Can I grow grafted walnut (akhrot) in the lower hills or plains of north India?

Walnut is a temperate crop that needs winter chilling to flower and fruit properly, so it does best in the cooler mid and higher hills, not in the warm plains. In the lower foothills, success depends on whether your specific location gets enough winter cold. Some lower chill situations may grow the tree but give poor or erratic nut set, while genuinely cold foothill pockets can work with suitable varieties. The plains generally do not suit walnut. Do not assume it will fruit just because the tree survives. Before planting, get your exact altitude and winter conditions assessed by the temperate horticulture research station or your KVK, and ask whether any lower chill walnut varieties suit your spot, rather than relying on a nursery's sales pitch.