The recovery of 15N-labelled fertilizer applied to Miscanthus × giganteus

Miscanthus is a perennial, rhizomatous grass which has potential for use in Europe as a biofuel crop. Little is known of its fertilizer nitrogen (N) requirements. To better understand the cycling of N within the crop-soil system, a field experiment is being conducted in which 60 kg ha−1 of 15N-labelled fertilizer is being added to Miscanthus plants of different ages. Results reported here are for the recovery, after one growing season, of labelled N applied to one-year-old plants. Harvestable product totalled 7.7 t ha−1 dry matter. Below ground, the rhizome and root mass increased by 6.2 t ha−1 compared to the previous year. The crop took up 117 kg ha−1 N during the year, of which only 23 kg ha−1 was derived from the labelled fertilizer. Most of this was found in the rhizome plus roots; only 14% of the applied N (36% of the total N taken up) was removed in the harvested crop. At harvest, 20% of the applied N remained in the topsoil (0–23 cm) and < 3% was found in the 23–50 cm layer. Almost 40% of the labelled N was lost from the crop-soil system. It seems likely that this loss was by denitrification soon after fertilizer application or by ammonia volatilization from the crop, particularly during senescence. The data indicates that year-old Miscanthus has a low requirement for fertilizer N. In time, information will be available on how effectively fertilizer N is used by more mature plants.