Long-term Fertilization Experiment Research Articles

Vertical migration and leaching behavior of antibiotic resistance genes in soil during rainfall: Impact by long-term fertilization

The vertical migration and leaching behavior of antibiotic resistance genes (ARGs) during rainfall in soils subjected to long-term fertilization remain largely unclear. In this study, ARGs in vertical profiles (0−60 cm) and leachates from three soils (acidic, neutral, and calcareous) in a long-term (13 years) field fertilization experiment were monitored by high-throughput quantitative PCR after each rainfall event throughout an entire year. The results showed that, compared with unfertilized soils, long-term manure fertilization mainly promoted the vertical migration and leaching of aminoglycoside, beta-lactam, and multidrug resistance genes in the soil profiles. As a result, the annual cumulative loads of ARGs in leachates from the three soils with long-term manure fertilization were significantly increased compared to the controls and were in the order of acidic soil > neutral soil > calcareous soil. SourceTracker analyses revealed that manured soil was the predominant source of the ARGs in the soil leachate samples. Pseudomonas, Anaeromyxobacter, IMCC26256, and MND1 were identified as the dominant potential hosts responsible for the vertical migration and leaching of ARGs in the three soils. PiecewiseSEM analysis further showed that long-term manure fertilization affected the vertical migration of ARGs during rainfall mainly by altering soil properties (i.e., pH, soil organic carbon, and sand). Our results suggest that the ARGs in soils with long-term manure fertilization are a significant potential source of ARG pollution in groundwater, and the measures should be taken to mitigate the vertical migration and leaching of ARGs during rainfall.

Clay Minerals and Long-Term Fertilization Effects on Soil Organic Carbon Stocks, Soil Carbon Pools, and Soil Enzymes in an Inceptisol of Coimbatore, Tamil Nadu

ABSTRACT Soil Organic Carbon (SOC) is an important indicator for soil health and quality. The present study was conducted in five-decade-old Long-Term Fertilizer Experiment involving the finger millet−maize cropping sequence in an Inceptisol to examine the effects of inorganic fertilizers and manures on soil organic carbon stock in relation to C sequestration. This study was based on 10 treatments: 50%NPK, 100%NPK, 150%NPK, 100%NPK + HW, 100%NPK + ZnSO4, 100%NP, 100%N, 100%NPK + FYM, 100%NPK (− S), and control. We assess the clay mineral interaction with soil organic carbon stock and soil enzyme activity. The semi-quantification and characterization of clay minerals were sourced from X-ray diffraction (XRD) analysis, and the SOC stock was calculated based on SOC concentration, Bulk density, and Depth. From the study, results revealed that clay minerals were studied by XRD and FTIR spectroscopy analysis. The results revealed that dominant clay minerals in the experimental soil were in the order of Montmorillonite, 2:1 interstratified minerals, Vermiculite, and Illite, and the buildup of SOC stock raised from 6.3 Mg C ha−1 to 12.9 Mg C ha−1 over five decades. The maximum SOC stock of 12.9 Mg ha−1 was recorded in 100% NPK + FYM while the control registered 7.5 Mg C ha−1. The study conclude that balanced fertilization of 100% NPK with FYM contributed toward the increase in SOC, SOC stock, and carbon sequestration for improving soil fertility status.

Impact of Long-term Application of Fertilizers and FYM on Nutrient Uptake by Soybean Crop and Properties of Black Soil

Long Term Fertilizer Experiment (LTFE) play an important role in understanding the complex interactions involving plant, soil, climate, management practices and their effect on soil productivity over a long period of time. The present investigation is a part of ongoing All India Coordinated Research Project on Long Term Fertilizer Experiment with Soybean-Wheat Cropping Sequence, which was initiated since 1972. The experiment was carried out in a randomized block design consisting of eight treatments, viz. 50% NPK, 100% NPK, 150% NPK, 100% NP, 100% N, FYM (100% NPK+FYM), 100% NPK (-S) and Control. The significant nutrient content with nutrient uptake by soybean was noted in 100% NPK+FYM treatment over the control plot. It was also observed that nutrient content with nutrient uptake increased significantly with consecutive doses of fertilizers. On the other hand, 100% N and in the control group had the lowest value. However, adding fertilizer P in addition to N (100% NP) increased nutrient content and nutrient uptake by soybean crop. The highest. Soil organic carbon content was recorded with 100% NPK dose+FYM followed by 150% NPK treatment combination which could apparently due to the synergistic contribution of integration of fertilizer and FYM application. Similarly, the available N,P, K and S content in soil were found highest with 100% NPK + FYM followed by 150% NPK fertilizer dose. However, the lowest content was noted in control where crop was grown without fertilizers. Available sulphur was significantly higher over control in all the treatments receiving single super phosphate.

