|Establishment of a vineyard is an expensive, long term investment.
Establishment cost, for trellised vineyards, can amount to as much as R40 000 per hectare. It is well-known that soil, in addition to climate and viticultural practices, is one of the most important factors with regard to yield and quality of the vineyard. It is impossible to modify physical and chemical soil limitations significantly once the vineyard has been planted. Detailed soil mapping and suitable soil preparation, before vineyard establishment, are therefore indispensible in order to accommodate differences in soil type and soil characteristics which may have a limiting effect on successful viticulture.
What does soil mapping entail
A soil survey and accompanying soil map are intended to provide you, the producer, with information about the soil and land form, as well as information required to take decisions about the use of the land and the planning of its development. Soil mapping means that “soil boundaries” should be indicated in some or other way on a map. Two kinds of soil surveys are relevant, namely a reconnaissance survey and a detailed survey. A reconnaissance survey, which also includes the interpretation of aerial photographs, is initially used to identify suitable localities and soils for viticulture. A detailed survey involves a field survey in terms of a specific grid system to provide representative coverage of soil variations so that mapping units may be composed. Detailed surveys are usually undertaken on a grid system of 75 x 75 metres. The minimum profile pit depth for soil description is 1,5 metres, unless an impenetrable layer occurs in the subsoil. For detailed identification and mapping of South African soils the revised system is used, namely Soil classification: A taxonomic system for South Africa (Soil classification work group, 1991). This system is based on the identification of diagnostic horizons and material. The various soil forms are defined in terms of the type and vertical sequence of diagnostic horizons and material. A description is given, inter alia, of the depth of all horizons and material, soil form and family, subsoil limitations and characteristics, texture and soil water conditions. Soil chemical analyses are important at this stage to rectify soil chemical limitations prior to soil preparation.
Soil analysis is essential to determine the suitability of the land for a specific crop. If suitable for viticulture, the interpretations and recommendations of the soil analysis should be done by an experienced soil scientist. Factors influencing suitability of the soil are texture, structure, chemical composition, mineralogical composition, parent material, depth, slope and drainage danger due to topographical position. To a large extent these factors determine the depth of root distribution and therefore the production potential of the soil. Soil potential also indicates dangers with regard to tilling, erosion, cultivation and application of water. Cultivar and rootstock selection, irrigation design and scheduling, soil and crop management and ameliorant programmes are facets which rely heavily on soil surveys. For you, the producer, it is extremely important to discuss the results of soil mapping thoroughly with a pedologist. Soil usually has one or more physical, chemical and/or morphological limitation(s) such as clay content, humidity, occurrence of coarse fragments and compacted subsoil layers, soil acidity levels and nutrition status. In the course of soil preparation, aspects such as i.a. compacted layers, soil acidity levels and nutrition status may be addressed. Since the water holding capacity of soil is adversely affected by a decline in clay percentage and an increase in the occurrence of coarse fragments, the initial irrigation design and scheduling should take this into account. The presence of green/gray soil colours may indicate periodic water saturation and soil management decisions should make provision for this. Soil texture refers to the relative relationship of particle size fractions in the soil and varies from sand to clay. An increase in clay content affects drainage. Soil structure degrees vary from apedal (structure-free, e.g. sand), weak, medium to strong in the case of block structure. Water movement and aeration as well as root development are influenced by soil structure. To a large extent the physical condition of the subsoil therefore determines root penetration. For economic production, vine roots require a minimum soil depth so that root development and water and nutrient uptake are not restricted. One of the aims of soil preparation is to increase root volume in order to buffer vines against unfavourable climatic conditions.
Soil and climatic requirements of crops
For a reliable evaluation of the suitability, potential and production ability of a certain land for a specific crop, it is essential to know the requirements, adjustments and tolerances of crops with regard to soil and climatic conditions. The expertise of various disciplines must be integrated to determine the most suitable use, from an economic point of view, for a specific piece of land. With economic conditions and market trends continuously changing, and with new and improved cultivars and farming practices coming into play, regular re-evaluation of land use is essential and if required, adjustments must be made to accommodate changing circumstances.
Optimal use of resources
For optimal use of your resources, as well as the preservation thereof for posterity, the producer must have access to useful, comprehensive knowledge of soil and climate. Various mechanisms, including the integrated production of wine (IPW guidelines), require the suitability of soil for specific cultivars and soil preparations to be based on soil profile descriptions. Soil chemical adjustments are dependent on a soil chemical analysis by a laboratory. The mapping of a farm entails a once-off expense and serves as a management tool and planning document for the future. However, small scale vineyard plantings are still frequently undertaken without having a soil survey done prior to planting. It is important to plant cultivars according to soil suitability so as to maintain sustainable, economic production without exhausting the soil as a natural resource. This also satisfies the winemaker’s requirements vis – vis quality and quantity.