In all plots one third emerged on June 4th and the other two thirds on June 12th after rain. During
the first days after plant emergence, the daylength was 12 h at ME, 14 h at SGE, 15 h 15 min at LE
and 15 h 30 min at ML. Fig. 2 summarizes the climatic conditions from emergence to the first
sampling date and between the successive sam- pling dates in each situation treatment. The
parameters shown were the air temperature, the daily mean balance between rainfall and maximal
evapotranspiration and the photothermal quo- tient. This quotient is the global radiation per
degree-day; it is an indicator for sourcesink ratio that can interact with daylength Rawson, 1993.
It was used by Fischer 1985 for comparisons between
crops grown
under very
different climates.
Light interceptions by the stands were not mea- sured. All time lengths are expressed in thermal
time with 0°C as base temperature Gallagher et al., 1983.
3. Results
3
.
1
. Crop phases and pre-anthesis stand biomasses
Fig. 3 shows the crop phases for each situation treatment and highlights the four sampling dates.
Apart from ME, differences appeared between stand densities right from the beginning of shoot-
ing. The sampling dates represent a compromise for the actual beginnings of stem elongation. The
‘ear-at-1 cm’ stage was earlier at SGE and LE than at ME, especially in dense stands. The range
of main-stem headings at ML is caused by the two emergence dates at that site while at LE the
differences were among individual plants. The interval between the ‘ear-at-1 cm’ and the ‘tiller-
ing architecture’ samplings was a quarter of the thermal time between the ‘ear-at-1 cm’ and the
‘heading’ samplings at ME, SGE and LE, and 30 at ML.
The stand biomasses of samples for the ‘head- ing’ stages Fig. 4 were greater in the dense
stands, regardless of the fertilizer regime, in the three long daylength treatments, especially at LE.
The predicted limited individual growth capacity prevented the stand growth being fitted to the
resources only. The dry mass of the ‘ear-at-1 cm’ samples in sparse stands Fig. 4 is mainly in
relation to the elapsed thermal time since emer- gence see Fig. 3.
3
.
2
. Tillering patterns and tillering types More than 96 of the plants at ME, SGE and
Fig. 2. Climatic conditions experienced by the crops in each cultural situation: mean air temperature °C — stars, mean daily balance between rainfall and maximal evapotranspiration mm — solid floating bargraphs and photothermal quotient global
radiation in MJ m
− 2
per degree-day — dotted bargraphs in four consecutive periods from emergence to the last sampling date. Situation treatments: ME, SGE and LE, end-of-winter sowings at 320 m a.s.l., 880 m and 1120 m, respectively. ML, late sowing at
320 m a.s.l. see Section 2.1. Periods: e1, from emergence to ‘ear-at-1 cm’ sampling date; 1t, from ‘ear-at-1 cm’ to ‘tillering architecture’ sampling dates; th, from ‘tillering architecture’ to ‘heading’ sampling dates; hp, from ‘heading’ to ‘pasty-ripe’ sampling
dates.
Fig. 3. Crop phases in each cultural situation and stand density. S, sparse stands; D, dense stands; ME, SGE, LE and ML, situation treatments as in Fig. 2. Samplings: 1, ear-at-1 cm; t, tillering architecture; h, heading; p, pasty-ripe. The dates of the plant emergence
and of the samplings are on the right side of the bargraphs.
LE — and 94 at ML — conformed with the tillering model see Section 2.3 and Fig. 1. Some
of the plants without tillers only bore five leaves at the sampling time. It is possible for these plants
to bear a tiller in the axil of the third leaf T3 during the unfolding of their sixth leaf see Fig.
1; therefore, T3 + and WT tillering types cannot be distinguished.
All tillering types can be found in all situation treatments. In all cropping conditions at ME and
in sparse stands at SGE and ML more than 80 of the plants sampled were T1 + plants, and the
other ones were mainly from the TC + type, except at ML Fig. 5. Dense stands at LE and
ML consisted mostly of plants of the T2 + and WTT3 + tillering types, that is plants with a
delayed tillering start. In sparse stands, despite high variability between plots, LE had signifi-
cantly more T2 + and WTT3 + tillering types than ME and SGE Fig. 5.