Nitrogen reduction enhances crop productivity, decreases soil nitrogen loss and optimize its balance in wheat-maize cropping area of the Loess Plateau, China

In winter wheat-summer maize double cropping, fertilization changes the nitrogen (N) balance in the soil N pool, grain N uptake, N loss, and nitrogen use efficiency (NUE), ultimately impacting crop productivity and environmental health. For agricultural systems to maintain yields at lower environmental costs, N budgets must be balanced. Still, there is a deficiency in the reporting of N budgets of farming systems that incorporate all N flows. We evaluated the effects of various N fertilizer application rates on soil N balance and crop productivity in the 2017–2021 winter wheat-summer maize growing seasons. These rates included non-N fertilization (N0), 75 kg·N·ha−1 (N75), 150 kg·N·ha−1 (N150), 225 kg·N·ha−1 (N225), and conventional N fertilizer application rate, 300 kg·N·ha−1 (N300). Our analysis was based on a long-term field fertilization experiment and in-situ observation (established in 2010). The results show that fertilization significantly increased crop yields (wheat: 29.2 %–97.6 %; maize:25.4 %–98.1 %; annal: 27.0 %–96.7 %), among which N225 showed the highest increase value, compared with N0. Moreover, the N225 maximized grain N uptake by 201.0 %, reducing N losses and increasing N sequestration compared to the conventional N application rate of N300. N balance changes from negative to positive as the N application rate increases (wheat: −63.78–85.24 kg·ha−1; maize: −55.77–82.25 kg·ha−1; annal: −119.58–167.46 kg·ha−1·yr−1). Combining years of N inputs and outputs, the N225 is more balanced. Therefore, our study shows that an appropriate reduction of N fertilizer (N225) can help maintain agricultural productivity and promote N sequestration in farmland by reducing environmental N loss. Maintaining the virtuous cycle of N in the farmland ecosystem is beneficial and essential for the efficient utilization, high yield, and sustainable development of farmland resources.

Defying the flat-Earth myth: Soil organic carbon monitoring in topographically complex temperate pasture landscapes

Soil sampling design to capture the spatiotemporal variability of soil organic carbon (SOC) stocks in complex landscapes is challenged by the influence of topographical features on primary production, animal behaviour, and carbon and nutrient return to grasslands. Here we explore a range of approaches for streamlining the sampling process using measures of SOC stock data (2003, 2020, 2021) from a long-term hill-country fertilizer experiment. The stepwise procedure included a) evaluation of sampling efficiency between stratified and random soil sampling designs to capture spatial variability of SOC stocks, b) semi-parametric regression analysis to evaluate the representativeness of certain strata (e.g. medium slopes), c) exploring the appropriateness of using shallow SOC stock estimates to represent the full sampling depth, and d) the use of a process-based model to determine expected SOC stock changes and temporal variability to estimate the number of representative soil samples required to achieve a significant minimum change. Our analyses suggest that a) the stratified sampling design was more efficient reflected in the number of samples required to identify 5 % deviation in SOC stocks, b) estimates obtained on the medium slope were a reasonable approximation of the SOC stocks and its spatial variation across the farmlets, c) shallow (0–75 mm) SOC stock estimates from an adjusted regression model offered an accurate inference of its vertical distribution (0–300 mm), and d) the Grass-NEXT model provided insights on where more intensive sampling is required to detect a significant minimum change in SOC stocks over time. Tailored, stratified soil sampling and context-specific strategies, such as using representative strata and shallow sampling as effective steps for estimating SOC stocks and addressing data gaps, are crucial for simplifying monitoring and minimizing the cost of on-farm soil sampling designs in topographically complex landscapes covered by long-term pastures.

