The potatois a cool-climate plant, and a moderate temperature is necessary for its best growth. Therefore, early-spring planting usually assures that the crop will be well established before the period of high temperatures. The potato grows best in regions where the mean summer temperatures are relatively low, generally not exceeding 29° C, and where ample soil moisture is available during the growing season. Adequate moisture is especially important from the time tubers begin to form until slightly before harvest.
In most years, rainfall in southern regions is sufficient for the production of the early and main crops. In nearly all areas the fall crop would be materially benefited if irrigation water could be applied at critical periods during the growth of the plant. The ideal condition is a uniformly ample supply of soil moisture throughout the growing season. This is especially important from the time tubers begin to form. Adequate moisture at the time of tuberization plays an important role in determining the number of tubers formed, or of the set. Uniform moisture after tuber formation is an important factor in determining the development of tubers, especially their size, smoothness, and shape.
Soil.The choice of soil for potato growing is very important because soil influences both growth and yield. The best soil for potatoes are well-drained, sandy, gravelly, or shale loams, and loams well — supplied with organic matter and available plant food; well-drained, friable loams and sandy loams are well suited for potato production, because they generally yield brighter skinned and better shaped tubers. Generally speaking the early potato crop is grown in sections where the soils are predominantly loams and light sandy loams; because these types of soils warm up faster than do the heavier types. The heavier soils such as clays and clay loams, are more difficult to prepare and often tend to puddle in periods of high rainfall if worked at the wrong time. Certain soils should be avoided because they lack the necessary physical and chemical qualities or are infested with disease-producing organisms. Soils that are neutral or alkaline or that have produced many scabbed tubers are likely to produce diseased potatoes. Heavy, poorly drained clay and clay loam having tight subsoil and poor tilth are also likely to produce small crops of ill-shaped, poor quality tubers. Premature ripening of vines and consequent reduction in yield occur also on deep sandy soils that tend to blow, are subject to leaching, or possess low water-holding capacity. An ideal potato soil must be high in fertility, friable, deep, and with an acid to slightly-acid reaction. Soil type definitely influences the shape of the tuber, light, well-aerated soils producing better shaped tubers than heavy soils. Sandy soils are excellent for early potatoes, but in dry seasons the crop may suffer for lack of moisture. Heavy clays fail to produce tubers of good quality or shape — sandy loams and medium loams are the most satisfactory upland soils. Peat and muck are excellent potato soils when they have adequate surface and subsoil drainage. Because of their high percentage of organic matter, and lower temperature they yield more heavily than mineral or upland soils, when properly managed.
Time of Planting.The time of planting depends upon the prevailing climatic conditions. Experiments conducted by many agricultural experiment stations on time of planting show definitely that the largest yields are secured when planting is early. Potatoes should be planted in our upland soil before it is safe to plant corn. Peat and muck soils as a rule cannot be worked as early as the upland soils and planting may have to be delayed until a proper seedbed can be prepared.
The critical period in the life of the potato occurs when it is developing its tubers, and it is very essential that the climatic conditions should be as favourable as possible at this time. The yield is very materially lessened if a protracted spell of heat and drought occurs during this period. If the weather is cool and if there is adequate moisture and proper disease control, a good yield is practically assured, provided the plants have been given proper cultural attention. In sections where the season is longer than it is necessary to mature a crop, the problem is to select a planting date which will provide the most favourable climatic conditions during the period of tuber development.
Depth of Planting.Since the tuber-producing stolons are formed above the seed pieces, it is important that seed pieces be planted deep enough to permit the development of a good set of tubers. The early crop should not be planted as deep as the main one. A depth of less than 10 cm on light soils is sufficient for the early crop and 6 cm for the main crop on heavy soils. The planting should be shallower in heavy than in light soils. Shallow planting in seasons of dry weather will result in small tubers. On the other hand, in more favourable seasons the tubers in shallow hills will push out of the soil and become sunburned.
Spacing and Rate of Planting.The distance between plants and between rows varies considerably as to the varieties. The spacing within the row and the distance between rows are determined in some localities by the natural fertility of the soil, its moisture-holding capacity and the supply of available plant food that is to be applied to the crop.
The quantity of seed to plant per hectare depends not only on the spacing but also on the size of the seed pieces. The spacing between tubers is usually 20—30 cm and the distance between rows may be 70 cm. When rows are less than 30 cm apart the use of a cultivator becomes difficult. Spacing in the row and the distance between rows should be such as to obtain a maximum yield of potatoes and at the ονε time permit tractor cultivation.
Cultivation.Cultivation practice will vary according to the type of soil and the district in which the potatoes are grown. The control of weeds is the principal benefit derived from cultivation, besides the objectives in cultivation are to aerate the soil, encourage root growth and supply soil covering for the developing tubers. In general,but two systems, level and ridge cultivation, are practised in the regions producing late potatoes. In the level system the weeder or smoothing harrow is usually used once or twice before the plants emerge. The teeth are angled back so as not to disturb the sprouted seed piece. Deep cultivation close to the rows follows as soon as the plants are high enough to distinguish the rows. In the ridge method, riding or walking cultivators are used to loosen the soil and to destroy weeds between the rows. Horse hoes with disks or wings are used after each cultivation to throw up earth and smother weeds along the row. With motorized equipment, cultivation and hilling are done in one operation. In the early cultivation the sprouting seed or young plants are buried once or twice to smother young weeds near the plants and protect the young potato plants from late frosts. The first cultivation should be deep and close to the plants. The soil between the rows should be stirred and every effort should be made to keep it loose.
Harvesting.The date of digging potatoes should be influenced largely by the condition of the crop. The tops should be dead and the tubers should be thoroughly hardened so that the skin will not peel easily or bruise. Potatoes can be dug when vines are still green, but maximum size of tubers is secured only if the vines are allowed to grow until the tops are dead. Potatoes should be picked up within a few minutes after digging and placed in the shade when they are dug during hot weather. Potatoes exposed to bright sunshine will rot quickly in storage.
The harvesting season for most late crops of the North begins in September and extends into late October. The crop is harvested with the elevator type of digger hauled either by a pair of horses or by a tractor.
Prevention of Mechanical Injuries.In general, more attention needs to be given to the prevention of mechanical injuries at the time of harvest. Skinned, bruised, or cut tubers will shrink more rapidly than sound ones. Also, disease-producing organisms may enter injured potatoes and cause decay. Allowing potatoes to mature before digging will help to prevent mechanical injury.