Field trials were conducted at the Teaching and Research Farm, Faculty of Agriculture, University of Maiduguri, Maiduguri (11°47.840′N; 13°12.021′E; elevation 319？m？asl), in Borno State in semiarid zone of Nigeria during the 2010 and 2011 rainy seasons. The objectives of the study were to evaluate the agronomic performances of some improved cowpea varieties and to identify the physiological traits associated with high grain yield in the semiarid zone of Nigeria. The trial consisted of eight treatments, which included two local varieties, namely, Kannanado White and Borno Brown and six improved varieties, namely, IT90K-277-2, IT97K-568-18, IT89KD-288, IT97K-499-35, IT98K-131-2, and IT89KD-391. The treatments were laid out in a randomized complete block design replicated three times. The gross plot size was 5.0？m × 4.0？m (20？m2) while the net plot size was 3.6？m × 3.0？m (10.8？m2). The results showed that the improved varieties, namely, IT90K-277-2, IT97K-499-35, IT98K-131-2, and IT89KD-288, had significantly higher grain yield per hectare and matured earlier to escape drought in this agroecological zone. The local varieties also had significantly heavier grains, took more days to reach first and 50% flowering, and matured later than the improved varieties. Cowpea grain yield per hectare was highly positively correlated with harvest index, shell weight, soil moisture suction measurements, shelling percentage, and grain yield per plant and also significant negative correlation between cowpea grain yield per hectare and number of days to first and 50% flowering, 100-grain weight, number of days to physiological maturity, and pod development period. The results also indicated that fodder yield per hectare was highly positively correlated with photosynthetically active radiation thereby indicating that higher photosynthetically active radiation produced higher yield of fodder. 1. Introduction Cowpea, Vigna unguiculata (L.) Walp, also popularly called “beans” in Nigeria is a legume of vital importance to the livelihood of millions of people in West and Central Africa. It provides nutritious grain and less expensive source of protein for both rural and urban consumers [1]. It is estimated that cowpea supplies 40% of the daily protein requirements to most people in Nigeria [2]. The use of cowpea haulms as fodder is attractive in mixed crop/livestock systems where both grain and fodder can be obtained from the same crop [3]. Some 8 million ha of cowpea are in West and Central Africa, especially in Nigeria, Burkina Faso, Mali, and Senegal. Nigeria is the largest
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