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.

The objective of the research was to study the removal of nitrogen, phosphorus and potassium with summer-pruned branches of apple-trees grown on dwarfing rootstocks under the influence of applied moisture regulation methods. The investigation was done at the Latvia State Institute of Fruit-Growing in Dobele, on the basis of an existing field experiment planted in 1997 with cultivar 'Melba' (rootstock B9) at 1.5 - 4 m trees spacing distances. Three different treatments of soil moisture management were compared: control (without moisture regime regulation), sawdust mulch and fertigation. Inter-row strips were covered by grass vegetation (Lolium perenne L. and Poa pratensis L., in proportion 1:3). Pruning of apple-trees was done in mid-July. The results of the research showed that the applied soil water regulation treatments (mulch and fertigation) had significant influence (p is less than 0.05) on the apple-tree biomass (leaves, one-year and older wood) removed by summer pruning, as well as on the content of dry matter in biomass. The contents of N and K were influenced both by the treatment and age of tree vegetative parts, but the content of P did not differ significantly among treatments or tree parts (p is greater than 0.05). Removal of N with summer-pruned leaves and branches was 30 kg haE-1 N in the mulch treatment and 16 - 17 kg haE-1 in control and fertigation treatments (p is less than 0.05). Removal of K in the control treatment was 19 kg haE-1, in the mulch treatment 40 kg haE-1, but in the fertigation treatment 27 kg haE-1 (p is less than 0.05). Removal of P varied from 5.04 to 9.84 kg haE-1, no significant differences were found among treatments (p is greater than 0.05).

Tryptophan (Trp) is an essential amino acid for mammals since they cannot synthesise it. Wheat (Triticum aestivum L.) is a major source of dietary Trp, and wheat high in Trp would thus be very beneficial. This study investigated the impact of location and wheat variety on the content of free Trp and mineral nutrients in wheat grain. Four wheat cultivars from national variety tests on wheat with varying protein contents were selected from seven different locations of Sweden representing different climatic zones and soil contents of trace elements. Grain was analysed for Trp content using reversed phase HPLC. Mineral nutrients were analysed using inductively coupled plasma emission spectrometry. Wheat yield and grain content of nutrients and Trp differed significantly between sites. High N content in grain was correlated with a high content of Cu, Fe and S, and also Ca and Mg. However, it was correlated with a low content of K and Na. Trp content was positively correlated with Na and Zn content and negatively correlated with K/Na and K/(Na+Zn) ratio. The varieties differed in Trp content and the two ratios, but there were no significant differences in yields between the varieties at any location. The results indicated salt stress induction of Trp synthesis, which may protect wheat against salt stress and yield losses.

The inoculation of the legume seed material with active nitrogen fixing bacteria strains before sowing has a significant role for the increase of the legume yield. Inoculation can improve crop yields in cases where appropriate rhizobia are not present in the soil or the soil contains a significant proportion of non-nodulating or ineffective nitrogen-fixing strains. The aim of the investigation was to detect the effectiveness of Rhizobium leguminosarum strains in field beans at different soil microbiological activity. The experiment was conducted at the Institute of Soil and Plant Sciences of the Faculty of Agriculture of the Latvian University of Agriculture from the 5th of June till the 17th of October 2008. The field bean (Vicia faba. L) cultivars - 'Ada', 'Lielplatones', Rhizobium leguminosarum bv. vicia strains No. 110; 408; 501 and 2 types of soils (with different microbiological activity) were used in vegetation pot experiment. The highest shoot dry matter was observed in cultivars cultivated in soil with higher microbiological activity. The highest pod dry matter was observed in cultivars cultivated in soil with higher microbiological activity. The highest total nitrogen amount was in field beans cultivated in soil with lower microbiological activity. Rh. leguminosarum strain resistance to streptomycin decreases with the plants age, from anthesis forward in both soil types and both cultivars. The fingerprinting showed significant difference between Rh. leguminosarum strains.

Maize (Zea mays L.) is one of the agricultural plants that is suitable substrate for biogas production. Fresh as well as ensiled maize can be used as biogas substrate. Practically, mainly maize silage is used because fresh maize is available only for short term during the vegetative period. The paper is aimed to determine the impact of ensiling on substrate composition of maize hybrids. A field trial was carried out in the Research and Study farm ''Vecauce'' of the Latvia University of Agriculture (LLU) in 2008 and 2009. Ten (in 2008) to eleven (2009) maize hybrids with different maturity rating according to FAO numbers (FAO 180 – 340) were harvested at three different times beginning on 5 September at fourteen-day intervals. Chopped maize samples of 1-3 kg were ensiled in plastic silos. Samples of fresh and ensiled (for at least 90 days) maize were analyzed detecting 14 parameters in the Scientific Laboratory of Agronomy Research of LLU using standard methods. Our results showed that ensilaging influence on organic dry matter and hemi-cellulose content was not substantial. High (p is less than 0.05) correlation between organic dry matter content of fresh and ensiled samples was noted. The crude protein, crude fibre, ash and cellulose concentration was greater in the ensiled samples if compared with fresh maize samples in 2008 and 2009. After ensilaging process neutral detergent fibre (NDF) concentration was higher compared with fresh samples in 2009 but lower in 2008.

