Long-term Fertilizer Application Research Articles

Microbial community structure and functional metabolic diversity are associated with organic carbon availability in an agricultural soil

Exploration of soil environmental characteristics governing soil microbial community structure and activity may improve our understanding of biogeochemical processes and soil quality. The impact of soil environmental characteristics especially organic carbon availability after 15-yr different organic and inorganic fertilizer inputs on soil bacterial community structure and functional metabolic diversity of soil microbial communities were evaluated in a 15-yr fertilizer experiment in Chang-ping County, Beijing, China. The experiment was a wheat-maize rotation system which was established in 1991 including four different fertilizer treatments. These treatments included: a non-amended control (CK), a commonly used application rate of inorganic fertilizer treatment (NPK); a commonly used application rate of inorganic fertilizer with swine manure incorporated treatment (NPKM), and a commonly used application rate of inorganic fertilizer with maize straw incorporated treatment (NPKS). Denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA gene was used to determine the bacterial community structure and single carbon source utilization profiles were determined to characterize the microbial community functional metabolic diversity of different fertilizer treatments using Biolog Eco plates. The results indicated that long-term fertilized treatments significantly increased soil bacterial community structure compared to CK. The use of inorganic fertilizer with organic amendments incorporated for long term (NPKM, NPKS) significantly promoted soil bacterial structure than the application of inorganic fertilizer only (NPK), and NPKM treatment was the most important driver for increases in the soil microbial community richness (S) and structural diversity (H). Overall utilization of carbon sources by soil microbial communities (average well color development, AWCD) and microbial substrate utilization diversity and evenness indices (H’ and E) indicated that long-term inorganic fertilizer with organic amendments incorporated (NPKM, NPKS) could significantly stimulate soil microbial metabolic activity and functional diversity relative to CK, while no differences of them were found between NPKS and NPK treatments. Principal component analysis (PCA) based on carbon source utilization profiles also showed significant separation of soil microbial community under long-term fertilization regimes and NPKM treatment was significantly separated from the other three treatments primarily according to the higher microbial utilization of carbohydrates, carboxylic acids, polymers, phenolic compounds, and amino acid, while higher utilization of amines/amides differed soil microbial community in NPKS treatment from those in the other three treatments. Redundancy analysis (RDA) indicated that soil organic carbon (SOC) availability, especially soil microbial biomass carbon (Cmic) and Cmic/SOC ratio are the key factors of soil environmental characteristics contributing to the increase of both soil microbial community structure and functional metabolic diversity in the long-term fertilization trial. Our results showed that long-term inorganic fertilizer and swine manure application could significantly improve soil bacterial community structure and soil microbial metabolic activity through the increases in SOC availability, which could provide insights into the sustainable management of China's soil resource.

Long-term organic and inorganic fertilization alters temperature sensitivity of potential N2O emissions and associated microbes

Emissions of the greenhouse gas nitrous oxide (N2O) from soil are sensitive to many factors including temperature, nutrient status, pH and bulk-density. Interactions among these are complex, particularly in agricultural systems where fertilizer-addition has interactive influences across many soil properties. Under laboratory conditions, the temperature sensitivity of N2O emissions, as measured by Q10 values (fractional change in rate with a 10 °C increase in temperature), was higher in soils receiving long-term fertilizer addition compared with control. Different fertilization regimes significantly influenced the emission pathways. Application of manure increased the proportion of potential N2O derived from denitrification although the incubation condition used in the present study might not be favorable for anaerobic denitrification. The abundance of archaeal amoA gene copies increased under all fertilizer treatments, but that of bacterial amoA only increased under mineral (NPK) fertilization. Meanwhile, abundance of nirS, nirK and nosZ only increased under OM and MNPK fertilization. T-RFLP analyses showed that both ammonia oxidizing and denitrifier community structures were altered by fertilization, but only the nirS community structure was sensitive to temperature change. Furthermore, a strong correlation was observed between nirS gene abundance and potential N2O emissions. Relationships between AOA, nirK gene abundances and potential N2O emission were significant but relatively weak. PLS path model revealed that besides direct effect, potential N2O emission was also indirectly influenced by temperature through mediation of NH4+ concentration and nirS-type denitrifier. Our work suggests that warming-induced elevation of potential N2O emission could be strengthened by long-term application of fertilizers, especially organic manure, via shifting community abundance and structure of nirS-type denitrifier.

