The recovery over several seasons of 15N-labelled fertilizer applied to Miscanthus×giganteus ranging from 1 to 3 years old

In a field experiment 60 kg N ha−1 of 15N-labelled fertilizer was applied to Miscanthus×giganteus planted 1, 2 or 3 years previously. Plots were destructively sampled at senescence 1, 2 or 3 years after labelled N was applied with aerial biomass harvested in intervening years. The objective was to quantify N uptake and distribution within the plant, labelled N remaining in the soil (0–50 cm) and overall losses. We report results for the 2nd and 3rd years and compare them to 1st year data previously published. Total biomass more than doubled over 2 years of growth but N concentration did not change. More labelled N was recovered by 3-year-old plants (65%) than by 2-year-old plants (55%) or 1-year-old plants (38%). Between 19% and 26% was found in the soil (0–50 cm) and more than 85% of this N was in topsoil (0–23 cm). Total recovery in plant and soil was 60–71% for 1-year-old plants, 76–81% for 2-year-old plants and 84% for 3-year-old plants. Overall losses (18–24%) from 2- and 3-year-old plants are similar to those from arable and permanent grass crops on the same soil type given similar amounts of N. Labelled (and unlabelled) N stored in rhizomes will take several years to decline because of transfers between rhizomes and shoots. Similarly, labelled N remaining in soil will decline slowly over many years; any N mineralized in subsequent years will be subject to plant uptake and/or loss.