The soils of potato growing areas of New Zealand

Abstract

Apart from climate and location, there are two factors which influence where potatoes are grown. These are the suitability of the soil and the end use of the potato crop. The New Zealand literature on potato growing is not very informative about the soil properties and qualities that influence yield and quality of crops. The ideal potato growing soil is said to consist of a deep, well-drained, relatively stone-free sandy loam, loam or silt-loam with good structure and a high air capacity. These soil properties and qualities determine the three key physical growth requirements; a relatively large volume of soil for growth and development of tubers and roots, an adequate and uniform supply of moisture and good aeration. Two other characteristics which are highly desirable where machinery is used to sow and harvest crops are: (1) that the land should be flat or gently sloping and (2) that the management areas (paddocks) should be relatively uniform in soil. Variations in soil that influence maturity or quality are undesirable. Not all potato growing soils have this ideal combination of characteristics. The end use of the potato crop, as well as the need to spread production through time as well as to provide crops near each major centre of consumption, also influences the selection of soil for potato growing. For example, the total area of early crops is small and consequently small holders can select soils in favoured microclimates such as the Pukekohe area. Main crops require larger areas of uniform soil near markets, whereas seed producers can select suitable soils in more remote locations. With process crops where quality is an additional requirement special attention must be given to selection of soil near processing plants. Contrary to common belief, potatoes are not grown on a wide range of soils in New Zealand. Most of our potatoes are grown on only four out of seventeen soil groups, and on about 35 out of about 2,000 soil series. Table 1 outlines the main soil groups and typical soil series used for potato growing. Small areas are also grown on peat (Waimairi) and immature yellow-grey earths (Ohakea). Natural soil fertility is much less important than favourable physical properties in the selection of soils for potatoes. It is much easier to correct for nutrient limitations but very difficult to modify soil physical properties.