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.

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.

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.

TThe aim of this study was to evaluate an impact of nitrogen fertilizer rates on industrial hemp’s (Cannabis sativa L.) growth and development in Latvia. The trial was carried out during 2012 on the Research and Study farm Peterlauki of the Latvia University of Agriculture in the sod calcareous soil. There were three industrial hemp cultivars ‘Futura 75’, ‘Tygra’ and ‘Felina 32’ tested under different fertilizer rates: N0P0K0 – control, N0P80K112 – background fertilizer (in text marked as F), F+N30, F+N60, F+N90, F+N120, F+N150, F+N180 kg haE-1. Weather conditions were proper for good hemp biomass production. Depending on the selected cultivars, the optimal fertilizer rate was in the range of 90 – 150 kg ha-1. Industrial hemp stalk length was significantly (p is less than 0.05) influenced by the applied nitrogen fertilizer rate and cultivars. The highest stalk length was observed in the cultivar ‘Futura 75’ under all nitrogen fertilizer rates. The highest stalk length (3.18 m) had reached under the nitrogen fertilizer rate 150 kg haE-1 at 138 growing day from sowing. At the beginning of growing season (June - July) the growth intensity of hemp stalk length is high. Within one month the stalk length grew up for 1.23 meters of cultivar ‘Futura 75’. The intensive growth of hemp stalk declines when the flowering stage is reached. Flowering stage occurred in early August, and it was dependent on nitrogen fertilizer rate. Under higher nitrogen fertilizer rate the flowering stage reached later.

The yield and quality (1000 kernel weight, protein, nitrogen, phosphorus and potassium content) of peas was studied in cultivar 'Madonna'. The peas (Pisum Sativum L.) were part of the five-year crop rotation experiment where red clover (Trifolium pratense L.), winter wheat (Triticum aestivum L.), peas, potato (Solarium 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 variants the background in all variants was N20, P25, and K95 kg haE-1. The previous crop was winter wheat which received in fertilized variants mineral fertilizers with the background of P25 and K95 kg haE-1, the N amount varied from 0 to 150 kg haE-1. The aim of this paper was to study a mineral fertilizing after-effect on the peas which followed the winter wheat. Herbicide MCPA 750 was used. In conversion to organic, the pea grains which followed the crop rotation and mineral fertilizing Nl50 after-effect variants had higher yield, protein and nitrogen content compared to the other variants where mineral fertilizing after-effect was investigated. Phosphorus contents were higher in NO, and conversion to organic variants. Potassium content remained lower in Nl00, and Nl50 mineral fertilizing after-effect variants. The 1000 kernel weight was significantly higher in the variant of conversion to organic compared to the other variants.

Winter oilseed rape is the main oilseed crop in Latvia. High yield production depends on applied plant nutrients, especially nitrogen. Nitrogen is one of the most mobile plant nutrients in the soil and, therefore, nitrogen fertilizer management is an important part of agriculture. The objective of this paper is to evaluate the effect of nitrogen fertilizer rate on nitrogen use efficiency (NUE) in winter oilseed rape. The field experiment was conducted during four growing seasons (2014/2015, 2015/2016, 2016/2017 and 2017/2018) at the Research and Study farm ‘Pēterlauki’ of Latvia University of Life Sciences and Technologies (56° 30.658´ N and 23° 41.580´ E). In total, eight nitrogen rates were used in this experiment (kg ha-1 of N pure matter): N0 or control, N60, N90, N120 (80+40), N150 (100+50), N180 (120+60), N210 (120+60+30) and N240 (140+60+40). All NUE parameters were calculated only for five nitrogen rates (N0; N60, N120, N180 and N 240). Results indicated that the nitrogen fertilizer rate had a significant (p is less than 0.001) effect on winter oilseed rape seed yield. The yield increased until the rate N120 – N180. Nitrogen fertilizer rate also significantly (p is less than 0.001) affected N, P2 O5 and K2 O removal with oilseed rape biomass. N and K2 O removal with seed yield significantly increased until the nitrogen rate N120 – N180, but P2 O5 until N60 – N180. Results showed that the nitrogen fertilizer significantly (p is less than 0.001) affected NUE, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE), but it did not have a significant (p=0.840) effect on nitrogen harvesting index (NHI). By increasing the nitrogen fertilizer rate, NUE, NUpE and NUtE decreased.

