Maize is increasingly used for energy production in agricultural biogas plants. The first biogas production project in agriculture is realized in the Research and Study Farm (RSF) Vecauce of the Latvia University of Agriculture in 2008 and animal manure together with plant biomass are planned to be used as substrate. The paper aimed to evaluate ten maize hybrids possibly suitable for biomass production at three different harvesting times. Field trial was carried out in Research and Study farm Vecauce of the Latvia University of Agriculture in 2008. Ten maize hybrids with different maturity rating according FAO numbers (FAO 180 - 270) were harvested at three different times beginning on 5 September at fourteen days intervals. Results showed that harvest time effect on maize yield was substantial (p is less than 0.05), but hybrid influence on the average yield per all harvest dates was not substantial (p is greater than 0.05). The highest organic dry matter yield was obtained harvesting maize on October 3. The Total N, crude ash, protein, fibre, cellulose, lignin, neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentration decreased, but crude fat concentration increased during plant development. Relevance was not noticed between harvest dates and total carbon and hemi - cellulose content. The C : N ration rose from 34.76 at first, early harvest on 5 September to 37.97 at the last harvest on 3 October.

Winter rape (Brassica napus L.) significance among field crops is unchangeable for last decade in Latvia. Rape plant development in autumn, plant wintering and plant yielding is partly influenced by plant density. The aim of our research, started in autumn 2007 in the Research and Study farm ''Vecauce'', was to investigate the influence of agro-ecological factors (sowing date, sowing rate and fungicide (as growth regulator in autumn) application) on two type (line and F1) winter rape varieties' plant density in autumn, in spring and at harvesting. Plant density in autumn, in spring and during harvesting was determined also by meteorological parameters as air temperature and precipitation. Oilseed rape field germination was observed from 84% sown on 1st of August in 2007 till 67% sown on 1st of August in 2008. A significant impact (p is less than 0.05) of the sowing rate was noted for plant winter hardiness (in points) for variety 'Californium' in both years: 2008 and 2009. Fungicide application effect on plant survival during winter was observed for treatments with greater plants density. A very little average plant number decrease per square m during summer growth period was noted for all treatments in both years - within 1 to 4% in some cases. The tendency was observed that final plant density at harvest if greater sowing rates had been used, was never high on average for 'Californium' from 75 plants per 1 square m (120 germinable seeds per square m) to 60 plants per 1 square m (100 germinable seeds per square m) in 2009. Correlations between plant density at harvest time and seed yield were found.

Biogas can be produced from industrial by-products, household waste and raw materials of agricultural origin. Agricultural resources can be agricultural by-products, for example, manure as well as biomass of energy crops. The objective of the trial was to evaluate the methane outcome from the winter wheat (Triticum aestivum L.) silage depending on the variety and the growth stage during the harvest. The trial was carried out in State Stende Cereals Breeding Institute in the autumn of 2009. The biomass of three varieties of winter wheat, harvested at three stages of maturity - at the beginning of flowering (GS 60-62), early milk ripeness (GS 70-72), and early yellow ripeness (GS 80-82) - was ensiled in laboratory conditions. The silage was analysed 180 days after it had been ensiled. The biogas and methane outcome in laboratory conditions (in Germany) was determined for samples of silage made from winter wheat variety ‘Skalmeje’ at all harvesting times according to VDI 4630 method. The theoretically obtainable methane outcome was calculated for silage samples of all varieties by using the results of chemical composition analysis (crude protein, crude fibre, crude fat, N-free-extracts). The highest methane outcome from one ton of winter wheat silage was acquired by harvesting and ensiling the biomass during the flowering stage. However, evaluating the methane yield from one hectare, the best results were obtained by harvesting and ensiling the biomass at the early milk stage of ripeness and at the stage of early yellow ripeness.

Horseradish (Armoracia rusticana L.) is a perennial plant, with a particularly pungent flavour and significant antioxidant properties. The aim of current research was to determine the total phenol content and antioxidant properties of horseradish depending on genotype and harvest time. For experiments nine genotypes of horseradish roots collected at different times were investigated. Fresh plant material was extracted with ethanol/water solution (80:20 v/v). Total phenols content (TPC) of plant extracts was determined according to the Folin-Ciocalteu spectrophotometric method and results were expressed as gallic acid equivalents (GAE). Antioxidant activity of the extracts was measured on the basis of DPPH˙ free radical scavenging activity and the final results were expressed as inhibition of 2,2-diphenyl-1- picrylhydraziyl (DPPH˙) in percent (I, %). Total phenols content varied among analysed types of horseradish. The highest TPC was detected in horseradish root genotype 280 harvested in September and it also demonstrated the highest DPPH˙ radical scavenging activity, whereas the lowest TPC was detected in horseradish root genotype 26B also harvested in September. TPC and DPPH˙ scavenging antioxidant activity were also significantly influenced by harvest time. Positive correlation was found between antiradical activity and the total phenols content in horseradish roots harvested in September. In further experiments, use of horseradish as natural antioxidants in different food matrixes should be studied.

In plot trials, seeded in a pure stand without a cover crop, tetraploid red clover varieties bred at Jogeva - 'Varte' (early) and 'Ilte' (late), outyielded the diploid standard varieties in crude protein yield at optimal harvest schedule by 30.8% as an average of two production years (the yields 2255 and 1724 kg ha*[-1), respectively) and 14.9% (the yields 2073 and 1804 kg ha*[-1), respectively), by 26.3% as an average of three production years (the yields 2254 and 1785 kg ha*[-1), respectively) and 28.4% (the yields 2173 and 1693 kg ha*[-1), respectively). Considering the crude protein content of dry matter and crude protein yield, a three-cut harvesting regime should be applied in early tetraploid red clover varieties to attain the best result. Then the first cut should be taken at the budding stage, the second at early bloom of regrowth and the third cut prior to the commencement of night frosts. The late tetraploid red clover varieties should be harvested twice-the first cut at the budding stage and the second cut prior to the first night frosts. The larger crude protein yield of tetraploid varieties was caused mainly by their higher dry matter yield; it was affected to a lesser extent by the crude protein content of dry matter. Yet, the tetraploid varieties exceeded in majority of harvest times the diploid varieties in dry matter's crude protein content but the excess was mainly insignificant.

The quality of forage grass mostly depends on the harvesting time. In early vegetation stages, grasses have a high protein and energy content and high dry matter digestibility. The data on the protein content and energy value of different grasses gives a possibility to choose the best conservation method. Changes in the chemical composition of perennial grasses during the vegetation were investigated at the Laboratory of Biochemistry of the LUA Research Centre "Sigra". The dynamics of the content of amino acids was evaluated.