The pollution of the river water with organic matter deteriorates the chemical, biological and microbiological quality of the water and has a negative effect upon the biological variety of the water environment. The paper analyses the study period (1996-2000) seasonal change of organic matter in the upper reaches of the River Nevezis (study sites upstream and downstream Panevezys). The highest amount of organic matter (according to chemical oxygen demand and biochemical oxygen demand) got into the river under the influence of concentrated pollution, the fewer amount - under the influence of agricultural pollution and in the course of natural processes. The concentration of organic substances in the river water had a seasonal character: rivers with a better ecological state (the Juosta) were more polluted with organic matter in spring, when water temperature was below 10 deg C, but rivers with a worse ecological state (the Nevezis upstream and downstream Panevezys) – in summer (water temperature was higher than 10 deg C). This may be related with fresh pollution; in the former case organic matter might have come from the environment together with the runoff, in the latter case - due to decomposition of water vegetation and fauna residues in the river itself. In all rivers water temperature was by 0.1-4.4 deg C higher in 1996-2000 in comparison to that in 1986-1989, a significant temperature increases were observed in winter and autumn. The water temperature arose mostly below the town.

Recently, a renewed interest in non-harmful, environmentally friendly adhesives has ensued among the industry professionals, both environmental and healthcare scientists. In this study, organic rich lake sediments (sapropel) from two lakes located in Latgale Region of Latvia were used as a glue to investigate the potential use of such adhesive for manufacture of composite materials from wood. Sapropel is a valuable resource with multiple areas of application, e.g., agriculture, balneology. Available amount of sapropel in Latvia is estimated at up to 2 billion m**3. Prior the tests, characterization of sapropel samples was done. Properties of the obtained composite material samples from wood and sapropel, as well as the mechanical properties were investigated. Tests involved the assessment of static bending strength and shear strength tests, durability according to their operating performance (D1-D4), as well as dried natural peat tensile strength perpendicular to the grain direction were determined and compared to the literature data; and the opportunities to use new composite materials in accordance with to the standards were discussed. The results of the study revealed an insight into possibilities to develop products of higher added value from sapropel as adhesive in combination with various resources. Results indicated that the samples made from Lake Pilvelis sapropel gain to better results of bending strength determination (parallel bending - 88.7 MPa). The aim of this study was to explore options to produce veneer using two kinds of sapropel as a glue and to determine the optimal properties according to the standards, as well as to characterize properties of the obtained composite material.

Maize yield and quality are affected by many factors, including production practices, diseases, pests, and differences in the climate. Usually it is not possible to do much to change the effect of temperature, but it is important to grow better adapted or characterized with right maturity rating hybrids. The paper is aimed to determine the impact of accumulated growing degree days (GDD) on maize development, organic dry matter yield, ODM and chemical composition of maize hybrids. A field trial was carried out in the Research and Study farm ’’Vecauce’’ of the Latvia University of Agriculture (LLU) from 2008 till 2010. Ten (in 2008), eleven (in 2009) and fifteen (2010) maize hybrids with different maturity ratings according to FAO numbers (FAO 180-340) were harvested at three different times beginning on 5 September at fourteen-day intervals. GDD were calculated when maize reached a certain growth stage (full emergence, first tassels, full tassels, first ears, full ears, specific harvest date) to characterize conditions for maize growing in a specific year. Composition of fresh maize was analyzed for all hybrids using standard methods. Results were statistically processed using methods of correlation and regression analysis. Our results presented evidence that ODM yield in 2008 and 2009 on last harvest dates was lower than that on the first harvest date in 2010. Organic dry matter yield was higher in years when more GDD were accumulated. Results also showed that GDD negatively correlated with the total N, protein, fibre cellulose, hemi-cellulose, NDF, and ADF concentration.

Agricultural farms in modern production system are specialized; therefore, animal-origin organic fertilizers are not available for many of them. Researches on the use of organic products in agriculture to restrict the use of pesticides and mineral fertilizers have been performed for a long time. Nowadays different organic preparations that are acquired as a result of complex processes are produced, ensuring ready-to-use biologically active substances in them and also activating their properties. One of the purposes of the research was to evaluate the impact of extracts from organic products on the potato (Solanum tuberosum) yield and tuber quality in the conventional cultivation system. A field experiment using cultivars ‘Borodyansky Rozovij’ (early maturity) and ‘Lenora’ (mid-early maturity) was arranged in the State Stende Cereals Breeding Institute in 2011 and 2012. Peat elixir and vermicompost extract obtained at different temperatures: + 45 °C and + 95 °C, as well as a mixture of these extracts were used for treatment of tubers and plants. The research included 24 treatments in total, including control (without treatment) and a standard potato cultivation technology. Tubers were treated immediately before planting, but plants were treated three times during the vegetation period. Average two-year research results showed that the use of organic product extracts significantly (p is less than 0.05) affected the tuber yield in different treatments for both cultivars ‘Borodyansky Rozovij’ and ‘Lenora’. The content of nitrates in tubers, using extracts, did not exceed the allowable level (160 mg kgE-1) in any of treatments.

