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Sirvi Autor "Jankevica, L." järgi

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  • Pisipilt
    Kirje
    Effects of fertilization on Picea abies stands situated on drained peat soils
    (2018) Cekstere, G.; Osvalde, A.; Nollendorfs, V.; Karlsons, A.; Pormale, J.; Zalitis, P.; Snepsts, G.; Minova, S.; Jankevica, L.; Laivins, M.
    Norway spruce used for afforestation of drained peat soils frequently has low productivity and decay in a long - term, which could be related to soil chemical composition and nutrient status. The research aim was to elucidate the effect of PSM on new Norway spruce plantings (1st experiment) and 20 - year - old spruce stands (2nd experiment) on drained peat soils by evaluating: (1) nutrient accumulation in soil - plant system, (2) soil microbiological activity, (3) health status of spruce individuals, (4) growth int ensity and productivity of spruce, (5) changes in composition of vascular plant and moss species. The study was conducted at two forest ( Myrtillosa turf.mel .) sites in Latvia, each consisting of two plots: control and treated with PMS (100 g m - 2 in Septemb er 2007, 50 g m - 2 in April 2008). During 2008 – 2016, regular analysis of soil, spruce needles, soil microbiology, assessment of tree crown vitality, stand productivity, inventory of vascular plant and moss species were done. The results showed that the fert ilization with PMS resulted in a significantly improved K, Ca, Zn, and N status of trees, crown vitality and up to three times increased tree growth parameters at both experiments during the study period. The average count of bacteria and fungi in soil of fertilized plots, accompanied by a remarkable variability in the study years, was significantly higher only for the 1 st experiment. Fungi : bacteria ratio for the fertilized and control plots differed significantly only for the 1 st experiment. Significant i ncrease of cover with nitrophilic plant ( Urtica dioica, Antriscus sylvestris, Rubus idaeus ) and moss ( Plagiomnium cuspidatum , P. ellipticum ) species at both fertilized sites were stated.
  • Pisipilt
    Kirje
    Environmental risk assessment studies on new plant protection products which have been elaborated from coniferous tree bark
    (2018) Jankevica, L.; Polis, O.; Korica, A.; Samsone, I.; Laugale, V.; Daugavietis, M.
    Nowadays there are still various chemical pesticides being applied in the course of ensuring plant protection. Since 2010, we have been working on the development of new, environmentally-friendly plant protection products which will provide an effective tool against pathogenic fungi and bacteria which cause disease in crop plants. The specific aim of this study was to evaluate a risk assessment for new plant protection products that have been elaborated on the basis of coniferous tree bark. Various products were tested which are extracted during the processing of wood bark from pine (Pinus sylvestris L.) and spruce (Picea abies (L.) Karst.). Ethanol extracts were formulated and applied during these experiments. Two formulations, which showed anti-fungal activity in vitro and in field trials on fruit crops (involving strawberries and raspberries) were selected for the risk assessment studies. The impact was studied of formulation treatment on crop plants and soil biological activity, and the accumulation of residues of active substances in crop plants and soil. The application of new formulations did not show any negative effect on the chlorophyll content and the chlorophyll fluorescence of plant leaves. The results showed that pine and spruce bark extract formulations contain active compounds (coumaric acid, quercetin, epicatechin, and ferulic acid) within the range of 5.1–5.9 mg kg-1 and 11.1– 443.9 mg kg-1 respectively. The amount of active substances which were determined in most cases was higher in the spruce bark extract formulation when compared to the pine bark extract formulation. Our results confirmed the presence of active compounds – epicatechin, quercetin, and coumaric acid – in strawberry fruits which remained untreated and in those that were treated with spruce ethanol extract formulation. Untreated raspberry fruits contained all four active substances within the range of 81–5,300 µg kg-1. We observed a significant increase of coumaric acid and quercetin in raspberries after their having been treated with spruce bark extract formulation in a 2% concentration, P < 0.05, and did not find any negative impact for spruce bark extract formulations when used on soil microbial biomass.