Micronutrients (Fe, Mn, Zn and Cu) balance under long-term application of fertilizer and manure in a tropical rice-rice system

Purpose The balance of micronutrients in soils is important in nutrient use efficiency, environmental protection and the sustainability of agro-ecological systems. The deficiency or excess of micronutrients in the plough layer may decrease crop yield and/or quality. Therefore, it is essential to maintain appropriate levels of micronutrients in soil, not only for satisfying plant needs in order to sustain agricultural production but also for preventing any potential build-up of certain nutrients.

Fertilization practices alter microbial nutrient limitations after alleviation of carbon limitation in a Ferric Acrisol

Microbial nutrient limitation was investigated in a 53-year-old field experiment in the Central-West of Burkina Faso under sorghum–cowpea rotation, comparing three fertilization practices: mineral fertilizer (MIN), mineral fertilizer and farmyard manure (MINFYM), and a non-fertilized control (CON). We assessed microbial N and P limitation after removal of C limitation by (i) determining microbial N and P, (ii) assessing respiration kinetics in incubated soil samples amended with easily available C (glucose) alone or in combination with N and/or P, or not amended, and (iii) evaluating changes in microbial biomass and community composition at the peak of microbial respiration by microbial P and phospholipid fatty acid (PLFA) analyses. Microbial N and P were very low in all fertilization practices, but greater in MINFYM than in CON. Easily available C was the first factor limiting microorganisms in all fertilization practices. After removal of C limitation, most indicators suggested N and P co-limitation in CON. In contrast, respiration kinetics in MINFYM and MIN were only N-limited, while biomass formation in MINFYM was also P-limited. PLFA analyses indicated preferential fungal growth on the added C, and P limitation of changes in microbial community composition in MIN. Long-term application of fertilizers mostly alleviated secondary microbial nutrient limitation by P but not by N, and C always remained the primary limiting factor for microbial growth.

Mechanisms of soil N dynamics following long-term application of organic fertilizers to subtropical rain-fed purple soil in China

In this study, a 15N tracing incubation experiment and an in situ monitoring study were combined to investigate the effects of different N fertilizer regimes on the mechanisms of soil N dynamics from a long-term repeated N application experiment. The field study was initiated in 2003 under a wheat-maize rotation system in the subtropical rain-fed purple soil region of China. The experiment included six fertilization treatments applied on an equivalent N basis (280 kg N ha−1), except for the residue only treatment which received 112 kg N ha−1: (1) UC, unfertilized control; (2) NPK, mineral fertilizer NPK; (3) OM, pig manure; (4) OM-NPK, pig manure (40% of applied N) with mineral NPK (60% of applied N); (5) RSD, crop straw; (6) RSD-NPK, crop straw (40% of applied N) with mineral NPK (60% of applied N). The results showed that long-term repeated applications of mineral or organic N fertilizer significantly stimulated soil gross N mineralization rates, which was associated with enhanced soil C and N contents following the application of N fertilizer. The crop N offtake and yield were positively correlated with gross mineralization. Gross autotrophic nitrification rates were enhanced by approximately 2.5-fold in the NPK, OM, OM-NPK, and RSD-NPK treatments, and to a lesser extent by RSD application, compared to the UC. A significant positive relationship between gross nitrification rates and cumulative N loss via interflow and runoff indicated that the mechanisms responsible for increasing N loss following long-term applications of N fertilizer were governed by the nitrification dynamics. Organic fertilizers stimulated gross ammonium (NH4+) immobilization rates and caused a strong competition with nitrifiers for NH4+, thus preventing a build-up of nitrate (NO3−). Overall, in this study, we found that partial or complete substitution of NPK fertilizers with organic fertilizers can reduce N losses and maintain high crop production, except for the treatment involving application of RSD alone. Therefore, based on the N transformation dynamics observed in this study, organic fertilizers in combination with mineral fertilizer applications (i.e. OM, OM-NPK, and RSD-NPK treatments) are recommended for crop production in the subtropical rain-fed purple soils in China.

