Effects of Phosphorus and Zinc on Net Assimilation Rate (NAR) of Cowpea (<i>Vigna unguiculata</i> (L.) Walp) Varieties Grown in Bauchi, Nigeria

Abstract

Plant growth analysis is today studied as it relates to change in capture and efficiency in the use of resources rather than as it relates to  relative growth rate in the past. Net assimilation rate (NAR) is the rate of increase in dry matter over unit area of leaf, which represented a  measurement of excess of photosynthesis overrespiratory losses of dry matter. Two field experiments 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 evaluate the influence of phosphorus (0, 25, 50 kg P/ha) and zinc levels (0, 2.5, 5 kg Zn/ha) on NAR of six  cowpea varieties namely: IT90K 277, IT93 455 1, IT89KD 288, IT97K 568 18, IT90K 82 2 and Kanannado. Results obtained showed that NAR  was not significantly influenced by P and Zn levels and therefore, 0 kg ha1 SSP and Zn rate produced the highest NAR than higher levels.  Neither applications of each of P and Zn at higher levels or their interactions, nor did year or variety were found to have significant effects on NAR; but rather NAR is being determined by number of factors such as nutrient supply, photosynthesis rate, etc and these are never  fixed or constant and hence a particular factor e.g., nutrient (P or Zn) cannot dictate NAR alone.