Effect of Phosphorus Fertilizer Rates on the Growth and Fresh Pod Yield of Two Vegetable Cowpea Varieties (Vigna unguiculata (l) walp.) In Umudike South Eastern Nigeria.

Abstract

The experiment which was conducted at the eastern farm of Michael Okpara University of Agriculture, Umudike, Abia State, in the 2006 and 2007 cropping seasons evaluated the effect of phosphorus fertilizer on the growth and fresh pod yield of two vegetable cowpea varieties (Vigna unguiculata (L) Walp) in Umudike South eastern Nigeria. Results revealed that the measured growth characters; leaf area index (LAI) and vine length were not significantly (P>0.05) influenced by both varieties and phosphorus fertilizer rates (0, 15, 30, kg P₂0₅/ha) in both 2006 and 2007. However, LAI for the evaluated phosphorus and varieties (IT81D-1228-12 and IT81D-1228-14) in 2006/2007 increased with age at 4WAP, 8WAP, 10WAP and depreciated at 12WAP, following compulsory leaf-fall due to senescence, with higher LAI obtained at 8WAP and 10WAP. The rate of phosphorus fertilizer at 15kg P₂0₅/ha gave higher LAI at 4WAP in 2006 and 2007, compared with what was obtained at 0kg P₂0₅/ha (control).  Although the vine length of both varieties were statistically similar, IT81D-1228-12 (semi erect) produced longer vines than IT81D-1228-14 (erect) proving that IT81D-1228-12 is a variety with high genetic potential for producing longer vines.  Number of fresh pods / plant in 2006 and 2007 increased from 0kg P₂0₅/ha to 15kg P₂0₅/ha where higher fresh pod/plant of 20.24 pods and 19.68 pods were recorded. Higher mean weight of fresh pod/plant of 51.8g (2006) and 48.59g (2007) as well as mean fresh pod yield of 14.80 t/ha (2006) and 13.88 t/ha (2007) were obtained at the rate of 0kg P₂0₅/ha. Although the yields of both varieties were statistically similar, erect variety (IT8ID-1228-14) yielded higher number of fresh pods/plant, weight of fresh pods/plant and fresh pod yield per hectare compared with that of semi-erect (IT8ID-1228-12). The successful cultivation of vegetable cowpea in south eastern Nigeria requires the adoption of improved variety such as IT8ID-1228-14 (erect) as well as phosphorus fertilizer application at 15 to 30kg P₂0₅/ha.