Contrasting effects of iron oxides on soil organic carbon accumulation in paddy and upland fields under long-term fertilization

Active iron oxides, especially poorly crystalline forms, benefit soil organic carbon (SOC) accumulation via directly bounding and indirectly promoting aggregation. However, it remains unclear on the impacts of active iron oxides on SOC accumulation in paddy and upland soils under long-term fertilization regimes. Here, we attempted to clarify the underlying mechanisms of amorphous (FeO) and organically complexed (FeP) iron oxides mediating SOC accumulation in paddy and upland soils based on two long-term fertilization experiments (both including no fertilization [CK]; chemical nitrogen, phosphorus and potassium [NPK] and NPK plus manure [NPKM] treatments). Results showed that compared to upland soil, Fe-bound organic carbon (Fe-bound OC) content in paddy soil, occupying 21–30% of SOC, was 77% higher on average, due to larger amounts of FeO (+31%) and FeP (+224%). The FeO and FeP were positively related to mean weight diameter (MWD) of soil aggregates across paddy and upland soils. Compared to NPK treatment, NPKM treatment strongly increased FeO (+41%), FeP (+60%) and associated Fe-bound OC (+19%) in paddy soil, and increased FeO (+17%) and FeP (+25%) while decreasing Fe-bound OC (−9%) in upland soil. These combined findings indicated the importance of poorly crystalline iron oxides facilitating Fe-bound OC formation and its contribution to SOC accumulation in paddy soil rather than upland soil. Moreover, long-term manure amendment could enhance SOC accumulation by increasing Fe-bound OC and aggregation stability in paddy soil and enhancing physical protection in upland soil, largely attributed to increased poorly crystalline iron oxides. Overall, these results highlight the potential mechanisms through which active iron oxides regulate SOC accumulation and guide fertilization management in paddy and upland soils.

Responses of soil fungal and bacterial communities to long-term organic and inorganic nitrogenous fertilizers in an alpine agriculture

Although nitrogen fertilizer is an important measure to increase grain yield, response of soil microbial community to nitrogen fertilizer is still unclear in alpine regions. Based on a long-term (>10 years) nitrogen fertilizer experiment (control, CF: chemical fertilizer, SM: sheep manure; CS: chemical fertilizer + sheep manure) in an alpine agroecosystem of the Lhasa, Xizang, responses of soil bacteria and fungi communities to nitrogen fertilizer was investigated. The CF treatment reduced fungi operational taxonomic unit (OTU) by 13.08 %, phylogenetic diversity by 11.13 % at 10–20 cm, but increased fungi guild number at 0–10 cm by 17.71 %. The SM treatment reduced fungi OTU at 10–20 cm by 11.82 %. Compared to CF and SM treatments, CS treatment had stronger positive effects on bacterial α-diversity, considering that CS treatment but not CF and SM treatments increased bacterial mean nearest taxon distance, species Shannon and Simpson at 10–20 cm. The CF, SM and CS treatments altered fungal community composition at 0–10 and 10–20 cm, bacterial community composition at 10–20 cm, and bacterial species composition at 0–10 cm. The CF and CS treatments altered bacterial phylogenetic composition at 0–10 cm, and the SM and CS treatments altered bacterial functional composition at 0–10 cm. The decreased magnitude of the relative abundance of symbiotroph fungi caused by CS treatment (90.44 %) was stronger than that (65.14 % and 53.62 %) caused by CF and SM treatments at 10–20 cm. Therefore, the SM and CS treatments had stronger effects on soil bacterial functional composition, but the CF treatment had stronger effects on fungal α-diversity. Compared with single application of organic or inorganic nitrogen fertilizer, mixed application of organic and inorganic nitrogen fertilizer was more beneficial to the maintenance and improvement of soil bacterial diversity, but caused more reduction of soil symbiotic fungi and in turn greater potential risk. These scientific findings observed by this study can provide guidance for fertilizer management and soil fertility improvement.

