Summary. Eleven field trials were sown in the north- eastern wheatbelt of Western Australia to test the hypothesis that if wheat cultivars with suitable maturity.
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Australian Journal of Experimental Agriculture, 1992,32,717-33
Early sowing with wheat cultivars of suitable maturity increases grain yield of spring wheat in a short season environment N. J. Kerr*, K. H. M. SiddiqueB and R. J. Delane* A
B
Western Australian Department of Agriculture, Marine Terrace, Geraldton, W.A. 6530, Australia. Western Australian Department of Agriculture,Division of Plant Industries, Baron-Hay Court, South Perth, W.A. 6151, Australia. Author for correspondence.
Summary. Eleven field trials were sown in the northeastern wheatbelt of Western Australia to test the hypothesis that if wheat cultivars with suitable maturity are sown earlier than current practice, then higher grain yields will be achieved. The experiments included time of sowing treatments that ranged from early May to late June in 1988, 1989 and 1990. Seven commercial cultivars with a wide range of developmentalpatterns and maturities were used. Sowing between mid May and early June produced the highest grain yields. For plantings after early June, yields declined by approximately 250 kg/ha (15%) per week. Delayed sowing caused a decrease in dry matter
and kernel number (per m*). In general this reduction in kernel number was not compensated by an improvement in kernel weight. At early times of sowing, the medium-long season cultivars generally had higher yields than short season cultivars. The short season cultivars were the highest yielding cultivars at the late times of sowing. These results suggest that cultivars should be chosen to suit the seasonal break, which may vary from late April to mid June. As a consequence, farmers should be encouraged to retain a number of cultivars with differing maturities suited to a range of planting times.
Introduction The time of sowing is an important factor influencing the grain yield of wheat crops in Australia. Many studies, including those in New South Wales (Kohn and Stomer 1970), South Australia (French and Schultz 1984) and Queensland (Woodruff and Tonks 1983), have demonstrated that wheat yields decrease when sowing is delayed. Reductions in yield with delayed sowing have been attributed to hastened crop development with low dry matter (Kohn and Stomer 1970; Marcellos and Single 1971; Doyle and Marcellos 1974; McDonald et al. 1983), and to a greater degree of moisture stress at and after anthesis, due to increasing daily mean temperatures and evaporative demand (Fischer and Kohn 1966; McDonald et al. 1983; Woodruff and Tonks 1983). Yields may also be reduced with very early sowing because of frost damage in frost susceptible areas (Doyle and Marcellos 1974; McDonald et al. 1983; French and Schultz 1984; Batten and Khan 1987), and by a higher incidence of leaf disease (Wilson 1989). The north-eastern wheatbelt of Western Australia has a Mediterranean-type climate with cool, wet winters and hot, dry summers. Average annual rainfall is 300-350 mm, with 200-260 mm falling in the growing season (May-October). The growing season is short with an unpredictable seasonal start (late April-mid June) and
a consistently dry finish with high evaporative demand; evaporation in September may exceed rainfall by as much as 140 mm. Summer rainfall is extremely variable but generally is low and does not contribute to the crop water supply. The very short growing season and sharp finish typical of this area impose severe limitations on yield. Common practice was to delay planting until June, &en if adequatirainfall for sowing was received earlier. This delay permitted mechanical weed control and seed bed preparation. The availability of modem herbicides and minimum tillage technology has provided the possibility for earlier sowing. Unlike many parts of eastern and southern Australia, frost is not considered a sufficiently serious risk (Loss 1989) to warrant a delay in sowing. Recent field studies in the central wheatbelt of Western Australia (between 31 and 33"S.), using 4 wheat cultivars, showed that semi-dwarf cultivars had greater grain yield than tall cultivars when sown early (May v. June) (Anderson and Smith 1990). This increased yield of semi-dwarf cultivars with early sowing was mainly due to greater head and kernel numbers. The work reported here extends this information on the effect of time of sowing on grain yield of wheat cultivars in the north-eastern wheatbelt, a major wheat growing area in Western Australia.
