Explanation:

Fertigation is a method of fertilizer application in which fertilizer is incorporated within the irrigation water by the drip system. In this system fertilizer solution is distributed evenly in irrigation.

• Statement 1 is correct: Fertigation can control alkalinity of irrigation water. For eg. Drip irrigation also avoids water spillage on the field which could have promoted weed growth or increase soil alkalinity due to water logging.
• Statement 2 is incorrect: Efficient application of all phosphatic fertilisers is not possible because Urea, potash and highly water soluble fertilizers are available for applying through fertigation. In fact, Urea is well suited for injection in micro irrigation system. It is highly soluble and dissolves in non-ionic form, so that it does not react with other substances in the water. But, Rock phosphate is not soluble and thus not suitable.
• Statement 3 is correct: Increased availability of nutrients to plants is possible because by this method, fertilizer use efficiency is increased from 80 to 90 per cent as they are delivered directly to roots via drip. As water and fertilizer are supplied evenly to all the crops through fertigation there is possibility for getting 25-50 per cent higher yield.
• Statement 4 is correct: Reduction in leaching is possible because overapplication and soil water logging is avoided.

Hence option 3rd is correct.

Also Check: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/fertigation