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Leaf appearance rate and tiller development rate in pre-grazing growth of wheat and oats under dual-purpose (grain and graze) management

Walter Kelman and Hugh Dove

CSIRO Plant Industry, Email


Dual-purpose use of cereal crops is an increasingly popular option for mixed farming enterprises in southern Australia. It is important for farmers to be able to assess the quantity of forage available at the start of grazing in order to determine stocking rate and duration of grazing. The duration of the pre-grazing phase is bounded by the opportunity for early sowing and the attainment of the stem elongation stage of growth, when elongating stem apices become vulnerable to grazing. We examined the pre-grazing growth rate of wheat and oats in terms of their leaf appearance rate (LAR) and tiller development rate (TDR) in 2004, when sowing date and early growth were delayed by low rainfall, and in 2005, when moisture conditions allowed earlier sowing. In 2004 Blackbutt oats established significantly greater plant populations than Whistler wheat and although growth rates were similar in the two cultivars, feed on offer at the start of grazing was 25 % higher in the oat cultivar (2.1 t dry weight/ha). In 2005, Blackbutt oats also established denser plant populations than Mackellar wheat, but the amount of feed on offer at the start of grazing was similar in the two cultivars (2.9 t dry weight/ha). This difference in biomass accumulation between seasons and cultivars was attributed to the faster LAR (98 GDD/leaf) and TDR (28 tiller/m2/day) of Mackellar wheat, compared with Whistler wheat (112 GDD/leaf and 21 tillers/m2/day) in 2004, and compared with Blackbutt oats (112 GDD/leaf and 23 tillers/m2/day) in 2005.

Key Words

Dual-purpose cereals, growth rate, leaf appearance rate, tiller development rate


In mixed farming systems in southern Australia, there is an opportunity to use part of the projected increase in area of cereal production (ABARE 2007) for dual-purpose, grazing and grain, production. Farmers who take this option face a complex network of management decisions, the analysis of which is best approached through modeling (Moore 2004). An important element of the plant growth models used in this work is the prediction of the amount of forage on offer at the start of grazing. The duration of the pre-grazing phase is determined at the start of the season by the opportunity for early sowing and at the end by the timing of reproductive initiation, after which there is a risk of grazing damage to elongating stem apices. Forage on offer is usually given in terms of dry matter accumulation. Model predictors of pre-grazing biomass accumulation would be improved by a better understanding of component processes of growth in different cereal species and how they are influenced by environmental variation. This paper describes two such determinants of growth, leaf appearance rate (LAR) and tiller development rate (TDR), for two wheat cultivars and one oat cultivar grown under dual-purpose management at Ginninderra Experiment Station, near Canberra, ACT, in 2004 and 2005.


Cultivars, sowing dates and rainfall

In 2004 sowing was delayed by lack of early rain. Whistler wheat (Triticum aestivum) and Blackbutt oats (Avena sativa) were sown on 27 May at 100kg/ha with 110 kg/ha Starter 15 (15% N, 12% P, 12% S) into 16 0.25 ha plots (8 of each cultivar) plots at the start of a grazing trial. The pre-grazing period was 116 days to 21 September, during which 71.5 mm rain was recorded. In 2005 sowing was earlier, on 29 March, and Mackellar wheat and Blackbutt oats were sown at the same sowing and starter fertiliser rates as 2004. Mackellar wheat was sown onto the 2004 oat plots and Blackbutt oats onto the 2004 wheat plots. The pre-grazing period was 117 days to 23 July, during which 138 mm of rain was recorded.

Emergence counts

Emergence was assessed on seedlings at the 1-2 leaf stage in 10 random sites per plot from 0.5 m of row length of two adjacent rows (10 m of row length per plot).

Biomass sampling and phenology

Growth stage (the number of expanded leaves on the main stem and the number of tillers; Tottman and Broad 1987) was recorded for individual plants from replicate 0.5 sections of row in 4 plots of each cultivar on 14 July, 5 August, 17 August and 2 September in 2004, and on 8 occasions at 2-week intervals between 19 April and 24 July in 2005. Dry weights of the bulked samples of individual plants were recorded after oven drying at 70oC for 48 h. Leaf appearance rate (LAR) was calculated from the difference in the modal number of main stem leaves between emergence and the final pre-grazing sampling in each year and was expressed in growing degree days per leaf, at a base temperature of 0oC. Tiller development rate (TDR) was calculated from the difference in total number of tillers per m2, between emergence and the final pre-grazing sampling in each year.

Statistical analyses

For emergence counts in each year, the 16 plots were divided into 4 replicates of 4 plots each and treated as a simple ANOVA of 2 cultivars with 4 replications. Pre-grazing growth rate in each year was determined by linear regression of accumulated dry weight on days from sowing. Differences in growth rates between wheat and oats in 2004 and 2005 were tested by comparing the residual sums of squares of separate analyses of the cultivars with that of a combined analysis of both cultivars.



