SPLIT NITROGEN APPLICATION TO SEED CROPS OF TIMOTHY (PHLEUM PRATENSE)

L.T. Havstad
The Norwegian Crop Research Institute, Div. Landvik, 4886 Grimstad, Norway

Split nitrogen application to seed crops of timothy was evaluated in 20 field trials (11 with cv. Grindstad and 9 with cv. Vega) in SE- and Mid-Norway during 1998-2000. Three different N-rates were applied in early spring (25, 50 and 75 kg ha^-1), combined with four N-rates at the start of tiller elongation (0, 25, 50 and 75 kg ha^-1). On average for all experiments, the highest seed yield was obtained when a total rate of 75 kg N ha^-1 was split into a main application in early spring (50 kg N ha^-1) and a supplemental application at the start of tiller elongation in mid May (25 kg ha^-1). The optimal strategy for split N-application, with the main portion of the total nitrogen rate applied in early spring, was in principal similar in the two cultivars. Chlorophyll-readings, using the handheld chlorophyll-meter Hydro N-Tester™, showed a relatively strong relationship with the optimal split N-applications rate at the start of tiller elongation in cv. Grindstad (r² = 0.46) but not in cv. Vega (r² < 0.01). In cv. Grindstad, it is concluded that chlorophyll-readings may be useful to determine the optimal split nitrogen application rate at the start of tiller elongation.