Long-term Fertilization Experiment Research Articles

Effects of long-term fertilization on calcium-associated soil organic carbon: Implications for C sequestration in agricultural soils

Although the contribution of calcium ion (Ca2+) to stabilizing organic carbon (OC) in soils has been known for years, we still have a limited understanding of the quantity and molecular composition of Ca2+ bound SOC (Ca-OC) evolution in response to long-term fertilization. Here we report the role of Ca2+ in the accumulation of OC in the topsoil (0–20 cm) from two long-term (25–37 years) fertilization experiment sites. Approximately 4.54–19.27% and 9.00–25.15% of SOC was bound with Ca2+ in the Ferric Acrisol and Fluvic Cambisol, respectively. The application of NPK mineral fertilizers (NPK) decreased (p < 0.05) the Ca-OC stocks from 3.40 t ha−1 to 0.96 t ha−1 and from 2.03 t ha−1 to 1.17 t ha−1 in the Ferric Acrisol and Fluvic Cambisol, respectively. Swine manure (M) addition did not change (p > 0.05) the Ca-OC stock in Ferric Acrisol, but enhanced (p < 0.05) that from 2.03 t ha−1 to 9.75 t ha−1 in Fluvic Cambisol. Fourier transform infrared and carbon (1s)-near X-ray absorption spectroscopies showed that Ca2+ was mainly bound with aromatic carbon and carboxylic carbon. Long-term M fertilization facilitated the binding of Ca2+ with O-alkyl C, suggesting an increment of Ca-linked polysaccharide. Calcium ion was preferentially associated with 13C enriched organic matter (OM). Mineral fertilization promoted the 13C-enriched organic compounds in the Ca-OC, while organic fertilization facilitated the binding of 13C-depleted organic C with Ca2+. This study suggests that Ca-OC may be a potentially vital and stable OC pool in arable soils, and provides direct evidence for the preferential association of OC with Ca2+ in edaphic environments.

Development of a Novel Model of Soil Legacy P Assessment for Calcareous and Acidic Soils

Phosphate (P) rock is a finite natural resource, and its use for P fertilizer production has resulted in its rapid depletion worldwide. In order to reduce the use of natural P resources, reducing the input of P into agricultural systems is necessary. The assessment of legacy P in soil is an option to maintain crop yield with low P fertilizer input. Many models have been tested to assess the contribution of legacy soil P to crop uptake. However, these models face a common challenge as conceptual soil P pools in models cannot be accurately initiated and evaluated using measured soil P indexes. In this study, a novel legacy P assessment (LePA) model was developed according to empirical equations about crop P uptake, soil Olsen-P, and total P from two long-term fertilizer experiments in typical calcareous and acidic soils in China. We used the DPPS (dynamic phosphorus pool simulator) model as a contrast model to estimate the simulation accuracy of the new LePA model. The calibration and validation datasets for both models were set-up by collecting data from two long-term fertilizer experiments in typical calcareous and acidic soils in China. The results showed that the LePA model simulated crop P uptake similar to the DPPS model in calcareous soil. While the DPPS model failed to depict crop P uptake under low pH conditions, the LePA model worked well after modification when limited crop growth caused by acidic conditions was considered. Moreover, the LePA model can also predict changes in soil TP and Olsen-P with P fertilizer application, which are new functions compared with the DPPS model. Based on a scenario analysis generated by the LePA model, P fertilizer application could be reduced by 52% in Yangling and 46% in Qiyang compared with the conventional application rate during this period to maintain the current yields if soil legacy P can be utilized efficiently. The LePA model is a useful tool for guiding soil P management from the field to country scales.

