Defoliation patterns and tillering dynamics in Italian ryegrass under different herbage allowances
This work was carried out in order to generate information on the tillering process and to contribute for the understanding of the defoliation process on Italian ryegrass (Lolium multiflorum Lam.) grazed by lambs under different herbage allowances: 6, 8 and 12 kg of dry matter per 100 kg of animal live weight per day. The grazing method was intermittent. The experimental design was completely randomized following a repeated measure arrangement, with three treatments and two area replications. The intensity of defoliation is greater at 6 and 9% herbage allowances. The defoliation interval is higher at 12% herbage allowance, intermediate at 9% and lower at 6%. The rates of tiller emergence, survival and death, stability index the tiller population are similar for the different herbage allowances and differ according to the phenological stage of ryegrass. Structural changes caused by canopy management with low herbage allowance and/or due to the advance in developmental stage of ryegrass alter defoliation strategies, with more intense and frequent grazing.
Tiller dynamics of perennial ryegrass cultivars derived from different New Zealand ecotypes: effects of cultivar, season, nitrogen fertiliser, and irrigation
A field study was made of the tiller dynamics of the New Zealand perennial ryegrass (Lolium perenne L.) cultivars Grasslands Ruanui, selected from a Hawke's Bay ecotype, and Ellett, selected from the Mangere ecotype. The work tested whether nitrogen (N) fertiliser or irrigation (Irr) could manipulate the persistence strategies of these morphologically distinct perennial ryegrass ecotypes, represented by these cultivars. Tiller births and deaths, and tiller survival, were monitored over 2 years, under rotational grazing by dairy cows. Patterns of cultivar tiller birth and death were similar. Much of the temporal change in tiller population density was shown to be a response to increasing or decreasing herbage mass associated with seasonal feed surplus or deficit. The probability of tiller survival between observation dates varied markedly with date, and was lowest in autumn. The cultivar effect on tiller survival was small but a significant (P < 0.05) cultivar × date interaction was detected, with survival probability for Ellett tending to be higher than for Grasslands Ruanui in March–April 1997 but lower from July 1997 until March 1998. A cohort effect on tiller survival was also identified, in that tillers formed in January, July, and August 1997 had lower survival probability than those formed at other times. N-treated plots produced 34% more tillers than did untreated plots, and irrigation had no effect on overall tiller density. N and Irr treatments had variable effects on tiller survival. Size density compensation theory and analysis of survival probability are introduced to aid the interpretation of tiller dynamics data.
Investigations on the rôle of organic matter in plant nutrition
1. As the result of decomposition of green manure in a swamp soil, the coarse fractions (including coarse and fine sand) of the surface layer (first 3 inches) decreased by 11·2 per cent. while the fine ones (silt+clay) increased by 9·8 per cent. in the course of 43 days. The effect was less pronounced in the manured soil maintained at 60 per cent. saturation, while no alteration was to be noticed in the case of the unmanured specimens. 2. Treatment with dilute hydrochloric acid prior to dispersion had no appreciable effect on the estimates of mechanical composition obtained in the different cases. Loss in solution was also comparatively small. 3. The silica-sesquioxide ratio increased slightly as the result of decomposition of green manure in swamp soil. The composition of the fine fractions was also altered, the total percentages of the oxides of iron, aluminium and silicon increasing from 90·5 to 99·3 in the course of 71 days. 4. The practical significance of the above and related observations has been discussed.