Long-term Fertilization Practices Research Articles

Maize functional requirements drive the selection of rhizobacteria under long-term fertilization practices.

Rhizosphere microbiomes are pivotal for crop fitness, but the principles underlying microbial assembly during root-soil interactions across soils with different nutrient statuses remain elusive. We examined the microbiomes in the rhizosphere and bulk soils of maize plants grown under six long-term (≥ 29 yr) fertilization experiments in three soil types across middle temperate to subtropical zones. The assembly of rhizosphere microbial communities was primarily driven by deterministic processes. Plant selection interacted with soil types and fertilization regimes to shape the structure and function of rhizosphere microbiomes. Predictive functional profiling showed that, to adapt to nutrient-deficient conditions, maize recruited more rhizobacteria involved in nutrient availability from bulk soil, although these functions were performed by different species. Metagenomic analyses confirmed that the number of significantly enriched Kyoto Encyclopedia of Genes and Genomes Orthology functional categories in the rhizosphere microbial community was significantly higher without fertilization than with fertilization. Notably, some key genes involved in carbon, nitrogen, and phosphorus cycling and purine metabolism were dominantly enriched in the rhizosphere soil without fertilizer input. In conclusion, our results show that maize selects microbes at the root-soil interface based on microbial functional traits beneficial to its own performance, rather than selecting particular species.

The addition of discrimination inhibitors stimulations discrimination potential and N2O emissions were linked to predation among microorganisms in long term nitrogen application and straw returning systems.

Ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) have been proven to be key microorganisms driving the ammonia oxidation process. However, under different fertilization practices, there is a lack of research on the impact of interaction between predators and AOA or AOB on nitrogen cycling at the multi-trophic level. In this study, a network-oriented microscopic culture experiment was established based on four different long-term fertilization practices soils. We used the nitrification inhibitors 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxide-3-oxyl (PTIO) and 3, 4-Dimethylpyrazole phosphate (DMPP) inhibited AOA and AOB, respectively, to explore the impact of interaction between protists and AOA or AOB on nitrogen transformation. The results showed that long-term nitrogen application promoted the potential nitrification rate (PNR) and nitrous oxide (N2O) emission, and significantly increased the gene abundance of AOB, but had no obvious effect on AOA gene abundance. DMPP significantly reduced N2O emission and PNR, while PTIO had no obvious effect on them. Accordingly, in the multi-trophic microbial network, Cercozoa and Proteobacteria were identified as keystone taxa of protists and AOB, respectively, and were significantly positively correlated with N2O, PNR and nitrate nitrogen. However, Nitrososphaerota archaeon as the keystone species of AOA, had an obvious negative linkage to these indicators. The structural equation model (SEM) showed that AOA and AOB may be competitors to each other. Protists may promote AOB diversity through direct trophic interaction with AOA. The interaction pattern between protists and ammonia-oxidizing microorganisms significantly affects potential nitrification rate and N2O emission, which has important implications for soil nitrogen cycle.

Nitrogen addition and mowing had only weak interactive effects on macronutrients in plant-soil systems of a typical steppe in Inner Mongolia

Effective management of macronutrients is pivotal in the optimization and provisioning of ecosystem services in grassland areas, particularly in degraded grasslands. In such instances where mowing and nitrogen (N) fertilization have emerged as predominant management strategies, nutrient management is especially important. However, the precise effects of these concurrent practices on the distribution of macronutrients in plant-soil systems remain unclear. Here we evaluated the effects of 12 years of N addition (2, 10, and 50 g N m−2 year−1) and mowing on the concentrations and pools of six macronutrients (i.e., N; phosphorus P; sulfur S, calcium Ca, magnesium Mg, and potassium K) in three plant components (aboveground plants, litter, and belowground roots) at the community level and in the soil in a typical steppe in Inner Mongolia. Our results revealed that N addition generally raised the N concentration in the entire plant-soil system, regardless of whether plots were mowed. Higher N addition (10 and 50 g N m−2 year−1) also led to higher concentrations of P (+22%, averaging two N addition rates), S (+16%), K (+22%), Ca (+22%), and Mg (+24%) in plants but lower concentrations of these nutrients in the litter. Similar decreases in K (−9%), Ca (−46%), and Mg (−8%) were observed in the roots. In light of the observed increases in vegetation biomass and the lack of pronounced changes in soil bulk density, we found that the ecosystem N enrichment resulted in increased pools of all measured macronutrients in plants, litter, and roots (with the exception of Ca in the roots) while concurrently decreased the pools of P (−20%, averaging two higher N addition rates), S (−12%), K (−10%), Ca (−37%), and Mg (−19%) in the soil, with no obvious effect of the mowing practice. Overall, mowing exhibited a very limited capacity to alleviate the effects of long-term N addition on macronutrients in the plant-soil system. These findings highlight the importance of considering the distribution of macronutrients across distinct plant organs and the dynamic nutrient interplay between plants and soil, particularly in the context of long-term fertilization and mowing practices, when formulating effective grassland management strategies.

