Long-term Fertilization Trial Research Articles

Transformation and Sequestration of Total Organic Carbon in Black Soil under Different Fertilization Regimes with Straw Carbon Inputs

In the context of the carbon peak and carbon-neutral era, it is crucial to effectively utilize maize straw as a resource for achieving carbon (C) sequestration and emission reduction in rural agriculture. Maize straw carbon undergoes two processes after being added to the soil: mineralization (decomposition) and humification (synthesis) by soil animals and microorganisms. These processes contribute to the reintegration of carbon into the agroecosystem’s carbon cycle. However, understanding of the transformation and stabilization of straw carbon, as well as the differences in C fixation capacity in soils with various fertilization treatments in black soils, remains limited. This study aims to quantify the relationship between straw carbon input and organic carbon sequestration in various fertilization treatments of black soil. Based on a long-term positional fertilization trial (45 years) in black soil, 13C-labeled maize straw (1.5 g in 120 g of dry soil) was applied and combined with an in situ incubation method using carborundum tubes. Throughout the 360-day trial, we observed the influence of fertilization on soil total organic C levels, organic carbon δ13C values, maize straw addition rate, and straw C fixation capacity. The decomposition of straw was most prominent during the initial 60 days of the incubation period, followed by a gradual decrease in the rate of decomposition. Compared with day 0, the SOC δ13C value and straw C residue rate were highest in the no-fertilization treatment (CK) after 360 days of incubation. The amount of organic carbon transformed and fixed in the soil was significantly higher in the organic fertilizer treatment (M) compared to other treatments, highlighting the stronger decomposition, transformation, and carbon fixation capacity of straw carbon in the M treatment. Moreover, the highest carbon storage of 43.23 Mg·ha−1 was observed in the M fertilization treatment after 360 days, which was significantly different from other treatments (p < 0.05). The study demonstrates that soil with low fertility exhibits increased sequestration potential for straw carbon. Additionally, organic fertilizer input would increase soil organic carbon storage and facilitate straw carbon conversion.

Effect of Long-term Locational Fertilisation on Soil Heavy Metal Content

The prolonged application of fertilizers, often conducted through long-term fertilization trials, offers a robust framework for assessing the effects of continued fertilizer use on agricultural output, soil fertility, and the broader ecological landscape . Despite a wealth of research on soil nutrient cycling and crop yields, there is a relative paucity of studies that address the changes in soil heavy metal concentrations from an environmental conservation perspective. This review aims to outline the implications and risks associated with heavy metals in soil and compile existing findings on how long-term fertilization affects soil heavy metal concentrations.

Climate-mediated lodgepole pine tree growth response to thinning and fertilization in interior British Columbia

In the interior British Columbia, forest managers use thinning to reduce inter-tree competition and soil fertilization to enhance the soil nutrient status for improved tree growth. In recent decades, thinning has been promoted as a tool to increase tree resilience to drought. However, fertilization may modulate tree response to drought by altering biomass allocation from below- to above-ground depending on soil moisture availability. Here, we analyzed two long-term thinning and fertilization trials set up in fire-origin lodgepole pine (Pinus contorta Douglas ex Loudon) stands in two biogeoclimatic subzones in interior British Columbia that differ in soil productivity. Both trials featured untreated control, fertilized-only, thinned-only, and the combination of thinning and fertilization treatments. Drought Index (i.e., Standardized Precipitation Evapotranspiration Index, SPEI) was estimated for each site and used as a covariate in a linear mixed effects model to assess the impacts of thinning and fertilization on tree growth sensitivity to drought. Tree growth was increased by fertilization at the very dry-cold site, and more so in the thinned plot than the unthinned plot. The opposite effect of thinning on tree growth was found at the dry-cold relatively fertilized site. Tree growth was less sensitive to drought in the thinned-only plots at both sites. Our results, however, showed increased tree growth sensitivity to drought under the thinning and fertilization combination treatment at the less dry and relatively more productive site. The results suggest that the combination of thinning and fertilization can increase tree growth on very dry-cold and dry-cold sites and may be a suitable strategy to mitigate drought stress on tree productivity.

Microplastic contamination of soil: Are input pathways by compost overridden by littering?

