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.
So Much depends on the conditions in the different districts, that seed bed preparation and planting methods differ somewhat.
The fundamentals, however, are the same everywhere. These are whatever cultural methods are necessary to make a deep, mellow seed bed or root nest. The success of the crop depends on the size and vigor of the root system.
The seed should be planted sufficiently near the surface to get the benefit of the heat of the sun, and deep enough that the root system be in contact with the moist earth.
The seed bed must be sufficiently firm that the rootlets come immediately in contact with the soil particles, yet open enough that they readily penetrate.
Humus - decayed vegetable matter - from every source is an essential in a good potato soil. Legumes and barnyard manure are valuable, and decayed turf, from meadows or pasture, is ideal for potato culture. It seems to "clean' the soil from injurious diseases, and because it has grown in it is thoroughly incorporated in the entire soil. All vegetable matter should be plowed under the fall previous to the cropping season.
The cover crop, or green manure - a mass of vegetation turned under in a green state - has a wonderfully beneficial effect on soils, both for the fertility it furnishes and the bettered mechanical condition. Some of the best cover crops are the clovers and alfalfa, peas, vetch, rye, and Italian Rae grass.
If the manager of an agricultural proposition knows the conditions necessary to accomplish a required result, his problem is to bring about these proper conditions. When Prof. F. H. King, one of the world's greatest soil authorities, was at the head of the Soil Physics Department of the Agricultural College of the University of Wisconsin, his slogan was "Learn to know why - for this teaches how and when."
The philosophy of seed-bed preparation for potatoes and the planting of the crop is simply this:
First. The soil must be loose and mellow to a sufficient depth to make it possible for the root system to spread freely, and for the tubers to form readily and develop uniformly and normally.
Second. The soil must be sufficiently firm that the rootlets may come in contact with the soil particles from which the nutriment for the plant is taken.
Third. There must be sufficient moisture, but not too much.
Fourth. There must be sufficient fertility, and it must be in such available form that the plant can use it readily.
Fifth. The soil must be warm enough at planting time to start the plant vigorously and rapidly.
All of these conditions in the nearest possible perfection are necessary for the production of the most profitable crops. A deficiency in any one will mean loss.
Thorough seed-bed preparation kills weeds and disease germs. The killing of weeds before the seed is planted makes the cultivation of the growing crop easier, and the constant stirring and working of the soil that kills the weeds aerates and makes possible sun action that kills spores and germs of disease. On Mt. Sopris Farm the soil is often worked six, seven, and eight times before planting. When the good results that are accomplished in the preparation are continued by deep cultivation closely following planting, a splendid crop is, in most instances, assured.
Where soils are badly infected with disease germs it is best to rotate the potato crop with grains and grasses. George Sinclair, farm manager of the Earl of Rosebery's Dalmeny Farms, a prominent British agriculturist, says that one year in grain and three in sod will free soils of most potato diseases, and that this practice will make possible the continual growing of big crops.
When crops are to be grown in succession it is found advantageous to open up the furrows in which the potatoes are to be planted and let the sun and air disinfect them for a day or longer before planting.
In the Twin Falls country in southern Idaho, or elsewhere throughout the mountain valleys of the Northwest, potatoes make the greatest yields on alfalfa or clover sod. It is always best to grow them in a crop rotation so that not more than two crops are raised in succession on the same land. Growing potatoes puts ground in excellent tilth for grain, because the thorough cultivation makes large quantities of plant food available for the rootlets of the grain plants. One of the most successful crop rotations practised by the best growers is three years of alfalfa or clover, the last cutting of the hay the third year being plowed under ten inches deep in the fall; two years in potatoes, and one year in grain, reseeding to grass with the grain.
Good crops are raised on both spring and fall plowing, but the latter has several advantages. The ground can be plowed to a greater depth, making a deeper seed bed and a larger storage capacity for moisture. The weathering through the winter makes fertility available, so that the same soil, if turned up, unweathered, in the spring would contain less food in shape to be used by the plant. Fall plowing for potatoes should be deep, at least eight inches, but ten is better.
Fall plowing in north latitudes or high altitudes makes possible the storage of heat from the sun's rays. Land that has been fall plowed is often eight to ten degrees warmer at planting time than land plowed deep in the spring (thereby turning up a cold subsoil). Fall plowing, in this way, lengthens the growing season, where seasons are short, and often eliminates fungous development that might be damaging to tender potato sprouts. Fall plowing should generally be followed by another plowing in the spring.
In the Channel Islands the potato land is plowed eighteen inches deep every four years.
When alfalfa or clover sod is turned under, the plow should be sharp enough to cut the roots; otherwise it is not all killed and the grass may come up later and bother in cultivation.
If manuring is done, it should be in the fall. Probably the best time to apply manure is to the crop that precedes the potatoes - on the clover or alfalfa sod. In this way there is no possibility of the fermenting or rotting manure making a breeding place for disease that might affect the potato. If manure is not applied, similar results in restoring vegetable matter and fertility to the soil are obtained by the turning under of the last crop of alfalfa or clover, should either of these crops precede the potatoes. The freezing and thawing of the average winter help to incorporate the vegetable matter in the soil.