Competition among pasture plants

Abstract

Simulated swards forming a replacement series of the ryegrass cultivars 'Grasslands Manawa' and 'Grasslands Ruanui' consisting of two monocultures and three mixtures were cut during establishment to two heights and at two frequencies. The cutting frequencies were continued for a year after the first cut, after which all swards were cut uniformly until the experiment was concluded 2 years after sowing.Yields, tiller numbers, and plant survival were recorded separately for the cultivars. These data were used to fit parameters to the twospecies competition model of de Wit (1960).Manawa was initially dominant in all cutting systems, and this dominance was greatest where cutting was infrequent. Initial lax cutting reduced the suppression of Ruanui. The suppression of Ruanui during establishment is largely attributed to shading by Manawa, and where hard cutting removed stubble, Ruanui tiller numbers were reduced and Ruanui plants died in the mixtures with Manawa. This effect hindered the transition to dominance of Ruanui in the summer and autumn after sowing.The results indicate that mixing of the cultivars would be advantageous as a function of both herbage yield and quality under the frequent lax cutting system, because the cutting did not markedly suppress Ruanui initially, allowing Ruanui to contribute substantially to the yields of the mixtures in the post-reproductive period when yields of Manawa were low. With infrequent hard cutting the yield contribution of Ruanui in mixture during the post-reproductive period was small and, because Manawa was unable to utilise the space made available by the death of Ruanui plants, depressed yields from mixing were observed. It is concluded that no advantage is gained by mixing Ruanui and Manawa where the management system in the first year tends to maximise the yield of Manawa.

Effect of porina caterpillar (wiseanaspp.) infestation on yield and competitive interactions of ryegrass and white clover varieties

“…The dominance of Manawa over Ruanui ryegrass (Table 7) conforms with previous measurements (Brougham and Harris 1967;Harris and Thomas 1970), and the indication that this dominance is decreased by porina infestation can be related to defoliation by porina reducing the shading of Ruanui by Manawa. which is heightened by the preference of porina for Manawa ryegrass (Table 4).…”

Effects of density and management on components of floret production inLolium(multiflorum lam.xperennel.) ‘grasslands manawa’ ryegrass

“…This resembles the pattern of growth of genotypes tending towards L. multiflorum when compared with L. perenne genotypes (Harris and Thomas 1970), and suggests that genotypes inclining towards the annual type would have increased in the resulting seed population. This trend would be enhanced by interference among plants, the quick-establishing, initially larger-growing genotypes suppressing the slower-growing genotypes in a way similar to that demonstrated for Manawa and Ruanui (L. perenne) ryegrass in sward establishment (Harris and Thomas 1970).…”

“…netting 3 ft wide was fixed to the soil surface as the grid for density determination. This technique for establishing separately identifiable plants in swards follows that used by Harris and Thomas (1970). The soil type was Manawatu fine sandy loam.…”

“…Mitchell (1954) indicated that the seedling growth and tillering rate of L. perenne were less than those of L. multitlorum X perenne; and Harris and Thomas (1970) found that, after flowering, L. multiflorum-like genotypes, unlike L. perennelike genotypes, either die or become practically dormant during summer. Further, seed populations of L. multiiiorum and L. perenne can be distinguished by the presence or absence of awns, which was one of the characters by which Rumball (1970) demonstrated a change in Manawa population structure with seed multiplication.…”

Competition among pasture plants

“…Competition between these ryegrass cultivars was examined previously (Harris and Thomas 1970), and as the present data came from the same experimental layout, points of technique will not be reiterated in detail. The experiment was arranged so that competition effects could be quantified by fitting parameters to the de Wit (1960) model of plant competition by a method described by Thomas (1970 For details of experimental site, method of establishment, maintenance of simulated swards, and sampling procedures refer to Harris and Thomas (1970). Seeding ratios (Z) of the nine swards considered in this paper were:…”