 and 22.49 μg pNP g−1 soil h−1, respectively), while ALP activity was reduced for the NK treatment (13.86 μg pNP g−1 soil h−1). The abundance and diversity index of phoC- and phoD-harboring bacteria differed among treatments. The two bacterial community structures exhibited similar trends in terms of the significant differences between N-free (CK and PK) and N-containing (NP, NK and NPK) treatments (Adonis, p < 0.01). Random forest model analysis revealed that the variations in ACP and ALP activities can be explained by microbial biomass P (MBP, 9.71% and 13.20%, respectively), soil total carbon (TC, 10.89% and 8.77%, respectively) and available P (AP, 9.10% and 7.15%, respectively), and microbial factors including community composition (5.94% and 4.48%, respectively) and network clustering coefficients (6.05% and 5.15%, respectively). Furthermore, the dominant genera Stenotrophomonas and Variibacter were positively correlated with ACP and ALP activities, respectively, with their members observed as keystone species in the community network. Overall, chemical N and P fertilization was generally observed to improve soil phosphatase activities in acidic soil, with soil TC and AP identified as the primary soil variables affecting phosphatase activities by altering the associated bacterial community composition and increasing MBP. These findings improve the understanding of how fertilization influences the community composition and function of phosphate-solubilizing microorganisms in acidic soils.