Kasvuregulaatori ja kevadise täiendava lämmastikväetise mõju põldtimuti (Phleum pratense L.) seemnesaagile ja seemnete kvaliteedile
The synergistic effect of the plant growth regulator Moddus 250 EC and nitrogen fertilizer on the seed yield and seed quality of timothy was investigated over a period of four years (2017–2020) in a field trial established with the cultivar 'Tika' in 2016 at the Estonian Crop Research Institute. The trial had three variants: variant 1 – without plant growth regulator (control), variant 2 – plant growth regulator sprayed twice at the rate of 0.4 + 0.4 l ha–1 and variant 3 – plant growth regulator sprayed once at the rate of 0.8 l ha–1 . In all three variants there were five nitrogen fertilizer rates between N 70–140 kg ha–1 . In the trial the lodging resistance of plant cover was monitored, the height of generative tillers was measured, the seed yield was determined by two-phase combine harvesting and the quality of seed was determined. No lodging of timothy was detected in trial variants throughout all trial years. The increase of nitrogen fertilizer rate did not reliably affect the height of generative tillers, the split application of plant growth regulator shortened the height of generative tillers on the average of four years by 7.4%, and one-time spraying by 6.2%. The use of plant growth regulator did not increase the seed yield, the split application of it even reduced the seed yield. The increase of nitrogen fertilizer rate up to N 122 kg ha–1 increased the seed yield reliably only in the first year of production, but not in the following years. The use of plant growth regulator slowed down seed maturation, in our trials it was confirmed by bigger amounts of seed in the second harvest phase. The increase of nitrogen fertilizer rate and the use of plant growth regulator did not have any effect on seed germination. In the first production year, the 1000 kernel weight increased under the influence of plant growth regulator, in the later years there was no effect. The germination energy of seed somewhat decreased under the influence of plant growth regulator.