Changes of soil test phosphorus and phosphorus fractions with single and blended soil chemical amendments

Phosphorus (P) loss from soils can contribute significantly toward P enrichment in water bodies, impairing water quality. Application of soil amendments is a viable strategy to decrease soluble P in surface soils. Since soluble P is reduced through different mechanisms that are amendment‐specific, blended amendments could be a better approach than single amendment applications; however, very little information is available on blended amendment effects in reducing P loss from soils. We compared the effectiveness of gypsum (CaSO4·2H2O), Epsom salt (MgSO4·7H2O), and alum [Al2(SO4)3·18H2O] applied singly or blended in different ratios in reducing water‐extractable P (WEP) and Mehlich‐3 P of two soils (0‐ to 15‐cm depth) with contrasting P status (Mehlich‐3 P of 7.1 mg kg−1 and 202 mg kg−1) from the Red River Valley region in MB, Canada. Ten treatments used for the laboratory incubation study were unamended control, gypsum or Epsom salt at 2.5 or 5 Mg ha−1, alum at 2.5 Mg ha−1, and four blended treatments of gypsum: alum or Epsom salt: alum at 1:1 or 2:1. Treated soils were saturated and incubated for 2 weeks and analyzed for WEP (an indicator of risk of P loss) and Mehlich‐3 P (plant‐available P) concentrations. All amendments significantly reduced the WEP concentrations compared to control in both soils. The blended amendments, particularly gypsum–alum blends, performed better than unblended amendments in reducing the potential risk of P loss. Mehlich‐3 P concentration was not influenced by amended treatments, suggesting no significant decrease in plant‐available P with amendments in both soils.

Snowmelt runoff is a dominant pathway of phosphorus (P) losses from agricultural lands in cold climatic regions. Soil amendments effectively reduce P losses from soils by converting P to less soluble forms; however, changes in P speciation in cold climatic regions with fall-applied amendments have not been investigated. This study evaluated P composition in soils from a manured field with fall-amended alum (Al2(SO4)3·18H2O), gypsum (CaSO4·2H2O), or Epsom salt (MgSO4·7H2O) using three complementary methods: sequential P fractionation, scanning electron microscopy with energy-dispersive X-rays (SEM-EDX) spectroscopy, and P K-edge X-ray absorption near-edge structure spectroscopy (XANES). Plots were established in an annual crop field in southern Manitoba, Canada, with unamended and amended (2.5 Mg ha-1) treatments having four replicates in 2020 fall. Soil samples (0-10cm) taken from each plot soon after spring snowmelt in 2021 were subjected to P fractionation. A composite soil sample for each treatment was analyzed using SEM-EDX and XANES. Alum- and Epsom salt-treated soils had significantly greater residual P fraction with a higher proportion of apatite-like P and a correspondingly lower proportion of P sorbed to calcite (CaCO3) than unamended and gypsum-amended soils. Backscattered electron imaging of SEM-EDX revealed that alum- and Epsom salt-amended treatments had P-enriched microsites frequently associated with aluminum (Al), iron (Fe), magnesium (Mg), and calcium (Ca), which was not observed in other treatments. Induced precipitation of apatite-like species may have been responsible for reduced P loss to snowmelt previously reported with fall application of amendments.

Widespread implementation of the phosphorus (P) index has focused attention on environmental manure tests that can be used to estimate the relative availability of P in manure to runoff water. This article describes the development and use of a water extractable P (WEP) test to assess the capacity of land‐applied manure to enrich P in runoff water. WEP of surface‐applied manure has been shown to be strongly correlated to dissolved P concentrations in runoff from agricultural soils. WEP tests that have a defined water‐to‐manure‐solids ratio and involve extraction times of 30 to 120 min provide the best prediction of dissolved P in runoff across a wide range of manures. Consistent measurement of manure WEP can be achieved with manure sample storage times of up to 22 days (4°C), acidified extract holding times of 18 days, and solid separation by either centrifugation or paper filtration. Reproducibility of WEP tests is comparable to that of other common manure tests (e.g., total P), as verified by within‐laboratory and inter laboratory evaluations. A survey of 140 livestock manures revealed significant differences in mean WEP among different livestock manures, with swine greater than poultry (turkey, broiler and layer chickens) and dairy cattle greater than beef cattle. Such results support the use of WEP‐based coefficients to modify the source component of the P index.

