Drainage is the most important requisite in a potato soil. It must either be present naturally or supplied artificially.

So important is this subject considered that a chapter on tile drainage is being included (Chapter V (Drainage)).

As in the subject of climatic requirements, much regarding the soil requirements of the potato may be learned from a study of the soil conditions in the home of the wild potato. In its native habitat the potato grows in loose, friable, well-drained, easily worked, perfectly aerated soil.

The physical or mechanical condition of a potato soil is a more important factor than the fertility, although any plant requires a rich soil for its greatest development.

For the uniform, perfect development of all parts of the potato plant there must be a constant supply of air and oxygen, moisture and fertility. It is impossible to grow good potatoes in a waterlogged soil.

Where soils are infected with disease it is found beneficial to turn out the furrow in which the potatoes are to be planted, allowing the sun and air free access to it. European growers who practise this believe that they lessen liability to infection.

In the Twin Falls country in southern Idaho - one of the best potato growing sections in the world the soil is called lava ash, is very mellow and friable, does not bake, can be worked at almost any time in the year, is rich and well drained both by a natural slope and by deep coulees running through it to Snake River.

At Greeley, Col., some of the soil in which potatoes are grown is a medium desert loam, drained by an underlying strata of coarse gravel; other soils are heavier.

The soils at Carbondale are a reddish granite formation and very mellow. The country is very steep. It is drained by the Crystal River, a rushing mountain stream with an abrupt fall. This gives ample drainage to the more level mesa or table lands on which potatoes are grown.

In Wisconsin, Michigan, and other Middle Western States many of the best potatoes are grown on river sands and sandy loams - soils that are very well drained naturally.

In the Salinas and Lompoc districts in California the best potato soils are friable, sandy loams.

In Aroostook County, Maine, the soil is rolling, well drained, of lime-shale formation, and easily worked at all times.

Large quantities of potatoes are now being grown in the Red River Valley, in Minnesota and North Dakota, on the big grain farms. The soil is a rich alluvial deposit.

Potatoes are grown on well-drained sandy soils in Great Britain, but also on heavier soils perfectly drained. The soil in some places in Europe has been made suitable to the crop, even when not naturally so. There are places where sand to a depth of five inches has been hauled on and incorporated with heavy clay. Other heavy soils are kept filled with humus by cover cropping and the use of barnyard manures.

These experiences show that districts not generally considered capable of growing potatoes - like the territory around Denver and some parts of California - can be made to produce the crop if proper methods of soil treatment are used.

The opinions of various authorities as regards potato soils are very interesting; because each is based on local conditions and experience. While there may seem to be differences of opinion, all really agree on the essentials - drainage, aeration, and easily worked, mellow, porous soils.

Wm, D. Hurd, of the University of Maine, says:

In its native state the potato is found growing on high, dry plateaus. One of the first essentials then is a well-drained soil. The kind of soil and proper drainage influence yield, cooking quality, liability to disease, and keeping quality of the tubers. ' Virgin soils' grow potato crops of the finest quality because they are usually free from diseases which affect the crop and have an abundance of organic matter and available plant food. The most desirable potato soil is a deep, free, easy working loam. Loams which are inclined to be sandy are usually too poor in plant food and dry out readily, while those inclined to clay may be too hard and apt to retain too much moisture. A proper supply of humus is very important in potato growing. The humus content determines to a great degree the moisture content of the soil. The potato is a crop which uses considerable water in making its growth. Much moisture is, of course, lost by evaporation from the soil, but aside from this it is estimated that a yield of 225 bushels of potatoes to the acre takes 1,420,000 pounds of moisture from the soil. Unless humus has been supplied in the application of stable manure to previous crops, green crops such as rye, oats, clover, etc., should be turned in to supply this."

David Young, editor of the North British Agriculturist, Glasgow, Scotland, says:

The potato crop is not at all fastidious as to the soil in which it is grown, provided the soil be properly cultivated and manured, and in practically all classes of soil, excepting the stiffest clays, this crop may be successfully grown."

Professor A. R. Kohler, Assistant in Horticulture, University of Minnesota, in "Bulletin 114," says:

A sandy loam soil usually produces potatoes of better quality than a heavier soil does. It also has the advantage of remaining in a more mellow condition during the growing season, thus giving the tubers a chance to become more shapely, and making it easier to dig the crop. A heavier soil will sometimes produce a larger yield because it is often more fertile, but brown rot of the tubers is apt to be worse on such soils. New land is the best for large yields, or sod land which has been in clover or meadow. Sod land is sometimes infested with white grubs and wire worms which may do much damage. These pests are not likely to be present in sufficient numbers to do very extensive injury unless the land has been sod for some years."

In a treatise on "Early Potato Growing" for the Department of Agriculture and Technical Instruction for Ireland, Matthew G. Wallace says:

Soils have considerable influence on earliness. Sandy loams are best, red or gray. It is wonderful what can be done even with poor sand under favorable circumstances and with generous treatment. Here again Rush (a district) may be cited. Much of the soil there appears to be drifting sand, and farmers have to resort to an expedient of lacing it with straw and seaweed to keep it from blowing away and laying bare the potato sets. Still it bears good crops of potatoes. Black lands, or bogs, are not suitable for early potatoes, as the frost seems to grip more keenly there, and, besides, the sample is not so nice, nor is the quality so good."

Walter P. Wright and Edward J. Castle, in "Pictorial Practical Potato Growing," say:

Potato soil is a loam with an inclination to heaviness rather than sandiness, but cultivation will do much to bring either a clay or a sandy loam into line."

Organic matter, or humus, is a great factor in potato soils. It tends to hold light, drifting soils and makes them more retentive of moisture.

When properly worked, loams, sandy soils, alluvial silt soils, lava ash soils, granite soils, limestone soils, and many others are good for potatoes.

The following by Lord Ogilvy, from the Denver (Col.) Post, is interesting to the student of potato soils:

A Greeley farmer said the other day that his soil was a good one, especially for potatoes, if he kept it built up so that it would not blow. This soil, twenty years ago, was considered about worthless, except to grow alfalfa, and there was considerable difficulty in securing a stand. Even in this unfavorable season (1910) the output of potatoes is 125 sacks to the acre.

This particular farmer moved off a very rich bottom farm, which was a heavy producer of all crops except potatoes, on to the land he occupies to-day. I remember that his neighbors said he was foolish for moving, that the bottom land had twice the productivity of the other tract.

The man who moved said that they were right in a general way, but that he had always made his money with potatoes, which blighted on the bottom lands and were only of moderate quality, and that the nature of the subsoil made their irrigation a matter of chance.

I have myself seen water turned on at one corner of a field in such lands, come bubbling up forty or sixty rods away, having in some places sub-irrigated considerable areas to the point of saturation, in others passing through contracted channels, leaving the surrounding soil as dry as a bone.

The man who moved and the man who succeeded him on the bottom farm have both done well by specializing (the latter growing sugar-beets) somewhat on the crops their lands were adapted to, but the potato man has made his money easier, has had less help than is entailed in growing beets, and has been able to make good with the help of his own family; in other words, has had the more self-contained business venture.

By the use of plenty of alfalfa, mostly fed on the place, he has added to his sandy soil the element it needed by increasing its organic and humus content, and the sand seems to contain those other elements necessary to the growth of good, clean potatoes."

The value of aeration is very convincingly illustrated by digging into a hill of potatoes grown on heavy, poorly drained and aired soil. The deeper into the hill that tubers are found, the rougher and more diseased they are. It is also a notable fact that the exhibit potatoes from an average field are those that develop close to the surface.