Effects of Lime Applications on Chemical Properties of Soil and Rice Yields in Long-term Fertilization Experiment

Monitoring of soil fertility and crop productivity in long-term application of fertilizers is necessary to use fertilizers efficiently. This study was conducted to investigate effects of continuous application of lime for rice cultivation from 1969 to 2014. The treatments were no lime treatments (N, NPK, NPKC, and NPKS) and lime treatments (N+L, NPK+L, NPKC+L, and NPKS+L). The application of lime in addition to N, NPK, and NPKC tended to increase pH, exchangeable Ca, and available SiO2. The input of mean annual 1,170 Mg ha -1 yr -1 of lime increased pH 0.0042 yr -1 , 0.0062 yr -1 , 0.0127 yr -1 , and 0.0041 yr -1 in lime treatments (N+L, NPK+L, NPKS+L, and NPKC+L) compared with no treatments (N, NPK, NPKS, and NPKC), respectively. The mean annual Ca field balance varied from 169 to 561 kg ha -1 yr -1 in no treatments, from 871 to 1,263 kg ha -1 yr -1 in lime treatments, indicating that Ca was accumulated in the soils. The mean annual Ca field balance in silicate fertilizer treatments (NPKS, NPKS+L) were higher than that of other treatments because silicate fertilizer included Ca component. Grain yield of rice had no significant differences between no lime treatments and lime treatments. Thus the application of lime led to changes in soil chemical properties but had no impact on the production of rice.

Responses of absolute and specific soil enzyme activities to long term additions of organic and mineral fertilizer

Long-term phosphorus (P) and nitrogen (N) applications may seriously affect soil microbial activity. A long-term field fertilizer application trial was established on reddish paddy soils in the subtropical region of southern China in 1998. We assessed the effects of swine manure and seven different rates or ratios of NPK fertilizer treatments on (1) the absolute and specific enzyme activities per unit of soil organic carbon (SOC) or microbial biomass carbon (MBC) involved in C, N, and P transformations and (2) their relationships with soil environmental factors and soil microbial community structures. The results showed that manure applications led to increases in the absolute and specific activities of soil β-1,4-glucosidase(βG), β-1,4-N-acetylglucosaminidase (NAG), and leucine aminopeptidase (LAP). The absolute and specific acid phosphatase (AP) activities decreased as mineral P fertilizer application rates and ratios increased. Redundancy analysis (RDA) showed that there were negative correlations between absolute and specific AP activities, pH, and total P contents, while there were positive correlations between soil absolute and specific βG, NAG, and LAP enzyme activities, and SOC and total N contents. RDA showed that the contents of actinomycete and Gram-positive bacterium PLFA biomarkers are more closely related to the absolute and specific enzyme activities than the other PLFA biomarkers (P<0.01). Our results suggest that both the absolute and specific enzyme activities could be used as sensitive soil quality indicators that provide useful linkages with the microbial community structures and environmental factors. To maintain microbial activity and to minimize environmental impacts, P should be applied as a combination of inorganic and organic forms, and total P fertilizer application rates to subtropical paddy soils should not exceed 44kgPha−1year−1.

