Growth and Yield Responses of Cowpea Cultivars to Inoculation and P Fertilization in Different Environments.

Cowpea is an important food crop and essential component of the cropping systems in arid and semi-arid regions of Mozambique. It is a major source of dietary protein for both rural and urban poor. Despite, its importance yields are very low due in part to limited access to improved varieties and lack of information on better crop and soil management practices. The objectives of this study were to assess the effects of inoculant and P on nodulation, N accumulation and yield of two cowpea cultivars in three agro-ecological zones of Mozambique. Field experiments were conducted on clay loam and sandy clay loam soils at three locations during the 2013/14 and 2014/15 growing seasons. Randomized complete block design with four replications was used. Treatment consisted of seed inoculation before planting, application of 40 kg P₂O₄ ha^-1, combination of the two factors and a non-inoculated control. Inoculation improved nodulation and yield in both cowpea cultivars across locations but P improved yield at only one location in 2013/14. Average nodule dry weight across locations and seasons ranged from 63-128 mg plant^-1 and was highest when inoculant and P were applied together. Inoculation alone significantly enhanced cowpea grain yield more than applying P alone and there was no significant yield difference between inoculation alone and applying inoculant and P together in 2013/14. However, in 2014/15, inoculant and P applied separately increased cowpea yield but the increase due to P was higher than that for the inoculant. Significant positive interaction between the inoculant and P occurred in 2014/15 in contrast to that for the previous year. The highest yield advantage for applying inoculant or P alone or in combination ranged from 625-1050 kg ha^-1. Shoot tissue and seed N and P concentrations were higher, in particular when inoculant and P were applied together than that for the non-inoculated plants.