The impact of climate and potassium nutrition on crop yields: Insights from a 30-year Swiss long-term fertilization experiment

Climate change will strongly influence agricultural practices in the future. In order to promote resource-efficient agriculture, it is important to analyse the impact of climate variation on crop yields. In this study, we report yields of spring wheat, winter barley, maize, potato and sugar beet from the long-term crop rotation and fertilization experiment Demo in Switzerland and analyze their response to different climate variables (e.g., annual and seasonal temperature, precipitation, evapotranspiration, number of heat days and days of heavy rainfall). In addition, we investigate the impact of readily plant-available soil potassium (K) on the relationship of crop yields and precipitation. Annual and summer temperatures increased by 1 °C and 1.5 °C, respectively, over the observation period, and both the number of heat days and days of heavy rainfall increased in summer. Rising summer temperatures have a negative impact on all crop yields, which was most prominent for spring wheat, potato and maize. Annual, spring and summer precipitation show varying effects on different crops. For maize, soil K has a mediating effect on yield reductions under low spring precipitation. Yields are significantly reduced by 1 t ha−1 per 100 mm reduction of precipitation below a soil K threshold of 7 mg K kg−1 soil. Based on these results and the future climate scenarios for Switzerland, crop rotations with less heat-sensitive species and early-maturing varieties should be considered. In order to keep future irrigation demands and costs as low as possible, the soil K fertility classes in the Swiss K fertilization guidelines might need to be revisited. Our study is one of a few long-term observations that show the impact of climate variation on crop yields and highlights the potential of K management as a climate change adaptation measure.

Soil Organic Carbon Dynamics in the Long-Term Field Experiments with Contrasting Crop Rotations

Trends in soil organic carbon (SOC) were analyzed in the soils from the oldest Czech long-term field experiment, the Prague-Ruzyně Long-Term Fertilizer Experiment, conducted on Haplic Luvisol since 1955. The aim of the work was to compare the long-term dynamics of SOC in contrasting crop rotations and different fertilization regimes. The trial design includes two crop rotations (CR): simple CR with two-year rotation of sugar beet and spring wheat, and multi-crop rotation (MCR) with nine crops. Four fertilization treatments were chosen for SOC analysis: unfertilized control, only mineral fertilization (NPK), farmyard manure application (FYM), as well as FYM and NPK application. SOC content was significantly affected by both fertilization and crop rotation practices. In the simple CR, both the unfertilized control and the NPK treatment exhibited a consistent decline in SOC content over the study period, with percentages decreasing from an initial 1.33% in 1955 to 1.15% and 1.14%, respectively. Although the FYM and FYM + NPK treatments showed an increase in SOC content in the 1990s, a gradual decline was recorded in the last two decades. This decrease was not observed in MCR: positive C balances were recorded in all treatments within MCR, with the largest increase in SOC stock occurring when NPK was combined with FYM. In contrast, over the last decade, C balances have decreased in simple CR for all treatments except FYM. This trend coincides with changes in the local climate, particularly rising temperatures. The results indicate that diversified crop rotations and FYM fertilization are effective in mitigating the negative impacts of changing environmental conditions on SOC stocks.

Effects of Long-Term Fertilizer Application on Crop Yield Stability and Water Use Efficiency in Diversified Planting Systems

Exploring crop yield stability and the relationship between the water–fertilizer effect and annual precipitation type in a broomcorn millet–potato–spring corn rotation system under long-term fertilization on chestnut cinnamon soil in loess tableland can provide a scientific basis for rational fertilization in the northwest Shanxi region in years with different precipitation. This study was based on a 33-year long-term fertilizer experiment, using four fertilizer treatments: no fertilizer as control (CT), single fertilizer nitrogen (N), single organic fertilizer (M), and nitrogen fertilizer with organic fertilizer (NM). The results showed that broomcorn millet and maize had the highest yield in wet years, while potatoes had the highest yield in normal years and the yield under NM treatment was the highest. The sustainable yield index (SYI) values for potato and maize were higher than the SYI for the broomcorn millet during years with different precipitation and the SYI for the NM treatment was the highest. The water use efficiency of NM treatment was the highest. The yield of broomcorn millet and maize was affected by nitrogen fertilizer, organic fertilizer, and precipitation during the growth period, while the potato yield was mainly affected by nitrogen fertilizer and organic fertilizer. Therefore, the rotation of potato–maize and the rational allocation of organic and inorganic fertilizer (NM) is the best planting system in this region.

