Integrated Soil Fertility Management Options To Improve Cassava (manihot Esculenta Crantz) Productivity In Zambia

Cassava is an important staple food for many smallholder farmers in Sub-Saharan Africa. Indeed, it is the second most important crop next to Maize in Zambia. However, its productivity is low as a result of declining soil fertility and low levels of fertilizer application. As evidenced from research, there is a huge gap between the actual yield on-farm and potential yield of the crop. The primary aim of this research was to search for options of Integrated Soil Fertility Management (ISFM) that can reduce the yield gap of Cassava production in Zambia. Field research was conducted in two different agroecologies: Mansa, is in agroecological zone III – with high rainfall on a highly acidic soil and Kabangwe, in agroecological zone II – which is characterized by relatively more fertile soils but low rainfall. rnEffect of four levels of chicken manure (0, 1.4, 2.8, 4.2 ton ha-1) were evaluated against a single level of recommended NPK fertilizer (100N-22P-83K kg ha-1). The results showed significant (p < 0.05) treatment effects on cassava root yields and yield components (leaf, stem, and total biomass) at both sites. The highest fresh root (27.66 ton ha-1), dry root (9.55 ton ha-1), and total fresh biomass (53.68 ton ha-1) yield were achieved with the application of 4.2 ton ha-1 of chicken manure. This treatment showed 71% and 81% fresh root yield advantage over the control at Mansa and Kabangwe, respectively. While the marginal rate of return (MRR) was negative for the mineral fertilizer, it was positive for all the chicken manure treatments with the maximum of 315% achieved with the application of 4.2 ton ha-1. As a second option, manure was combined with NPK fertilizers to see how cassava responds to the factorial combinations of nutrients. In addition to the four levels of chicken manure, four levels of NPK (no fertilizer applied (control), 50 N-11 P-41.5 K– 50% below the recommended rate, 100 N-22 P-83 K – the recommended rate, and 150 N-33 P-124.5 K kg ha-1– 50% above the recommended rate) were tested leading to a total of 16 rnrntreatments. The combined application of 4.2 ton ha-1 of manure and 100N-22P-83K kg ha-1 of mineral fertilizer resulted in the highest fresh yields of 35.2 ton ha-1 and 34.4 ton ha-1 at Kabangwe and Mansa, respectively. This combination increased yield by 24 and 29% over the sole NPK fertilizer application at Mansa and Kabangwe, respectively. Harvest index and agronomic efficiencies were higher when 2.8 ton ha-1 manure was applied in combination with 100 N-22 P-83 K kg ha-1 than other treatments at both sites. In addition, the soil fertility status as influenced by cassava production under combined application of manure and NPK was examined. Soil samples were collected before planting and at different growth stages of the crop at 4, 8, and 12 months after planting (MAP). The samples were analysed to determine soil pH, available phosphorus (AP), total nitrogen (TN), organic carbon (OC), cation exchange capacity (CEC), exchangeable bases and some micronutrients. The results indicated that manure application significantly (p < 0.05) increased soil pH, OC, TN and Zn levels at all the plant growth stages when compared to before planting and the control. In contrast, the application of mineral fertilizer significantly (p < 0.05) reduced soil pH, OC and TN. But, AP levels increased following the application of both fertilizers. The study concludes that the application of chicken manure, in isolation or in combination with mineral fertilizer, improves cassava yield and soil nutrient status while mineral fertilizer is crucially important to improve cassava yields. Whenever available, it is advisable to apply mineral fertilizer in combination with organic manure to improve both soil health and crop yields.

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