Long-term effect of nutrient management on soil microbial properties and nitrogen fixation in a vertisol under soybean-wheat cropping sequence

The present experiment was conducted during 2018-19 under the ongoing All India Coordinated Research Project on Long-term Fertilizer Experiment with soybean-wheat cropping sequence since 1972 at the Research Farm of Department of Soil Science and Agricultural Chemistry, Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur, Madhya Pradesh, India. The microbial properties and nitrogen (N2) fixation of soil under different nutrient combinations were studied in a 46-year old long-term fertilizer experiment in a Vertisol. The experiment was conducted in a randomized block design comprising of 10 treatments viz., T1: 50% NPK, T2: 100% NPK, T3: 150% NPK, T4: 100% NPK + Hand weeding (100% NPK+HW), T5: 100% NPK + zinc (100% NPK + Zn), T6: 100% NP, T7: 100% N, T8: 100% NPK+ 5 t FYM ha-1 (100% NPK+FYM), T9: 100% NPK(–S) and T10: Control, each treatment being replicated four times in a randomized block design. Soil samples from all the treatments were collected from 0–15 cm depth and microbial properties and N2 fixation of soil were estimated. Significant increase in soil organic carbon, total N and available N were recorded with 100% NPK+FYM. Similarly, the maximum number of nodules and their biomass were also recorded in 100% NPK+FYM treatment at 30, 45 and 60 days after sowing. The bacteria, fungi and actinomycetes population counts in soil were 39.1×107, 42.7×104 and 39.1×105 cfu g-1 soil, respectively with the integrated application of inorganic fertilizer and organic manure (100% NPK+FYM) over control (11.7×107, 18.5×104 and 13.6×105 cfu g-1 soil, respectively). Further, the conjoint use of balance dose of fertilizers with FYM was also significantly superior in terms of soil microbial biomass carbon and microbial biomass N over other treatments even after 46 years of experimentation. The grain and straw yield of soybean and their N uptake were also significantly increased with graded dose of fertilizers and maximum yield and N uptake were noted in 100% NPK+FYM treatments over control plot.

Sugar Beet Shoot and Root Phenotypic Plasticity to Nitrogen, Phosphorus, Potassium and Lime Omission

In low input agriculture, a thorough understanding of the plant-nutrient interactions plays a central role. This study aims to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) and liming omission on shoot growth as well as on topsoil root biomass, growth and morphology (tuber and fibrous roots) of sugar beet grown under field conditions at the Dikopshof long-term fertilizer experiment (Germany). Classical shoot observation methods were combined with root morphology and link measurements using an image analysis program. Omission of the nutrients N, P and K as well as of liming led to a significant decrease in shoot growth. Tuber yield was lowest for the unfertilized and the K omission treatment. The root shoot ratio was highest in the N deficient treatment. In the K omission treatment, a strategic change from a less herringbone root type (early stage) to a more herringbone root type (late stage), which is more efficient for the acquisition of mobile nutrients, was observed. By contrast, a change from a more herringbone (early stage) to a less herringbone root type (late stage) which is less expensive to produce and maintain was observed in the unfertilized treatment. We conclude that sugar beet alters its root morphology as a nutrient acquisition strategy.

Impact of Continuous Fertilization on Heavy Metals Content in Soil and Food Grains under 25 Years of Long-Term Fertilizer Experiment

ABSTRACT In the present investigation, an attempt was made to determine the direct effects of fertilizers on various soil properties like acidification, organic matter content, the content of essential and toxic trace metals in soils and food grains under long term (>25 years) fertilizer experiment. Soil and plant samples were collected from Bengaluru center of All India Coordinated Research Project on Long-Term Fertilizer Experimental site in the sub-regions AESR 8.1 of India, with the treatments e.g. control, 100% N, 100% NP, 100% NPK, 150% NPK, 100% NPK + Lime, 100% NPK+ farmyard manure (FYM) at 0 to 60 cm depth with an interval of 15 cm. Laboratory analysis was conducted to know the vertical distribution of heavy metals and micronutrient cations in soil and plant produce by following the standard method. The DTPA soil Zn remained unchanged with the higher rates of N application, i.e. 100% N. There was very little effect of N, NP, and NPK application on the buildup of DTPA-able Zn, Fe, Mn, and Cu content in both the soils. However, the application of NPK + FYM showed a buildup in comparison to control for Fe 10 mg kg−1, Mn 18 mg kg−1, Zn 1.23 mg kg−1, and Cu 0.84 mg kg−1 in soil. Continuous fertilizer application contributed a meager amount accumulation of Cd, Pb, Ni, Co, and Cr in the soil under the finger millet – maize cropping sequence. The estimation of heavy metals in food grains, supposed to come from fertilizers, lime materials applied in soil was also of our concern. All the cited heavy metals were present in the maize and finger-millet grains. Risk assessment to human health (Hazard Quotient, HQ) for the intake of heavy metals through consumption of contaminated food grains was computed and observed that the values of ‘HQ’ for all the crops were far less than unity (<1) and safe for the consumers.