Soil ecosystem multifunctionality is strongly linked with crop yield after four decades chemical fertilization in black soil

Soil ecosystem multifunctionality (EMF), the ability of an ecosystem to perform multiple functions, remains uncertain in its contribution to crop production, especially in the context of long-term fertilization ecosystems. This study was carried out on a 40-year-old long-term fertilization experiment in black soil in China. Soil samples were collected from four treatments: control (CK); nitrogen (N) fertilizer; phosphorus (P) fertilizer; and a combination of nitrogen and phosphorus (NP) in both maize and wheat planting seasons. The results showed significant effects of N, P fertilizers and crop season on soil biotic and abiotic properties, especially on soil enzyme activities. Crop productivity and soil EMF showed a similar pattern across different treatments and both crop seasons, with significant higher values recorded in treatments with N addition (i.e. N and NP). Soil EMF was strongly associated with crop productivity in both maize and wheat seasons, while soil pH had a negative impact on crop yield. Random forest analysis revealed that microbial functional gene structure was significantly correlated with both soil ecosystem multifunctionality and crop yield. This suggested that fertilization leads to alterations in soil nutrients and the composition of functional microbial communities, subsequently impacting ecological functions and crop growth. These findings indicated that mineral fertilizers can enhance crop yield through soil EMF in the black soils, while exerted substantial impact on soil properties, raising concerns about the sustainability of soils under continuous chemical fertilization.

Maize functional requirements drive the selection of rhizobacteria under long-term fertilization practices.

Rhizosphere microbiomes are pivotal for crop fitness, but the principles underlying microbial assembly during root-soil interactions across soils with different nutrient statuses remain elusive. We examined the microbiomes in the rhizosphere and bulk soils of maize plants grown under six long-term (≥ 29 yr) fertilization experiments in three soil types across middle temperate to subtropical zones. The assembly of rhizosphere microbial communities was primarily driven by deterministic processes. Plant selection interacted with soil types and fertilization regimes to shape the structure and function of rhizosphere microbiomes. Predictive functional profiling showed that, to adapt to nutrient-deficient conditions, maize recruited more rhizobacteria involved in nutrient availability from bulk soil, although these functions were performed by different species. Metagenomic analyses confirmed that the number of significantly enriched Kyoto Encyclopedia of Genes and Genomes Orthology functional categories in the rhizosphere microbial community was significantly higher without fertilization than with fertilization. Notably, some key genes involved in carbon, nitrogen, and phosphorus cycling and purine metabolism were dominantly enriched in the rhizosphere soil without fertilizer input. In conclusion, our results show that maize selects microbes at the root-soil interface based on microbial functional traits beneficial to its own performance, rather than selecting particular species.

Effect of Balance and Imbalanced Fertilization on Soil Physical Properties, Growth and Yield of Rice in Chhattisgarh, India

