Soil Phosphorus Availability Research Articles

Effects of Plantation Type and Soil Depth on Microbial Community Structure and Nutrient Cycling Function.

Declining soil quality and microecological imbalances were evaluated in larch plantations in this study. One potential solution to this problem is the cultivation of mixed coniferous and broad-leaved plantations. However, it is unclear whether and how soil microbial community structure and nutrient cycling function would be affected by mixed plantations and soil depths. In this study, we used high-throughput sequencing technology to investigate bacterial 16S and fungal ITS regions for comparisons of soil microbial diversity among plantation types (a Larix gmelinii pure plantation, a Fraxinus mandshurica pure plantation, a Larix–Fraxinus mixed plantation within the Larix row, the Fraxinus row, and between the Larix and Fraxinus rows) and soil depths (0–10, 10–20, and 20–40 cm). These data were used to evaluate variations in microbial communities and nutrient cycling function with the determining environmental factors. Our results indicated that bacteria had a stronger spatial dependence than did fungi, while plantation types significantly affected the fungal community. The relative abundance of Gaiellaceae, as well as bacterial ligninolysis, nitrate ammonification, and nitrite ammonification functions significantly increased with increasing soil depth. Compared with other plantations, the relative abundance of Inocybaceae was significantly higher in the Larix plantation. Distance-based redundancy analysis (db-RDA) showed that Gaiellaceae and Inocybaceae abundances were positively correlated with ammonium nitrogen content, available phosphorus content, and phosphatase activity. Our findings indicate that variations in soil available phosphorus are closely related to the relative abundances of Gaiellaceae at different soil depths and Inocybaceae in different plantation types. Mixed plantations might change the availability of soil phosphorus by controlling the relative abundance of Inocybaceae. We recommend that fungal community changes be considered in the sustainable management of mixed plantations.

Palm Species Traits Determine Soil Nutrient Effects on Seedling Performance

Environmental gradients influence plant establishment, survival, and functional traits. Along the Panama Canal Isthmus there is a strong rainfall gradient with an underlying mosaic of soil types ranging in soil nutrient availability. In this region, tree species distribution patterns are correlated with soil phosphorus availability and rainfall patterns, but how understory plant species such as palms relate to these factors is less clear. We hypothesized that due to greater resource use efficiency and optimal biomass allocation, specialist species will have greater seedling performance growing in home soil and sites compared to species not occurring there. To test this hypothesis, we used two specialist species (Chamaedorea tepejilote and Geonoma congesta) and two generalist species (Geonoma cuneata var. cuneata and Chamaedorea pinnatifrons), and for these four species we measured traits on seedlings and assessed their performance in shade house and field transplant experiments using five soils. Soils were sourced from five sites which varied in nutrient availability and rainfall, and were distributed along lowland tropical forests of the Panama Canal Isthmus. In the shadehouse experiment, leaf functional traits were determined by species rather than soil nutrient availability. However, in the shadehouse experiment, seedling biomass allocation, and relative growth rate were determined by interactions between species and soil, with weak support for home-site advantage for one of the species. In the field transplant experiment, seedling survival was strongly related to dry season water availability. However, species tended to have high survival at home sites and other sites with higher dry season rainfall. Together, results from these experiments suggest that understory palm species seedling performance are determined by species-specific responses to the combination of soil nutrient and water availability. This indicates that while soil nutrients influence seedling biomass allocation, dry season water availability determines both specialist and generalist seedling survival and therefore distributions along the soil nutrient and moisture gradient.

