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In this research, the reliability and overall cost of unmanned aerial vehicle hangar were studied for two aspects: fault diagnosis and preventive maintenance. The maximum entropy ordered weighted average algorithm was adopted to predict the fault diagnosis of per module in the unmanned aerial vehicle hangar. The cost of preventive maintenance was controlled by adopting the optimal number of preventive maintenances under the object of minimum reliability. The optimization of maintenance cost could be achieved by repairing modules with excessive fault diagnosis rates under the determining preventive maintenance times and reliability. The reliability model of the unmanned aerial vehicle hangar was founded to the series–parallel structure of per module, and its reliability was compared between the regular maintenance and the irregular maintenance. The result showed that the reliability of the unmanned aerial vehicle hangar was more stable under the irregular maintenance. [ABSTRACT FROM AUTHOR]

In this paper, a preventive maintenance scheme for a rotary ultrasonic vibration-assisted EDM machine is investigated. A preventive maintenance cost optimization model for machine tools was developed under the constraint of reliability. The model is simple and efficient and can be applied to rotary ultrasonic vibration-assisted EDM machine tool. The mathematical model is based on particle swarm optimization, which is solved by MATLAB to compare the differences in optimization results under different iterations, and the optimal preventive maintenance interval for the machine tool is 417 h according to the constraints, corresponding to a minimum maintenance cost, which effectively reduces the downtime loss and maintenance cost caused by the failure of machine tools, and provides a theoretical basis for the preventive maintenance plan of machine tools. [ABSTRACT FROM AUTHOR]

In this paper, the reliability allocation and index of overall cost of rotary ultrasonic vibration-assisted EDM machine tool were studied. The failure rate of each module of the rotary ultrasonic vibration-assisted EDM machine tool can be accurately predicted by the maximum entropy ordered weighted average algorithm so that the corrected maintenance cost can be predicted. And effective control of preventive maintenance costs can be achieved by selecting the best maintenance times under the premise of reliability. The cost of corrective maintenance can be reduced by improving modules with a high failure rate, so as to realize the purpose of cost optimization under the premise of determining the maintenance time and reliability. The reliability function of the rotary ultrasonic vibration-assisted EDM machine tool is established according to the series-parallel relationship of each module. The results showed that the reliability of rotary ultrasonic vibration-assisted EDM machine tool is stabler at the non-fixed maintenance period according to the comparison between the non-fixed and the fixed maintenance period. [ABSTRACT FROM AUTHOR]

Impact of land surface characteristics on plant-soil processes Six studies in this special issue focused on how land surface characteristics (such as soil characteristics, topography, vegetation and hydrological process) can modulate plant-soil interactions. The karst landscape, one of the most fragile terrestrial ecosystems occupying 15-20% of the word's land area, has been undergone severe soil/land degradation (rocky desertification) and re-vegetation or ecological restoration is thus vital to halt rocky desertification in karst regions. [Extracted from the article]

Rotating ultrasonic vibration assisted EDM is a composite machining method that uses EDM to etch a metal surface and adds rotating and ultrasonic vibration. It has high efficiency and a wide range of workpiece materials. Aiming at the structural characteristics of rotary ultrasonic vibration assisted EDM machine tool, the errors caused by the main moving parts of the machine tool were analyzed. The structure relationship is described by multi-body system theory, and the geometric error model is deduced by homogeneous coordinate transformation method. The aim was to improve the overall accuracy, reduce the cost, trace the error source, and get the corresponding relationship between the basic geometric errors and the precision parameters of the related parts. Under the requirement of ensuring the overall accuracy, an optimization function was established that minimizes the cost and relaxes all accuracy parameters to the greatest extent. Finally, MATLAB and its genetic algorithm toolbox was used for analysis. Verification shows that this model can properly reduce the cost on the premise of ensuring the accuracy. [ABSTRACT FROM AUTHOR]

Highlights • Manure and synthetic fertilizer accounted for 39% and 21% of crop yields. • Synthetic fertilizer affected yields by weakly increasing soil nutrients and decreasing SOC and pH. • Manure affected yields by strongly increasing soil nutrients, SOC and pH. Abstract Fertilization is an important management strategy for crop yields by mediating soil fertility. However, rare studies quantitatively assessed the interactions among fertilization, crop yields, and soil fertility. Here, data from a 25-year fertilization experiment in the humid subtropical region of Southern China were used to evaluate and quantify the effect of fertilization on crop yields via soil fertility. Seven treatments were chosen: CK (non-fertilizer); N (synthetic nitrogen); NP (synthetic N and phosphorus); NPK (synthetic N, P and potassium); NPKM 1 (synthetic NPK with manure); 1.5NPKM 1 (1.5 times of NPKM 1); and M 2 (manure alone). Overall, the crop yields of wheat and maize under manure (1.36–1.58 and 3.85-5.82 Mg ha−1) were higher than those under CK (0.34 and 0.25 Mg ha−1) and synthetic fertilized treatments (0.27–0.97 and 0.48–2.65 Mg ha−1), as the averaged of 1991–2015. Higher SOC stocks were found under the NPKM 1 , 1.5NPKM 1 , and M 2 treatments with a pronounced increase in SOC over the first 10 years and stable over the last 15 years. By the boosted regression trees, manure, synthetic fertilizer and soil properties (SOC storage, soil pH, and soil nutrients) accounted for 39%, 21%, and 40% of the variation of the relative yield, respectively. Path analysis identified a network of inter-relations of manure, synthetic fertilizer, and soil properties in the relative yields. Compared to synthetic fertilized treatments, manure application strongly and positively affected the relative yield by increasing SOC storage, soil nutrients, and soil pH (path coefficients: 0.90, 0.88, and 0.76). These factors explained 72% of the crop yields' variance. These results suggest that manure application is a viable strategy for regulating crop yields due to its improvement in soil fertility. [ABSTRACT FROM AUTHOR]

The effects of soil type and organic material quality on the microbial biomass and functional diversity of cropland soils were studied in a transplant experiment in the same climate during a 1-year field experiment. Six organic materials (WS: wheat straw, CS: corn straw, WR: wheat root, CR: corn root, PM: pig manure, CM: cattle manure), and three contrasting soils (Ferralic Cambisol, Calcaric Cambisol and Luvic Phaeozem) were chosen. At two time points (at the end of the 1st and 12th months), soil microbial biomass carbon (C) and nitrogen (N) (MBC and MBN) and Biolog Ecoplate substrate use patterns were determined, and the average well color development and the microbial functional diversity indices (Shannon, Simpson and McIntosh indices) were calculated. Organic material quality explained 29.5–50.9% of the variance in MBC and MBN when compared with the minor role of soil type (1.4–9.3%) at the end of the 1st and 12th months, and C/N ratio and total N of organic material were the main parameters. Soil properties, e.g., organic C and clay content were the predominant influence on microbial functional diversity in particular at the end of the 12th month (61.8–82.8% of the variance explained). The treatments of WS and CS significantly improved the MBC and microbial functional diversity indices over the control in the three soils in both sampling periods (P < 0.05). These results suggest that the application of crop straw is a long-term effective measure to increase microbial biomass, and can further induce the changes of soil properties to regulate soil microbial community. [ABSTRACT FROM AUTHOR]

