Key points to remember about soil

• Humus: Amorphous, non-crystalline
• Order of strength of adsorption : Al⁺⁺⁺ , Ca ⁺⁺ > Mg⁺⁺> K⁺ = NH₄⁺ > Na⁺
• Rain water has pH : 5-5.6
• Na₂CO₃ and NaHCO₃ are much more soluble in water than CaCO₃ and Ca(HCO₃)₂.
• If EC> 4 decisiemens (dcm^-1); saline soil.
• Saline soil has 15% exchangeable sodium % (ESP).
• Buffering capacity of soil depends upon the texture of soil.
• Primary source of Sulphur is rain water.
• Boron helps in nodulation in legumes.
• There is antagonistic effect between Zn and P and Mg and Fe.
• Acidic cations: H⁺ , Al⁺⁺⁺ ; soil is acidic in humid region due to leaching by rainfall.
• Basic cations: Ca⁺⁺, Mg⁺⁺, K⁺, Na⁺; soil tends to be basic due to evapotranspiration > precipitation
• Kaolinite: 1:1, non-expanding type
• Montmorillonite, smectite and vermiculite: 2:1 , expanding type
• Illite: 2:1 ; non-expanding type
• Na₂CO₃ and NaHCO₃ is more soluble in water than CaCO₃ and Ca(HCO₃)₂ hence pH will be high in soil containing Na₂CO₃ and NaHCO
• EC> 4 d/cm in saline soil
• 15% ESP in saline soil
• Cultivated soil contains 1-5% organic matter in top 15 cm soil.
• First Nitrogenous fertilizer made industrially is CaCN₂.
• Field kit is used for fresh tissue analysis
• Best time for tissue testing : Blooming to early fruiting
• Sampling should be done in mid afternoon
• Hard pan form takes place in podzols.
• Partially decomposed litter is called duff.
• Sun radiate a solar radiation of about 1.94 Cal/cm²/min continuously.
• Maximum temperature is on 2pm and maximum solar radiation is around 12 pm.