Bioenergy production growth rates in the recent years are leading to waste – digestate and wood ash amount increases, which are essential to be managed in the most efficient and safe way. In the formation of plant nutrient recycling these waste products are useful to be included in the energy crop fertilisation plan. In order to study the waste products application options for energy crops – reed canary grass (Phalaris arundinacea L.) and festulolium (×Festulolium pabulare) fertilisation trials were arranged in 2012 at the Skriveri Latvian University of Agriculture (LLU) Research Institute of Agriculture. In all fertiliser treatments: wood ash; digestate one time per season; digestate two times per season and mineral fertilisers the same doses of the main plant nutrients (N, P, K) were provided, the missing quantities of elements compensating with mineral fertilisers. To obtain the grass biomass, two cutting regimes were used – two-cut and one-cut harvest system. This article summarizes the findings on the productivity of the 1st year of use grassland swards and sward structure data. The productivity of perennial grass biomass was dependent on the type of applied fertilisers, grass species and cutting regime. In the first production year the highest average dry matter yield (7.30 t haE-1) was produced by reed canary grass. The highest DM yields in average for both grass species were obtained by mowing once per season – in autumn at crop senescence (7.01 t haE-1) and in fertilisation treatments of wood ash (WA) – 8.06 t haE-1 and mineral fertilisers (MF) – 7.24 t haE-1.

The stump lifting trials were implemented in 5 forest compartments of the JSC ‘’Latvia state forest’’ Vidusdaugava, Rietumvidzeme, Zemgale and Ziemeļkurzeme forestries in autumn, 2012. Total extracted area was 3.5 ha, excluding control. Two stump extraction buckets were compared in these trials – CBI (made in Canada) and MCR-500 (made in Latvia). The scope of the study was to estimate if the prototype of the MCR-500 can compete with stump lifting buckets having positive feedback from industry. Considering that the CBI head cannot prepare soil, this operation was not done by the MCR-500 either. In total 1796 stumps were marked and their main parameters were taken in all trial areas. Extracted biomass was estimated theoretically using biomass expansion factors elaborated in Nordic countries. Allegro CX field computers with SDI software were used in time studies to obtain information about productivity and distribution of productive time in a work cycle. The study demonstrated that productivity of stump extraction with both stump lifting buckets did not differ significantly in 6 cases out of total 10 comparisons.

Lack of data about effect of meteorological conditions, sowing date, sowing rate, fungicide as growth regulator application and other agroecological factors on rape autumn growth is observed in Latvia. The aim of our research, started in autumn 2007 and continued up to autumn 2010 in Research and Study farm ''Vecauce'', was to investigate the influence of agroecological factors (sowing date, sowing rate and fungicide (as growth regulator in autumn)) application as well as meteorological conditions on autumn plant growth of two types of winter rape varieties. Winter rape biometrical parameters were estimated, and meteorological parameters (hydrothermal coefficient (HTC) and growing degree days (GDD)) were calculated. Four year results showed that winter oilseed rape seed germination was affected by precipitation and air temperature around the sowing time. Calculated GDD correlated with plant biometrical parameters during trial years. HTC showed moisture effect on rape emergence time. Sowing date was important factor which had strong and significant impact on biometrical parameters of rape plants in autumn. Earlier sowing date increased height of growth point, root neck diameter, plant and root mass, and main root length significantly for both cultivars in four trial years. Such agro-ecological factor as sowing rate (plant density) affected plant biometrical parameters only in some trial years. Plant weight was significantly influenced by sowing rate for both cultivars if sowing rates were equal. Other important parameter - height of growth point - was not significantly influenced by sowing rate for both cultivars when similar sowing rates were used in all years; exception was year 2009 for 'Californium'.

Field trials were carried out at Jõgeva Plant Breeding Institute in 2008 – 2011 to identify the possibilities of using early red clover (Trifolium pratense L.) ‘Jõgeva 433’ (diploid), Washington lupine (Lupinus polyphyllus Lind.) ‘Lupi’ and crimson clover (Trifolium incarnatum L.) as green manure. Fresh material of the above species was ploughed into the soil in autumn of the sowing year. Fertilizer value was quantified through yield and grain quality of spring wheat ‘Vinjett’ and barley ‘Inari’. The composition and amount of ploughed biomass were recorded. By the time of ploughing, Washington lupine had produced the most abundant biomass. >From studied species crimson clover had the lowest fertilizer value – only by 6–7% extra yield of spring wheat in the following year. Crimson clover had no residual effect of fertilization in the second year. The fertilizer values of red clover and Washington lupine were approximately equal. Their effect on yield increase of spring wheat and barley lasted for three years, on grain quality for two years. Red clover, ploughed into the soil in the year of sowing, resulted in maximum spring wheat yield increase of 23.9%, compared with N 0 treatments; that of Washington lupine was 21.3%. The residual positive effect in the second year quantified as barley production increased by 6.2% in Washington lupine and 7.9% in red clover. The yield increase in the third year was 3.9% and 12.1%, respectively. Green manure increased the contents of crude protein and gluten in spring wheat and crude protein content in barley.

