Erasmus Otabbong

Phosphorus sorption in relation to soil properties in some cultivated Swedish soils

Phosphorus (P) sorption properties are poorly documented for Swedish soils. In this study, P sorption capacity and its relation to soil properties were determined and evaluated in 10 representative Swedish topsoils depleted in available P. P sorption indices were estimated from sorption isotherms using Langmuir and Freundlich equations (Xm and aF, respectively) and P buffering capacity (PBC). Xm ranged from 6.0 to 12.2 mmol kg−1. All indices obtained from sorption isotherms were significantly correlated with each other (r=0.96*** to r=0.99***). Two single-point sorption indices (PSI1 and PSI2) were also determined, with additions of 19.4 and 50 mmol P kg−1 soil, respectively. Both PSI indices were well correlated with Xm (r≥0.98***), with PSI1 giving the highest correlation. As isotherms for determining P sorption capacities involve laborious analytical operations, PSI1 would be preferable for routine analyses. Xm was significantly correlated with Fe extracted by sodium pyrophosphate and ammonium oxalate, to Al extracted by ammonium oxalate and dithionite-citrate-bicarbonate and to organic c. Xm was also significantly correlated with the sum of Fe and Al extracted by ammonium oxalate. The best prediction of Xm through multiple regression was obtained when Fe extracted in ammonium oxalate and Al extracted in dithionite-citrate-bicarbonate were used. Based on the results obtained, both PSI1 and oxalate-extractable Fe plus Al can be used for predicting P sorption capacity in Swedish soils.

The Ultuna long-term soil organic matter experiment

In 1991, soil samples were taken from the long-term (40 years old) field trial at Ultuna in order to investigate soil P status and the distribution of its various forms. Among the treatments investigated, two were inorganic PK additions only – one to continuous fallow (PK-fallow) and the other to cropped fields (PK). There were also treatments amended with PK in combination with applications of straw, green manure composed of grass (GM), farmyard manure (FYM) or sewage sludge (SS). A total of 720, 720, 883, 1154, 1941 and 6617 kg P h-1 had been supplied in the PK-fallow, PK, Straw, GM, FYM and SS treatments, respectively up to 1991. The soil P distribution was determined by step-wise fractionation using anion exchange resin (resin-P), sodium bicarbonate (bicarb-P), sodium hydroxide (hyd-P), and HCl (HCl-P). Finally, the soil was digested to obtain residual P (resid-P). The amendments resulted in a significant (p=0.05) enrichment of total P in soils relative to the initial value. A breakdown of the bicarb-P and hyd-P into inorganic P (Pi) and organic P (Po) was manifested as considerable transformations within these P compartments compared with the initial values. Thus, total Pi (Σresin-P, bicarb-Pi, hyd-Pi, HC1-P, resid-P)/total Po (Σbicarb-Po, hyd-Po) ratios markedly decreased in all treatments relative to control. The two P compartments were significantly and negatively (p =0.05) correlated. On average, the total Po increase was about 380 mg kg-1 (range 270–715). The results suggested that an equilibrium between Pi immobilization and Po mineralization was difficult to attain under any of the experimental management regimes used, which exclude inorganic N application. The balance sheet calculations revealed P deficits ranging from about 10 to 60 kg ha-1, indicating that some P had migrated to the subsoil.

The variability of polychlorinated biphenyls levels in urban soils from five European cities

The concentration of PCBs in topsoils from five European cities was assessed and the highest levels were found in Glasgow (Scotland), followed by Torino (Italy), Aveiro (Portugal), Ljubljana (Slovenia) and Uppsala (Sweden). All cities showed the presence of local sources in addition to diffuse contamination from global atmospheric transport. The association of general soil parameters with PCBs in Glasgow and with heavier congeners in Torino and Ljubljana indicates that retention of these compounds is occurring. The profiles obtained resemble Aroclor 1254 and 1260, which are important local sources. Nevertheless, differences in PCB profiles were observed among cities, due to the combined effects of the age of the contamination (which determines the time available for volatilisation and degradation), different sources of PCBs and differences in climate (which influence volatilisation and deposition).

Comparison of four low-technology composting methods for market crop wastes.

