Soil Science and Soil Fertility Management
What this domain tests
Soil Science and Soil Fertility Management tests soil formation, texture and structure, pH and salinity, organic matter, essential plant nutrients, fertilizer grades, soil testing and integrated nutrient management. Maharashtra questions often use black cotton soil, laterite soil and problem soils as contexts.
Core rules and concepts
- Soil texture is the proportion of sand, silt and clay; structure is the arrangement of soil particles into aggregates.
- Cation exchange capacity (CEC) is the soil's capacity to hold exchangeable cations; clay and organic matter raise CEC.
- Soil pH controls nutrient availability. Most crops grow best near pH 6.0-7.5; strongly acid soils may need lime, and sodic soils need gypsum.
- Nitrogen promotes vegetative growth; phosphorus supports root development and energy transfer; potassium regulates water relations and quality.
- Fertilizer grades are expressed as N-P2O5-K2O, not as elemental P and K. Urea is 46% N, single superphosphate (SSP) is 16% P2O5, and muriate of potash (MOP) is 60% K2O.
- Integrated nutrient management combines organic manures, biofertilizers and mineral fertilizers with soil-test-based doses.
Worked example
A recommendation is 100 kg N, 50 kg P2O5 and 50 kg K2O per hectare. Urea needed = 100 ÷ 0.46 = 217.4 kg. SSP needed = 50 ÷ 0.16 = 312.5 kg. MOP needed = 50 ÷ 0.60 = 83.3 kg. The reasoning is to divide the nutrient dose by the fraction of that nutrient in the fertilizer. If DAP were used instead of SSP, its nitrogen content would have to be credited against the N dose.
Traps that cost marks
Do not compare P2O5 with elemental P or K2O with elemental K. Do not ignore nutrients supplied by FYM or previous legumes. Do not confuse soil pH with irrigation-water pH. Do not recommend lime for sodic soils or gypsum for strongly acid soils.