Cassava (Manihot esculenta Crantz) Tuber Quality as Measured by Starch and Cyanide (HCN) Affected by Nitrogen, Phosphorus, and Potassium Fertilizer Rates

Abstract

Cassava (Manihot esculenta Crantz) is an important subsistence crop for many poor rural families in Africa. Cassava contains cyanogenic glucosides (linamarin and lotaustralin) which liberate hydrogen cyanide (HCN) during tuber processing. Once liberated, HCN attaches to the processed tuber. Continuous consumption of processed tuber containing high HCN concentration coupled with low protein intake causes Konzo-a paralyzing disorder that impacts children and women of childbearing age. There are ways to reduce HCN concentration during tuber processing; however, this can also reduce the overall starch content in the cassava tuber. A study comprising twenty treatments consisting of different combinations of nitrogen (N), phosphorus (P), and potassium (K) fertilizer rates was initiated in 2013 in the coastal Dondo District of Mozambique to assess cassava tuber quality as measured by starch and HCN. Significant differences were observed in starch content (CSC) of unprocessed tubers due to combined addition of N, P and K fertilizer rates, sample size, and estimation procedure. However, no significant differences were observed in HCN concentration in tubers due to the addition of N, P and K fertilizer. The HCN concentration in cassava tuber appears to be a function of the physiology of the crop or possibly cassava variety rather than the environment or conditions under which the crop is grown.

Cyanogenic glucoside production in cassava: The comparable influences of varieties, soil moisture content and nutrient supply

“…Wellwatered conditions are thus needed for Kiroba to experience the reducing effects of sole K application. The results of the present study give a probable explanation for the inconsistent results obtained with sole K fertiliser application; that is, with it either reducing [19,42] or having no effect [13] on cyanogenic glucoside production in cassava. Increased cyanogenic glucosides in cassava with sole K application have however hardly been reported.…”

“…Other studies have also reported increased cyanogenic glucoside levels with a high supply of N, P and K (with N > 50 kg/ha) [3,43]. Some studies have however reported nonsignificant responses to N, P and K supply with moderate levels of N, P and K [13] and even with high levels of N, P and K [44], highlighting that there are further differences in how cassava varieties respond to soil nutrient supply. Reductions in leaf cyanogenic glucosides with the non-significant responses to changes in soil moisture by Salanga supplied with moderate amounts of N, P and K were however absent in Kiroba.…”

“…The importance of the less considered role of soil nutrient supply was hence once again highlighted in the odd result of the combined effects of soil moisture content and nutrient supply. The cancelling of the individual effects of the two environmental factors (soil moisture content and nutrient supply) could explain why cyanogenic glucoside production is not always influenced by soil nutrient supply [13]. The different effects that agro-climatic environments have on cyanogenic glucoside production in cassava varieties [14][15][16] could also be a result of the little understood effects of soil nutrient supply and its interaction with other agronomic factors.…”

Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: a case of konzo-affected Mtwara region, Tanzania

“…An adequate supply of soil K, through fertilizer application has been shown to often reduce HCN levels in cassava roots [3,38,39]. Some studies have however shown no effects on root HCN with an improved supply of K [40]. The low soil K levels on these cassava fields could thus contribute to increased root cyanogenic glucoside levels in cassava produced in the region.…”

Cyanide in Cassava Varieties and People’s Perception on Cyanide Poisoning in Selected Regions of Tanzania

“…Moreover, the noted inconsistency of cyanide levels within samples of the same variety means that cyanide level in one sample tuber can in no way be used as a standard for other samples of the same variety collected from different geographical areas. In other words, the same variety can exist in both sweet and bitter forms due to factors that affect cyanide levels in cassava including water stress (Tan, 1995;Bokanga et al, 2004;Gitebo et al, 2009), soil type (CIAT, 1989;Ekanayake, 1994;CHU, 2015) and application of fertilizers (De Bruijn, 1973;Endris, 1977;Wheeler et al, 1990;Cuvaca et al, 2015).…”