Long-term Fertilization Experiment Research Articles

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.

Soil properties currently limiting crop yields in Swedish agriculture – An analysis of 90 yield survey districts and 10 long-term field experiments

• Among manageable soil properties, soil pH and extractable soil P had the largest impact on Swedish crop yields. • Current recommendations on soil pH and soil P require upward adjustment. • Surprisingly, increasing soil organic matter (SOM) reduced yields, most probably due to lower pH in soils richer in SOM. This study evaluated yield statistics and data from a comprehensive national soil inventory representing 90 yield survey districts and from the Swedish long-term soil fertility experiments. The aim was to identify the most yield-limiting soil properties and best agronomic practices in order to further improve yield. Principal Component Analysis, multi-variate analysis, step-wise regression, and tree partitioning analysis identified the same variables affecting yields in the national and experimental datasets. Crop yields were significantly affected by soil pH, soil organic matter (SOM), plant-available soil phosphorus (P-AL) and mean annual temperature. Contents of plant-available potassium and magnesium in soil had no significant impact on yield, except in potatoes. Soil pH was found to have the greatest potential to affect crop yields, even at values >6.5 (pH (H2O) ). Soil organic matter ranging from 3 to 6% in Swedish arable soils had an indirect negative effect on crop yields by lowering soil pH values with higher SOM content. To fully exploit the known benefits of SOM, liming requires more attention. One important finding was that current Swedish agricultural recommendations require updating. High-yielding crops demand more plant-available soil P and a range of 60−100 mg P-AL kg −1 soil is needed for sufficient P supply. A new target value of pH 7 for all crops except potatoes is recommended.

Long – term effect of integrated nutrient management on soil organic carbon fractions in vertisol under sorghum wheat cropping system

The field experiment was conducted the year 2014-2015 on the old long-term fertilizer experiment started since 1983 to assess the long – term effect of integrated nutrient management on soil organic carbon fractions in vertisol under sorghum wheat cropping system. The study showed that there was slight decrease in soil bulk density and calcium carbonate increase in porosity and water holding capacity and slightly increase pH and EC of soil over 33 years of sorghum-wheat cropping system receiving organic manures in combination with inorganic fertilizer. And it was observed that various forms of carbon and fractions of humus tended to decrease with depth and use of organics like subabul and FYM in conjunction with NPK fertilizers exerted a remarkable impact on the distribution and built up of various carbon and humus fractions in soil.

Weed Dynamics and Yield of Wheat in Long Term Soil Fertility Experiment under Rice-Rice-Wheat Cropping System

Weed dynamics and yield and yield parameters of wheat was studied in long-term soil fertility experiment under rice-rice-wheat system during winter season of 2018-19. The experiment was laid out in randomized complete block design with nine treatments replicated three times. Treatments were applied as: T1- no nutrients added, T2- N added; T3- N and P added; T4- N and K added; T5- N2:P2O5:K2O added at recommended rate for all crops. Similarly, T6- only N added in rice and N2:P2O5:K2O in wheat at recommended rate; T7- half N; T8- half NP of recommended rate for both crops; and T9- farmyard manure @10 t ha-1 for all crops in rotation. The results revealed that the use of Farm Yard Manure @ 10 t ha-1 gave significantly higher yield of 2393 kg ha-1 followed by recommended chemical fertilizer dose of 100:40:30 N:P2O5:K20 kg ha-1 of 2383 kg ha-1. Considerably, lower grain yield was obtained from treatments that did not receive phosphorus. Similarly, application of FYM @10 t ha-1 followed by recommended fertilizer dose recorded higher weed density and dry weed weight with compared to any of N,P2O5 and K2O or all nutrient omitted treatments.

