Long-term Fertilizer Management Research Articles

Vertical migration and leaching behavior of antibiotic resistance genes in soil during rainfall: Impact by long-term fertilization

The vertical migration and leaching behavior of antibiotic resistance genes (ARGs) during rainfall in soils subjected to long-term fertilization remain largely unclear. In this study, ARGs in vertical profiles (0−60 cm) and leachates from three soils (acidic, neutral, and calcareous) in a long-term (13 years) field fertilization experiment were monitored by high-throughput quantitative PCR after each rainfall event throughout an entire year. The results showed that, compared with unfertilized soils, long-term manure fertilization mainly promoted the vertical migration and leaching of aminoglycoside, beta-lactam, and multidrug resistance genes in the soil profiles. As a result, the annual cumulative loads of ARGs in leachates from the three soils with long-term manure fertilization were significantly increased compared to the controls and were in the order of acidic soil > neutral soil > calcareous soil. SourceTracker analyses revealed that manured soil was the predominant source of the ARGs in the soil leachate samples. Pseudomonas, Anaeromyxobacter, IMCC26256, and MND1 were identified as the dominant potential hosts responsible for the vertical migration and leaching of ARGs in the three soils. PiecewiseSEM analysis further showed that long-term manure fertilization affected the vertical migration of ARGs during rainfall mainly by altering soil properties (i.e., pH, soil organic carbon, and sand). Our results suggest that the ARGs in soils with long-term manure fertilization are a significant potential source of ARG pollution in groundwater, and the measures should be taken to mitigate the vertical migration and leaching of ARGs during rainfall.

The long-term nitrogen fertilizer management strategy based on straw return can improve the productivity of wheat-maize rotation system and reduce carbon emissions by increasing soil carbon and nitrogen sequestration

ProblemFacing the multiple objectives of increasing production, carbon sequestration, and nitrogen reduction in farmland, optimizing straw and nitrogen fertilizer management to achieve a balance between grain production and ecological safety in the wheat-maize rotation system has become increasingly critical and urgent. MethodsThis study conducted a five-year field experiment in the Guanzhong Plain of China from 2017 to 2021 to investigate the effects and synergistic regulatory mechanisms of straw disposal methods (straw return, no-straw return) and nitrogen application rates (0, 150, 225, 300 kg ha−1) during the maize season on soil greenhouse gas (GHG) emissions, crop yield, and soil organic carbon (SOC) and soil toatl nitrogen (STN) content. ResultsThe results showed that under the scenario of no-straw return, fertilization increased soil nitrous oxide (N2O) emissions by 35.9–64.0 %, and annual total crop yield by 16.4–22.8 %; however, under the straw return scenario, the increase in soil N2O emissions due to fertilization decreased to 26.7–62.0 %, while the yield increase rose to 19.5–25.9 %. The interaction effect between straw return and nitrogen application was significant, with straw return boosting the contribution rate of nitrogen application to yield (2.2–4.4 %) and simultaneously reducing the contribution rate of nitrogen application to N2O emissions (3.0–27.5 %). The study also indicated that the yield-increasing effect of straw return continued to increase with the duration of straw return, with the contribution rate to yield reaching 9.9 % after three years of continuous straw return, while the contribution rate of nitrogen application to yield increased by an average of 3.0 % per year. This suggests that there is significant potential for coupling straw return with reduced nitrogen application. Straw return combined with nitrogen fertilizer increased SOC content by 7.9–40.1 % and 3.7–12.5 %, STN content by 1.0–22.8 % and 6.1–13.9 %, respectively, compared to sole nitrogen application and sole straw return. Pathway analysis indicated that straw return combined with nitrogen fertilizer mainly enhanced soil carbon-nitrogen sequestration, improved fertilizer utilization efficiency and crop nutrition levels, reduced net global warming potential (GWP) and greenhouse gas intensity (GHGI), and synergistically regulated to increase yield while reducing GHG emissions. ConclusionThe study highlights that straw return lowers the threshold for nitrogen application levels, suggesting that regulating nitrogen application levels between 224 and 256 kg ha−1 during the maize season, and maintaining a nitrogen application level of 195 kg ha−1 during the wheat season, is beneficial for long-term stable production and emission reduction in the wheat-maize rotation system farmland.

