Soil Phosphorus Cycling Research Articles

Effect of freezing and thawing on available phosphorus content of soil

The process of freeze-thaw not only directly affects the phosphorus cycle in non growing season, but also shows that the impact of cold winter and frequent freeze-thaw on the ecosystem will continue to the following growing season. This effect is closely related to soil properties, microbial activity and community structure, climate conditions, vegetation composition and management methods. However, due to the differences in research methods, many results about the effects of freeze-thaw on soil nitrogen and phosphorus cycle are quite different. After the freeze-thaw cycle, the content of available phosphorus in the two soils decreased, and the decreasing trend was Lou soil > arsenic sandstone.

Simulating long-term carbon nitrogen and phosphorus biogeochemical cycling in agricultural environments

Understanding how agricultural practices alter biogeochemical cycles is vital for maintaining land productivity, food security, and other ecosystem services such as carbon sequestration. However, these are complex, highly coupled long-term processes that are difficult to observe or explore through empirical science alone. Models are required that capture the main anthropogenic disturbances, whilst operating across regions and long timescales, simulating both natural and agricultural environments, and shifts among these. Many biogeochemical models neglect agriculture or interactions between carbon and nutrient cycles, which is surprising given the scale of intervention in nitrogen and phosphorus cycles introduced by agriculture. This gap is addressed here, using a plant-soil model that simulates integrated soil carbon, nitrogen and phosphorus (CNP) cycling across natural, semi-natural and agricultural environments. The model is rigorously tested both spatially and temporally using data from long-term agricultural experiments across temperate environments. The model proved capable of reproducing the magnitude of and trends in soil nutrient stocks, and yield responses to nutrient addition. The model has potential to simulate anthropogenic effects on biogeochemical cycles across northern Europe, for long timescales (centuries) without site-specific calibration, using easily accessible input data. The results demonstrate that weatherable P from parent material has a considerable effect on modern pools of soil C and N, despite significant perturbation of nutrient cycling from agricultural practices, highlighting the need to integrate both geological and agricultural processes to understand effects of land-use change on food security, C storage and nutrient sustainability. The results suggest that an important process or source of P is currently missing in our understanding of agricultural biogeochemical cycles. The model could not explain how yields were sustained in plots with low P fertiliser addition. We suggest that plant access to organic P is a key uncertainty warranting further research, particularly given sustainability concerns surrounding rock sources of P fertiliser.

Responses of litter, organic and mineral soil enzyme kinetics to 6 years of canopy and understory nitrogen additions in a temperate forest

Increasing atmospheric nitrogen (N) deposition could profoundly impact soil carbon, N and phosphorus cycling that are often regulated by extracellular enzymes. The potential activities of enzymes in response to N deposition have been studied extensively, but the kinetic mechanisms in response to canopy and understory N additions in different soil layers are poorly understood. Here, we conducted a six-year-long field manipulation experiment in a temperate deciduous forest to reveal the kinetic characteristics of seven extracellular hydrolytic enzymes in the litter, organic and mineral soil layers in response to canopy and understory N additions. Canopy N addition and understory N addition exerted similar effects on the kinetics parameters (Vmax and Km) of most enzymes under study. The kinetics parameters of most enzymes generally increased in the litter layer but decreased in the organic layer and had little change in the mineral soil layer in response to N addition. In addition, the changed kinetic parameters were mainly correlated with moisture in the litter layer, with pH, substrate properties (TC, TN, DOC and DON) and microbial communities (G+, G−, total bacterial and fungal biomass) in the organic and mineral soil layers. These findings indicate that enzyme kinetics responses to N deposition differ in soil layers with varying determinant factors, and therefore are driven by various physical, chemical and microbial mechanisms.

Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Ecoenzymatic stoichiometry and microbial nutrient limitations in rhizosphere soil along the Hailuogou Glacier forefield chronosequence

Mountain glaciers retreat at an increased rate under global warming, resulting in exposed barren surfaces for primary succession. Soil microbes are an important driver of ecosystem processes. Although variations in soil microbes after deglaciation have been studied extensively, the roles of rhizosphere soil microbes in the biogeochemistry cycle during primary succession are less understood. In this study, Populus purdomii was present throughout the 123-year chronosequence as a representative tree species. We therefore investigated variations in the rhizosphere enzyme activity, microbial community structure, and ecoenzymatic stoichiometry of P. purdomii along Hailuogou Glacier chronosequences. The objective was to determinechanges in rhizosphere enzyme activities and microbial communities, as well as the effects of nutrient limitation on rhizosphere microbes. According to the results, the enzyme activities and microbial group biomass in rhizosphere soil all showed a bimodal trend and were highest at the 43rd or 123rd year, and enzyme activity varied with succession time but not microbial community structure. The rhizosphere soil bacterial community was the dominant community during the 123-year chronosequence. Ecoenzymatic stoichiometry indicated nitrogen restrictions on microbial activity throughout primary succession, with early succession stages (5–15 years) showing greater carbon restriction than late succession stages. Moreover, redundancy and correlation analyses demonstrated that soil microbial phospholipid fatty acid biomass was an important factor for increases in enzyme activities and that enzyme activities in turn played important roles in carbon, nitrogen and phosphorus cycling in rhizosphere soil. Additionally, rhizosphere soil microbial development significantly affected soil organic carbon, total nitrogen and dissolved organic carbon accumulation. Overall, our study links the rhizosphere microbial community and activity to successional chronosequences, providing a deeper understanding of the dynamics of ecosystem succession.

Urbanization aggravates imbalances in the active C, N and P pools of terrestrial ecosystems

Urbanization causes increases in temperature and alters soil carbon (C), nitrogen (N), and phosphorus (P) cycles, but the degree to which these processes vary in temperature sensitivity along the urban-rural gradient are unclear. We selected three typical vegetation types (forests, shrub, and lawn) along an urban-subruban-rural gradient in Nanchang, China, and collected topsoil (at 0–15 cm depth) from 27 plots in each to measure the C, N, and P mineralization rates using thermostatic incubation. This was performed at ambient temperatures of 5 °C, 15 °C, 25 °C, 35 °C and 45 °C, respectively. Our results showed that soil microbial C and N content, as well as the rates of soil C mineralization, nitrification, and P mineralization generally decreased along the urban-rural gradient (P < 0.05). Moreover, the temperature sensitivity (Q10) of soil C mineralization was highest at urban sites, followed by suburban, then at rural sites. In contrast, the Q10 value of ammonification was lower in urban than suburban and rural sites, and a difference in nitrification response to temperature alteration was only found at urban sites. The phosphorus mineralization rate showed minimal variation across incubation temperatures. Taken together, we found that soil C and nutrient fluxes in response to elevated temperature might be more asynchronous in urban than in rural sites, and thus urbanization may aggravate imbalances in the active C, N and P pools of terrestrial ecosystems. Global warming may thus help accelerate soil organic C decomposition, N leaching, and P enrichment in urban vegetations in subtropical China.

Warming and nitrogen deposition accelerate soil phosphorus cycling in a temperate meadow ecosystem

Phosphorus (P) is an essential element for living organisms and a major limiting factor in many ecosystems. In recent years, global warming and nitrogen (N) deposition have become increasingly serious, with significant effects on the P cycle in terrestrial ecosystems. A series of studies were carried out on the soil P cycle, but how climate change affects this remains unclear. Field experiments with warming and N addition were implemented since April 2007. Infrared radiators manipulated temperature, and aqueous ammonium nitrate (10 g m–2 year–1) was added to simulate N deposition. Compared with the control, N addition reduced soil total P; warming and N addition decreased soil available P; warming, N addition and warming plus N addition decreased microbial biomass P, but increased litter P; and warming and N addition increased phosphatase activity significantly. Correlation analysis showed that soil total P, available P, microbial biomass P and phosphatase activity were positively correlated with soil temperature and water content. Soil total P was positively correlated with microbial biomass P and phosphatase activity; and available P was positively correlated with microbial biomass P but negatively correlated with litter P. The results showed that warming and N deposition accelerated the soil P cycle by changing soil physical and chemical properties and soil biological activities (microbial and phosphatase activities). However, N addition reduced the capacity of microbes to fix P and reduced microbial biomass P, resulting in losses to the soil P pool, further aggravating P limitation in the Songnen Grassland ecosystem.

