А. Г. Дзюин The problem of increasing soil fertility is one of the main tasks of agriculture in the Udmurt Republic and the Non-Chernozem region. The most acceptable way of solving this problem is biologisation, which provides for a decrease in the amount of chemicals and an increase in the amount of biologicalagents. If there is a lack of fertiliser, the use of green manure or straw alone will not solve the problem. On acidic soils, a complex action on the soil is needed, starting with liming and the use of optimal doses of mineral fertiliser, which help to increase land productivity and crop rotation in a short period of time. Since 1971, the Udmurt Research Institute of Agriculture has been studying different fertilizer systems in 8-field crop rotations (1 – fallow; 2 – winter rye; 3 – potato, corn; 4 – spring wheat; 5 – clover; 6 – clover; 7 – winter rye; 8 – barley). Factor A are backgrounds: 0 – “zero” [10]; I 2 – lime per one hydrolytic acidity (4.9 t/ha CaCO 3 ) in the first rotation + two hydrolytic acidities (7.5 t/ha) in the second rotation; Н 5 С – manure 40 (first rotation) + 60 t/ha (2d‑5th rotations) + green manure (6th rotation); L 2 M 5 GM – lime + manure + green manure similarly. Factor B are options. Options without fertiliser and NPK are considered. Lime reduced soil acidity to a neutral level, slightly increased in the 4th rotation. The content of P 2 O 5 , K 2 O, and humus reached the highest level in the 5th rotation on manured backgrounds, resulting in 3.23 and 3.31 tce/ha in six rotations (18.3 and 22.0% more than without fertiliser). In lime and manure systems, mineral fertiliser increased crop rotation productivity by 32.4–35.7% on average over the entire period. Optimal doses for 3.0–4.0 t grain units/ha were 40–50 kg NPK/ha. Reducing the doses from 40–60 to 10–30 kg/ha of NPK in the last two rotations led to a decrease in crop rotation productivity (2.74–2.84) by 0.41–0.49 t grain units /ha. The lime-organomineral fertiliser system in the 3d, 4th and 5th rotations with “the addition of micronutrient fertiliser (zinc for winter rye, cobalt for potatoes, copper for spring wheat and barley, boron and molybdenum for clover)” [9] provided the highest crop rotation productivity – 4.67; 4.25; 3.32 t grain units/ha, with the highest increases – 2.05; 1.12; 1.05 t grain units/ha or 78.2; 35.8; 46.2%, respectively, in rotations. Manure can only be replaced periodically with a pea-oat mixture.
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