Impact of long-term fertilization on soil organic carbon dynamics and biological health of soils under Pearl millet -mustard-cowpea cropping sequence in an inceptisol of Gujarat

The study was undertaken by utilizing an ongoing long-term experiment on continuous cropping at Anand Agricultural University that began in 1980. From 1994 onwards, a modification was made by including Farmyard Manure (FYM) treatments for studying the following objectives: long-term effect of fertility levels with and without FYM on changes in soil organic carbon pools for assessing the role of organics and chemical fertilizers on soil organic carbon buildup and their interrelationship with soil aggregate stability under the pearl millet-mustard-cowpea (F) cropping sequence. Under F1 (FYM @ 10 t/ha) and FL3 (NP application @150 percent of RDF), there was a considerable improvement in the status of Walkley and Black C (WBC), Soil Microbial Biomass Carbon (SMBC), and Total Organic Carbon (TOC) compared to the control in both depths (0-15 and 15-30 cm). Long-term manuring and fertilization practices affect aggregate development and stabilization. In all depths, the highest soil macroaggregates and microaggregates were found when FYM @ 10 t/ha and FL3 (150 percent NP) were applied. Under FYM treated plots and with the greater dose of NP (NP application @150 percent of RDF) in both the surface and sub-surface layers, the maximum water-stable aggregate expressed as mean weight diameter (MWD) was recorded. Furthermore, a significantly positive correlation was observed between SMBC and enzymatic activities (phosphatase, urease, and dehydrogenase) in both the soil depths; indicating the effect of labile C on the biological activities of soil which might be achieved by means of changes in microbial diversity of the soil.

Co-Responses of Soil Organic Carbon Pool and Biogeochemistry to Different Long-Term Fertilization Practices in Paddy Fields

Long-term application of soil organic amendments (SOA) can improve the formation of soil organic carbon (SOC) pool as well as soil fertility and health of paddy lands. However, the effects of SOA may vary with the input amount and its characteristics. In this work, a descriptive field research was conducted during one cropping season to investigate the responses of various SOC fractions to different long-term fertilization practices in rice fields and their relationships with soil biogeochemical properties and the emission of greenhouse gases (GHG). The field sites included two conventional paddies applied with chemical fertilizer (CF) or CF + rice straw (RS) and six organic agriculture paddies applied with oilseed cake manure (OCM) + wheat straw (WS), cow manure (CM) + WS, or CM + RS. The two paddy soils treated with CM + RS had significantly higher concentrations of recalcitrant to labile C forms, such as loss-on-ignition C (LOIC; 56-73 g kg-1), Walkley-Black C (WBC; 20-25 g kg-1), permanganate oxidizable C (POXC; 835-853 mg kg-1), and microbial biomass carbon (MBC; 133-141 mg kg-1), than soils treated with other SOA. Likewise, long-term application of CM + RS seemed to be the best for regulating soil fertility parameters, such as ammonium (11-141 mg kg-1); phosphate (61-106 mg kg-1); and soluble Ca, K, and Mg (7-10, 0.5-1.2, and 1.9-3.8 mg kg-1, respectively), although the results varied with the location and soil properties of rice fields. Additionally, the two paddy sites had the largest cumulative methane emission (754-762 kg ha-1), seemingly attributed to increased microbial biomass and labile C fractions. The significant correlations of most SOC fractions with soil microbial biomass, trophic factors, and methane emissions were confirmed with multivariate data analysis. It was also possible to infer that long-term SOA application, especially with CM + RS, enhanced interaction in belowground paddy fields, contributing to soil fertility and rice production sustainability. Based on our findings, we suggest the need for analysis of various types of SOC fractions to efficiently manage soil fertility and quality of paddy fields, C sequestration, and GHG emissions.

