Soil Phosphorus Dynamics Research Articles

Cover crop species and mycorrhizal colonization on soil phosphorus dynamics

Phosphorus (P) plays an important role in the physiological plant processes; however, in tropical soils, P is one of the most limiting nutrients for crop yield due to its low mobility, determined by the adsorption of this element to the soil. To enhance P-use and P-acquisition efficiency, this research aimed to evaluate the effect of cover crops and mycorrhizal colonization on changing soil P fractions, both organic and inorganic. A complete randomized block design was adopted in a field experiment, with four replications using four cover crops: i) pigeon pea (Cajanus cajan); ii) crotalaria (Crotalaria juncea); iii) millet (Pennisetum glaucum); iv) brachiaria (Brachiaria ruziziensis) and v) fallow, as control. The arbuscular mycorrhizal fungus colonization, the fungal spore density, soil P fractionation, and N, P, and K uptake were assessed. Our results show that cover crops affected the soil P cycling in deeper soil layers. Cover crops may increase arbuscular mycorrhizal inoculum potential for the succeeding crop in rotation or intercropping, when used as a green manure.

Variable impact of compost on phosphorus dynamics in organic dryland soils following a one‐time application

AbstractProlonged benefits following a single application of compost in organic dryland wheat (Triticum aestivum L.) in the western United States have been documented, including the long‐term bioavailability of phosphorus (P). Information on the bioavailability and forms of P following a one‐time compost application in marginal organic agroecosystems with low and infrequent use of fertilizers is required to promote sustainability. The goal of this study was to evaluate changes in Hedley P pools following a one‐time application of manure compost and its potential influence on short‐term (3‐yr) P bioavailability. Steer manure compost at 0, 25, and 50 Mg dry weight ha–1 was applied to two organic dryland sites, Snowville and Blue Creek, with contrasting soil characteristics in northern Utah in a randomized complete block design. Potential phosphatase assays, a laboratory aerobic incubation study, and soil P fractionations were carried out to assess the transformation of P 1 and 3 yr after a one‐time compost application. At 0–10 cm, compost application resulted in increased acid phosphatase at Snowville (67.3 vs. 42.7 μg p‐nitrophenol g–1 soil, p = .003), while alkaline phosphatase increased at Blue Creek (124 vs. 49 μg p‐nitrophenol g–1 soil, p = .0185). The path coefficient between compost P and Hedley labile inorganic P was significant at Snowville, but not at Blue Creek, suggesting that the pathways of P differed between the sites. The Hedley stable P pool was a sink of compost P at Snowville but a source at Blue Creek. In conclusion, our work shows that a one‐time compost application had a differential effect on the variation in P dynamics in organic dryland winter wheat–fallow soils. The potential long‐term benefits may be greater in semiarid soils with lower available P levels, higher carbonate levels and pH, and drier conditions.

Impact of manure and biochar additions on annual crop growth, nutrient uptake, and fate of 15N-labelled fertilizer in two contrasting temperate prairie soils after four years

Liquid hog manure (LHM) and solid cattle manure (SCM) co-applied with biochar could beneficially influence soil nitrogen (N) and phosphorus (P) dynamics. A split-plot design was used at two sites (Brown and Black) in Saskatchewan to assess LHM and SCM (100 kg N·ha−1) applied alone or in combination with biochars (8 Mg carbon·ha−1) produced using slow or fast pyrolysis. Crop growth and nutrient uptake, along with fertilizer 15N recovery, were followed over four years in a cereal–oilseed rotation. Crop growth on the Brown soil was more responsive to the treatments than the Black soil, reflecting lower fertility of the Brown soil. The manure and biochar, applied alone or in combination, had little impact on available soil P. Manure and biochar effects on crop growth and nutrient uptake were attributed to temporal effects on soil N immobilization–mineralization influencing plant-available soil N. A negative impact of the fast pyrolysis biochar on growth and plant uptake was observed and attributable to its greater labile-carbon content, which likely promoted soil N immobilization. Synergism observed between SCM and the slow pyrolysis biochar may reflect enhanced net SCM-N mineralization and increased water-holding capacity. The majority (55%–80%) of plant 15N recovery occurred during the first year, with 86% of fertilizer 15N conserved within the soil–plant system after four years. Greater (40%) plant 15N recovery without biochar addition, coupled with increased (38%) soil 15N recovery with added biochar, suggests biochar-related immobilization and (or) sorption in the biochar-amended soils.