Glucose Increases the Abundance of Phosphate Solubilizing Bacterial Community for Better Apple Seedling Growth and Phosphate Uptake

Phosphorus-solubilizing microorganisms play an important role in soil nutrient phosphorus cycling. In order to clarify the effect of glucose (C6H12O6) on soil phosphorus transformation, the effects of glucose additions on the bacterial community, soil phosphorus status, and plant phosphorus uptake in apple rhizosphere soil were investigated. A 90-day pot experiment was carried out, and the experiment was repeated three times. Glucose additions were 0, 2.5, 5, 7.5, 10, and 12.5 g glucose per kg of soil. We measured soil bacteria and phosphorus related indexes using Illumina MiSeq sequencing technology and chemical methods. The results showed that when the glucose application rate was 2.5–7.5 g·kg−1, the soil total phosphorus content decreased by 4.4–7.3%; however, the soil acid phosphatase activity increased by 0.5–1.3 times, and the microbial biomass phosphorus increased by 29.1% and 37.0%. The content of Al-P and Fe-P in the rhizosphere soil decreased by 14.4 to 32.7 mg·kg−1 and 16.04 to 28.7 mg·kg−1, respectively. The compositional difference of the bacterial community became larger, and the relative abundance of 11 bacterial phyla changed significantly, among which the most significant change was found in Proteobacteria. This study also found that the relative abundances of Bacillus, Pseudomonas, Arthrobacter, and Cuprococcus increased by 0.9%, 2.2%, 2.4%, and 0.8%, respectively. Applying 7.5 g glucose per kg of soil can significantly increase the relative abundance of phosphorus solubilizing bacteria (Bacillus, Pseudomonas, Arthrobacter et al.) in rhizosphere soil, activate Al-P and Fe-P, and improve the availability of soil phosphorus.

Soil mineralogy-controlled phosphorus availability in soils mixed with phosphate fertilizer and biochar

The biochar amendment to soil proved to be beneficial to improve soil quality and provide nutrients. However, the effect of biochar on the availability of P are still controversial. We aim to study the effect of adding phosphate fertilizer and biochar on the P bioavailability in soils of different mineralogies. Eight biochars derived from biomass (rice husk and coffee husk), soil (sandy and clayey), and phosphate fertilizer (triple superphosphate) were produced. The biochar enrichment process with superphosphate was carried out before and after pyrolysis. Thus, we tested two biochar groups: 1) enriched biochars prior to pyrolysis; 2) enriched biochars after pyrolysis. These biochars were tested as P sources in soils of three mineralogies (kaolinite/oxide, kaolinite, and smectite). Batch sorption-desorption experiments were conducted. The sorbed P was fractionated to examine the factors controlling the retention of applied P. In the three soil mineralogies the use of enriched biochars prior to pyrolysis results in lower availability of P. In contrast, the enriched biochars after pyrolysis increase the bioavailability of P. The coffee husk biochar is more suitable than rice husk biochar to protect P from soil retention reactions. The use of sandy soil rather than clayey soil in enriched biochars compositions results in higher P content availability when applied to soils. The factor that controls the retention of P is the reaction between P, organic compounds, and Fe and Al compounds. The greater the relationship between biochar and soluble P in the fertilizer, the higher the increase of P retention.

Impact of Low Molecular Weight Organic Acids on Soil Phosphorus Release and Availability to Wheat

ABSTRACT Phosphorus (P) use efficiency (FPUE) is very low due to fixation of P with the hydrous oxides of iron and aluminum in acid soils and calcium in neutral to calcareous soil. The roots of wheat (Triticum aestivum) excrete low molecular weight organic acids (LMWOAs) to increase P bioavailability in P-deficient soil through acidification, chelation, and exchange mechanisms. However, the amount of LMWOAs excreted in the rhizosphere is small, and they undergo rapid microbial degradation. The present study was undertaken by applying different levels of LMWOAs and phosphorus to the soil followed by sowing of wheat seeds to learn the impact of applying LMWOAs, especially oxalic (OA) and citric acid (CA), on the yield and FPUE of wheat. The results showed that application of P fertilizer along with OA and CA significantly increased the Olsen P concentration in soil and in turn increased P uptake, FPUE, and yields of wheat. Application of OA @ 15 mg kg−1 recorded 20% (±0.22%) and 30% (±0.55%) higher grain and straw yield, respectively, over control and was more effective than CA. Among LMWOAs, application of OA @ 15 mg kg−1 was more effective than CA. Therefore, the application of OA has the potential to reduce the excess application of phosphorus and its buildup in soils and cause eutrophication of water bodies.