Effect of balance and imbalanced fertilization on soil physical Properties, nutrient uptake, growth and yield of rice in Chhattisgarh was studied under long-term fertilizer experiment during kharif 2019-20 at research farm of Indira Gandhi Krishi Vishwavidyalaya, Raipur (C.G.). The experiment comprised of different levels or doses of NPK fertilizers alone and in combination with zinc sulphate, farmyard manure (FYM), blue green algae (BGA) and green manuring (GM) was laid out in randomized block design with four replications and ten treatments viz. Control, 50% NPK, 100% NPK, 150% NPK, 100% NPK+ZnSO4@ 10kgha-1,100% NP, 100% N, 100% NPK + FYM @5t ha-1, 50% NPK+BGA@ 10kg ha-1 and 50% NPK + GM @40kg ha-1. The results showed that the physical properties like total porosity, gravimetric and volumetric moisture content, hydraulic conductivity, infiltration rate, water stable aggregates and mean weight diameter of the soil were increased, while the bulk density was reduced significantly with the 100% NPK FYM treatment over all other treatments. However, the use of imbalanced (100% N and 100% NP) fertilizer, super optimal (150% NPK) and sub optimal (50% NPK) rate of inorganic fertilizer as compared to the unfertilized control showed significant effect on the physical properties of soil. Integrated nutrient management practice including FYM and recommended dose of NPK showed as best treatment with respect to growth and yield parameters like plant height, no. of tillers and no. of grains as compare to other treatments. The grain (5065 kg ha-1) and straw (7075 kg ha-1) yield of rice was registered higher in 150% NPK treatment followed by 100% NPK FYM treatment (4855 kg ha-1 and 6565 kg ha-1) and lowest in control treatment (2350 kg ha-1 and 2680 kg ha-1).

Impact of Integrated Nutrient Management on Soil Properties under Long-Term Fertilizer Experiment in Vertisol

Aims: To study the effect of continuous fertilization on soil properties and soil carbon stock, in a long-term experiment under a wheat-soybean cropping system in Vertisol.
 Study Design: The experiment was laid in a Randomized block design and consisted of three replications and nine treatments.
 Place and Duration of Study: Soil samples were collected during April 2022 following the harvest of Wheat from the on-going long-term fertilizer experiment at Jawahar Nehru Krishi Viswa Vidyalaya, Jabalpur, Madhya Pradesh, India
 Methodology: The soil samples were collected from two depths (0-15 and 15-30cm) and were analyzed for properties such as pH, electrical conductivity, available N, available P and available K using standard procedures.
 Results: The results indicated that out of all the treatments continued application of 100% NPK+ Farm yard manure had a significant effect (P<0.05) on all the parameters. This treatment had the highest value for in both 0-15 and 15-30 cm: SOC%(0.79% and 0.73%), available N(319.3 kg ha-1 , 275.00), available P(40.11 kg ha-1, 37.85 kg ha-1), available K (326.33 kg ha-1, 302.9 kg ha-1).
 Conclusion: Continued application of both 100%NPK along with FYM has a significant positive impact on the build-up of nutrients in the soil. This indicates that integrated application of nutrition assures productivity soil in the long.

Influence of mineral fertilization of common bean (Phaseolus vulgaris L.) on yield and damage by Bean weevil (Acanthoscelides obtectus SAY) in a long-term stationary fertilizer experiment

Influence of mineral fertilization of common bean (Phaseolus vulgaris L.) on yield and damage by Bean weevil (Acanthoscelides obtectus SAY) in a long-term stationary fertilizer experiment

Mycorrhizal effects on crop yield and soil ecosystem functions in a long-term tillage and fertilization experiment.

It is well understood that agricultural management influences arbuscular mycorrhizal (AM) fungi, but there is controversy about whether farmers should manage for AM symbiosis. We assessed AM fungal communities colonizing wheat roots for three consecutive years in a long-term (> 14 yr) tillage and fertilization experiment. Relationships among mycorrhizas, crop performance, and soil ecosystem functions were quantified. Tillage, fertilizers and continuous monoculture all reduced AM fungal richness and shifted community composition toward dominance of a few ruderal taxa. Rhizophagus and Dominikia were depressed by tillage and/or fertilization, and their abundances as well as AM fungal richness correlated positively with soil aggregate stability and nutrient cycling functions across all or no-tilled samples. In the field, wheat yield was unrelated to AM fungal abundance and correlated negatively with AM fungal richness. In a complementary glasshouse study, wheat biomass was enhanced by soil inoculum from unfertilized, no-till plots while neutral to depressed growth was observed in wheat inoculated with soils from fertilized and conventionally tilled plots. This study demonstrates contrasting impacts of low-input and conventional agricultural practices on AM symbiosis and highlights the importance of considering both crop yield and soil ecosystem functions when managing mycorrhizas for more sustainable agroecosystems.

