THE EFFECT OF SOIL CULTIVATION AND FORECROP ON THE REDUCTION OF THE WINTER-WHEAT YIELD BY FOOT AND ROOT-ROT DISEASES OF WINTER-WHEAT

In two crop rotations with 50 per cent representation of cereals (two times lucerne - two times winter wheat; two times grain maize - two times winter wheat) established at Hrusovany u Brna (maize-growing region, Chernozem), three systems of soil cultivation were applied to cereals. The first one - the soil was cultivated in traditional way to the depth of 0.20 to O.22 m (I), the second one - shallow to the depth of 0.12 to 0.15 m (II) and in the third one - cereals were seeded into untreated soil (III). Tillage to the root crops and ploughing-in of lucerne were conducted uniformly. In the years 1984 to 1988, the yield and wheat infestation with the foot and root rot diseases (Pseudocercosporcella herpotrichoides and Gaemannomyces graminis). The infestation was expressed through the index of infestation (Nilsson, 1969 : I % = 25.N-1.(f1.ni), where: N - number of analyzed plants; fi - number of stems (roots) infested with the degree of infestation under question; ni - rate of infestation (0 healthy, 4 - completely damaged). The loss of the yield was expressed by the sum of losses in the grain weight from the particular infested stems (plants). The individual rates of infestation were determined in per cent as follows (Herman, 1988): [GRAPHICS] The year was found to be the most important factor influencing the yields in the studied period. The winter wheat yield fluctuated between 4.87 t per 1 ha and 7.1 t per 1 ha. The lowest yield recorded in 1986 is linked up with bad weather conditions in autumn of the preceding year when some stands were ploughed-in for bad conditions (Tab. I). The selection of soil cultivation and the crop rotation had no effect on the level of the yield, except the year 1988 after two maize rotations - winter wheat, when slightly higher yield was obtained after shallow soil cultivation in comparison with the variant no-tillage of soil. Winter wheat plant infestation with eyespot was affected with soil cultivation only meaningless (spreading through conidia), though a forecrop played a more important role (Tab. II). Average infestation 5 (I %) was reached after the rotation maize-maize, after other less favourable rotations this was several times higher. In the rotations with lucerne, the infestation was always stronger than in rotations with maize. The dependence of expansion of the disease on soil cultivation was confirmed in take all. After traditional soil cultivation, the infestation (I %) was 7.7 on an average, after shallow cultivation, this was 6.3 and after seeding into uncultivated soil - only 5.6 (Tab. III). The loss of the yield caused by infestation reached even 6 % (average for 1988). The soil cultivation shared less in this loss, the more marked was the effect of a forecrop (Tab. IV). After the rotation maize - maize, the loss was only 1 %, after the rotation - two times lucerne - wheat 5.5 %. The losses determined in this way are significant for economic reasons. This is only a part of losses of yields, as the plants and shoots dead till the time of harvest are not included.