Assessing the Alteration of Soil Quality under Long-Term Fertilization Management in Farmland Soil: Integrating a Minimum Data Set and Developing New Biological Indicators

The key role of soil quality improvement in achieving sustainable agricultural development based on highly intensive use of farmland is increasingly being recognized, as is the ponderance of suitable evaluation of the soil quality. The overarching goal of this study was to determine an accurate assessment framework by the comparison of the scoring function (linear and non-linear) and integration method (area and weighted additive), which integrally evaluates the soil quality of an eleven-year field fertilization experiment (including CK, no fertilizer; CF, conventional fertilization; SF, formulated fertilization; SFO, SF with organic fertilizer). Thirty-three properties, including eighteen physiochemical-related and fifteen biological-related properties, associated with soil functions were measured as potential soil quality indicators, and the soil multifunctionality (SMF) was applied to validate the soil quality indices (SQIs). Principal component analysis and relationship analysis were used with indicators sensitive to management to determine a minimum data set (MDS). The results showed that the electrical conductivity, large macroaggregate-associated total nitrogen, small macroaggregate-associated organic carbon, carbon fixation, and enzyme activities of phenol oxidase and cellulase were chosen as the MDS. All the SQIs were significantly correlated with the SMF (p < 0.05). The fertilization strategies affected most indicators in different ways, and the index developed using the non-linear function and weighted additive integration method (SQI-NL) had the best sensibility and discriminability. The SQI value with the SQI-NL-MDS method was higher following the fertilization treatments than that of no fertilizer (p < 0.05), and the treatment of the organic fertilizer had the highest SQI value (0.66). Soil quality evaluation in long-term fertilized farmland suggested that the soil quality constraints between treatments of synthetic and organic fertilizer are related to the soil functions of nutrient cycling and sustain biological activity due to their higher contribution rates to the SQI in the organic fertilizer treatment, which provides insights into ways to reduce the gap in soil quality. The framework method can provide an accurate quantitative tool for the evaluation of soil quality from the target indicators by bridging management objectives and field-level actions.

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.

Active role of iron-dependent AOM in paddy fields under different long-term fertilizer management schemes

Iron-dependent anaerobic oxidation of methane (iron-AOM) has recently been reported to occur in paddy soils, but its actual role and regulation remain unclear. Here, we confirmed the occurrence of iron-AOM at different layers of paddy soils (0–10 cm, 10–20 cm, and 30–40 cm) across tillering, elongation, flowering, and ripening periods under three long-term fertilizer management schemes (CK-unamended, CF-chemical fertilizer, and CFS-chemical fertilizer with straw). The iron-AOM activity contributed 41 % to total AOM, which was greater than that of nitrite- (32 %) and nitrate-AOM (27 %). The iron-AOM activity varied significantly with soil layers, growth periods and fertilizer types, with layer being the most important variable. Soil moisture content and organic carbon content were most significant influencing factors on the AOM activity, and a Candidatus Methanoperedens ferrireducens-like lineage potentially catalyzed iron-AOM. Our results suggest that iron-AOM has an important potential for mitigating methane emissions from rice paddies.

Insights from Fertilization and Cultivation Management for Interpreting the Variations in the Quantity and Quality of Dissolved Organic Carbon and Microbial Community Structure on Purple Soil Sloping Farmland in Southwest China