Long-term continuous farmyard manure application increases soil carbon when combined with mineral fertilizers due to lower priming effects

Organic and synthetic fertilizers not only increase soil fertility and crop productivity but also enhance soil organic carbon (SOC). However, the priming effect (PE) leads to increased soil carbon (C) loss through native SOC mineralization. To date, the mechanisms by which long-term (>66 years) synthetic and/or organic fertilization alters net SOC sequestration remain a matter of debate. This study aimed to assess the effects of different fertilization practices on SOC decomposition and PE in agricultural systems subjected to long-term annual synthetic and/or organic fertilizer application. This aim was achieved by collecting topsoil samples (0–20 cm) from four long-term fertilization practices, i.e., unfertilized, synthetic supplemental (+s), cattle farmyard manure (+m, similar nutrient amount to +s), and synthetic fertilizer with farmyard manure (+s +m, the highest nutrient amount). The soil samples were incubated for 33 days with and without 13C-glucose addition, and a CO2 isotope analyzer combined with a modeling approach was used to establish a real-time method to monitor CO2 and 13CO2 production rates during the incubation period. Overall, +m increased the cumulative SOC-derived CO2 (SOC-CO2) by 107, 74, and 24 % compared to the unfertilized, +s and +s +m, respectively. The higher SOC-CO2 in +m treatment was associated with the greatest priming effect (PE, 390 ± 21 mg C kg soil−1), which corresponded to a 30 % increase compared to the average of the treatments that involved synthetic fertilizer (+s and +s +m) and a 137 % increase compared to the unfertilized control. The results were explained by the lower dissolved nitrogen (N), a proxy of available mineral N, in +m compared to +s +m, thus enhancing microbial mining for additional N via increasing SOC mineralization. However, the combined application of synthetic fertilizer and manure in the +s +m treatment provided enough easily accessible nutrients for microbial growth and activities from the applied synthetic fertilizer, leading to lower SOC mineralization than manure (+m) alone. Nevertheless, the treatments with manure application (i.e., +m and +s +m) significantly increased net SOC compared to the synthetically fertilized treatment and unfertilized control, suggesting greater C inputs than outputs and leading to high SOC accumulation over time. These results indicated that organic manure has a great potential to mitigate climate change by increasing SOC over time, which can be fostered by the addition of synthetic fertilizer; however, caution still needs to be taken regarding the quality and quantity of the added fertilizer.

Effects of Long-Term Fertilizer Practices on Rhizosphere Soil Autotrophic CO2-Fixing Bacteria under Double Rice Ecosystem in Southern China.

Soil autotrophic bacterial communities play a significant role in the soil carbon (C) cycle in paddy fields, but little is known about how rhizosphere soil microorganisms respond to different long-term (35 years) fertilization practices under double rice cropping ecosystems in southern China. Here, we investigated the variation characteristics of rhizosphere soil RubisCO gene cbbL in the double rice ecosystems of in southern China where such fertilization practices are used. For this experiment we set up the following fertilizer regime: without any fertilizer input as a control (CK), inorganic fertilizer (MF), straw returning (RF), and organic and inorganic fertilizer (OM). We found that abundances of cbbL, 16S rRNA genes and RubisCO activity in rhizosphere soil with OM, RF and MF treatments were significantly higher than that of CK treatment. The abundances of cbbL and 16S rRNA genes in rhizosphere soil with OM treatment were 5.46 and 3.64 times higher than that of CK treatment, respectively. Rhizosphere soil RubisCO activity with OM and RF treatments increased by 50.56 and 45.22%, compared to CK treatment. Shannon and Chao1 indices for rhizosphere soil cbbL libraries with RF and OM treatments increased by 44.28, 28.56, 29.60, and 23.13% compared to CK treatment. Rhizosphere soil cbbL sequences with MF, RF and OM treatments mainly belonged to Variovorax paradoxus, uncultured proteobacterium, Ralstonia pickettii, Thermononospora curvata, and Azoarcus sp.KH33C. Meanwhile, cbbL-carrying bacterial composition was obviously influenced by soil bulk density, rhizosphere soil dissolved organic C, soil organic C, and microbial biomass C contents. Fertilizer practices were the principal factor influencing rhizosphere soil cbbL-carrying bacterial communities. These results showed that rhizosphere soil autotrophic bacterial communities were significantly changed under conditions of different long-term fertilization practices Therefore, increasing rhizosphere soil autotrophic bacteria community with crop residue and organic manure practices was found to be beneficial for management of double rice ecosystems in southern China.