Vertical distribution of different pools of soil organic carbon under long-term fertilizer experiment on rice-wheat sequence in mollisols of North India

ABSTRACT A profound consideration of soil organic carbon (SOC) and SOC pools as affected by the long-term use of fertilizer in a fixed crop sequence is essential to understand and maintain the health and productivity of soil. The dynamics of SOC pools, i.e. total soil organic carbon (TOC) and its different fractions under a rice-wheat cropping system subjected to various fertilizer management strategies over 42 years was investigated near Uttarakhand, India. The soil at the experimental site was an Aquic Hapludoll consisting of a poorly drained silty clay loam (1–1.5 m deep) overlying loamy to sandy sediments. Over 42 years, application of 100% NPK+ FYM (Farm Yard Manure) was the most effective management system in increasing organic C up to 0 to 60 cm soil depths under rice-wheat sequence. The combination of this integrated input application (100% NPK + 15 t ha−1 FYM) significantly built organic carbon fractions like total organic carbon, microbial biomass C (MBC), particulate organic C (POC), KMnO4 oxidizable C, Humic C, Fulvic C, Humin C, water-soluble carbon and hot water extractable carbohydrates at all four soil depths. Hence, application of FYM along with NPK resulted in a significant positive building up of all pools in the treatment at all four depths. Therefore, balance fertilization is panaceally important for sustaining improved soil health with balanced organic status and production potentiality of the soil for rice-wheat cropping sequence.

Saprotrophic fungal communities in arable soils are strongly associated with soil fertility and stoichiometry

The importance of soil saprotrophic fungi in agroecosystems is receiving increasing attention. However, the linkages between saprotrophic fungal communities and soil fertility and stoichiometry in agroecosystems are poorly understood. Here, four long-term field fertilization experiments with three treatments (i.e., no fertilizer (control), chemical nitrogen (N), phosphorus (P), and potassium (K) fertilizer (NPK), chemical combined with organic fertilizer (NPKM)) were performed to evaluate the associations of saprotrophic fungal communities with the soil fertility index (SFI) and stoichiometric carbon (C):N:P ratios. Long-term NPKM application increased the SFI by 57.66%–129.50% at the four sites, and the SFI was strongly correlated with the saprotrophic fungal community composition, which indicated that exogenous organic matter improved soil fertility to a large extent and stimulated the growth of saprotrophic fungi in arable soils. The soil C:P and N:P ratios were notably decreased in the fertilization treatment, indicated that P was sufficient. Further, the composition of saprotrophic fungi was significantly related to the C:N and N:P ratios, suggested that N status is an important factor for soil saprotrophic fungal communities. Our study provides empirical evidence that the saprotrophic fungal communities in arable soils are strongly associated with soil fertility and stoichiometry and offers guidance for improving soil fertility by regulating the saprophytic fungal community.

Nutrient supply affects the yield stability of major European crops—a 50 year study

