According to the Kurukshetra Magazine November 2017 special issue on irrigation: Tillage exposes the soil to drying, conversely, reductions in tillage help conserve soil water. So #1 is right. The retention of crop residues helps in reducing water loss from the soil to the air and cools the soil. So, #3 is right. According to some random research papers & Google books even gypsum application helps in water conservation so experts were divided between Option cor d. But in the official answer key UPSC has kept c as the correct answer.