Four methods for composting, pit-cover (PC), pit-open (PO), above ground-open (AO) and above ground-covered (AC), were compared for their effect in accelerating compost maturity using market crop waste (MCW). The composting process was monitored through determining changes in temperature and pH, with compost maturity indices measured in terms of variations in water-soluble carbon (WSC), ammonium-N (NH(4)(+)-N) and nitrate-N (NO(3)(-)-N), and C/N, NH(4)(+)-N/NO(3)(-)-N, WSC/organic N and WSC/total N (TN). Total organic carbon (TOC), nitrogen (TN), potassium (TK) and phosphorus (TP) were also determined. Temperature rapidly increased from mesophilic to thermophilic and gradually reduced through maturation phases. A similar pattern was recorded for pH, which reached a slightly alkaline level at maturity. Composting significantly (p<0.05) decreased the concentrations of TOC, TN, TP, TK, NH(4)(+)-N and WSC and increased that of NO(3)(-)-N. All four low-technology composting methods used in this study produced mature composts within 63 days. Suitable maturity indicators for MCW compost were C/N ratio<12, WSC<1%, NH(4)(+)-N<400 mg kg(-1), NH(4)(+)-N/NO(3)(-)-N<0.2, WSC/TN, WSC/organic-N<1. On the basis of these indicators, the AC method generally enhanced maturity faster than the AO, PC and PO methods. Pit methods require less investment and are recommended for the smallhold farmers.

Dynamic transformation of sewage sludge and farmyard manure components. 1. Content of humic substances and mineralisation of organic carbon and nitrogen in incubated soils

Abstract An incubation experiment was conducted with farmyard manure (FYM) and two municipal sewage sludges (SS): one from Russia (SSR) and one from Sweden (SSS) using a sandy loam soil at 25°C for 6 weeks. The objectives were to investigate mineralisation of organic C and N and transformations of humic substances (HS). Cumulative C mineralisation was about 0.8–1% of total C and cumulative N mineralised was about 3–7% of the pre-incubation total N contents in the treatments. The organic materials contained 1.2–1.5% humic acids (HA) and 0.8–1.4% fulvic acids (FA). Incubating the soils with manures did not markedly influence soil humus composition, indicating that SS-borne organic C was not converted into HS during the short-term incubation. SSR was more resistant to decomposition than SSS, although both SS were less susceptible than FYM to changes in all parameters.

Impact of long-term inorganic phosphorus fertilization on accumulation, sorption and release of phosphorus in five Swedish soil profiles

The impact of long-term fertilization with inorganic P was studied in soil profiles (0–100 cm) from five sites in Sweden. Accumulation of P was studied by comparing P extracted with ammonium lactate/acetic acid (P-AL) and NaHCO3 (Olsen-P) in non-fertilized and fertilized soil profiles. The fertilized soils had received 42–49 kg P ha–1y–1 for more than 30 years. P-AL and Olsen-P were significantly higher in the fertilized than in the non-fertilized profiles down to 40 cm depth. The P sorption index (PSI2) based on a single-point P addition of 50 mmol P kg–1 soil was used to estimate P sorption capacity in the soils. The variation in PSI2 with depth was not consistent between the five soil profiles. PSI2 did not vary with depth in one soil, while it decreased in one and increased in the other three, and it was weakly but significantly correlated with the sum of Fe and Al extracted with ammonium oxalate (Feox +Alox) (r = 0.65**) and with clay content (r = 0.69***). To estimate P release in the soils, P was extracted with CaCl2 (CaCl2-P) and water (Pw). CaCl2-P and Pw were significantly higher in the fertilized treatment than in the non-fertilized treatment in the top 20 cm. Below 30 cm depth, CaCl2-P was very low in all soils, while Pw was relatively high in two soils and low in the other three soils. To estimate the degree of P saturation, the ratio of P-AL/PSI2 and Olsen-P/PSI2 was calculated. P-AL/PSI2 was significantly higher in the fertilized treatment in the 0–20 cm layer, while Olsen-P/PSI2 was significantly higher in the fertilized treatment in the 0–40 cm layer. P-AL/PSI2 was correlated with CaCl2-P and Pw when all soils and horizons were included (r≥0.78***), but the correlation increased markedly when only 0–40 cm was included (r≥0.94***). Olsen-P/PSI2 was well correlated with CaCl2-P and Pw (r≥0.94***) for all soils and depths. Thus the two indices, P-AL/PSI2 and Olsen-P/PSI2, were comparable in their ability to predict P release in the top 40 cm, whereas Olsen-P/PSI2 was better when all depths were included. The overall conclusion was that P fertilization had an impact on P properties down to 40 cm depth, while the effects were small below this depth.