Effect of long-term application of inorganic fertilizers, farm yard manure and lime on wheat (Triticum aestivum L.) productivity, quality and nutrient content in an acid alfisol

The effect of long-term addition of fertilizers and amendments on productivity, quality and nutrient content of wheat (Triticum aestivum L.) in an acid Alfisol was evaluated in field experiment at the research farm of the Department of Soil Science, Chaudhary Sarwan Kumar Himachal Pradesh Krishi Vishvavidyalaya (CSKHPKV) Palampur, Himachal Pradesh (India). The Long-Term Fertilizer Experiment was initiated during 1972 in randomized block design (RBD) with 11 treatments which were replicated three times. The soil of the experimental area was silt loam and classified taxonomically as “Typic Hapludalf”. The highest productivity of wheat (2822 kg ha−1) was recorded in the treatment comprising the recommended dose of fertilizer along with farmyard manure (FYM) @ 10t ha−1 and was statistically comparable with 100% NPK + lime (2589 kg ha−1). Continuous application of nitrogen (N) alone through urea (100%) in an acid alfisol has resulted in zero yield of wheat. Application of FYM and lime along with recommended doses of fertilizers improved all the crop quality parameters viz. crude protein, gluten, ash, fat, fiber and carbohydrate as compared to control and imbalanced fertilization for the last 45 years led to decline in crop quality parameters. Nutrient content in wheat grain i.e., phosphorus (P), magnesium (Mg) and iron (Fe) content was also the highest in FYM amended treatment and lowest in control. Whereas, calcium (Ca) content was the highest in lime amended plot and the lowest in control.

Soil aggregation and soil aggregate stability regulate organic carbon and nitrogen storage in a red soil of southern China

Soil aggregation plays a critical role in the maintenance of soil structure, as well as in its productivity. Fertilization influences soil aggregation, especially by regulating soil organic carbon (SOC) and total nitrogen (TN) contents in aggregate fractions. The present study evaluated the influence of three contrasting fertilizer regimes (unfertilized control –CK-, mineral fertilization –NPK- and manure combined with NPK –NPKM) on soil aggregate stability, aggregate-associated organic carbon and total nitrogen sequestration and mineralization of SOC. Soil samples from (20 cm) depth were collected from a long-term fertilization experiment and analysed for size distribution ranging (>250 μm, 250-53 μm and <53 μm sizes), SOC and TN contents, as well as for mineralization of bulk and aggregate associated-SOC. Both NPK and NPKM fertilizations significantly enhanced SOC and TN contents in bulk soil and its constituent aggregates of >250 μm, 250-53 μm and <53 μm sizes, as compared to CK. Long-term NPK and NPKM increased SOC and TN stock in bulk soil by 45 and 98%, and by 70 and 144%, respectively, as compared to CK. Similarly, higher values of SOC and TN stock in all aggregate fractions was observed with the application of NPKM. Application of NPK and NPKM for 26 years significantly increased aggregate stability, which was positively correlated with total SOC contents in terms of mean weight diameter (MWD) (Adj. R2 = 0.689, p < 0.03) and geometric mean diameter (GMD) (Adj. R2 = 0.471, p < 0.24). Moreover, higher scores regarding cumulative mineralization for bulk soil and aggregate associated OC were observed with the application of NPK and NPKM. Irrespective of treatments, higher cumulative C-mineralization was observed for macro-aggregates (>250 μm size) followed by 250-53 μm and <53 μm size aggregates. Interestingly, a highly positive correlation was observed between aggregate stability and the cumulative amount of mineralization for bulk soil and aggregate fractions, with R2 ranging from 0.84 to 0.99. This study evidenced that long-term fertilization of NPK and NPKM can improve soil aggregation, stability and associated OC and TN stock in aggregates, as well as aggregate-associated OC mineralization, which was further governed by aggregate size.

Phosphorus loss through surface runoff and leaching in response to the long-term application of different organic amendments on sloping croplands

Sustaining crop yield and decreasing the environmental risk of phosphorus (P) loss are key challenges for P fertilization management, which is helpful for achieving the goals for agriculture sustainable development. The effects of the long-term application of different organic amendments on P loss through surface runoff and leaching on sloping croplands have not been studied until now. We simultaneously measured the P loss based on a long-term fertilization experiment using a lysimeter (8 × 4 m2) with four treatments: control (no fertilizer; CK), mineral fertilizer (MF), mineral fertilizer combined with swine manure (MFSM), and mineral fertilizer combined with crop straw (MFCS). Annual P loss loads through surface runoff and leaching in the MF treatment were 90.3 ± 29.4 and 39.2 ± 13.2 mg m−2, respectively. The quantitative relationship between soil P surplus and total P loss load was described by a positive linear function, which suggested that a total P loss of approximately 2.9 kg ha−1 occurred with each 100 kg ha−1 of P surplus. P recovery efficiencies in the MFSM and MFCS treatments increased obviously by 24.0% and 34.5%, whereas soil P surplus decreased by 10.5% and 62.4%, respectively. Overall, the yield-scaled total P losses for the MFSM and MFCS treatments decreased significantly by 71% and 200%, respectively, compared with the MF treatment (0.12 ± 0.04 kg t−1). Long-term organic amendment application, especially for crop straw, effectively decreased P surplus and P loss, thereby increasing P efficiency. We recommend the combined application of mineral fertilizer with crop straw as a sustainable agronomic P management practice to achieve sustainable goals for development of the United Nations and the land degradation neutrality challenge.