Reduction of orthophosphates loss in agricultural soil by nano calcium sulfate

A 9-month incubation study was conducted to investigate the effectiveness of amending dairy cattle slurry with either alum, lime, poly-aluminum chloride (PAC), or ferric chloride (FeCl3) in reducing water-extractable P (WEP) levels in five soils (four mineral and one organic). Alum, lime, and PAC were the most effective amendments in decreasing WEP (compared to a slurry-control) for the four mineral soils (by an average of 47% at the end the 9-month incubation period). In comparison, FeCl3 increased WEP (compared to the slurry-control) by an average of 35% at the end the study. None of the amendments examined effectively reduced WEP of the organic soil. No amendment reduced soil-test P [(Morgan’s P (Pm) and Mehlich 3 P (M3P)] compared to the soil-only treatment. Alum maintained the greatest levels of M3P across the four mineral soils with the least risk of P loss to overlying water.

Little is known about the effects of air-drying and freezing on the transformation of phosphorus (P) fractions in soils. It is important that the way in which soils respond to such perturbations is better understood as there are implications for both P availability and loss to surface waters from soils. In this study, the effects of air-drying and freezing were investigated using two soils, one being a forest soil (FS) high in organic matter and the other being a sterile soil (SS) low in organic matter. Soil P was fractionated using a modified Hedley fractionation method to examine the changes of phosphorus fractions induced by air-drying and freezing. Generally, there were no significant differences of total phosphorus among the three treatments (CV% < 10%). Compared with field moist soils, freezing the soil evoked few changes on phosphorus fractions except that the resin-P increased in FS soil. On the contrary, air-drying significantly changed the distribution of phosphors fractions for both soils: increased the labile-P (especially resin-P) and organic-P (NaHCO<sub>3</sub>-Po, NaOH-Po and Con.HCl-Po) at the expense of NaOH-Pi and occlude-P (Dil.HCl-P and Con.HCl-Pi). Resin-P significantly increased by 31% for SS soil and by 121% for FS soil upon air-drying. The effect of air-drying seemed to be more pronounced in the FS soil with high organic matter content. These results indicated that drying seem to drive the P transformation form occlude-P to labile-P and organic-P and accelerated the weathering of stable P pool. This potentially could be significant for soil P supply to plants and P losses from soils to surface waters under changing patterns of rainfall and temperature as predicted by some climate change scenarios.  

Aims: The aim of this study is to determine the amount and distribution of inorganic phosphorus fractions in soil profiles classified as Mollisol and Entisol, which are common in the Eastern Anatolian region, and to determine their soil properties and their relationships with each other, and to evaluate the contribution of inorganic phosphorus fractions to available soil phosphorus (Olsen-P).Methods and Results: The total amount of phosphorus in these soils with calcareous and slightly alkaline reactions has been determined as 280-1713 mg kg-1 and an average of 713 mg kg-1. Ca-P’, which make up an average of 80.9% of the total phosphorus and which are determined as the first phosphorus fraction in these soils, have been determined between 163.2-951.1 mg kg-1. The occluded phosphates (CDB-P), which rank second in quantity in these soils after Ca-P2, are between 2.07-105.6 mg kg-1, and thirdly, phosphates (CB-P) held by carbonates during the first extraction are 0.76-52.83 mg kg-1. In the fourth and last row, nonoccluded aluminum and iron phosphates (Al-P + Fe-P) were found as the least amount of phosphorus fractions in these soils between 0.09-5.0 mg kg-1.Conclusions: In summary, the order of inorganic phosphorus fractions in these soils was determined as Ca-P> CDB-P> CB-P> Al-P+Fe-P. Significance and Impact of the Study: It was determined that two fractions contribute to phosphorus (Olsen-P), nonoccluded aluminum and iron phosphates (AI-P + Fe-P) and occluded phosphates (CDB-P) in these soils.