The investigation was done at the Latvia State Institute of Fruit-Growing in Dobele in 2009, on the basis of an established field experiment planted in 1997 with apple (Malus domestica Borh.) cultivar 'Melba' (rootstock B9) trees spaced at 1.5 × 4 m distances. Three different treatments of soil moisture management were compared: control, sawdust mulch and fertigation. Soil of the experimental plot was Haplic Luvisol (Hypereutric), sandy loam, interspaced with Cutanic Luvisol, sandy loam. Organic matter – 25 g kgE-1, soil reaction pH – 6.5. Plant available P was 130.9, K – 157.7, and Mg – 102.2 mg kgE-1. The aim of the investigation was to determine nitrogen removal with fruit yield taking into consideration the used soil moisture regulation method – sawdust mulch or fertigation. The applied soil moisture regulation methods (mulch and fertigation) had significant influence on the content of dry matter in apple fruits (p is less than 0.05). The highest content of dry matter was found in the control treatment. A significantly higher nitrogen concentration (47 g kgE-1) in apple dry matter was in the control treatment, whereas in mulch and fertigation treatments nitrogen concentrations were lower (36 and 42 g kgE-1). The highest nitrogen concentration in dry matter was found in fruits with the biggest mass (r=0.61). A negative significant (p is less than 0.05) correlation was found between nitrogen concentration and trunk diameter (r=–0.85), and between nitrogen concentration and yield (r=–0.84). Removal of N was 24.4 kg haE-1 in the control, 22.3 kg haE-1 in the mulch, and 25.0 kg haE-1 in the fertigation treatment.

Both the rowanberries (Sorbus) and the chokeberries (Aronia) belong to the family Rosaceae. The berries of these cultivars are suitable for production of health-food products. The main components in the dry matter of fruits are carbohydrates, primarily sugars. The aim of this experiment was to determine the content of simple sugars and sorbitol in different fresh rowanberry cultivars and chokeberries and to compare the composition of these compounds after freezing and thawing of berries. The experiments were done in the Customs laboratory of the National Customs Board, State Revenue Service (Latvia). The rowanberries were picked in the Pure Horticultural Research centre, and black chokeberries were obtained from farm 'Ceplīši' (rural municipality of Pure). The contents of dry matter and soluble solids were analyzed in fresh berries, and the contents of sugars and sorbitol were analyzed both in fresh berries and in berries after freezing and thawing of 13 different cultivars of rowanberries and one black chokeberry. For determination of the soluble solids content, the refractometric method was used, and for determination of the glucose, fructose, sucrose and sorbitol content, high performance liquid chromatography was used. The results showed that rowanberries and chokeberries contained 3.24-7.24 g 100 gE-1 of sorbitol which was the dominant compound in all investigated berries. The highest content of sorbitol was found in the wild rowanberries and rowanberries Sorbus aucuparia var. sibirica, but fruits of rowanberry×pear 'Alaya Krupnaya' contained the least content of sorbitol. After freezing and thawing of berries, the content of sugars and sorbitol were decreased by 5-23% with some exclusion.

The experiment was carried out in the Latvia University of Agriculture. The objectives of this research were to study changes of bean (Phaseolus) protein fractions occurring under the thermal treatment conditions and determine the critical temperature for Maillard reactions in beans. In these reactions lignified protein is made from amino acids and sugars, and it decreases the nutrition value of the food. If lignified protein exceeds 50% of crude protein content in food, then food is considered unsuitable for daily diet. In this experiment beans were milled and then heated at 50 ± 3 °C, 75 ± 3 °C, 100 ± 3 °C, 125 ± 3 °C and 150 ± 3 °C temperature in the drying oven for 20 h. As a control sample non heated beans were used, and they all were kept in a plastic jar at room temperature (20 ± 1 °C). Dry matter, crude protein, starch, sugar and lignified protein content were determined in heated beans and control samples. No significant changes of crude protein content were observed due to thermal treatment. It was from 24.3 ± 0.3 g 100 g-1 of dry matter. Similarly, no significant changes were observed in starch content, as it stayed averagely 47.1 ± 0.2 g 100 g-1 of dry matter. Medium high correlation was observed (0.64) between lignified protein content and sugar content for in different temperature treated beans. Lignified protein showed exponential growth if the samples were heated at a temperature of 100 ± 3 °C and higher, giving exponential change.

Abstract Studies comparing slurry injection versus spreading have reported inconsistent results so far. The objective of the study was to compare two slurry application methods, injecting and spreading, in terms of influence on sward yields and leaching of nitrogen (N) and potassium (K) from grassland. The experiment was conducted from 2008 to 2011 at the Eerika Experimental Station, Estonian University of Life Sciences. Mini-lysimeters filled with loamy sand soil embedded in three swards (three-species grass mixture (Phleum pratense, Lolium perenne and Poa pratensis), grasses mixture with white clover (Trifolium repens), and grasses mixture with lucerne (Medicago sativa)) were used. Three annual nitrogen rates (60, 120, 180 kg haE-1) in conjunction with the two slurry application methods (injecting and spreading) were applied. Percolated water quantities, N and K content in leachate and the sward yield were measured. N leaching was significantly less with slurry injection while K leaching did not depend on slurry application method. N and K leaching was more affected by sward botanical composition and applied N rate and N:K ratio n slurry than by slurry application method. Sward yields did not depend significantly on slurry application method. Slurry injection is rational only in grasses sward when used N rates are above 120 kg haE-1 yrE-1. Slurry injection may have negative influence on the distribution of white clover in the grasses + white clover sward and thus lead to sward yield decrease.

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.