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Thermal requirements of three brassica species under various seeding dates

Diwan Singh, V. Umamaheswara Rao and O. P. Bishnoi

Department of Agricultural Meteorology, Haryana Agricultural University, Hisar-125004,India

Heat units have often been used to predict the phenological development and maturity of crops (1, 2). However, for rape and mustard the relationship between heat units and growth stage does not appear to have been quantified. This work studies the development of Brassica species in relation to the environment.

Methods

Field experiments were carried out at HAU, Hisar, India during the winter seasons (Oct-April) of 1984-5 to 1986-7. The treatments consisted of three seeding dates, Oct 10 (S1), Oct 25 (S2), Nov 5 (S3); and two cultivars each of the Brassica species B. juncea, B. napus and B. carinata. The treatments were replicated three times and received normal fertiliser application and recommended agronomic practices for the region.

The number of days required for vegetative stage, bolting, termination of flowering on the main shoot and harvest were recorded when 50% of the plants reached the specified growth stages. Heat units (day C) per day were calculated as the difference between the daily mean temperature and the growth threshold temperature of 5C (1). Cumulative heat units were recorded from seeding to the various growth stages.

Results and discussion

The data indicates that the accumulated heat units to reach different growth stages from seeding decreased with delay in seeding in almost all cases. The differences between S1 and S2 being more pronounced as compared to S2 and S3 seeding dates. In general the crops took fewer days to reach maturity as the seeding was delayed (Table 1).

Table 1. Heat units (HU) and days required to reach harvest (GS4) in cultivars of Brassica species sown on three dates

There were considerable differences in accumulated heat units and days to reach different growth stages amongst species and cultivars. This is consistent with previous findings (3). B. juncea (RH-30) and B. napus (HNS-8) had the shortest duration amongst the six cultivars, reaching harvest in 1439 day C (132 days). On the other hand the latest was B. carinata (BC-2) which took 2,115 day C (174 days).

1. Gilmore, E. C. & Rogers, J. S. (1958). Agron. J. 50,611-15.

2. Bishnoi, O. P., Rao, V. U. M.,& Diwan Singh, (1985). Annals of Arid Zone, 24,241-250.

3. Kasa, G. R., & Kondra, Z. P. (1986). Field Crops Res. 14,361-370.

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