EFFECTS OF CROPPING SYSTEM AND RATES OF NITROGEN IN ANIMAL SLURRY ANDMINERAL FERTILIZER ON NITRATE LEACHING FROM A SANDY LOAM

Leaching of nitrate from a sandy loam cropped with spring barley, wint er wheat and grass was compared in a 4-year lysimeter study. Crops wer e grown continuously or in a sequence including sugarbeet. Lysimeters were unfertilized or supplied with equivalent amounts of inorganic nit rogen in calcium ammonium nitrate (CAN) or animal slurry according to recommended rates (1N) or 50% above recommended rates (1.5N). Compared with unfertilized crops, leaching of nitrate increased only slightly when 1N (CAN) was added. Successive annual additions of 1.5N (CAN) or IN and 1.5N (animal slurry) caused the cumulative loss of nitrate to i ncrease significantly. More nitrate was leached after application of s lurry because organic nitrogen in the slurry was mineralized. With IN (CAN) the leaching losses of nitrate were in the following order: cont inuous spring barley undersown with Italian ryegrass < continuous ley of perennial ryegrass < spring barley in rotation and undersown with g rass < perennial ryegrass grown in rotation = winter wheat grown in ro tation < sugarbeet in rotation < continuous winter wheat < continuous barley < bare fallow. At recommended levels of CAN (1N), cumulative ni trate losses over the four years were similar for the crops when grown in rotation or continuously. When crops received 1:5N (CAN) or animal slurry, nitrate losses from the crops grown continuously exceeded tho se from crops in rotation. Including a catch crop in the continuous cr opping system eliminated the differences in nitrate leaching between t he two cropping systems.