Yield and quality of potato depend on nutrient availability in soil, especially regarding nitrogen. Nitrogen (N) is a very dynamic plant nutrient and its uncontrolled application can considerably raise the price of agricultural production. If N is insufficiently utilised by plants environmental pollution can occur. The aim of the study was to investigate efficiency of nitrogen fertiliser use by potato. The field trials were carried out at the State Priekuïi Plant Breeding Institute from 2009 till 2012. Nine fertilisation variants were applied: no fertilisation; PK dose to provide potato yield of 40 t ha-1; and the remaining seven variants with a PK dose plus plus increasing N amount from 30 to 210 kg ha-1. The results of the four-year experiment years indicated that an increase in nitrogen fertilizer rate up to N120 kg ha-1 increased the potato yield. Nitrogen fertilizer rates should be applied depending on potato variety and planned use of the grown potato crop. Tuber nitrogen content increased with nitrogen fertilizer level from 1.09% in the treatment N0PK up to 1.53% in treatment N120, and practically remained at that level in treatments with higher N application levels. Nitrogen content in potato foliage was twice as high as that in tubers and continuously increased with the N amount applied, and particularly with higher nitrogen fertilizer rates of N150-210. In regard only to tuber yield, the N utilization coefficient at a nitrogen fertilizer rate up to N120 was on average 0.60. A further increase in nitrogen rate reduced the N utilization coefficient with each successive step.

Wheat (Triticum aestivum) is one of the main crops grown in Latvia. Nitrogen fertilizer is one of the most important factors affecting the acquired yield and its quality. The aim of this paper is to describe the nitrogen fertilization impact on winter wheat yield and yield components under two soil tillage systems and after two forecrops. Field trials were carried out at Research and Study farm 'Peterlauki' of Latvia University of Agriculture (56° 30.658°C N and 23° 41.580°C E) in 2014/2015 and 2015/2016. Researched factors were (1) crop rotation (continuous wheat and wheat/oilseed rape (Brassica napus ssp. oleifera), (2) soil tillage (traditional soil tillage with mould-board ploughing at a depth of 22 -24 cm and reduced soil tillage with disc harrowing at a depth below 10 cm), and (3) nitrogen fertilizer rate (N0 or control, N60, N90, N120(90+30), N150(90+60), N180(90+60+30), N210(90+70+50), and N240(120+60+60). Results showed that the nitrogen fertilization significantly increased winter wheat grain yield after both forecrops and in both soil tillage variants. Grain yield significantly increased until the nitrogen fertilizer rate N180. Nitrogen fertilizer significantly affected all tested yield components. Values of yield components increased enhancing N-rate of N150 -N180. The forecrop had a significant impact on wheat yield and 1000 grain weight (both increased when wheat was sown after oilseed rape). Yield and grain number per ear were significantly higher when conventional tillage was used, but number of ears per m 2 -when the reduced tillage was used.

Abstract. Nitrogen management strategy in plant growth period based on chlorophyll content evaluation in plant can improve nitrogen usage efficiency and reduce environmental contamination. This study is aimed to determine the impact of different nitrogen and sulphur fertilizer rates on dynamics of chlorophyll content in winter wheat during vegetative growth and to determine the relationship between nitrogen and chlorophyll content and grain yield of winter wheat. Field trial involving a winter wheat (Triticum aestivum L.) variety 'Kranich' was conducted at the LUA Research and Study Farm Vecauce during a three-year period (2012)(2013)(2014)(2015). The treatments were 0, 85, 153, 175+S21, 175 (in 2015), 187 N kg ha -1 and different nitrogen norms according to chlorophyll meter Yara N-tester (Konica Minolta Ltd.) data: 180, 150, 205 N kg ha -1 depending on the year. The results of the trial show that the maximum chlorophyll content in different plant parts was observed at the end of flowering stage. The chlorophyll content depended on the level of mineral fertilisation. The highest chlorophyll content in leaves, stems and ears was obtained by using additional sulphur in two trial years. Usage of chlorophyll meter Yara N-tester obtained the highest chlorophyll content in all analyzed plant parts in one trial year. Chlorophyll content was significantly dependant on plant growth stage in stems in all trial years, in leaves in two trial years, and in ears in one year. Nitrogen fertilization significantly affected chlorophyll content in leaves and stems in one trial year. Close positive correlation was observed between grain yield and wheat plant chlorophyll content and average nitrogen concentration at the end of flowering stage in all three trial years.

Winter wheat is one of the most profitable crops in Latvia. Different growing technologies, including reduced soil tillage and continuous wheat sowing, have become more popular in recent years. The aim of this study was to characterise the development of winter wheat leaf diseases with respect to the soil tillage method and crop rotation under typical wheat growing conditions in the central region of Latvia. Experiments were carried out at the Pēterlauki Study and Research Farm of Latvia University of Agriculture in 2010, 2012 and 2013. Trials were conducted in two blocks: 1) conventional tillage with mouldboard ploughing at a depth of 22-23 cm and 2) reduced tillage with disc harrowing at a depth of 10-12 cm. Different crop rotations were established in each block, but crop sequences differed slightly depending on the year. Continuous wheat sowing and reduced soil tillage increased the level of tan spot infection, especially when these two factors were combined. The level of infection with Septoria leaf blotch was influenced by the soil tillage method and the year.

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