Diedrich Steffens

Organic amendments application has been proposed as an efficient method for remediation of heavy metals-contaminated soils. This study evaluated the performance of the water-insoluble organic material polyvinylpolypyrrolidone on decontaminating water and soil polluted by heavy metals Cu, Cd and Zn via batch trials, soil incubation and pot experiments with oilseed rape. The adsorption process of Cu, Cd and Zn by polyvinylpolypyrrolidone included a rapid step which achieved 92%, 76% and 87% of adsorption capacities within 10 min, followed with a slow step before reaching equilibrium which varied from 4 to 24 h among the three heavy metals. The maximum adsorption capacities were 327, 330 and 186 mg g⁻¹ for Cu, Cd and Zn, respectively. With application doses of polyvinylpolypyrrolidone ranging from 10 to 60 g kg⁻¹, the DTPA-extracted Cu, Cd and Zn showed 59–96%, 27–93% and 13–83% reduction compared to no addition. Moreover, the uptake of Cu, Cd and Zn by oilseed rape were significantly inhibited with polyvinylpolypyrrolidone amendments, and the effects improved with the accrual of polyvinylpolypyrrolidone. Intriguingly, the application of polyvinylpolypyrrolidone showed insignificant influences on nutrients taken up by oilseed rape. Results of the present study indicated that polyvinylpolypyrrolidone is a promising organic amendment for heavy metal (Cu, Cd and Zn) stabilization in polluted water and soil.

In upper layer of arable soils, the percentage of organically bound phosphorus (P) can range from 20% to 80% of total P concentration. Approximately 40% of organic soil P is in the inositol‐P fraction. The objective of our study was to evaluate various soil‐testing methods in measuring phytate soil P as an important source of organic soil P, and to determine the bioavailability of phytate soil P for summer wheat (Triticum aestivum L.), rape (Brassica napus L.), sugar beet (Beta vulgaris L. var. altissima Döll), phacelia (Phacelia tanacetifolia L.), maize (Zea mays L.), white lupin (Lupinus albus L.), Mexican sunflower (Tithonia diversifolia Hemsley Gray), summer rye (Secale cereale L.), buckwheat (Fagopyrum esculentum L.), and pigeon pea (Cajanus cajan L.). Plants were cultivated in a growth chamber on a subsoil as a substrate with very low organic‐matter content and negligible microbial activity in order to restrict the contribution of mycorrhiza and soil microbial activity for organic–soil P mobilization. Application of organic P (100 mg P [kg soil]^–1 as Na‐hexaphytate, C₆H₆O₂₄P₆Na₁₂) did not result in a significant increase of extractable soil P measured with routine soil‐testing methods (CAL, DL, NaHCO₃, EUF, Me‐III) although the applied organic P was available for all tested plant species. The relative P‐uptake efficiency for Na‐hexaphytate compared to Ca(H₂PO₄)₂ was for rape, pigeon pea, and phacelia approximately 100%, for white lupin and maize 80%, for sugar beet, Mexican sunflower, wheat, and buckwheat approximately 60%, and for rye 35%. The results indicate that the bioavailability of organic soil P is not taken into account by routine soil‐testing methods.

The rate of nonexchangeable NH ₄ ⁺ release from soils can have a significant effect on N dynamics and environmental quality. Nonexchangeable NH ₄ ⁺ is that N fraction which is fixed in the interlayers of clay minerals. The objective of this study was to determine the kinetics of nonexchangeable NH ₄ ⁺ release from two topsoils from Germany [Giessen Ap (Aqualf) and Hungen Ap (Alfisol)] and from two subsoils, one from Germany [Hungen C (Alfisol)] and one from Kentucky [Shrouts Bt (Hapludalf)]. Calcium‐saturated, freeze‐dried soils were extracted with H‐resin for 0.25 to 384 h. Sodiumethylmercurythio‐salisylate (Thimerosal) was added to the soil/H‐resin suspension to inhibit microbiological ammonification. The kinetics of nonexchangeable NH ₄ ⁺ release from the soils were biphasic and were best described by Elovich and heterogeneous diffusion models. The release of nonexchangeable NH ₄ ⁺ as a percentage of total nonexchangeable NH ₄ ⁺ in the soils ranged from 4 to 25% and was lower in subsoils than in topsoils. This was ascribed to the higher levels of indigenous nonexchangeable NH ₄ ⁺ in the subsoils, which is more tightly held than recently fixed nonexchangeable NH ₄ ⁺ .