Long‐Term Tillage, Crop Rotation, and Nitrogen Fertilizer Effects on Wheat Yield under Rainfed Mediterranean Conditions

Abstract

AbstractThe combined long‐term effects of tillage method and crop rotation on crop yield have not been studied in rainfed systems under Mediterranean climates. A field study was conducted from 1988 to 1994 to determine the effects of tillage (TILL), crop rotation and (ROT) N fertilizer on wheat (Triticum aestivum L.) yield in a rainfed Mediterranean region. Tillage treatments include no tillage (NT) and conventional tillage (CT). Crop rotations were wheat‐sunflower (Helianthus annuus L.) (WS), wheat‐chickpea (Cicer arietinum L.) (WCP), wheatfababean (Vicia faba L.) (WFB), wheat‐fallow (WF), and continuous wheat (CW), with N fertilizer rates of 50, 100, and 150 kg N ha−1. A split‐split plot design with four replications was used. Differences in rainfall during the growing season had a marked effect on wheat yield. Amount of rainfall during the vegetative period for wheat (November‐February) was highly correlated with yield because of the high water‐retention capacity of Vertisols (Typic Haploxerert). In dry years, wheat yield was greater under NT than under CT; the opposite was true in wet years. The TILL ✕ ROT interaction was also significant in the drought years; the wheat yield under NT was greater for CW and the WFB and WF rotations than under CT. Wheat yields ranked by crop rotation were: WFB > WF >> WCP > WS >> CW. Wheat did not respond to N fertilizer when rainfall was below 450 mm during the growing season. Using these results strategies can be developed for establishing the N fertilizer rate applied to wheat as a function of rainfall, the preceding crop, and residual N in soil in order to optimize wheat yield and reduce nitrate pollution to groundwater.