Browsing by Subject "Mobilisierung"

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Einfluss moderner Pflanzenschutzmittel auf die Mobilität von POP-belasteten Agrarflächen am Beispiel von DDT : ein Feldversuch
(2023) Neitsch, Julia Simone; Vetter, Walter
Due to their recalcitrance, the chloropesticide DDT and its structurally related compounds (DDX) are difficult to degrade. Consequently, farmers are still frequently confronted with DDX contamination in their fields that was left over from the 1960s. This problem is particularly prevalent in contaminated soils that are intended to cultivate plants of the Cucurbitaceae family. These plants release so-called root exudates, which function as natural surfactants that mobilize the DDX present in the soils. Furthermore, surfactants are a common constituent of modern plant protection product (PPP) formulations, which can likewise cause DDX mobilization. The higher mobility of DDX caused by these surfactants can result in the absorption and accumulation of chlorinated pesticides in plants. The side effects of such surfactant-containing PPP formulations have historically been overlooked in the context of standard spraying protocols. The potential mobilization of DDX in soils and its accumulation in Cucurbita pepo due to the surfactants present in standard PPPs formulations was investigated using two field trials. One field was treated with a conventional PPP, while the other was treated with a biological PPP; a control field was left untreated, within which pumpkins were cultivated. Soil samples were taken before and after the application of PPP. The DDX content was subsequently determined in extracts from the soil phase samples and soil water fractions. The background DDX contamination of the soils was comparable in all three test fields. The comparative evaluation showed that the field treated with the biological PPP formulation exhibited a considerable increase in DDX mobility compared to the untreated and conventionally cultivated areas (Paper 1). An analysis of its respective water fraction revealed that it was more contaminated with DDX than the control treatments. This increase suggests a higher bioavailability that can be traced back to the presence of surfactants and oils in the PPP formulations (Paper 1). This higher bioavailability may have been accompanied by an increase in the DDX uptake of the cultivated plants. Furthermore, it was found that treatment with specific formulations of emulsifiable concentrates (EC) promoted DDX mobilization. This mobilizing effect was most likely due to the differing composition of the surfactant and proportions of oils in the PPPs. The second field test focused on differential DDX accumulation in Cucurbita pepo cv. Howden by different PPPs. Fields were treated with PPP in accordance with the official spraying plans and regulations set out by the Federal Ministry of Food and Agriculture (BMEL). Samples from the pumpkin plants roots, shoots, as well as the pumpkins themselves were taken during the cultivation period. The DDX content in the roots from the control fields and the fields with conventional PPP treatments remained virtually unchanged; however, the DDX content increased in the biologically treated area (Paper 2). The pumpkin shoots did not exhibit any increases in DDX concentration during the growing phase regardless of the field sampled. However, an increased DDX content was detected in the shoots of the plants in all test fields shortly before harvesting. At the end of the growing phase, fruits from the biologically treated area showed a higher DDX content than those from the control and conventionally treated areas. In addition, the most critical DDT metabolite, DDE, was found to have been transported to distant parts of the plant, while DDD was detectable in the roots and shoots but not in the fruits of the pumpkins (Paper 2). An assessment of the results of both experiments confirmed a direct correlation between DDX mobilization in the soil and plant uptake. In addition, the bioaccumulation factors of the biologically treated areas were markedly higher than those seen in the conventionally treated and control areas. The results of the field trials show that the mobilization of DDT, as well as the likely mobilization of other lipophilic contaminants, can become problematic for farmers using surfactant-containing EC formulations. However, this observation also provides opportunities for improved phytoremediation by applying EC formulations with high mobilization potentials. The field trials indicate that the mobilizing effects of DDT prompted by EC mixtures depend on the surfactant content in the PPP formulations as well as environmental conditions such as soil conditions, soil water content, and precipitation. Unravelling the optimal range of surfactant-rich formulations and environmental conditions could lead to a promising strategy for soil phytoremediation.
Phosphorus bioavailability of fertilizers recycled from sewage sludge and their suitability for organic crop production
(2020) Wollmann, Iris; Möller, Kurt
Phosphorus (P) nutrition of plants is a key production factor in agriculture. In an approach to recycle P from urban areas back to agriculture, technologies have been developed to produce mineral P fertilizers out of municipal sewage sludge. In this study, different P fertilizers recycled from sewage sludge have been investigated in pot and field experiments for their bioavailability to maize and several plant species of a crop rotation. It was also investigated, if bioavailability of recycled P fertilizers can be enhanced either by a soil inoculation with different bacteria strains that are efficient in P solubilizing, or by a cultivation of red clover in the crop rotation. As there is a lack of bioavailable P fertilizers in organic cropping systems, P fertilizers recycled from sewage sludge were evaluated for their suitability to be used in organic crop production. It has been shown that most of the investigated fertilizers recycled from sewage sludge have a higher P bioavailability than Phosphate Rock (PR). Fertilizer efficacy seems very dependent from specific production conditions which are decisive for the final product. Among the tested fertilizers, struvite (MgNH4PO4 . 6 H2O) was most efficient in increasing plant P offtake of maize (+ 27.5% in the field, and more than sixfold in a pot experiment, compared to the unfertilized control). Struvite and calcined sewage sludge ash (SSA) are efficient fertilizers at both acidic and neutral soil pH. Other fertilizers (e.g. untreated incineration ashes) have low solubility at soil with pH > 6, and thus, might be used on acidic soil only, or as raw material for fertilizer production. In the field experiment, the overall response to P fertilizer input was low, which probably can be attributed to a sufficient inherent P supply on the used site. An immobilization of fertilizer P over time could be shown in all experiments. Thus, recycled P fertilizers should be applied to responsive crops in the rotation. An improved P supply of maize could be shown when grown after red clover in the crop rotation. This might be attributed to a combination of different factors, such as a solubilization of sparingly soluble P forms in recycled fertilizers, following a drop in soil pH due to biological N2 fixation of clover. A recycling of P to maize via decomposed clover roots might in addition have contributed to an increased P supply of the subsequent maize. Despite this promising effect, P mobilization by clover cultivation was not sufficient to cover the entire P demand of maize. Thus, additional fertilizer P inputs to maize might still be necessary to ensure optimal plant growth on P deficient soils. With one exception, an application of different bacteria strains generally did not affect P supply of the plants. Applied bacteria seem very dependent on the environmental conditions. It is conceivable, that especially in organic systems, a soil application with external bacteria does not enhance the beneficial effects of a high microbial abundance and activity which often is already present in organic cropping systems. From an agronomic point of view, P fertilizers recycled from sewage sludge are better alternatives for organic crop production than PR. A recycling of nutrients generally fits well with basic organic principles. By introducing those fertilizers, the organic system could make a decisive contribution to the ongoing effort of closing the P cycle, and, once more, develop towards a farming system of the future.