Effects of long-term application of chemical and organic fertilizers on the abundance of microbial communities involved in the nitrogen cycle

Long-term agricultural fertilization significantly affects nitrogen cycling in soils. However, there is little information about the response of different functional genes involved in the nitrogen cycle to chemical and organic fertilization, and the key factor influencing the community abundance. We investigated the influence of long-term application of chemical fertilizer (NPK) and combined with wheat straw or livestock manures on the abundance of six nitrogen cycle genes (nifH, archaeal and bacterial amoA, nirS, nirK and nosZ) by quantitative PCR. Compared with non-fertilization treatment, long-term application of NPK fertilizers significantly increased the abundance of nirK, nosZ and bacterial amoA genes but decreased archaeal amoA gene abundance, with no significant effect on the abundance of nifH and nirS genes. Compared with NPK treatment, the application of NPK+organic manure increased the abundance of all the nitrogen-cycling genes while the application of NPK+wheat straw had little effect. The abundance of amoA genes contributed the most to the variations in the abundance of the nitrogen cycling community between different fertilization strategies. Soil available P and total N were the most important factors influencing the abundance of microbial communities involved in the nitrogen cycle. These results indicated that, under the application of chemical fertilizers, the addition of livestock manures had much stronger effects on the abundance of nitrogen cycle genes than the addition of wheat straw, and bacterial and archaeal amoA genes were more sensitive to fertilization than other functional genes.

Changes in the physicochemical properties of gray forest soils in the Opol’e region under the long-term application of fertilizers

Models of changes in the acid properties of gray forest soils of the Opol’e region have been developed. It is shown that soil acidity increases at the application of phosphorus—potassium fertilizers and with increasing rates of the complete fertilizer. Organic fertilizers suppress the increase of soil acidity. The changes in the acid properties of these soils reflect the interaction of fertilizers with humus.

Maize straw effects on soil aggregation and other properties in arid land

Soil structure has been destroyed due to long-term application of inorganic fertilizer in the Loess Plateau of China. Our objective was to determine how incorporation of three different rates of maize (Zea mays L.) straw affected soil aggregate size and stability within the top 30cm of arid soil on the Loess Plateau of China to provide basic theory of land utilization. Three rates of maize straw (4.5, 9.0, or 13.5Mgha−1, hereafter referred to as LS, MS, and HS) were incorporated with 255 and 90kg/ha of inorganic N and P fertilizer, respectively, 2 times in a 4-year field experiment. Water stability of five aggregate size classes (>5, 2–5, 1–2, 0.5–1, and 0.25–0.5mm) in the 0–10, 10–20, and 20–30cm depth increments was measured 3 times for each treatment and a check (CK) that received only the inorganic fertilizers. Incorporation of 13.5Mgha−1 of straw significantly increased water stability of three aggregate classes (>5, 1–2, 0.5–1mm) compared with CK and LS treatments within the surface 10cm and for aggregates >0.5mm in the 10–20cm depth increment. Within the 20–30cm depth increment water-stablity of aggregates in the 0.25–0.5mm class increased significantly as the rate of straw incorporation increased. Overall, aggregate stability was primarily increased through changes in microaggregate size distribution, especially for aggregate classes >5, 0.5–1, 0.25–0.5mm within the 0–10, 10–20, 20–30cm soil depth, respectively. Straw incorporation is a positive and effective agriculture measure to improve soil structure.

The impact of mineral fertilizers and lime on the transformation of humic acids in a soddy-podzolic heavy loamy soil of the Cis-Ural region

The composition and structure of humic acids in a soddy-podzolic heavy loamy soil (Retisol) of the Cis-Ural region after the long-term application of mineral fertilizers and lime was studied by the methods of elemental analysis, infrared spectroscopy, and thermogravimetry. It was found that mineral fertilizers and lime did not change the ranges of C, H, O, and N contents and general structure typical of humic acids in soddy-podzolic soils. The long-term anthropogenic impact on the soil resulted in some transformation of the composition and properties of humic acids. Clear absorption bands in the area of 1700 cm−1 (C=O of carbonyl group) and 1620 cm−1 (C=C of aromatic rings), which characterize the benzenoid structures of molecules, were found in the infrared spectra of humic acids from the soil treated with lime at the rate to compensate for the total acidity. Soil liming favored the accumulation of thermodynamically stable fragments of the central part of humic acid molecules and the destruction of peripheral radicals. The application of mineral fertilizers resulted in the enrichment of humic acids with aliphatic fragments. The combined application of mineral fertilizers and lime increased the portion of aromatic structures and, at the same time, enriched humic acids in aliphatic fragments less resistant to pyrolysis. These fragments are biologically and chemically active and can be readily involved in the element turnover processes, thus protecting the stable part of humus from the biological destruction.

