Sowing date and N application effects on tap root and above-ground dry matter of winter oilseed rape in autumn

Abstract

Abstract In many parts of Europe, farmers often replace winter barley by winter wheat as preceding crop for winter oilseed rape (WOSR) resulting in a delayed WOSR sowing and poor autumn growth. Based on data from a field trial running in 2009/10, 2010/1l, and 2012/13, this study aims i) to investigate how a delayed sowing impairs autumnal above-ground and tap root growth of winter WOSR and ii) to test the ability of an additional N supply in autumn to compensate for the negative effects of an unfavorable sowing date. In order to create sufficiently differentiated canopies, 4 sowing dates (first decade of August till the third decade of September) and 4 autumn N treatments (0, 30, 60, and 90 kg N ha−1) combined. Above-ground and tap root dry matter (DM) as well as green area index (GAI) were determined in autumn. On average of the three years, delaying sowing date significantly decreased above-ground and tap root DM accumulation and GAI of oilseed rape at the end of autumn growth. The reduction in tap root DM was more pronounced compared to that in above-ground DM. N supply in autumn significantly boosted above-ground and tap root DM. However, the N effect was less distinct compared to that of the sowing date. Green area of all autumn N treatments increased according to a logistic function, reaching its maximum at a thermal time (Tbase = 3 °C) of about 650°d. N supply in autumn significantly enhanced GAI formation. The current results clearly revealed that a delayed sowing date of OSR decreased both the above-ground and tap root DM. An additional N supply was only partly able to compensate for a poor autumn growth, especially that of the tap root.