Soil Science and Soil Fertility Management
What this domain tests
Soil profile and texture, the soil types of Maharashtra, soil reaction and salinity, organic carbon, cation exchange and the interpretation of a soil test report.
Core concepts
- Maharashtra soils: black cotton soil (vertisol) dominates the Deccan - high clay, high water-holding capacity, low infiltration, self-mulching, pH 7.5–8.5; laterite and red soils on the Konkan and eastern hills, often acidic and low in bases; alluvial soils in river valleys and coastal plains; saline-sodic patches in rain-shadow and irrigated commands.
- Soil reaction: below pH 6.0 apply agricultural lime; 6.5–7.5 suits most crops; above pH 8.5 with high exchangeable sodium apply gypsum. Never lime a sodic soil.
- Organic carbon is the best single index of fertility; below 0.5% is rated low. One per cent organic carbon equals about 1.724% organic matter.
- Cation exchange capacity: black soils hold 30–60 cmol/kg and buffer strongly; sandy red soils have low CEC, respond fast to fertilizer and leach easily.
- Conversion: values in ppm become kg/ha for a 15 cm furrow slice by multiplying by 2 (about 2 million kg soil per hectare).
- Erosion control: contour bunding and trenching, compartment bunding, terracing on steep Konkan slopes, grass waterways, mulching and vegetative barriers.
Worked example
A report reads pH 8.6, EC 0.9 dS/m, organic carbon 0.35%, available N 180 kg/ha, P 14 kg/ha, K 340 kg/ha. Reasoning: pH above 8.5 indicates sodicity, so gypsum with FYM and a tolerant crop are called for, not acidifying fertilizer; EC 0.9 dS/m is borderline saline but not yet a hazard; organic carbon 0.35% is low, so add compost and plan green manuring; N is low, P medium, K high, so the fertilizer plan is nitrogen-heavy with little or no potash.
Traps
Reading EC as pH; recommending lime for an alkaline soil; confusing organic carbon with organic matter; and ignoring the depth assumption when converting ppm to kg/ha.