Yield stability is important for food security and a sustainable crop production, especially under changing climatic conditions. It is well known that the variability of yields is linked to changes in meteorological conditions. However, little is known about the long-term effects of agronomic management strategies, such as the supply of important nutrients. We analysed the stability of four major European crops grown between 1955 and 2008 at a long-term fertilization experiment located in Germany. Six fertilizer treatments ranged from no fertilization over the omission of individual macronutrients to complete mineral fertilization with all major macronutrients (nitrogen, phosphorus, potassium and calcium). Yield stability was estimated for each crop × treatment combination using the relative yield deviation in each year from the corresponding (nonlinear) trend value (relative yield anomalies (RYA)). Stability was lowest for potato, followed by sugar beet and winter wheat and highest for winter rye. Stability was highest when soils had received all nutrients with the standard deviation of RYA being two to three times lower than for unfertilized plots. The omission of nitrogen and potassium was associated with a decrease in yield stability and a decrease in the number of simultaneous positive and negative yield anomalies among treatments. Especially in root crops nutrient supply strongly influenced both annual yield anomalies and changes in anomalies over time. During the second half of the observation period yield stability decreased for sugar beet and increased for winter wheat. Potato yields were more stable during the second period, but only under complete nutrient supply. The critical role of potassium supply for yield stability suggests potential links to changes in the water balance during the last decades. Results demonstrate the need to explicitly consider the response of crops to long-term nutrient supply for understanding and predicting changes in yield stability.

Nitrification under the influence of long-term fertilizer application in a tropical vertisol

ABSTRACT The current experiment envisages estimating nitrification and elucidates the mechanistic processes of nitrogen mineralization in a long-term fertilizer experiment (LTFE) on a soybean-wheat cropping system. The experiment had four treatments: fallow (no fertilizer and no crop), control (no fertilizer), inorganic (recommended dose as 100% NPK), and integrated (100% NPK + farmyard manure FYM). The potential nitrification rate (PNR) estimated as µg NO3 − produced g−1 soil d−1 was 0.88 in fallow, 1.86 in control, 1.278 in 100% NPK, and 1.493 in 100% NPK + FYM. Real-time PCR quantification of bacterial amoA gene (× 104 amoA gene copies g−1 soil) was 19.33 in fallow, 43.33 in control, 30.33 in 100% NPK, and 29.33 in 100% NPK + FYM. The amoA gene copies (x 104 gene copies g−1 soil) of archaea ranged from 11.67 to 38.67. The X-ray diffraction (XRD) of soils indicated that the intensity of the NH4 + minerals was highest in control and lowest in fallow. Soybean grain and biomass yields were highest in 100% NPK + FYM and lowest in control. The study highlights that continuous cropping without fertilizer may alter soil microbial metabolism for the acquisition of nitrogen from mineralization of readily unavailable mineral fractions.

Impact of long-term manure and mineral fertilization on yield and nutritive value of lucerne (Medicago sativa) in relation to changes in canopy structure

Fertilization management influences not only productivity but also the nutritive value of forage legumes. However, there have been few studies about these effects in long-term fertilization experiments. Our objectives were: (i) to compare the effects of mineral fertilization and organic manure on lucerne forage yield and leaf and stem nutritive value over a 2-year period following 60 years of different fertilization managements, and (ii) to investigate relationships among canopy structure traits and forage nutritive value in association with these fertilization treatments. The long-term fertilization experiment was established with four replications in the Czech Republic in 1955. Three levels of mineral N, P and K application (0:0:0, 39:24:109 and 91:31:146) were investigated, each with and without farmyard manure, resulting in six treatments. Lucerne stands were established in 2012 and 2013 in two strips. Forage yield was measured in two cuts in 2014 and 2015, respectively. Canopy structure traits and forage nutritive value (crude protein, ash, neutral detergent fibre (NDF) and NDF digestibility (NDFD) were analysed in the first cut in each year. Intensive mineral fertilization reduced lucerne nutritive value through a reduction in stem NDFD (-6%) and leaf weight ratio (-10 %) under higher forage productivity (+10 % of annual yield). Manure fertilization improved nutritive value of leaves and stems, with an associated increase in whole plant nutritive value as leaf proportion was maintained with increased yield (+8%). This positive response could be attributed to a soil environment effect: greater root development in soil that had received long-term manure fertilization probably reduced forage lignification and maintained leaf proportion in association with reduced drought stress. Long-term manure fertilization demonstrated potential for improvement of lucerne nutritive value despite the negative relationships between increased plant growth under higher nutrient supply and forage nutritive value.