It is crucial to comprehend how fertilization and cultivation management alter the composition of dissolved organic carbon (DOC) and microbial communities to regulate the biogeochemical cycling of soil nutrients and mitigate adverse impacts on soil–water quality. Based on 15 years of long-term field trials conducted in purple soil on farmland with a slope of 15° in southwestern China, the following five treatments were examined: CK (no fertilizer was applied), T1 (NPK plus organic manure and downslope cultivation), T2 (NPK and downslope cultivation), T3 (1.5-fold NPK and downslope cultivation), and T4 (NPK and contour cultivation). Soil samples were obtained from summer maize at two soil depths (0–10 and 10–20 cm) and from rhizospheric soil, and the changes in the DOC content, UV–visible (UV–Vis) absorptivity, and phospholipid fatty acids (PLFAs) were assessed. Our results revealed a significant change in the DOC content following fertilization, especially in T1, as it was 136.0%, 179.4%, and 132.2% higher, respectively, than that in CK at the 0–10 and 10–20 cm depths and rhizospheric soil. Fertilization decreased the UV–Vis absorptivity variables of DOC (i.e., SUVA254, SUVA260, SUVA400, SUVA465, SUVA665, and C:C ratio) and raised the E4:E6 ratio (fulvic acid to humic acid in DOC), regardless of T2 and T3 at the 10–20 cm depth and in the rhizospheric soil compared with those in CK, respectively. Fertilization significantly increased the total PLFA content and selected microbial groups relative to CK. Among the treatments, T1 significantly increased the total PLFA content by 50.6%, 59.0%, and 46.2%, respectively, relative to CK, at the 0–10 and 10–20 cm depths and in the rhizospheric soil. The microbial community structure in contour cultivation (T4) was significantly greater than in downslope cultivation (T2). Random forest analysis (RFA) revealed that SOC and DOC were likely the primary variables for regulating the total PLFAs in the examined soil. Partial least squares path modeling (PLS-PM) further indicated that the DOC content and the ratio of E4:E6 among DOC compositions had greater effects on the soil microbial community structure in the examined soil. These observations suggested that long-term fertilization and cultivation management are effective approaches to regulating the soil microbial community structure by altering the composition of DOC in sloping farmland.

Long-term Fertility Management Effect on Soil Carbon Fractions under Godavari Zone

Long-term Fertility Management Effect on Soil Carbon Fractions under Godavari Zone

Soil multifunctionality predicted by bacterial network complexity explains differences in wheat productivity induced by fertilization management

Fertilization will cause changes in crop growth, soil microbial community and multiple ecosystem functions, but it is unclear whether and how the optimal productivity obtained by manure application and optimizing nitrogen is driven by microbial community and ecosystem multifunctionality. We explore this mechanism based on a field fertilization experiment using a split-plot design that began in 2014 with five N rates (N0, N75, N150, N225, N300) as main plots and two manure rates (M0, NPK group; M1, MNPK group) as subplots, respectively. In general, (1) grain yield was parabolically related to the N application rate. The N rates that obtained the highest yield were 150 kg ha−1 and 225 kg ha−1 for the MNPK and NPK groups, respectively. The average yield of the MNPK group was 10.5% higher than that of the NPK group. (2) Long-term fertilization management resulted in regular changes in soil multifunctionality (SMF) and the properties of various microbial communities. The richness, network complexity and soil multifunctionality of bacterial and fungal communities also increased initially and then decreased as the N rate. On average, the response ratio of soil multifunctionality to N75, N150, N225, N300 (control is N0) and M1 (control is M0) were 0.11, 0.41, 0.53, 0.44 and 1.19, respectively. The soil multifunctionality of MNPK was 260%, 722% and 101% higher than that of NPK at the tillering, jointing and harvest stages, respectively. (3) Soil multifunctionality not only always had a significant positive effect on aboveground biomass at all growth stages, but also had significant positive correlations with bacterial richness and network complexity. Based on the existing framework, we further demonstrated that high microbial richness supports multifunctionality by ensuring strong associative complexity among microorganisms. However, only bacterial network complexity always positively drove soil multifunctionality and indirectly influenced wheat growth at all growth stages in SEMs where multiple drivers were considered simultaneously (i.e., pH, SOC and biological factors). Random forest regression analysis showed that rare bacterial taxa had stronger predictive effects on soil multifunctionality than abundant taxa. Our results validate that M1N150 can ensure high yield in the study area while maintaining a high level of ecosystem function in the soil, which also contributes to the reduction of adverse environmental risks caused by fertilizer application. Importantly, the potential of microbial network complexity, especially bacterial network complexity, to influence crop growth by driving farmland ecosystem functions deserves to be explored under different crop types, cropping systems, and irrigation conditions, compared to previous microbial richness that has been simply quantified.

