DISCUSSION
Mechanical harvesting effects on seed yield loss
and quality traits
In this study, seed yield in 2009-2010 was higher than
that in 2010-2011, it was perhaps caused by late sowing
in 2010 and stressed by higher temperature after
flowering in 2011, so growth period was shortened and
the yield was declined as well. It was interesting to
note that the seed loss in 2010-2011 was lower than
that in 2009-2010, the reason perhaps lied in the dry
weather and low disease occurrence at maturity in 2011,
which was amenable to mechanical harvesting. Previous
studies have proved that seed loss of rapeseed
dropped 5-10% when direct harvesting with a combine
harvester (Price et al. 1996; Špokas et al. 2004). In
this study, the minimum seed loss happened in CHB.
One of the important reasons was attributed to high
pod shattering resistance of Zhongshuang 11. In another
experiment with different cultivars, the pod shattering
resistance index of Zhongshuang 11 and the control
cultivar Deyou 16 was 0.85 and 0.21, as well as
the harvesting loss rate was 5.7 and 15.7%, respectively.
It indicated that high pod shattering resistance could
help greatly to decrease seed loss of rapeseed.
Additionally, although 20% of brown and green seeds
were harvested in CHB, little negative effect on seed oil
content was happened, suggesting that Zhongshuang
11 could be harvested earlier.
A certain optimal level of moisture content for seeds
and stalks was available to decreasing seed loss and
damage during harvesting with combine harvester
(Mohammad et al. 2007). It was shown that moisture
content of seeds at 11 to 15% was reasonable (Szwed
and ukaszuk 2007). Our results indicated that the
optimum moisture content of seeds and stalks was 20
and 70%, respectively, which were a little lower than
the reports before (Mohammad et al. 2007). Present
study showed that CH time for winter oilseed rape could
be determined by two methods, one was the color of
pods and seeds as above description, the other was the
moisture contents of stalks and seeds.