Bengaluru, March 17 -- For Subhonanda Singha, a third-generation farmer in Dubanochi village, Darjeeling, rocks were something you cleared out of a field, not something you brought in by the truckload. But for the last three cropping seasons, Singha has been spreading a thin layer of grey basalt powder over his paddy fields.

The basalt dust disappears once a tractor folds it into the soil. In Singha's field, it looks like soil treatment. But in a corporate climate report generated thousands of kilometres away, it is logged as carbon removal.

Singha's improved yield after spreading the basalt dust, called Hari Mati, is not part of any government programme. The material is supplied free of cost by Bengaluru-based climate tech startup Alt ...