Abstract
Water deficit limits cassava (Manihot esculenta Crantz) productivity in drought-prone areas and alters the nutritive quality of the crop. Potassium (K) may mitigate the effects of water deficit and improve the nutritional content of cassava, which would alleviate malnutrition among the human population in the tropics who depend on cassava as a staple food. Pot experiments were conducted under controlled glasshouse conditions to investigate the influence of deficit irrigation and K fertigation on the nutritive and anti-nutritive quality of biofortified cassava during the early growth phase. Treatments initiated at 30 days after planting were three irrigation doses (30%, 60%, 100% pot capacity) that were split to five K (0.01, 1, 4, 16 and 32 mM) concentrations. Plants were harvested at 90 days after planting, and the starch, energy, carotenoid, crude protein, fiber, minerals and cyanide concentration of the leaves and roots were determined. Irrigation and K treatments showed significant (P < 0.05) interactions for starch, carotenoid, energy and cyanide concentration. An irrigation dose of 30% together with 0.01 mM K resulted in the lowest starch, carotenoid, energy, and fiber content, but highest cyanide concentration, relative to full-irrigated (100%) plants together with 16 mM K. When the K application rate was 16 mM the best nutritional quality was obtained, with the lowest cyanide concentration, regardless of irrigation dose. Moreover, nutritional traits showed strong positive associations, whereas cyanide concentration correlated negatively with all the nutritional traits. Notably, an irrigation dose of 60% together with 16 mM K reduced the nutritional content the least and showed minimal increase in cyanide concentration. The results indicate that K fertigation with adjusted irrigation may improve the dietary quality of young cassava and reduce antinutrients, which could enhance the nutrient bioavailability of cassava grown in drought-prone areas.
Highlights
The main challenge of crop production in the tropics is water deficit, which limits yield and alters the nutritive quality of crops (Cakmak, 2010)
An irrigation dose of 30% together with 0.01 mM K reduced starch content in leaves by 79% and in roots by 82%; the reduction in starch content was only 37% in both leaves and roots when the K application rate was 32 mM
Santisopasri et al (2000) reported lower starch content (1.2–3.5% dry matter (DM)) in cassava that was subjected to water deficit in the first 6 months after planting compared to higher starch content (20.4–25.9% DM) in control plants
Summary
The main challenge of crop production in the tropics is water deficit, which limits yield and alters the nutritive quality of crops (Cakmak, 2010). Low bioavailability of minerals and proteins from consumption of cassava leaves and roots remains a challenge in the tropics (Gegios et al, 2010); yet, the nutritional value of cassava is comparable to most cereals, legumes and vegetables. Rural households use processing techniques, such as drying, pounding, boiling, and fermentation, which can reduce cyanide concentration by half (Essers, 1995), but are inefficient in eliminating all the cyanide, which can remain at lethal levels (Ngudi et al, 2003) These processing methods degrade total carotenoid content (Oliveira et al, 2010), reduce starch content (Cuvaca et al, 2015), and result in loss of minerals (Achidi et al, 2008; Latif and Müller, 2015) leading to dietary deficiencies
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