Dynamic transformation of sewage sludge and farmyard manure components. 2. Copper, lead and cadmium forms in incubated soils

Abstract An incubation experiment was conducted with farmyard manure (FYM), a Russian and a Swedish municipal sewage sludge (SSR and SSS, respectively) suing a sandy loam soil (pHwater 6.8) at 25°C for 6 weeks to study the Cu, Cd and Pb contents of soils. The metals were sequentially extracted with 1 M NH4NO3 (available forms) and 0.1 M Na4P2O7 (organically bound forms). There was a shift from the pyrophosphate-soluble pool to the NH4NO3-soluble pool, regardless of treatment. Thus, incubating soils increased available metal forms and decreased organically bound forms. SSS and FYM did not cause marked changes in the two metal fractions, whereas SSR application significantly (P = 0.05) affected them. The two pools were positively correlated (r = 0.993, P = 0.001), indicating that the pools did not change at the expense of each other. The increase in metal solubility in the 1 M NH4NO3 solution is important from both plant nutrition and environmental viewpoints.

Sewage sludge: Soil conditioner and nutrient source II. Availability of Cu, Zn, Pb and Cd to barley in a pot experiment

The effects of sewage sludge (SS) application on NH4NO3‐extractable Cu, Zn, Pb and Cd as well as metal uptake by barley (Hordeum vulgare L.) were investigated using a sandy loam soil (pH in water = 6.7). Treatments comprised three replicates each and were as follows: untreated soil (control), two that received a Russian (SSR) and two that received a Swedish SS (SSS). The SS application based on N applied at rates of 100 (SSR1 and SSS1) and 300 (SSR3 and SSS3) mg N kg−1 dry soil, respectively. Soil metal levels determined immediately after mixing the soils with SS were markedly increased. However, cropping the soils strongly decreased their Cu, Zn and Pb levels, while leaving substantial amounts of residual Cd in the soils, regardless of the treatment. Metal uptake in shoots and roots was significantly (P = 0.05) enhanced by SS applications. Rates of metal uptake in roots were significantly (P = 0.05, n = 64) correlated with the pre‐cropping soil metal contents. The bulk of the metals absorbed by the plant...

Compatibility of the ammonium lactate (AL) and sodium bicarbonate (Olsen) methods for determining available phosphorus in Swedish soils

Abstract Plant-available P was first extracted in soils 114 years ago and a number of different analytical methods have since been developed, but for good reasons none of these methods has been adopted as a standard for all soils. With increasing cooperation within research, there is a need to harmonise the interpretation of analytical data for fertiliser recommendations, research, and environmental control. This paper evaluates the compatibility of the Swedish standard ammonium lactate (PAL) method and the widely used Olsons sodium bicarbonate (POls) method in 82 topsoil samples taken from Swedish long-term soil fertility field trials. The PAL-values were usually larger than POls, with a mean PAL/POls quotient of 2.30±1.04 (0.67–6.58). The PAL and POls means and ranges were 126±89 (5–360) and 55.1±33 (3.1–122.8) mg P kg−1 dry soil, respectively. Stepwise multiple linear regression analysis was used to evaluate the relationship between PAL and POls and how this relationship was affected by clay content, pH, and soil organic carbon content (SOC). After statistical transformation, it emerged that the square root of clay content (17.4%±13.82, range 1–54.4) and pH (6.45±0.54, range 5.5–7.7) significantly affected the relationship at partial R 2-values of 2 and 12%, respectively, while ln(SOC) (2.54%±1.21, range 1–6.03) did not, apparently due the narrow range. The regressions of predicted vs. measured values explained 95 and 94% of the variation in PAL and POls, respectively. The mean deviation of predicted compared with measured values was 21.3 and 8.3 mg P kg−1 dry soil for PAL and POls, respectively, corresponding to 20 or 19% of the measured values. We conclude that a data set consisting of PAL-values can be converted into POls-values and vice versa with reasonably high accuracy when accounting for clay content and pH.

Chemistry of Cr in Some Swedish Soils: 2. Fate and Impact of Added Cr on pH and Status of Soluble Mn in Four Soils

Abstract Retention and recovery of Cr(III) and Cr(VI) added to four mineral soils and their impact on pH and status of soluble Mn were investigated. Undried soil portions (≤4 mm) equal to 50 g dry matter were packed in glass columns and eluted with CrCl3 solution containing 6250 μg Cr(III) or K2Cr2O7 solution containing 1000 μg Cr(VI), displacing the retained Cr(III) and Cr(VI) with NH4Cl and KH2PO4 solutions respectively. Mn was measured in all effluents. Total Cr, Cr(III) and Mn were determined on an atomic absorption spectrometer with a graphite furnace and D2-background compensation and Cr(VI) on a photometer. Cr(III) strongly acidified and Cr(VI) weakly acidified the soils. The soils possessed a high affinity for retention of Cr(III) and a low one for retention of Cr(VI). Recovery of the retained Cr was very low and tended to be greater the lower the soil pH. Oxidation of Cr(III) was not detected. Reduction of Cr(VI) was substantial in the soils. It increased linearly with decreasing pH (R 2=0.71) an...