Straw returning mediates soil microbial biomass carbon and phosphorus turnover to enhance soil phosphorus availability in a rice-oilseed rape rotation with different soil phosphorus levels

The alleviation of phosphorus (P) limitation by increasing carbon (C) input is an effective strategy for improving crop production and P uptake efficiency. However, the effects of straw returning on soil microbial biomass P (MBP) turnover and P fractions in paddy-upland rotation remain poorly understood. Soil MBP turnover involves the mineralization and immobilization of organic P (Po), potentially altering P fractions and reducing the risk of P loss. The effects of straw returning on soil MBP turnover, P fractions and crop P utilization during the rice-oilseed rape rotation were evaluated in two field experiments with different soil Po levels. The treatments included no P fertilizer (-P), P fertilizer (+P) and P fertilizer plus straw returning (+P + S). The crop P uptake and cumulative P utilization efficiency were increased by straw returning. Straw addition promoted microbial biomass, decreased the MBC:MBP ratio in Po-high soil, increased the MBC:MBP ratio in Po-low soil, and increased the MBP turnover rates and fluxes in both soils. According to structural equation modeling (SEM), soil MBC and MBP had significant effects on crop P uptake directly or via P fractions. In Po-high soil, straw addition increased inorganic P (Pi) (NaHCO3 and NaOH) and decreased Po content by increasing the MBP turnover, while the Po-low soil mainly increased Po content. Among multiple observed variables, MBP was the most important driving factor controlling P uptake in Po-high soil, while MBC and NaOH-Pi were the best driving factors in Po-low soil. Additionally, the soil MBC, MBP and MBC:MBP ratios were higher in the oilseed rape season than in the rice season. Consequently, straw returning improves soil P availability by increasing MBP turnover, which is beneficial for improving P utilization.

Floating Rice Cultivation: a Solution to Reduce Crop Failure in Flood-Prone Areas

Bojonegoro is a regency in Indonesia located downstream of the Bengawan Solo River, a flood-prone area that caused crop damage and failure. The farmers need appropriate technology as an adaptation to reduce the loss of crop failure. Therefore, this study aims to determine the potential of floating rice cultivation as a solution for reducing crop failure. The experiment was arranged in Randomized Complete Block Design with two factors, namely planting media (soil:organic fertilizer (1:1) (M1); soil:rice husk (1:1) (M2); soil:organic fertilizer:rice husk (1:1:1) (M3)), and plant spacing (15 cm x 15 cm (J1); 20 cm x 20 cm (J2); 25 cm x 25 cm (J3)). Each unit treatment was replicated 3 times. The results showed M2J3 gave the best outcome on plant height of 94.3 cm, the tillers number of 21.7, and produced the highest rice yield of 14.16 tons ha-1. This treatment provides optimal soil conditions, high cation exchange capacity (CEC) of 26.6 cmol (+) kg-1, phosphorus availability (Av-P) 48.5 ppm, and potassium availability 0.9 ppm. The planting media compositions significantly affected soil cation exchange capacity, soil phosphorus availability, plant height, tillers number, and rice yield. The yield on floating rice cultivation was approximately similar when compared to the local farmer's fields. Floating rice cultivation can be used as a solution to reduce crop failure in flood-prone areas in Bojonegoro.

Plant growth and phosphorus uptake of coffee seedlings through mycorrhizal inoculation

Soil phosphorus (P) availability is a limiting factor for coffee seedling growth. Usually, large amounts of P fertilizers are required, generating nutritional imbalance, increasing production costs, and raising environmental concerns in water pollution. The use of arbuscular mycorrhizal fungi (AMF) can enhance plant P uptake and growth and reduce the dose of P fertilizers. A greenhouse experiment was conducted in a substrate containing Paleudult soil and quartz sand, with low level of soluble P (1 mg kg-1), to establish the effect of AMF inoculation with Rhizoglomus fasciculatum on coffee (Coffea arabica L. cv. Colombia) seedlings growth and P uptake under three levels of P in soil solution (0.002, 0.02, and 0.2 mg L-1). AMF colonization was significantly reduced when contents of P in solution increased. Shoot dry weight and P foliar concentration were increased by the AMF inoculation when soil P in solution was 0.02 mg L-1; these effects were lower at 0.2 mg L-1 and null at 0.002 mg L-1 P. Results showed that AMF inoculation can play an important role in the growth of coffee seedlings as long as the content P in soil solution maintains intermediate level. At the lowest P level, the response of coffee seedlings to AMF inoculation was ineffective, while at the highest level, AMF application was unnecessary for coffee growth.

