Studies in crop variation. VIII. An application of the resistance formula to potato data

The table of results given in the last section shows that for all experiments for which the Resistance Formula has been fitted the values of the constants are consistent, bearing in mind the standard errors to which these values are subject. The constants for nitrogen may be held to have been determined with some approach to precision, but those for potash are not so well determined. We find at Rothamsted, for example, that the crop responds to a moderate dressing of potash, but higher dressings do not usually improve the yields any further. This fact limits the precision of the formula. The reader is asked to refer at this point to the full descriptions as to the meaning to be attached to the constants of the formula given by Bh. Balmukand in the earlier paper(1). The constants an and ak, called the importance factors, are interpreted as determining the capacity of the crop to recover the particular nutrient out of the soil. The chemical analysis of the tubers grown under nitrogen and potash starvation conditions should, therefore, furnish us with values which should be of the same order of magnitude as obtained by the formula. The minimum nitrogen percentage figure is 0.204, which when reduced to our units is equivalent to 4.57 lb. of nitrogen per ton of potato. The values obtained from the Resistance Formula are as close as the standard errors allow us to expect, and are also of the same order of magnitude as the chemical composition of the tubers demands