Long initial day length and high stand densities delayed the start of tillering: almost no TC +
plants at LE, ML and in dense stands of SGE, and very few T1 + plants in dense stands of LE
Fig. 4. Means 9 S.E. of stand dry masses of the ‘ear-at-1 cm’ and ‘heading’ samples bar graphs, and the range of stand dry-masses observed by Biscoe et al. 1975 at the closure of spring barley canopies hatched strip. ME, SGE, LE and ML, situation
treatments as in Fig. 2 or Fig. 3. SO, SN, sparse stands without or with nitrogen fertilization; DO, DN, dense stands without or with nitrogen fertilization.
Fig. 5. Percent of plants 9 S.E. of each tillering type in each cultural situation and cropping condition. Tillering types: plants with its first tiller at the coleoptile node TC + , or in the axil of the first T1 + , the second T2 + or the third T3 + leaf and plants
without any tiller WT. WT and T3 + tillering types are grouped together because they are not distinguishable on all plants see Section 3.2. ME, SGE, LE and ML, situation treatments as in Figs. 2 and 3 or Fig. 4. SO, SN, DO and DN, cropping conditions
as in Fig. 4.
and ML. Nitrogen fertiliser favoured an earlier start to tillering at all sites: there are more TC +
plants at ME, and there are more T1 + plants at LE and in the dense stands of SGE with nitrogen
supply Fig. 5. Nevertheless, differences between sparse stands at LE and ML are not explainable
by daylength, density or nitrogen.
3
.
3
. Tillering dynamics Some plants which were already tillering were
able to continue tillering after the sampling dates in May-sown situations, especially at LE and
unlike ME and SGE. Many WT plants are still able to bear T3 in dense stands at LE and ML
Table 2. The rate of the tillering cessation was different: two phyllochrons were enough to stop
the tillering of 88 – 97 of the bearing-tiller plants in all conditions of ME and SGE, but in LE
sparse stands only 45 – 65 of these plants stopped their tillering in two phyllochrons. In the
LE sparse stands, some plants started to tiller after others had stopped in a same sample plot
data not shown.
The differences in shoot numbers between the ‘pasty-ripe’ samples and the ‘tillering architecture’
samples Table 2 showed that the dynamics of the stand differed between situation treatments.
At ME, a general and quick cessation of tiller- ing occurred inside the first quarter of the dura-
tion of stem elongation. No more tillers appeared afterwards and the usual disappearance of dead
tillers was observed in dense stands.
In SGE sparse stands, 130 additional shoots per square meter must come from a late resump-
tion of tillering after a general cessation which was observed at the beginning of stem elongation.
In dense stands, some plants were still tillering at the ‘tillering architecture’ sampling date, but they
stopped immediately afterwards.
At LE, further tillering must have also occurred to account for the observed final numbers of
shoots, even in dense stands. Many of the plants were still able to tiller in accordance with the
model after the ‘tillering architecture’ sampling date. Except in SN conditions, a short time of
further tillering is enough to produce the addi- tional number of shoots which was observed at
the ‘pasty-ripe’ stage, if all plants capable did, actually tiller Table 2. In SN conditions, a quar-
ter of the plants had to double the shoot number of the stand; with at least three phyllochrons
required to end tillering Table 2, the last tillering cessation occurred towards the ‘heading’ stage at
the earliest. In dense stands, almost all plants that were able to tiller in the future were young WT
plants. It is unlikely that most of these plants were beginning to tiller at this time. Therefore, more
tillering time than one phyllochron would be needed on the other plants.
At ML, many plants were capable of tillering after the ‘tillering architecture’ sampling date, but
in reality no more shoots emerged afterwards Table 2. The last tillering cessation occurred at
the ‘tillering architecture’ sampling date.
4. Discussion