Accumulation, availability, and uptake of heavy metals in a red soil after 22-year fertilization and cropping.

Fertilization is important to increase crop yields, but long-term application of fertilizers probably aggravated the risk of heavy metals in acidic soils. In this study, the effect of 22-year fertilization and cropping on accumulation, availability, and uptake of heavy metals in red soil was investigated. The results showed that pig manure promoted significantly cadmium (Cd) accumulation (average 1.1 mg kg(-1)), nearly three times higher than national soil standards and, thus, increased metal availability. But the enrichment of heavy metals decreased remarkably by 50.5 % under manure fertilization, compared with CK (control without fertilization). On the contrary, chemical fertilizers increased greatly lead (Pb) availability and Cd activity; in particular, exceeding 85 % of soil Cd became available to plant under N (nitrogen) treatment during 9-16 years of fertilization, which correspondingly increased their enrichment by 29.5 %. Long-term application of chemical fertilizers caused soil acidification and manure fertilization led to the increase in soil pH, soil organic matter (SOM), and available phosphorus (Olsen P), which influenced strongly metal behavior in red soil, and their effect had extended to deeper soil layer (20∼40 cm). It is advisable to increase application of manure alone with low content of heavy metals or in combination with chemical fertilizers to acidic soils in order to reduce toxic metal risk.

Distribution of soil nutrients, extracellular enzyme activities and microbial communities across particle-size fractions in a long-term fertilizer experiment

Soils were particle-size fractionated to evaluate changes in carbon and nitrogen contents, enzyme activities and microbial community composition in response to 33 years of fertilization. This study focused on yellow–brown paddy soil and the particle-size fractions of >2000, 2000–200, 200–63, 63–2 and 2–0.1μm. Microplate fluorometric assays and phospholipid fatty acid analysis (PLFA) were used to determine soil biological characteristics under no fertilizer (control, CK), fertilizer N (N), fertilizer N and P (NP), fertilizer N, P and K (NPK), organic manure plus fertilizer N, P and K (NPKM) and organic manure (M) treatments. The results showed that fertilizer and soil fraction individually and interactively (P<0.05) affected soil C, N contents, enzyme activities and microbial communities except for α-glucosidase activity, bacterial relative abundance and the G+:G− ratio. Particularly, organic treatments significantly increased soil organic carbon (SOC) and total nitrogen (N) contents of all five fractions. The highest C and N contents and enzyme activities were observed in the 200–63μm fraction, except for phosphatase and sulfatase, which showed the highest activities in the 2–0.1μm fraction. The highest activities of β-glucosidase, β-cellobiosidase, α-glucosidase, aminopeptidase, phenol oxidase and peroxidase in each fraction were obtained in the organic treatments (NPKM and M). Activities of phosphatase, sulfatase, N-acetyl-glucosaminidase and β-xylosidase in the 2000–200μm fraction were highest under NPK treatment. PLFA analysis showed that the >63μm fraction contained higher abundance of total PLFAs than that in the 63–0.1μm fraction. Organic treatments significantly enhanced total PLFAs abundance in >2000μm fraction, but decreased PLFAs abundance in the 2000–200μm fraction compared with the NPK treatment. Larger fractions (>2000μm and 2000–200μm) held relatively lower G+:G− ratios and higher fungi:bacteria ratios, which indicated better soil conditions in these fractions. Principal component analysis showed a smaller variability of microbial community composition among treatments than particle-size fractions. Most treatments of larger fractions (>2000μm and 2000–2μm) were well separated from the other fractions. Redundancy analysis showed total N, C:N ratio, phosphatase, sulfatase, N-acetyl-glucosaminidase and β-cellobiosidase activities significantly affected the composition of the microbial community. Significant correlations were also obtained between enzyme activities with SOC, total N and C:N ratio. We concluded that the long-term application of organic fertilizers contributed to improvements in the soil organic carbon and total nitrogen and most of the enzyme activities, especially for the 200–63μm fraction, along with abundant and diverse microbial community composition in larger particles.