Compost application is a widely recommended agricultural practice to improve soil fertility. As almost all compost is likely polluted with plastic we hypothesize that compost application is a major input pathway for microplastics (MPs) into agricultural soil. To attribute the plastic load of soil to compost application, we investigated MPs in topsoil (0–30 cm) of a controlled, long-term fertilizer trial with application of compost made of municipal biowaste (0, 5, 10, and 20 t ha−1a−1), which ended 11 years ago. Microplastics were analyzed via density separation (ZnCl2) and light microscopy; testing this method recovered 92 ± 10 % of spiked plastic items. The fields of the long-term compost trial showed a MP load of 0–64 items kg−1, corresponding to MP stocks in the plough layer (0–30 cm) that ranged from 38.2 ± 55.5 million to 171.4 ± 57.5 million items ha−1. Microplastic stocks and contents increased with increasing amount of compost application. Thus, we confirm compost as a major input pathway for MPs into agricultural soil, with the effect still visible after 11 years. Comparison of calculated plastic input based on MP contents of recent German compost with MP loads found in soil revealed that overall compost application explained <6 % of total MP stocks. We assume that compost applied in earlier days contained higher plastic loads than recent ones, reflecting current awareness and successful efforts in reducing plastic loads during compost production. However, as the plots at the border of the field had up to 18 times higher MP loads than the inner plots of the trial, we suggest that littering also contributed significantly to MP pollution. Thus, even if given compost applications still add plastics to environment, other sources such as littering can already have become the dominating input pathway.

The metabolic potential of soil microorganisms and enzymes in phosphorus-deficient KwaZulu-Natal grassland ecosystem soils

The relationship between soil microbial communities and enzymes on the nutrient dynamics in phosphorus (P) deficient grassland ecosystem soils of KwaZulu-Natal province, South Africa was studied. The long-term veld fertilization trial (VFT) soils used for this study were fertilized with 366 kg of superphosphate per hectare per season (P) and non-superphosphate fertilizer (−P). The macronutrient concentrations in P-treated soil were higher and significantly different from that of −P treated soil (P ≤ 0.05), except for the N concentration. Culture-dependent techniques revealed that the bacterial dominance in both soil treatments was mainly represented by species belonging to the Proteobacteria phyla, including the genera; Pseudomonas, Sphingomonas, Caulobacter and Variovorax forming the N-cycling, N-fixing and P-cycling bacterial communities. The −P treated soil showed increased β-Glucosaminidase, acid phosphatase and alkaline phosphatase activities of 194.4 nmolh−1 g−1, 1424.8 nmolh−1 g−1 and 2487.0 nmolh−1 g−1 respectively compared to that of the P treated soil with 160.2 nmolh−1 g−1, 967.3 nmolh−1 g−1 and 1770.5 nmolh−1 g−1 respectively. Pseudomonas nitroreducens and Variovorax paradoxus as representatives of P-cycling bacteria were selected and screened to gain insight into the P-solubilization mechanisms of the bacteria, based on qualitative and quantitative assay. A maximum P-solubilization by P. nitroreducens was achieved under acidic pH (4.2), accompanied by acid phosphatase activity of 45.3 U/mL while that of V. paradoxus was obtained under acidic pH (4.9) condition, and accompanied by alkaline phosphatase activity of 94.0 U/mL after a 10-day incubation period of the liquid medium. This study reveals that soil microorganisms and enzymes play a significant role in the nutrient bioavailability in phosphorous-deficient soil. This information has demonstrated the selection of these microbial communities for potential biotechnological applications.

Sheep dung disappearance from grazed hill country landscapes

Two experiments were conducted to examine the effects of biological (composition and site history) and topographic (slope and aspect) factors affecting sheep dung disappearance rates in hill country pastures. We used three of the farmlets that have been receiving 0 (NF), 125 (LF) or 375 (HF) kg of single superphosphate (SSP)/ha since 1980) from the long-term phosphorus fertiliser trial at Ballantrae. Experiment one examined the effect of farmlet, slope (low and medium slope class), and aspect (E, SW, NW), whereas Experiment two examined the effect of farmlet, both as a source of dung (from LF or HF farmlets) and as a site in the landscape (on LF or HF farmlets). In both experiments, disappearance of dung followed a quadratic curve, and no improvements were made using higher-order polynomials. Despite a lower fibre concentration, dung from sheep grazing the HF farmlet did not disappear at a faster rate than dung from the other farmlets, but soil activity in situ (placement) was pivotal to the rate of dung disappearance. A faster rate of dung disappearance on the HF farmlet is consistent with a greater capacity for turnover of plant biomass and animal excreta in this high fertility environment. These experiments contribute to our understanding of the influence of biological and topographic drivers of dung disappearance rates, and enable further advances to be made in the modelling of nutrients in these topographically complex agroecosystems.

