Optimizing nitrogen fertilizer source and potassium fertilization rate to enhance growth, yield, and quality of cassava (Manihot esculenta Crantz) in newly reclaimed sandy soils

Cassava (Manihot esculenta Crantz) is a promising crop for Egypt’s newly reclaimed sandy soils due to its tolerance to low fertility and drought. Integrating cassava into the national cropping system could reduce wheat import dependency by partially substituting wheat flour with cassava flour in bread production. A two-year split-plot field experiment (2023–2025) was conducted in El-Minia Governorate, Egypt. A study evaluated the interactive effects of three nitrogen(N) fertilizer sources, ammonium sulphate (AS, 20.6% N), ammonium nitrate (AN, 33.5% N), and urea (U, 46% N) with application a rate of 125 kg N ha-1, and three potassium (K) fertilization rates of potassium sulphate (48% K2O) were applied at 50%, 75%, and 100% of the recommended fertilization rate (250 kg K2O ha⁻¹) on cassava growth, yield, tuber quality, and post-harvest soil properties. Results showed that AN significantly enhanced vegetative growth traits, whereas AS produced the highest tuber yield and superior quality attributes, including higher starch, carbohydrate, and soluble sugar contents, and lower nitrate, fiber and moisture content. Urea consistently resulted in lower yield and quality, with higher moisture and fiber accumulation. Increasing K fertilization rates improved most quality parameters, but 75% K₂O achieved results comparable to 100% K2O on several traits, indicating potential for reduced K application without compromising performance. The combination of AS with 75–100% K₂O maximized cassava yield and quality while improving nutrient uptake efficiency. These findings provide a practical fertilization strategy for sustainable cassava production under newly reclaimed sandy soils poor in plant nutrients.