AbstractHydrothermal time (HTT) models describe the time course of seed germination for a population of seeds under specific temperature and water potential conditions. The parameters of the HTT model are usually estimated using either a linear regression, non-linear least squares estimation or a generalized linear regression model. There are problems with these approaches, including loss of information, and censoring and lack of independence in the germination data. Model estimation may require optimization, and this can have a heavy computational burden. Here, we compare non-linear regression with survival and Bayesian methods, to estimate HTT models for germination of two clover species. All three methods estimated similar HTT model parameters with similar root mean squared errors. However, the Bayesian approach allowed (1) efficient estimation of model parameters without the need for computation-intensive methods and (2) easy comparison of HTT parameters for the two clover species. HTT models that accounted for a species effect were superior to those that did not. Inspection of credibility intervals and estimated posterior distributions for the Bayesian HTT model shows that it is credible that most HTT model parameters were different for the two clover species, and these differences were consistent with known biological differences between species in their germination behaviour.

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The objective of this study was to quantify the combined effects of temperature and moisture on germination of tall fescue seed. Seeds were incubated for up to 50 days at a range of constant temperatures (5-35ºC) and germinated at five water potentials (0, -0.18, -0.37, -0.63 and -0.95 MPa). The maximum final germination percentages were 94 to 98 at 15-30ºC when water was not limited (0 MPa). Germination rate increased linearly from 5 to 27.5ºC, and then decreased linearly from 27.5 to 32.5ºC. Extrapolation of the sub-optimal temperatures identified a base temperature of 3.5 ± 0.5ºC and an optimum temperature of 27.5ºC. More negative water potential indicative of drier conditions, delayed germination and reduced germination rate. The average base water potential was -0.95 MPa at the suboptimal range of temperatures. An optimum range of germination (80-100%) occurred when temperatures were between 10 and 30ºC and water potential was between 0 to -0.37 MPa (moderate stress). These results provide a matrix of soil temperature and moisture conditions that are expected to result in successful germination and therefore provide the maximum opportunity for emergence of tall fescue seedlings. Keywords: Festuca arundinacea, 'Finesse Q', hydrothermal time

Nitrogen (N) and water availability affect pasture production and persistence. Yield and botanical composition of four monocultures of brome (BR), cocksfoot (CF), perennial ryegrass (RG) and tall fescue (TF) were evaluated with (+N) or without (-N) N at Ashley Dene farm, Canterbury, over six growth seasons from establishment in 2014/15 (Year 1) to 2019/20 (Year 6). Total annual yields ranged from 2.04 (RG-N; Year 1) to 12.7 t DM/ha/yr (CF+N; Year 3). Yields differed among species in Years 1, 3, 4 and 6 when TF pastures had the lowest production. There was no difference in DM production from BR, CF and RG pastures. Additionally, +N pastures produced ~55% more yield than –N pastures in Years 3 and 5 when spring/summer rainfall was adequate to maintain growth. Sown grasses accounted for >89% of total DM yield in Years 1 and 2 but the proportion of total annual DM production from sown species declined from Year 3. By Year 6, sown species accounted for 48±3.3 (TF) to 64±3.3% (BR, CF and RG) of total annual DM production. Generally, TF failed to perform in this dryland environment. In contrast, the production and persistence of the other three species were not different when subjected to water deficits alone.