Subsoils\u2014a sink for excess fertilizer P but a minor contribution to P plant nutrition: evidence from long-term fertilization trials

BackgroundThe phosphorus (P) stocks of arable subsoils not only influence crop production but also fertilizer P sequestration. However, the extent of this influence is largely unknown. This study aimed to (i) determine the extent of P sequestration with soil depth, (ii) analyze P speciation after long-term P fertilization, and (iii) compare soil P tests in predicting crop yields. We analyzed four long-term fertilizer trials in Germany to a depth of 90 cm. Treatments received either mineral or organic P, or a combination of both, for 16 to 113 years. We determined inorganic and organic P pools using sequential extraction, and P speciation using 31P nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) spectroscopy. In addition, we applied three P soil tests, double-lactate (DL), calcium acetate lactate (CAL), and diffusive gradients in thin films (DGT).ResultsThe results suggested that plants are capable of mobilizing P from deeper soil layers when there is a negative P budget of the topsoil. However, fertilization mostly only showed insignificant effects on P pools, which were most pronounced in the topsoil, with a 1.6- to 4.4-fold increase in labile inorganic P (Pi; resin-P, NaHCO3–Pi) after mineral fertilization and a 0- to 1.9-fold increase of organic P (Po; NaHCO3–Po, NaOH–Po) after organic P fertilization. The differences in Po and Pi speciation were mainly controlled by site-specific factors, e.g., soil properties or soil management practice rather than by fertilization. When modeling crop yield response using the Mitscherlich equation, we obtained the highest R2 (R2 = 0.61, P < 0.001) among the soil P tests when using topsoil PDGT. However, the fit became less pronounced when incorporating the subsoil.ConclusionWe conclude that if the soil has a good P supply, the majority of P taken up by plants originates from the topsoil and that the DGT method is a mechanistic surrogate of P plant uptake. Thus, DGT is a basis for optimization of P fertilizer recommendation to add as much P fertilizer as required to sustain crop yields but as low as necessary to prevent harmful P leaching of excess fertilizer P.

Thirty years of agronomy research for development in irrigated rice-based cropping systems in the West African Sahel: Achievements and perspectives

Rice (Oryza spp.) is an important food crop and plays an essential role in food security in the Sahel region in West Africa. The Africa Rice Center (AfricaRice) Regional Station for the Sahel was established in 1976 to respond to the demand for increased domestic production through research for development (R4D). This paper aims to review 30 years of rice agronomy R4D in this region and provide perspectives for future research. Rice is mainly grown by smallholders in irrigated systems in the Sahel, where productivity is higher than in other African regions. However, there is still a large gap between potential yield and actual yield obtained by farmers, due to various factors including sub-optimal crop management (e.g. nutrient, weed, water management) and abiotic stresses (e.g. extreme temperatures, salt-affected soils). AfricaRice has developed crop simulation models, integrated crop management practices, water-saving technologies, agronomic interventions alongside salt-tolerant varieties, and decision-support tools for field-specific nutrient management (e.g. “RiceAdvice”). While evaluation of agronomic options is well covered in the literature, there is limited information on scaling and impact in terms of improved smallholder livelihoods. While results from long-term soil fertility trials show that double-cropping rice with appropriate fertilizer application can be sustainable, models that integrate climate change indicate a huge risk of yield reduction due to heat stress, especially in the dry season, unless adaptations such as change in sowing date and varietal improvement are applied. There has been limited research on farming systems beyond plot-level agronomy, and less focus on environmental and social sustainability than economic sustainability (i.e. yield and profit). Further R4D efforts are needed to scale out and scale-up agronomic options for enhancing the productivity and sustainability of irrigated rice-based cropping systems in the Sahel in the context of increasing competition for water, land, and labor under increasingly extreme weather conditions. Digital approaches such as the decision support tool “RiceAdvice” could play an important role in out-scaling of productive, profitable, and sustainable agronomic options.

