Evaluation of different planting dates on quantitative and qualitative yield of four rapeseed (Brassica napus L.) cultivars in Jiroft

Introduction
Rapeseed (Brassica napus L.) is one of the most important oily seeds that can be planted under different climatic conditions of Iran (Koocheki & Khajehossini, 2008). One of the factors affecting the performance of rapeseed is planting date. Determining the response of different varieties of crops to environmental variables from planting to harvest is one of the basic principles of agricultural planning in order to achieve maximum yield and quality. Delay in planting results in prolonged grain filling period and high temperature. These conditions result in a decrease in grain yield (Ehshamami et al., 2016). Saberi and Arazmjo (2015) in the study of the effect of planting date on yield and some of agronomic traits of five rapeseed cultivars in Birjand region observed that the cultivars that flowered at the right time produced more pods per plant and had higher seed weight than other cultivars.
Materials and Methods
A field experiment was conducted at the experimental station of Faculty of Agriculture, University of Jiroft (latitude: 28°40´ N; longitude: 57°44´ E; elevation: 650 m) in the growing season of 2016-2017. A split plot layout with a randomized complete block design with three replications was used. The main plots were sowing date at six levels of November 1st, 15th and 29th, December 15th and 27th and January 10th, Rapeseed cultivars were Hyola, Agamax, Traper and Delgan as the sub plot. Each plot was 3×6 m2 and the cultivars were sown in 30 cm intra-rows and 6 cm inter-rows. During the growing season, hand weeding was performed for several times. Drip system was used for irrigation. After harvest, the following traits were measured; number of pods per plant, pod weight per plant, number of seeds per pod, pod length, 1000 seed weight, seed yield, biomass yield, harvest index, protein yield and oil yield. Soxhlet method was used to measure oil content and Kjeldahl method was used to measure protein.

Results and Discussion
The results showed that planting date had a significant effect on all traits (p < 0.05). Interaction effect of planting date × cultivar was significant in the studied traits except for pod length and harvest index. The highest number of pods per plant (52.42), number of seeds per pod (30.96), grain yield (1613.3 kg ha-1), protein yield (234.3 kg / ha-1) and oil yield (68 / 826 kg ha-1) was achieved at the planting date of November 29th with Agamax cultivar. The planting dates of November 1st and 29th produced the highest pod weight per plant of 3.1 g and 1.34 g in Agamax cultivar and of 1.28 g in Teraper cultivar, respectively. The highest 1000-seed weight was observed in Delgan cultivar (5.58 g) at the planting date of November 29th which was followed by Agamax cultivar (3.6 g) at the planting date of November 1st. The highest seed and biomass yield at the planting dates of November 1st, 15th and 29th was recorded with Agamax cultivar, which averaged 6500, 6463.3 and 7043.3 kg/ha, respectively. The highest oil and protein yield was related to Agamax cultivar on November 29th and the lowest protein yield was observed with Dalgan on December 13th. The results of this study were similar to Ehshamami et al., 2016.
Conclusion
In general, the results of this study showed that planting date had a significant effect on phenological and morphological attributes, oil and protein yields of the rapeseed cultivars. Changes in rapeseed planting date made the plant developmental stages encounter different ecological factors that consequently affected the production of this crop. Delay in planting resulted in the loss of suitable growing conditions and the failure of the crop to reach its potential. Also, delay in planting caused the grain filling period and the accumulation of oil to coincide with higher temperatures, which led to a decrease in seed, oil, and protein yields. Also, according to the climatic conditions of the region during the 2016-2017 growing season, the most appropriate date for sowing of rapeseed in Jiroft was November 29th. The planting dates of December 27th and January 10th were considered inappropriate as the cultivars failed to enter reproductive phase. Based on our results, the most suitable cultivar for cultivation in the region was Agamax.