Bacterial diversity in soils subjected to long-term chemical fertilization can be more stably maintained with the addition of livestock manure than wheat straw

Addition of organic matter such as livestock manures and plant residues is a feasible practice to mitigate soil degradation caused by long-term application of chemical fertilizers, and the mitigation is largely mediated though activities of the soil-dwelling microorganisms. However, the roles of different kinds of organic matter in maintaining bacterial community structure have not been assessed in a comparative manner. In this study, 454 pyrosequencing of 16S rRNA gene was employed to compare the bacterial community structure among soils that had been subjected to 30 years of NPK fertilization under six treatment regimes: non-fertilization control, fertilization only, and fertilization combined with the use of pig manure, cow manure or low- and high-level of wheat straws. Consistent with expectation, long-term application of NPK chemical fertilizers caused a significant decrease of bacterial diversity in terms of species richness (i.e. number of unique operational taxonomic units (OTU)), Faith's index of phylogenetic diversity and Chao 1 index. Incorporation of wheat straw into soil produced little effects on bacterial community, whereas addition of either pig manure or cow manure restored bacterial diversity to levels that are comparable to that of the non-fertilization control. Moreover, bacterial abundance determined by quantitative PCR was positively correlated with the nutritional status of the soil (e.g., nitrate, total nitrogen, total carbon, available phosphorus); however, bacterial diversity was predominantly determined by soil pH. Together, our data implicate the role of livestock manures in preventing the loss of bacterial diversity during long-term chemical fertilization, and highlight pH as the major deterministic factor for soil bacterial community structure.

Effect of Long-Term Fertilization on Soil Productivity on the North China Plain

Soil productivity is the ability of a soil, in its normal environment, to support plant growth and can be evaluated with respect to crop production in unfertilized soil within the agricultural ecosystem. Both soil productivity and fertilizer applications affect crop yields. A long-term experiment with a winter wheat-summer maize rotation was established in 1989 in a field of the Fengqiu State Key Agro-Ecological Experimental Station, a region typical of the North China Plain, including seven treatments: 1) a balanced application of NPK chemical fertilizers (NPK); 2) application of organic fertilizer (OM); 3) application of 50% organic fertilizer and 50% NPK chemical fertilizers (1/2OMN); 4) application of NP chemical fertilizers (NP); 5) application of PK chemical fertilizer (PK); 6) application of NK chemical fertilizers (NK); and 7) unfertilized control (CK). To investigate the effects of fertilization practices on soil productivity, further pot tests were conducted in 2007–2008 using soil samples from the different fertilization treatments of the long-term field experiment. The soil sample of each treatment of the long-term experiment was divided into three pots to grow wheat: with no fertilization (Potunf), with balanced NPK fertilization (PotNPK), and with the same fertilizer(s) of the long-term field experiment (Potori). The fertilized soils of the field experiment used in all the pot tests showed a higher wheat grain yield and higher nutrient uptake levels than the unfertilized soil. Soil productivity of the treatments of the field experiment after 18 years of continuous fertilizer applications were ranked in the order of OM > 1/2OMN > NPK > NP > PK > NK > CK. The contribution of soil productivity of the different treatments of the field experiment to the wheat grain yield of Potori was 36.0%–76.7%, with the PK and NK treatments being higher than the OM, 1/2OMN, NPK, and NP treatments since the soil in this area was deficient in N and P and rich in K. Wheat grain yields of PotNPK were higher than those of Potori and Potunf. The N, P, and K use efficiencies were higher in PotNPK than Potori and significantly positively correlated with wheat grain yield. Soil organic matter could be a better predictor of soil productivity because it correlated more strongly than other nutrients with the wheat grain yield of Potunf. Wheat yields of PotNPK showed a similar trend to those of Potunf, indicating that soil productivity improvement was essential for a further increase in crop yield. The long-term applications of both organic and chemical fertilizers were capable of increasing soil productivity on the North China Plain, but the former was more effective than the latter. The balanced application of NPK chemical fertilizers not only increased soil productivity, but also largely increased crop yields, especially in soils with lower productivity. Thus, such an approach should be a feasible practice for the sustainable use of agricultural soils on the North China Plain, particularly when taking into account crop yields, labor costs, and the limited availability of organic fertilizers.