Soil aggregate fractionation and phosphorus fraction driven by long-term fertilization regimes affect the abundance and composition of P-cycling-related bacteria

Fertilization could promote phosphorus (P) cycling in soil; however, it is unclear how long-term fertilization regimes affect P-cycling-related microbial communities in different soil aggregates. In this study, we compiled promising strategies to evaluate the effect of 40-year long-term fertilization treatments on the P-cycling-related bacterial communities associated with different soil aggregates, of which P fraction and physicochemical properties were also measured. We found that both organic and mineral fertilization treatments increased the proportion of silt + clay (< 53 μm) and decreased the proportion of macroaggregate (250–2000 μm). Organic fertilization increased microaggregate (53–250 μm) proportion while mineral fertilization resulted in the opposite. The abundances of phoC-, phoD-, phnX-, gcd-, and pstS-harboring bacteria increased in silt + clay in five fertilization treatments, while bpp-harboring bacterial abundance increased in microaggregate applied with nitrogen chemical fertilizer and nitrogen with combined manure fertilizer. Phytase activity was higher in macroaggregate in no fertilizer and mineral fertilization treatments, while phosphatase activity was higher in silt + clay in five fertilization treatments. Besides, fertilization significantly affected P fraction, with higher proportions of inorganic P, organic P, non-apatite inorganic P, and apatite inorganic P in silt + clay. For P-cycling-related bacterial community composition, 43.09% of the variation explained by fertilization treatment and aggregate fractionation, 73.92% of the variation explained by soil physicochemical properties and P fraction were found. Besides, P components especially organic P, non-apatite inorganic P, and labile P presented great effects on P-cycling-related bacterial community composition. To our knowledge, our findings first suggest that silt + clay is beneficial to enrich P-cycling-related bacteria, nutrient-driven aggregate fractionation and P fraction via fertilization treatments can shape P-cycling-related bacterial community composition.

Plant-microbe networks in soil are weakened by century-long use of inorganic fertilizers.

SummaryUnderstanding the changes in plant–microbe interactions is critically important for predicting ecosystem functioning in response to human‐induced environmental changes such as nitrogen (N) addition. In this study, the effects of a century‐long fertilization treatment (> 150 years) on the networks between plants and soil microbial functional communities, detected by GeoChip, in grassland were determined in the Park Grass Experiment at Rothamsted Research, UK. Our results showed that plants and soil microbes have a consistent response to long‐term fertilization—both richness and diversity of plants and soil microbes are significantly decreased, as well as microbial functional genes involved in soil carbon (C), nitrogen (N) and phosphorus (P) cycling. The network‐based analyses showed that long‐term fertilization decreased the complexity of networks between plant and microbial functional communities in terms of node numbers, connectivity, network density and the clustering coefficient. Similarly, within the soil microbial community, the strength of microbial associations was also weakened in response to long‐term fertilization. Mantel path analysis showed that soil C and N contents were the main factors affecting the network between plants and microbes. Our results indicate that century‐long fertilization weakens the plant–microbe networks, which is important in improving our understanding of grassland ecosystem functions and stability under long‐term agriculture management.

Options for Improved Phosphorus Cycling and Use in Agriculture at the Field and Regional Scales.