BACKGROUND: Soil fumigation can change soil nutrient cycling processes by affecting soil beneficial microorganisms, which is a key issue for soil fertility. However, the effect of combined application of fumigant and fungicide on soil phosphorus (P) availability remains largely unclear. We investigated the effects of the fumigant chloropicrin (CP) and the fungicide azoxystrobin (AZO) on soil phosphatase activity and soil P fractions in ginger production using a 28‐week pot experiment with six treatments: control (CK), a single application of AZO (AZO1), double applications of AZO (AZO2), CP‐fumigated soil without AZO (CP), CP combined with AZO1 (CP + AZO1) and CP combined with AZO2 (CP + AZO2). RESULTS: AZO application alone significantly increased the soil labile P fractions (Resin‐P + NaHCO3‐Pi + NaOH‐Pi) at 9 weeks after planting (WAP) but decreased the soil phosphatase activity at 28 WAP. CP fumigation significantly reduced the soil phosphatase activity but increased the proportions of soil labile P fractions (Resin‐P + NaHCO3‐Pi + NaHCO3‐Po) to total P (TP) by 9.0–15.5% throughout the experiment. The combined application of CP and AZO had a synergistic effect on soil phosphatase activity and soil P fractions compared with a single application. CONCLUSION: Although AZO application and CP fumigation can increase soil available P in the short term, they might negatively affect soil fertility in the long run by inhibiting soil phosphatase activity. Soil microbial activities, especially microorganisms related to P cycling, may be responsible for the variations in soil P availability, but further research is needed. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Optimal nitrogen (N) management is critical for efficient crop production and agricultural pollution control. Approximate 210–220 kg ha−1 N fertilizer was applied in millions of small plots through broadcasting way in China, resulting in over and loss of N fertilizers. However, it is difficult to implement advanced management practices on smallholder farms due to a lack of knowledge. Here, using 35,502 on-farm fertilization experiments, we demonstrated that smallholders in China could actually produce more grain with less N fertilizer use only through optimizing N application rate. The yields of wheat, maize and rice were shown to increase between 10% and 19% while N application rates were reduced by 15–19%. These changes resulted in an increase in N use efficiency (NUE) by 32–46% and a reduction in N surplus by 40% without actually changing farmers' operational practices. By reducing N application rates in line with official recommendations would not only save fertilizer cost while increasing crop yield, but also at the same time reduce environmental N pollution in China. Beyond of optimizing N application rate, improved management practices were required to produce more grain with less pollution, which would need about 11.8 billion US dollars for the implementation and reducing N loss reduction by 1.75 million tons to the environment. [Display omitted] • Optimizing N fertilizer rate was estimated based on 35,502 field experiments nationally. • Optimizing N rate increased NUE by 32–46% with 40% lower N surplus. • Environmental N loss was predicted to be reduced by 5.06 million t by optimizing N rate. • Best management strategies could result in 1.75 million tons N loss reduction. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) transfer plant photosynthate underground which can stimulate soil microbial growth. In this study, we examined whether there was a potential link between carbon (C) release from an AMF and phosphorus (P) availability via a phosphate-solubilizing bacterium ( PSB)., We investigated the outcome of the interaction between the AMF and the PSB by conducting a microcosm and two Petri plate experiments. An in vitro culture experiment was also conducted to determine the direct impact of AMF hyphal exudates on growth of the PSB., The AMF released substantial C to the environment, triggering PSB growth and activity. In return, the PSB enhanced mineralization of organic P, increasing P availability for the AMF. When soil available P was low, the PSB competed with the AMF for P, and its activity was not stimulated by the fungus. When additional P was added to increase soil available P, the PSB enhanced AMF hyphal growth, and PSB activity was also stimulated by the fungus., Our results suggest that an AMF and a free-living PSB interacted to the benefit of each other by providing the C or P that the other microorganism required, but these interactions depended upon background P availability. [ABSTRACT FROM AUTHOR]

Changes in field management and climate will alter soil organic carbon (SOC) and nitrogen (SN) cycling in the coming decades. This study is to quantify the effects of various fertilisation strategies and climate change scenarios on crop yield, and soil C and N cycling by the end of this century. Data from a long-term experiment with a winter-wheat ( Triticum aestivium L.) and summer maize ( Zea mays L.) rotation in Northern China was used to calibrate and validate the SPACSYS model. Five fertiliser practices were used: control (CK); combined mineral nitrogen, phosphorus and potassium (NPK); NPK plus manure (NPKM); high application rate of NPK fertilisers plus manure (hNPKM) and NPK with straw incorporation (NPKS). Crop yields, and SOC and SN stocks by 2100 were predicted under four climate scenarios (Baseline, RCP2.6, RCP4.5 and RCP4.5). Results showed that the SPACSYS model can adequately simulate the dynamics of SOC and SN stocks and the yields of winter wheat and summer maize. An application of NPK plus manure or straw not only enhanced crop yield, but also substantially increased SOC and SN stocks. The predictions showed the positive effects of fertilisation and climate change on crop yields and SOC stocks compared with those under the baseline. However, SN stock under the RCP8.5 decreased by 3–14% by 2100 for various fertilisation strategies compared with that under the baseline. On the other hand, mineral fertiliser plus manure led to a higher soil respiration rate and nitrogen losses through leaching and surface runoff under all the climate scenarios. Therefore, application of mineral fertilisers plus manure could enhance crop productivity and sustain soil fertility but cause more carbon emitted to the atmosphere and nitrogen losses. More attention should be paid on optimising fertilisation in order to increase crop productivity while minimising environmental risks. [ABSTRACT FROM AUTHOR]

Accurate modelling of agricultural management impacts on greenhouse gas emissions and the cycling of carbon and nitrogen is complicated due to interactions between various processes and the disturbance caused by field management. In this study, a process-based model, the Soil-Plant-Atmosphere Continuum System (SPACSYS), was used to simulate the effects of different fertilisation regimes on crop yields, the dynamics of soil organic carbon (SOC) and total nitrogen (SN) stocks from 1990 to 2010, and soil CO 2 (2007–2010) and N 2 O (2007–2008) emissions based on a long-term fertilisation experiment with a winter-wheat ( Triticum Aestivum L.) and summer-maize ( Zea mays L.) intercropping system in Eutric Cambisol (FAO) soil in southern China. Three fertilisation treatments were 1) unfertilised (Control), 2) chemical nitrogen, phosphorus and potassium (NPK), and 3) NPK plus pig manure (NPKM). Statistical analyses indicated that the SPACSYS model can reasonably simulate the yields of wheat and maize, the evolution of SOC and SN stocks and soil CO 2 and N 2 O emissions. The simulations showed that the NPKM treatment had the highest values of crop yields, SOC and SN stocks, and soil CO 2 and N 2 O emissions were the lowest from the Control treatment. Furthermore, the simulated results showed that manure amendment along with chemical fertiliser applications led to both C (1017 ± 470 kg C ha −1 yr −1 ) and N gains (91.7 ± 15.1 kg N ha −1 yr −1 ) in the plant-soil system, while the Control treatment caused a slight loss in C and N. In conclusion, the SPACSYS model can accurately simulate the processes of C and N as affected by various fertilisation treatments in the red soil. Furthermore, application of chemical fertilisers plus manure could be a suitable management for ensuring crop yield and sustaining soil fertility in the red soil region, but the ratio of chemical fertilisers to manure should be optimized to reduce C and N losses to the environment. [ABSTRACT FROM AUTHOR]

An effective N management could match N availability with crop demand to maximize nitrogen use efficiency (NUE) and to optimize N application rate. Using polyolefin-coated urea (POCU) to replace regular or non-coated urea (NCU) might be an option to achieve such objectives. A 2-year field study with five fertilization treatments was conducted in a rice-rice cropping system, in Qiyang, Hunan, southern China. The treatments include a control, both NCU and POCU at 150 and 300 kg N ha-1 yr-1. The results showed that average annual NUE and grain yield over 2-years were significantly greater under POCU (50% and 11.4 t ha-1 yr-1, respectively) than under NCU (36% and 10.6 t ha-1 yr-1, respectively). Based on their price of both rice grains and fertilizers in 2014 with a quadratic model, an optimal N rate was calculated as 178-203 kg N ha-1 yr-1 under POCU but 364-374 kg N ha-1 yr1 under NCU. A decrease of 46-50% N inputs could be thus achieved under POCU than under NCU. The use of slow release urea fertilizer such as POCU could maintain high grain yield and grower's income, increase NUE and decrease N losses in such rice-rice cropping systems in southern China. Application of POCU was hence agronomically practical and cost-effective over NCU in rice plantation. © 2015 Friends Science Publishers [ABSTRACT FROM AUTHOR]

