Critical evaluation of the performance of rhamnolipids as surfactants for (phyto)extraction of Cd, Cu, Fe, Pb and Zn from copper smelter-affected soil.

Rhamnolipids are biosurfactants produced by bacteria belonging to the Pseudomonas genus. They are discussed to complex heavy metal cations stronger than cations of Fe, Ca, Mg. It is therefore suggested to employ rhamnolipids in phytoextraction where their addition to soil should result in preferential complexation of heavy metals that can be taken up by plants, thus enabling rapid and ecological clean-up of contaminated soil. In order to test this concept, we evaluated the rhamnolipid-mediated phytoextraction of heavy metal from soil collected from the vicinity of a copper smelter. The following aspects were investigated: i) selectivity of rhamnolipids towards Cu, Zn, Pb, Cd and Fe during soil washing; ii) phytoextraction efficiency of each ion with respect to the effective concentration of rhamnolipids; iii) possible phytotoxic effects; iv) effect of micro-sized polystyrene amendment. The experiments evaluated soil washing efficiency, BCR (Community Bureau of Reference) sequential extraction to determine the impact of rhamnolipids on the mobility of metal ions, phytoextraction with maize (Zea mays L.) and phytotoxic effects based on dry matter, chlorophyll fluorescence and content. The obtained results indicated that rhamnolipids lack desired selectivity towards heavy metal ions as Fe was complexed more efficiently by 80 % of the available rhamnolipids compared to priority pollutants like Zn, Cu, Pb, which were complexed by only 20 % of the tested rhamnolipids. With increased concentration of rhamnolipids, the soil washing efficiency increased and shifted in favour of Fe, reaching values of approx. 469 mg for Fe and only 118 mg in total of all tested heavy metals. Phytoextraction also favoured the accumulation of Fe, while Cd was not removed from the soil even at the highest applied rhamnolipid concentrations. Considering the selectivity of rhamnolipids and the costs associated with their production, our results suggest the need to search for other alternative (bio)surfactants with better selectivity and lower price.

Impact of Crop Sequence and Fertilization on Potato Yield in a Long-Term Study.

The research was conducted during the years 2007-2013, on the base of a long-term study established in 1958, at the Experimental Station Brody (52°26' N; 16°18' E), belonging to the Poznan University of Life Sciences. Varieties of potatoes resistant to cyst nematodes were grown in a seven-course crop rotation (potato-spring barley-alfalfa-alfalfa-spring oilseed rape-winter wheat-winter rye) and in continuous monoculture. The presented study from the years 2007-2013 covers the next 8th rotation of the 7-field crop rotation (since 1958). With regard to continuous cultivation, this is the period between the 50th and 56th year of the potato monoculture. The experiment included 11 fertilization variants, of which the following 7 were included in the study: 1-control object without fertilization, 2-manure, 3-manure + NPK, 4-NPKCa, 5-NPK, 6-NP, 7-NK and 8-PK. Every year, mineral and organic fertilization was applied in the following doses per 1 ha: N-90 kg, P-26 kg, K-100 kg, manure-30 t and Ca-0.7 t. Potato cultivation in monoculture resulted in a significant reduction in tuber yield compared to crop rotation and a reduction in the number of tubers per plant and the average weight of one tuber. Manure fertilization, especially in combination with NPK mineral fertilizer, had a more favorable effect on the level of potato yielding and the content of N, P, K and Mg in tubers compared to only mineral fertilization, but decreased the content of dry matter, starch and Ca. The results of long-term experiment indicate that the most effective in potato cultivation is the combined application of both manure and full mineral fertilization (NPK) with the proper sequence of plants (crop rotation).

Hermetia illucens frass improves the physiological state of basil (Ocimum basilicum L.) and its nutritional value under drought.

To counterbalance the growing human population and its increasing demands from the ecosystem, and the impacts on it, new strategies are needed. Use of organic fertilizers boosted the agricultural production, but further increased the ecological burden posed by this indispensable activity. One possible solution to this conundrum is the development and application of more environmentally neutral biofertilizers. The aim of this study was to compare the effectiveness of two doses of Hermetia illucens frass (HI frass) with the commercial cattle manure in the cultivation of basil under drought. Soil without the addition of any organic fertilizer was used as a baseline control substrate for basil cultivation. Plants were grown with cattle manure (10 g/L of the pot volume) or HI frass at two doses (10 and 12.5 g/L). The health and physiological condition of plants were assessed based on the photosynthetic activity and the efficiency of photosystem II (chlorophyll fluorescence). Gas exchange between soil and the atmosphere were also assessed to verify the effect of fertilizer on soil condition. In addition, the mineral profile of basil and its antioxidant activity were assessed, along with the determination of the main polyphenolic compounds content. Biofertilizers improved the fresh mass yield and physiological condition of plants, both under optimal watering and drought, in comparison with the non-fertilized controls. Use of cattle manure in both water regimes resulted in a comparably lower yield and a stronger physiological response to drought. As a result, using HI frass is a superior strategy to boost output and reduce the effects of drought on basil production.