Blueberry cultivation is becoming more and more popular in Latvia, and several commercial plantations have been established recently. Highbush blueberries (Vaccinium corymbosum L.) are perennial and can grow without replanting for 50 years; therefore a choice of soil and its preparation have a great role. This article summarizes results of research carried out in commercial blueberry plantation established in 2004 on loamy Haplic Cambisol. Soil properties, especially reaction and organic matter content, initially were not suitable for blueberry cultivation, therefore deep tillage and application of soil conditioner (acid sphagnum peat) were done before planting and similar peat mulch was applied every second year. Berry yield of 4 blueberry cultivars, soil properties and the nitrogen, phosphorous and potassium content in growing plant leaves were determined. The obtained results showed that sphagnum peat is an effective material for lowering of soil pH in plant root layer (0 – 40 cm). Data about plant nutrient content in topsoil and subsoil as well as in growing plant leaves will help to develop criteria for soil fertility assessment and diagnosis of plant nutrition.

The agronomic role of legumes in cropping systems is well understood with the respect to N2 fixation, mechanisms of precrop effects, and environmental impacts. The combined inoculation and tripartite symbiosis between leguminous plants, Rhizobium spp. and vesicular-arbuscular mycorrhizal fungi has been the subject of intensive research. Less attention has been paid to their effects on subsequent crops. Pot experiments were carried out in the greenhouse of Latvia University of Agriculture in 2015 and 2016. Soil used for this experiment was taken from the previous trial, where broad beans (Vicia faba var. major Harz.) were grown. Bean seeds, depending on the variant, were inoculated with rhizobia bacteria or mycorrhiza fungi, or the mixture of both microorganisms. Onions were grown as a subsequent crop. During the experiment, fresh and dry weight of onion leaves was determined. Onion root mycorrhizal colonization frequency and arbuscule abundance in the onion root system were determined. The activity of soil microorganisms was determined by soil respiration intensity. Results showed that the use of microsymbionts increased the subsequent onion leaf harvest in 2014 by 2.3% and in 2015 by 9.5%. In 2015 the highest increase of onion leaf yield was detected in variants were rhizobia strain RP023 was used. Rhizobia strain RV407 gave a positive effect only in combination with mycorrhiza fungi. Precrop treatment with mineral nitrogen fertilizer increased the onion yield in both years – by 12.4 and 14.3%, respectively. In all treatments, a decrease in dry matter content was observed. The highest incidence of mycorrhiza fungi structures was detected under mycorrhiza treatment. Tripartite symbiosis promoted the soil respiration rate.

The research paper focuses on description of the pig (Sus scrofa domestica) farming tendencies in Latvia with the scope to give feeding characteristics in relation to emission outcome. In the recent years the concentration of pigs in farms with a herd size more than 10,000 has increased. With increase of the large farms the average feed consumption is more affected by one operator. Efficient utilization of nutrients content in feeding is crucial to meet environmental goals. It is one of the steps to achieve Nutrient Use Efficiency. There is relationship between crude protein and reduction of reactive nitrogen. Feed content not only affects excreted nitrogen, but also pH of manure and total ammonia Cal nitrogen. It is complex abatement measure to quantify reduction of the emission because of impact of various environmental factors. In Latvia, the most common are sows cross breeds (Yorkshire × Landrace) and on January 1, 2019 the biggest group accounted was fattening pigs with average dry feed consumption per day from 0.33 kg (live weight from 5 to 6 kg) up to 3.6 kg (live weight from 80 to 120 kg) with crude protein value from 163.5 g to 155.3 g per 1 kg feed dry matter. Excreted nitrogen (Nex) was calculated for these groups of pigs less than suggested values in guidelines for emission calculation. The highest calculated total NH3 emission is from fattening pigs group with live weight from 55 to 90 kg although the highest calculated Nex is for lactating sows. NOx also calculates as NO2 and the highest value was 3.23 g per one lactating sow.

In Estonia, the most promising perennial grass used as raw material for production of heat energy is reed canarygrass (Phalaris arundinacea L.). Nordic countries (Finland, Sweden) implement a technology including single harvest of the above-ground biomass from frozen soil early in spring. This technology cannot be used in Estonia as the ground does not freeze to the extent of bearing harvesting machines every year. Harvesting in spring is virtually impossible as herbage lodges excessively under the snow weight. A divided harvesting method of reed canarygrass was tested in field trials in 2010–2013 at the Estonian Crop Research Institute. Herbages were cut in July at the height of 60–65 cm, mass was dried as hay, stubble hay was left to grow and was harvested next spring before the growth started but soil had become dry. The effect of seeding rate, row spacing and nitrogen fertilizer on the dry matter yield of reed canarygrass was investigated. The amount of produced heat by trial variants was calculated. The variant with narrow spacing (15 cm), seeding rate of 8 kg haE-1 and usage of fertilizer N70 in the beginning of growth and N70 kg haE-1 after the first cut was giving the best results. Two cuts of this variant yielded on average 8.12 t haE-1 per year, of which the stubble hay, harvested in spring and with better combustion properties, made 64%. Energetic value of the yield was 138 GJ haE-1 per year.

Heat is one of the most important types of energy at northern latitudes. In 2013 the total consumption of renewable energy resources (RER) in Latvia was 68 PJ. The heating systems can function on plant or other organic material, for example, wood chips or agricultural residues. By using local biomass resources it is possible to reduce the pollution of atmosphere caused by greenhouse gas emissions. Different variety of winter wheat (Triticum aestivum), triticale (Triticosecale) and rye (Secale cereale) were used in the research. The following aspects were determined during the research: dry matter yield, chemical composition and the higher heating value of grains and straw. The evaluation of grains and straw of winter cereals showed that the higher heating value (MJ kgE-1) was acquired from the straw of winter cereals, whereas the grains had the highest dry matter yield, thus the grains of winter cereals had the highest heating yield from one hectare (GJ haE-1).