Impacts of Long-term Application of Fertilizer and Manures on Physico-chemical Properties, Phosphorus Uptake and Crop Yield at Different Growth Stages of Wheat

A field experiment was conducted on wheat in a sandy loam soil (Typic Haplustept) at IARI farm, New Delhi during 2018-19 in a long-term fertilizer experiment to study the physico-chemical properties of soil, crop yield, phosphorus uptake and phosphorus availability. The experiment was designed with seven different treatments, replicated thrice in a randomized complete block design. The treatments details were T1: Control, T2: 100%N, T3: 100%NP, T4: 100%NPK, T5: 150% NPK, T6: 100%NPK+5t FYM and T7: 100% NPK+ Zn-5 kgha-1. The results revealed that pH and electrical conductivity were highest under control and lowest recorded under 100% NPK+FYM. Available phosphorus content at all four stages was wheat significantly greater under NPK+FYM followed by 150% NPK treatment and lowest under nitrogen alone (100% N) and unfertilized treatment (control). Initially available phosphorus in soil ranged from 13.5 to 39.8 and 15.4 to 37.9 kg ha-1 at 0-15 cm and 15-30 cm depth, respectively. At the tillering stage, available P was 20.7 to 43.7 and 16.5 to 38.1 kg ha-1 at 0-15 cm and 15-30 cm depth, respectively. At panicle emergence, it was 24.1 to 48.4 kg ha-1 and 18.6 to 42.3 at 0-15 cm and 15-30 cm depth. At harvest of wheat crop, available P ranged from 20.5 to 41.8 and 16.5 to 39.1 kg ha-1 at 0-15 cm and 15-30 cm depth, respectively. Total phosphorus uptake and crop yield significantly increased under 150% NPK treatment followed by 100% NPK+FYM.

Responses of Crop and Soil Phosphorus Fractions to Long-Term Fertilization Regimes in a Loess Soil in Northwest China

Contrasting fertilization modifies soil phosphorus (P) transformation and bioavailability, which impact crop P uptake and P migration in the soil profile. A long-term (25-year) fertilizer experiment was employed to investigate crop yield, P uptake and changes in sequentially extracted P fractions in the soil profile, and their relationships on a calcareous soil derived from loess material under a winter wheat and summer maize double-cropping system. The experiment involved seven nutrient management treatments: control (CK, no nutrient input), N, NK, NP, and NPK, representing various combinations of synthetic nitrogen (N), phosphate (P), and potassium (K) applications, as well as combinations of NPK fertilizers with either crop residues (SNPK, where S refers to maize stalk or wheat straw) or manure (MNPK, where M refers to dairy manure). Wheat and maize yields were significantly higher with P input fertilizer relative to the P-omitted treatments. Long-term application of P-containing fertilizers markedly raised the contents of inorganic (Pi) and organic (Po) P fractions at 0–20 cm depth compared with the P-omitted treatments. Moreover, both Pi and Po fractions were markedly higher under MNPK than under NPK and SNPK treatments. For achieving high yield for wheat and maize, the critical contents of labile P were 54 and 63 mg kg−1, and those of moderately labile P were 48 and 49 mg kg−1, respectively, defined by the linear plateau model. In addition, the change points of labile P and moderately labile P were 99 and 70 mg kg−1, above which CaCl2-P content significantly increased. Moreover, long-term P input significantly accumulated different P fractions in the deeper soil layers up to 100 cm, with large portions of organic P being a composite of labile and moderately labile P, especially in MNPK treatment. Our results suggest that excessive P supply with organic manure resulted in massive P accumulation in the topsoil and promoted soil P fraction transformation and availability in the deep soil layers, especially in an organic P form that has often been neglected.