Pethoxamid dissipation and microbial activity and structure in an agricultural soil: Effect of herbicide rate and organic residues

Biosolids and manures provide nutrients and organic matter to soils but can also pollute runoff. Phosphorus (P) is the limiting nutrient for eutrophication in most fresh water systems, and states are developing strategies to reduce P losses from cropland amended with manure and biosolids. The water extractable P (WEP) of manures and biosolids has been proposed as a predictor of potential to enrich drainage and surface runoff P. A rainfall simulation study was conducted to investigate the relationship between the percent extractable P (PWEP = [WEP ÷ PT] × 100) and runoff P levels. Five P-sources [fresh dairy manure, anaerobically digested biosolids produced without Fe or Al addition, aerobically digested biosolids (elevated Al), anaerobically digested biosolids (elevated Fe), and composted biosolids (elevated Fe)] were surface applied at 112 kg P ha -1 to runoff trays containing an acid-shale and a calcareous soil, each with high and low soiltest P background levels (four soils in all). Trays were sloped at 3% and subjected to 30-min rainfall events (intensity = 7.1 cm hr -1 ). Two rainfall events were performed, separated by a 48hour rest period between events. Collected runoff was analyzed for total mass, runoff dissolved P (RDP), and total (sediment plus dissolved) runoff P (TRP). For all soil treatments, the trend of RDP (mg L -1 ) consistently followed the pattern: dairy manure >> biosolids without Al or Fe > biosolids with Al >composted biosolids with high Fe ≈ biosolids cake with high Fe. The effect of soil type on RDP was found to be statistically different only for the acid-shale high-P (Mehlich-3 P = 520-ppm) material. Runoff DP for all soils was highly correlated (r 2 > 0.98) with the PWEP of the P-source. Average runoff DP from high-Fe biosolids (both cake and compost) was not statistically different from unamended soil control treatments. Total RP (mg L -1 ) was also significantly greater for dairy manure than for biosolids. As P-based nutrient management is implemented for land application, it is imperative that policies reflect different runoff P potentials of biosolids and manures. Moreover, WEP is a simple test that could be developed for routine use as a measure of P-source availability in the P site indices being developed in several states.

Soil nitrogen and phosphorus are two key elements limiting tree growth in subtropical areas. Understanding the regulation of soil microorganisms on nitrogen and phosphorus nutrition is beneficial to reveal maintenance mechanism of soil fertility in plantations. We analyzed the characteristics of soil nitrogen and phosphorus fractions, soil microbial community composition and function, and their relationship across three stands of two-layered Cunninghumia lanceolata + Phoebe bournei with different ages (4, 7 and 11 a) and the pure C. lanceolata plantation. The results showed that the contents of most soil phosphorus fractions increased with increasing two-layered stand age. The increase in active phosphorus fractions with increasing stand age was dominated by the inorganic phosphorus (9.9%-159.0%), while the stable phosphorus was dominated by the organic phosphorus (7.1%-328.4%). The content of soil inorganic and organic nitrogen also increased with increasing two-layered stand age, with NH4+-N and acid hydrolyzed ammonium N contents showing the strongest enhancement, by 152.9% and 80.2%, respectively. With the increase of stand age, the composition and functional groups of bacterial and fungal communities were significantly different, and the relative abundance of some dominant microbial genera (such as Acidothermus, Saitozyma and Mortierella) increased. The relative abundance of phosphorus solubilization and mineralization function genes, nitrogen nitrification function and aerobic ammonia oxidation function genes tended to increase. The functional taxa of fungi explained 48.9% variation of different phosphorus fractions. The conversion of pure plantations to two-layered mixed plantation affected soil phosphorus fractions transformation via changing the functional groups of saprophytes (litter saprophytes and soil saprophytes). Changes in fungal community composition explained 45.0% variation of different nitrogen fractions. Some key genera (e.g., Saitozyma and Mortierella) play a key role in promoting soil nitrogen transformation and accumulation. Therefore, the conversion of pure C. lanceolata plantation to two-layered C. lanceolata + P. bournei plantation was conducive to improving soil nitrogen and phosphorus availability. Bacteria and fungi played important roles in the transformation process of soil nitrogen and phosphorus forms, with greater contribution of soil fungi.

