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.

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.

Maize yield and quality are affected by many factors, including production practices, diseases, pests, and differences in the climate. Usually it is not possible to do much to change the effect of temperature, but it is important to grow better adapted or characterized with right maturity rating hybrids. The paper is aimed to determine the impact of accumulated growing degree days (GDD) on maize development, organic dry matter yield, ODM and chemical composition of maize hybrids. A field trial was carried out in the Research and Study farm ’’Vecauce’’ of the Latvia University of Agriculture (LLU) from 2008 till 2010. Ten (in 2008), eleven (in 2009) and fifteen (2010) maize hybrids with different maturity ratings according to FAO numbers (FAO 180-340) were harvested at three different times beginning on 5 September at fourteen-day intervals. GDD were calculated when maize reached a certain growth stage (full emergence, first tassels, full tassels, first ears, full ears, specific harvest date) to characterize conditions for maize growing in a specific year. Composition of fresh maize was analyzed for all hybrids using standard methods. Results were statistically processed using methods of correlation and regression analysis. Our results presented evidence that ODM yield in 2008 and 2009 on last harvest dates was lower than that on the first harvest date in 2010. Organic dry matter yield was higher in years when more GDD were accumulated. Results also showed that GDD negatively correlated with the total N, protein, fibre cellulose, hemi-cellulose, NDF, and ADF concentration.

In Latvia, different breeds of beef cattle are grown; therefore, it is important to explain their suitability to organic farming systems, because most Latvian beef cattle breeders work with organic farming methods. The aim of this research was to compare fattening of different beef breed bulls (Bos Taurus) in organic farming system at similar housing and feeding conditions. In the research, there were included Blonde d’Aquitaine (BA), Hereford (HE), Simmental (SI) and crossbred (CB) bulls. Fattening period started after calf weaning from suckler cows at 7 – 8 months of age. Fattening results were significantly affected by factors like breed, live weight and age before fattening, but slaughter results were significantly affected by breed, live weight and age before slaughter. During the fattening period the biggest daily weight gain was showed for SI breed bulls (849 g), but the biggest live weight increase was recognized for BA breed bulls (295 kg). The required slaughter weight the fastest was reached for XG bulls, which average slaughter age was 532 days (p is less than 0.05). The greatest slaughter weight – 342 kg (p is less than 0.05) and dressing percentage (58% (p is less than 0.05)) was recognized for BA breed bulls; also, carcass conformation score in muscle development was the highest for BA bulls (2.0 points (p is less than 0.05)). The greatest economic benefit was from CB bulls, income calculated per one rearing day from CB bulls was - EUR 1.80.