Soil and Its Interaction with the Climate Jointly Drive the Change in Basic Soil Productivity under Long-Term Fertilizer Management

Basic soil productivity (BSP) is the productive capacity of farmland soils with their own physical and chemical properties during a specific crop season under local field management. Improving BSP as an effective way to increase or maintain crop yield, and researching its changes and potential driving factors under long-term fertilization are crucial for ensuring high and stable crop yields. In this study, the yields of BSP were simulated using the decision support system for agrotechnology transfer (DSSAT) crop model based on three long-term experiments, and its changing characteristics and driving factors were investigated under various fertilization treatments in wheat–maize rotation systems during 1991–2019. Five treatments were included: (1) unfertilized control (CK); (2) balanced mineral fertilization (NPK); (3) NPK plus manure (NPKM); (4) high dose of NPK plus manure (1.5NPKM); and (5) NPK plus crop straw (NPKS). This study found that the BSP of wheat and maize exhibited a fluctuating increase or stable change trend under four fertilization treatments at the Yangling (YL) and Zhengzhou (ZZ) sites, while a fluctuating reduction trend was observed at the Qiyang (QY) site. Compared with CK, NPKM, 1.5NPKM and NPKS significantly (p &lt; 0.05) improved the BSP of wheat and maize at the YL and ZZ sites. The BSP of both maize and wheat under NPKM and 1.5NPKM was significantly (p &lt; 0.05) higher than that under NPK or NPKS, whereas no statistically significant difference was found between NPK and NPKS at the QY site. The contribution rates of basic soil productivity (CBSP) of maize and wheat at the YL (41.5–60.7% and 53.0–64.3%) and ZZ sites (44.4–59.2% and 56.8–66.7%) were overall higher than that at the QY site (25.8–37.6% and 48.3–60.1%). In most cases, the difference in CBSP among different fertilization treatments was consistent with that in BSP. Moreover, a significant positive correlation was recorded between BSP and soil pH (r = 0.73, p &lt; 0.01; r = 0.87, p &lt; 0.01), TN (r = 0.56, p &lt; 0.01; r = 0.62, p &lt; 0.01) and TK content (r = 0.49, p &lt; 0.01; r = 0.58, p &lt; 0.01) in maize and wheat. Soil pH significantly correlated positively with the BSP of maize (R2 = 0.54, p &lt; 0.001) and wheat (R2 = 0.49, p &lt; 0.001) at the QY site, but negative correlation (R2 = 0.20, p &lt; 0.001; R2 = 0.30, p &lt; 0.001) was only found in maize at the YL and ZZ sites. The BSP of maize and wheat showed a significant negative linear correlation with MAP (R2 = 0.49–0.67, p &lt; 0.001) and MAT (R2 = 0.36–0.62, p &lt; 0.001). Random forests (RF) and variance partitioning analysis (VPA) revealed that soil properties and its interaction with the climate showed a higher explanation rate for BSP, indicating that these factors are the key drivers of BSP change. Overall, chemical fertilizers combined with manure can effectively increase BSP, while the effects of fertilizer combined with straw on BSP vary by region. The changes in BSP in wheat–maize cropping were mainly driven by both the soil and its interactions with the climate.

Impacts of long-term organic manure inputs on cultivated soils with various degradation degrees

With an increasing concern of soil health and sustainable development, organic manure application has been readdressed in recent years. In Northeast China, the agricultural industry is highly developed and organic manure resources are abundant, but soil degradation is serious due to extensive expansion of cultivation. Currently, limited information is available on how soils with various degradation degrees respond to long-term manure fertilization. Given that, a comparative study was conducted based on soil functional assessment of croplands with over 35 years of manure fertilization (maize straw compost, SA; cattle manure, CA) and various degradation degrees (none, light, moderate, and heavy). Soils in these croplands were loess-derived Mollisols and concentrated on a gentle to flat slope. Except for the difference in manure fertilization (SA and CA), similar field managements were adopted for these croplands during the past 35 years. Results showed that the impacts of erosion degradation and manure fertilization on soil physical structure lasted across the whole profile (0 ∼ 120 cm), while their impacts on soil nutrient properties were concentrated in shallow layers (<50 cm). Meanwhile, erosion degradation dominated 17.9% of the variance of soil physical structure, and soil profile depth contributed to 15.9% of soil nutrient variation. According to field validation regarding soil erosion modulus and crop yield, principal component analysis (PCA) with a nonlinear scoring method showed a good performance on the integrated soil functional index (ISI) assessment in this study area. The ISI of these croplands was found to be minimally characterized by BD, SOC, TN, AK, sand content, and CEC (R2 >0.64, p < 0.001). In addition, manure fertilization could significantly improve the ISI and maize yield for degraded soils, but had a slight impact on these two indicators for non-degraded soils. In terms of contribution to ISI improvement, SA (1.79% ∼ 283.73%) generally outperformed CA (4.53% ∼ 212.83%), while the latter was more effective in altering soil structure in deep layers (>70 cm). Generally, the ISI and maize yield were more susceptible to erosion degradation than manure fertilization. The obtained results provide useful information for a better cropland management in Northeast China.