Forest Productivity Enhancement and Compensatory Growth: A Review and Synthesis

This review and synthesis article attempts to integrate observations from forestry to contemporary development in related biological research fields to explore the issue of forest productivity enhancement and its contributions in mitigating the wood supply shortage now facing the forest sector. Compensatory growth has been clearly demonstrated in the long-term precommercial thinning and fertilization trial near the Shawnigan Lake, British Columbia, Canada. This phenomenon appears similar to many observations from other biological fields. The concept of compensatory growth can be applied to forest productivity enhancement through overcompensation, by taking advantage of theories and methods developed in other compensatory growth research. Modeling technology provides an alternative approach in elucidating the mechanisms of overcompensation, which could reveal whether the Shawnigan Lake case could be generalized to other tree species and regions. A new mitigation strategy for dealing with issues related to wood supply shortage could be formed through searching for and creating conditions promoting overcompensation. A forest growth model that is state dependent could provide a way of investigating the effect of partial harvest on forest growth trajectories and stand dynamics. Results from such a study could provide cost-effective decision support tools to practitioners.

Effect of Missing Nutrient Elements on Grain Yield of Wet Season Rice in Bangladesh

Background and objective: Long-term fertility study is one of the important factors to monitor changes in yield because of different nutrient management options and cropping systems involved in Asian regions. Many short-term and long-term fertilizer trials were conducted for intensive irrigated rice cropping patterns mostly to provide fertilizer rate, but did not considered sustainable soil management for soil health. The objective of the present study was to examine the effect of missing nutrient elements for a long time on rice yield, photosynthetic rate and residual soil fertility. Materials and Methods: The experiment was initiated on a permanent layout at the Bangladesh Rice Research Institute (BRRI) farm, Gazipur during 2000 to 2008 in wet season. Seven treatments in randomized complete block design with four replications were imposed. Grain yield was determined at physiological maturity from three 5 m2 areas within each plot followed by bagging and threshing. Photosynthetic was measure by Li Cor 6400 (USA) machine during study period. Soil sample was analyzed for following standard methods. Results: It was found that grain yield was in decreasing trends for the missing elements that were similar with BR 11 and BRRI dhan 31. On an average, grain yield reductions were 11.6, 7.0, 10.6, 1.1 and 3.4 percent for -N, -P, -K, -S and -Zn, than complete fertilizer treatment (NPKSZn) respectively. Under no fertilization, the ability of soil was to produce 2.9 t·ha-1 of BR11 and 3.1 t·ha-1 of BRRI dhan 31 respectively. Photosynthetic rate of rice plant was always higher in complete fertilizer treatment (NPKSZn) than missing of any nutrient element. The decrease in photosynthetic rate was more pronounced with N missing than others for both the rice varieties. Conclusion: It is concluded that balance chemical fertilizers (NPKSZn) are to be used for sustained and/or increased rice production and to maintain soil fertility.

Precision agriculture in oil palm plantations: diagnostic tools for sustainable N and K nutrient supply

Predicting the fertilizer requirements of an oil palm plantation has long been a difficult task. Two main methods have emerged. Leaf analyses (LA) were used for fertilization management as early as the 1950s. Leaf contents are compared to optimum references, making it possible to adjust the fertilizer rates applied in each block. Another approach, based on the nutrient balance (NB), is to evaluate and replace nutrients that are exported from the field, or immobilized by the plant. Plantations must adopt environmentally friendly practices; in particular, fertilizer inputs must be estimated with sufficient precision to achieve the highest possible yields, without applying excessive amounts of nutrients in relation to plant demand and the storage capacity of soils. We questioned the relevance of each method for achieving these objectives. We did so using some long-term fertilization trials to compare the optimum N and K rates recommended by each method in the adult phase. It appeared that LA led to moderate rates compared to NB. It also appeared that calculating a precise nutrient balance on a field scale was hampered by a lack of precise information (i) about the biomasses produced and their composition and (ii) about the highly variable outputs of the environmental losses. On the other hand, LA provided a simple indicator of the ability for each block to achieve its potential yield. We believe that this perfectible method is more protective of the environment, without the risk of a significant decrease in yields or a decrease in soil mineral reserves.

