A field experiment was conducted at Sakha Agricultural Research Station, Kafr El- Sheikh Governorate, North Nile Delta area, Egypt during the two successive growing seasons 2018 and 2019 to assess the interaction effect of skipping irrigation and co-inoculation of cowpea (Vigna unguiculata L.), with Bradyrhizobium sp. and some strains of Bacillus bacteria on growth dynamics, yield and water productivity. Spilt- plot design was used, the main plots were assigned to four treatments of water stress; I1: control treatment (no stress); I2: withholding one irrigation at the vegetative growth stage; I3: withholding one irrigation at the flowering growth stage; I4: withholding one irrigation at pod formation stage; while inoculation treatments were assign to sub main plots which were T1: inoculation with Bradyrhizobium sp. TAL 169 (control); T2: inoculation with Bradyrhizobium sp. TAL 169 + B. subtilis MF497446; T3: inoculation with Bradyrhizobium sp. TAL 169 + B. coagulans NCAIM B.01123; T4: inoculation with Bradyrhizobium sp. TAL 169 + B. circulance NCAIM B.02324.
Our results of this present investigation showed that the flowering stage is the most sensitive stage in connection with cowpea watering following with vegetative and pod formation stages. Also, treatment I4T4 recorded high values 7.61 g plant-1, 39.00, 0.388 g plant-1, 256.00 mg plant-1 and 1.054 mg g-1 FW at the first growing season for dry weight of plant, number of nodules plant-1, dry weight of nodules, N and total chlorophyll contents compared to other different treatments at 45 days after sowing (DAS), respectively. Similar trend was observed at 60 DAS. Irrigation at all stages accompanied with inoculation with Bradyrhizobium + B. circulance (I1T4 treatment) gave the highest number of pods plant-1, 100 seed weight and yield which the corresponding decrease in yield was 11.8, 1.4 and 0.4 %, for flowering, vegetative and pod formation stages, respectively. On the contrary, withdrawn irrigation at formation (I4) under T4 produced the highest values of productivity of irrigation water (PIW) and water productivity (WP). Herein, irrigation treatments followed the descending order of I1 > I2 > I3 > I4. However, it followed as T4 > T3 > T2 > T1 under inoculation treatments. Thus, inoculation with Bradyrhizobium sp. + B. circulance under withholding one irrigation at pod formation stage could be efficiently used to partially eliminate the effects of water stress on growth dynamics of cowpea.