Herbage accumulation rates and tiller demography of North Island hill country pastures

Abstract

Herbage accumulation and tiller demography of hill country pastures were studied after severe defoliation in May, July, and September. Ten, unequally spaced harvest dates were used to estimate regrowth and maximum yield. Individual tillers were identified and examined periodically to estimate appearance and death rates. Only the regrowth from the September enclosure showed a sigmoid curve with an estimated maximum green herbage accumulation of 8116 kg DM/ha. The maximum average growth rate for September enclosure occuned at 7250 kg green DM/ha. Incremental growth rate had a bimodal pattern attributed to the early flowering of sweet vernal (Anthoxanthum odoratum) and Poa spp. and later flowering of brown-top (Agrostis capillaris). Perennial ryegrass (Lolium perenne) accumulation rates were severely decreased during the flowering period of this species. The increased herbage mass and stem accumulation resulting from later enclosures was associated with decreasing plant tissue nitrogen (N)—2.6, 1.5, and 1.2% and decreasing in vitro DM digestibility—65.4, 62.6, and 55.5% at final harvest for May, July, and September enclosures respectively. Tiller appearance rates were 70–100 tillers/m² per day for the first 5 weeks after all three enclosure times. These rates were maintained for 12 weeks for May and July enclosures but decreased rapidly after 5 weeks for September. The proportion of tillers marked just after enclosure and surviving to the final harvest was close to 0.48 for all species and enclosure times. The survival rate of tillers initiated during regrowth was more variable, but generally lower (mean=0.34). The possible value of longer regrowth periods on hill country pastures is discussed.

Keywords:

• perennial ryegrass
• Lolium perenne
• browntop
• Agrostis capillaris
• herbage accumulation rate
• roots
• hill country
• tiller appearance rate
• tiller deathrate
• tiller density