The yield and quality (volume weight, 1000 kernel weight, protein content, falling number, gluten content, gluten index, gluten content in dry matter) of winter wheat was studied in variety 'Portal'. The wheat was part of the five-year crop rotation experiment where red clover (Trifolium pratense L.), winter wheat (Triticum aestivum L.), peas (Pisum sativum L.), potato (Solanum 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 variant, on the background of P25 and K95 kg haE-1 the N amount varied from 0 to 150 kg haE-1 and herbicide Mustang (preparation norm 0.5 L haE-1, active substance florasulam, 6.25 g LE-1; 2.4-D, 300 g LE-1), insecticide Fastac 50 (preparation norm 0.2 L haE-1, active substance 50 g LE-1 alphacypermethrin) fungicide Falcon EC 460 (preparation norm 0.4 L haE-1, active substances 167 g tebuconazole, 250 g spiroxamine, 43 g triadimenol) and growth regulator Moddus (preparation norm 0.4 L haE-1, active substance 250 g LE-1 trinexapac-ethyl) were used. In conversion to organic the winter wheat grains which followed the red clovers after effect had higher volume weight, 1000 kernel weight and gluten index compared to the variants where mineral fertilizers were used. The yield, protein content, falling number and gluten content in dry matter increased with increase of the amount of mineral N. The wet gluten content was significantly higher compared to the other variants where the N amount was 50 kg haE-1.

After regaining independence the agricultural production in Estonia has undergone a drastic decline. Due to the inadequate application of fertilizers and pesticides, the yield of field crops and grasslands has decreased 1-7 % per year. The balance of nitrogen in the arable soils is negative, particularly respecting fodder crops. At present, in Estonia most of grasslands are practically not fertilized, or they are fertilized in the last order. The amount of nitrogen removed with the yield of fodder crops, cereals and potato are by 45, 20 and 17 kg ha*[-1) higher, respectively, compared with the amounts of N applied to the soil with organic and mineral fertilizers, available for those crops. The effectiveness of nitrogen fertilizers depends largely on weather conditions during the vegetation period and is the lower, the higher is soil humus content. On gleyic and gley soils, whose humus content is higher, the efficiency of nitrogen fertilizers is 2-3 times lower and the agroecological and economic fertilization risks are higher. On sown grasslands, the efficiency of nitrogen fertilizers depends not so much on soil fertility as on soil water supply, humus content and grass sward type. With proper application of fertilizers, use of suitable plant species and varieties, it is possible to increase significantly not only the yield per unit area but also its nutritive value.