Where does all the phosphorus go? Mass balance modelling of phosphorus in the Swedish long-term soil fertility experiments

To gain insights into phosphorus (P) dynamics in soils and the ability to predict soil responses to varying fertilizer inputs, mass balance models prove to be valuable tools. In this study, a new dynamic mass balance model, PBalD8, was used to describe the change in extracted P in the A horizon of soils subjected to diverse fertilizer treatments over a period of 50 to 60 years in five soil fertility experiments. The model employed a Freundlich equation to describe soil-solution partitioning of P and assumed that acid-lactate-extractable P represented a labile pool of P in instant equilibrium with soil solution P. Additionally, oxalate-extractable inorganic P was presumed to comprise the sum of the labile and stable pools of P, with mass flux to and from the latter described by Fick’s first law. The model was evaluated using results from extractions and P K-edge XANES spectroscopy. Notably, organic P, as revealed by P K-edge XANES, did not substantially contribute to long-term changes in soil P content and was therefore excluded from consideration. In general, the model offered reasonable fits to the extracted P concentrations. However, for the P-depleted treatments, a prerequisite was that the P removal through harvest was lower compared to measurements. Conversely, in three of the soils, the modelled fertilizer inputs needed to be reduced to 70 % to 85 % of the known additions. These discrepancies may be attributed to the involvement of deeper soil horizons, including deep crop uptake and mixing with lower soil layers, although other factors such as lateral dispersion and inaccuracies in estimating applied fertilizers cannot be discounted. These results underscore the necessity of gaining a more comprehensive understanding of how deeper soil horizons influence P mass balances in agricultural soils. In one of the soils, Fjärdingslöv, P K-edge XANES results demonstrated the formation of calcium phosphate over time in the highest fertilization treatment, consistent with the model. Additionally, in two soils, Kungsängen and the P-depleted Vreta Kloster soil, the model predicted a significant contribution from mineral weathering. However, the PBalD8 model also projected higher P leaching rates than those observed, suggesting that the model may not fully capture this P output term.

Long-term organic fertilization reshapes the communities of bacteria and fungi and enhances the activities of C- and P-cycling enzymes in calcareous alluvial soil

Soil microbial communities and extracellular enzymes are pivotal in governing the dynamics of soil carbon (C) and phosphorus (P) cycling. Nevertheless, comprehending the underlying regulatory factors and intricate interactions among these vital indicators remains an inadequately explored aspect, especially within the scenario of long-term fertilization. Long-term fertilization experiments were conducted on calcareous alluvial soil. The five fertilization regimes selected were as follows: without fertilization treatment (CK); inorganic NK fertilization treatment (NK); inorganic NPK fertilization treatment (NPK); organic fertilization treatment (M); and combined inorganic NPK with organic fertilization treatment (NPKM). The soil physicochemical properties, β-glucosidase (BG), and alkaline phosphomonoesterase (ALP) activities were determined, together with microbial (bacterial and fungal) community DNA sequences and subsequent bioinformatics analysis after 38 years of different fertilization. The results showed that the content of soil organic carbon (SOC) and available P and the activities of BG and ALP were the highest after M and NPKM treatments, which were 79–104 %, 26–36 times, 161–171 %, and 75–91 % higher than CK, respectively. Hierarchical clustering analysis showed that the bacterial and fungal community structures in M and NPKM treatments were similar, but the community structures in non-organic fertilization treatments (CK, NK, and NPK) were significantly different from those in organic fertilization treatments. The indicator species and correlation analysis combined revealed that most indicator species in organic fertilizer treatments were significantly positively correlated with soil BG and ALP, while most indicator species in non-organic fertilizer (CK and NK) treatments were significantly negatively correlated with soil BG and ALP. Organic fertilization treatments favored the growth of the bacterial genus Lysobacter and the fungal genera Acremonium and Mortierella and were significantly positively correlated with BG and ALP activities. Redundancy analysis revealed that SOC is the most important factor in shaping microbial community structure. Co-occurrence network analysis showed organic fertilization had higher network complexity, more keystone taxa, and more associations among microbial taxa compared with non-organic fertilization (CK + NK). Structural equation models revealed that microbial community structure is the direct driving factor of BG and ALP activities and their interactions, and SOC modulated the relationship between microbial community structure and BG and ALP activities. This study highlights how the application of organic fertilizer enhanced the C- and P-cycling enzyme activities, reshaped the soil microbial communities, and regulated these crucial indicators and their interactions by SOC.