Tillage system, preceding crop, and nitrogen fertilizer in wheat crop: II. Water utilization

Under rainfed Mediterranean conditions, where water constitutes the limiting factor, the aim is to obtain the highest production per unit of available water. A 6-yr study in a Vertisol was undertaken to determine in wheat (Triticum aestivum L.) the effects of tillage system, preceding crop, and N fertilizer on water utilization. Tillage treatments were no-tillage and conventional tillage. Preceding crops, in 2-yr rotations, were sunflower (Helianthus annuus L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), fallow, and continuous wheat. The mean crop precipitation interception index (CPI) was low (43%). Rotations including spring-planted crops such as chickpea and sunflower, or including fallow, reduced the CPI, increasing the risk of erosion. The tillage system did not affect any of the parameters studied. Water use efficiency (WUE) ranged from 5 to 14 kg ha(-1) mm(-1). Wheat and sunflower as preceding crops yielded poorer values for productivity and water utilization, while the best results were obtained with faba bean. The highest values of precipitation use efficiency (PUE) and WUE were reached with 100 kg N ha(-1) in all rotations except for wheat-sunflower, which needed 150 kg N ha(-1). The inclusion of faba bean or chickpea in a 2-yr rotation contributes to improve the WUE by wheat crop.