Water and fertilizer play an important role in crop growth in dryland areas. It is a necessity to improve the water use efficiency (WUE) of the crop once the water resource is limited. In northern China, where there is a wide shortage of water resources, it is therefore necessary to investigate how fertilization affects the WUE of spring maize and to quantify the effects. A total of 33 published peer-reviewed papers were collected, and a meta-analysis and random forest model analysis were performed with 364 WUE comparisons, aiming to explore the effects of fertilization on the WUE of spring maize and to clarify the optimal conditions for WUE under fertilizer management. The results showed that fertilization significantly increased the WUE of spring maize by 56.72% (P < 0.01) when compared with non-fertilization. The WUE effect under the organic–inorganic fertilizer combination (MNPK) was approximately twice as high as that under inorganic fertilizer (NPK) or organic fertilizer (M). The greatest increase in WUE occurred at 0–100 kg ha−1 of nitrogen application (NA). Under environmental conditions including 7 ≤ mean annual temperature in the test year (T) ≤ 10 °C, 400 ≤ mean annual precipitation in the test year (P) ≤ 600 mm, and mean altitude (A) > 1500 m, and soil conditions including 10 ≤ soil organic matter content (SOM) ≤ 14 g kg−1 and available phosphorus (AP) < 5 mg kg−1, the fertilization optimally enhanced the WUE of spring maize when the agronomic measures of ridge–furrow planting (RFP) and mulching film (MF) were used. The random forest model analysis indicated that the influence factors (i.e., fertilizer regimes, environmental factors, soil factors, and agronomic measures) caused 65.62% of the variation in spring maize WUE effects, while in all influence factors, fertilizer types related to fertilizer regimes caused the most variation. The initial available potassium (AK) and available nitrogen (AN) of the soil were negatively correlated to the WUE effect, indicating that fertilization imposed a better effect on the WUE of spring maize when the soil was infertile. Fertilization significantly increased the WUE of spring maize, and organic and inorganic fertilizer application provided an effective measure for the sustainable development of spring maize in northern China. After clarifying the required conditions for fertilization increasing WUE, high-efficiency water use may be achieved. [ABSTRACT FROM AUTHOR]

Laser melting deposition (LMD) additive manufacturing process has been attractive to the fabrications of pure tantalum due to the advantage of fast near net shaping of complex shaped components. In the present study, the LMD process has been applied to the fabrication of tantalum using two kinds of powders with different interstitial contents. The microstructure, chemistry, and mechanical properties of the LMD samples have been investigated to understand the strengthening mechanisms. The results show that the tantalum samples have near full dense, and large columnar grains with the growth direction slightly deviated from the deposition direction. The LMD tantalum can have high hardness of up to 300 HV, mainly due to the solid solution strengthening of nitrogen and oxygen interstitials. With relative low interstitial contents of about 400 ppm, the LMD tantalum can have ductile properties, showing ultimate tensile strength above 400 MPa, and elongations of about 14–16%, which are comparable to the properties of cold-worked tantalum. The present work suggests the LMD tantalum could have potential usages in the industry fields. • Near full dense pure tantalum has been fabricated by laser melting deposition. • The tantalum has large epitaxially grown columnar grains. • Solid solution strengthening of interstitials lead to high hardness and high strength. [ABSTRACT FROM AUTHOR]

Abstract: Soil degradation and water pollution could have resulted from inappropriate phosphorus (P) supply. Soil Olsen P is generally a good indicator to estimate bio-availability of P and environmental risk in alkaline soil. The change in Olsen P is always strongly affected by soil organic carbon (SOC) when different forms of inorganic and/or organic P are applied to farmlands with chemical fertilizer and/or manure. We related soil Olsen P to apparent P balance (APB) and SOC in alkaline soils at three 15-year (1991–2005) fertilization sites of northern China. Six treatments were examined: unfertilized control, chemical nitrogen (N), chemical NP, chemical N plus potassium (NK), chemical NPK, and chemical NPK plus animal manure (NPKM, same total N but 20–80% more P). Compared to the initial Olsen P in 1990, after 15years Olsen P was increased under P fertilization but decreased under no-P fertilization. At the three 15-year fertilization sites, annual mean Olsen P was 4.9–12.3 times higher under NPKM, 1.9–2.8 times higher under NP and NPK, but only 28.3–84.8% under Control, N and NK. Annual mean percentage of Olsen P to total P was higher under NPKM (4.6–8.1%) than under other five fertilizations (0.4–2.9%). Change in Olsen P significantly positively correlated with accumulated APB under all fertilizations (r 2 =0.10–0.31, P <0.05). At these three sites, Olsen P could be increased by 5.2, 5.8 and 12.1% respectively under NP, NPK and NPKM when 1kgP/ha was in surplus, meanwhile Olsen P was decreased by 2.1, 4.0 and 6.4% under Control, N and NK when 1kgP/ha was in deficit. Significantly higher SOC accumulation was under NPKM than under other five fertilizations when calculated by the same unit of P input. The combination of chemical P and manure P with organic C input is a better strategy to increase soil Olsen P and SOC accumulation on farmland with maize–wheat rotation in northern China. [Copyright &y& Elsevier]

Highlights: [•] Long-term field research proved that manure application with chemical fertilizer improved the nitrogen use efficiency (NUE) of wheat–corn rotation system the most especially in acid soil. [•] Phosphorus is found to be another important factor to improve NUE up to 40–60% if soil is P deficient. [•] Between the rotation crops, both grain yield and NUE of wheat were determined more responsive to P fertilization, and that for corn were more responsive to manure application. [Copyright &y& Elsevier]

Abstract: Long-term fertilization has a significant impact on total soil organic carbon (SOC) stock. However, fertilization impact on physical fractions of SOC is still poorly understood for red soils in southern China. This study assessed the impact of 17years (1990–2007) of long-term fertilization on the changes in different SOC fractions under an intensive maize (Zea mays L)–wheat (Triticum Aestivium L) cropping system in a red soil of southern China through various treatments: the unfertilized control (CK), the recommended applied rates of N (N), NP (NP), NPK (NPK), NPK+manure (NPKM), NPK+straw (NPKS) and manure only (M), and a 150% recommended applied rate of NPK+manure (1.5NPKM). Soil samples from 0 to 20cm soil layer taken in September, 2007, were separated into free particulate organic C (fPOC), intra-microaggregate particulate organic C (iPOC), and mineral associated organic C (MOC) with physical fractionation. In comparison with CK, all the C fractions and maize and wheat yields were significantly increased, except for N and NP treatments. The treatments with manure (M, NPKM, and 1.5NPKM) showed higher C sequestration rates in MOC (323–515kgha−1 yr−1), fPOC (291–408kgha−1 yr−1) and iPOC (162–179kgha−1 yr−1). It was estimated that 8.0 to 35.7% of the gross C input from manure and crop residues over a period of seventeen years contributed to the increase of total SOC stock. Both MOC C sequestration efficiency (CES) and C sequestration distribution (CSD) were the highest among the C fractions for all the treatments. Significantly positive linear correlations were observed between accumulated C sequestrations in all fractions with gross C input and both maize and wheat yields. Our result indicated that MOC was the primary fraction of C sequestration in the red soils. The most efficient fertilization practice for sequestering C in each fraction in the red soils was continuous applications of either manure or manure plus mineral fertilizers. [Copyright &y& Elsevier]

