Riassunti VERIFICATO
Riassunti LABORATORI - Chimica del Terreno
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This document details essential laboratory methods for soil analysis in viticulture and enology. Learn to calculate total limestone using the calcimeter of Scheiber, determining soil pH, and quantifying active limestone reacting with ammonium oxalate. Explore soil texture analysis via sedimentation (Stokes' Law) and the Walkley-Black wet method for organic matter content. Finally, understand the cation exchange capacity (CSC) assessment involving barium chloride and magnesium sulfate titrations. These techniques are crucial for evaluating soil health and fertility for optimal vine growth.
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- Total Limestone Calculation:
- Utilizes the "calcimetro di Scheiber" to measure CO2 produced from soil's reaction with hydrochloric acid (CaCO3 + 2HCl → CaCl2 + H2O + CO2).
- Results are expressed as % CaCO3.
- High calcareous soil (>10%) can lead to insolubilization of phosphorus and iron.
- Soil pH Calculation:
- Involves mixing 10g of soil with 25ml of pure or distilled water.
- After agitation and settling, the pH is measured using a portable pH meter.
- Active Limestone Calculation (for total limestone >10%):
- Measures limestone reacting with ammonium oxalate (COONH4)2, considering crystal structure (calcite/aragonite) and fineness.
- Procedure includes reacting 2g of soil with 0.5ml of 0.2N ammonium oxalate, agitation, filtration, and subsequent titration with 0.1N potassium permanganate in both blank and sample tests.
- The percentage of active CaCO3 is calculated from the titrated volumes.
- Texture Determination:
- Based on the sedimentation of soil particles in a liquid, following Stokes' Law.
- 10g of fine soil is mixed with 200ml of water and sodium hexametaphosphate to separate sand, silt, and clay.
- Utilizes an "Esenwein sedimenter" for sequential sedimentation of sand (after 12 min), silt (after 20 hours), and remaining clay.
- Particle fractions are determined by weighing dried samples taken at specific intervals.
- An "optimal soil" (franco) typically contains 70% sand, 20% silt, and 10% clay.
- Organic Matter Determination:
- Uses the Walkley-Black wet method.
- Soil (0.5-1g) reacts with 1N potassium dichromate and concentrated sulfuric acid, causing carbon oxidation and chromium reduction.
- Both blank and sample titrations are performed with potassium permanganate to calculate the organic carbon percentage.
- Cation Exchange Capacity (CSC) Determination:
- Involves three main steps:
- Barium Saturation: 2g of soil is treated with 10% barium chloride to replace all adsorbed cations. The supernatant is discarded.
- Magnesium Replacement: 25ml of 0.1N magnesium sulfate is added to replace the adsorbed barium.
- Titration: The resulting supernatant (containing the released magnesium) is titrated with EDTA using Eriochrome Black T indicator, comparing blank and sample values to determine CSC (meq/100g).
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