Characteristics of inorganic phosphorus fractions and their correlations with soil properties in three non-acidic soils

Understanding the characteristics and influences of various factors on phosphorus (P) fractions is of significance for promoting the efficiency of soil P. Based on long-term experiments on black soil, fluvo-aquic soil, and loess soil, which belong to Phaeozems, Cambisols, and Anthrosols in the World Reference Base for Soil Resources (WRB), respectively, five fertilization practices were selected and divided into three groups: no P fertilizer (CK/NK), balanced fertilizer (NPK/NPKS), and manure plus mineral fertilizer (NPKM). Soil inorganic P (Pi) fractions and soil properties were analyzed to investigate the characteristics of the Pi fractions and the relationships between Pi fractions and various soil properties. The results showed that the proportion of Ca10-P in the sum of total Pi fractions was the highest in the three soils, accounting for 33.5% in black soil, 48.8% in fluvo-aquic soil, and 44.8% in loess soil. Long-term fertilization practices resulted in periodic changes in soil Pi accumulation or depletion. For black soil and fluvo-aquic soil, the Pi accumulation was higher in the late period (10–20 years) of fertilization than in the early period (0–10 years) under NPK/NPKS and NPKM, whereas the opposite result was found in loess soil. The Pi accumulation occurred in all Pi fractions in black soil; mainly in Ca8-P, Fe-P, and Ca10-P in fluvo-aquic soil; and in Ca2-P, Ca8-P, and O-P in loess soil. Under CK/NK, the soil Pi was depleted mainly in the early period in each of the three soils. In addition to the labile Pi (Ca2-P) and moderately labile Pi (Ca8-P, Fe-P, Al-P), the Ca10-P in black soil and fluvo-aquic soil and O-P in loess soil could also be used by crops. Redundancy analysis showed that soil properties explained more than 90% of the variation in the Pi fractions in each soil, and the explanatory percentages of soil organic matter (SOM) were 43.6% in black soil, 74.6% in fluvo-aquic, and 38.2% in loess soil. Consequently, decisions regarding the application of P fertilizer should consider the accumulation rate and the variations in Pi fractions driven by soil properties in non-acidic soils.

Differences in total stored C and N in dryland red soil caused by different long-term fertilization practices

Fertilizer application is important to achieve sustainable agriculture. However, it remains unclear about the effects of long term fertilization on C and N immobilization as well as C/N ratios in soil aggregates at different depths. Samples taken at depths of 0 to 40 cm from dryland red soil subjected to long-term fertilization were analyzed. Four treatments were involved in the long term fertilization including no fertilizer (control), chemical fertilizer applied at two different rates, and manure combined with chemical fertilizers (MNPK). The C and N concentrations in the soil aggregates of different sizes were significantly higher (P < 0.05) and the C/N ratios in the particulate organic matter were significantly lower (P < 0.05) for soil to 20 cm deep for the MNPK treatment than for the other treatments. ANOVA indicated that the C and N concentration and C/N ratios in different sizes of aggregates significantly varied with soil depth (P < 0.05). Microaggregates contained most of the C and N, and the C/N ratios for silt–clay particles in macroaggregates were 1.37 unit (ranging − 0.25 to 2.44) lower than for other soil particles with diameters < 53 µm. The C and N contents in aggregates of different sizes increased as the C input rate increased to a depth of 40 cm because of the fertilization practices. Overall, both increased C input and deep application of C sources promoted the storage of C and N in microaggregates, which in turn increased C and N sequestration in dryland red soils.

Impact of Combining Long-Term Subsoiling and Organic Fertilizer on Soil Microbial Biomass Carbon and Nitrogen, Soil Enzyme Activity, and Water Use of Winter Wheat.