Distribution and chemical species of phosphorus across density fractions in Andisols of contrasting mineralogy

Strong control of iron (Fe) and aluminum (Al) phases on soil phosphorus (P) dynamics is well established. How organic and inorganic P forms are associated with Fe and Al phases remains poorly understood, and sequential density fractionation thus allows one to assess the soil continuum from organic-rich particles (< 1.8 g cm−3) to organo-mineral particles (1.8–2.25 g cm−3), and finally to mineral rich particles (> 2.25 g cm−3). We combined the density fractionation approach with wet extraction techniques, 31P NMR spectroscopy and X-ray absorption near-edge structure (XANES) spectroscopy to investigate the distribution and chemical species of P in relation to Fe and Al phases for two Andisols: an allophanic Andisol rich in short-range-order aluminosilicates (silandic) and a non-allophanic Andisol rich in organic matter (OM) and organo-aluminum complexes (aluandic). We fractionated the soils to the density classes of 1.6–1.8, 1.8–2.0, 2.0–2.25, 2.25–2.5, and > 2.5 g cm−3 using the sodium polytungstate solutions. Across five density fractions, inorganic and total P were distributed in low to meso-density fractions (1.6–2.25 g cm−3) where major portions of extractable Fe and Al were found. The major P pool was found in the NaOH extraction step for low- to meso-density ranges (< 2.25 g cm−3), suggesting that Al and Fe (oxyhydr)oxides and aluminosilicates have significant roles in P sorption in allophanic and non-allophanic Andisols. In contrast, the residual P remaining after the sequential extraction was predominant in heavier-density fractions (> 2.25 g cm−3). Molybdate-reactive and total P extracted by NaOH in the density fractions were positively correlated with oxalate extractable Al (Alox) in the allophanic Andisol (r > 0.91) and with pyrophosphate extractable Al (Alp) in the non-allophanic Andisol (r > 0.97), suggesting stronger control of Al phases to P over Fe phases. The non-destructive XANES analysis confirmed that P in both Andisols was associated primarily with Al, not Fe, and suggested the presence of P bound to organo-Al complexes in the non-allophanic Andisol (up to 76% of P in the 1.6–1.8 g cm−3 fraction where Alp is enriched). Solution 31P NMR spectra of NaOH-EDTA soil extracts showed that the primary organic P group was phosphomonoesters that decreased with increasing density in allophanic and non-allophanic Andisols. Myo-inositol hexakisphosphate (IHP) and scyllo-IHP were identified in a density fraction between 1.8 and 2.25 g cm−3 of non-allophanic Andisol. Our study highlights the importance of low- to meso-density fractions in organic and inorganic P reservoirs in Andisols.

Decoupling of soil nitrogen and phosphorus dynamics along a temperature gradient on the Qinghai-Tibetan Plateau

Responses of soil nitrogen (N) and phosphorus (P) dynamics to global warming have received much attention. However, there are a lot of uncertainties. Given that a large-scale field investigation along a temperature gradient can provide deep insight into the long-term effect of climate warming, we conducted a soil sampling along a temperature gradient across a 1500-km transect on the Qinghai-Tibetan Plateau. To minimize the interference of the collinearity between temperature and precipitation on the temperature patterns of soil N and P dynamics, the sampling was performed along the 400 mm isohyet. We wanted to clarify the alterations of soil N and P dynamics in response to increasing temperature when the precipitation effect was minimized. Soil N content and N storage decreased, whereas soil P content and P stocks were stable with increasing temperature, leading to a decreased soil N:P ratio along the temperature gradient. This means that soil N and P dynamics are decoupled under the condition of increasing temperature. Soil N dynamics were associated with the variations in soil organic matter content, silt content, pH and vegetation type, and the effect of temperature on soil N dynamics was mainly through the influence of temperature on soil organic matter content. Soil P dynamics were related to the changes of soil silt content, precipitation, vegetation and soil type. Our results suggest that global warming may negatively affect soil N dynamics, but have no or only a small effect on soil P dynamics, and at the same time may cause the ecosystem to change from P limited to N limited.

