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.

Formation of yield in crop cultivation is affected by influence of many factors. Simple summation of individual factors is quite rare occasion. Interaction among factors is a dynamic value. The effect of interactions varies depending on the crop development stages as well as by graduation of factors. The study aimed to evaluate the soil penetration resistance effect on winter wheat grain yield and development. It allows specifying recommendations for soil treatment difference criteria for use in site-specific soil tillage. Field trials were carried out at the Research and Study farm Vecauce of Latvia University of Agriculture during the years 2005-2007 to investigate factors influencing formation of winter wheat grain yield. Forty seven points (distributed as grid 50x50 m) were selected in the winter wheat Triticum aestivum L. field. All points were attached to their geographic coordinates. Data shows significant effect of soil resistance to grain yield - increase of soil penetration resistance by 100 kPa cmE-2 reduced yield of winter wheat by 0.37 to 0.48 t haE-1. By contrast in 2007 a significant linear regression relationship between soil penetration resistance and the yield was not detected. Differences of fresh weight of winter wheat plants in tillering stage and the beginning of stem elongation were insignificant compared to different groups of soil penetration resistance at soil layers 0.10-0.30 m in both experimental years. Higher impact of soil penetration resistance on flag leaf area difference had soil resistance at the layer of 0.20 - 0.30 m and differences were significant in both trial years.

Winter hardiness is very important for introducing and commercial cultivation of blueberries in North Europe. Winter survival in the field is influenced by multiple factors that are influenced by uncontrollable environmental parameters. In the years 2006-2008, in eight farms were surveyed in different fruit-growing areas of Latvia, which produce highbush blueberries. We were interested in the plants physiological conditions (winter hardiness) after the winter, yields and the growth conditions. All study sites were evaluated by 6-year-old plant of highbush blueberry cultivars 'Polaris', 'Chippewa', 'Patriot', 'Northblue' and 'Duke'. After the year 2006/2007, the highest winter hardiness was observed for 'Polaris', 'Chippewa', 'Northblue' and 'Patriot'. The lowest winter hardiness was observed in 'Duke'. December 2007, January and February 2008 changing weather conditions did not do significant damage in plantations. 'Patriot' and 'Chippewa' had the highest average yield (kg per bush) throughout the production period, cultivar 'Northblue' had the lowest yield. On the other hand, 'Northblue' had the highest 100 berry weight. Cultivar 'Patriot' had the largest berry size - most of the berries had a diameter of 15 - 16 mm.

Under open environmental conditions, Trihodermin and BioMikss were used for trial purposes to study lettuce (Lactuca sativa L.) and strawberry (Fragaria x ananassa Duch) yields in 2008. Experiments were carried out in the Region of Riga at the farm 'Pukulejas'. The lettuce cultivar 'May King' and the strawberry cultivar 'Senga Sengana' were both used in the trial. The purpose of the trial was to evaluate the use of biological products when applied on the above mentioned trial plants. In the field trial, both Trihodermin and BioMikss in dry powder form in peat mixture were applied for soil treatment 10 kg haE-1. Trihodermin contains cells of microscopic fungus Trichoderma harzianum 8-21 and Trichoderma viride 1-5. BioMikss is a mixture of microorganisms, containing cells of seven various bacteria (Azotobacter chroococcum 23, Polyangium cellulosum 5-t, Polyangium 56, Pseudomonas putida 48-t, Rhizobium meliloti 15, Streptomyces griseoviridis P-t and Streptomyces cellulosae D) and cells of two various fungus (Trichoderma harzianum 7-t and Trichoderma viride A-L). Three times during the growing period Trichodermin and BioMikss water solution 100 g kgE-1 was applied on the trial plants. When compared to non-treated plants, significantly increased yield was observed on BioMikss-treated lettuce. A significantly increased yield was also observed on BioMikss-treated strawberries. The results of the experiments showed that in open environment, both strawberry and lettuce plants treated with BioMikss showed resistance to the grey mould, caused by a parasitic fungus Botrytis cinerea. The results prove that biological products, by environmentally friendly means, revitalize soils, protect plants, and enhance growth, immunity and productive potential.