Metaproteome of the microbial community in paddy soil after long-term treatment with mineral and organic fertilizers

The soil microbial community research conducted in the field has focused on the genetic diversity of these organisms. In this study, we assessed the proteins expressed in soil microbial communities following the long-term application of mineral fertilizer (NPK) and organic manure (M) to paddy soil, indirect extraction method and separated via two-dimensional (2D) gel electrophoresis and identified using a matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) approach. We found that the number of cells in the primary soil in the M treatment was significantly greater than in the NPK and CK treatments. The numbers of cells extracted were consistent with the total cell numbers and the concentration of extracted proteins (CK &lt; NPK &lt; M). 303 and 306 protein spots being detected in the CK map and NPK map, respectively. Eleven spots of interest were identified in the 2D gels, including 8 different protein spots and 3 unique protein spots. Three common proteins involved in protein hydrolysis and glutamate synthesis and metabolism. Eight differentially expressed proteins involved in DNA replication, transcription, protein folding and energy metabolism, the processes of cofactor and vitamin metabolism, transcriptional regulation, recombination and xenobiotic compound biodegradation and metabolism. The long-term application of fertilization resulted in significant changes in the microbial community structure and function, and the long-term application of pig manure significantly increased the microbial biomass and the functional and structural diversity in the soil. It is very interesting to address the MS identification of intracellular proteins from microbial communities under different fertilizer treatments in a paddy soil.

Long-term application of organic manure changes abundance and composition of ammonia-oxidizing archaea in an acidic red soil

Ammonia-oxidizing archaea (AOA) have more importance in ammonia oxidation than ammonia-oxidizing bacteria (AOB) in acidic red soils. The aim of this study was to investigate if the abundance and composition of AOA could be altered by long-term application of organic manure in an acidic red soil. The abundance and composition of AOA were evaluated by polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) targeting archaeal amoA genes after long-term (24-year) application of mineral fertilizer and/or organic manure. The treatments were: non-fertilized control, mineral nitrogen (N) fertilizer only, mineral N, phosphorus (P) and potassium (K) fertilizer only, organic manure only, and organic manure plus mineral NPK fertilizer. The abundance of archaeal amoA genes was significantly increased after the long-term application of organic manures, either with or without mineral NPK fertilizer. So were the Shannon and Richness diversity indices of AOA deduced from the DGGE patterns. Phylogenetic analyses showed that most of the AOA sequences from various fertilization treatments were affiliated with group 1.1b thaumarchaea and only one with the group 1.1a-associated thaumarchaea. Nitrification potential was significantly increased after the long-term application of organic manures in comparison with the non-fertilized control. Our results strengthened the importance of organic manure in promoting the growth of AOA and thus nitrification potential in the acidic red soils.

