liminfoSoil Analysis Reference
Free reference guide: Soil Analysis Reference
About Soil Analysis Reference
The Soil Analysis Reference is a searchable guide to soil testing parameters, interpretation standards, and fertilizer calculations used in agriculture and environmental science. It covers the full spectrum of chemical analysis indicators including pH (soil acidity from strongly acidic below 4.5 to alkaline above 7.5), EC (electrical conductivity for salt concentration in dS/m), organic matter content (OM in g/kg), available phosphorus (Av.P2O5 in mg/kg), and cation exchange capacity (CEC in cmol+/kg).
The reference provides detailed optimal ranges for exchangeable cations (K, Ca, Mg) with specific targets for paddy fields, upland fields, orchards, and greenhouse cultivation. It includes physical property analysis covering soil texture classification (sand to clay), bulk density, porosity, and hydraulic conductivity. Trace element diagnostics for iron, manganese, boron, zinc, and copper include deficiency thresholds, visual symptoms, and corrective measures.
For practical field application, this guide includes fertilizer calculation methods: N-P-K standard application rates for major crops (rice, pepper), fertilizer conversion from nutrient content to actual product weight, compost application rates for organic matter supplementation, and lime requirement calculations for pH correction. It also covers interpretation standards including soil test grading systems, cation balance ratios (Ca:Mg:K), salt accumulation diagnosis for greenhouses, soil contamination concern/action standards for heavy metals, and proper soil sampling protocols.
Key Features
- Complete chemical analysis parameter guide with optimal ranges for paddy, upland, orchard, and greenhouse soils
- Exchangeable cation reference (K, Ca, Mg) including Ca:Mg:K balance ratios and deficiency symptoms
- Physical property analysis covering soil texture, bulk density, porosity, and hydraulic conductivity
- N-P-K standard fertilizer rates for major Korean crops with soil test correction coefficients
- Fertilizer conversion calculator from nutrient content percentages to actual product quantities
- Trace element deficiency diagnostics for Fe, Mn, B, Zn, Cu with thresholds and corrective measures
- Soil contamination standards for Cd, Pb, As, Cu with concern and action level thresholds
- Soil sampling protocol guide covering timing, depth, number of samples, and preparation methods
Frequently Asked Questions
What is the optimal soil pH for most crops?
Most crops grow best in slightly acidic to neutral soil with a pH of 5.5-6.5, with 6.5-7.0 being optimal. Strongly acidic soil (below pH 4.5) requires lime application to raise the pH, while alkaline soil (above pH 7.5) may need sulfur application. The specific optimal range varies: paddy rice tolerates slightly more acidic conditions, while some vegetable crops prefer near-neutral pH.
How do I interpret EC (electrical conductivity) readings?
EC below 2.0 dS/m is normal for most crops. Values between 2.0-4.0 dS/m are slightly elevated and suitable only for salt-tolerant crops. EC of 4.0-8.0 dS/m inhibits growth for most plants, and above 8.0 dS/m is unsuitable for nearly all crops. High EC in greenhouses indicates salt accumulation, which can be remediated through flood leaching, deep tillage, or growing green manure crops.
What does CEC tell me about my soil?
CEC (Cation Exchange Capacity) measures the soil's ability to hold positively charged nutrients (K+, Ca2+, Mg2+). Sandy soils typically have CEC below 5 cmol+/kg (poor nutrient retention), loamy soils range 15-25 cmol+/kg (moderate retention), and clay-rich or organic soils exceed 25 cmol+/kg (high retention). Higher CEC generally means the soil can buffer nutrient applications better and requires less frequent fertilization.
How do I calculate lime requirement for pH correction?
Lime requirement (kg/10a) = (target pH - current pH) x buffering capacity. For paddy soil needing correction from pH 5.0 to 6.5, approximately 200-300 kg/10a of limestone is typical. Common liming materials include ground limestone (calcium carbonate), hydrated lime (faster acting), and dolomitic lime (also supplies magnesium). Apply lime 2-4 weeks before planting.
What is the ideal Ca:Mg:K ratio in soil?
The ideal cation saturation percentages relative to CEC are approximately Ca 60-70%, Mg 10-20%, K 2-5%, with H+Al making up 10-20%. This translates to a Ca:Mg:K ratio of roughly 65:15:4. The Ca/Mg ratio should be 5-8:1, and the Mg/K ratio should be 2-4:1. Imbalanced ratios can cause nutrient antagonism even when individual levels appear adequate.
How do I convert nutrient requirements to actual fertilizer amounts?
Divide the required nutrient amount by the fertilizer's nutrient percentage. For example: to supply 10 kg of N using urea (46% N), you need 10/0.46 = 21.7 kg of urea. For 5 kg of P2O5 using fused phosphate (20% P2O5), you need 5/0.20 = 25 kg. For 8 kg of K2O using potassium chloride (60% K2O), you need 8/0.60 = 13.3 kg.
What are the signs of boron deficiency in crops?
Boron deficiency (below 0.5 mg/kg hot-water extractable B) causes growing point death, fruit cracking, and hollow stems. Crops particularly susceptible include Chinese cabbage, radish, apple, and grape. Corrective measures include applying borax (11% B) or boric acid (17% B), but exercise caution as boron toxicity can occur above 3.0 mg/kg, making the optimal range quite narrow.
How should I collect soil samples for testing?
Collect samples 2-4 weeks before planting or transplanting. Sampling depth varies: 15 cm for paddy fields, 20 cm for upland fields, and 30 cm for orchards. Take 5-10 subsamples per field and mix them into one composite sample of 500g-1kg. Air-dry the sample and sieve through a 2mm screen. Never sample immediately after fertilizer application, as this will skew results.