Evaluating changes in nitrogen and sulphur content in a soil-plant system in a long-term fertilization experiment

The objective of this study was to evaluate the impact of long term NPK fertilization (considering that S containing superphosphate was supplied for 26 years of experiment, but since 9 years S has not used any longer) on sulphur- and nitrogen content and N/S ratio of winter wheat. The second objective of this work was to determine the changes of the amount of the different nitrogen and sulphur fraction in chernozem soil in a long term fertilization experiment. The third aim of the work was to determine if a relationship could be established between the studied parameters. Based on our results, it can be stated that the sulphur containing superphosphate supplied in the period of 1984-2010 has no longer significant effect on total sulphur content of plant in 2018. The NPK fertilization treatments had positive effect on total nitrogen content of winter wheat. In general, increasing NPK doses resulted in significantly higher nitrogen. The effect of irrigation applied in previous years has no statistically significant effect on the sulphur and nitrogen content of wheat. The wheat grain produced in our experiment, especially in fertilized treatments showed S deficiency. Analysing the changes of CaCl2 soluble nitrate-N and total N of the soil, it can be stated that the effect of increasing fertilizer doses clearly appears in these parameters, because the treatment with increasing fertilizer doses resulted higher CaCl2 soluble N forms compared to the control treatment in soil. These values increased until flowering stage of wheat and after that a slightly decrease was observed as a result of higher N uptake of plant. In overall, it can be stated, that the effect of superphosphate on measured sulphur fraction is prevailed. With increasing fertilizer doses higher sulphate content was detected in soil, but the sulphate content measured in different soil extractant is not enough for the wheat in this experiment area. Studying the correlation between the measured parameters of plant and soil, it can be concluded, that the relationships between nitrogen in the plant and in the soil is stable, and did not change during the growing season. The correlation between plant S and soil S varied in the measured periods and the r value was low in most cases. At the stage of flowering the highest r value was found between KCl-SO4 and plant S. In the stage of ripening the strongest correlation was detected between KH2PO4-SO4 and grain S content.

Statistical Analysis versus the M5P Machine Learning Algorithm to Analyze the Yield of Winter Wheat in a Long-Term Fertilizer Experiment

To compare how different analytical methods explain crop yields from a long-term field experiment (LTFE), we analyzed the grain yield of winter wheat (WW) under different fertilizer applications in Müncheberg, Germany. An analysis of variance (ANOVA), linear mixed-effects model (LMM), and MP5 regression tree model were used to evaluate the grain yield response. All the methods identified fertilizer application and environmental factors as the main variables that explained 80% of the variance in grain yields. Mineral nitrogen fertilizer (NF) application was the major factor that influenced the grain yield in all methods. Farmyard manure slightly influenced the grain yield with no NF application in the ANOVA and M5P regression tree. While sources of environmental factors were unmeasured in the ANOVA test, they were quantified in detail in the LMM and M5P model. The LMM and M5P model identified the cumulative number of freezing days in December as the main climate-based determinant of the grain yield variation. Additionally, the temperature in October, the cumulative number of freezing days in February, the yield of the preceding crop, and the total nitrogen in the soil were determinants of the grain yield in both models. Apart from the common determinants that appeared in both models, the LMM additionally showed precipitation in June and the cumulative number of days in July with temperatures above 30 °C, while the M5P model showed soil organic carbon as an influencing factor of the grain yield. The ANOVA results provide only the main factors affecting the WW yield. The LMM had a better predictive performance compared to the M5P, with smaller root mean square and mean absolute errors. However, they were richer regressors than the ANOVA. The M5P model presented an intuitive visualization of important variables and their critical thresholds, and revealed other variables that were not captured by the LMM model. Hence, the use of different methods can strengthen the statement of the analysis, and thus, the co-use of the LMM and M5P model should be considered, especially in large databases involving multiple variables.

Deep Learning for Non-Invasive Diagnosis of Nutrient Deficiencies in Sugar Beet Using RGB Images.