Measuring and estimating sulfur mineralization potential in soils amended with poultry litter or inorganic fertilizer

The effect of long-term (more than 10 years) application of poultry litter (PL) or inorganic fertilizer (IF) on sulfur (S) mineralization potential (So) was evaluated using four different soils (Delaware 1, Delaware 2, Iowa, and Georgia). Also, different methods to estimate S availability (extraction with KCl, NaHCO3, and KCl after a wetting-drying cycle, aerobic incubations for 7 and 14 days, and NH4+ quantification after an anaerobic incubation) were compared to So. When compared to long-term application of IF, long-term application of PL generated an increase in total soil S ranging from 0 to 0.14 g kg−1, which was positively associated with the soil clay content (R2 = 0.98), and resulted in an increase in So ranging from 0 to 21.2 g kg−1. From the evaluated methods to estimate So, only three of them were significantly (p < 0.05) correlated to So: aerobic incubation for 7 days (r = 0.85), extraction with NaHCO3 (r = 0.85), and nitrogen anaerobic incubation (r = 0.99). Based on the reduced time and labor involved and in their capacity to distinguish between treatments, we recommend further use and further evaluation of the last two methods as estimators of So.

Long-term fertilizer application effects on the soil, root arbuscular mycorrhizal fungi and community composition in rotation agriculture

Arbuscular mycorrhizal fungi (AMF) play key roles in plant growth, ecosystem sustainability and stability. However, it is still unclear how the soil, root AMF growth and community composition are affected by fertilizer application in subtropical wheat–rice rotation agro-ecosystems. We investigated the impact of different organic and/or inorganic fertilizers on AMF growth and community composition in a long-term experiment field in Zhejiang Province, east China. AMF biomass was determined using 16:1ω5 phospholipid fatty acids (PLFAs) and neutral lipid fatty acids (NLFAs) content. Soil and root AMF community compositions were determined by DGGE analysis, cloning, sequencing and phylogenetic analyses. The root colonization rate was not significantly affected by different fertilizer regimes. Manure amendment significantly enhanced both AMF hyphal (i.e., 16:1ω5 PLFA) and spore (i.e., 16:1ω5 NLFA) biomass content, while inorganic fertilizer only increased the AMF spore biomass. A total of 10 and 11 Glomeromycota phylotypes were detected in soil and root samples, respectively. Glomus was the dominant genus in both soil and root samples, while Acaulospora genus occurred in roots only. Although the different fertilizers altered soil AMF communities, the root AMF community structure was not significantly altered. Soil pH (F=5.695, P<0.01) and available K (F=4.888, P<0.01) contributed to both soil and root AMF community composition, while the C/P ratio (F=3.893, P<0.01) only contributed to soil AMF community. The data suggests that high soil organic C content benefits AMF growth, while soil pH and available K concentration strongly influence AMF community. The root AMF community was much more resilient to the changes caused by long-term fertilizer application than the soil community.

Carbon Pools and Associated Soil Enzymatic Activities as Influenced by Long-term Application of Fertilizers and Manure in Lowland Rice Soil

The effect of long-term (21 years) fertilizer application on soil carbon pools, its functional groups in humic acids and associated soil enzymatic activities was investigated in tropical flooded rice. The five treatments were non-fertilized control, nitrogen (N) (90 kg ha−1), farmyard manure (FYM) (10 t ha−1), NPK (90: 45: 45 kg ha−1:: N: P2O5: K2O) and FYM+NPK. On average, the microbial biomass carbon (MBC) content was significantly higher in FYM+NPK treatment as compared to control (by 30%), 100% N, 100% NPK + FYM treatments. The enzyme activities, viz. dehydrogenase, β-glucosidase, acid and alkaline phosphatase were found significantly higher under FYM + NPK treated plots compared with control by 107, 170, 133 and 190 per cent, respectively. The characteristic humic acid spectra revealed that FYM and NPK treated plot contains aromatic functional C groups, which have the potential to sequester C in the long run. Therefore, the combined application of FYM + NPK is a viable option for managing soil fertility as well as sustaining rice yield (4.1–5.7 t ha−1) in tropical flooded soils. The study is novel in the sense it describes soil carbon pools including labile active and passive pools in relation to soil functional microbial diversity under lowland flooded rice.