Soil Available Phosphorus Deficiency Reduces Boll Biomass and Lint Yield by Affecting Sucrose Metabolism in Cotton-Boll Subtending Leaves

Soil available phosphorus (AP) deficiency and shortage of phosphate rocks limit cotton production in China. Therefore, pool-culture experiments were conducted in 2019 and 2020 using two cotton cultivars (CCRI-79, low-P tolerant; SCRC-28, low-P sensitive) under three soil AP levels (P0: 3 ± 0.5, P1: 6 ± 0.5, and P2 (control): 15 ± 0.5 mg kg−1) to ascertain the effect of soil AP on boll biomass and lint yield. P0 and P1 decreased the P concentration and net photosynthetic rate (Pn) of subtending leaves, thus, reducing boll biomass and lint yield. Additionally, soil AP deficiency decreased boll wall:boll, lint:boll, and lint:seed, and increased seed:boll ratio. Upper fruiting branch positions (FB9–12) had higher lint:seed ratio and proportion of the total lint yield under low soil AP. Moreover, soil AP deficiency also reduced the sucrose transformation rate (Tr) and activities of sucrose-metabolizing enzymes, such as ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), sucrose phosphate synthase (SPS), and sucrose synthase (SuSy), while increased carbohydrate levels (soluble sugar, sucrose, and starch) and the activity of cytosolic fructose-1,6-bisphosphatase (cy-FBPase) in the subtending leaves. The sucrose and starch contents, cy-FBPase, and SPS activities of SCRC-28 were more sensitive to low soil AP than CCRI-79. Higher Tr and activities of initial Rubisco and SuSy in the subtending leaves improved boll biomass and lint yield.

Insight into soil nitrogen and phosphorus availability and agricultural sustainability by plant growth-promoting rhizobacteria.

Nitrogen and phosphorus are critical for the vegetation ecosystem and two of the most insufficient nutrients in the soil. In agriculture practice, many chemical fertilizers are being applied to soil to improve soil nutrients and yield. This farming procedure poses considerable environmental risks which affect agricultural sustainability. As robust soil microorganisms, plant growth-promoting rhizobacteria (PGPR) have emerged as an environmentally friendly way of maintaining and improving the soil's available nitrogen and phosphorus. As a special PGPR, rhizospheric diazotrophs can fix nitrogen in the rhizosphere and promote plant growth. However, the mechanisms and influences of rhizospheric nitrogen fixation (NF) are not well researched as symbiotic NF lacks summarizing. Phosphate-solubilizing bacteria (PSB) are important members of PGPR. They can dissolve both insoluble mineral and organic phosphate in soil and enhance the phosphorus uptake of plants. The application of PSB can significantly increase plant biomass and yield. Co-inoculating PSB with other PGPR shows better performance in plant growth promotion, and the mechanisms are more complicated. Here, we provide a comprehensive review of rhizospheric NF and phosphate solubilization by PGPR. Deeper genetic insights would provide a better understanding of the NF mechanisms of PGPR, and co-inoculation with rhizospheric diazotrophs and PSB strains would be a strategy in enhancing the sustainability of soil nutrients.

