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.

Land use efficiency is based on agricultural production. Correct and effective land use could solve several problems – food production, improving the welfare and provision of social stability. The use of land and natural resources is an important issue in the development of the country; therefore, many researchers and scientists have analysed and studied the use of agricultural land and land use efficiency. Efficient land use has an impact on different types of factors, which are mutually contradictory. In the paper several authors researches are analysed, studying influencing factors of the use of agricultural land. Influenced by several factors the main problems associated with the use of agricultural land are the increase of unused agricultural land, the continued degradation of land, but the major problem of land use is the existence of a fragmented property structure. For the efficient use of agricultural land, there are several conditions that need to be met or improved to achieve effective land use. The main conclusion is that analysing the problems that are associated with the use of agricultural land is seen as interactive interaction, as the fragmented property structure is one of the reasons influencing the use of agricultural land, which leads to an increase in unused areas of agricultural land, while unused areas of agricultural land are often overgrown with shrubs while promoting degradation of land.

Liming soils make both direct and indirect effects on greenhouse gas (GHG) emissions. If raising the pH of soil, the amount of N2 O emissions in the result of nitrification decreases; therefore, it is important to perform also maintenance liming if applying nitrogen fertilisers. Liming acidic soils contributes to the absorption of nutrients supplied by means of fertilisers by plants, limits the spread of plant diseases, forms better soil moisture and air regimes for plants, improves the structure of soil and activates microorganisms. The aim of this study was to assess liming effect on nitrogen use efficiency and nitrogen oxide emissions in crop farming. To achieve the aim, this study proceeds in two stages: 1) to analyse the scientific literature on the liming effect on nitrogen use efficiency and nitrogen oxide emissions in other countries, as a few such research studies are available in Latvia; 2) to calculate potential gains and losses from liming acid soils in order to examine the real situation concerning liming and its effects on the economy of farms. The research finds out that at the farm level in Latvia liming gives a positive economic effect (41.6 EUR haE-1) however, it is essential for maintaining soil fertility, increasing yields, and presumably for more efficient circulation of nitrogen, which decreases nitric oxide emissions.