Demand-driven fertilization. Part I: Nitrogen productivity in four high-maintenance turf grass species

The effect of four nitrogen (N) availabilities on growth, leaf N concentration, N productivity (dry matter production per unit time and unit N taken up), shoot: root ratio and carbohydrate storage was studied in velvet bentgrass (Agrostis canina 'Legendary'), creeping bentgrass (A. stolonifera 'Independence'), slender creeping red fescue (Festuca rubra ssp. trichophylla 'Cezanne') and chewings fescue (F. rubra ssp. commutata 'Center'). In growth chamber experiments, plants were grown for 3 weeks in sand with 12.5, 25, 50 or 200 mg N L-1 in the irrigation water and at two mowing intensities, cut at 5 mm twice per week or uncut. It proved possible to control important turf grass traits such as shoot growth rate, shoot: root ratio, leaf morphology and carbohydrate storage through leaf N concentration. The relationship between leaf N concentration and aboveground growth was linear for both cut and uncut turf. The relative N demand of the studied species, based on their N productivity, was 1: 0.67: 0.67: 0.37 for creeping bentgrass, velvet bentgrass, chewings fescue and slender creeping red fescue, respectively. Clipping significantly reduced N productivity, and hence turf N demand. The lowest possible leaf N concentration without adverse effects on plant health and appearance was between 3.1 and 3.5% of dry matter (DM) in both bentgrasses and fescues. This value can be used as a target in minimizing fertilizer usage and N leaching losses. In conclusion, fertilization based on the influence of leaf N concentration on growth-related processes offers possibilities to control growth in a predictable and desirable manner under varying climate and growth conditions. This could provide more environmentally friendly and economic fertilization regimes and also better playing quality.