The paper describes the influence of long-term (more than 30 years) fertilizer and lime application on the soil acidity (pH Cl ) and identifies the influence of soil acidity on the productivity of crops. Since 1994, a seven-year crop rotation was created: (1) winter triticale → (2) potatoes → (3) spring wheat → (4) spring oilseed rape → (5) spring barley → (6) and (7) perennial grasses (red clover, timothy), 1 st and 2 nd year of use. At the beginning of the experiment, the soil in treatments F0 and F2 was very strongly acid (pH KCl 4.7) but in treatments F1 and F3 -moderately acid (pH KCl 5.6). In limed treatments the soil acidity decreased from pH 4.8 to pH 5.8-6.0. In the following years till 1994, the soil acidity in limed treatments gradually increased (for about 0.4-0.6 pH units). After the first maintenance liming, the soil acidity reached nearly the previous highest level. Within the next twenty years, in the treatments with highest liming rate (11.40 t ha -1 CaCO 3 ) the soil acidity increased to pH 5.2. In treatments with low liming rate (2.58 t ha -1 CaCO 3 ), the soil acidity increased to pH 4.6, which was even lower than at the beginning of the experiment (pH 4.8). Without maintenance liming, the soil acidity during 20 years increased by 0.7-0.8 pH units. In the unlimed treatments, the soil acidity gradually increased from pH 4.8 to 4.4.

Winter wheat (Triticum aestivum L.) leaf diseases is an important risk factor that influences the productivity and quality of wheat production. The aim of the present study was to review published scientific literature about the possibilities for integrated control of winter wheat leaf diseases. The most common and economically important wheat leaf diseases are Septoria leaf blotch (caused by Zymoseptoria tritici), tan spot (caused by Pyrenophora triticirepentis), yellow rust (caused by Puccinia striiformis), and powdery mildew (caused by Blumeria graminis). The severity of winter wheat diseases has varied significantly over the years and depended on meteorological conditions, variety resistance to pathogen, and tillage system. The crop rotation and an efficient residue management significantly decrease the development of tan spot. The development of Septoria leaf blotch mainly depends on meteorological conditions, but agronomic practice is less important. The use of disease-resistant varieties is the most economical, safe, and effective way to prevent and control wheat leaf diseases. Many European countries have a number of decision support systems for optimizing and minimizing the use of fungicides. Decision support systems are based on control thresholds and meteorological observations. Most used parameters are: air temperature, relative air humidity, and precipitation. These systems have been developed in the countries with a milder climate and a longer vegetation period than Latvia, and systems need to be adapted to Latvian conditions. The main groups of fungicides for disease control in winter wheat are azoles, strobilurin, and carboxamides. The results of many studies about the effectiveness of fungicide groups show that the obtained results differ and further research is needed.

Cereal crops are cultivated worldwide in diverse environments. In Latvia wheat (Triticum aestivum L.) is the most common cereals. One of the most important wheat quality indices are gluten quantity and quality. The aim of this experiment was to assess the effect of different farming systems (organic and conventional) on wet gluten and quality of four winter wheat cultivars and one grain line. Field investigation with winter wheat cultivars 'Fredis', 'Edvins', 'Skagen', 'SW Magnific' and line '94-5-N' were carried out within the framework of value for cultivation and use of plant variety testing system (VCU) at the Research Institute of Agronomy (in Skriveri) of Latvia University of Life Sciences and Technologies, in 2017/2018. Gluten content, index and water-binding capacity were significantly (p<0.05) affected by the agricultural production systems and cultivars. In our trial were found statistically significant differences among agricultural production systems. Significantly lower gluten content and water binding capacity had in organic winter wheat grains, while gluten was significantly stronger, compared to the conventional. A statistically significant (p<0.01) positive correlation was found between winter wheat gluten content and water-binding capacity (r=0.999) for both production systems. The cultivars 'Fredis' and 'Edvins' had better gluten content and water-binding capacity that make them more suitable for the organic production systems, compared to other cultivars.

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Lignosilicon (LSi), a plant growth activator, was synthesized at the Latvian State Institute of Wood Chemistry (LS IWC) on the basis of the wood lignocellulosic complex. It is shown that LSi, used for treatment of potato tubers before sowing at low application rates of 20-40 kg/ha, has a favourable action on the yield and quality of the tubers. In comparison with the control, the additional yield achieved on the background of LSi (20-40 kg/ha) was 18-20%. The best biochemical composition was for the tubers wetted with water and LSi-treated before the sowing, i.e., the content of dry matter and starch increased by 16% and 18%, respectively, but the content of nitrates in the tubers decreased 1.6 times. LSi can be recommended for potato cultivation under conditions of conventional and organic agriculture.