(a) What are the factors responsible for declining soil fertility? Discuss various measures adopted for improving soil…

(a) Declining soil fertility and measures to improve productivity

Natural causes are intense weathering and leaching in high-rainfall zones and loss of topsoil to wind and water erosion. Human causes accelerate decline: intensive tillage, cereal-cereal monocropping, residue burning, falling soil organic carbon and imbalanced NPK use that mines secondary and micronutrients, leading to widespread sulphur, zinc and boron deficiency. Salinity, sodicity and acidity, from poor irrigation water and drainage, add to the loss.

Measures, matched to causes: Integrated Nutrient Management combining organics with balanced fertilisers, guided by Soil Health Card soil tests (2015); targeted zinc sulphate, borax and sulphur for micronutrient and secondary-nutrient deficiencies; FYM, compost and residue incorporation to rebuild organic matter; green manuring with Sesbania aculeata (dhaincha) and legumes in rotation for nitrogen; biofertilisers such as Rhizobium, Azotobacter and phosphate-solubilising bacteria; gypsum for sodic soils and lime for acid soils; conservation tillage and mulching against erosion; and Leaf Colour Charts and fertigation for nutrient-use efficiency.

(b) Integrated Farming System (IFS) and income across landholding groups

IFS combines crops with livestock, fisheries, agroforestry and allied enterprises on one farm, so that the by-product of one enterprise (manure, crop residue, water) becomes the input of another, recycling resources and spreading risk. It is more than mixed farming because the components are planned to interact.

Marginal farmers (below 1 ha) gain steady weekly cash and nutrition from kitchen gardens, goats and backyard poultry on a small area. Small farmers (1-2 ha) can add rice-fish or rice-fish-duck systems, where fish and ducks eat pests and weeds and their droppings fertilise the crop, cutting pesticide cost and adding fish and egg income. Medium and large farmers (above 2 ha) can integrate crop-dairy-biogas-vermicomposting, converting dung and residue into biogas and vermicompost, lowering input costs and adding milk, slurry and manure income. Income from several enterprises throughout the year also cushions crop failure and price falls. Models developed by ICAR's Indian Institute of Farming Systems Research, Modipuram are promoted through extension and state programmes.

(c) Biological control of weeds

Biological control uses living organisms to hold weeds below economic injury levels.

Classical control introduces host-specific natural enemies of introduced weeds: the Mexican beetle Zygogramma bicolorata against Parthenium; the lace bug Teleonemia scrupulosa against Lantana; the weevils Neochetina eichhorniae and N. bruchi against water hyacinth; and the cochineal insect Dactylopius against prickly pear.

Bioherbicides apply native pathogens, mass-cultured and sprayed on weeds, for example fungi such as Alternaria and Colletotrichum species researched against water hyacinth and Parthenium at the ICAR Directorate of Weed Research, Jabalpur.

Cultural biological suppression uses smother crops such as cowpea and sunn hemp and allelopathic crops such as sorghum and sunflower that exude growth inhibitors, reducing weed emergence as part of Integrated Weed Management.