Speciation and sorption of phosphorus in agricultural soil profiles of redoximorphic character

Controlled drainage is considered as a soil management tool to improve water supply to crops and reduce nutrient losses from fields; however, its closure may affect phosphorus (P) mobilization in soil. To assess the P mobilization potential, three soil profiles with redoximorphic features were selected along a slight hill in Northern Germany. Soil samples from three depths of each profile were characterized for basic properties, total element content, oxalate- and dithionite-extractable pedogenic Al, Fe and Mn (hydr)oxides, P pools (sequential extraction), P species [P K-edge X-ray absorption near-edge structure (XANES) spectroscopy] and P sorption behavior. In topsoil (~ 10 cm depth), labile P (H2O-P + resin-P + NaHCO3-P) accounted for 26–32% of total P (Pt). Phosphorus K-edge XANES revealed that up to 49% of Pt was bound to Al and/or Fe (hydr)oxides, but sequential fractionation indicated that > 30% of this P was occluded within sesquioxide aggregates. A low binding capacity for P was demonstrated by P sorption capacity and low Kf coefficients (20–33 $${\text{mg}}^{{1 - n_{\text{f}} }} \,{\text{L}}^{{n_{\text{f}} }} \,{\text{kg}}^{ - 1}$$ mg 1 - n f L n f kg - 1 ) of the Freundlich equation. In the subsoil layers (~ 30 and ~ 65 cm depth), higher proportions of Al- and Fe-bound P along with other characteristics suggested that all profiles might be prone to P mobilization/leaching risk under reducing conditions even if the degree of P saturation (DPS) of a profile under oxic conditions was < 25%. The results suggest that a closure of the controlled drainage may pose a risk of increased P mobilization, but this needs to be compared with the risk of uncontrolled drainage and P losses to avoid P leaching into the aquatic ecosystem.

Risk of phosphorus loss in surface runoff from agricultural land in the Baltic Commune of Puck

Background. Risk assessment of Phosphorus (P) losses in surface runoff from agricultural land is the basic measure that should be used as a part of actions taken to counteract the water eutrophication in watercourses and water reservoirs. To assess this risk, a new method has been recently developed based on the determination of degree of P saturation (DPS) which depends on P content in soil determined with the use of distilled water (water-soluble P – WSP). Methods. Based on DPS method, the risk of P losses in surface runoff from agricultural land in Puck Commune (Baltic Sea Coast) was assessed and a critical analysis of assessment results was carried out. The research was conducted on mineral and organic soils from 50 and 11 separate agricultural plots with a total area of 133.82 and 37.23 ha, respectively. In collected soil samples, P content was determined using distilled water (all soil samples), Egner-Riehm method (mineral soils) and extract of 0.5 mol HCl ∙ dm-3 (organic soils). The results of determinations P content in water extract from soils were converted to DPS values, which were classified by appropriate limit intervals. Results & Discussion. It was found that on 96.7% of tested agricultural parcels (96% plots with mineral soils and 100% plots with organic soils) there was a potentially high risk of P losses from soil by surface runoff. At the same time, it was ascertained that in soils from 62% of agricultural plots, there was a large deficiency of plant available P. Due to the above, as well as due to the lack of connection with other factors affecting the P losses in surface runoff such as type of crop and area inclination, it was considered that the assessment based on the DPS index may be unreliable.

Risk of phosphorus loss in surface runoff from agricultural land in the Baltic Commune of Puck

Background. Risk assessment of Phosphorus (P) losses in surface runoff from agricultural land is the basic measure that should be used as a part of actions taken to counteract the water eutrophication in watercourses and water reservoirs. To assess this risk, a new method has been recently developed based on the determination of degree of P saturation (DPS) which depends on P content in soil determined with the use of distilled water (water-soluble P – WSP). Methods. Based on DPS method, the risk of P losses in surface runoff from agricultural land in Puck Commune (Baltic Sea Coast) was assessed and a critical analysis of assessment results was carried out. The research was conducted on mineral and organic soils from 50 and 11 separate agricultural plots with a total area of 133.82 and 37.23 ha, respectively. In collected soil samples, P content was determined using distilled water (all soil samples), Egner-Riehm method (mineral soils) and extract of 0.5 mol HCl ∙ dm-3 (organic soils). The results of determinations P content in water extract from soils were converted to DPS values, which were classified by appropriate limit intervals. Results & Discussion. It was found that on 96.7% of tested agricultural parcels (96% plots with mineral soils and 100% plots with organic soils) there was a potentially high risk of P losses from soil by surface runoff. At the same time, it was ascertained that in soils from 62% of agricultural plots, there was a large deficiency of plant available P. Due to the above, as well as due to the lack of connection with other factors affecting the P losses in surface runoff such as type of crop and area inclination, it was considered that the assessment based on the DPS index may be unreliable.

Degree of phosphorus saturation threshold for minimizing P losses by runoff in cropland soils of Southern Brazil

The objective of this work was to assess the risk of phosphorus losses by runoff through an index based on the degree of P saturation (DPS), in cropland soils of Southern Brazil. Sixty-five highly representative cropland soils from the region were evaluated. Three labile P forms were measured (Mehlich-1, Mehlich-3, and ammonium oxalate), and four P sorption indexes were tested (phosphorus single sorption point and Fe+Al determined with the three extractors). Water-extractable P (WEP) was used as an index of P susceptibility to losses by surface runoff. The DPS was determined from the ratio between labile P and each sorption index. DPS values obtained from the ratio between Mehlich-1 P and the single P sorption point ranged from 1 to 25%, whereas those from Mehlich-1 P and Fe+Al (ammonium oxalate) ranged from 1 to 55%. All DPS types were highly correlated with WEP. From a practical stand point, the DPS obtained with both P and Fe+Al extracted with Mehlich-1 can be used to estimate the risk of P losses by runoff in soils of Southern Brazil.

