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.

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.

Japanese quince (Chaenomeles japonica) is cultivated as a fruit crop because its fruit possesses valuable properties. The total area of Japanese quince in Latvia is continuously increasing; therefore, fruit rot can become an important reason of yield loss. The aim of this study was to clarify the fruit rot incidence in Japanese quince plantations in Latvia and explore the influencing factors of rot development in the year 2017. The evaluation of fruit rot was carried out during the fruit development in eight places of different regions of Latvia where Japanese quince is grown commercially. Three plantations of different Japanese quince cultivars in Dobele and seven plantations where Japanese quince is grown from seedlings were observed. Fruit rot incidence among plantations had no significant differences. Statistically significant differences in fruit rot incidence depending on quince growth stage (p is less than 0.05) were found. Significant differences in fruit rot incidence were found between cultivars in Dobele.