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.

The most important reason for growing field crops is food consumption. Only some of the total amounts of field crop species are mostly used for cultivation in the largest part of arable land. These crops ensure high economic income. This is the reason why biological diversity has decreased. Crop rotation is considered to be an instrument of sustainable cropping system and this is confirmed again nowadays. Higher cereal yields have been gained by including oil crops or pulses in the rotation. Each field crop has its own calorific value (MJ kgE-1). Grains/seeds and above-ground biomass may have different calorific values because of their chemical composition. Research results from literature confirm that the average net calorific value of winter wheat (Triticum aestivum) and triticale (Triticosecale) grain and straw are ~17 MJ kgE-1, but the net calorific values for oilseed rape (Brassica napus ssp. oleifera) seeds and straw are – 25.70 MJ kgE-1 and 16.37 MJ kgE-1, respectively. Oilseed rape is also known as energy rich crop. It is reported that diversified crop rotations also have greater energetic productivity from above-ground biomass (grain/seed yield and by-products) if compared with crops grown in repeated sowings or in monoculture. Crop rotation in combination with different tillage methods (conventional tillage, reduced or minimum tillage and no-tillage) is the way to improve soil quality, but it is not clear whether the soil treatment method has a significant impact on the overall crop rotational energy productivity.

Healthy seeds are essential for the optimal plant population and yield, but seed-borne pathogens, such as Fusarium spp., may reduce seed germination, quality and cause damping-off of the seedlings. Fusarium graminearum is a dominant pathogen of cereal crops and can cause significant losses of grain yield and quality. It is important to evaluate the role of alternative inoculum source in crop rotation. The aim of this study was to assess the impact of F. graminearum infection on different plant seed germination and seed infestation. The research was conducted at the Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry, in 2017. Visually healthy seeds of bean (Vicia faba L.), pea (Pisum sativum L.), lupine (Lupinus angustifolius L.), soybean (Glycine max. (L.) Merr.), lucerne (Medicago sativa L.), white (Trifolium repens L.) and red (Trifolium pratense L.) clover were inoculated with 10 mL of F. graminearum suspension, adjusted to 1×106 conidia per mL. Seed infection was counted 2 and 6 days after inoculation (DAI), seed germination energy and reduction rate – after 3 DAI and germination index – 6 DAI. Results showed that all inoculated seeds were covered with typical to F. graminearum red-purple mycelium. The results of inoculated seeds with F. graminearum showed red-purple mycelium growth on the seeds (infection from 21.25 up to 100%). The results showed that germination energy decreased on pea (2.56%) and lupine (7.79%) seeds. Our results suggest that various plant seeds differently react to F. graminearum infection. The highest infection of F. graminearum was obtained on pea, lupine seeds and the least on red clover.

Due to large diversity of site conditions suitable for Scots pine growth in Latvia, it is important to evaluate their influence on growth and survival of particular Scots pine families. To do so, open pollinated progenies from phenotypically selected plus trees of 35 at the age of 32 years have been evaluated in 2 forest types (Cladinosa-callunosa and Hylocomyosa). Investigation revealed that forest type and family influence had a great significance to height, diameter at breast height, and diameter of thickest branch up to 2 meters' height (alpha is less than 0.001), but clone influence had lower significance (alpha=0.008). Proportion of influence to height growth caused by tree family was 70% at the age of 6 years and 17% at the age of 32 years. Proportion of influence on survival caused by tree family was 57% and 44% respectively. The corresponding influence of forest type was 12% and 28% to height, 15% and 39% to survival. Diameter at breast height at the age of 32 years was equally influenced by forest type and family (~11%). Equal breeding effect - but not with the same families - can be reached both in fertile and poor soils. In group (20%) selection this effect was ~8% for height, 11% for diameter, and 30% for survival; in individual selection ~10% for height, and ~17% for diameter.

Flax (Linum usitatissimum L.) fibre and seeds are widely used to produce healthy and environmentally friendly products. It is known that the main factors that influence flax fibre’ and seeds’ yield are genotype and growing conditions. The main task of the Latvian flax breeding program is to develop flax genotypes that are highly productive (both fibre and seeds) and well adaptable to changing environmental conditions. Goal of this study is to identify high yielding genotypes with good adaptation to local variable agro-ecological conditions. The agronomically important traits, such as yield of stem and seeds, total and technical plant height and fibre content were evaluated for 13 Latvian origin flax lines and standard variety ‘Vega 2’. The field trials have been carried out over the period from 2012 to 2015 at the Agricultural Scientific Centre of Latgale. The regression, correlation, coefficient of variation and cluster analysis between yield and yield provided components were used for identification of high yielding genotypes with good adaptation. On the basis of cluster analysis the genotypes were classified in two groups by lower and higher yield of stem, fibre content, total plant height and technical plant height. The line ‘I18-1’ was identifying as genotype with the highest average yield of stem (751.25 g mE-2) as well as highest yield against other genotypes in moisture and drought years. Most valuable by the average technical plant height was line ‘L26-1’ (73.05 cm).

Problems in hulless barley growing are caused by a low germination ability and emergence. Grain quality for feed and food are influenced by threshability and infection with fungal diseases. The aim of experiments was to investigate the possible hulless barley seed and grain quality problems under Latvia's conditions. Germination, emergence, test weight, 1000 grain weight and threshability of 77 hulless barley genotypes of diverse origin were determined and compared to hulled control varieties. Correlation between hulless barley germination, grain germ damage and grain infection with Fusarium, Helmintosporium and Penicillum was analyzed. The seed material structure (content of grains with damaged germ, broken grains and grains with undetached hulls) of 5 hulless barley genotypes was determined.

A field trial concerning optimisation of a mineral fertiliser (NPK) in the production of perennial ryegrass 'Spidola' seeds was established at the Skriveri Research Centre of the Latvia University of Agriculture in 1999. Experiments were conducted on sod-podzolic sandy loam soil (Luvic Phaeozem, WRB 1994). In 2000, the first seed production year, which was quite unsuitable in terms of climatic conditions, the nitrogen fertiliser showed significant influence on seed and straw yields. The use of phosphorous and potassium fertilisers in all combinations with nitrogen decreased the resistance of the crop to lodging.

Major diseases occurring on flax crops in Lithuania are caused by Fusarium spp., Colletotrichum lini Manns et Bolley, Polyspora lini Laff. et Peth., Septoria linicola (Speg.) Gar. They can spread through seed, especially when the seed material does not meet quality standards. Microscopic fungi of other species can be found on flaxseed as well. Chemical seed treatment is one of the ways to control disease agents. When treated seed is sown, the seed treaters affect the indigenous micro-biota of the soil. The trial was carried out at the Upyte Research Station of the Lithuanian Institute of Agriculture in 1999. The tested seed treaters are registered for cereals in Lithuania. Our experimental results suggest that chemical treatment of flaxseeds is an efficient method to control seed-borne diseases. The microscopic fungi on seeds and roots of seedlings were analysed at the Institute of Botany. The data on the effect of seed treaters on the diversity of pathogenic fungi of flaxseed and seedlings, and the impact of treatment on the seedling infection are discussed in this paper.