Effect of Lolium perenne population differences on shoot tissue nitrogen concentrations when grown on a peat soil.

Grass nitrogen (N) concentrations of dairy grasslands are higher on peat soil than on mineral soils. This can lead to increased N losses to air and water from dairy farming systems on peat soils. Our hypothesis was that the use of low-N perennial ryegrass (Lolium perenne L.) genotypes could be a means to lower grass N concentrations, when grown on peat soils. Our objective was to determine whether perennial ryegrass populations with different shoot tissue N concentrations, recorded on a sandy soil, would show different shoot tissue N concentrations and N use efficiencies (NUE) or N uptake efficiencies (NUptE) when grown on a peat soil. First, a pot experiment lasting 62 days was carried out with nine diploid and seven tetraploid populations, followed by a field experiment with two diploid and two tetraploid populations and a control lasting 30 months. Both experiments had three N fertilization levels. In the pot experiment, populations explained 3% of the variation in shoot tissue N concentration among tetraploids, 5 and 7% of the variation in NUE among diploids and tetraploids and 12% of the variation in NUptE among diploids. In the field experiment, populations explained 44% of the variation in NUptE. A higher NUE coincided with lower shoot tissue N concentrations among tetraploid populations in the pot experiment. We conclude that there is potential to alter the shoot tissue N concentrations of perennial ryegrass grown on peat soil, via selection for shoot tissue N concentrations and NUE. [ABSTRACT FROM AUTHOR]