Soil aggregate size and long-term fertilization effects on the function and community of ammonia oxidizers

Long-term field fertilization trials have suggested that reduced chemical nitrogen (N) plus organic fertilization can effectively reduce N loss without sacrificing crop yield, while the knowledge of how organic fertilizers regulate soil microorganisms and their function in N transformation are limited. In this study, the response of net nitrification rate and the ammonia-oxidizer community within soil aggregates to long-term combined organic N and reduced chemical N fertilization was evaluated to understand the underlying mechanism of the practice in mitigating soil N loss. The fertilization experiment included an unfertilized control; chemical N fertilizer (N), superphosphate (P) and potassium sulfate (K) fertilizer (NPK); NPK plus straw (NPKS); and NPK plus manure (NPKM). The results showed that the large macro-aggregates mass (>2 mm) in soil significantly increased from 34.1% in NPK to 47.2% in NPKS (P < 0.05). NPKS and NPKM both had positive effects on soil moisture retention, total N (TN), soil organic carbon (SOC), ammonium (NH4+-N) and nitrate (NO3−-N) accumulation, particularly within micro- (<0.25 mm) and small macro-aggregates. Compared with the NPK treatment, soil net nitrification rate (NNR) and ammonia-oxidizing bacterial (AOB) abundance decreased by 67.1% and 40.7% respectively under NPKS (P < 0.05), and the decrease mainly appeared in large macro-aggregate and micro-aggregates. The net nitrification rate was significantly correlated with ammonia-oxidizing archaea (AOA) abundance only in small macro-aggregates (r = 0.642, n = 12, P < 0.05). In contrast, NRR was positively correlated with AOB abundance within small macro- and micro-aggregate size classes (r values ranged from 0.654 to 0.813, P < 0.05). The community structure of AOB varied among different fertilization treatments, while AOA community differentiation was mainly dependent on aggregate size. The shift of the AOA and AOB communities corresponded with high moisture and lower ammonia content in the large macro-aggregates and were potentially responsible for the suppressed nitrification activity in the NPKS treatment. These results indicated that reduced chemical N plus organic fertilization is beneficial for increasing N concentration in large macro-aggregates.

Fertilizer regime changes the competitive uptake of organic nitrogen by wheat and soil microorganisms: An in-situ uptake test using 13C, 15N labelling, and 13C-PLFA analysis

Fertilizer regime affects plant growth and soil microbial community composition, however, its impact on organic nitrogen (N) uptake by plants remains poorly understood. To address this, we undertook an in-situ, short-term uptake experiment based on 13C, 15N labelling, and 13C-PLFA analysis at two long-term (6 year) fertilizer trial sites (Jintan and Changshu). Each site had five treatments: a control without fertilizers, NPK fertilizers, 50% NPK fertilizer +6 t/ha pig manure, 100% NPK fertilizer + cereal straw, and 50% NPK fertilizer +6 t/ha pig manure and cereal straw. Overall, we found that 6–21% and 6–11% of the added 13C-15N-glycine was taken up intact by wheat, while 18–35% and 8–20% was captured by soil microorganisms in Jintan and Changshu locations, respectively. These results indicate that wheat has an appreciable capacity to utilize organic N, even in fertile agricultural soils. Organic N uptake by wheat correlated positively with ammonium and nitrate soil contents, indicating that inorganic N may enhance organic N capture by increasing plant biomass. The 13C:15N ratio in the microbial biomass showed that 32–71% and 13–71% of the 15N was absorbed through a direct uptake route in Jintan and Changshu soils. Chemical fertilizer reduced microbial biomass and increased the proportion of intact glycine uptake by wheat. Gram-positive bacteria accounted for 18–23%, and 13–15% of the total 13C labelled PLFA in Jintan and Changshu, respectively, while Gram-negative bacteria accounted for 43–48% and 66–72% indicating that they are the dominant competitors with plants for soil nutrients. Total 15N uptake by wheat and microorganisms was highest in the 50% NPK fertilizer + pig manure and cereal straw treatment at both sites, indicating that it represents the best fertilizer practice for sustainable food production, as it not only reduced chemical fertilizer application, improved wheat growth and microbial biomass, but also increased wheat utilization of soil organic N.

