Efficiency of nitrogen in wheat under Mediterranean conditions: effect of tillage, crop rotation and N fertilization

Abstract

Within the framework of a long-term experiment started in 1986, a 3-year field study was carried out under rainfed Mediterranean conditions to determine the effect of tillage, crop rotation and N fertilization on the efficiency of nitrogen in wheat. Tillage treatments included no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower ( Helianthus annuus L.) (WS), wheat–chickpea ( Cicer arietinum L.) (WC), wheat–faba bean ( Vicia faba L.) (WB), wheat–fallow (WF) and continuous wheat (WW). Nitrogen fertilizer rates were 0, 50, 100 and 150 kg N ha −1. A split–split plot design with four replications was used. The high rainfall recorded over the three study years (60% above average) had a negative influence on wheat growth and yield. Soil NO 3 −-N and mineralized N content did not vary with tillage treatment. Residual NO 3 −-N was greater in WW and in the WB and WF rotations, whereas lower levels were recorded with the WS rotation. Mineralized N levels fell sharply for WW and were higher for WS and WF. Wheat yield was greater with CT than with NT. Clear differences in yield were recorded for all 2-year rotations with respect to WW. Wheat yield showed no additional response to N fertilizer rates above 100 kg ha −1. N use efficiency (NUE) and N uptake efficiency (NU pE) were greater with CT than with NT. These indices, together with N utilization efficiency (NU tE), N harvest index (NHI), N physiological efficiency (NPE), N agronomic efficiency (NAE) and N apparent recovery fraction (NRF) generally pointed to greater NUE for the WS rotation, and poor efficiency for wheat monoculture. Moreover, all indices except NPE fell as N fertilizer rates increased, indicating poor N utilization.