Reductions in soil productivity and soil water retention capacity, and water scarcity during crop growth, may occur due to long-term suboptimal tillage and fertilization practices. Therefore, the application of appropriate tillage (subsoiling) and fertilization (organic fertilizer) practices is important for improving soil structure, water conservation and soil productivity. We hypothesize that subsoiling tillage combined with organic fertilizer has a better effect than subsoiling or organic fertilizer alone. A field experiment in Henan, China, has been conducted since 2011 to explore the effects of subsoiling and organic fertilizer, in combination, on winter wheat (Triticum aestivum L.) farming. We studied the effects of conventional tillage (CT), subsoiling (S), organic fertilizer (OF), and organic fertilizer combined with subsoiling (S+OF) treatments on dry matter accumulation (DM), water consumption (ET), water use efficiency (WUE) at different growth stages, yield, and water production efficiency (WPE) of winter wheat over 3 years (2016–2017, 2017–2018, 2018–2019). We also analyzed the soil structure, soil organic carbon, soil microbial biomass carbon and nitrogen, and soil enzymes in 2019. The results indicate that compared with CT, the S, OF and S+OF treatments increased the proportion of >0.25 mm aggregates, and S+OF especially led to increased soil organic carbon, soil microbial biomass carbon and nitrogen, soil enzyme activity (sucrase, cellulose, and urease). S+OF treatment was most effective in reducing ET, and increasing DM and WUE during the entire growth period of wheat. S+OF treatment also increased the total dry matter accumulation (Total DM) and total water use efficiency (total WUE) by 18.6–32.0% and 36.6–42.7%, respectively, during these 3 years. Wheat yield and WPE under S+OF treatment increased by 11.6–28.6% and 26.8–43.6%, respectively, in these 3 years. Therefore, S+OF in combination was found to be superior to S or OF alone, which in turn yielded better results than the CT.

Varying microbial utilization of straw-derived carbon with different long-term fertilization regimes explored by DNA stable-isotope probing

The decomposition processes of crop residues, which represent the largest organic carbon input in agricultural ecosystems, are determined by soil microbes. However, the impact of different long-term fertilization practices on residue decomposition has not been clearly established. In this study, a microcosm experiment using 13C-labeled maize residues and high-throughput sequencing was performed to investigate bacterial and fungal microbes utilizing straw-derived carbon in soils under separate regimes of long-term fertilization (CK: no fertilizer; NPK: mineral fertilizers; NPKS: mineral fertilizers plus straw). During the 60-day incubation period, a total of 524 bacterial OTUs and 72 fungal OTUs, which utilized straw-derived carbon, were identified and were found to be primarily distributed in the bacterial phyla of Proteobacteria, Actinobacteria and Bacteroidetes, and the fungal class of Sordariomycetes within Ascomycota. The three fertilized soils exhibited distinct straw-utilizing microbial communities along the decomposition process, in which key bacterial taxa (Flavobacterium, Nocardioides, Pseudomonas, Pseudoxanthomonas, Agromyces and Herpetosiphon) and key fungal taxa (Pleosporaceae, Lasiosphaeriaceae and Chaetomiaceae) exhibited significantly positive relationships with extracellular enzymes activities, thereby accelerating the straw decomposition process. Furthermore, due to higher nutrient availability, microbes can rapidly respond to straw addition, therefore, more bacteria and fungi, which are referred to as rapid responders, were identified in NPK and NPKS soils, relative to CK soils. Hierarchical and variation Partitioning (HP) analysis revealed a strong potential impact of multiple edaphic factors in shaping the microbial community to utilize the straw-derived carbon. N resources (NO3−-N and TN) and β-glucosidase were found to be significantly positively correlated with microbial utilizers’ community. In conclusion, our findings elucidate the processes of establishment of microbial community and straw decomposition, as well as the association between microbial communities and edaphic factors under different long-term fertilization regimes.

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.

Long-Term Fertilization Shapes the Putative Electrotrophic Microbial Community in Paddy Soils Revealed by Microbial Electrosynthesis Systems.

Electrotrophs play an important role in biogeochemical cycles, but the effects of long-term fertilization on electrotrophic communities in paddy soils remain unclear. Here, we explored the responses of electrotrophic communities in paddy soil-based microcosms to different long-term fertilization practices using microbial electrosynthesis systems (MESs), high-throughput quantitative PCR, and 16s rRNA gene-based Illumina sequencing techniques. Compared to the case in the unfertilized soil (CK), applications of only manure (M); only chemical nitrogen, phosphorous, and potassium fertilizers (NPK); and M plus NPK (MNPK) clearly changed the electrotrophic bacterial community structure. The Streptomyces genus of the Actinobacteria phylum was the dominant electrotroph in the CK, M, and MNPK soils. The latter two soils also favored Truepera of Deinococcus-Thermus or Arenimonas and Thioalkalispira of Proteobacteria. Furthermore, Pseudomonas of Proteobacteria and Bacillus of Firmicutes were major electrotrophs in the NPK soil. These electrotrophs consumed biocathodic currents coupled with nitrate reduction and recovered 18-38% of electrons via dissimilatory nitrate reduction to ammonium (DNRA). The increased abundances of the nrfA gene for DNRA induced by electrical potential further supported that the electrotrophs enhanced DNRA for all soils. These expand our knowledge about the diversity of electrotrophs and their roles in N cycle in paddy soils and highlight the importance of fertilization in shaping electrotrophic communities.

