The effect of differences in intensity and frequency of defoliation on the growth of Sirolan phalaris in the field

A two-year old sward of Phalaris aquatica cultivar Sirolan was cut at 2-, 4-, 6- or 12-week intervals and at heights of 2 or 7 cm over two 12-week cycles from June to November 1986. Defoliation treatments were split and 100 kg ha-1 of nitrogen was applied to half the plot at the beginning of each cycle. Tiller density and dry matter production were measured throughout winter and spring of 1986, and in two 6-week regrowth periods in 1987.During winter, high cutting always gave less harvested dry matter than low cutting. In spring, the regression lines relating cutting frequency to cumulative harvested dry matter crossed over at a frequency of about 5 weeks. Below this frequency high cutting yielded more harvested dry matter than low cutting. High cutting gradually changed sward appearance in winter, resulting in better yields at later harvests. At the conclusion of spring cutting, there were more dead tillers on plots cut at 6- and 12-week intervals than on those cut every 2 or 4 weeks, while numbers of live tillers increased progressively as cutting interval rose from 2 to 12 weeks. Regrowth in autumn 1987 was much better on plots cut every 12 weeks than on other plots, primarily owing to the greater vigour of individual tillers, but also owing to higher tiller numbers. The timing of defoliation in spring appeared to be the most important factor governing crown bud production and regrowth in the following season. Spelling in spring is recommended to permit reproductive and crown bud development in Sirolan.