Soil phosphorus (P) cycling in agroecosystems is highly complex, with many chemical, physical, and biological processes affecting the availability of P to plants. Traditionally, P fertilizer recommendations have been made using an insurance-based approach, which has resulted in the accumulation of P in many intensively managed agricultural soils worldwide and contributed to the widespread water quality issue of eutrophication. To mitigate further environmental degradation and because future P fertilizer supplies are threatened due to finite phosphate rock resources and associated geopolitical and quality issues, there is an immediate need to increase P use efficiency (PUE) in agroecosystems. Through cultivar selection and improved cropping system design, contemporary research suggests that sufficient crop yields could be maintained at reduced soil test P (STP) concentrations. In addition, more efficient P cycling at the field scale can be achieved through agroecosystem management that increases soil organic matter and organic P mineralization and optimizes arbuscular mycorrhizal fungi (AMF) symbioses. This review paper provides a perspective on how agriculture has the potential to utilize plant and microbial traits to improve PUE at the field scale and accordingly, maintain crop yields at lower STP concentrations. It also links with the need to tighten the P cycle at the regional scale, including a discussion of P recovery and recycling technologies, with a particular focus on the use of struvite as a recycled P fertilizer. Guidance on directions for future research is provided.

A novel isotope pool dilution approach to quantify gross rates of key abiotic and biological processes in the soil phosphorus cycle

Abstract. Efforts to understand and model the current and future behavior of the global phosphorus (P) cycle are limited by the availability of global data on rates of soil P processes, as well as their environmental controls. Here, we present a novel isotope pool dilution approach using 33P labeling of live and sterile soils, which allows for high-quality data on gross fluxes of soil inorganic P (Pi) sorption and desorption, as well as of gross fluxes of organic P mineralization and microbial Pi uptake to be obtained. At the same time, net immobilization of 33Pi by soil microbes and abiotic sorption can be easily derived and partitioned. Compared with other approaches, we used short incubation times (up to 48 h), avoiding tracer remineralization, which was confirmed by the separation of organic P and Pi using isobutanol fractionation. This approach is also suitable for strongly weathered and P-impoverished soils, as the sensitivity is increased by the extraction of exchangeable bioavailable Pi (Olsen Pi; 0.5 M NaHCO3) followed by Pi measurement using the malachite green assay. Biotic processes were corrected for desorption/sorption processes using adequate sterile abiotic controls that exhibited negligible microbial and extracellular phosphatase activities. Gross rates were calculated using analytical solutions of tracer kinetics, which also allowed for the study of gross soil P dynamics under non-steady-state conditions. Finally, we present major environmental controls of gross P-cycle processes that were measured for three P-poor tropical forest and three P-rich temperate grassland soils.

Ectomycorrhizal and Saprotrophic Fungal Communities Vary Across mm-Scale Soil Microsites Differing in Phosphatase Activity

To understand nutrient cycling in soils, soil processes and microorganisms need be better characterized. To determine whether specific trophic groups of fungi are associated with soil enzyme activity, we used soil imprinting to guide mm-scale sampling from microsites with high and low phosphatase activities in birch/Douglas-fir stands. Study 1 involved sampling one root window per site at 12 sites of different ages (stands); study 2 was conducted at one of the stem-exclusion stands, at which 5 root windows had been installed. Total fungal and ectomycorrhizal (EM) fungal terminal-restriction fragment length polymorphism (TRFLP) fingerprints differed between high- and low-phosphatase activity microsites at 8 of 12 root windows across 12 sites. Where differences were detected, fewer EM fungi were detected in high- than low-phosphatase activity microsites. Using 5 root windows at one site, next-generation sequencing detected similar fungal communities across microsites, but the ratio of saprotrophic to EM fungal reads was higher in high-phosphatase activity microsites in the two windows that had low EM fungal richness. In windows with differences in fungal communities, both studies indicated that EM fungi were less successful than saprotrophic fungi in colonizing fine-scale, organic matter-rich microsites. Fine-scale sampling linked with in situ detection of enzyme activity revealed relationships between soil fungal communities and phosphatase activity that could not be observed at the scales employed by conventional approaches, thereby contributing to the understanding of fine-scale phosphorus cycling in forest soils.

