Effects of high nitrogen application on the dry matter yield, nitrogen content and nitrate-N concentration of sugarcane

In Japan a high dependency on imported food, particularly livestock feed, has resulted in the accumulation of large amounts of nutrients, especially nitrogen, in the form of livestock manure. Cultivating feed crops that can take up a large amount of N would not only mitigate the water pollution caused by the nitrate leached from the livestock sector, but would also improve food self sufficiency. Sugarcane (Saccharum spp.) is considered to be a promising candidate in this respect. Two field experiments were conducted in 2006 and 2007 in Kagawa to evaluate the dry matter (DM) yield, N content and nitrate-N concentration of sugarcane under high N input. The first experiment was designed as a factorial experiment with two factors, varieties/lines/clones and N rates set at two levels, 30 g m(-2) year(-1) and 60 g m(-1) year(-1), with three replicates. In the second experiment, 30 varieties/lines/clones of sugarcane and related genera as well as control crops were planted (n = 2) and a single N rate of 45 g m(-2) year(-1) was applied. Some varieties/lines of sugarcane produced an above-ground DM yield greater than 4.0 kg m(-2) and contained more than 40 g m(-2) of N in the above-ground part. Erianthus clones, IK76-126 and IJ76-349 tended to accumulate nitrate-N when high rates of N were applied. No sugarcane varieties out of the 28 varieties/lines tested in the present study accumulated nitrate-N beyond the allowed limit for feed use, irrespective of the N rates tested in the experiments. The ability of sugarcane not to accumulate nitrate-N under conditions of high N input was considered to be an advantage in double-purpose cultivation; that is, sugarcane can be used as a feed and cleaning crop.