Contrasting patterns of microbial nutrient limitations between rhizosphere and bulk soil during stump sprout restoration in a clear-cut oak forest

Microbial metabolism changes in soil systems along a vegetation restoration gradient have attracted considerable attention; however, the differences in microbial metabolic limitations between the rhizosphere and bulk soil and their drivers during natural secondary forest restoration after disturbance have rarely been investigated. Here, we used multiple methods based on extracellular enzymatic stoichiometry to examine the microbial metabolic limitations in the rhizosphere and bulk soils along with a clear-cut oak (Quercus aliena var. acuteserrata) forest restoration over 58 years in the Qinling Mountains, China. Overall, the microbial metabolisms in both rhizosphere and bulk soils were co-limited by the availability of soil carbon (C) and phosphorus (P), and the limitations tended to decrease during restoration. Rhizosphere soil microorganisms were subject to relatively strong C limitation and weak P limitation compared with those in bulk soil. Microbial C and P limitations in the bulk soil were regulated by the nutrient ratios, and those in the rhizosphere soil were mainly dependent on the available nutrients mediated by soil moisture. Our results indicate that variations in the soil nutrients caused by oak forest restoration and water differences caused by the rhizosphere effect regulated microbial C and P metabolism in the rhizosphere and bulk soils. This study highlights the microbial metabolism difference between rhizosphere and bulk soil and its drivers during oak forest restoration and provides insights into the microbial resource limitation, nutrient cycling, and rhizosphere processes in the natural secondary forests after clear-cutting.

Temporal dynamics of soil nutrients in the riparian zone: Effects of water fluctuations after construction of the Three Gorges Dam

The Three Gorges Dam (TGD) plays a vital role in the hydropower supply of China, which has a substantial impact on the riparian zones along the Yangtze River. Knowledge about how riparian soil properties respond to such changes remains limited. To explore how water regulation disturbs the status of soil nutrients in the riparian zone, a long-term monitoring program was implemented at sites with secondary shrubland (SB) and abandoned farmland (AFD). A total of 288 composite soil samples collected from the two riparian areas were investigated. Compared with 2009, long-term flooding changed the distribution of soil organic matter (SOM) and available phosphorus (AP) contents in various soil layers. The fluctuation of the water level reduced the SOM content, which the range of SOM variation was greater in the early stage of submergence. In 2018, the SOM content in the 10–20 cm at 155–165 m above sea level (a.s.l.) of the AFD was 9.46 g/kg, which reduced by 74.30% compared with 2019. In all the 0–10 cm soil layer, except for 145–155 (a.s.l.) in the AFD plot, soil total nitrogen contents in 2018 were significantly higher than those in 2009. Compared with 2009, the soil AP content in the 10–20 cm layer at 145–155 m (a.s.l.) of SB decreased by 90.90% in 2018. The total potassium (TK) content of AFD increased from 2009 to 2015 but decreased in 2018. However, the soil TK content in 2018 was significantly higher than that in 2009. In AFD, soil pH increased from 2009 to 2015 and reached a maximum value (8.21). In 2018, the pH value of some soil samples showed a downward trend but was always significantly higher than during 2009. Moreover, according to the redundancy analysis, the elevation, soil layer, and flood cycle could explain 56.64% of the changes in soil properties. Our study demonstrates that dam operation was an indirect driver for the changes in the temporal dynamics of soil nutrients, providing a reference for the management of the TGD.

Integrated use of phosphorus, farmyard manure and biofertilizer improves the yield and phosphorus uptake of black gram in silt loam soil.

An experiment on the use of farmyard manure and biofertilizer along with application of chemical phosphorus was conducted to assess the impact of differential doses of phosphorus, farmyard manure and consortium biofertilizer application on the development, yield and phosphorus uptake during the year 2018 and 2019. The impact of different treatments was recorded on the plant height, dry matter partition, yield and yield attributes, phosphorus uptake and soil phosphorus availability using standard methods. The data revealed significant improvement in yield, yield attributes, phosphorus uptake and soil phosphorus availability. The integration of farmyard manure and biofertilizer with 60 kg ha-1 SSP (single superphosphate) has improved the black gram yield by 7.4% and 3.28% respectively over the use of 60 SSP alone. The phosphorus uptake in black gram with application of Farm yard manure and biofertilizer along with 60 kg ha-1 SSP has improved the uptake by 7.18% and 2.51% respectively over the use of 60 kg ha-1 SSP alone. The results highlight the need of integrated application of farm yard manure, biofertilizer for sustainable production of black gram in the region.