In order to enable timely actions to prevent major losses of crops caused by lack of nutrients and, hence, increase the potential yield throughout the growing season while at the same time prevent excess fertilization with detrimental environmental consequences, early, non-invasive, and on-site detection of nutrient deficiency is required. Current non-invasive methods for assessing the nutrient status of crops deal in most cases with nitrogen (N) deficiency only and optical sensors to diagnose N deficiency, such as chlorophyll meters or canopy reflectance sensors, do not monitor N, but instead measure changes in leaf spectral properties that may or may not be caused by N deficiency. In this work, we study how well nutrient deficiency symptoms can be recognized in RGB images of sugar beets. To this end, we collected the Deep Nutrient Deficiency for Sugar Beet (DND-SB) dataset, which contains 5648 images of sugar beets growing on a long-term fertilizer experiment with nutrient deficiency plots comprising N, phosphorous (P), and potassium (K) deficiency, as well as the omission of liming (Ca), full fertilization, and no fertilization at all. We use the dataset to analyse the performance of five convolutional neural networks for recognizing nutrient deficiency symptoms and discuss their limitations.

Simulating the Impact of Long-Term Fertilization on Basic Soil Productivity in a Rainfed Winter Wheat System

Basic soil productivity (BSP) is the ability of a soil, in its normal environment to support plant growth. However, the assessment of BSP remains controversial. The aim of this study is to quantify and analyze the trends of BSP in winter wheat seasons using the decision support system for agrotechnologie transfer (DSSAT) model under a long-term fertilization experiment in the dark loessal soil region of the Loess Plateau of China. In addition, we evaluated the contribution percentage of BSP to yield and its influencing factors. A long-term fertilization experiment with a winter wheat/spring maize rotation was established in 1979 in a field of the Gaoping Agronomy Farm, Pingliang, Gansu, China, including six treatments: (1) no fertilizer as a control (CK), (2) chemical nitrogen fertilizer input annually (N), (3) chemical nitrogen and phosphorus fertilizer input annually (NP), (4) straw return and chemical nitrogen fertilizer input annually plus phosphorus fertilizer added every second year (SNP), (5) manure input annually (M), and (6) M plus N and P fertilizers added annually (MNP). The application of the DSSAT-CERES-Wheat model showed a satisfactory performance with good Wilmott d-index (0.78~0.95) and normalized root mean square error (NRMSE) (7.03%~18.72%) values for the tested genetic parameters of winter wheat. After the 26-years experiment, the yield by BSP of winter wheat under the M and MNP treatment significantly increased, at the rate of 2.7% and 3.82% a year, respectively, whereas that of CK and N treatments significantly decreased, at the rate of 0.23% and 3.03%. Moreover, the average contribution percentage of BSP to yield was 47.0%, 39.4%, 56.3%, 50.0%, and 61.9% in N, NP, SNP, M, and MNP treatments, respectively. In addition, soil organic carbon contents were the main controls of BSP under the different fertilization conditions in the dark loessial soil area. As a result, the combined application of organic fertilizer or straw and chemical fertilizer can be an effective form of fertilization management to greatly enrich basic soil productivity, continually promote the contribution percentage of BSP, and ultimately increase crop yield.

Fractions of copper in soil and their contribution to copper availability and uptake in maize–wheat cropping system under Typic hapludalfs

Long-term effects of integrated application of organics and chemical fertilizers on transformation of copper (Cu) into various chemical pools and their availability under maize–wheat cropping system were investigated in the ongoing long-term fertilizer experiment initiated in 1972 at the research farm of Chaudhary Sarwan Kumar Himachal Pradesh Agricultural University on an acidic soil in the Western Himalayas of India. The continuous use of chemical fertilizers alone for 36 years brought about marked depletion in all forms of copper except organically bound Cu (Cu-III) compared to buffer plots. Integrated use of organics and chemical fertilizers gave higher content of Cu forms over chemically treated plots except Cu occluded by free oxides (Cu-IV). Residual Cu was the most dominant form of copper contributing about 62% of the total Cu. Organically bound Cu (Cu-III) was the most important fraction of copper contributing toward DTPA (diethylene triamine pentaacetic acid) extractable Cu. Content of DTPA-extractable Cu increased over control when chemical fertilizers were applied in conjunction with different organics, whereas DTPA-Cu content declined over control with application of chemical fertilizers alone for the last 36 years.

