Vineyard Soil
What this domain tests
Vineyard Soil tests how physical, chemical and biological soil properties affect rooting, water supply, nutrient availability and vine health. The exam favours practical interpretation: a soil report, a chlorotic leaf or a drainage problem must be translated into a management response.
Physical properties
Texture is the proportion of sand, silt and clay; structure is how particles aggregate. Loam and clay-loam soils usually hold more water than sandy soils, but clay-rich soils drain slowly and can waterlog. Vine roots need air-filled pores, so compacted or poorly drained subsoil limits rooting depth and increases drought susceptibility. Organic matter improves aggregation, water-holding capacity and biological activity. Topsoil depth and the presence of a restricting layer are often more important than surface texture alone.
Chemical properties
Soil pH controls nutrient availability. Calcareous soils with high active lime can induce iron chlorosis because iron becomes insoluble; total calcium carbonate is less diagnostic than active lime. Cation exchange capacity indicates the soil’s ability to retain calcium, magnesium and potassium. Salinity, measured as electrical conductivity, can reduce water uptake. Soil sampling must be representative: sample the rootzone at the correct depth, mix subsamples and avoid fertiliser bands.
Worked example
A vineyard block has pH 8.3, 14% active lime and leaves with interveinal yellowing while veins remain green. The likely diagnosis is lime-induced iron chlorosis. Options include selecting a more tolerant rootstock, improving organic matter and drainage, avoiding excessive irrigation, and applying chelated iron through the soil or correctly timed foliar sprays. Simply lowering pH over a large vineyard is rarely practical.
Traps that cost marks
Do not confuse total lime with active lime. Do not interpret pH measured in water as if it were measured in KCl. Do not recommend nitrogen for every yellow leaf: chlorosis may be iron, magnesium or waterlogging related. Do not sample only the surface when rooting depth is the issue.
Key points
- Texture, structure and depth control water and air supply.
- Active lime is the key indicator of lime-induced chlorosis risk.
- Soil pH affects nutrient availability, not just acidity.
- Representative sampling depth and mixing are essential.
- Drainage and compaction often explain poor vigour better than fertility.