N. J. Kerr et al.
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Table 1. Site, soil type, previous crop history and sowing dates of experimental trials Trial
Site Balla Balla North Mullewa North Mullewa Morawa Morawa East Perenjori Latham Kalannie East Pithara Cadoux
Soil type
Paddock history
Yellow sandplain Yellow sandplain Shallow red Sandy clay loam Red sandy loam Red sandy loam Yellow loamy sand Sandy clay loam Red sandy loam Light acidic grey sand over clay Pale light-medium sand
The aims of this study were to test the hypothesis that early sowing of wheat cultivars with suitable maturity would increase wheat yield in the north-eastern wheatbelt of Western Australia.
Materials and methods Eleven experiments were undertaken at 8 locations throughout the north-eastern wheatbelt of Western Australia (between 28 and 31°S.) during the 1988, 1989 and 1990 seasons. The experimental crops were grown in rotations common to that area, namely pasture-wheat, lupin-wheat, or continuous wheat (Table 1). The 3 seasons had very different rainfall patterns (Table 2). The 'low rainfall' regions received above average rainfall during the 1988 season. The North Mullewa site, for example, received 300 mm May-October rainfall (average 253 mm), placing the 1988 season in the top 20% of years. In 1989, good May rainfall was received but the finish to the season was very dry. During July-October, 59 mm was recorded at the Morawa site compared with the long term average of 132 mm. Annual rainfall for 1990 also was above average; however much of this rainfall was received outside the growing season. Heavy rains were recorded
Year
Sowing dates 18 May, 1 and 15 June 23 May, 5 and 18 June 27 May, 10 and 24 June 25 May, 8 and 21 June 24 May, 6 and 20 June 18 and 31 May and 13 June 20 May, 8 and 26 June 4 and 31 May and 21 June 15 May, 5 and 26 June 19 May, 9 and 30 June 16 May, 1 June and 1 July
1988 pasture 1989 pasture Continuous wheat Continuous wheat 1988 pasture 1989 lupins 1988 wheat 1987 pasture 1989 pasture 1988 lupins 1987 pasture
in January and October, but the October rains were generally too late to be used by any but the late sown or long season cultivars. The experimental design was a split-plot design involving 3 sowing times, 12-15 cultivars, and 3 replicates. Times of sowing ranged from early May to early July (Table 1). The first sowing date was always as early as the season would allow, which in some instances was not until late May. A selection of commercial cultivars and crossbreds from the Western Australian Department of Agriculture's wheat breeding program was used. Seven cultivars, common to all experiments, with a range of maturities (Table 3) were selected for detailed analysis in this paper. Six of the cultivars are recommended for sowing in the north-eastern wheatbelt (Brown 1991). Aroona is not recommended for this area, but was included because it is a control used in Western Australian wheat cultivar evaluation trials. Leaf diseases, mainly yellow spot (Pyrenophora tritici-repentis) and septoria nodorum blotch (Septoria nodorum) were observed to be present at low levels at most sites each year. Leaf disease was more prevalent at the early times of planting and at the North Mullewa site where trials were in a con&nuous wheat rotation.
Table 2. Growing season (May-October), annual and long term average rainfall (mm) for various locations
Trial:
BallaA 1 2 Av. 1989 1990
Mullewa 3 4 Av. 1988 1989
Morawa
5
6 Av. 1989 1990
Perenjori 7 Av. 1989
Latham 8 Av. 1988
May June July August September October Totals Jan.-Dec. May-Oct. A
38-year averages (L. Bums pers. comm.).
Averages are for Dalwallinu, 15 km north of Pithara.
Kalannie 9 Av. 1990
PitharaB 10 Av. 1989
Cadoux 11 Av. 1988
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Early sowing and grain yield of wheat cultivars Table 3. Characteristics of seven cultivars used in experiments Cultivar
Year of release
Wilgoyne Gutha Kulin Eradu Aroona Reeves Spear
1989 1983 1986 1982 1981 1990 1983
Development Class DaysA
Height
-8
Very early Very early Early Medium Medium Medium Late
sowing gave the highest or equal highest yield at every site except Latham (trial 8). Yields from sowings after early June generally declined rapidly. There was a significant interaction (P
