Soils differ in physical and chemical properties that affect crop productivity. Soil chemical properties and soil reaction can be managed relatively easily by adding fertilizers, organic amendments and lime. Changing the physical characteristics of the field, however, can be more difficult, sometimes impossible. This is why field selection (matching the physical characteristics of the field with crop requirements) is so important. Soil survey reports, maps, on-site soil profile investigations, and producer's experiences are valuable managerial tools in this respect. The following is intended to assist in field selection by identifying and quantifying the major soil physical characteristics that influence crop performance.

Soil texture refers to the relative proportions of sand, silt and clay particles present in the soil. Potatoes grow well in loams, sandy loams, sandy clay loams and silt loams. These soils have a potentially well-balanced capacity to retain water, form a stable structure, provide adequate aeration, and possess a suitable thermal regime. The more sandy or gravely soils present an increased risk of drought, lower nutrient retention capacities and a higher potential for nutrient leaching. The more clayey soils, on the other hand, have a tendency to compact and crust, thus presenting a higher risk of both drainage impedance and water erosion.

Potato crops grow best in porous, non-compacted soils that ensure optimum water, nutrient and oxygen supply. Deeper soils provide a greater volume of soil from which the roots can access nutrients and water. Shallow soils limit root growth. A lack of adequate root growth restricts the plant's ability to obtain needed nutrients and to withstand periods of moisture stress, thereby increasing the risk of drought damage. The risk of drought damage is particularly high for tubers during their differentiation and early development stages in June and July.

Much of the soil in the Atlantic region has a naturally occurring compacted subsoil. In addition to restricting root penetration and growth, the compact layers inhibit water movement through the soil profile and can create perched water tables. The depth of soil above the compacted layer will also determine the susceptibility of the soil to further degradation from compaction and erosion.

Approximately 80 % of the potato roots occur in the top 30 cm of soil with the remaining 20 % occurring below 30 cm. The ideal soil depth is at least 40 cm above compacted subsoil or 75 cm above bedrock. However, because the potato crop is shallow rooting, it is still able to produce good crops in shallower soils when rainfall is adequate. Fields that have less than 20 cm of loose soil above compacted subsoil or less than 40 cm above bedrock, however, should not be selected for potato production. Management practices that will increase soil conservation and improve soil quality are especially necessary on the shallower soils.

Well to moderately well drained soils are ideal for potato production. Although rapidly drained soils will support potato production, management practices that increase organic matter and soil moisture holding capacity should be implemented. Where rainfall is inadequate, these soils may also respond well to irrigation. However, due to increasing concern about non-point-source pollution, the suitability of rapidly drained soils should also be evaluated from the standpoint of possible contamination of ground water with agricultural chemicals.

Imperfectly drained soils will support potato production, although subsurface drainage may be necessary to overcome the limitations caused by excess moisture. Excessive water in soil limits the free movement of oxygen that is necessary for healthy root and tuber development. Excessive water in soil also decreases the efficiency of nutrient uptake, increases the incidence of fungal diseases, delays spring tillage and planting and increases the risk of soil compaction. Poorly and very poorly drained fields should not be selected for potato production.

Potato production is not suited to potentially erodible soils because of tillage requirements and the lack of plant cover in the early part of the growing season and after harvest (where soil conservation measures are not applied). Soil erosion results in the loss of the most productive layer of soil which, over time, decreases rooting depth often leaving a compacted, very slowly permeable, acid subsoil to produce potatoes. Not only is the subsoil less productive, but it is also more susceptible to further erosion. In addition to decreasing soil productivity, soil erosion can also threaten the quality of nearby surface waters.

The risk of soil erosion is proportional to the length of the slope and the severity of the grade. Practicing potato production on steep slopes presents a high erosion risk. The steeper the field's grade, the less suitable the field is for potato production. Ideal sites for potato production have slopes of less than 5 %. These sites do not require engineering soil conservation measures unless slope lengths are excessive. Slopes from 5 to 9 % will support potato production although agronomic and engineering conservation measures to reduce the risk of soil erosion should be adopted. Slopes greater than 9 % are not recommended unless engineering conservation measures are in place.

Gravels, stones and cobbles can be beneficial by helping to reduce the effects of compaction by heavy machinery, increasing infiltration and helping to prevent soil erosion. However, because large stones hinder soil preparation, can damage harvesting equipment and increase the chances of potato bruising during harvest, they must be removed from fields. Soils with up to 20 % gravel (7.5 cm in diameter or less) can have enhanced water holding capacity, water infiltration and thermal regimes. Soils with greater than 30 % stones are not recommended.

Rock outcrops hinder soil preparation, seeding and harvest. Fields that have more than 10 % rock outcrops are not recommended for potato production.