Abstract: The effects of conservation tillage on profile distributions of soil organic carbon (SOC), total N (TN), and C:N ratios were not well documented in China. The work was conducted at two field experimental sites in the northeast of China. Soils were Cambisols and continuously cultivated with maize (Zea mays L.) for 12years (Jianping site) and 5years (Changtu site). Two treatments were conducted at each site and were traditional tillage (TT, i.e., mouldboard plow with residue incorporation) and conservation tillage (CT, i.e., no-tillage with residues left on the soil surface). The responses of SOC and TN stocks to CT differed between the sites and among the soil depths. In the surface soil (0–20cm), SOC and TN concentrations and C:N ratio were uniformly-distributed under TT. These same response variables decreased with increasing depth under CT. The stratification ratios of SOC for surface to deeper depth (i.e., 0–5cm:20–40cm) ranged from 1.5 to 1.8 under CT but only from 1.2 to 1.3 under TT. CT also increased stratification of soil TN and the C:N ratio compared to TT. [Copyright &y& Elsevier]

Changes in total organic C ( C), water-soluble organic C ( C), microbial biomass C ( C), C mineralization, particulate organic C ( C), labile organic C ( C), C management index (CMI), and C storage in surface Hapli-Ustic Cambisol (0-20 cm) under straw incorporation after both 2- and 10-year durations were investigated in a maize ( Zea mays L.) field experiment in northeast China, in order to examine the effectiveness of these active C fractions and CMI as early indicators for total C change. The treatments included straw removal (0%S), 50% of straw incorporation (50%S), and 100% of straw incorporation (100%S). Under the straw incorporation, C concentration and C storage did not significantly change under 2-year duration, while were significantly increased under 10-year duration. However, C, total C mineralization ( C), C, and C, and CMI were significantly increased under the straw incorporation even after only 2-year duration, and the responses were more significant after 10-year duration. There were positive correlations between all these C indicators with each other. Our findings demonstrate that the measured active C fractions (except for C) and CMI can provide an early indication of change in total soil organic C induced by straw incorporation. [ABSTRACT FROM AUTHOR]

The effect of long-term fertilization and cropping on soil potassium (K)-supplying capacity has not been extensively studied. Five treatments [control, nitrogen (N), N-potassium (P), NPK, and NPK + manure (NPKM)] were used to evaluate the quantity and intensity relationship (Q/I) of K in black soil (Luvic Phaeozems soil) after a 15-year (1990-2005) long-term fertilization with a continuous corn cropping located in Changchun, Jilin Province, northeast China. Results showed that the long-term K fertilization of NPK or NPKM markedly increased the values of equilibrium active ratio (AR0K) and nonspecifically available K (-ΔK0) but decreased the potential buffering capacity (PBCK) value. Values of the AR0K and -ΔK0 in the NPK and NPKM treatment were about four and two times greater than those in the control, N, and NP treatments, respectively. Compared with the non-K fertilization, PBCK values were decreased by 40-49% under the K fertilization. The black soil suffered from K deficiency even with NPK fertilization as evidenced from the greater free energies of K+ exchanging for calcium (Ca2+) and magnesium (Mg2+) (-ΔG) (14.7-18.8 kJ mol-1) than the threshold value of 14.6 kJ mol-1, from the lower soil K+ saturation (1.34%-1.44%) than the critical value of 2.00%, and from the response of corn yield to K fertilization. Our results demonstrated that the increment of the current K application rate through fertilizer and/or manure is needed to improve corn yield in the long run in northeastern China. [ABSTRACT FROM AUTHOR]

Abstract: A 12-year field experiment was used to examine effects of return rates of crop straw residue on organic C sequestration by chemical fertilization in surface (0–20cm) soil. The tested soil was a Hapli-Ustic Cambosol (FAO taxonomy) and the used crop was maize (Zea mays L.). The four main treatments were consisted of a gradient of return rate of straw residue, namely 0%, 25%, 50% and 100% of shattered straw residue (referred to as 0%S, 25%S, 50%S and 100%S, respectively). The three sub-treatments contained unfertilized control (CK), unbalanced N fertilization (N) and balanced NPK fertilization (NPK). Along the gradient of straw return rate, topsoil C storage significantly increased. The balanced NPK fertilization was more effective in sequestrating topsoil C than the unbalanced N fertilization. Responses of topsoil C storage to the straw return and fertilization significantly increased with the experimental duration. With increasing straw return rates, C-sequestration effects of the N, and NPK treatments in topsoil changed from not significant to significant or from significant to more significant in statistics. Our findings demonstrate that C-sequestration effects of chemical fertilization in topsoil strongly depend on return regime of straw residue. [Copyright &y& Elsevier]

Potassium (K) fixation by seven soils, including black soil, fluvo-aquic soil, grey desert soil, loess soil, paddy soil, red soil and purple soil, was determined by laboratory simulation under a fifteen-year-period of long-term fertilization. Factors affecting soil K fixation were then discussed by factor analysis and stepwise regression. Magnitude of soil K fixation rate was as follows: the black soil > the purple soil > the loess soil > the fluvo-aquic soil > the paddy soil > the grey desert soil > the red soil. Our results showed that soil K fixation capacity was significantly affected by the clay mineral types in the soils. Potassium fixation capacity of soils, whose 2:1 layer silicates were dominant minerals, was affected by two components extracted by the method of principal component analysis: the first including soil available K, slow available K and K+ saturation, and the second including cation exchange capacity (CEC), soil organic matter (SOM) and <0.002 mm clay contents. Potassium fixation rate was mainly affected by K+ saturation and CEC with lower added K concentration (from 0.4 to 1.6 g/L), and by K+ saturation and <0.002 mm clay content with higher added K concentration (from 2.4 to 4.0 g/L). [ABSTRACT FROM AUTHOR]

Crop productivity and soil health are limited by organic carbon (OC), however, the variations in the mechanisms of SOC preservation in a complete soil profile subjected to long-term fertilization remains unclear. The objective of the study was to examined the content and profile distribution of the distinctive SOC protection mechanisms on a complete profile (0–100 cm) of Eumorthic Anthrosols in Northwest China after 23 years of chemical and manure fertilization. The soil was fractionated by combined physical-chemical and density floatation techniques. Throughout the profile, significant variations were observed among fractions. In the topsoil (0–20 and 20–40 cm), mineral coupling with the fertilization of manure (MNPK) enhanced total SOC content and recorded for 29% of SOC in the 0–20 and 20–40 cm layers. Moreover, MNPK increased the SOC content of the unprotected cPOC fraction by 60.9% and 61.5% in the 0–20 and 20–40 cm layer, while SOC content was low in the subsoil layers (40–60, 60–80 and 80–100 cm, respectively) compared with the control (C). The highest OC under MNPK in physically protected micro-aggregates (μagg) (6.36 and 6.06 g C kg−1), and occluded particulate organic carbon (iPOC) (1.41 and 1.29 g C kg−1) was found in the topsoil layers. The unprotected cPOC fraction was the greatest C accumulating fraction in the topsoil layers, followed by μagg and H-μSilt fractions in the soil profile, implying that these fractions were the most sensitive to the fertilization treatments. Overall, the unprotected, physically protected, and physico-chemically protected fractions were the dominant fractions for the sequestration of carbon across fertilization treatments and soil layers. Image 1 • Physical protection mechanisms were the most dominant in soil profile. • CPOC was the most sensitive fractions. • MNPK and SNPK caused accretion of total SOC content in a soil profile. • The correlations suggested that this soil has not yet reached C saturation. [ABSTRACT FROM AUTHOR]