Fluorine in soils under pasture following long-term application of phosphate fertiliser in New Zealand

An understanding of the rate at which fluorine (F) accumulates in soil from phosphorus fertiliser and how much is lost via leaching are important because of the challenge elevated F may pose to soil, plant and animal health. This study measured F accumulation in a soil under pasture (Inceptisol) that received single superphosphate (SSP) fertiliser over 63 years in a long-term fertiliser trial. It also assessed the downward movement of F in soil and effect of irrigation in a long-term irrigation trial. Results showed total F concentrations in topsoil (0–7.5 cm) that received 188 kg SSP ha−1 and 376 kg SSP ha−1 fertiliser increased from 251 mg kg−1 to 349 and 430 mg kg−1, respectively. The rates of F accumulation were estimated at 1.1 and 2.1 kg ha−1 yr−1 respectively, low compared to previous studies. The F concentration in the 376 kg SSP ha−1 treatment decreased with depth, but was significantly higher than the control treatment to 50 cm, suggesting movement of F down the soil. Fluorine concentrations also decreased with depth to 50 cm in soils that received either no irrigation or up to 770 mm yr−1 from irrigation. However there was no significant difference in the amount of F with depth between irrigation treatments. We postulate that F was moving predominately in drainage water in the period immediately after P fertiliser application in mid-winter and wasn't enhanced by irrigation. This study should be repeated for other soil types to help our understanding of the potential for ongoing F accumulation in soil and implications this may have on future land use.

Assessment of soil quality and identification of parameters influencing system yield under long-term fertilizer trial

Yield sustainability issues are always related to soil quality, its assessment is very vital. Thus, a long-term experiment (after 31st cycle) was targeted to recognise the soil indicators related to the system productivity of rice-wheat. To achieve the objective, system productivity was calculated and it was observed that treatments supplemented with organic residues were more productive (11.6–12.2 t ha−1). Soil qualities under each of the treatments were assessed by integrating the sensitive physical, chemical and biological parameters. All the soil parameters were improved under the treatments supplemented with organic residues. The soil quality index (SQI) was 0.26 for control (T1) and 0.59–0.63 for the integrated treatments (T6, T8 and T10). The SQI was highly correlated (R2=0.928) with the system yield. The soil factors like electrical conductivity, available phosphorus, soil organic carbon, porosity, microbial biomass carbon and dehydrogenase activity are identified as the key variables affecting the yield of the rice-wheat cropping system under long-term fertilizer trial.

Influence of long-term fertilization on soil physicochemical properties in a brown soil

This study aims to explore the influence on soil physicochemical properties under a 38-y long-term fertilization in a brown soil. Soil samples (0-20 cm)were taken from the six treatments of the long-term fertilization trial in October 2016:no fertilizer (CK), N1(mineral nitrogen fertilizer), N1P (mineral nitrogen and phosphate fertilizer), N1PK (mineral nitrogen, phosphate and potassic fertilizer), pig manure (M2), M2N1P (pig manure, mineral nitrogen and phosphate fertilizer).The results showed thatthe long-term application of chemical fertilizers reduced soil pH value, while the application of organic fertilizers increased pH value. Fertilization significantly increased the content of AHN, TN and SOM. Compared with the CK treatment and chemical fertilizer treatments, organic fertilizer treatments significantly increased the content of AP and TP. The content of AK and TK were no significant difference in different treatment.

Root-Associated Bacterial and Fungal Community Profiles of Arabidopsis thaliana Are Robust Across Contrasting Soil P Levels

Plant survival depends on the ability of roots to sense and acquire nutrients in soils, which harbor a rich diversity of microbes. A subset of this microcosm interacts with plant roots and collectively forms root-associated microbial communities, termed the root microbiota. Under phosphorus-limiting conditions, some plants can engage in mutualistic interactions, for example with arbuscular mycorrhizal fungi. Here, we describe how Arabidopsis thaliana, which lacks the genetic capacity for establishing the aforementioned symbiosis, interacts with soil-resident bacteria and fungi in soil from a long-term phosphorus fertilization trial. Long-term, contrasting fertilization regimes resulted in an ∼6-fold and ∼2.4-fold disparity in bioavailable and total phosphorous, respectively, which may explain differences in biomass of A. thaliana plants. Sequencing of marker genes enabled us to characterize bacterial and fungal communities present in the bulk soil, rhizosphere, and root compartments. Phosphorus had little effect on alpha- or beta-diversity indices, but more strongly influences bacterial and fungal community shifts in plant-associated compartments compared with bulk soil. The significant impact of soil P abundance could only be resolved at operational taxonomic unit level, and these subtle differences are more pronounced in the root compartment. We conclude that despite decades of different fertilization, both bacterial and fungal soil communities remained unexpectedly stable in soils tested, suggesting that the soil biota is resilient over time to nutrient supplementation. Conversely, low-abundance, root-associated microbes, which collectively represent 2 to 3% of the relative abundance of bacteria and fungi in the roots, exhibited a subtle, yet significant shift between the two soils. [Formula: see text] Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Influence of Long-Term Fertilization on Spore Density and Colonization of Arbuscular Mycorrhizal Fungi in a Brown Soil