One of the factors affecting winter wheat grain yields are leaf blotches. The two-factorial trial was conducted in the Research and Study farm ‘Pēterlauki’ in 2017/2018 and 2018/2019 (Latvia). Four nitrogen rates and five fungicide treatment schemes were used. The aim was to clarify the impact of leaf blotches on the winter wheat yield. In winter wheat plots, the tan spot (caused by Pyrenophora tritici-repentis) dominated but also Septoria leaf blotch (caused by Zymoseptoria tritici) was found. The severity of leaf blotches in winter wheat was low in both years due to dry and warm weather. The development of leaf blotches was influenced by fungicide application schemes, but not by nitrogen fertilizer rate. The total disease impact during the vegetation period was estimated by calculation the area under the disease progress curve (AUDPC). AUDPC for both diseases were significantly higher in the variant without fungicides (F0) and in the variant, where half of dose of fungicides at the growth stage (GS) 55–59 (F1) was used. The using of full dose of fungicide at the GS 55–59 (F2) as well as using of fungicides two (F3) or three (F4) times in growing season significantly decreased the values of AUDPC for both diseases, but differences among AUDPC values in mentioned three variants were not significant. Results showed that the nitrogen fertilization significantly increased the average per both years grain yield until the nitrogen rate N180. Fungicide treatment schemes had no significant effect on the average grain yield.

A demand for wood resources is increasing. In addition to drainage and appropriate regeneration and thinning, the forest soil fertilization may increase the future harvest rates. Therefore, the improved growth of forest stands raises in priority among the research topics related to forestry. The objective of the study is to evaluate the impact of nitrogen fertilizer on soil water and throughfall water chemical composition to elaborate recommendations for the forest fertilization. The trials were conducted in a birch stand and in three coniferous stands. Nitrogen containing mineral fertilizer (ammonium nitrate) was distributed in the study sites, while the control plots were left without any treatment. The water samples were collected a season before and a season after the soil treatment. The pH level, total nitrogen, potassium and phosphate were determined in throughfall and soil water samples. The chemical properties of throughfall water differed depending on the forest stand type. The concentration of nitrogen was higher in throughfall water samples collected from the birch stand. The mean concentration of total nitrogen was 1.6 ± 0.3 mg LE−1 in the throughfall water samples from the birch stand compared to 1.03 ± 0.11 mg LE−1 in the throughfall water samples from the coniferous stands. Although the forest soil was enriched with the nitrogen fertilizer, there was a significant increase in concentrations of potassium and phosphate in soil water samples from certain stands. It can be explained with changes in pH level that occurred after the forest soil treatment with ammonium nitrate. There was also a significant increase in total nitrogen concentrations in soil water samples at the depth of 30 cm from the treated plots of the coniferous stands – 15 ± 6 mg LE−1, compared to 1.5 ± 0.03 mg LE−1 in the samples from the control plots. However, the concentrations decreased within two months and remained at a steady rate – slightly above the control level.

Effects of nitrogen fertilizers and weather conditions on spring barley (Hordeum vulgare L.) yield and grain quality were investigated at the Rumokai Experimental Station of the Lithuanian Institute of Agriculture in the period of 1998-2000 and 2003-2004. The soil of the experimental site was Hapli Epihypogleyic Luvisol. Analyses were made with fertilisers rates of 0 and 90 kg haE-1. The data of analyses indicated a positive and reliable correlation between the yield of spring barley and the amount of precipitation in May (rate of correlation was 0.70**) and a negative and reliable correlation with the amount of precipitation in June and July (rates of correlation were -0.80** and -0.29* respectively). A reliable though weak correlation was found between the application of nitrogen fertilisers and the yield of grains. The amount of precipitation in April and the spring barley leaf diseases had a considerable negative effect on 1000 grain weight and grain size. Strong correlation was identified between the amount of precipitation in May and June and the protein content in grain. Nitrogen fertilisers promoted protein accumulation in grain.

The aim of this research was to compare effects of fertilization with various ratios of N, P and K (N:P:K) on arbuscular mycorrhizal fungi (AMF) infection in roots of Dactylis glomerata in Ca-carbonate (limed) and non-limed meadow plots at the Research Centre of Skriveri, Latvia University of Agriculture. Dactylis glomerata roots were excavated from variously fertilizer plots, a minimum 3 root samples per plot and analysed for two consecutive years. Arbuscular mycorrhizal fungi infection rates were estimated according to accepted scoring tables used for determination of AMF colonization.