In 2004, emergence of Blackbutt oats (288 plants/m2) was significantly greater (P < 0.001) than in Whistler wheat (236 plants/m2). Although at the uniform sowing rate of 100kg/ha, more oat seeds were sown per square meter (370) than wheat seeds (333), when the counts were analysed on the basis of the number of seeds sown /m2, emergence of Blackbutt oats (78%) was still significantly greater (P = 0.001) than Whistler wheat (71%).

In 2005, establishment counts were 253 and 144 plants/m2 for Blackbutt oats and Mackellar wheat, respectively (P<0.05). When emergence counts were standardized for the different numbers of seed sown at 100 kg/ha sowing rate, the percentage emergence of Blackbutt oats (67%) was still significantly (P = 0.02) greater than that of Mackellar wheat (46%).

Figure 1. Dry weight accumulation over days from sowing of Blackbutt oats (■) and Whistler wheat (♦) in 2004 (a), and of Blackbutt oats (■) and Mackellar wheat (♦) in 2005 (b).

Growth rate

After the late sowing in 2004, there was a long delay before significant dry matter was accumulated (Fig. 1). Thereafter, when rain fell in early August, the growth rate of Blackbutt oats (37 kgDM/ha/day) and Whistler wheat (30 kgDM/ha/day) were not significantly different, but the final pre-grazing dry weight of Blackbutt oats was 2.0 tDM/ha, compared with 1.5 t DM/ha for Whistler wheat. In 2005, rain initiated earlier sowing and growth occurred during a more prolonged period than in the previous year (Fig. 1b). The growth rates of Mackellar wheat (25 kg DM/ha/day ) and Blackbutt oats (27 kg DM/ha/day) were not significantly different and the final pre-grazing biomass of Blackbutt oats and Mackellar wheat were similar (2.9 tDM/ha; Fig. 1b).

Leaf appearance rate

At the commencement of grazing in 2004, the modal leaf stage of the main stem of both Whistler wheat and Blackbutt oats was 8 leaves, and therefore the calculated LAR from emergence to the start of grazing for both cultivars was 112 GDD/leaf (Table 1). In 2005, the corresponding modal leaf stages of Mackellar and Blackbutt were 8 and 7 leaves, respectively, and thus the LAR for Blackbutt was slightly lower than Mackellar. LAR of Blackbutt oats in 2004 was the same as that in 2005, despite the earlier sowing date and lower GDD accumulation during the pre-grazing period in 2005 (Table 1). This result supports a stronger link between LAR and temperature (Jamieson et al 1995) than between LAR and day-length as affected by sowing time (Kirby 1995). LAR of Mackellar was markedly faster than that of Blackbutt oats in 2005 and that of Whistler wheat in 2004.

Tiller development rate

TDR was greater in Whistler wheat than in Blackbutt oats in 2004 and greater in Mackellar wheat than in Blackbutt oats in 2005 (Table 1). The higher tiller development rates of the wheat cultivars, compared with Blackbutt oats, was associated their relatively lower plant population densities at emergence.

Table 1: Pre-grazing phenology and growth rate of wheat and oats in 2 years at Ginninderra Experiment Station, Canberra, ACT


Pre-grazing period of growth

Growing degree days (GDD) from emergence to start of grazing

Leaf appearance rate

Tiller development rate






Whistler wheat
Blackbutt oats

27 May-21 Sep. (116)




Mackellar wheat
Blackbutt oats

29 Mar.–23 Jul. (117)





The interactions of established plant population density with LAR and TDR were the important factors underlying the differences in biomass accumulation between wheat and oat cultivars in seasons with different sowing dates and experiencing variable rainfall in the pre-grazing phase of growth. Higher LAR and TDR combined to offset the effect lower plant establishment of Mackellar wheat in comparison with Blackbutt oats, in the attainment of similar forage dry weight on offer at the start of grazing.


ABARE (2007). ‘Australian Grains 07.2 – Outlook for 2007-8 and industry productivity (Australian Bureau of Agricultural Research Economics: Canberra) Available at:

Jamieson PD, Brooking IR, Porter JR, Wilson DR (1995) Prediction of leaf appearance in wheat: a question of temperature. Field Crops Research 41, 35-44.

Kirby EJM (1995) Factors affecting rate of leaf emergence in barley and wheat. Crop Science 35, 11-19.

Moore AD, Salmon L, Dove H (2004). The whole farm impact of including dual purpose winter wheat and forage brassica crops in a grazing system: a simulation analysis. In ‘Proceedings of the 4th international crop science congress, Brisbane, Australia’.

Tottman DR, Broad H (1987). The decimal code for the growth stages of cereals, with illustrations. Annals of Applied Biology 110, 441-454.

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