The impact of nitrogen fertilizer rate and variety on biochemical compositions of Cassava (Manihot esculenta Crantz) under different locations

• Nitrogen fertilizer plays a vital role in HCN Biosynthesis • HCN of cassava varieties significantly increased as N application increases • Varieties treated with low or no N fertilizer resulted in low HCN content • N application significantly increased starch production • Interaction effect N locations and varieties affect proximate compositions. Cassava is an important food crop and can be processed to food products. However, it contains potentially harmful cyanogenic glucosides which can hydrolyse to release toxic hydrogen cyanide (HCN). The biochemical compositions mainly affected by variety, soil conditions, management and environmental factors. Therefore, the study was designed to investigate the effect of nitrogen fertilizer on HCN concentration, starch production and proximate composition of cassava varieties at different locations. The study was conducted at Hawassa, Belela, and Bilate in southern Ethiopia with altitudes of 1708, 1897 and 1332 masl, respectively. This experiment comprised four varieties of cassava (Hawassa 04, Qulle, Chichu and Kello) with three levels of nitrogen fertilizer rates (0, 50, 100 Kg ha -1 N). In this experiment, a randomized complete block design in a 4 × 3 factorial arrangement with three replications was used. Fresh cassava root samples were collected from the three locations for laboratory analysis. The collected data were analysed using SAS software. The results showed that the three-way interaction had a highly significant variation for all parameters, except starch concentration. Cassava varieties treated with lower and no nitrogen levels gave low HCN concentration compared to those with higher fertilizer indicating that nitrogen fertilizer increases the HCN accumulation. Furthermore, a higher level of nitrogen leads to higher starch accumulation. The highest crude fiber, ash, fat and crude protein concentrations were obtained at Hawassa location using Chichu variety with 100 Kg ha -1 N. However, the highest carbohydrate concentration was recorded from Qulle variety in unfertilized plot at Bilate location.