This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
Further experiments conducted by the department proved that not only was there a great increase in yield obtained from boxed as against unboxed seed, but that the system of spraying with the sulphate of copper solution, if efficiently and timeously carried out, had not only a most marked effect in preventing or checking disease, but that it had also a most marked further effect in prolonging the growing period of the crop, and in that way increasing the yield. Mr. Wallace unhesitatingly and emphatically declared his settled conviction that, when once the Irish growers had learned to box and spray, the Green Isle, with its potato area of 600,000 acres and its relatively small population of 4,250,000 souls, would be able not only to supply the wants of its own people, but would also be able to regularly export enormous quantities to the British markets instead of requiring to import large quantities, as had often been the case in former years. The Irish department has therefore concentrated its efforts on stimulating and encouraging the Irish cultivators to box and spray, and the Irish growers have been quick to learn a lesson which promises to be so very profitable to them.
Last year the Irish growers who had learned to box and spray had very heavy and sound crops and the total output of potatoes in the Green Isle was so heavy and plentiful that it is having a most decided effect, and keeping prices at a very low level in this country. There seems no reason to doubt that as more and more Irish growers are led to box and spray, the crops grown on the vast area under potatoes in Ireland will be heavier year by year, and the effect of that on the prices in the home market will be keenly felt by British growers. "Within the last few years also another great change, which promises to increase the total average yield of the potato crops of Great Britain, has been taking place. The change in question was due to what may be called the rediscovery of a fact which was well known to the gardeners and other growers of potatoes more than half a century ago - namely, that in getting seed potatoes it was always desirable to get them from a colder and later district and climate than that to which they were taken. In comparatively recent years many English growers frequently obtained potato seed from Scotland, and found that in almost every case the seed tubers grown in Scotland yielded much better crops than those obtained from the use of seed grown in England. The great yield of crop obtained through the use of Scotch-grown seed was, however, generally ascribed to superiority of variety, as the tubers taken south to England for seed were generally of a different variety from those previously grown. That, however, was not the correct explanation. Certain it is that, as a general rule, seed tubers grown in the colder and later climate of Scotland give much better results than tubers grown in the warmer and earlier climate of England. Several reasons may be adduced in partial explanation of this fact. For one thing, owing to the climate of Scotland being colder and later than that of England, the potato crop in Scotland is not usually so fully ripened when it is harvested as the potato crop in England is when harvested, and it is an old but recently rediscovered fact that potatoes harvested before being fully matured are much better for seeding purposes than potatoes which have, in a way, exhausted their vitality in ripening. For another thing, again owing to the climate of Scotland being colder and later than that of England, seed tubers taken from Scotland to England for seeding purposes are not usually so much sprouted as those in the warmer south at the same time of year, and consequently do not lose so much of their stamina and vitality through the breaking of sprouts in handling.
But over and above these considerations there is undoubtedly in the potatoes grown in the colder and more bracing climate of Scotland some subtle force which makes for greater constitutional vigor and habit of growth than is characteristic of those grown in the warmer and more relaxing climate of England.
In 1903 Professor Seton, at the Yorkshire College farm, carried out an experiment on this point, and found that seed grown in Scotland, when planted in Yorkshire, showed an increase of crop to the extent of two tons per acre, and was much freer from disease than the adjoining crop of the same variety grown from native seed. Much attention was attracted to these findings at the time; but since then they have been very fully confirmed, not only by the experience of hundreds of English growers, but also by scientific and careful experiments at practically all the agricultural colleges in England. At the Cambridge University farm Professor Middleton found that the crop from Scotch-grown seed was so vastly heavier than the crop from native seed of the same variety that he was fairly staggered at the result, and half inclined to doubt the accuracy of his own findings. At the Northumberland County Council farm of Cockle Park, Professor Gilchrist found similar results, but found that these were only in accord-dance with the experience of growers seventy or eighty years ago.
At date of writing, the latest series of experiments recorded in this connection is a most exhaustive one from the Lancashire County Council farm, where four different tests, all in duplicate, were carried out with wonderfully uniform results, which led the experimenters to draw the following conclusion - viz., seed potatoes brought from a northern to a southern latitude give a larger crop than those from a southern to a northern latitude, the difference, according to this experiment, being on the average about one hundred bushels per acre.
If the English growers not only learn to box and spray as the Irish farmers are learning to do, but also learn that seed potatoes brought from a northern to a southern latitude give a crop of three tons per acre more than English-grown seed, that will all make for a greatly increased average yield per acre in England and a comparatively lower range of prices per ton.