Soil-Test-Based Phosphorus Recommendations for Commercial Agricultural Production in Florida

This new 6-page publication of the UF/IFAS Department of Soil and Water Sciences is intended to address agronomic and environmental issues related to phosphorus (P) dynamics in Florida agricultural soils and soil test P interpretation and management for agricultural crops. This document aims to provide science-based information to agricultural clientele, including commercial producers, small farmers, Extension agents, crop consultants, landscape professionals, representatives of the fertilizer industry, state and local agencies, students and instructors of high schools and colleges, researchers, and interested Florida citizens. Written by Rao Mylavarapu, Yuncong Li, Maria Silveira, Cheryl Mackowiak, and Mabry McCray.https://edis.ifas.ufl.edu/ss699

Influence of Application of Organic Residues of Different Biochemical Quality on Phosphorus Fractions in a Tropical Sandy Soil

Understanding phosphorus (P) dynamics in tropical sandy soil treated with organic residues of contrasting quality is crucial for P management using organic amendments. This research determined P fractions in a tropical sandy soil under the application of organic residues of different quality, including groundnut stover (GN), tamarind leaf litter (TM), dipterocarp leaf litter (DP), and rice straw (RS). The organic residues were applied at the rate of 10 t DM ha−1 year−1. The P fractions were examined by a sequential extraction procedure. Organic residue application, regardless of residue quality, resulted in P accumulation in soils. For unamended soil, 55% of total P was mainly associated with Al (hydr)oxides. Organic residue application, regardless of residue quality, diminished the NH4F-extractable P (Al-P) fraction, but it had a nonsignificant effect on NaOH-extractable P (Fe-P). The majority of Al-P and Fe-P fractions were associated with crystalline Al and Fe (hydr)oxides. NH4Cl-extractable P (labile P), NaHCO3-extractable P (exchangeable P and mineralizable organic P), HCl-extractable P (Ca-P), and residual P fractions in soil were significantly increased as a result of the incorporation of organic residues. The application of organic residues, particularly those high in ash alkalinity, increase soil pH, labile P, and Ca-P fractions. In contrast, applications of residues high in lignin and polyphenols increase residual P fraction, which is associated with organo-mineral complexes and clay mineral kaolinite.

Decreased soil total phosphorus following artificial plantation in the Loess Plateau of China

Artificial plantation, established on non-forest lands in recent decades in China’s Loess Plateau, play an important role in enhancing ecological restoration. However, soil phosphorus (P) dynamics following artificial plantation still remain unclear, especially at the regional scale. We aim to determine how do soil total P (TP) and available P (AP) change and how do drivers affect the dynamics of soil P following artificial plantation. Here we examined the effects of climate (precipitation and temperature), prior land use cover (cropland and barren land), current land use cover (forest, grassland, and shrubland), soil properties (soil organic carbon, bulk density, and pH), tree species, and plantation age on changes in soil TP and AP in top 100 cm following artificial plantation. Our examination was conducted based on a meta-analysis of 740 independent observations from 67 articles. The results showed that, across all the variations, TP concentrations significantly decreased by 17.5% in the top 100 cm soil layer following artificial plantation, with no significant change in AP. Concentration of TP in the 100 cm soil depth had a similar spatial pattern, characterized by a higher depletion in northwest area but lower depletion in southeast area. Climate, prior land use, tree species, and soil properties all played an important role on TP, while only tree species influenced AP response to artificial plantation. Our findings suggest that artificial plantation did not appear to directly induce P limitation because of the nearly unaltered AP in the regional scale. However, compared with lower TP depletion in southeast area, substantial declines in TP in northwest area may drive such region toward greater P limitation with the decrease of AP replenishment capacity in the future.

