Effect of Phosphorus and Zinc Interactions on Leaf Area Index (LAI) of Cowpea (<i>Vigna unguiculata</i> (L.) Walp) Varieties in North Eastern Nigeria

Abstract

Leaf area index (LAI) is a measure of leafiness per unit ground area. In other words, Leaf area index is defined as the projected area of leaves over a unit  of land and denotes the extent of photosynthetic machinery. It is an important growth and yield-determining factor because it is a major determinant of  light interception and transpiration. Phosphorus (P) and Zinc (Zn) are the most important factors affecting LAI of cowpea (Vigna unguiculata L. Walp). Two  field trials were conducted at the Faculty of Agriculture and Agricultural Engineering Research Farm of Abubakar Tafawa Balewa University, Bauchi,  North  Eastern, Nigeria, between 2006 and 2007 to assess the effect of phosphorus (0, 25, 50 kg P/ha) and zinc levels (0, 2.5, 5 kg Zn/ha) on LAI of six  cowpea varieties namely: IT90K277, IT93-455-1, IT89KD-288, IT97K-568-18, IT90K-82-2 and Kanannado. The main objective of this experiment was to  investigate whether there is any difference in the LAI of cowpea varieties at various P and Zn levels or not? Bauchi is situated at 100 22’ , N latitude and  900 47’ E longitude at about 109.45m above sea level. The increase in LAI was attributed to the increase in leaf number and leaf area/hill. The differences  in LAI observed in the varieties may be attributed to the differences in phenotypes and climatic factors such as rainfall, sunshine and availability of  nutrients. The increase in LAI showed a positive impact on crop growth rate, dry matter, and yield. Application of 25 kg P+2.5 kg Zn/ha to cowpea variety  IT93-455-1 was more beneficial in terms of higher LAI and productivity in Bauchi.