Growth and Persistenceof Common Temperature Pasture Species under Low Light and Low R:FR Ratio

Abstract

The effects of varied PAR and R:FR ratio on tillering and shoot dry weight production of temperate pasture species were evaluated at Massey University New Zealand using split-plot design with four blocks. The main plots were % transmitted PAR (photosynthetically active radiation; mmoles photons m-2 s-1, 400- 700 nm) and R:FR ratios (red to far red ratios) with 2 x 2 factors of PAR and R: FR, i.e. medium (38 and 39%) and low (16 and 17%) PAR-each with two natural (1.33 and 1.34) and two reduced (0.57 each) R:FR ratios. The treatment combination was such that each low and medium PAR level had a natural and a reduced R:FR ratio. PAR levels with natural R: FR ratio were imposed by differing densities of neutral shade cloth (Sarlon) with a layer of clear filter, while low R:FR ratio was created with the use of a blue filter. Nine pasture cultivars of seven pasture species: Dactylis glomerata L., Grasslands Wana (cocksfoot); Dactylis glomerata L., PG 74 (cocksfoot); Dactylis glomerata L., PG 321 (cocksfoot); Lolium perenne L. (perennial ryegrass); Holcus lanatus L. (Yorkshire fog); Agrostis capillaris (browntop); Poa trivialis; Trifolium repens L. (white clover), and Lotus uliginosus (lotus) were grown in pots as subplots with four replicate blocks. Six plants were maintained per pot. Plants were harvested at 61 days after imposing shade. There was no effect of R:FR ratio (P>0.05) on the shoot dry weight per plant, however, significant differences (P<0.05) for PAR, species, and interaction of PAR, species for shoot dry weight was observed. At low PAR, Lolium perenne, Dactylis glomerata (Wana) and Holcus lanatus had the highest and similar yields, whereas the yield of white clover and lotus were similar and less than for all the grass species. Effects of PAR as well as R:FR were significant (P<0.001) for total tillers per plant in the shade. Poa trivialis, Agrostis capillaris and Lolium perenne had the highest number of tillers/plant at the low PAR and low R:FR, but did not contribute to higher shoot dry weight at the low PAR, mainly due to their low weight per tiller. Likewise, SLA was significantly (P<0.01) increased by low PAR but not by low R:FR. Lotus produced a higher (P<0.001) number of branches at the low PAR than white clover. Comparatively better performance of cocksfoot, especially at low PAR, was mainly due to the ability to produce higher leaf area, higher SLA, and more tillers per plant. The results are discussed in terms of the effects of PAR and R:FR on the yield and yield components with respect to the attributes of shade tolerant pasture species. 
 
 Key words: PAR, R:FR ratio, wana cocksfoot, nui perennial ryegrass, shade 
 
 J. Inst. Agric. Anim. Sci. 27:111-118 (2006)