THE EFFECTS OF NITROGEN-FERTILIZER RATE, CULTIVATION AND STRAW DISPOSAL ON THE NITRATE LEACHING FROM A SHALLOW LIMESTONE SOIL CROPPED WITH WINTER BARLEY

Monoculture winter barley was grown for 5 years with 80 or 160 kg/ha o f fertilizer nitrogen (N) and established by either shallow cultivatio n (straw removed) or ploughing (straw incorporated) in a replicated 2 x 2 split plot experiment. The lower N rate reduced average grain yiel d from 6.85 t/ha to 5.61 t/ha. The cultivation/straw disposal system h ad no effect on yield. Halving the N rate reduced the amount of N remo ved in the crop by an average of 40 kg/ha and reduced the amount of ni trogen leached by 11 kg/ha per year. Using a shallow cultivation syste m for crop establishment, following the removal of straw; initially re duced N leaching compared to ploughing in the straw, but in the later years of the experiment losses were similar. Over the five years the f ull N rate with ploughing system resulted in a small positive nitrogen balance of 66 kg/ha, but all other treatment combinations resulted in a negative balance.