INVESTIGATING THE EFFECT(S) OF CONTRASTING NITROGEN (N), PHOSPHORUS (P), AND POTASSIUM (K) FERTILIZER RATES ON CASSAVA TUBER YIELD AND QUALITY AND MAIZE GRAIN YIELD IN SOUTHERN AFRICA

Fertilizer is a major limiting factor to agriculture in southern Africa (SA). Coupled with this is lack of appropriate fertilizer recommendation rates for high productivity in existing agricultural systems. Field experiments were conducted to determine nitrogen (N), phosphorus (P), and potassium (K) fertilizer rates for high cassava tuber yield and quality for the coastal semiarid Dondo District of Mozambique, and high maize grain yields for both vertisol and inceptisol of Maphutseng in Lesotho. In general, the results showed that cassava tuber yield, cassava tuber quality as measured by tuber starch content, and maize grain yield were significantly increased by fertilizer addition (p0.05). The results also showed that maize grain yield was not significantly affected by tillage practices (p>0.05). Combined applications of 60 kg N-60 kg P-0 kg K and 60 kg N-90 kg P-150 kg K kg per ha are suggested for high cassava tuber yield, and high cassava tuber starch content for the coastal semiarid Dondo District of Mozambique, respectively. Economically optimum maize grain yields (EOY) and profits (EOP) for the southwest lowlands of Maphutseng village, Mohale’s Hoek District, Lesotho, were estimated at 222 kg, 182 kg, and 123 kg of N (applied as limestone ammonium nitrate) per ha for no-till vertisol, no-till inceptisol, and till vertisol maize systems, respectively. The results suggest that an application of 30 kg of P (P₂O₅) per ha is required for high grain yields in inceptisol maize system. The results also confirmed that the benefits of not tilling the soil are not immediate. On the whole, the results suggest that there is potential to increase productivity in existing agricultural systems with the use of fertilizer in both Mozambique and Lesotho. However, this will not be possible without increasing farmers’ access to fertilizer given that fertilizer use in both countries is still very low (< 20 kg per ha).