Journal of Experimental Agriculture International

Plectranthus esculentus N.E.Br. locally known as “rizga” is an important indigenous tuber crop in Nigeria which is currently endangered. One major factor that causes disappearance of this species, is the lower agronomic recommendations developed for growers and lack of information about nutrient contents leading to loss of interest in its cultivation. A field experiment was therefore conducted during the 2016 and 2017 rainy seasons to determine the effect of nitrogen, phosphorus and variety on physiological indices as an attempt to conserve and evaluate the potential of the crop in food security, source of income and its adaptation in the Northern Guinea Savannah of Nigeria. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. Treatments consisted four levels of nitrogen and phosphorus (­0_, 60, 90 and 120 kg/ha), respectively and two varieties (vat Riyom and vat Loang’at). Results from analysis of variance showed that nitrogen and phosphorus applied at 90 kg/ha significantly produced higher physiological indices in both years. Beyond this rate, there was a decline in physiological indices resulting in decrease in starch content and dry matter accumulation. Harvest index indicated a positive relationship between the proportion of the biological yield and nutrient levels. Although, varietal difference was not significant on harvest index. This is an indication that HI is purely a genetic trait as affected by environmental factors. It was therefore concluded that, for high yield of livingstone potato, soils should be treated with a moderate application rate of 90 kg/ha nitrogen and phosphorus for enhanced physiological indices which are measures of growth and productivity per unit area of land in the Northern Guinea Savanna of Nigeria.