Phosphorus Status, Inorganic Phosphorus Forms, and Other Physicochemical Properties of Acid Soils of Farta District, Northwestern Highlands of Ethiopia

Soil acidity and low availability of P limit crop production in the highlands of Ethiopia. The objective of this study was to determine the P status, distribution and forms of inorganic P and relate them to selected chemical properties of eight representative acidic surface soil samples from Farta District. Soil pH (H2O) varied between 4.74 and 5.50. The moderate to high CEC suggests that besides kaolinite, the soils also contain expandable 2 : 1 clay minerals. Though the total P content was high, the available Olsen P content was very low or low in all soils except one. In most soils, the abundance of inorganic P fractions was as follows: P bound by oxalate extractable iron (Feox-P)>reductant soluble Fe-P>occluded Al-Fe-P>P bound by oxalate extractable aluminum (Alox-P)>calcium bound P (Ca-P). Olsen P had a very strong positive correlation (P≤0.01) withAlox-P (r=0.98),Feox-P (r=0.96), and oxalate extractable P (r=0.94). Though Fe bound P reserves were quite abundant and the degree of P saturation ofAlox+Feox(median 3.3%) was moderate, the extremely low P saturation ofAlox(median 0.5%) explains the P deficiency of the soils.

Phosphorus Sorption and Sedimentation in a Multipond System within a Headstream Agricultural Watershed

The movement, transformation, and assimilation of phosphorus (P) in a watershed are often related to the physicochemical characteristics of the sediments of the water storage structures in the watershed. Field and laboratory experiments were conducted to study P sorption by pond sediments in a multipond system in a watershed of 6.9 km2 in southeastern China. Being scattered in different ambient land uses, and receiving soil particles from various sources, the multipond system provides an excellent research example for P sorption as well as the relationship between pond properties and their location in a watershed. It was found that the pond sediments showed largely variable P sorption capacities in this watershed. The P sorption maximum (Smax) ranged from 390.0 to 729.2 mg/kg, and equilibrium P concentration (EPC0) ranged from 0.007 to 0.023 mg/L. The mean degree of P saturation (DPS) of the pond sediments was only 9.5%. Due to the large annual delivery of sediments to the ponds by soil erosion, the pond sediments never reached saturation. The location of the ponds could influence the physicochemical properties of sediments and their sorption characteristics. For Smax, the Hill pond value was significantly higher than that for the Village pond. For EPC0, the result was reverse. The oxalate-extractable Fe (Ox-Fe) and KCl-extractable P (KCl-P) were the key factors that influenced P sorption of the pond sediments. Ox-Fe could explain 84% of the variability in Smax and KCl-P could explain 82% of the variability in EPC0. The acidic and high Fe contents of laterite soil in southeastern China was the most important cause of the high P sorption capacity of the pond sediments.

Influence of biosolids on phosphorus sorption characteristics of a Vertisol in comparison with manures and fertilizer

Regulation of manure application in Manitoba has raised the question of whether or not biosolids application should be regulated in the same way. This study examined the effects of biosolids (BIO) applications on P sorption characteristics of a Vertisol in comparison with dairy cattle (DAIRY) and hog (HOG) manures, and monoammonium phosphate (MAP) fertilizer using the classical sorption isotherm and single point sorption index. Pertinent chemical properties and degree of P saturation (DPS) were also determined. The sorption maximum (Smax) in the control was reduced from 655 mg kg-1, to a range of 536–655 mg kg-1 with BIO, 559–650 mg kg-1 with MAP, 402–568 mg kg-1 with DAIRY, and 350–587 mg kg-1 with HOG depending upon the rate of P added. The lower DPS in the soil amended with BIO suggests a lower risk of P loss with biosolids compared with manures. The higher P sorption capacity of biosolids-amended soils compared with soils amended with manures suggest that Ca added with BIO increased the number of P sorption sites by a similar proportion to the amount of P added. Key words: Biosolids, P sorption isotherm, degree of P saturation, labile P, non-labile P

Phosphorus sorption - desorption by purple soils of China in relation to their properties

The understanding of phosphorus (P) sorption and desorption by soil is important for better managing soil P source and relieving water eutrophication. In this study, sorption–desorption behaviour of P was investigated in purple soils, collected from 3 kinds of purple parent materials with different kinds of land cover, in the upper reaches of Yangtze River, China, using a batch equilibrium technique. Results showed that most of the farmed purple soils had P sorption capacity (PSC) values ranging from 476 to 685 mg P/kg, while higher PSC values were observed in the soils from forestland and paddy field. A single-point P sorption index (PSI) was found to be significantly correlated with PSC (R2 = 0.94, P < 0.001), suggesting its use in estimating PSC across different types of purple soils. The PSC of purple soils was positively and strongly related to the contents of amorphous Fe and Al oxides (r = 0.73, P < 0.001), clay (r = 0.55, P < 0.01), and organic matter (r = 0.50, P < 0.05). Furthermore, the constant relating to binding strength was positively correlated with the content of amorphous Fe and Al oxides (r = 0.66, P < 0.01), but negatively correlated with labile Ca (r = –0.43, P < 0.05) and soil pH (r = –0.53, P < 0.01). Some acidic purple soils with high binding energy featured a power desorption curve, suggesting that P release risk can be accelerated once the P sorbed exceeds a certain threshold. Other soils with low binding energy demonstrated a linear desorption curve. The P desorption percentage was significantly correlated with soil test P (r = 0.78, P < 0.01) and the degree of P saturation (r = 0.82, P < 0.01), but negatively correlated with PSC (r = –0.66, P < 0.01).