Essential Soil Physical & Chemical Formulas
Numerical problems in ICAR PG, ASRB NET, and IBPS AFO test standard soil mechanics and nutrient stoichiometry formulas.
| Soil Parameter | Standard Formula | Typical Normal Range / Value |
|---|---|---|
| Bulk Density (Db) | Db = Mass of oven-dry soil (g) / Total soil volume (cm³) | 1.1 to 1.6 g/cm³ |
| Particle Density (Dp) | Dp = Mass of solid soil particles (g) / Volume of solids (cm³) | 2.65 g/cm³ (Quartz standard) |
| Total Soil Porosity (%) | Porosity = [1 - (Db / Dp)] x 100 | 40% to 60% |
| Sodium Adsorption Ratio (SAR) | SAR = [Na+] / sqrt(([Ca2+] + [Mg2+]) / 2) | < 13 in normal soils; > 13 in Sodic soils |
| Exchangeable Sodium % (ESP) | ESP = [Exchangeable Na+ (cmol/kg) / CEC (cmol/kg)] x 100 | < 15% normal; > 15% Sodic |
Step-by-Step Fertilizer Application Numerical
Problem: A field requires 120 kg N, 60 kg P2O5, and 40 kg K2O per hectare. Calculate the quantity of DAP (18% N, 46% P2O5), Urea (46% N), and MOP (60% K2O) required.
Key Exam Takeaways:
- Step 1: Supply all 60 kg P2O5 through DAP. DAP required = (60 / 46) x 100 = 130.43 kg DAP.
- Step 2: Calculate N supplied by 130.43 kg DAP. N from DAP = 130.43 x 0.18 = 23.48 kg N.
- Step 3: Remaining N needed = 120 - 23.48 = 96.52 kg N.
- Step 4: Urea required = (96.52 / 46) x 100 = 209.82 kg Urea.
- Step 5: MOP required for 40 kg K2O = (40 / 60) x 100 = 66.67 kg MOP.
RECOMMENDED PRACTICE BUNDLE
AGRI-KATYAYAN
Fundamentals of Agriculture by Arun Katyayan sir – 25+1 Complimentary Set
₹196₹260
26 curated test sets (25 structured practice + 1 complimentary bonus set) with 2,600 MCQs comprehensively covering essential agricultural concepts.
26 CBT Tests60 hours60 days validity
FREE CBT PRACTICE TEST
Attempt Free 104-Question Agriculture CBT Demo Exam
Experience real NTA/ASRB exam conditions: 90-minute live countdown timer, 104-question status palette, and instant answer keys with verified scientific explanations.