Dynamics of soil phosphorus measured by ammonium lactate extraction as a function of the soil phosphorus balance and soil properties

A sustainable supply of phosphorus (P) to agricultural soils should maintain soil fertility without jeopardizing the environment. This study analyzed the change in the soil P as a function of the net soil P mass balance, i.e. the input minus removal by the harvested crop. The P available for crops was estimated by the P extracted by ammonium lactate at pH 3.75 (P-AL). First, laboratory and pot-trial data showed that the net change in soil P-AL was only 68% of the change in total soil P, either when P had been added to soil or when P had been mined by plants for 1–2 years, indicating removal to or release from the non-extractable pool depending on the balance. Secondly, data were collated from 33 field trials in Europe with a wide range of cumulative soil P balances (−1200 to +2500 kg P ha−1) in time spans ranging from 3 to 51 years. The average change in P-AL across the negative and positive balance was only 27% (95% confidence interval 25–30%) of the net balance. The change in P-AL was larger as the net balance increased and as the initial P-AL decreased. The slope of the change versus the balance was smaller as time increased and initial P-AL decreased. The other soil characteristics did not affect these changes, and the model developed was not different for negative or positive P balances. Our results suggest that a steady state P-AL concentration at optimal P supply for crops is obtained at a net P balance of about 1–10 kg P ha−1. The P mass balance of a 51 year-old trial showed that the aqua regia soluble P of the 0–90 cm layer accounted for only 64% of the net P balances at the surface. This still incomplete P balance could be related to upward P transport by plant uptake from > 90 cm soil layers, lateral P movement in the field, and changes in the soil P fraction that could not be extracted with aqua regia. This study quantified the long-term dynamics of P-AL, which is useful for agronomic and environmental purposes and policy, and pointed out the importance of non-extractable P and vertical P movement.

Long term sugarcane straw removal affects soil phosphorus dynamics

Brazil is the world's largest sugarcane producer. This crop leaves huge amounts of straw behind which have to be managed with innovative approaches. In this study, a field experiment was carried out over six successive years of sugarcane harvests to evaluate the effect of straw maintenance on the field on changes in soil phosphorus (P) fractions. Four straw maintenance rates were tested: (i) maintaining 15 Mg ha−1 (SM15); (ii) maintaining 10 Mg ha−1 (SM10); (iii) maintaining 5 Mg ha−1 (SM5), and (iv) maintaining 0 Mg ha−1 (SM0). Our results showed that low maintenance of straw (SM5) resulted in the highest amount of P extracted by anion exchange resin and inorganic P extracted by 0.5 mol L−1 NaHCO3 in 0−5 and 5−10 cm soil depths. While total removal of residues resulted in soil P deficiency after six crop cycles, keeping straw on the soil surface at the rate of 5 Mg ha−1 supports plant growth without the need for P fertilizer application. We detected inorganic P extracted by 0.1 mol L−1 NaOH as the sink of P derived from straw since it was the only P fraction which increased with increasing straw on the soil surface. Non-labile P fractions were not influenced by straw maintenance rates in all depths. This is a promising result since it shows that P derived from straw does not accumulate in non-labile P fractions which are not plant available. Inorganic P was not influenced by straw removal rates and total P was only changed in 0−5 cm soil layer, while organic P was affected in all depths. We observed that organic P is available to sugarcane plants under SM0, SM5, and SM10, while under SM15, organic P does not play a role in sugarcane nutrition.

Long Term Effect of Organic, Inorganic and Integrated Nutrient Management on Phosphorous Dynamics under Different Cropping Systems of Typic Ustochrept Soil of India

