Enthused by rising potato prices after a prolonged slump, Pradeep Shar-ma was planning to sow the crop on his 15-acre farm near Agra slightly earlier than usual. The delayed departure of the southwest monsoon also prompted his decision, since the good soil moisture would have saved at least one initial irrigation.

       But the acute shortage of diammonium phosphate (DAP), a crucial nutrient ahead of the sowing season for potatoes, nipped those hopes in the bud. DAP is the second-most used fertiliser in the country after urea. Stocks of this and other complex fertilisers fell sharply ...