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.

Soil organic carbon priming co-regulated by labile carbon input level and long-term fertilization history

Labile carbon (C) input and fertilization have important consequences for soil organic matter (SOM) decomposition via the priming effect (PE), thereby impacting soil fertility and C sequestration. However, it remains largely uncertain on how the labile C input levels interact with long-term fertilization history to control PE intensity. To clarify this question, soil samples were collected from a 38-year fertilization field experiment (including five treatments: chemical nitrogen fertilizer, N; chemical fertilizer, NPK; manure, M1; 200 % manure, M2; NPK plus M2, NPKM2), with strongly altered soil physiochemical properties (i.e., soil aggregation, organic C and nutrient availability). These soil samples were incubated with three input levels of 13C-glucose (without glucose, control; low, 0.4 % SOC; high, 2.0 % SOC) to clarify the underlying mechanisms of PE. Results showed that the PE significantly increased with glucose input levels, with values increasing from negative or weak (−2.21 to 3.55 mg C g−1 SOC) at low input level to strongly positive (5.62 to 8.57 mg C g−1 SOC) at high input level across fertilization treatments. The increased PE intensity occurred along with decreased dissolved total nitrogen (DTN) contents and increased ratios of dissolved organic C to DTN, implying that the decline in N availability largely increased PE via enhanced microbial N mining from SOM. Compared to N and NPK treatments, the PE was significantly lower in the manure-amendment treatments, especially for low input level, due to more stable SOM by aggregate protection and higher N and phosphorus availability. These results suggested that manure application could alleviate SOM priming via increased soil C stability and nutrient availability. Collectively, our findings emphasize the importance of long-term fertilization-driven changes in labile C inputs, SOM stability, and nutrient availability in regulating PE and soil C dynamics. This knowledge advances our understanding of the long-term fertilization management for soil C sequestration.

Impacts of Different Long-Term Fertilizer Management Regimes on Soil Nitrogen Mineralization and Its Enzyme Activities under a Double-Cropping Rice System in Southern China

Soil extracellular enzyme activities play an important role in regulating the soil nitrogen (N) mineralization process in paddy fields. However, there is still a need to further study how N mineralization responds to different fertilizer management techniques and the soil extracellular enzyme activities for N mineralization in paddy fields. Therefore, the influence of different long-term (35 years) fertilizer regimes on soil N mineralization, hydrolysable N fractions—such as hydrolyzed unknown nitrogen (HUN), amino acid nitrogen (AAN), amino sugar nitrogen (ASN), ammonia nitrogen (AN), and total acid-hydrolyzed nitrogen (TAN)—and their extracellular enzyme activities (soil urease, L-glutaminase, β-glucosidase, arylamidase, and β-glucosaminidase) in a double-cropping rice field in southern China were investigated in this study. The field experiment included the following fertilizer regimes: rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), inorganic fertilizer alone (MF), and no application of inorganic fertilizer as a control (CK). The results show that the soil ammonium N, amino sugar N, hydrolysable unidentified N, and amino acid N contents in the paddy field with RF treatment increased by 30.56%, 5.51%, and 62.74% compared with the CK treatment. The results show that the soil aerobic and anaerobic N mineralization rates in the paddy fields with OM and RF treatments increased by 22.92% and 18.27% compared with those with MF treatment. Moreover, soil extracellular enzyme activities under RF and OM treatments significantly increased, which indicated that the main substrate of microbial activity was effective. Correlation analysis indicated that the soil L-glutaminase activity, amino sugar N, amino acid N, and total acid-hydrolysable N contents were positively correlated with soil aerobic and anaerobic N mineralization rates in paddy fields. However, there was a negative correlation between the soil N mineralization rate and soil β-glucosaminidase activity in paddy fields. This finding shows that the yields of early rice and late rice under the RF and OM treatments were significantly higher than those under the MF and CK treatments. Compared with the MF treatment, the yields of double-cropping rice with RF and OM treatments increased by 9.84% and 11.37%, respectively. As a result, the application of straw or organic manure and inorganic fertilizer was effective for improving soil N mineralization, the soil acid-hydrolyzed N content, and extracellular enzyme activities in double-cropping rice fields.