ABSTRACT Information on phosphorus (P) dynamics in soil is crucial for careful management of phosphorus fertilization in respect to the sustainable development of agriculture in IGP regions. The sorption and desorption of phosphate, different fractions of phosphate, dehydrogenase activity, acid and alkaline phosphatase activity were studied in soils under organic inorganic and integrated nutrient management practices in four different cropping systems. The P adsorption maxima of long-term organic soil was highest (77.52 µg P g−1) under coarse rice-barley-green gram cropping system. The bonding energy of phosphorus in the soil solution varies from 0.38 to 0.20 ml µ−1. Average across the cropping systems, the bonding energy of adsorb P were 68.54% and 39.05% higher under organic and integrated nutrient-managed plots respectively as compared to the inorganic nutrient management. Maximum buffering capacity of phosphate was observed (29.59 ml g−1 soil) under Coarse rice-barley-green gram cropping systems in organic nutrient management practice. Application of organic nutrient management practice increases 26.04% higher water-soluble phosphorus (WSP) as compared to the inorganic nutrient management practice, average across the cropping systems. All other fractions of phosphorus in the soil were higher under inorganic nutrient management that leads to higher amount of total of phosphorus, average across the cropping systems. Long-term application of organic for 14 years increases the bonding energy and adsorption capacity for P in soil but decreased its desorption potential, increasing P availability to the plant and leading to higher P uptake irrespective of cropping systems.

Repeated drying and rewetting differently affect abiotic and biotic soil phosphorus (P) dynamics in a sandy soil: A 33P soil incubation study

Soil drying and rewetting (DRW) events are expected to occur at higher frequencies because of alterations in climate patterns. Readily extractable inorganic and microbial soil phosphorus (P) pools may be affected due to rapid changes in soil water availability. We aimed to determine how soil P dynamics are affected by repeated soil DRW using a sandy grassland soil that regularly experiences DRW. In a laboratory soil incubation study, the soil was exposed to three DRW cycles, with each cycle consisting of a two-day drying phase, a three-day dryness phase and a four-day moist phase after rapid rewetting. The indicators of abiotic processes (P sorption) and biotic processes (respiration, microbial abundance, potential phosphatase enzyme activities) were regularly determined together with water-extractable P, resin-extractable P and microbial P in a 33P-labelled soil.During the first DRW cycle, microbial P was reduced by half and accompanied by a concomitant but not equivalent increase in water-extractable P and a slight as well as delayed increase in resin-extractable P. Thus, increases in water-extractable P were explained by microbial P released during drying but also by microbial P occupying soil P sorption sites, thereby decreasing soil P sorption. Changes in the 33P-isotopic composition of microbial P at the same time suggested that microorganisms did not respond homogenously to the DRW treatment and indicated an increased mineralisation of previously unavailable organic P compounds. However, during the second and third DRW cycles, only water-extractable P, soil P sorption and potential phosphatase activities were affected by the DRW treatment, whereas all other parameters remained similar in values to the constant moist treatment. The effects of DRW on soil P dynamics appeared to affect water-extractable P more long-lastingly, whereas microbial P and most of the biotic indicators quickly adjusted to the DRW treatment. We conclude that the current concepts suggesting an increased mobility of soil P towards other environmental compartments due to soil DRW should consider that abiotic and biotic soil P dynamics are not equally affected in the case of short repetition of DRW incidences.

From sinks to sources: The role of Fe oxyhydroxide transformations on phosphorus dynamics in estuarine soils

The availability of phosphorus (P) in estuarine ecosystems is ultimately controlled by the nature of interactions between dissolved P and the soil components (e.g., soil minerals), especially iron (Fe) oxyhydroxides. P retention on Fe oxyhydroxides and its subsequent availability depends on mineral crystallinity and susceptibility to dissolution. However, in estuarine soils, geochemical conditions (e.g., redox oscillation and high soil organic matter content) may alter the fate of P and decrease the environmental quality of estuarine waters. The large input of Fe-rich tailings into the Rio Doce Estuary in Brazil in 2015 after a rupture of a Fe ore tailings dam (i.e., “Mariana mine disaster”) offers a unique framework to evaluate the Fe oxyhydroxides role in P availability in estuarine soils, their potential effects on the cycling of P and eutrophication. We observed a significant correlation between Fe minerals and the P content in the estuary soils, suggesting that P enrichment was promoted by the deposited Fe-rich tailings. Adsorption isotherm curves indicated that mine tailings had a strong affinity for P due to presence of crystalline Fe oxyhydroxides in the tailings. Significant losses of Fe (62%) and P (56%) from the estuarine soil was observed two years after the initial impact and in response to redox conditions oscillations. Additionally, the content of high crystallinity Fe oxyhydroxides decreased significantly, whereas that of low crystallinity Fe oxyhydroxides showed an increase over time. These changes were associated with the dissimilatory Fe reduction, which led an increase in the concentrations of readily available P (2015: 2.30 ± 0.41 mg kg−1; 2017: 3.83 ± 1.82 mg kg−1; p < 0.001) in the studied soils. Moreover, in 2017, the dissolved P content exceeded the recommended environmental safety limits by five times. Our results indicate that Fe oxyhydroxides are a continuous source of dissolved P for the ecosystem, and Fe-rich tailings deposited in the estuarine ecosystem may be linked to a potential eutrophication.

