An example of fractional replication in an experiment on sugar cane manuring

Abstract

Study of the nutritional requirements of sugar cane on a Jamaican estate necessitated simultaneous experimentation with five manurial factors: sulphate of ammonia, superphosphate, muriate of potash, bagasse, and filter press mud. By adopting a one-third replication of a 35 factorial scheme, each factor could be tested at single and double levels for comparison with the absence of the factor.The structure and confounding system of the design adopted have been described and the method of computing the analysis of variance has been explained. Fractional replication introduces special problems of interpretation, and this experiment illustrates how they may be resolved. Each fertilizer clearly benefited the crop, and several interactions appeared; some ambiguity of meaning is an inevitable concomitant of fractional replication, so that care was needed in order to assign effects to the right causes. The most clearly marked effects were:(i) Without phosphate, nitrogen failed to produce any response; where phosphatic manuring was adequate the crop responded well to nitrogen.(ii) Superphosphate and filter press mud were practically interchangeable as sources of phosphate.(iii) Bagasse appears to act as a source of potash; the interaction of responses is not very clearly established, but little extra response to artificial potash occurred when bagasse was given.(iv) No evidence was obtained that the double level of any fertilizer was superior to the single.There was also a suggestion of a reduced superphosphate response in the presence of bagasse.If a recommendation on manuring were to be based on this experiment, it would be that a maximum of 3 cwt. sulphate of ammonia per acre be used with either 4 cwt. 18% superphosphate and 1 cwt. muriate of potash per acre or 10 tons filter press mud and 20 tons bagasse per acre. In reality, of course, no attempt ought to be made to determine a general manurial policy from results of a single year of experimentation on plant cane at one place.The experiment should be regarded rather as typical of what can be done than as a complete investigation of manurial needs.