The modern farmer is guided by satellite imagery and navigation to those parts of his fields where treatment in the form of additional fertiliser or disease control is required. The intention is not only to manage cost but to avoid waste both of valuable crops and materials, and is a world away from that presented by Rose Prince (“Take the pulse”, 5 October). The synthesis of ammonia from methane forms the first step in the synthesis of the synthetic fertiliser ammonium nitrate. The yield and energy efficiency of these processes are subject to very careful scrutiny in the name of staying in business and don’t need much input from government in that direction. Diesel is not required. The world is set to enjoy a record harvest this year, with a cereal crop close to 2.5 b