Long term fertilization may have a significant effect on soil organic carbon (SOC) fractions and profile distribution. However, previous research mostly explored the SOC in the topsoil and provided little or no information about its distribution in deeper layers and various protection mechanisms particularly under long-term fertilization. The present study investigated the contents and profile distribution (0–100 cm) of distinct SOC protection mechanisms in the Mollisol (black soil) of Northeast China after 35 years of mineral and manure application. The initial Organic Matter content of the topsoil (0–20 cm) ranged from 26.4 to 27.0 g kg−1 soil, and ploughing depth was up to 20 cm. A combination of physical-chemical fractionation methods was employed to study various SOC fractions. There were significant variations throughout the profile among the various fractions and protection mechanisms. In topsoil (to 40 cm), mineral plus manure fertilization (MNPK) increased the total SOC content and accounted for 16.15% in the 0–20 cm and 12.34% in the 20–40 cm layer, while the manure alone (M) increased the total SOC by 56.14%, 48.73% and 27.73% in the subsoil (40–60, 60–80 and 80–100 cm, respectively). Moreover, MNPK and M in the topsoil and subsoil, respectively increased the unprotected coarse particulate organic carbon (cPOC) (48% and 26%, respectively), physically protected micro-aggregate (μagg) (20% and 18%, respectively) and occluded particulate organic carbon (iPOC) contents (279% and 93%, respectively) compared with the control (CK). A positive linear correlation was observed between total SOC and the cPOC, iPOC, physico-biochemically protected NH-μSilt and physico-chemically protected H-μSilt (p < 0.01) across the whole profile. Overall, physical, physico-biochemical and physico-chemical protection were the predominant mechanisms to sequester carbon in the whole profile, whereas the biochemical protection mechanisms were only relevant in the topsoil, thus demonstrating the differential mechanistic sensitivity of fractions for organic carbon cycling across the profile. Unlabelled Image • Sole application of manure enhanced SOC content in the subsoil. • cPOC and iPOC were the most robust indicators of SOC sequestration throughout the profile. • Physical protection was important for C sequestration in top- as well as in the subsoil. • Aggregate-related chemical and biochemical protection was dominant across the profile. [ABSTRACT FROM AUTHOR]

The soil organic carbon (SOC) saturation deficit (Csd) of silt and clay fractions represents the potential for SOC sequestration in a stable form and can influence organic C stabilization efficiency. Little is known, however, about temporal changes of stable soil Csd and how it is affected by soil properties, climate and C inputs. We investigated the temporal changes in the Csd of fine fractions (<53 μm) and examined the factors controlling these changes at three dry-land sites with 17-year fertilizer management histories in China. The rates of change in the stable soil Csd under manure treatments varied from −0.72 to −1.24% yr−1 after 17 years of fertilization, indicating that stable C levels under manure treatments were significantly higher than those under other treatments. Stable soil Csd was controlled by a combination of soil properties, temperature, and C inputs at all sites, and the higher variance of Csd of fine fractions can be explained by the soil properties (up to 50%). Furthermore, the quantity of C inputs was the most influential variable for stable soil Csd. These results revealed key controls on stable C sequestration potential and indicated the need to develop management strategies to promote stable C sequestration under long-term intensive fertilization. [ABSTRACT FROM AUTHOR]

To improve the potassium availability of feldspar at ordinary temperatures, the mechanical grinding and addition of sodium hydroxide/salts were employed to study the effects of mechanical activation and strong alkali addition on particle characteristics, water-soluble potassium, and the available potassium of feldspar. A laser particle size analyzer was utilized for the direct determination of particle size distribution (PSD) using ground samples. The Brunauer–Emmett–Teller (BET) method was employed for specific surface areas. X-ray diffraction (XRD) was employed for structural characterization, scanning electron microscopy (SEM) for morphology exploration, and energy dispersive spectroscopy (EDS) to determine the chemical composition of potassium feldspar powder. The results revealed that the mechanical activation of potassium feldspar could reduce the particle size and produce agglomerated nanoparticles in the later period. The addition of NaOH and sodium salt did not cause agglomeration, and NaOH dissolved the nanoparticles. The water-soluble potassium content of feldspar in each treatment increased during mechanical grinding, from 21.64 mg kg−1 to 1495.81 mg·kg−1, by adding NaOH 5% weight of potassium feldspar powder and to 3044.08 mg·kg−1 by adding NaOH 10% weight with effects different from those of mechanical shaking. By comparison, only 162.93 mg·kg−1 water-soluble potassium was obtained by adding NaOH 5% weight. The dissolved potassium in the former case was significantly higher than in the latter, and the addition of NaOH and sodium salts significantly enhanced the water-soluble potassium contents due to ion exchange. Furthermore, the addition of sodium hydroxide improved the water-soluble potassium due to its mechanochemical action on potassium feldspar. The mechanical energy changed the crystal structure of potassium feldspar, explaining the increase in available potassium. The addition of sodium salts did not promote change in the feldspar's structure, thereby did not raise the available potassium content. The reason for this was related to the mechanochemical action on sodium hydroxide and feldspar, which could promote the dissolution of fine particles, thereby incrementing the available potassium. [ABSTRACT FROM AUTHOR]

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

Partial substitution of synthetic nitrogen fertilizer with manure (organic substitution) is highly recommended to minimize environmental risks without compromising crop productivity in intensive agricultural systems. However, our understanding of the effect of organic substitution on soil organic carbon (OC) and total nitrogen (TN) in deep soil and its impact on crop productivity remains limited. Here we investigated OC and TN changes in soil profile down to 100 cm, crop yield, and sustainable yield index under synthetic nitrogen, phosphate, and potassium fertilizers (NPK), NPK plus straw (NPKS), and organic substitution (NPKM) treatments over two decades in four upland fields across different climate zones. Compared with the initial values, two decades of NPKM treatment significantly (p < 0.05) increased OC and TN stocks in either topsoil (by 25.6–103.8 and 15.8–89.8%) or deep soil (by 2.9–71.3 and 5.7–36.9%), respectively, across all sites. The increases in OC and TN stocks in 0–100 cm soil receiving NPKM were significantly higher than those receiving NPK at all sites and NPKS at three high-evaporation sites. Compared with NPKS and NPK treatments, crop yield and N uptake were significantly increased under NPKM treatment only at the Qiyang site. Furthermore, OC sequestration in the entire soil profile down to 100 cm and TN accumulation in topsoil exhibited significant positive correlations with crop N uptake, relative crop yield, and sustainable yield index. In conclusion, long-term partial substitution of synthetic N fertilizer with manure facilitates soil OC and TN sequestration in the entire 100 cm profile and thus maintains high crop productivity in upland areas. [ABSTRACT FROM AUTHOR]

Abstract Long-term application of organic fertilizers in acidified agricultural soils could alter soil nitrogen (N) immobilization by providing carbon (C) source and alleviating soil acidification. However, an understanding of the relative importance of abiotic and biotic N immobilization in acidified agricultural soils following long-term organic fertilizer application is largely lacking. Generally, the application of crop straw, which has a higher C/N ratio than animal manure, results in higher biotic N immobilization in soils. In contrast, the application of animal manure can result in greater stimulation of soil microbial activity due to a higher capacity to alleviate acidification. Resolving this contradiction is critical for predicting microbial N retention capacity and the effects of different types of organic fertilizer in acidified agricultural soils. A laboratory 15N tracer experiment was carried out to examine the effects of long-term animal manure and crop straw application on abiotic and biotic N immobilization in an acidified agricultural soil in China. Animal manure application had a higher stimulation effect on abiotic and biotic N immobilization than crop straw. Microbial NH 4 +-N immobilization, as opposed to abiotic NH 4 +-N immobilization, largely contributed to the retention of NH 4 +-N. In contrast, abiotic NO 3 −-N immobilization had a more significant role in NO 3 −-N retention than microbial NO 3 −-N immobilization under elevated C conditions. Animal manure-induced increases in microbial NH 4 +-N and NO 3 −-N immobilization could be attributed to both increased C availability and enhanced soil microbial activity due to an increase in soil pH. The results suggest that long-term inputs of organic material to acidified agricultural soils could enhance abiotic and biotic N immobilization capacity. Highlights • Animal manure stimulated N immobilization more than straw. • High microbial N immobilization in animal manure due to high C availability and soil pH. • Microbial immobilization largely contributed to NH 4 +-N retention. • Abiotic immobilization had a more significant role in NO 3 −-N retention. [ABSTRACT FROM AUTHOR]

