THE COMBINED EFFECT OF MINERAL FERTILIZERS AND MEADOW CLOVER ON THE PRODUCTIVITY OF FORAGE CROPS IN CROP ROTATIONS IN THE BAIKAL REGION
The studies were conducted in the test field of the Irkutsk SRIA, on the average for two years, on three five-course fodder crop rotations. One of them was without clover and fertilizers, the second one - with 20 % clover saturation, the third one - with 40 % clover saturation used for one year. In the phase of full blossoming, the fodder mass of clover was harvested for haylage. A clover-free rotation had three fields of grain forages, two fields of silage. In the second crop rotation, clover of one-year use and corn took one year each, and three fields of grain forages. In the third one, two fields were taken by clover, corn, pea-oats for silage and barley took one field each. The observations were carried out on three backgrounds of fertilizers: without fertilizers, the first background (the average level of fertilizers), under corn N60P30K30, grain forages N45P30K30, annual crops and clover N40, the second recommended level under corn N90P40K40, grain forages N60P30K30, annual crops N60, clover N40.The results of our research have shown that, on the average for two years, the productivity of a five-course fodder crop rotation without clover and fertilizers was 2.20 t/ha of f.un. With application of fertilizers under the crops of the first background the productivity grew to 2.84 t/ha, or by 29 %, and the second background - by 41.3 %. Due to fertilizers, the protein content in 1 f.un. rose from 88.4 to 98.2 g. Introduced with one field of clover (20 %) to this crop rotation, the yield and the protein content in feed increased. Without application of fertilizers the yield raised by 0.26 t/ha of f.un., or by 11.8 % from 1 ha of rotational area. When applied with mineral fertilizers (the first background), the yield from 1 ha of rotational area rose to 3.14 t/haof f.un., or by 27.6 %. Further growth of fertilizer rates (background 2) gave the yield increment from 1 ha of rotational area 39.0 % and the higher protein content in 1 f.un. up to 102.0 g. Saturated with 40 % red clover, 20 % corn, 20 % pea-oats for green forage, haylage and 20 % barley, the productivity amounted to 2.85 t/ha, or grew by 29.5 %, without application of fertilizers. The reduction of mineral fertilizers in crops of the rotation with 40 % clover saturation is clarified by nitric fixation of biological nitrogen by clover. When placing forages and grains in crop rotations along the clover layer, the corn yield raised due only to biological nitrogen from 2.60 t/ha of f.un. to 3.93 t/ha of f.un., pea-oats - from 2.31 to 3.04 t/ha of f.un., barley - from 1.47 to 2.46 t/ha of f.un. Compared to the crop rotation without clover and fertilizers, 20 % clover saturation increased the productivity of 1 ha of rotational area by 11,8 %, and 40 % clover saturation - by 29.5 % thanks to biological nitrogen. On the whole, on all fertilization backgrounds, forage crops in terms of productivity in the system of fodder crop rotations exceeded grain forage crops