The effects of different drainage intensities on groundwater, runoff, nitrogen loss, N-use efficiency and yield under ley production in Western Norway

Abstract

Abstract. In 2013 a new experimental drainage field was constructed near Askvoll, located in Western Norway. The site was chosen as it consists of soil types being representative for many agricultural areas along the coast in Western Norway. The main objective of the experimental field was to investigate the effect of a subsurface drainage system on yield, runoff and nitrogen loss, nitrogen use efficiency and trafficability of ley production along the western coast of Norway and as such provide detailed information/knowledge about drainage criteria under present condition but not least under future condition with climate change. The experiment consists of four alternatives each having 4 subsurface drains. Two alternatives have a drain spacing of 6 m while the remaining two alternatives have a drain spacing of 12 m. Each of the 4 plots is divided into two subplots with two and three ley harvest respectively and two different levels of fertilizer application, being 190 and 290 kg ha 1 nitrogen(N) respectively. The first results indicated that both drainage alternatives function satisfactorily. The measurements indicate that a part of the excess precipitation passes the subsurface drainage system towards the groundwater which implies also drainage of excess nitrogen towards the groundwater. The observations at Askvoll show large diurnal variations in discharge resulting in a significant difference in flashiness index (FI) when using hourly or average daily discharge values. The FI-values indicate that a narrower drain spacing has a higher FI, and thereby faster response to excess precipitation compared to a larger spacing.