Divergent soil health responses to long-term inorganic and organic fertilization management on subtropical upland red soil in China

To optimize soil health, land use, and soil management decisions need to be guided by an understanding of the underlying soil health. Although widely used fertilizers guarantee crop production, they ultimately damage agricultural soil environmental quality and threaten the overall food chain safety. Thus, an integrative assessment considering both environmental safety and soil fertility is required for the sustainable development of long-term fertilization systems. In this study, we conducted a comprehensive assessment of soil health using 20 soil physical, chemical, and biological indicators and assessed them according to four heavy metals—copper, zinc, cadmium, and lead. This experiment was conducted in an area where there is an ongoing, 23-year-long fertilization experiment in a typical red soil region of southern China, including four treatments of common inorganic chemical fertilizer (CF), CF mixed with micronutrients (CF + T), CF mixed with pig manure (PM), and PM mixed with micronutrients (PM + T). To assess the soil fertility quality, we selected a minimum data set consisting of soil water-stable aggregates mean weight diameter, available phosphorus, total nitrogen, microbial biomass carbon, and dehydrogenase activity. The results revealed that soil fertility quality followed the order of PM + T ≈ PM > CF + T > CF. We also used a modified potential ecological risk index to assess the soil environmental quality. This approach considered the acid-soluble and exchangeable fraction of heavy metals as the bioavailability component. Both PM and PM + T treated soils were significantly contaminated by heavy metals, with particularly large amounts of Cd contamination. The soil health index escalated from CF, CF + T, PM to PM + T, which indicated that the use of pig manure allowed for more fertile soil relative to standard chemical fertilization. Moreover, applying additional micronutrients also had a significant influence on soil fertility. Therefore, our study revealed that long-term fertilization using organic pig manure was beneficial to overall soil fertility; however, these benefits were coupled with significant limitations regarding heavy metal contamination. Collectively, this study provides a better supporting method for soil health management and long-term fertilization strategies.

Long-term field application of manure induces deep selection of antibiotic resistomes in leaf endophytes of Chinese cabbage

Antibiotic resistomes in leaf endophytes of vegetables threaten human health through the food chain. However, little is known about the ability of long-term manure fertilization to impact the deep selection of antibiotic resistance genes (ARGs) in leaf endophytes of vegetables planted in different types of soils. Here, by high-throughput quantitative PCR, we characterized the ARGs of leaf endophytes of Chinese cabbage (Brassica pekinensis (Lour.) Rupr.) grown in long-term (14 year) manure-amended acidic, neutral and calcareous soils. In total, 87 ARGs and 4 mobile genetic elements (MGEs) were detected in all the samples. Manure fertilization significantly increased the ARG numbers and normalized abundance in leaf endophytes, especially in acidic soil. Moreover, in acidic soil, manure application also led to a higher increase in the normalized abundance of opportunist and specialist ARGs, and more opportunist and specialist ARGs posed a high risk according to their risk ranks. Random forest analysis revealed that Proteobacteria and MGEs were the major drivers affecting the normalized abundance of opportunist and specialist ARGs in both acidic and neutral soils, respectively. In calcareous soil, Cyanobacteria and Actinobacteria were the most important contributors. Collectively, this study expands our knowledge about the deep selection of plant resistomes under long-term manure application.

