The effect of date of primary growth harvest and levels of nitrogen and potassium fertilizers on the dry matter production of timothy ( Phleum pratense )

Scots timothy was harvested three times a year for 3 years under four harvesting patterns and at all combinations of three levels of application of nitrogen and four of potassium. Harvesting patterns, H1, H2, H3 and H4, comprised cutting primary growth on 27–29 May or 14, 28 or 42 d later followed by cutting a first regrowth 8 weeks afterwards and a second regrowth on 15–16 October. N treatments, N0, N1 and N2, involved annual totals of 0,108 and 216 kg ha ‐1 N in three equal doses. K treatments, K0, K1, K2 and K4, involved annual totals of 0, 54, 108 and 216 kg ha ‐1 K also in three equal doses. Mean herbage DM yields in successive years were 8·90, 9·54 and 9·61 t ha ‐1 containing92·4%, 93·1% and 94·5% timothy, respectively. Systems H3 and H4 had 24% higher yields than H1 and H2. The superiority of the late systems derived from higher yields of primary growth. Mean response to 108 kg ha ‐1 N at 36·7 kg DM per kg N was significantly higher than the response to an additional 108 kg ha ‐1 N. Response in primary growth to successive increments of 36 kg ha ‐1 N averaged 53·9 and 27·5 kg DM per kg N. The first regrowth gave linear responses up to 72 kg ha ‐1 N. The possibility is discussed of more effective use of N by increasing the proportion applied to regrowth. Response to K was low except in the third year when there was a marked response at N2. It was calculated that to maintain soil potash it is necessary to apply 23·9, 47·7 and 86·6 kg ha ‐1 fertilizer K for each harvest at N0, N1 and N2 respectively.