The application of nitrogen (N) fertilizer is key to realize high crop yields and ensure food security. Excessive N application and relatively low N use efficiency (NUE), however, have led to substantial N losses to air and water with related impacts on biodiversity and health. We used historical data from 13 long-term experiments to unravel how the NUE depends on fertilizer strategy and site conditions such as crop rotation, soil properties and climate. During nearly 40 years of fertilization, NUE decreased when crops were fertilized with N and potassium fertilizers only, while the NUE increased when multi-nutrient or organic fertilizers were used. The highest NUE was found when 25–30% of the total N input was supplied in organic form. Among the site conditions analysed, soil pH was the most important factor controlling NUE with an optimum pH around 6. In addition to soil acidity, phosphorus availability increased NUE. Crop rotation, soil properties and fertilizer management together explained 46–85% of the variation in NUE, allowing site specific fertilizer strategies to be developed boosting NUE. Current NUE equalled on average 30% in paddy soils, 39% in upland soils and 42% in paddy upland soils. Optimizing all fertilizer inputs and soil nutrient levels might increase the NUE up to 40–47% in paddy soils, up to 40–77% in upland soils and even up to 40–87% in a paddy upland soils. [Display omitted] • Data from 13 experimental sites were used to assess nitrogen use efficiency (NUE). • Site conditions and fertilizer management explained 46–85% of the NUE variation. • Soil pH was a very important factor controlling NUE, with an optimum around 6. • Phosphorus and potassium availability had a substantial impact on the NUE. • The highest NUE was found when 25–30% of the N input was supplied in organic form. [ABSTRACT FROM AUTHOR]

The application of manure (M) and straw (S) will increase the Olsen P and phosphorus activation coefficient (PAC) in soil. Clarifying the increasing trend of Olsen P and PAC is crucial for rational fertilization. This study fitted the equation between the accumulated P surplus, Olsen P, and PAC in four treatments for 28 years and analyzed the changes and rates of P fractions. The results showed Olsen P and PAC increase linearly with NPK and NPKS treatments; for every 100 kg ha−1 of P surplus, Olsen P increased by 5.9 and 6.7 mg kg−1, and PAC increased by 0.52% and 0.50%. With M and MNPK treatments, the sigmoid curve equation was the best fitting method. The equilibrium values were 167 and 164 mg kg−1 for Olsen P, and 10.4 and 10.2 mg kg−1 for PAC. There was a correlation between Al-P, Ca2-P, Resin-P, NaOH-Pi, C/N, SOC, and pH, which had the highest interpretation rates for Olsen P and PAC. Manure is significantly better than straw in improving Olsen P in red soil. It is recommended to reduce the amount of manure applied for a long time to avoid a zero increase in Olsen P. [ABSTRACT FROM AUTHOR]

The storage of soil organic carbon (SOC) in cropland soils is an essential strategy that serves the dual purpose of enhancing soil fertility and mitigating climate change. However, how the stability of stored carbon is altered under long-term fertilization has not been well understood, especially in the double rice cropping system in Chinese paddy soils. In this study, we explored the SOC storage and consequent stability of SOC under long-term fertilization. The soil samples were fractionated chemically to isolate various fractions and constituent pools of SOC (i.e., very labile C/VLC, labile C/LC, less labile C/LLC, and non-labile C/NLC). The following treatments were tested: control (CK), recommended rate of inorganic fertilizer (NPK), double the amount of recommended rate of inorganic fertilizer (2NPK), and NPK combined with manure (NPKM). The results showed that, relative to the initial level, the application of NPKM significantly improved the SOC storage as compared to the control. The long-term NPKM increased the total SOC in the paddy soil and this increased SOC was mainly stored in LLC, as revealed by the highest increase (142%) over the control. Furthermore, the highest proportion of labile pool was associated with unfertilized CK, while the reverse was true for the recalcitrant pool, which was highest under NPKM. This supports the role of combining manure with NPK to improve the stability of SOC, further verified by the high recalcitrance index under NPKM (56.75% for 0–20 cm and 57.69% for 20–40 cm) as compared to the control. [ABSTRACT FROM AUTHOR]

Potassium thiosulfate (KTS, K 2 S 2 O 3 ) has been shown to function as a nitrification inhibitor, thus has the potential to reduce nitrous oxide (N 2 O) emissions and play an important role in effective N management. The objective of this research was to determine the potential effects of KTS on N 2 O emissions and N transformation processes in comparison with commercial N transformation inhibitors (stabilizers). A laboratory incubation experiment was conducted using urea and ammonium nitrate (UAN) applied at 150 mg N kg − 1 in a Hanford sandy loam soil (coarse-loamy, mixed, superactive, nonacid, thermic Typic Xerorthents). Treatments included three rates of KTS (26, 51, and 102 mg S 2 O 3 2 − -S kg − 1 ), a urease and nitrification inhibitor (Agrotain® Plus), a nitrification inhibitor (N-Serve® 24), and an untreated control. Nitrous oxide emission, soil pH, and mineral N species were monitored for 35 days. Total N 2 O emissions were reduced significantly by all KTS treatments as a function of KTS rate. At 102 mg S 2 O 3 2 − -S kg − 1 , KTS reduced N 2 O emissions by 48% (0.18% of total inorganic N), which was statistically similar to the N-Serve® 24 treatment (60% reduction) although lower than Agrotain® Plus (78% reduction). The KTS resulted in significantly less unaccounted (total N) loss compared to the commercial inhibitors. If the N 2 O emissions reductions observed in this laboratory study are validated in the field, using KTS for this purpose can also provide a fertility benefit and may reduce total chemical inputs into agronomic systems. Future research needs to determine the effectiveness of thiosulfate for improving overall nutrient management while reducing N 2 O emissions under field conditions. [ABSTRACT FROM AUTHOR]

P or PK addition significantly affected microbial CUE. The pure N addition was used to analyze the N effect on microbial CUE, but the data of N addition rate was not entirely correct in the dataset of Hu et al. ([2]). [Extracted from the article]

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

Long-term use of artificial fertiliser has a significant impact on soil organic carbon (SOC). We used physical–chemical fractionation methods to assess the impact of long-term (26 years) fertilisation in a maize cropping system developed on Brown Earth in Northeast China. Plot treatments consisted of control (CK); nitrogen (N) fertiliser (N2); low-level organic manure combined with inorganic N and phosphorus (P) fertiliser (M1N1P1); medium-level organic manure combined with inorganic N fertiliser (M2N2); and high-level organic manure combined with inorganic N and P fertiliser (M4N2P1). Our objectives were to (1) determine the contents of and variations in the SOC fractions; (2) explore the relationship between total SOC and its fractions. In treatments involving organic manure (M1N1P1, M2N2, and M4N2P1), total SOC and physically protected microaggregate (μagg) and μagg occluded particulate organic carbon (iPOC) contents increased by 9.9–58.9%, 1.3–34.7%, 29.5–127.9% relative to control, respectively. But there no significant differences ( P > 0.05) were detected for the chemically, physically–chemically, and physically–biochemically protected fractions among the M1N1P1, M2N2, and M4N2P1 treatments. Regression analysis revealed that there was a linear positive correlation between SOC and the unprotected coarse particulate organic carbon (cPOC), physically protected μagg, and iPOC fractions ( P < 0.05). However, physically–chemically, and physically–biochemically protected fractions responded negatively to SOC content. The highest rate of C accumulation among the SOC fractions occurred in the cPOC fraction, which accounted for as much as 32% of C accumulation as total SOC increased, suggesting that cPOC may be the most sensitive fraction to fertiliser application. We found that treatments had no effect on C levels in H-μsilt and NH-μsilt, indicating that the microaggregated silt C-fractions may have reached a steady state in terms of C saturation in the Brown Earth of Northeast China. [ABSTRACT FROM AUTHOR]