The chemical nature of soil phosphorus in response to long-term fertilization practices: Implications for sustainable phosphorus management

Developing sustainable phosphorus (P) management strategies is a worldwide challenge in the face of growing food demand, dwindling rock phosphate resources, and deteriorating environmental quality. This requires improved knowledge on the effect of current fertilization practices on long-term P accumulation, bioavailability and mobility, which are functions of the chemical nature of soil P. Using state-of-the-art techniques such as solution 31P-NMR and P K-edge XANES spectroscopy, combined with sequential fractionation, this study investigated the chemical speciation and transformation of P in soils under three fertilization treatments (no fertilization, CK; chemical nitrogen (N), P and potassium (K) fertilization, NPK; and partial substitution of chemical fertilizer with sheep manure, NPKM) from a long-term experiment in China initiated in 1990. Compared to the NPK soil, total P and organic P (Po) concentrations were lower in the NPKM soil in the sampling years of 2000 and 2015, suggesting reduced P accumulation under the NPKM treatment. The NaHCO3-extracted P, considered the most readily plant-available P fraction, significantly increased in the NPKM soil relative to the NPK soil in 2000. The P-XANES results revealed the formation of the magnesium (Mg)–P compound newberyite, which probably contributed to soil P availability with NPKM application. Moreover, P-NMR analysis showed higher deoxyribonucleic acid content and ratio of orthophosphate diesters to monoesters in the NPKM soil relative to the NPK soil, which implied the stronger soil Po lability with NPKM fertilization. This study provides new insights on the significant role of NPKM treatment in optimizing soil P fertilization regimes, which benefits sustainable crop production.

Gross N2O Production Process, Not Consumption, Determines the Temperature Sensitivity of Net N2O Emission in Arable Soil Subject to Different Long-Term Fertilization Practices.

Chronic amendment of agricultural soil with synthetic nitrogen fertilization and/or livestock manure has been demonstrated to enhance the feedback intensity of net N2O emission to temperature variation (i.e., temperature sensitivity, TS). Yet few studies have explored the relevance of changes in underlying gross N2O production and consumption processes toward explaining this phenomenon, in particular for the latter. Furthermore, the microbe-based mechanisms associated with the variation of N2O consumption process remain largely unexplored. To address this knowledge gap, a temperature- (15, 25, and 35°C) and moisture-controlled (50% water holding capacity) microcosm incubation experiment was established using an arable soil subject to long-term addition of synthetic fertilizer (NPK), a mixture of synthetic fertilizer with livestock manure (MNPK), or with no fertilizer treatment (CT). Over the incubation time period, the C2H2 inhibition method was adopted to monitor reaction rates of gross N2O production and consumption; the population sizes and community structures of nosZI- and nosZII-N2O reducers were analyzed using quantitative PCR (Q-PCR) and terminal restriction fragment length polymorphism (T-RFLP). The results indicated that only NPK significantly increased the TS of net N2O emission, and gross N2O consumption process consistently occurred under all treatment combinations (temperature and fertilization) at each sampling time point. The responses of gross N2O production and consumption processes to temperature elevation exhibited fertilization- and sampling time-dependent pattern, and the higher net N2O production TS in the NPK treatment was underlain by its higher TS of gross production process and insensitivity of gross consumption process to temperature. The size and structure of nosZII-N2O reducers, as well as the community structure of nosZI-N2O reducers, were positively correlated with variation of gross N2O production and consumption rates across all fertilization regimes. NosZII-N2O reducer abundance was less responsive to temperature change, and its community structure less susceptible to fertilization, as compared with nosZI-N2O reducers. Overall, our results demonstrate that the TS of the gross N2O production process, not gross consumption, is the key step regulating the TS of net N2O production, and both nosZI- and nosZII-N2O clades are likely active N2O reducers in the tested soil.

