Effect of nitrogen fertilizer levels and their application time on yield and yield component of rapeseed in minimum tillage in paddyfieields of Guilan.

To determine the proper nitrogen fertilizer rates and its application time in minimum tillage method for achieving high grain and oil yields of rapeseed cultivar, Hyola 401, a research work was carried out at paddy fields of Rice Research Institute of Iran in Rasht during 2005-2007 cropping seasons. A factorial experiment was conducted in complete randomized block design with three replications. The first factor was pure nitrogen fertilizer rate at five levels of 0, 60, 120, 180 and 240 Kg ha-1 from urea source. Second factor was fertilizer application time at five levels of all fertilizer at planting; 1/3 at planting + 2/3 in stem elongation; 1/3 at planting + 1/3 in stem elongation + 1/3 before flowering; 1/3 in 3-4 leaf stages + 1/3 in stem elongation +1/3 before flowering; 1/4 at planting + 1/4 in 3-4 leaf stages + 1/4 in stem elongation + 1/4 before flowering. In this experiment, some important traits such as plant height, number of auxiliary branches per plant, number of seeds per siliques, 1000-seed weight, number of siliquess per plant, siliques length, oil percent, oil yield, grain yield, and some morphological charactristics were studied. The results of the combined analysis of variance showed that significant difference between different years for grain yield. The first year with an average grain yield ( 2082.4 Kg ha-1 ) was superior compared to the second year with average of 1735.5 Kg ha-1. Significant difference was also observed between nitrogen rates in the case of grain yield and application of 240 Kg N ha-1 and 180 Kg N ha-1 with average production of 2505 Kg ha-1 and 2596 Kg ha-1 respectively showed the highest grain yield and were in the same class. Nitrogen application time of 1/3 at planting, 1/3 in stem elongation and 1/3 before flowering had the highest grain and oil yields with average of 2155.3 Kg ha-1 and 9865 Kg ha-1, respectively and was in the class A. The interaction between nitrogen rates and application time was significant. Maximum oil percent was observed in control treatment (without N-fertilizer application) and the highest oil yield was for nitrogen rates of 180 and 240 Kg ha-1. Maximum 1000-seed weight was observed for the treatment of 240 Kg nitrogen and application time of 1/4 at planting, 1/4 at 3-4 leaf stage, 1/4 at stem elongation and 1/4 in before flowering. The highest growth period was observed for the treatment of 240 Kg nitrogen with 206.3 days. The results showed that nonsignificant difference exist between the nitrogen rates of 180 and 240 Kg ha-1 in grain and oil yields. Therefore, the rate of 180 Kg ha-1 is recomended due to less fertilizer consumption and prevention of destroying effect on the environment.