May 6 (Reuters) - Canada's Nutrien reported a rise in first-quarter profit on Wednesday, benefiting from higher sales and prices across its fertilizer ‌segments, with the world's top potash producer also flagging tighter nitrogen market ‌conditions going forward. Fertilizer prices rose during the quarter, led by a surge in nitrogen rates ​as global supplies tightened due to the Middle East conflict, while phosphate prices were broadly higher and potash held relatively firm, supporting margins for producer ...