Soil phosphorus dynamics along a short‐term ecological restoration trajectory of a coastal sandplain forest in New Zealand

AbstractWe aim to understand the impact of ecological restoration on soil biogeochemistry, and the interrelationship between vegetation and soil phosphorus. In a study of two different‐aged soils in coastal New Zealand, soils are described along a transition from abandoned agricultural pasture, through 6‐year old restoration plots, towards forest fragments that have been largely undisturbed for 75 and 166 years. Soil biogeochemistry varied spatially along this restoration trajectory; there were profound changes in surface soil, but little impact on deeper soil horizons. In the early stages, soil organic matter accumulation and decomposition, and increasing demand of N from fast‐growing plants corresponded with rapid nutrient mineralization. Loss of soil total P, an increase of occluded P, and the increasing importance of soil organic P as soils weathered and aged, supported conceptual models of longer‐term soil pedogenesis. There was no evidence that the success of the establishment of plants varied across the site, but this is a first report of vegetation establishment during ecological restoration markedly impacting soil P dynamics and biogeochemistry.

Interacting effects of urea and water addition on soil mineral‐bound phosphorus dynamics in semi‐arid grasslands with different land‐use history

AbstractNitrogen (N) addition and precipitation increment can greatly influence soil phosphorus (P) dynamics, with much emphasis on total and available P, yet little is known about their interactive effects on soil mineral‐bound inorganic P (Pi) fractions under different historical land uses of grasslands and old fields. Thus, we compared (i) plant readily available P, (ii) less available Pi (sum of NH4F‐extractable Pi, NaOH‐Na2CO3‐extractable Pi and NaHCO3‐extracted Pi), (iii) refractory forms of Pi (NH4Ac‐extractable Pi, H2SO4‐extractable Pi and Na3(citrate)‐dithionite‐extractable Pi) and (iv) organic P under the same urea and water treatments in an old‐field grassland with a semi‐arid steppe. Soil total P remained unchanged with 10‐year urea addition in both sites, with lower organic P but higher Pi concentrations in the old field. Urea addition promoted transformation of refractory Pi into less available Pi in both sites, which potentially was related to higher plant productivity and thus enhanced plant P accumulation. Specifically, urea addition increased less available Pi fractions by as much as 42%, but decreased refractory Pi fractions by as much as 24%, for two sites under ambient precipitation. Water addition decreased less available Pi in the steppe under higher urea addition rates, whereas it increased less available and refractory Pi but only in the control plot of the old field. Irrespective of urea and water treatments, the old field had a higher Pi pool, which could replenish plant readily available P in the longer term and be less prone to P‐limitation than the steppe. We conclude that conversion of semi‐arid steppe to farmland causes long‐term increases in the soil Pi pool, possibly by enhancing organic P mineralization and anthropogenic fertilization during cultivation. Urea addition accelerated soil P cycling via promoting refractory Pi, transforming into less available Pi, with the process being strongly mediated by water availability, whereas the projected precipitation increment could decrease less available Pi via promoting plant P uptake and P leaching out of the plant–soil system.Highlights Urea addition promoted transformation of refractory Pi into less available Pi fractions. Water addition counteracted the positive urea effect on NH4F‐Pi in both steppe and old field. Less responsive organic P suggested that Pi fractions were more essential in soil P cycling. Water addition decreased NH4F‐Pi in both sites, potentially due to higher plant uptake and leaching. Conversion of steppe to farmland increased the soil Pi pool by enhancing organic P mineralization.

