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Response of cotton cultivars to planting date

V.E. Mungomery1, G.T. Mcintyre2 and J.M. Hare1

1Department of Primary Industries Research Station, Biloela, Q. 4715.
2 Department of Primary Industries, Toowoomba, Q. 4350.

Early maturity is generally accepted as a beneficial characteristic of commercial cotton cultivars. Early cultivars are exposed to attack by insects for a shorter period and management inputs such as insecticides and irrigation water may be reduced. However, early cultivars have generally produced lower lint yields than commercial full-season cultivars such as Deltapine 16 when planted in mid-October in Central Queensland. Results have been inconsistent in South Queensland. We considered that early cultivars may produce higher yields, relative to Deltapine 16, if planted later.

In 1977-78, trials were established at Brookstead and St. George in South Queensland, and at Biloela and Emerald in Central Queensland. At each site three early and three late maturing cultivars were planted at three planting times, mid October, mid November and mid December. In 1978-79, the experiment was repeated at Brookstead and Emerald.

There was a substantial planting date x cultivar interaction in both years at the Central Queensland sites, but no such interaction in south Queensland. The early maturing cultivar Tamcot SP37 produced higher lint yields than Deltapine 16 at all planting dates in both years at Brookstead. In Central Queensland, the early maturing cultivars yielded more relative to the later cultivars when planted late, but their absolute yields were still lower than Deltapine 16.

The relative performance of two late cultivars, Namcala and Deltapine 16 was of more interest in Central Queensland. Namcala has higher lint quality than Deltapine 16, but its yield in Central Queensland was substantially less than that of Deltapine 16 when both were planted early. This is in contrast to the relative performance of these cultivars in North-west N.S.W. where Namcala has a yielding ability similar to Deltapine 16 (Thomson, personal communication). The difference in response may be associated with higher night temperatures in Central Queensland. In late plantings in Central Queensland however, the yield of Namcala equalled or exceeded that of Deltapine 16 in both years.

Differential responses and absolute performances of early and late-maturing cultivars changed from South to Central Queensland. This indicates that specific adaptation of cultivars with characteristics such as early maturity and high fibre quality should be considered in a breeding and selection program. In a more practical sense, these results indicate that Namcala should be considered for late plantings in Central Queensland if planting is unavoidably delayed. Further, early maturity in the Brookstead environment is clearly important for optimum production.

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