EFFECT OF WATER STRESS, BIOFERTILIZERS AND NITROGEN APPLICATION RATES ON COWPEA YIELD AND SOME WATER RELATIONS IN THE NORTH MIDDLE NILE DELTA REGION

Two field experiments were carried out at Sakha Agricultural Research station (31 o o5` N latitude and 30 o 57` E longitude) Kafr El-Sheikh governorate during the two successive summer growing seasons 2012 and 2013 to investigate the effect of water stress through various growth stages, biofertilizers and nitrogen application rates on cowpea yield, its components, uptake of phosphorus, nitrogen and protein content in some plant organs and some water relations in the North Middle Nile Delta region. A split split plot design with four replicates was used in this present study where the main treatments were randomly assigned by irrigation treatments which were I1 (control treatment), I2 (withholding one irrigation at the vegetative growth stage), I3 (withholding one irrigation at the flowering growth stage) and I4 (withholding one irrigation at pod formation stage), where the sub-plot were randomly assigned by application of nitrogen which were three rates of application, N1 (control treatment, without nitrogen application), N2 (application of 15 kg N/fed.) and N3 (application of 30 kg N/fed. which considers the recommended dose for cowpea). where the sub sub plot were randomly assigned by biofertilizers which were b1 (without biofertilizers application) and b2 (application of biofertilizers for the soil after emergence), The main results of this present investigation can be summarized as follows: amount of seasonal water applied were clearly affected by irrigation treatments. The highest values were recorded under irrigation treatment I1 comparing with other irrigation treatments I2, I3 and I4 in the two growing seasons. The highest values were 2950 m 3 /fed. (70.2 cm) and 2980 m 3 /fed (70.95 cm) in the first and second growing seasons, respectively. Concerning the effect of irrigation treatments on the mean values of seasonal consumptive use, the highest values were also recorded under irrigation treatment I1 in the two growing seasons and the mean values were 1823.3 and 1846.7 m 3 /fed in the first and second growing seasons, respectively. On the contrary, under other irrigation treatments, I2, I3 and I4 recorded mean values which less than that recorded under irrigation treatment (I1). The highest mean values for both (WP) and (PIW) were recorded under stress conditions I2, I3 and I4 comparing with non-stressed treatments I1 (traditional irrigation) in the two growing seasons. also, both biofertilizers application and nitrogen rates have an effect on both (WP) and (PIW) where the highest mean values for both the two irrigation efficiencies , cowpea yield and yield components, nitrogen, phosphorus percentage and protein content were recorded under N3 b2 . Concerning with the nitrogen percentage and protein content the highest overall mean values were recorded under irrigation treatment I1 and the values are 3.336 and 3.277% for nitrogen and 20.85 and 20.48% for protein content in the first and second growing seasons, respectively. On the contrary, the lowest overall mean values were recorded under irrigation treatment I4 the overall mean values are 3.191 and 2.942% for nitrogen and 19.94 and 18.39% for protein content in the first and second growing seasons, respectively. Also, data showed that the highest overall mean values for Moursi, E. A. et al. 1290 phosphorus percentage in the two growing seasons were also recorded under irrigation treatment I1 and the overall mean values are 0.201 and 0.195% in the first and second growing seasons, respectively. On the contrary, the lowest overall mean values were recorded under water stress conditions in the two growing seasons.