Unexpected bulk density and microstructures response to long-term pig manure application in a Ferralic Cambisol Soil: Implications for rebuilding a healthy soil

Excessive applications of chemical fertilizers (e.g., nitrogen fertilizers) result in soil degradation, while organic manure application can alleviate soil degradation and rebuild a healthy soil. However, the effect of organic manure application on alleviating soil degradation over long-term fertilization remains poorly understood. Using soils (Ferralic Cambisol) that had been collected from a long-term fertilization experiment for 23 years (1990 − 2013) in subtropic South China, we showed that soil organic carbon (SOC) stocks increased by 2.5 times following 23 years of manure fertilizations (pig manure or a combination of manure and chemical fertilizers) or by 1.4 − 1.8 times following non-manure fertilizations, compared to the initial SOC stock in 1990. Strikingly, soil bulk density after 23 years fertilizations decreased in the order: 1.41 g cm−3 (manure) > 1.26 g cm−3 (no fertilizer) > 1.12 g cm−3 (chemical fertilizer), suggesting that long-term manure fertilization increased soil bulk density when compared to the non-manure treatments. The X-ray micro-computed tomography further demonstrated that compared to the non-manure treatments, manure fertilizations decreased the number of pores, throats and paths as well as porosity. In addition, the stock of oxalate-extractable Al and Fe increased by 2 times following 23 years of manure fertilizations, relative to the initial soil. In summary, this study for the first time showed that changes in mineral reactivity impact soil physical properties and the potential of soils to stabilize C, strengthening the possibility in alleviating soil degradation and rebuilding a healthy soil.

Differences in labile soil organic matter explain potential denitrification and denitrifying communities in a long-term fertilization experiment

Content and quality of organic matter (OM) may strongly affect the denitrification potential of soils. In particular, the impact of soil OM fractions of differing bioavailability (soluble, particulate, and mineral-associated OM) on denitrification remains unresolved. We determined the potential N2O and N2 as well as CO2 production for samples of a Haplic Chernozem from six treatment plots (control, mineral N and NP, farmyard manure - FYM, and FYM + mineral N or NP) of the Static Fertilization Experiment Bad Lauchstädt (Germany) as related to OM properties and denitrifier gene abundances. Soil OM was analyzed for bulk chemical composition (13C-CPMAS NMR spectroscopy) as well as water-extractable, particulate, and mineral-associated fractions. Soils receiving FYM had more total OM and larger portions of labile fractions such as particulate and water-extractable OM. Incubations were run under anoxic conditions without nitrate limitation for seven days at 25 °C in the dark to determine the denitrification potential (N2O and N2) using the acetylene inhibition technique. Abundances of nirS, nirK, and nosZ (I + II) genes were analyzed before and after incubation. The denitrification potential, defined as the combined amount of N released as N2O + N2 over the experimental period, was larger for plots receiving FYM (25.9–27.2 mg N kg−1) than pure mineral fertilization (17.1–19.2 mg N kg−1) or no fertilization (12.6 mg N kg−1). The CO2 and N2O production were well related and up to three-fold larger for FYM-receiving soils than under pure mineral fertilization. The N2 production differed significantly only between all manured and non-manured soils. Nitrogenous gas emissions related most closely to water-extractable organic carbon (WEOC), which again related well to free particulate OM. The larger contribution of N2 production in soils without FYM application, and thus, with less readily decomposable OM, coincided with decreasing abundances of nirS genes (NO2− reductase) and increasing abundances of genes indicating complete denitrifying organisms (nosZ I) during anoxic conditions. Limited OM sources, thus, favored a microbial community more efficient in resource use. This study suggests that WEOC, representing readily bioavailable OM, is a straightforward indicator of the denitrification potential of soils.