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 EU Directive on the promotion of the use of biofuels or other renewable fuels for transport (CO M 2003/30/EC) states that the proportion of biofuels in 2010 must make 5.75% of non-renewable fuels, but in 2020 - 10%. The only way for Latvia to fulfil the Directive 2003/30/EC is to use winter rye because it is one of the oldest cereals grown in Latvia, and Latvia has a long-lasting experience in growing it. A field trial of winter rye (Secale cereale L.) was arranged in the Agricultural Science Centre of Latgale from 2005 to 2007. The influence of four winter rye varieties and five fertilizer rates on grain yield and starch content was researched for three years. The year (factor A), the varieties (factor B), the fertilizer rates (factor C), and the interaction of factors AB, AC , BC, and ABC significantly influenced the yield of grain and the starch content with 95% probability. It is recommended to use good quality grain with high starch content and low protein content for bioethanol production. The varieties of winter rye 'Kaupo', 'Amilo', and 'Walet' are the most suitable for ethanol production in Latgale region.

It is important to define which of the plant growth factors determines the yield level. During recent years in Latvia, in most cases it was moisture. Grain yield level mostly depends on meteorological conditions during the tillering stage. Plants do not utilize all water from precipitation. Rain water efficacy depends on soil granulometric composition and content of humus. Humus content could be considered as regulated factor. Important is also distribution of precipitation during the vegetation period as well as run-off of rain water which depends on micro-relief, soil tillage type, and direction in accordance with the slope gradient. It is very important for cereal growing in what conditions tillering is done, because during that time productive stems as well as ear sprouts are formed. The aim of this research was to determine the effect of soil moisture on the growth and development of winter wheat Triticum aestivum L. Field trials were carried out during 2005-2007 in Kurpnieki field at the Research and Study farm „Vecauce” of the Latvia University of Agriculture. A total of 47 points (distributed as a grid of 50×50 m) were selected for sampling in the winter wheat field. In both experimental years, the increasing soil moisture in spring had a significant positive effect on the flag leaf area, which, in its turn, increased also the level of grain yield. Partial correlation analysis showed that exclusion of organic matter content and altitude above the sea level as factors, changes soil moisture at different layers of the soil insignificantly.

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.

The yield and quality (volume weight, 1000 kernel weight, protein content, falling number, gluten content, gluten index, gluten content in dry matter) of winter wheat was studied in variety 'Portal'. The wheat was part of the five-year crop rotation experiment where red clover (Trifolium pratense L.), winter wheat (Triticum aestivum L.), peas (Pisum sativum L.), potato (Solanum tuberosum L.) and barley (Hordeum vulgare L.) were following each other. There were two production variants which followed the crop rotation. In one variant mineral fertilizers and pesticides were used, and the other variant was conversion to organic without any synthetic agrochemicals. In mineral fertilizing variant, on the background of P25 and K95 kg haE-1 the N amount varied from 0 to 150 kg haE-1 and herbicide Mustang (preparation norm 0.5 L haE-1, active substance florasulam, 6.25 g LE-1; 2.4-D, 300 g LE-1), insecticide Fastac 50 (preparation norm 0.2 L haE-1, active substance 50 g LE-1 alphacypermethrin) fungicide Falcon EC 460 (preparation norm 0.4 L haE-1, active substances 167 g tebuconazole, 250 g spiroxamine, 43 g triadimenol) and growth regulator Moddus (preparation norm 0.4 L haE-1, active substance 250 g LE-1 trinexapac-ethyl) were used. In conversion to organic the winter wheat grains which followed the red clovers after effect had higher volume weight, 1000 kernel weight and gluten index compared to the variants where mineral fertilizers were used. The yield, protein content, falling number and gluten content in dry matter increased with increase of the amount of mineral N. The wet gluten content was significantly higher compared to the other variants where the N amount was 50 kg haE-1.

Precocity of fruit plants enables early obtaining of yield and income. But precocity can be influenced by drought. In some cases precocity is related to insufficient growth and insufficient yield in the succeeding years. The precocity of sour cherries was investigated in the trial established at the Latvia State Institute of Fruit Growing. Soil moisture treatments - woodchip mulch and drip irrigation as well as cultivars ‘Bulatnikovskaya’, ‘Desertnaya Morozovoi’, ‘Latvijas Zemais’, ‘Orlica’, ‘Shokoladnica’, ‘Tamaris’, and ‘Zentenes’ were used as trial factors. The flowering and yielding was observed in 2008 and 2009. Flowering, fruit set, fruit mass, and yield were characterized in order to evaluate precocity of cherries in different soil moisture treatment variants. The use of drip irrigation did not influence the yield of sour cherries, but the use of woodchip mulch decreased the yield in the third growing year. The cultivar ‘Tamaris’ was the most precocious, and the cultivar ‘Bulatnikovskaya’ was the most productive.