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

In a field experiment 60 kg N ha-1 of 15N-labelled fertilizer was applied to Miscanthusxgiganteus 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