Yield formation of soybean as influenced by conventional and reduced tillage | Formovanie úrody sóje fazuľovej v závislosti od klasického a redukovaného systému obrábania pôdy

The effect of two tillage systems on alluvial soil at the research locality of Vysoká nad Uhom (110 m a.s.l.) and on gleyey alluvial soil at the locality of Milhostov (101 m a.s.l.) in the trial years of 2003-2005 was tested. Conventional tillage - stubble cleaning, autumnal ploughing to the depth of 250 mm, spring seedbed preparation by combined tillage implement followed by drilling and reduced tillage - spring shallow cultivation to the depth of 100 mm by a stubble cultivator followed by drilling were used in the trial. The Canadian variety Korada was chosen for this trial. The seeding rate was set at 650,000 viable seeds per ha. Fertilizer doses of 25 kg per ha N, 50 kg per ha P and 80 kg per ha K were applied in spring every year. The trial was organized in a complete randomized block design with four replicates. The trial plot had an area of 50 sqm (5x10 m). The collected data - seed yield, thousand seed weight (TSW), and seed number per sqm were subjected to the ANOVA and the LSD test using Statgraphics. Seed yields affected by the tillage system, the soil type, and the trial year were in a wide range from 2.75 to 4.85 t per ha with the variability of 76.4%. The tillage system highly significantly affected the seed yield, whereas the affect of the trial year was just significant. The influence of the soil type was not significant. The order of their influence was as follows: the tillage system - 91.4%, the trial year - 5.3%, and finally the soil type - 3.1%. The difference in the seed yield between the tillage systems was 0.80 t per ha (23.9%) on average in favour of the conventional tillage. Relatively lower seed yield difference between the tillage systems found on gleyey alluvial soil - 0.42 t per ha (12.1%) revealed the fact that this soil type is more suitable for both tested tillage systems in contrast to alluvial soil, where yield difference was very high - 1.17 t per ha (36.1%). Owing to these findings, conventional tillage can be recommended only for the use on alluvial soil. TSW was highly significantly affected by the trial year - 82.7%, followed by the tillage system, also with highly significant influence - 15.7% influence of all tested factors. The soil type affected TSW insignificantly. The most important factor affecting seed number per sqm highly significantly was trial year - 66.8%, followed by tillage system also with highly significant influence - 33.0% influence of all tested factors. The soil type influence on the seed number per sqm was not significant. The risk of the yield depression caused by unfavourable weather conditions during the growing season can be decreased by choosing the right combination of soil type and tillage system.