Acidification and anaerobic digestion change the phosphorus forms and distribution in particle fractions of cattle slurry and phosphorus dynamics in soil after application

Advanced slurry processing (anaerobic digestion, acidification and separation) is being promoted to generate renewable energy, reduce ammonia emissions and optimise storage and transport, respectively. However, these processes could affect slurry phosphorus (P) forms and bioavailability, and hence P dynamics in soil after application. This study investigated the effect of slurry processing, viz. separation, acidification and anaerobic digestion on P forms and distribution of cattle slurry, as well as P dynamics in soil following application of mechanically separated solid and liquid cattle slurry. The results showed that acidification and anaerobic digestion had little impact on TP distribution among particle fractions of slurry, but had substantial influence on P speciation and distribution. Acidification increased the dissolved inorganic-P (IP–H2O) proportion in cattle slurry, by reducing the mineral surface adsorbed (IP–NaHCO3) and precipitated inorganic P (IP–HCl) proportion. Anaerobic digestion decreased OP-NaHCO3 proportion by degradation and increased the IP-NaHCO3 and IP-HCl proportion by adsorption and precipitation. Particles <63 μm accounted for over 65% of P present in cattle slurry. The above changes in whole slurry made by acidification and anaerobic digestion were dominated by the <63 μm fraction. Slurry-derived soluble inorganic-P in soil decreased with time, due to adsorption and microbial immobilisation. This decrease was slower in the soil amended with anaerobically digested slurry. Results suggest that anaerobic digestion and acidification change P speciation of separated solid and liquid slurry and the subsequent P dynamics in soil after application.

Effects of nitrogen deposition and increased precipitation on soil phosphorus dynamics in a temperate forest

Nitrogen (N) deposition has increased dramatically since the industrial revolution due to anthropogenic activities. Meanwhile, global mean precipitation was predicted to rise. Although these two global change factors are co-occurring naturally, rare studies were contributed to understand how N deposition and increased precipitation interactively affect soil phosphorus (P) dynamics. In the present study, we conducted a novel canopy N and water addition experiment to investigate the effects of N deposition, increased precipitation, and their interactions on soil P dynamics in a temperate forest. We found that soil primary mineral P was significantly reduced after six years of canopy N deposition mainly due to N-induced soil acidification. Along with the reduction of primary mineral P, soil secondary mineral P was increased with N deposition due to increased exchangeable Al and Fe. Soil organic P associated with Al and Fe, microbial biomass P and phosphatase activity were also increased by N deposition. Our results also revealed that soil primary mineral P was reduced, and secondary mineral P was increased by increased precipitation. Increasing precipitation also significantly prompted soil microbial biomass P, which could explain the increase of soil secondary mineral organic P. In addition, we also found there were interactive effects between N deposition and precipitation on soil primary mineral P and secondary mineral organic P. The effect of N on these properties was strengthened by precipitation increase. Collectively, our results suggest that N deposition and increased precipitation can shift the composition of soil P fractions and drive the depletion of the primary mineral P. Thus, these two global change factors could synergistically affect soil P dynamics.

Soil Phosphorus Dynamics Across a Holocene Chronosequence of Aeolian Sand Dunes in a Hypermaritime Environment on Calvert Island, BC, Canada