Abundance, diversity, and structure of Geobacteraceae community in paddy soil under long-term fertilization practices

Geobacteraceae is an important dissimilatory Fe(III) reducer that affects the cycles of multiple elements. However, the way in which different long-term fertilization regimes influence the Geobacteraceae community in paddy soils remains unknown. Therefore, the objective of this study was to explore the responses of Geobacteraceae community in paddy soil to long-term chemical (nitrogen, phosphorus, and potassium) and/or organic (manure) fertilization practices. Illumina sequencing results showed that the species richness and diversity of Geobacteraceae community were not significantly changed by fertilizer treatments. Geobacteraceae in the treatments consisted of Geobacter (accounting for 90%–95% of total reads) and Geothermobacter genera (5%–10%), and all fertilizer treatments induced a significant (P < 0.05) decline in Geobacter and a marked enrichment of Geothermobacter. The taxonomic (based on Bray-Curtis distance) and phylogenetic structures (weighted-UniFrac distance) of the Geobacteraceae communities in all fertilizer treatments were clearly different from those in the non-fertilizer treatment; however, there were no significant changes among the different fertilization treatments. The variations in the Geobacteraceae community induced by long-term fertilization were mainly determined by changes in soil pH, total carbon, and total nitrogen. These findings provide an insight into the biogeochemistry of paddy soils and pave the way for harnessing the microbiome to improve soil fertility and environmental quality.

Soil water use and crop yield increase under different long-term fertilization practices incorporated with two-year tillage rotations

Water shortage and soil nutritionally depleted are the most limiting factors of crop production on the Loess Plateau. Conservation tillage rotation, conserved soil water and enhanced soil fertility effectively, produced high and stable crop yields in a spring maize-winter wheat-fallow rotation over a two-year period (hereafter called maize-wheat-fallow rotation). Corresponding and appropriate fertilization practices should enable the full potential of tillage rotation. Therefore, a long-term two-factor split-plot experiment (2007–2016) was established in Heyang County, Shaanxi Province, China, a typical rainfed dryland agricultural region. Beginning in 2007, three fertilization practices (balanced fertilization (BF), low fertilization (LF) and conventional fertilization (CF)) and four tillage systems (no tillage rotated with subsoiling annually (NS), subsoiling rotated with conventional tillage annually (SC), conventional tillage rotated with no tillage annually (CN), and continuous conventional tillage (CT)) were conducted to assess crop yield and soil water variation. The results showed that CCN (CF + CN, 5440 kg ha−1) and BNS (BF+NS, 8415 kg ha −1) produced the highest crop yield for winter wheat and spring maize, respectively. LNS (LF + NS, 419 mm) had a better soil water condition in fallow periods. NS and CN rotations had a better soil water condition (reserved more soil water for crop growth) than SC and CT during the wheat and maize growth season. However, both the average ET of winter wheat and spring maize under all of the treatments had no significant differences (P > 0.05) in ten years. In ten years, NS and CN rotations had higher water use efficiency (WUEs) than the SC rotation and CT, BNS had the highest WUE (19.0 kg ha −1 mm−1) for the spring maize – winter wheat rotation. Tillage rotation and fertilization had an interactive effect on soil water use and crop growth, and the results might clarify the response of crop yield and soil water variation to fertilization and tillage rotations. For further and sustainable development of crop production, BNS (5133 and 8415 kg ha −1 for wheat and maize yield, respectively; soil water in fallow: 386 mm) and BCN (5221 and 8116 kg ha −1 for wheat and maize yield, respectively; soil water in fallow: 388 mm) are recommended as the optimal fertilization and tillage rotations for rainfed crop production on the Loess Plateau.

Effects of Rhizosphere and Long-Term Fertilization Practices on the Activity and Community Structure of Denitrifiers Under Double-Cropping Rice Field

ABSTRACTThe soil physicochemical properties, soil denitrification rates (PDR), denitrifiers via nitrite reductases (nirK and nirS) and nitrous oxide reductase (nosZ), abundance and community composition of denitrifiers in both the rhizosphere and bulk soil from a long-term (32 year) fertilizer field experiment conducted during late rice season were investigated by using the MiSeq sequencing, quantitative PCR, terminal restriction fragment polymorphism (T-RFLP). The experiment including four treatments: without fertilizer input (CK), chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), and organic manure and chemical fertilizer (OM). The results showed that the application of rice straw residue and organic manure increased soil organic carbon (C), total nitrogen (N), and NH4+-N contents. The nirK, nirS, and nosZ copy numbers with OM and RF treatments were significant higher than that of the MF and CK treatments in the rhizosphere and bulk soil (p < 0.05). The principal coordinate analysis (PCoA) analysis showed that the different parts of root zone are the most important factors for the variation of denitrifying bacteria community, and the different fertilization treatments is the second important factors for the variation of denitrifying bacteria community. The MiSeq sequencing result showed that nirK, nirS and nosZ-type denitrifiers communities within bulk soil had lower species diversity compared with rhizosphere soil, and were dominated by Rhizobiales, Rhodobacterales, Burkholderiales, and Pseudomonadales. As a result, the application of fertilization practices had significant effects on soil N and PDR levels, and affected the abundance and community composition of N-functional microbes.

