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Published online by Cambridge University Press: 03 April 2017
An attempt is made to investigate some techniques of experimentation, based on data from uniformity trials and experiments on tea conducted in different regions of north-east India. The study showed that:
i. Adjustment of yield due to covariance generally ceased to be efficient after the first four years of experimentation in manurial trials and after two years in pruning trials. Adjustment based on average yield over a period of four to six years resulted in an increase in efficiency.
ii. Among the ancillary variables of pretreatment yield and pruning weight, the former proved to be generally more efficient, but when cost of operation is taken into account the latter was economical and, therefore, preferable. The two variables together, in a multiple regression, did not show any extra gain. Use of the pretreatment late crop, from September to December, was generally more efficient than using the whole season's crop.
iii. Coefficient of variation showed a declining tendency with age, the fall being more marked up to six years of age. This suggests that, for a given degree of precision, more replication would be required for experiments with young tea than with mature tea.
iv. Increase in plot size, up to 48 bushes, resulted in an increase in information per replicate in Darjeeling, though plots of smaller size would be more economical.
v. On the basis of five uniformity trials in the Assam valley, Darjeeling and Cachar district, it was observed that for the same values of cost components proportional to number of replications and total area under experiment, the optimum plot size in Darjeeling and Cachar was about half that for the Assam valley.
vi. Long and narrow plots, oriented with their longer sides extending along the contour lines, within blocks of which the longer sides ran down the slope, proved more efficient than other alternatives in Darjeeling district.
vii. Systematic plucking of 1 in 2 out of the totality of plucking rounds, for experiments running for two or more years, provided estimates of treatment contrasts within 5 per cent of the population mean (P = 0-05). For a higher margin of error, of 10 per cent of the mean, systematic pluckings of 1 in 3 or even 1 in 4 would suffice if the treatment comparisons were based on five or more years.