Soil Amendments
Soil amendments — organic matter, lime, gypsum, compost, vermicompost, biofertilizers, green manure crops, micronutrient correctives. Integrated nutrient management for sustainable and productive agriculture.
Frequently Asked Questions
What is gypsum used for in soil reclamation and what is the gypsum requirement formula?
Gypsum (CaSO₄·2H₂O) is used to reclaim sodic (alkali) soils — soils with high exchangeable sodium percentage (ESP > 15) and pH > 8.5. Gypsum replaces sodium on exchange sites with calcium, allowing sodium to be leached out. Gypsum requirement (GR) = ESP × CEC × soil weight factor. For black sodic soils, typical GR is 5–10 tonnes/ha. After gypsum application, leaching with good quality water is essential.
What is the C:N ratio and why does it matter for composting?
The C:N ratio is the ratio of carbon to nitrogen in organic material. It determines the rate of decomposition. C:N ratios: fresh straw 80:1 (slow decomposition, N immobilization), farmyard manure 20–25:1 (moderate), well-decomposed compost 12–15:1 (ideal for release), vermicompost 15–20:1. The critical C:N ratio for net N mineralization is ~25:1 — materials above this immobilize soil N; below this, they release N.
What are the NPK contents of vermicompost and farmyard manure?
Vermicompost NPK: approximately 1.6% N, 0.7% P₂O₅, 0.85% K₂O — significantly higher than FYM. Farmyard manure (FYM) NPK: 0.5% N, 0.2% P₂O₅, 0.5% K₂O. Vermicompost also contains beneficial plant growth hormones and microbial populations. These figures are directly tested in IBPS AFO and NABARD exams.
What nitrogen does green manuring add to soil and which crops are used?
Green manuring can add 60–150 kg N/ha to soil through biological nitrogen fixation by legume root nodules. Common green manure crops: Dhaincha (Sesbania bispinosa) — most popular, adds 100–130 kg N/ha; Sunhemp (Crotalaria juncea) — 100–120 kg N/ha; Sesbania rostrata — fixes N in both root and stem nodules; Pillipesara (Phaseolus trilobus) — used in rice fallows.
What is lime requirement and when is liming recommended?
Lime requirement (LR) is the amount of liming material needed to raise soil pH to the target level (usually 6.5). It depends on soil buffer pH, CEC, and texture — higher CEC soils need more lime. Liming is recommended when soil pH < 5.5 (for most crops) or < 6.0 (for sensitive crops). Common liming materials: agricultural lime (CaCO₃), dolomitic lime (CaCO₃ + MgCO₃), quick lime (CaO), slaked lime (Ca(OH)₂).
What is the role of biofertilizers and which organisms are tested in exams?
Biofertilizers are microbial inoculants that improve nutrient availability to plants. Key organisms for exams: Rhizobium (symbiotic N fixation in legume nodules — 50–150 kg N/ha), Azotobacter (free-living N fixation in aerobic soils), Azospirillum (associative N fixation in rice and cereals), PSB (Phosphate Solubilizing Bacteria — solubilize fixed P), VAM/mycorrhiza (improves P uptake and drought tolerance). BGA (Blue-Green Algae) fix N in flooded rice fields.