Weed density in the spring rape crops sown at different dates

Abstract

In 2015, a statistically significant relationship was established between the dry matter mass of weeds and rapeseed yield (r = −0.84, P < 0.001). A statistically significant correlation was also determined between the length of the period from oilseed rape sowing to complete maturity and dry matter mass of weeds (r = −0.89, P < 0.01). In 2016, no statistically significant correlations were found between the weed incidence in the spring oilseed rape crop and rapeseed yield. The climate warming and earlier beginning of the vegetation period have enabled earlier sowing of agricultural crops. Sowing date can affect weed density in crops, including spring oilseed rape. Field experiments were carried out in 2015 and 2016 at the Experimental Station of Aleksandras Stulginskis University. The soil of the experimental site is Calc(ar)i-Endohypogleyic Luvisol (LVg-n-w-cc). The aim of the investigation was to evaluate the response of weed density in spring oilseed crop to the sowing date. In 2015, the first sowing date was 15 April. Afterwards the sowing was performed every 5 days until 20 May. In 2016, the first sowing date was 10 April. Afterwards the sowing was performed every 5 days until 25 May (except for the 7th and 8th sowing date, the interval between which was 10 days because of the adverse weather conditions). The number of weed seedlings and the number of weeds before harvesting differed between the experimental years. In 2015, with a delay in spring oilseed sowing until 5 May, the number of weed seedlings decreased. The highest number of weed seedlings was recorded in the plots sown on 10 May, and later it declined. In 2016, a 10–15 day delay in sowing resulted in significantly the highest number of emerged weeds, and in the plots sown at later dates the number of weeds inconsistently decreased. In 2015, with a delay in spring oilseed rape sowing until 20 May, the number of weeds before harvesting had decreased by 67.8%. In the crops sown on 30 April and at later dates, the dry mass of weeds before harvesting increased from 2.7 to 27.1 times in the crop sown at the last sowing date and had significant effect on rapeseed yield. In 2016, significantly the lowest number and dry mass of weeds were established in the crops sown at the earliest dates (10 and 15 April) and in those sown at the latest dates (10, 20 and 25 May).