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THE EFFECT OF TEMPERATURE ON LEAF APPEARANCE RATE IN
DRUMMOND OATS

R.J. Martin, S.M. Sinton, P.D. Jamieson and M. Snego

N.Z. Institute for Crop & Food Research Ltd., Private Bag 4704, Christchurch, New Zealand.

Abstract

Oats cv. Drummond were sown on six dates in the 1994-95 season. The emergence date of each leaf tip on the main stem of six tagged plants was recorded. Leaf tip emergence was related closely to thermal time calculated using soil temperature at 10 cm depth up to the time that the sixth leaf tip emerged, and using air temperature after that.

Keywords: oats, Avena sativa L., temperature, thermal time, leaves.

The duration of a cereal crop?s growth depends on the number of leaves produced sequentially on the mainstem and the rate at which they are produced. We have shown that the number of leaves produced in oats cv. Drummond (Avena sativa L.) depended on the photoperiod at the time when the sixth leaf tip emerged (3). In wheat, the rate of leaf appearance depends on temperature (1). We investigated whether there is a similar response to temperature in oats.

Materials and methods

An experiment was carried out at Lincoln, New Zealand (latitude 43o39'S, longitude 172o30'E). Oats cv. Drummond were sown on 16 September, 2 November and 21 December, 1994, and 7 February, 3 April and 16 May, 1995. Experimental and sampling details are given in (3). Air temperature and soil temperature at 10 cm depth were logged hourly at the Lincoln Meteorological Station, 100 m south of the experimental site. Mean daily temperature was taken as the average of the 24 hourly readings.

Results and discussion

 

Days from sowing

Final leaf number

Sowing date

50% emerg

Leaf tip 6

Last ligule

 

16 Sep
2 Nov
21 Dec
7 Feb
3 Apr
16 May

16
7
7
7
8
17

51
34
29
31
74
113

76
54
47
73
225
187

8.6
7.7
8.3
9.5
11.3
10.0

The number of leaves produced ranged from 7.7 to 11.3 and the duration from plant emergence to the appearance of the last leaf ligule varied over a wide range, from 40 to 217 days (Table 1).

When the number of leaf tips was plotted against thermal time calculated using air temperature with a base of 0oC, the four spring and summer sowings had a more rapid appearance rate than the two autumn sowings (Fig. 1). This result is similar to those from earlier studies with wheat (1, 2). Also, there was a change of slope about when the sixth leaf tip emerged. Before this, the stem apex was under or close to the soil surface. Thermal time calculated using soil temperature at 10 cm depth gave a more consistent fit for data from all sowings than the relationship based on air temperature up to this stage, but not thereafter. The lowest coefficient of variation for the relationship up to this stage was when thermal time was calculated using soil temperature above a base of 1.5oC, and after this stage with thermal time calculated above a base of 4.5oC. Number of leaf tips (NL) is plotted against thermal time (TT) calculated using this combination in Figure 2. The combined regression for all sowing dates is:

NL = 0.826(0.4157) + 0.0121(0.00020) TT (r2 = 0.974, d.f. 97) (i)

Temperature at the stem apex was not measured, so we used 10 cm soil temperature as a proxy. More detailed studies are currently under way where temperature at the depth of the shoot apex is being measured. Also, screen air temperature may not accurately represent the temperature of the shoot apex in the canopy which can be modified by latent heat flux from transpiration.

However, these results do show that, like wheat (2), oat leaf appearance rate is related to temperature. As final leaf number is related to photoperiod (3), the time from plant emergence to the appearance of the last leaf ligule in oats can be predicted readily from these two factors.

Conclusions

Leaf emergence in oats cv. Drummond was related to temperature. The best combination for describing the response was to calculate thermal time using soil temperature at 10 cm depth and with a base of 1.5oC up to the time when the sixth leaf tip had emerged, and using air temperature with a base of 4.5oC from then until when the last ligule emerged.

References

1. Jamieson, P.D., Brooking, I.R., Porter, J.R. and Wilson, D.R. 1995. Field Crops Res., 41, 35-44.

2. Jamieson, P.D., Brooking, I.R. and Porter, J.R. 1996. Proc. 8th Aust. Agron. Conf. Toowoomba. pp 337-340.

3. Martin, R.J., Sinton, S.M., Jamieson, P.D. and Snego, M. 1998. Proc. 9th Aust. Agron. Conf. Wagga Wagga. This volume.

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