U.S. Crop Yields Redux: Weather Effects versus Human Inputs

Agriculture is a resource-intensive activity. It currently uses a substantial portion of the Earth’s natural resources: crop production, pasture and livestock grazing systems occupy around 40% of total land area, nitrogen fertilizer applied to agricultural land comprises more than half of the global reactive nitrogen attributable to human activity and agricultural production consumes more fresh water than any other human activity since it accounts for 80% of all freshwater consumption (Cassman 2003). Water is one of the key determinants of agricultural land productivity. Adequate water supply to crops is essential to achieve maximum yield and greater stability, enabling also greater scope for diversification. The success of irrigation in improving food security and fostering rural welfare during the last decades is undeniable but inappropriate water management can contribute to a series of environmental problems