Two field experiments were carried out in privet farm at Bani Mazar region, North Al-Minia Governorate, Egypt, during the two fall seasons of 2016 and 2017, respectively under drip irrigation system, in sandy soil conditions. The objectives of this experiment were to study the effect of two factors i.e. determine the proper planting date from three planting dates i.e. at middle of July (as a control), 7th and 28th of August at twenty one days interval as well as two water schedule regimes treatments i.e. 80 and 60 % from water requirements/ fed. as compared with the control treatment i.e. 100 % from the cowpea (Vigna unguiculata L. Walp) plants irrigation requirements/ fed. and their interactions on growth, yield, its components, water use efficiency as well as some chemical constituents of the leaves and dry seeds under the condition of the newly reclaimed soil on the cowpea Kaha 1 cv. The experimental design was split–plot, i.e. the three planting dates devoted in the main plots and the water schedule regimes randomly distributed in the sub plots with three replications per treatment.
The results indicated that, the best planting date under this investigation was at middle of July as compared with the two other planting dates i.e. 7th and 28th of August which occurred the highest significantly increased in vegetative growth characters, dry seeds yield (ton/ fed.), its components, water use efficiency, total chlorophyll content in the fresh leaves, proline contents in the dry leaves, protein, nitrogen, phosphorus and potassium (%) in the cowpea dry seeds.
Concerning to the influence of schedule water regime, it was found that, the cowpea plants received the complete irrigation treatment (100 %/ fed.) as compared with increasing water deficient from 80 % to 60 % from the cowpea plants irrigation requirements/ fed. produced no significant increases in some characters i.e. plant height, dry weight of the foliage/ plant, average weight of dry pods, number of dry seeds/ pod, weight of 100 dry seeds and total chlorophyll content in the fresh leaves.
Whereas, the cowpea plants irrigated with the moderate irrigation treatment (80 % from the cowpea plants irrigation requirements/ fed.) led to no significant increases in number of branches, dry seeds yield, number and weight of dry pods/ plant, proline contents in the dry leaves, protein, nitrogen and potassium (%) contents in the dry seeds.
The lowest results of all previous characters were obtained when the plants were irrigated with the lowest water amount i.e. 60 % from the cowpea plants irrigation requirements/ fed. as compared with the two other water schedule regimes. On the other hand, water use efficiency significantly increased with irrigation the cowpea plants with 60 %/ fed. followed with irrigation with 80 % and 100 % from water requirements / fed.
Regarding to the results of the interactions between the two studied factors used in this study showed that, the distinguished interactions treatment which led to the highest antecedent means values over all the other interactions was obtained with the interaction between the 1st planting date at the middle of July and irrigation the cowpea plants by the moderate irrigation regime (80 % from the cowpea plants irrigation requirements/ fed.) specially, its produced significant increases in dry seed yield and its components as well as water use efficiency as compared with the rest of the two interactions, these findings were true in the both fall seasons.