This study aims to explore changes of long-term fertilization on spore density and colonization of AMF (Arbuscular mycorrhizal fungi) under a 38-y long-term fertilization in a brown soil. Soil samples (0-20 cm,20-40cm,40-60cm)were taken from the six treatments of the long-term fertilization trial in October 2016:no fertilizer (CK), N1(mineral nitrogen fertilizer), N1P (mineral nitrogen and phosphate fertilizer), N1PK (mineral nitrogen, phosphate and potassic fertilizer), pig manure (M2), M2N1P (pig manure, mineral nitrogen andphosphate fertilizer).Spores were isolated from soils by wet sieving and sucrose density gradient centrifugation; mycorrhizal colonization levels were determined by the gridline intersect. The spore density was highest in the topsoils (0-20 cm), and was decreased with increasing of soil depth in each treatment. The spores density of M2N1P treatment was significantly higher than that of other treatments in each soil layer. Application of inorganic fertilizer (especially inorganic with organic fertilizer) can greatly improve the level of colonization. Our results suggested that long-term fertilization significantly affects spore density and colonization of AMF, however, spore density is not related to colonization rate.

Total and active microbial communities and phoD as affected by phosphate depletion and pH in soil

Soil microbial communities contribute to organic phosphorus cycling in a variety of ways, including secretion of the PhoD alkaline phosphatase. We sampled a long-term grassland fertilization trial in Switzerland characterized by a natural pH gradient. We examined the effects of phosphate depletion and pH on total and active microbial community structures and on the structure and composition of the total and active phoD-harboring community. Archaeal, bacterial and fungal communities were investigated using T-RFLP and phoD-harboring members of these communities were identified by 454-sequencing. Phosphate depletion decreased total, resin-extractable and organic phosphorus and changed the structure of all active microbial communities, and of the total archaeal and phoD-harboring communities. Organic carbon, nitrogen and phosphorus increased with pH, and the structures of all total and active microbial communities except the total fungal community differed between the two pH levels. phoD-harboring members were affiliated to Actinomycetales, Bacilliales, Gloeobacterales, Planctomycetales and Rhizobiales. Our results suggest that pH and associated soil factors are important determinants of microbial and phoD-harboring community structures. These associated factors include organic carbon and total nitrogen, and to a lesser degree phosphorus status, and active communities are more responsive than total communities. Key players in organic P mineralization are affiliated to phyla that are known to be important in organic matter decomposition.

Quantitative PCR shows propagation of Plasmodiophora brassicae in Swedish long term field trials

Clubroot (Plasmodiophora brassicae) is a serious soil-borne disease in brassica crops world-wide. We report on a time series of soil samples from Swedish long-term fertility trials started in 1957, 1963 and 1966, which were analyzed for the amount of P. brassicae DNA. The crop rotations included a brassica crop every 4 or 6 years. All experimental sites with a 4-year rotation of oilseed rape, except one with calcium carbonate in the soil profile, showed high (>1000 fg DNA g−1 soil) levels of P. brassicae DNA after 9, 11 and 12 rotations. In contrast, detectable levels (>5 fg DNA g−1 soil) of P. brassicae were found only at one of five sites with a 6-year rotation of spring oilseed rape. In years with high levels of P. brassicae DNA, low yield was reported and a subsequent decline in P. brassicae DNA in soil was observed. Different NPK (nitrogen/phosphorus/potassium) fertiliser regimes resulted in similar P. brassicae DNA levels. The robustness and reliability of the method applied was verified by analyses of soil from individual plots compared with a mixture of plots and by repeated analyses of selected samples, which showed that P. brassicae DNA remained stable during dry storage.