Study of Physico-chemical and Nutrient Status of the Soil in Chiraigaon Block, Varanasi District, Uttar Pradesh, India

A study was conducted to evaluate the soil fertility and their quality parameters of Chiraigaon Block of Varanasi district Uttar Pradesh (U.P.) which is located at Latitude 25.3°N, and Longitude is 82.9°E and at elevation of 81m above mean sea level (AMSL) in the centre of Gangatic plain of Northern India. A total of 54 soil samples were collected from the farmland of six different villages of Chiraigaon Block. Physico-chemical property analyses showed average bulk density and particle density of 1.22 and 2.37 mg/m3 respectively whereas water holding capacity ranged from 29.80 to 51.70 %, pH ranged from 7.1 to 8.3, EC ranged from 0.18 to 1.68 dSm-1 and organic carbon content ranged from 0.21 to 0.76 % with low organic carbon content in 70.37% of the soil samples. Macronutrient analysis showed low to medium range for nitrogen, phosphorus and sulphur with average values of 244.15 Kg/ha, 14.78 kg/ha and 10.60 mg/kg respectively whereas medium to high range of potassium (481.7 kg/ha) and high range of exchangeable calcium (11.82 mEq/100g) and magnesium (9.89 mEq/100g) were found. Micro-nutrient analysis showed low to high range for manganese and zinc with values ranging from 3.08 to 56.1 mg/kg and 0.58 to 19.62 mg/kg respectively, with iron in the medium to high range (5.1 to 72 mg/kg) while available copper (2.2 to 4.08 mg/kg) was in the high range in the tested samples. The current study is expected to help the farmers of the study location in providing guidelines required for long-term soil fertility management and to improve soil quality and for developing suitable crop varieties that can grow without any yield reduction.

Accumulation of Labile P Forms and Promotion of Microbial Community Diversity in Mollisol with Long-Term Manure Fertilization

Soil phosphorus (P) can be divided into inorganic P (Pi) and organic P (Po). Microorganisms play essential roles in soil P transformation. However, there are many ways to detect P transformation, and the relationship between P forms and microorganisms under long-term fertilization is largely unclear. In this study, soil P forms were analyzed by a chemical sequential fractionation method and solution 31P nuclear magnetic resonance (31P-NMR) technique. Phospholipid fatty acid (PLFA) contents were measured by gas chromatography as the characterization of soil microbial community structures. The objective was to determine the changes of soil P forms and associated microbial community composition in mollisol with long-term fertilization. We sampled soil from a field experiment with 26-year-old continuous maize (Zea mays L.) cropping in Northeastern China. Three fertilization treatments were selected as chemical fertilization (NPK), NPK with crop straw (NPKS), and NPK with manure (NPKM). As shown in 31P-NMR spectra, orthophosphate accounted for 62.8–85.8% of total extract P. Comparison to NPK and NPKS treatments, NPKM application notably increased the concentrations of Po, Olsen-P, orthophosphate, orthophosphate monoester, and total P. Soil P fractions including resin-Pi, NaHCO3-P, NaOH-P, and HCl-P, especially Pi fractions, were enhanced by NPKM. The amounts of total PLFAs and PLFAs in bacteria, Gram-positive (G+) and Gram-negative (G−) bacteria, actinomycetes, and fungi were high in NPKM-treated soil. The percentages of PLFAs in bacteria and fungi in total soil PLFAs were 56.8% and 9.7%, respectively, which did not show any significant difference among the treatments. NPKM increased the proportions (%) of PLFAs in G+ bacteria, and NPKS increased the proportions (%) of G− bacteria in total PLFAs. The composition of soil microbial community was found to be significantly affected by soil total carbon and pH. There was a close relationship between HCl-Pi, NaHCO3-Po, orthophosphate, and pyrophosphate with anaerobe, aerobes, and G+. Manure addition directly increased soil available P concentrations, and indirectly acted through the alterations of anaerobe, aerobes, and G+. It is concluded that long-term NPKM application would lead to the accumulation of labile P and moderately labile P in mollisol through the activity of soil microbes.