Olsen phosphorus (Olsen P) is an important indicator of soil labile phosphorus. Determining the effect of fertilization on Olsen P and P fractions (labile phosphorus, medium labile phosphorus and stable phosphorus) can guide the application of phosphate fertilizer. Therefore, it is of great significance to clarify the changes of Olsen P and P fractions and the influencing factors under long-term fertilization. This study investigated changes in Olsen P and P fractions in haplic phaeozems soils (0–20 cm) in two 30-year fertilization sites (Harbin, Gongzhuling) of northern China. Four treatments were examined: treatment with no fertilizer or manure (CK), nitrogen and potassium (NK), nitrogen, phosphorus and potassium (NPK), and manure, nitrogen, phosphorus and potassium (MNPK). The results showed that after NK application, Olsen P decreased by an average of 1.5 mg kg−1 for every 100 kg ha−2 of soil phosphorus lost due to continuous phosphorus uptake by the crop; with NPK, Olsen P increased by an average of 17.6 mg kg−1 for every 100 kg ha−2 of P surplus; with MNPK, the increase curve of Olsen P was similar to an S-curve with periods of rapid growth and periods of equilibrium. In the equilibrium period of Olsen P, the equilibrium values were 52.0 and 156.2 mg kg−1 in Harbin and Gongzhuling. After 20 years of long-term different fertilization, labile P (LP), medium labile P (MLP) and stable P (SP) decreased by 21.1, 16.6 and 15.1 mg kg−1 on average for the treatment without P application (NK), and the percentage decreases were 2.8, 5.7 and 2.1%, respectively. With the treatment of NPK, LP and MLP increased by 25.5 and 79.2 mg kg−1, and the percentage increases were 1.8 and 16.1%. With the treatment of MNPK, the increase in LP and MLP was significantly higher than that with NPK. Soil organic carbon (SOC), total nitrogen (TN) and carbon/nitrogen (C/N) had the greatest effects on Olsen P and P fractions and the total contribution rate was >40%. In summary, fertilization system caused significant changes in Olsen P and P fractions. After about 20 years of long-term combined application of MNPK, the growth of Olsen P can be kept constant. SOC and TN had important effects on Olsen P and P fractions in black soil. Therefore, the application of phosphorus fertilizer should be adjusted according to the type and time of fertilization in black soil in order to avoid waste of phosphorus fertilizer. [ABSTRACT FROM AUTHOR]

Salinity and water stress are serious environmental issues that reduced crop production worldwide. The current research was initiated (2012) in the wirehouse of the Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan to investigate the growth, stress tolerance, and physiological responses of guava to salinity and water shortage. Guava was grown for one year in pots containing soil with Eight treatments (control, 10 dS m−1, 20 dS m−1, 40 dS m−1, control + water stress (WS), 10 dS m−1 + WS, 20 dS m−1 + WS, 40 dS m−1 + WS) in a completely randomized design. The results indicated that plant growth, stress tolerance, and physiological parameters declined at higher salinity and water stress and could not survive at 40 dS m−1. The 20 dS m−1 + WS caused a > 70% decline in dry weights of shoot and root regarding control. Similarly, the highest decrease in stress tolerance was noticed in 20 dS m−1 + WS followed by the 20 dS m−1 treatment than control. Our findings validated that guava can be cultivated on soils having salinity ≤ 10 dS m−1 but it could not be cultivated on soils having salinity ≥ 20 dS m−1 with limited water supply. [ABSTRACT FROM AUTHOR]

Aims: Soil organic carbon (SOC) plays an important role in improving soil quality, however, how long-term fertilization influences SOC and contrasting active C (AC) and passive C (PC) pools at large scale remains unclear. The aim of this study was to examine the effect of long-term fertilization on SOC, including AC and PC, across four typical croplands in China and to explore the potential relationships and mechanisms. Methods: We assessed the effect of chemical fertilizer and manure amendment (standard rate and 1.5 × standard rate of inorganic fertilizer (NPK) with or without manure (M), with a Control for comparison) at three soil depths (0–20 cm, 20–40 cm, 40–60 cm) on SOC, AC and PC. Results: We found that SOC, AC and PC increased in the order NPK < NPKM < 1.5NPKM. 1.5NPKM resulting in a significant increase in SOC, AC and PC, of 76.3%, 53.0% and 108.5% respectively across the soil profile (0–60 cm) compared with Control. The response ratio of PC to long-term fertilization was 2.1 times greater than that of AC across four sites on average. In addition, clay was identified as the most important factor in explaining the response of AC and PC to different fertilization application. Conclusions: Long-term fertilization enhanced both AC and PC, but the greater response of PC suggests that fertilization application could enhance the stability of C and thus the potential of cropland for SOC accumulation. [ABSTRACT FROM AUTHOR]

Soil microbes and nematodes are important components of soil biota that strongly affect agricultural productivity and sustainability. Currently, our knowledge on the response of soil biota to agricultural management is restricted. This study aimed to identify the relationship between microbial and nematode communities and explore the resource path that flows within the soil micro-food web under different fertilization practices in a winter-wheat/summer-maize rotation system. The experiment was a randomized complete block design with three replicates for each treatment that included unfertilized control; inorganic N, P and K fertilizer (NPK); NPK plus manure; and NPK plus maize straw. Soil samples were taken at a 0–20 cm depth when wheat and maize were harvested. The results showed that organic manure or maize straw combined with NPK fertilizers had positive effects on the soil microbial and nematode communities. For example, the incorporation of straw increased the fungal biomass. Long-term inorganic fertilization might restrain nematode biomass accumulation especially in fungivorous nematodes. The analysis of the metabolic footprints of nematodes suggested that the incorporation of straw could enhance the carbon resource flow into the soil food web by enhancing nematode biomass. Structural equation modeling analysis suggested that the bottom–up control from the microbial community to the nematode community was more obvious in the wheat season in comparison with the maize season. In addition, a relatively stronger predation relationship was found between omnivores–predators and bacterivores rather than fungivores. Our study suggests that organic management combined with NPK fertilization could effectively enhance the association between microbial and nematode communities, while a crop rotation system with maize may have a negative influence on the structure of the soil micro-food web. [ABSTRACT FROM AUTHOR]

Animal manures positively affect soil microbial activity and inorganic phosphorus (Pi) accumulation. However, how different types of manures affect microbial-driven Pi transformation at the aggregate scale is largely unclear. Here, we conducted a field experiment focused on maize cultivation in a reclamation site. Five fertilization treatments included no fertilizer (CK), chemical fertilizer (CF), chicken manure (CHM), pig manure (PM), and cow manure (CM). We examined microbial biomass, soil extracellular enzyme activities associated with carbon and phosphorus cycling, and Pi fractions (Labile-P, Moderately labile-P, and Stable-P) in three aggregate sizes (> 2 mm large macro-aggregates, 0.25–2 mm small macro-aggregates, and < 0.25 mm micro-aggregates), as well as grain yield. The results showed that manures addition significantly increased the proportion of large macro-aggregates and aggregate stability compared to chemical fertilizer. Stable-P constituted the largest proportion among the Pi fractions, accounting for 63 %–72 %. However, manures reduced Stable-P (5.4 %–10.7 %) and increased Labile-P (111 %–190 %) in Pi, especially in micro-aggregates. Both chemical fertilizer and manures increased microbial biomass and enzyme activities in aggregates, with manures causing a greater enhancement of soil microbial biomass carbon (SMBC) and C-cycling enzymes, especially under pig manure, and improving soil microbial biomass phosphorus (SMBP) and P-cycling enzymes, especially under chicken manure. Phytase, phosphatase and SMBP accounted for 81.4 %, 81.2 % and 87 % of the differences in large macro-aggregates, small macro-aggregates, and micro-aggregates, respectively. The structural equation model (SEM) demonstrated that manures facilitated the transformation of Stable-P to Labile-P by regulating aggregates and microbial activity, which consequently increased yield. In summary, manures addition, particularly chicken manure, can enhance inorganic phosphate (Pi) accumulation and transformation, thereby mitigating phosphorus (P) limitation in calcareous reclamation soils. • Manures (especially chicken manure) promoted Pi accumulation and transformation. • Phytase, phosphatase, and soil microbial biomass phosphorus were the main factors causing the differences in Pi. • Manures promote Stable-P to Labile-P via interactions with aggregates and microbes. [ABSTRACT FROM AUTHOR]