Microbial nutrient limitation and catalytic adjustments revealed from a long‐term nutrient restriction experiment

AbstractIntroductionMicrobial abundance and activities in soils are predominantly determined by soil carbon (C), nitrogen (N) and phosphorus (P) availability. Much research has focused on the effects of soil N than P availability on soil microbial biomass and enzyme activities as sensitive proxies of microbial ecophysiology highlighting the need to investigate how microbes will respond to P availability in soil, especially in cropping systems.Materials and MethodsThe effect of P fertilisation on microbial biomass‐C, ‐N and ‐P, and the kinetic parameters (maximal velocity [Vmax], Michaelis constant [Km] and catalytic efficiency [Ka]) of β‐1,4‐glucosidase (BG; C‐acquiring), leucine‐aminopeptidase (LAP; predominantly N‐acquiring) and acid phosphomonoesterase (PHO; P‐acquiring) were measured in a nutrient‐poor agricultural soil (devoid of fertiliser application since 1942).ResultsThis study showed that P fertilisation led to a 65% and 56% increase in microbial biomass‐N and ‐P, respectively, indicating severe P limitation and inefficient N acquisition by microbes without P availability. Increased Ka values of LAP with P fertilisation further hint toward the production of efficient isoenzymes to avoid resource tradeoffs for nutrient acquisition.ConclusionsOverall, these results decipher microbial metabolic and catalytic adjustments mediated by soil P availability. Increased microbial biomass‐N and ‐P with P fertilisation indicated microbial N and P colimitation that was partly overcome by the production of efficient enzymes for N acquisition with P fertilisation. We argue to incorporate microbial enzyme activities as a response to different management strategies to better inform us about soil biogeochemical cycles in cropping systems.

Environmental factors and land use changes controlling the availability of phosphorus in dryland soils

The wide climatic and lithological variability observed in drylands form soils with peculiar characteristics, whose phosphorus (P) dynamics is poorly understood. In this study, we used 93 samples from the surface layer of soils located in tropical drylands in northeastern Brazil, to estimate the effects of climate, land use, parent material, topography and altitude on soil P availability. Our results indicated that the climate affected the availability of P in the soil by its effect in the dynamics of pH values. The increase in pH values in the most arid environments explained 21.9% of the increase in P availability in the soils. We observed that the P available content in soils originated from river sediments was 286, 202 and 168% higher than those found in soils from sedimentary, igneous and metamorphic rocks, respectively. We observed that agricultural cultivation (>20 years) and pasture (>20 years) increased the available P content in the soil by 60 and 51%, respectively, when compared to the reference native forest. We observed that soils located in flat and gently wavy topography had the highest contents of P. The results of our study can be useful for the sustainable use of soils in tropical drylands.

Species ecological strategy and soil phosphorus supply interactively affect plant biomass and phosphorus concentration

Excess soil phosphorus often constrains ecological restoration of degraded semi-natural grasslands in Western-Europe. Slow-growing species, often target of restoration (measures), are at a disadvantage because they are outcompeted by fast-growing species. Gaining insight into the responses of plant species and communities to soil phosphorus availability will help understanding restoration trajectories of grassland ecosystems. We set up two pot experiments using twenty grassland species with contrasting growth forms (i.e. grasses versus forbs) and nutrient use strategies (i.e. acquisitive versus conservative nutrient use). We quantified the nutrient use strategy of a species based on the stress-tolerance value of the CSR framework (StrateFy et al. 2017). We grew these species (1) as monocultures and (2) in mixtures along a soil phosphorus gradient and measured the aboveground biomass and plant phosphorus concentrations. Plant phosphorus concentration generally increased with soil phosphorus supply and biomass increased with soil phosphorus supply only in conservative communities. Forbs had higher plant phosphorus concentrations compared to grasses both in monocultures and mixtures. The species’ nutrient use strategy had contrasting effects on plant tissue phosphorus concentrations, depending on soil phosphorus supply (interaction effect) and vegetation biomass (dilution effect). Our findings contribute to the knowledge required for successful ecological restoration of species-rich grasslands. Our results suggest that under specific conditions (i.e. nitrogen limitation, no dispersal limitation, no light limitation), slow-growing species can survive and even thrive under excess soil phosphorus availability. In the field, competition by fast-growing species may be reduced by increased mowing or grazing management.

