Effects of Tillage, Crop Rotation, and Nitrogen Fertilization on Wheat under Rainfed Mediterranean Conditions

Abstract

The combined long‐term effects of tillage method, crop rotation, and N fertilizer rates on grain yield have not been studied in rainfed systems under Mediterranean climates. As part of a long‐term experiment started in 1986, a field study was conducted between 1994 and 1998 to determine the effects of tillage (TILL), crop rotation (ROT), and N fertilization on wheat (Triticum aestivum L.) growth and yield in a rainfed Mediterranean region. Tillage treatments included no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annuus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–faba bean (Vicia faba L.) (WFB), wheat–fallow (WF), and continuous wheat (CW). Nitrogen fertilizer rates were 0, 50, 100, and 150 kg N ha−1 on a Vertisol (Typic Haploxerert). A split–split plot design with four replications was used. Heavy rainfall during this research negatively impacted vegetative growth and grain yield of the wheat due to waterlogging. Wheat yield in the wet years was lower under NT than under CT. Yield decreased in the following crop rotation sequence: WFB ≫ WF > WS > WCP ≫ CW. Wheat responded to N fertilizer at rates up to 100 kg N ha−1 in the wet years but exhibited no response in the dry years. Yield under CT was higher at all N rate applied to wheat. The effect of N fertilizer on yield was more marked for the rotations with no legumes. The incorporation of the results for the 4‐yr period to those of the long‐term experiment provides more consistent information on the characterization and performance of the various systems.