Understanding dynamics of soil organic carbon (SOC) stock in agroecosystems under climate change is imperative for maintaining soil productivity and offsetting greenhouse gas emissions. Simulations with the SPACSYS model were conducted to assess the effects of future climate scenarios (RCP2.6, RCP4.5 and RCP8.5) and fertilisation practices on crop yield and SOC stock by 2100 for a continuous winter wheat cropping system in southeast England. Weather data between 1921 and 2000 was considered as the baseline. SPACSYS was first calibrated and validated with the data of the Broadbalk continuous winter wheat experiment for over a century. Six treatments were used: no fertiliser, a combination of chemical nitrogen, phosphorus and potassium with three nitrogen application rates (N1PK, N3PK and N5PK), manure only (FYM, close N application rate to N5PK) and a combination of manure and chemical nitrogen application (FYMN, the same chemical N application rate as N3PK). Compared with the observations, SPACSYS was able to simulate grain yields and dynamics of SOC and TN stocks. Our predications showed that wheat yield would increase by 5.8–13.5% for all the fertiliser application treatments under future climate scenarios compared to that under the baseline because of a gradual increase in atmospheric CO 2 concentration. Meanwhile, the SOC stock can increase for the practices under the scenarios except the NPK fertiliser practices under RCP2.6. Increased C input through "CO 2 -fertilisation effects" can compensate C losses by soil respiration under the RCP scenarios. We concluded that manure application practices can be considered as a sustainable strategy for enhancing wheat yield and soil C sequestration under the future climate scenarios. [Display omitted] • SPACSYS was able to simulate wheat yield of different varieties, SOC and TN stocks. • Future climate change positively impacts wheat yield. • Climate change effects on SOC varied among RCP scenarios and fertiliser practices. • Manuring acts as a sustainable strategy for soil productivity and C sequestration. [ABSTRACT FROM AUTHOR]

The determination of organic nitrogen (N) mineralization is crucial for estimating N availability, quantifying exogenous inputs, and estimating associated environmental impacts. The objective of this study was to explore the effect of long-term various fertilization on soil organic N mineralization potential (NMP), which influences plant N accessibility. Treatments from a 26-year long-term field experiment with no fertilization (CK), chemical fertilizer N at 165 kg N ha−1 and P at 82.5 kg P2O5 ha−1 (NP), NP with K fertilizer at 165, 82.5, 82.5 kg ha−1 N, P2O5 and K2O (NPK), NPK at 165, 82.5, 82.5 kg ha−1 N, P2O5 and K2O with manure at 7857.14 kg ha−1 (NPKM), and NPKM at 165, 82.5, 82.5 kg ha−1 N, P2O5 and K2O with manure at 1.5× application rate (11,785.71 kg ha−1) (1.5NPKM) were examined for potentially mineralizable N by aerobic incubation at 35 °C for 30 weeks. Three pools (Pools I, II, and III) of mineralizable N were recognized. Pool I, the mineralization flush on rewetting in the first 2 weeks; Pool II, gross N mineralization between weeks 2 and 30; and Pool III, the potentially mineralizable N, predicted from the fitted curve, that did not mineralize during the incubation period. Soil microbial biomass carbon (SMBC) and N (SMBN) as well as fixed ammonium (NH4+) contents and relationship with N mineralization rate (k) were also studied. Long-term manure application yielded a significantly higher k (0.32 week−1) than other treatments (0.12–0.22 week−1) but not a significantly higher NMP. Nitrogen mineralization during the wheat and maize-growing seasons was predicted to be 8.7–26.3 (mg N kg−1 soil) and 25.9–42.1 (mg N kg−1 soil), respectively. Both labile mineralizable N pools (Pools I and II) followed the same patterns in the treatments: 1.5NPKM > NPKM > NPK > NP > CK, while the reverse was true for stable N (Pool III). The significant positive correlation between k with SMBC and SMBN (R2 = 0.93, p = 0.008 and R2 = 0.94, p = 0.006) suggested that the higher mineralization rate might be contributed by the higher soil microbial biomass in NPKM. The trends of fixed NH4+ and mineralized N were coupled. Long-term manure application significantly improved the N mineralization rate in soil. Manure application is an effective strategy to enhance soil microbial biomass and soil N availability and has the potential to reduce the dependence upon chemical N fertilization. [ABSTRACT FROM AUTHOR]

The carbon-to-phosphorus (C:P) ratios of microorganisms were quantified in the rhizosphere and bulk soil collected from six typical fertilization regimes across three long-term experiments in humid (wheat–maize rotation), semiarid (wheat–maize rotation), and arid (maize–wheat–cotton rotation) climate zones. A 32P labeling incubation experiment allowed to test the relationship between microbial biomass P (MBP) turnover time and the C:P stoichiometric imbalance (SoilC:P/MicrobC:P) between soil (dissolved organic carbon:Olsen-P) and microorganisms (MBC:MBP). The MBC and MBN in the rhizosphere were 1.2 and 1.3 times higher than those in bulk soils, respectively, while the MBP was similar. The MBC:MBP ratio in the rhizosphere was 1.1 times higher than that in bulk soil, while the MBC:MBN ratio was similar. This finding suggested that C and P accumulation in the rhizosphere microorganisms was decoupled from that in the bulk soil. Compared to that in bulk soil, the MBP turnover in the rhizosphere was 1.1 times faster and microbially mediated P release was increased by 13% because of the decrease in the SoilC:P/MicrobC:P. Shoot P content was correlated with the rhizosphere SoilC:P/MicrobC:P and P flux mediated by microorganisms. The SoilC:P/MicrobC:P thresholds allowed to predict the start of an intensive competition between plants and microorganisms for P. Concluding, the stronger the SoilC:P/MicrobC:P in the rhizosphere decrease, the faster is the MBP turnover of homeostatic microorganisms, and furthermore, the microbially mediated P release leads to the decoupling of microbial biomass C and P at the root–soil interface. SoilC:P/MicrobC:P may be a predictor of the competition between plants and microorganisms. [ABSTRACT FROM AUTHOR]

Fertilizer application can potentially change soil organic C (SOC) sequestration of croplands. However, how fertilization affects SOC sequestration and soil C fractions has not been sufficiently investigated. Here, we studied this issue in a rice-barley system of eastern China after 23-year repeated organic and chemical fertilizer amendments. The fertilization treatments were as follows: unfertilized control (CK), pig manure (M), chemical fertilizer NPK (NPK), and pig manure combined with NPK (MNPK). Our results showed that M, NPK, and MNPK significantly increased 25, 13, and 30 % of SOC content as compared with CK. Compared with CK, the three fertilizations, especially manure addition, significantly increased the content of SOC fractions such as microbial biomass C, dissolved organic C, labile organic C, and particulate organic C. Compared with the initial SOC stock at 0-20-cm depth (41.2 Mg C ha), M, NPK, and MNPK increased 11, 1, and 16 % of SOC storage, respectively, whereas CK decreased 9 % of SOC pool. The SOC sequestration was positively correlated with the cumulative C input (root residue-C + manure-C) (SOC sequestration = 0.21 × C input − 5.67, R = 0.88, P < 0.001). This linear relationship suggested that (i) the soil had not reached a SOC saturation, (ii) the conversion rate from input-C to SOC was 21 %, and (iii) a C input threshold of 1.17 Mg C ha year was needed for maintaining the initial SOC level. Therefore, manure application is recommended for promoting SOC sequestration in the rice-barley cropping system of eastern China. [ABSTRACT FROM AUTHOR]