Detailed Explanation:

Answer: Option 3 — 1, 3 and 4 only

Fertigation is the technique of applying fertilizers through irrigation systems, allowing precise nutrient delivery to the root zone. This method enables control over irrigation water pH, increases nutrient availability to plants, and reduces nutrient leaching, but cannot be used for water-insoluble fertilizers like rock phosphate.

✅ Statement 1 – Correct: Fertigation allows control of irrigation water alkalinity/pH by adjusting it to optimal levels for nutrient absorption.
❌ Statement 2 – Incorrect: Rock phosphate is not water-soluble and cannot be efficiently applied through fertigation systems, which require water-soluble fertilizers.
✅ Statement 3 – Correct: Fertigation delivers nutrients directly to the root zone, significantly increasing nutrient availability and uptake efficiency.
✅ Statement 4 – Correct: Precise nutrient application through fertigation reduces excess fertilizer use and minimizes nutrient leaching into groundwater.

📝 Short Notes: Fertigation

• Definition: Application of fertilizers through irrigation systems (drip, sprinkler) directly to the crop root zone.
• Water-soluble fertilizers used: Urea, potassium nitrate, calcium nitrate, mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP).
• Key advantages: Uniform nutrient distribution, higher nutrient use efficiency (30-50% savings), labor reduction, timely nutrient supply.
• pH management: Allows adjustment of irrigation water pH through acid injection (phosphoric acid, sulfuric acid) to optimize nutrient availability.
• Reduced leaching: Controlled application prevents over-fertilization and groundwater contamination.
• Limitations: Requires soluble fertilizers, initial setup cost, technical knowledge, and regular maintenance of irrigation system.