Aggregate Stability under Long-Term Fertilization Practices: The Case of Eroded Ultisols of South-Central China

Soil aggregate stability is an important aspect of soil function and health. Fertilization could potentially alter soil properties and thereby affect aggregate stability. To determine which fertilizer is useful for improving soil fertility and stabilizing soil aggregates and thereby reducing soil erodibility, we examined three types of fertilizer, and measured how soil organic carbon, carbohydrates, and related soil properties influenced aggregate stability in eroded Ultisols. Treatments included control (CK), mineral fertilizer nitrogen (N), phosphorus (P), potassium (K) (NPK), fertilizer NPK plus straw (NPKS), and farmyard manure (FYM). Aggregate stability was tested according to Le Bissonnais method, involving three disruptive tests: fast wetting (FW), slow wetting (SW), and mechanical breakdown (WS). Total organic carbon, particulate organic carbon, mineral-associated carbon, and cold-water-soluble carbohydrate, hot-water-soluble carbohydrate, and dilute acid hydrolysable carbohydrate were measured, as well as soil intrinsic properties (including pH, bulk density, iron and aluminum oxides). The 12-year fertilization had a larger effect on aggregate stability and related soil properties in a 0–15 cm soil layer, whereas no effect was evident at a soil depth of 15–40 cm. MWD (mean weight diameter) under the three tests decreased with increasing soil depth. Fertilization, especially farmyard manure evidently improved MWDFW and MWDWS at a depth of 0–15 cm. Slaking was the main mechanism of aggregate breakdown in Ultisols studied, followed by mechanical breakdown. Correlation analysis showed that MWDFW and MWDWS at a depth of 0–15 cm increased with the increase of particulate organic carbon, total organic carbon, hot-water-soluble carbohydrate and pH. Furthermore, their interaction with amorphous iron oxides enhanced aggregate stability against slaking or, with amorphous aluminum oxides, modified aggregate stability against mechanical breakdown. Consequently, particulate organic carbon was the dominant cementing agent for aggregation in Ultisols studied, and its combination with pH, amorphous aluminum oxides, amorphous iron oxides, and free aluminum oxides play a synergetic role in stabilizing soil aggregate. Accordingly, farmyard manure or fertilizer NPK plus straw improved soil fertility and the ability to resist slaking.

Two-decade long fertilization induced changes in subsurface soil organic carbon stock vary with indigenous site characteristics

Soil organic carbon (SOC) sequestration at subsurface layers (i.e. >20 cm) remains unclear under long-term fertilization practices. Based on long-term datasets of fertilization experiments in four typical Chinese croplands, representing soils with high fertility at Gongzhuling (GZL, black soil) and Chongqing (CQ, purple soil), and low fertility at Zhengzhou (ZZ, aquatic Chao soil) and Qiyang (QY, red soil), we calculated SOC storage, its change relative to initial condition (ΔSOC) in 0–20, 20–40 and 40–60 cm. We also obtained annual organic C inputs (OCI; stubble, roots and manure amendment) and derived soil C sequestration efficiency (CSE: the ratio of ΔSOC over OCI) in 0–20 cm and 0–60 cm. The fertilization treatments include cropping with no fertilization (CK), chemical nitrogen, phosphorus and potassium fertilizers (NPK) and combined chemical fertilizers and manure (NPKM). Results showed SOC stock significantly increased with fertilizations (i.e. initial, CK < NPK < NPKM). Relative to initial condition, surface (0–20 cm) and subsurface (20–60 cm) SOC stocks significantly decreased under CK at all sites except GZL, a site with elevated SOC stocks under all fertilizations and depths. Subsurface SOC stocks significantly increased at high fertility soils (i.e., GZL and CQ) but remained no change or significantly decreased at low fertility soils (i.e., ZZ and QY) under NPK and NPKM. Accordingly, CSE derived in 0–60 cm was consistently higher than that in 0–20 cm in high fertility soils but lower in low fertility soils. These results demonstrated that subsurface soils (20–60 cm) remained as C sinks in indigenously high fertility sites but experienced substantial C depletions in low fertility sites. This study informed the need to account for subsurface soil carbon changes for accurate estimates of soil C sequestration capacity under long-term fertilization.