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

Model of inner-sphere adsorption of oxyanions in goethite - Why is phosphate adsorption more significant than that of sulfate?

Phosphorus availability in soils is low due to its strong retention by inner-sphere complexation on minerals in the clay fraction with pH-dependent charges, such as goethite. On the other hand, sulfur has greater availability because it is retained mainly by electrostatic attraction. We evaluated the intensities of the inner-sphere complexation of orthophosphate and sulfate (H2PO4-/HPO42- and SO42- – generically treated as PO4 and SO4) under different experimental conditions (pH, goethite purity, and contact times) on synthetic goethite samples to [...]

Straw retention combined with phosphorus fertilizer promotes soil phosphorus availability by enhancing soil P-related enzymes and the abundance of phoC and phoD genes

Straw retention has the potential to improve soil phosphorus (P) availability, but the question on how straw retention under different P level influences the activity of soil P-related enzymes and thus the transformfiation of soil organic P (Po) remains poorly understood. A four-year field experiment (2016–2019) was established to investigate the impacts of straw retention under different P fertilizer levels (0, 44, 88 kg P ha–1) on soil P fractions, the activity of P-related enzymes, and the abundance of phoC and phoD genes. Results demonstrated that P application alone significantly increased all soil inorganic P (Pi) fractions, but had no significant impact on soil Po fractions. Straw retention combined with P fertilizer mainly improved the proportion of NaHCO3-Po (labile P) and NaOH-Pi (moderately labile P), while decreased the proportion of dilute HCl-P and residual-P (non-labile P). The application of straw plus P fertilizer of 44 kg P ha−1 increased the contents of resin-Pi and NaHCO3-Pi more than straw plus 88 kg P ha−1. Also, the former had higher activity of alkaline (ALP) and acid phosphatase (ACP) and abundance of phoD gene than the latter. The structural equation model indicated that soil ALP and phytase (PHY) had a significant and positive effects in P cycling. Soil organic carbon (C), C:P ratio, and water-organic C were positively correlated with the activity of ALP and PHY, and the abundance of phoD gene. These findings together demonstrate that crop straw combined with a moderate amount of P fertilizer (44 kg P ha−1) is more beneficial for soil P availability through enhancing the activity of PHY and ALP and the abundance of phoD and phoC genes.

Application of Fourier transform mid-infrared photoacoustic spectroscopy for rapid assessment of phosphorus availability in digestates and digestate-amended soils

Digestate is the anaerobic digestion by-product of biogas production that can be used as a phosphorus (P) fertilizer. To achieve the efficient utilization of digestate as a P fertilizer and evaluate P availability in digestate-amended soils, it is necessary to assess both available P in different digestates and digestate-amended soils. In this study, Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) combined with multivariate analysis was applied to predict water-extractable P (WEP) in digestates and plant-available P in digestate-amended soils. The plant-available P was determined by the diffusive gradients in thin films (DGT) technique. 45 digestate samples were collected both from laboratory-scale digesters (26 samples) and operating biogas plants (19 samples) in Denmark for WEP determination. Three soils amended with the collected 19 digestate samples from biogas plants (that results to 57 digestate-amended soil samples in total) were deployed for DGT measurement of plant- available P. The WEP predicting model had a coefficient of determination (R2) of 0.80 and a root mean square error of 0.78 g kg−1 while the plant-available P predicting model exhibited an R2 of 0.70 and a root mean square error of 134.09 μg P L−1. Furthermore, regression coefficients with a significant contribution of the plant-available P predicting model were identified, indicating that FTIR-PAS is capable for correlating spectra information with plant-available P related chemical bonds. In conclusion, FTIR-PAS can be used as a faster and non-destructive alternative for the assessment of both WEP in digestates and plant-available P in digestate-amended soils.