Biochar phosphorus concentration dictates mycorrhizal colonisation, plant growth and soil phosphorus cycling

We aimed to determine the relationship between biochar properties and colonisation of roots by arbuscular mycorrhizal (AM) fungi in agricultural soil. We used a range of biochars that differed in pH, water holding capacity, C, N and P concentrations to investigate interactions between biochar and AM fungi. A glasshouse experiment was conducted with subterranean clover and wheat, amended separately with 34 sources of biochar (applied at 1% w/w), to investigate potential responses in a phosphorus (P) deficient agricultural soil. Plant growth responses to biochar ranged from positive to negative and were dependent on biochar P concentration, available soil P and AM root colonisation. The higher the nutrient P concentration in biochar, the lower was AM colonisation. Growth responses of wheat and clover to the application of various biochars were mostly positive, and their growth was correlated, but biochar contributions to soil fertility varied with biochar properties. When nutrient concentrations are higher in biochars, especially for P and N, plants can gain access to nutrients via the plant roots and mycorrhizal hyphae. Thus biochar amendments can increase both plant nutrient uptake and crop production in nutrient deficient soil.

Regulation of soil phosphorus cycling in grasslands by shrubs

The globally expanding colonization of grasslands by shrubs increases soil organic carbon and nitrogen, but the effects of shrubs on phosphorus (P) cycling have been rarely studied. We compared P contents in roots and soil fractions, phosphatase activity in the 1 m profile, and in situ net P mineralization between shrubby Potentilla fruticosa patches and grassy interspaces in grazed shrubby meadows at three representative sites on the eastern Tibetan Plateau. The P uptake of P. fruticosa exceeded 1 m soil depth, whereas grasses acquired P mainly within the upper 0.6 m. The P contents in shoots, aboveground litter and roots under P. fruticosa were greater than those under grasses. Litter P stock under the shrubs was 4–8 times higher than that under grasses and the root P stock doubled compared to that in grass areas. P. fruticosa generally increased the organic P (OP) content in the topsoil but decreased inorganic P (IP) in the subsoil. Phosphorus availability increased in the topsoil but decreased in the subsoil under the shrubs compared to grasses. Microbial biomass P (MBP), the activities of acid and alkaline phosphatases, and OP lability were all greater in the 1 m soil under P. fruticosa than grasses, leading to faster P mineralization and the P turnover under the shrubs. In the 1 m soil, P. fruticosa increased MBP and OP stocks but decreased IP and available P stocks. The larger and deeply distributed root system of P. fruticosa improved its P uptake ability especially from the subsoil. The subsequent greater organic matter input through litter fall and root turnover under P. fruticosa fed a larger microbial biomass that synthesized more microbial-derived OP in the topsoil. We concluded that shrubs increase the biological (plant and microbial) P transformation in the soil, the P uplift in the profile, and P cycling in shrubby grassland ecosystems. Such mechanisms structuring spatial heterogeneity of P content, transformation, turnover and fluxes are common in shrubby grasslands worldwide.

Responses of Soil Bacterial and Fungal Communities to Organic and Conventional Farming Systems in East China.

Organic farming is considered an effective form of sustainable agricultural management. However, understanding of soil microbial diversity and composition under long-term organic and conventional farming is still limited and controversial. In this study, the Illumina MiSeq platform was applied to investigate the responses of soil bacterial and fungal diversity and compositions to organic farming (OF) and improved conventional farming (CF, applied straw retention) in the rice-wheat rotation system. The results highlighted that the alpha diversity of microbial communities did not differ significantly, except for higher bacterial diversity under OF. However, there were significant differences in the compositions of the soil bacterial and fungal communities between organic and conventional farming. Under our experimental conditions, through the ecological functional analysis of significant different or unique bacterial and fungal taxonomic members at the phyla and genus level, OF enhanced nitrogen, sulfur, phosphorus and carbon dynamic cycling in soil with the presence of Nodosilinea, Nitrospira, LCP-6, HB118, Lyngbya, GOUTA19, Mesorhizobium, Sandaracinobacter, Syntrophobacter and Sphingosinicella, and has the potential to strengthen soil metabolic ability with Novosphingobium. On the other hand, CF increased the intensity of nitrogen cycling with Ardenscatena, KD1-23, Iamia, Nitrosovibrio and Devosia, but enriched several pathogen fungal members, including Coniochaeta, Corallomycetella, Cyclaneusma, Cystostereum, Fistulina, Curvularia and Dissoconium.

