{{cite journal | last1=Hiama | first1=P. D. | author2=N. Ewusi-Mensah | author3=V. Logah | year=2019 | title=NUTRIENT UPTAKE AND BIOLOGICAL NITROGEN FIXATION IN COWPEA UNDER BIOCHAR-PHOSPHORUS INTERACTION | journal=Journal of Animal and Plant Sciences | volume=29 | issue=6 | pages=1654-1663 | issn=1018-7081 | eissn=2309-8694 | publisher=Pakistan Agricultural Scientists Forum | url=https://thejaps.org.pk/AbstractView.aspx?mid=2019-JAPS-617}}