Effect of seeding rate and seeding date on creation of yield of selected winter oilseed rape varieties and hybrids

The aim of the experiment, realized at the Research Institute of Plant Production Piešťany, was to determine the effect of different seeding rates and seeding dates on agricultural productivity of selected winter rape (Brassica napus L. var. napus) varieties. The field trials took place in the years 2003, 2004, and 2005, in the maize production area of south-western part of the Slovak Republic at altitude of 167 m, with the average annual temperatures of 9.2 degree C, and the average annual sum of rainfall 595 mm. The soil is loamy luvic chernozem with pH 5.5 - 7.2. The experiment was conducted with the aim to evaluate a yield production of chosen varieties and hybrids of winter rape and to define the limit number of plants, which winter rape is able to compensate by the increased production of generative organs. The influence of various seeding rates and terms of seeding was examined. In the experiment, the following factors affecting the yield and yield components of winter rape were estimated: - variety: hybrids Artus and Fanal, line varieties Linfort and Rasmus, - seeding rate: 0.3 - 0.4 - 0.6 - 0.8 millions of germinable seeds per hectare, - seeding date: agronomical seeding term (variant AT) and agronomical seeding term delayed 20 days (variant AT+20), - years: 2003, 2004, 2005. The results showed that the seeding rate did not have any influence on yield. The seeding term delayed by 20 days after agronomical seeding term caused a large reduction in yield. Variety had a significant influence on yield. The line variety Linfort achieved the lowest yield, on average, in both monitored terms of seeding. Hybrid Fanal achieved the highest yield, on average, from the monitored set and also had the highest degree of tolerance to the delayed terms of seeding. By using the agronomical term of seeding, Artus turned out to be the most fertile hybrid. It can be said that the line variety Rasmus achieved the yield on the level of hybrids, when the seeding in time was used. The amount of seeding rate only had a little influence on yield, but significant interaction between seeding rate and variety points out a positive response of Artus variety to 0.8 million of germinable seeds seeding rate and Fanal variety to the lowest seeding rate used. The amount of yield was significantly influenced by weather conditions in a particular year. The most crucial was the period of establishment and germination of plants, and winter season. Taking into account the previous, 2002/2003 was the most critical season, since the extreme weather conditions decreased the yield to 0.56 t. per ha. When the yield of winter oilseed rape is formed, there appear mutual compensating relations among the number of plants, number of siliques and their arrangement on the plant, number of seeds per silique and weight of thousand seeds. With increasing number of plants per unit area the number of siliques per plant declines. The plants growing in the rape stand with a higher number of plants per unit area had a smaller number of siliques on an apical branch than on the secondary branches. Varieties with the highest number of siliques per plant had the lowest number of seeds per silique, but with a delayed date of seeding the value of this attribute decreased as well. Decreasing number of siliques per plant caused the increase of thousand seed weight.