The Inorganic Carbon Fixation Improved by Long-Term Manure Fertilization in Kastanozems under Rotation System of North China

In China, manure is the most abundant organic fertilizer product. Understanding the changes in soil inorganic carbon (SIC) resulting from long-term manure fertilization is vital for accurately evaluating agricultural soil carbon stocks and predicting global change. However, a comprehensive and quantitative understanding of the impacts of long-term fertilization on SIC is lacking. This study was conducted to assess the effects of SIC changes in topsoil (0–20 cm), aggregates of kastanozems and influencing factors under the potato-rape-naked oats cultivation system after 16 years of long-term different fertilization in Wuchuan station. The results showed that 16 years of application of manure promoted the fixation of SIC by 2.25 t ha−1–3.25 t ha−1. As soil organic carbon (SOC) content, exchangeable calcium and magnesium concentrations in free coarse particulate organic matter (cfPOM) increased, the crystallization of carbonate was promoted at the aggregate level. The distribution proportion of free-coarse particulate organic matter (cfPOM) and microaggregates in mineral-related organic matter (iMOM) were also increased which affected the content of SIC. However, the pH value of NPKM treatment was lower than that of M treatment, which reduced the amount of carbonate crystallization. Thus, the application of manure alone was the best way to promote the fixation of SIC in topsoil rather than manure combined with chemical NPK fertilize. This work provides a new insight into the conversion of inorganic carbon, which is beneficial to promote the sequestration of inorganic carbon.

Synergistic use of optical and biophysical traits to assess Bromus inermis pasture performance and quality under different management strategies in Eastern Nebraska, U.S.

We investigated the synergic use of optical and biophysical traits to characterize Bromus inermis (smooth bromegrass) pasture lands and assess the combined effects of long-term (15-years) rotational grazing and management strategies of (i) no fertilization (C), (ii) mineral nitrogen (N) fertilization (HF), and (iii) supplemented fertilization through dry distiller grains plus soluble (DDGS; SF)- on forage growth, performance, and quality. We found that fertilization improved pasture’s biomass, specific leaf area, leaf area index (LAI), as well as forage quality. The use of N fertilization did not offer an advantage (e.g., forage quality, yield) over DDGS under both grazed and ungrazed conditions. Optical, proximal sensing techniques allowed the characterization of pasture lands in a non-invasive and time-efficient manner. We tested established vegetation indices (VIs) for their accuracy in identifying and quantifying important physiological and morphological traits. Results showed that the Normalized Difference Vegetation Index (NDVI) and Vogelmann (VOG) were among the best performing indices. Results contribute to our understanding of the impact of long-term fertilization management on Bromus inermis pastures and validate the use of proximal sensing methods. Proximal sensing methods provide direct, non-invasive, and time efficient tool for assessment of the performance and health of vegetation, keys to successful integrative management strategies.

The role of long-term mineral and manure fertilization on P species accumulation and phosphate-solubilizing microorganisms in paddy red soils

Abstract. Understanding soil phosphorus (P) transformation and turnover under various fertilization managements is important for evaluating sustainable P fertility and potential bioavailability in agriculture managements. Thus, long-term fertilization experiments (∼ 38 years) with the application of different inorganic and organic fertilizers in paddy red soils were conducted to determine the effect of different fertilizer applications on P pool accumulation and microbial communities, especially for phosphate-solubilizing microorganisms (PSMs). Long-term inorganic P (IP) fertilization increased the concentrations of total P (TP) (∼ 479 mg kg−1), available P (AP) (∼ 417 mg kg−1) and inorganic P (∼ 18 mg kg−1), but manure fertilization accelerated the accumulation of organic P, especially for orthophosphate monoesters (e.g., myo-IHP, ∼ 12 mg kg−1). Long-term mineral fertilization decreased bacterial richness, evenness and complexation of bacterial networks. In contrast, long-term manure fertilization and rhizosphere accumulated more amounts of total carbon, total nitrogen, and organic carbon, as well as regulated the soil pH, thus improving the separation of bacterial communities. Furthermore, PSM compositions were greatly influenced by fertilization managements and rhizosphere. For example, inorganic P fertilization increased the abundance of Thiobacillus (i.e., the most abundant phosphate-solubilizing bacteria (PSB) in this study) and shifted the community structure of PSB. Correspondingly, the concentrations of inorganic and total P were the key factors for the variation of the PSB community structure. These findings are beneficial for understanding the variation of inorganic and organic P pools and the microbial community, especially for PSMs under long-term inorganic and/or organic fertilization.