The purpose of the study was to compare forest and postagrogenic soils by parameters such as carbon content in organic matter and total nitrogen to predict the fertility state of lands that are at the stage of restoration of woody vegetation. Areas with similar soil formation conditions were selected on the postagrogenic and forested lands having mature forest stands related with such types of forest: Myrtillosum forest, Oxalidosum and Herbosa-Composita forest, and also areas under the soil complexes of postagrogenic fallow lands. A number of physico-chemical indicators for the soil were assessed according to the methods generally accepted in soil science: the particle size distribution, the bulk density and the thickness of the pedogenic horizons were determined. An analysis of the carbon stocks in organic matter (Corg) and nitrogen (Ntotal) in the genetic horizons of the soils of myrtillosum, Oxalidosum and Herbosa-Composita forest types shows an increase in the content of organic matter and total nitrogen from Myrtillosum to Herbosa-Composita forest type. A comparative analysis of the physical and agrochemical state of postagrogenic and forest soils showed that, despite the previous anthropogenic impact, the agroland horizon retains a high content of organic matter and total nitrogen. The properties of postagrogenic soils in the studied areas are not deteriorated, and the transformation towards the natural forest soils of the region is not observed, despite the long period of fallowing.

The article provides the research data on the variation of organic matter in the Jaugila Stream, which flows through drained fields fertilized with organic fertilizers. The aim of the research was to determine the effect of manure application in drainage basin to the changes of organic matter concentration in the Jaugila Stream. Water samples for chemical analysis were taken once a month from the drainage water and the river. The samples from the river were taken upstream and downstream manure fertilized fields and the drainage water – from the outlets of the drainage system, which drains the fertilized area. Water analysis was performed by the Analytical Laboratory of Chemical Analysis of the ASU Water Research Institute. BOD7 was determined by titrimetric method. The research has shown that a greater impact on the increase of BOD7 concentrations in the Jaugila Stream was due to the stream water, saturated with the organic matter, flowing from the upstream areas, rather than the drainage water flowing into this stream from manure fertilized area. The assessment of BOD7 concentrations according to the water quality requirements for surface waters determined that in most cases the water of the Jaugila Stream, both in above and below fertilized areas, was in a very good or good ecological status. The impact of manure fertilized areas on the organic matter concentration in the stream was determined to be minimal, as the statistical analysis of the data has shown that the difference between BOD7 concentrations above and below fertilized areas is negligible.

Highly polluted wastewater is formed on private farms. The wastewater contains Ntotal and Ptotal concentrations up to 150 mg lE-1 and 30 mg lE-1 respectively, which is 2-3 times higher than that contained in domestic wastewater. During the biological treatment of wastewater the removal of organic pollutants (BOD5- biochemical oxygen demand, and SS - suspended solids) is about 96% and the treatment efficiency satisfies the environment protection standards. However, the removal of biogenic pollutants is only 55%, thus the residual pollution with biogenic substances exceeds the maximum allowable rate according to Ntotal and Ptotal for wastewater released into the environment. Currently, different natural and artificial powdery mineral materials (zeolite, filtralite, etc.) containing metals and carbon compounds are transported into Lithuania. Such materials could be used as Ntotal and Ptotal adsorbing filters. In respect of the filter load with pollutants, biologically pre-treated wastewater treatment efficiency of Ntotal and Ptotal was determined to be from 50 to 91% and from 49 to 90% respectively. Having filtrated to the wastewater through a filter containing 50% of zeolite and 50% of filtralite, Ntotal and Ptotal removal efficiency was fluctuating from 28 to 60% and from 23 to 70% respectively. Having made the investigations with different loads of minerals, it was determined that N removal is more efficient in the zeolite mineral filter, while P removal is more efficient in the filtralite filter. In order to reach the best results of biogenic pollution removal, both mineral mixtures should be used for the load of the filter.

The objective of the present studies has been to estimate peculiarities of nitrogen removal in constructed wetlands of different construction. In limited companies (LTD) 'Pastoge' and 'Nikola', constructed wetlands of vertical flow (VFCW) are arranged, while limited company (LTD) 'Agaras' has two-stage constructed wetlands of horizontal flow (HFCW). In all the objects the supplied wastewater is after primary treatment. Having compared the efficiency of ammonium and nitrite nitrogen removal in two types of constructed wetlands (VFCW and HFCW) it was determined that larger amounts of total nitrogen are removed in HFCW (38.1%) rather than in VFCW (24.4%). However, in VFCW smaller amounts of ammonium and nitrite nitrogen are discharged with wastewater. No significant effect of the fluctuations of ambient temperature on the removal of ammonium and nitrite nitrogen was observed in HFCW (difference in average values of cold and warm periods was 3-8%). A rather reliable relation (R2 = 0:738) was determined between ammonium nitrogen concentrations in wastewater outflow and HFCW load according to total nitrogen, however, ammonium nitrogen amounts in treated wastewater (when filter load according to total nitrogen is 0.3 to 4.6 g mE-2 dE-1) exceeded the maximum allowable concentration (MAC) and were fluctuating from 6 to 32 mg lE-1.