Phosphorus (P) is an essential nutrient for plant growth, but soil P concentrations decline with increasing soil age. Phosphorus often limits tree growth within the hypermaritime Coastal Western Hemlock zone in British Columbia, Canada, particularly where parent material with low P concentrations have experienced rapid weathering. To sustainably manage forests in this region, more information is needed about changes in soil P concentrations and dynamics that occur with time. This study characterized the forms and abundance of soil and foliar P compounds using a soil chronosequence developed on aeolian sand dunes on Calvert Island and compared results to chronosequences in other locations. Eight time points were examined, from a modern foredune to a relict, stabilized dune (~10,760 years old). Soil horizons were analyzed for bulk density, pH, and concentrations of total carbon (C), nitrogen (N) and total P (TP), iron (Fe) and aluminum (Al), total organic P (Po), and Mehlich-extractable P and cations. For each site, P forms in L, H and organically-enriched mineral (M) horizons were characterized with solution 31P nuclear magnetic resonance spectroscopy (P-NMR), as were foliar samples from tree species spanning all age classes except the youngest dune. This chronosequence followed the Walker and Syers (1976) model, with an exponential decline in TP mass and a humped-shape curve in Po mass with increasing age. The L horizon had lower TP concentrations than foliage samples, but similar P forms. The H horizons had a greater proportion of DNA, phosphonates and nucleotides than the L horizon and increased proportions of myo- and scyllo-inositol hexakisphosphate (IHP) with increasing age. The mineral horizons had much lower TP concentrations than other horizons and increased proportions of IHP and DNA with increasing age, which were correlated to increased exchangeable and amorphous Al concentrations. In all sample types, the proportion of orthophosphate declined with increasing age. These results enhance knowledge of P cycling within hypermaritime soils, particularly the P decline that will occur with age. This will aid in the sustainable management of the low-productivity forests typical of these ecosystems.

Effects of cropping system and fertilization regime on soil phosphorous are mediated by rhizosphere-microbial processes in a semi-arid agroecosystem

In semi-arid regions, soil phosphorus (P) dynamics in cereal-legume intercropping are not yet fully elucidated, particularly in relation to integrated application of fertilizers. To this aim, we investigate the effects of different fertilizers on various P fractions in relation to the rhizosphere-microbial processes in a cowpea/maize intercropping system. Field experiments were conducted during two consecutive years (2016–2017) in a split-plot design by establishing cowpea/maize alone or intercropped onto the main plot, while the sub-plot was treated with four types of fertilization, i.e. no fertilizer addition (control), organic amendment (compost), mineral fertilizers (NPK) and multi-nutrient enriched compost (NPKEC). Our results showed that NPKEC fertilizer increased NaHCO3-Pi by 69% in maize, 62% in cowpea and 93% in intercropped plots compared to control plots. Similarly, a significant increase in the NaHCO3-Po fraction was also recorded with NPKEC treatment in all cropping systems. In case of moderately labile P, NPKEC fertilizer caused the highest increase of NaOH-Po (12.87 ± 0.50 mg P kg−1 soil) and NaOH-Pi (22.29 ± 0.83 mg P kg−1 soil) fractions in intercropped plots. Except for intercropping, NPK application caused an increase in the non-available P fraction (HCl-Pi), while the use of NPKEC decreased the HCl-Pi concentration in all cropping systems, suggesting stronger merits both for intercropping and NPKEC. Surprisingly, maize exhibited substantially higher phosphatases activity compared to cowpea in monoculture amended with compost, implying distinct crop strategies for adaptation under low P conditions. Based on the multi-factor analysis, the close association of NaHCO3–P with P solubilizing bacteria, root carboxylates and pH indicated that rhizosphere processes are the strongest predictors of immediately available P. Since alkaline phosphatase (ALP) is a P-degrading enzyme of microbial origin, rhizosphere related ALP association may have originated from root-associated microflora promoting P mobilization. Furthermore, the strong association of microbial biomass P (MBP) and acid phosphates (ACP) with NaOH–P fraction indicated moderately available P cycle in soil was mainly driven by microbial-related processes. Factor analysis map and two-way ANOVA confirmed that fertilization regime had a stronger effect on all tested variables compared to cropping system. Altogether, our results suggest that a combination of microbial-rhizosphere processes controls the dynamics of P fertility in semi-arid soils. In the broader context of improving soil P fertility, it is highly recommended the use of environmentally sustainable sources of fertilizer, such as NPKEC, which can enhance the competitive performance of legume-cereal intercropping under semi-arid agroecosystems.

Formation of dauciform roots by Japanese native Cyperaceae and their contribution to phosphorus dynamics in soils

Formation of dauciform roots by Japanese native Cyperaceae and their contribution to phosphorus dynamics in soils