The phosphate-solubilizing ability of Penicillium guanacastense and its effects on the growth of Pinus massoniana in phosphate-limiting conditions.

ABSTRACTMicrobes in soil can degrade insoluble inorganic and organic phosphorus, which are components of the soil phosphorus cycle and play an important role in plant growth. Pinus massoniana is a pioneer tree species used for afforestation in southern China and grows in poor, acidic soil. A shortage of available phosphorus in soil limits the growth of P. massoniana. To alleviate this situation, it is necessary to improve soil fertility. A fungal strain (JP-NJ2) with the ability to solubilize phosphate was isolated from the P. massoniana rhizosphere. The ability of JP-NJ2 to solubilize inorganic and organic phosphorus and promote the growth of P. massoniana was evaluated. It showed that JP-NJ2 could grow in NBRIP inorganic phosphate (AlPO4, FePO4·4H2O, and Ca3[PO4]2) fermentation broths, with the highest phosphorus concentration (1.93 mg/ml) and phosphate-solubilizing rate (43.7%) for AlPO4 and in Monkina organic phosphate fermentation broth with a phosphorus concentration of 0.153 mg/ml. The phosphate-solubilizing capability in inorganic and organic fermentation broths was negatively correlated with pH. JP-NJ2-produced acids at a total concentration of 4.7 g/l, which included gluconic (2.3 g/l), oxalic (1.1 g/l), lactic (0.7 g/l) and malonic (0.5 g/l) acids. It prioritized extracellular acidic phosphatase and combined with phytase to solubilize organic phosphates. The fungal suspension and extracellular metabolites from phosphate-solubilizing fungi promoted the shoot length of P. massoniana seedlings by 97.7% and 59.5%, respectively, while increasing the root crown diameter by 46.8% and 27.7%. JP-NJ2 was identified as Penicillium guanacastense based on its morphology and phylogenetic analyses of five genes/regions (ITS, ben A, cmd, cox1 and tef). This is the first report on P. guanacastense isolated from pine tree rhizosphere soil in China and its high phosphate-solubilizing capability, which promoted the growth of P. massoniana. P. guanacastense JP-NJ2 has potential use as a biological fertilizer in forestry and farming.

Soil Chemistry Aspects of Predicting Future Phosphorus Requirements in Sub‐Saharan Africa

AbstractPhosphorus (P) is a finite resource and critical to plant growth and therefore food security. Regional‐ and continental‐scale studies propose how much P would be required to feed the world by 2050. These indicate that Sub‐Saharan Africa soils have the highest soil P deficit globally. However, the spatial heterogeneity of the P deficit caused by heterogeneous soil chemistry in the continental scale has never been addressed. We provide a combination of a broadly adopted P‐sorption model that is integrated into a highly influential, large‐scale soil phosphorus cycling model. As a result, we show significant differences between the model outputs in both the soil‐P concentrations and total P required to produce future crops for the same predicted scenarios. These results indicate the importance of soil chemistry for soil‐nutrient modeling and highlight that previous influential studies may have overestimated P required. This is particularly the case in Somalia where conventional modeling predicts twice as much P required to 2050 as our new proposed model.

