Production of rainfed and irrigated crops under different crop rotations and input levels in southwestern France

Crop production in southwestern France is primarily limited by water availability. This long-term research was conducted to evaluate the performance of 9 rainfed and irrigated crops grown under 10 crop rotations. Increasing levels of management inputs (e.g., water and fertilizer) were applied to barley (Hordeum polystichum L.), corn (Zea mays L.), faba bean (Vicia faba L.), pea (Pisum sativum L.), rapeseed [Brassica napus L. ssp. oleifera (Metzg.) Sinsk], wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max. (L.) Merrill)], and sunflower (Helianthus annuus L.) from 1984 to 1992 on a deep silty clay loam. Two or three management alternatives were applied to each crop rotation during 9 yr; they were defined at the crop level by an expected grain yield and a consistent combination of crop management factors (planting date, crop density, N-P-K fertilization, irrigation, and pesticides). Under irrigated management, corn, sunflower and soybean responded markedly to increased levels of inputs while sorghum did not respond significantly. In summer crops (corn, sorghum, sunflower), the intensification of inputs was generally ineffective under non-irrigated conditions. In winter wheat, grain yield increased with input levels but differential responses were observed with crop rotation. Variability in yield from year-to-year was reduced with irrigation. We concluded that low-input rainfed and medium-input with limited irrigation are productive agronomic systems for deep soils in southwestern France.