Information on the P fractions in soils treated with different organic amendments is needed to better manage land application of organic amendments to agricultural soils. This study investigated the forms and distribution of P after 1, 4 and 16 wk in a Lakeland silty clay loam soil using a sequential fractionation procedure. Phosphorus was added at rates of 0, 123, 307 and 614 mg P kg-1 in the form of biosolids, hog manure, cattle manure and fertilizer P. The largest difference among the amendments was in the water-extractable P fraction, which was significantly lower in soil amended with biosolids. Regression analysis showed that the slope of P increment in the H2O fraction as a function of P application rate was four times lower for biosolids (0.06) than for hog manure (0.24) and seven times lower than for fertilizer (0.42) amended soils. In the biosolids-amended soil, there was a net increase of H2O-P, NaOH-Pi and HCl-P fractions at the expense of organic P (NaOH-Po) and residual P fractions after 16 wk of incubation, signifying net P mineralization. In hog manure amended soil, H2O-P decreased by 128 mg kg-1 with a corresponding increase in the NaHCO3-P, possibly due to P sorption during the 16 wk of incubation. The results for cattle manure indicated net immobilization of P as the H2O-P and NaHCO3-P declined while the inorganic P (NaOHPi), HCl-P and residual P increased with incubation time. The transformation of P in fertilizer-amended soil was similar to that of hog manure amended soil. The amount of labile P (defined as H2O-P plus NaHCO3-P) in amended soils followed the order of fertilizer P > hog manure > cattle manure > biosolids. Key words: Phosphorus fractions, sequential P extraction, incubation, organic amendments

Influence of the tropical millipede, Glyphiulus granulatus (Gervais, 1847), on aggregation, enzymatic activity, and phosphorus fractions in the soil

A total of 115 samples of particulate matter from the Jade Bay and the backbarrier area of the island of Norderney, Lower Saxonian Wadden Sea, was analysed for three different phosphorus fractions. Water extractable P (WEP) accounted for 29.3±12.9%, particulate inorganic P (PIP) for 35.1±10.0% and particulate organic P (POP) for 35.7±10.5% (mean±1 SD) of total particulate P. WEP was lower in late summer than in spring/early summer while POP showed the opposite behaviour. PIP did not show pronounced seasonal changes.

Calcium silicate-based sealers (CSBS) vary in chemical composition, which can influence treatment outcomes. Therefore, the study aimed at comparing several commercially available CSBS regarding microstructure and elemental characterization. Four CSBS (AH Plus Bioceramic Sealer, BioRoot RCS, BioRoot Flow, TotalFill BC Sealer) and a control resin-based sealer (AH Plus) were evaluated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray powder diffraction analysis (XRD). The specimens were analyzed after setting (SEM, EDX, XRD), as well as after 7 (SEM) and 28 days (SEM, EDX) of incubation in Hank's balanced salt solution. AH Plus exhibited a uniform matrix and small amounts of calcium (Ca), significantly decreasing after incubation. In contrast, CSBSs exhibited crystalline forms on the surface and increased Ca content, significantly increasing after 28 days of incubation. The main crystalline phase for all tested CSBS was zirconium oxide, while for ERBS it was calcium tungstate. In conclusion, the amount of calcium increased on the surface of CSBSs after incubation, which alkalinized the pH, promoting mineralization, apatite formation, and antibacterial potential. Despite this, the formation of a hydroxyapatite layer was not demonstrated, possibly due to the high dissolution potential of CSBSs.

Metal oxide modified biochars for fertile soil management: Effects on soil phosphorus transformation, enzyme activity, microbe community, and plant growth