Seasonal pattern of nitrate losses from cultivated soil with subsurface drainage

Subsurface drainage systems have been installed in about 10000 ha of agricultural land in the flat part of the Emilia-Romagna Region in northern Italy. Nitrate loss in drainage water from a representative farm in this area was measured for three consecutive years (1986, 1987, 1988). During this period a total of 369 water samples were collected, filtered at 0.45 µm and analyzed. The nitrate concentration exceeded the limits for surface water set by Italian law regarding water pollution (90 mg NO₃ ^?L^?1 = 20 mg N L^?1) in 84% of the samples. The greatest nitrate loss was recorded during the winter and early spring when drainage was high. After this period loss of nitrate, via drainage water, progressively decreased. This was attributed to a decrease in the amount of drainage water and increase in crop uptake of N. The average annual nitrate loss via drainage water was around 200 kg of NO _inf3 ^sup? ha^?1. Annual nitrate losses of this order of magnitude (? 50 kg N ha^?1) indicate an urgent need for implementation of management practices directed towards achieving considerable reductions in these losses.