Influence of 37 Years of Nitrogen and Phosphorus Fertilization on Composition of Rhizosphere Arbuscular Mycorrhizal Fungi Communities in Black Soil of Northeast China

Increased inorganic nitrogen (N) and phosphorus (P) additions expected in the future will endanger the biodiversity and stability of agricultural ecosystems. In this context, a long-term fertilizer experiment (37 years) was set up in the black soil of northeast China. We examined interaction impacts of elevated fertilizer and host selection processes on arbuscular mycorrhizal fungi (AMF) communities in wheat rhizosphere soil using the Illumina MiSeq platform. The soil samples were subjected to five fertilization regimes: no fertilizer (CK) and low N (N1), low N plus low P (N1P1), high N (N2), and high N plus high P (N2P2) fertilizer. Long-term fertilization resulted in a significant shift in rhizosphere soil nutrient concentrations. The N fertilization (N1 and N2) did not significantly change rhizosphere AMF species diversity, but N plus P fertilization (N1P1 and N2P2) decreased it compared with CK. Non-metric multidimensional scaling showed that the rhizosphere AMF communities in CK, N1, N2, N1P1 and N2P2 treatments were distinct from each other. The AMF communities were predominantly composed of Glomeraceae, accounting for 30.0–39.1% of the sequences, and the relative abundance of family Glomeraceae was more abundance in fertilized soils, while family Paraglomeraceae were increased in N1 and N2 compared with CK. Analysis shown that AMF diversity was directly affected by soil C:P ratio but indirectly affected by plant under long-term fertilization. Overall, the results indicated that long-term N and P fertilization regimes changed rhizosphere AMF diversity and community composition, and rhizosphere AMF diversity was both affected by soil C:P ratio and plant.

Synthetic Fertilizer Increases Denitrifier Abundance and Depletes Subsoil Total N in a Long-Term Fertilization Experiment.

Chronic synthetic nitrogen (N) application can result in a significant accumulation of nitrate in the subsoil, which could alter subsoil N cycle and subsequently affect subsoil N levels. To understand how elemental interactions affect the cycle and storage of subsoil N, we examined the soils receiving no fertilizer control (CK), 30-year applications of synthetic fertilizer (CF), and CF plus organic manure (CF + OM). The N cycling microbial groups and activity were investigated through analyzing abundance of bacteria, nitrifiers and denitrifiers, potential nitrification (PNA) and denitrification (DEA) rates in the topsoil (0–20 cm) and subsoil depths (20–80 cm). Compared with the CK, the CF application increased subsoil nitrate but reduced or did not change subsoil microbial biomass N and total N. Corresponding to the increased nitrate, the abundances of denitrifiers increased in the CF subsoils. By contrast, the abundances of nitrifiers increased in the CF topsoil. Significant correlation between the abundances of nitrifiers and soil PNA was found in the topsoil, while significant correlation was also found in the subsoil between the abundances of nirS- and/or nirK-type denitrifiers and DEA. These results suggest that the depleted or less changed subsoil total N by CF application might be partly related to the enriched denitrifiers groups and the related potential activity. The contrasting responses of nitrifiers and denitrifiers in the CF subsoil indicate a decoupling of both processes. Our findings highlight that the leached nitrate by synthetic fertilizer addition not only occurs as an environmental risk causing groundwater contamination but may also alter the subsoil N cycle through the denitrifier groups.