Combining spectroscopic and isotopic techniques gives a dynamic view of phosphorus cycling in soil

Current understanding of phosphorus (P) cycling in soils can be enhanced by integrating previously discrete findings concerning P speciation, exchange kinetics, and the underlying biological and geochemical processes. Here, we combine sequential extraction with P K-edge X-ray absorption spectroscopy and isotopic methods (33P and 18O in phosphate) to characterize P cycling on a climatic gradient in Hawaii. We link P pools to P species and estimate the turnover times for commonly considered P pools. Dissolved P turned over in seconds, resin-extractable P in minutes, NaOH-extractable inorganic P in weeks to months, and HCl-extractable P in years to millennia. Furthermore, we show that in arid-zone soils, some primary mineral P remains even after 150 ky of soil development, whereas in humid-zone soils of the same age, all P in all pools has been biologically cycled. The integrative information we provide makes possible a more dynamic, process-oriented conceptual model of P cycling in soils.

Impact of two centuries of intensive agriculture on soil carbon, nitrogen and phosphorus cycling in the UK

This paper describes an agricultural model (Roth-CNP) that estimates carbon (C), nitrogen (N) and phosphorus (P) pools, pool changes, their balance and the nutrient fluxes exported from arable and grassland systems in the UK during 1800–2010. The Roth-CNP model was developed as part of an Integrated Model (IM) to simulate C, N and P cycling for the whole of UK, by loosely coupling terrestrial, hydrological and hydro-chemical models. The model was calibrated and tested using long term experiment (LTE) data from Broadbalk (1843) and Park Grass (1856) at Rothamsted. We estimated C, N and P balance and their fluxes exported from arable and grassland systems on a 5km×5km grid across the whole of UK by using the area of arable of crops and livestock numbers in each grid and their management. The model estimated crop and grass yields, soil organic carbon (SOC) stocks and nutrient fluxes in the form of NH4-N, NO3-N and PO4-P. The simulated crop yields were compared to that reported by national agricultural statistics for the historical to the current period. Overall, arable land in the UK have lost SOC by −0.18, −0.25 and −0.08MgCha−1y−1 whereas land under improved grassland SOC stock has increased by 0.20, 0.47 and 0.24MgCha−1y−1 during 1800–1950, 1950–1970 and 1970–2010 simulated in this study. Simulated N loss (by leaching, runoff, soil erosion and denitrification) increased both under arable (−15, −18 and −53kgNha−1y−1) and grass (−18, −22 and −36kgNha−1y−1) during different time periods. Simulated P surplus increased from 2.6, 10.8 and 18.1kgPha−1y−1 under arable and 2.8, 11.3 and 3.6kgPha−1y−1 under grass lands 1800–1950, 1950–1970 and 1970–2010.

Effects of climate on soil phosphorus cycle and availability in natural terrestrial ecosystems.

Climate is predicted to change over the 21st century. However, little is known about how climate change can affect soil phosphorus (P) cycle and availability in global terrestrial ecosystems, where P is a key limiting nutrient. With a global database of Hedley P fractions and key-associated physiochemical properties of 760 (seminatural) natural soils compiled from 96 published studies, this study evaluated how climate pattern affected soil P cycle and availability in global terrestrial ecosystems. Overall, soil available P, indexed by Hedley labile inorganic P fraction, significantly decreased with increasing mean annual temperature (MAT) and precipitation (MAP). Hypothesis-oriented path model analysis suggests that MAT negatively affected soil available P mainly by decreasing soil organic P and primary mineral P and increasing soil sand content. MAP negatively affected soil available P both directly and indirectly through decreasing soil primary mineral P; however, these negative effects were offset by the positive effects of MAP on soil organic P and fine soil particles, resulting in a relatively minor total MAP effect on soil available P. As aridity degree was mainly determined by MAP, aridity also had a relatively minor total effect on soil available P. These global patterns generally hold true irrespective of soil depth (≤10cm or >10cm) or site aridity index (≤1.0 or >1.0), and were also true for the low-sand (≤50%) soils. In contrast, available P of the high-sand (>50%) soils was positively affected by MAT and aridity and negatively affected by MAP. Our results suggest that temperature and precipitation have contrasting effects on soil P availability and can interact with soil particle size to control soil P availability.