Many factors influence the choices we make during farm planning. Some may be a tradition, others could be the market trend and the most popular by far is whether the neighbour is doing it. Unfortunately, these anecdotal approaches can cost the farmer dearly since these choices may negatively affect the long-term performance of your 20 to 30-year vineyard investment.
Detailed scientific information about your farm’s soil, climate and terrain (natural terroir resources) is a skilled viticulturist’s essential decision support tools, and should not be omitted during farm planning. To achieve a healthy, balanced and homogeneous vineyard block without factors limiting growth and production, you need to take the proper steps and obtain the right advice at least a year before establishment. The following surveys are required to obtain this information:
Terroir – soil classification
Soil classification will determine the inherent physical properties, limitations and suitability of the soil. This information is vital during vineyard planning decisions, such as choosing rootstock, cultivar, clone, inter-vine planting distance, type and size of trellis system, soil preparation actions, irrigation, subsoil drainage, ridging, mulching and most important, block layout. Consult your local pedologist to assist you with a once-off soil classification survey, ideally for the whole farm to acquire important physical soil information that will guide farm planning for generations to come. This information can also assist significantly before purchasing a farm.
Soil sampling and chemical analysis
Soil sampling and chemical analysis will determine the fertility status of your soil. In addition, the soil scientist will identify nutrient deficiencies, toxicities and antagonisms through chemical soil analysis. Based on this analysis, the soil scientist will prescribe the correct amount of suitable fertilisers to rectify any nutrient deficiencies directly affecting plant growth. Soil amendments, like lime and gypsum, indirectly affect plant growth by improving soil structure, soil pH or helping leach toxic salts out of the soil. The soil scientist should take soil physical characteristics into account when recommending these amendments. Specific amendments and fertilisers, such as lime, phosphate and gypsum, must be calculated and applied before soil preparation. During soil preparation, these amendments and fertilisers will be worked mechanically into the soil. They are basically insoluble and will not work if applied after soil preparation. The uptake and leaching of certain nutrients cause the soil chemistry to change over short periods of time. Chemical analyses older than three years are deemed useless.
Variable-rate application technology
Variable-rate application technology (VRT) helps the spreader apply only the prescribed amount of costly fertilisers and amendments in the right place using a GPS. This technology decreases the total amount of fertilisers and amendments needed and reduces the chemical variability of your block.
Soil health or microbial diversity is often overlooked, but is essential for healthy vineyards. Most of these microbes occur in the topsoil. Therefore, preserving the topsoil is of utmost importance. Improper soil preparation can invert the soil causing the organic, microbe-rich topsoil to be lost in the subsoil, while the chemical unfavourable, organic poor subsoil is brought up to the surface. Planting inter-row cover crops and adding compost can significantly boost soil health. However, manure additions must be made carefully to avoid the toxic build-up of salts. Analysing topsoil and fine-root samples for nematode and other pathogens is a wise investment and can influence factors such as rootstock choice.
Climate analysis of your location can be done by studying long-term data obtained from the closest weather station. However, the climate varies over short distances due to altitude and proximity to water bodies. Interpolated climate grids consider these factors and better estimate your farm’s climate. Important climate indices, such as growing degree days, mean diurnal temperature range, annual rainfall, rainfall seasonality and maximum growing season temperatures, are essential when choosing suitable cultivars. Combined climate and soil data of the farm will also provide a base for realistic yield estimates for a specific vine/rootstock combination.
Terrain analysis maps show visual terrain variability on your farm, which influences the microclimate, soil variability and water movement. Using Geographic Information Systems (GIS), a terrain analysis helps grasp this complex and obscured part of terroir. Digital Elevation Modelling (DEM) uses precise contours to create and visualise the following seven terrain elements:
- Altitude or mean height above sea level, affects the lapse rate (the rate at which temperature decreases with increasing height), the site’s wind exposure and the water pressure needed for irrigation.
- Aspect or the direction which a slope faces, affects the amount and timing of solar irradiation received (eastern slopes get more sun in the morning, while western slopes get more sun in the afternoon), which significantly affects the daily temperature curve within the vineyard. South-facing slopes are colder than north-facing slopes in the Southern Hemisphere at the same altitude and nearby location. Aspects facing prevailing winds have a cooling effect, and aspects facing strong storm winds lie at risk of damage.
- Slope steepness affects mechanical factors, such as tractor and harvest machine movement, need for terracing, subsoil drainage and erosion hazards. When the slope becomes too steep (> 11°), the construction of terraces must be considered since the use of tractors and other implements become too dangerous. The slope is vital in all aspects of farming. It will determine row direction for adequate drainage, mechanisation and labour intensity. Steep northerly slopes also receive more solar irradiation than flat ones. Although steeper slopes are more challenging to manage, these slopes are where some of the best wines in the world are grown.
- Curvature is the form of the slope and it determines the surface drainage capability of that slope. Convex slopes redirect water and are well-drained, while concave slopes accumulate water and are usually wetter. Concave slopes also collect colluvium and organic matter from higher-lying areas. The soil on concave slopes tends to be deeper, more fertile and have a higher water holding capacity than soils on convex slopes. These sites are generally chosen for cultivars that ripen later, while early varieties prefer convex slopes.
- Day length is the amount of time that direct sunlight exposure is received. It is measured in hours of sunlight for a specific day of the year. Sites with longer day lengths are usually on crests. Deep valley bottoms have the shortest day lengths created by the surrounding hills and mountains’ shadowing effect. The less the direct radiation duration is for a site, the longer the cooling period will be during the night. Day length has an immediate effect on the crop’s available time for photosynthesis and night-time respiration.
- Solar radiation is the number of photons that are emitted by the sun, and irradiation is the received amount that is measured on a specific surface. Altitude, latitude, slope orientation and angle of a particular surface (with respect to the sun) and atmospheric variables (thickness and permeability) all influence the amount of energy a site receives. This amount of received energy is measured in watt-hours/m2 and is used by the leaves for photosynthesis. It is not directly correlated to ambient temperatures. Air molecules absorb this energy which leads to a rise in temperatures. Although higher altitudes receive more radiation, the less-dense air absorbs less energy, leading to lower temperatures at higher altitudes.
- Surface hydrology is always essential on a farm and influences various farming activities such as drainage, erosion control, dam locality, etcetera. The water accumulation model shows the direction and accumulation of surface water according to the surface model. The darker blue lines will accumulate more water than the lighter blue lines. This model can help to identify erosion risk areas, install drainage and redirect water to dams.
– For more information about these services, contact the Vinpro Soil and GIS consultation team at 021 276 0432.