Comparison of effects exerted by bio-fertilizers, NPK fertilizers, and cultivation methods on soil respiration in Chernozem soil

Soil respiration is a significant indicator of soil microbial activity; global soil respiration and decomposition processes release yearly to the atmosphere a total of 220 billion tons of carbon dioxide. Therefore, studies on the whole- or one particular aspect of soil carbon cycle aiming at optimizing agricultural carbon dioxide emissions or improving carbon sequestration contribute to a sustainable agriculture practice. In this paper we present the effects of biofertilizer application (Bacillus megaterium, Bacillus circulans, and Pseudomonas putida) on soil respiration in chernozem soil. Experiments were performed at Látókép Experimental Station, belonging to the University of Debrecen, Hungary. Additionally, we compare our results with findings of prior studies related to commercial NPK fertilizer applications (in four doses: N60P45K45; N120P90K90; N180 P135K135; and N240P180K180), and two different cultivation methods (ploughed, loosened, RTK in rows, and RTK between rows); these investigations were conducted at the same experimental station. Our results indicate lower tendency for soil respiration, when biofertilizers are applied as compared to commercialNPK fertilizers, which enables to decrease CO2 emission in the environment.We also discuss a unit change indifferent alkali absorption-based methods (Oxitop and Witkamp) to facilitate comparability of recently acquired data with results of previous long-term fertilization experiments.

Depth Distribution of Bulk and Aggregate-Associated Manganese Oxides Mediated by Soil Chemical Properties in a Long-Term Fertilized Paddy Soil

Fertilization regimes greatly influence how manganese (Mn) oxides are recycled. However, information on this subject is scarce in rice managed paddies. The objective of this study was to examine the distributions of Mn pools in bulk soil and aggregates under different chemical and organic fertilizer ratios at both surface (0–20 cm) and subsurface (20–40 cm) soil depths. Depth distributions of Mn pools in bulk soil and aggregates were extracted using Mehlich 3 (M3-Mn), dithionite (Mnd), oxalate (Mno), and pyrophosphate (Mnp) solutions under a long-term fertilization experiment in a double rice cropping system. Fertilizer treatments comprised unfertilized control (CK), mineral nitrogen, phosphorus, and potassium (NPK), 30% mineral NPK + 70% organic fertilizer (30F; pig manure + milk vetch), 50% mineral NPK + 50% organic fertilizer (50F), and 70% mineral NPK + 30% organic fertilizer (70F) under a randomly complete block design (RCBD) in paddy conditions. A pattern of 30F > 50F > 70F > NPK > CK was established with positive and significant correlations among total organic carbon (TOC), total nitrogen (TN), and pH. All pools of Mn were in higher concentrations at the subsurface compared to the surface layer, where all aggregate sizes contributed equally to the enrichment of the metal oxides except for Mno in the 0.25–2.0 mm sizes at the surface layer. Distribution of manganese oxides was equal among the different soil aggregates which could cause the microaggregates to transport Mn oxides and pollute both surface and underground water sources.

Denitrification Potential of Paddy and Upland Soils Derived From the Same Parent Material Respond Differently to Long-Term Fertilization

To investigate the effect of land use and fertilization regimes on soil denitrification potential (SDP), two more than 30-year long-term fertilization experiments derived from same parent material (paddy soil and upland soil) were selected. Generally, the SDP in paddy soil was 6.82 times higher than the upland soil, which was due to the higher abundances of narG, nirS, and nirK genes and nirS-denitrifying bacteria (Bradyrhizobium, Cupriavidus, and Herbaspirillum) in paddy soil. Inorganic fertilization regimes in upland soil did not significantly affect the SDP over Control, while the SDP in NPK and 2NPK of paddy soil decreased by 26.48% and 75.65%, respectively. Compared with Control, NPKOM consistently yielded the highest SDP in both two soils, with 2.47 times and 2.86 times higher for paddy soil and upland soil. The SDP of paddy soil showed correlation with narG and nirS genes mainly regulated by Alo, while the difference in the SDP of upland soil largely depended on the change of nirS-denitrifying bacteria at genus level (Herbaspirillum, Sulfuritalea, and Cupriavidus) and species level, which was mainly controlled by soil pH. PLS path modeling further demonstrated that direct effect of functional genes on the SDP was the greatest for paddy soil, while nirS-denitrifying bacterial communities for upland soil. The results presented herein represent a key step toward understanding the mechanisms that govern SDP under land use and long-term fertilization.