Combined effects of irrigation management and nitrogen fertilization on soft wheat productive responses under Mediterranean conditions

Abstract

Wheat yield responses to water and nitrogen vary widely among different environments and they can be shifted due to technological, environmental, or economic factors. In regions with a Mediterranean-type climate, the balance between the key climate variables and the most critical stages of wheat grow implies that the success of the crop depends to a very large degree on the knowledge of proper water management combined with suitable fertilization strategies. For this purpose, we studied the productive responses of soft wheat to the interactive effects of irrigation and nitrogen (N) fertilization. Two trials were carried out during 2016/2017 in Beja (Southern Portugal). In both experiments, wheat responses were assessed under two water supply regimes: D1 (100% of full irrigation throughout the cycle) and D2 (100% of full irrigation at four stages: stem extension; booting; heading; grain filling). In the first trial, 165 kg of slow-release and stabilized N fertilizers were applied through 6 splitting treatments, five of them (A1 to A5) with a slow-release N fertilizer (A1 – 100% at sowing; A2 – 50% at sowing and 50% at booting; A3 - 50% at sowing, and 25% at stem extension and at heading; A4 – 75% at sowing and 25% at booting; A5 - 75% at sowing and 25% at stem extension) and another one (A6) with a stabilized N fertilizer 100% applied at sowing. In the second trial, 165 kg of conventional N fertilizer was applied through 5 splitting treatments (A1 – 33% at sowing, at tillering and at stem extension; A2 – 25% at sowing, at tillering, at stem extension and at heading; A3 - 25% at sowing, at tillering, at stem extension and at booting; A4 – 50% at tillering and 25% at booting and at heading; A5 - 50% at sowing and 25% at stem extension and at booting). In the first trial, only the number of heads per square meter showed significant influence of the irrigation regime, the highest values being registered in the D1 treatment. In the trial with conventional fertilizer, significantly higher yields and weights of 1000 grains were obtained in the D1 irrigation treatment. Significant effects of split N fertilizer application occurred only in the first trial: yield was higher in the A5 treatment, showing that early N applications with this type of fertilizers do not compromise N availability throughout the wheat grow cycle and therefore the grain production; grain protein content was higher in the A2 treatment, indicating the importance of N availability at the booting stage in order to obtain grains with desirable quality traits.