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Declining soil fertility in Nitisols and Planosols, which dominate major potato (Solanum tuberosum L.) growing areas of Kenya, is a hindrance to sustainable production of the crop. A study was conducted in Nyandarua County, Kenya, to assess performance of potato and the agronomic efficiencies of three fertilizer types: diammonium phosphate (DAP) (N–P2O5–K2O: 18–46–0), Mavuno Peas, Beans and Root Vegetables (MRV) (15N:8 P2O5:15 K2O plus S, Ca, Mg, Fe, Cu, Zn, B, Mn, Mo), and new Mavuno blend (18N:24 P2O5:10 K2O plus 5S, 0.04B, 0.02 Zn). The experiments were established on Nitisol and Planosol soil types in farmers' fields. Two potato varieties were evaluated in a split plot layout design. Diammonium phosphate had the highest and significant influence on potato haulm, giving 16.5 and 15.5 g plant–1 on variety Sherekea growing on Nitisol and Planosol, respectively. Fertilizer type significantly influenced potato yield, which was recorded at 29.2 t ha–1 with DAP and 26.6 t ha–1 with new Mavuno on variety Sherekea grown on Nitisol. A significant positive interaction (P <.05) of fertilizer type and soil type was observed. Fertilizers also gave significant effect on agronomic efficiency of N, P, and K. Potato yield and agronomic nutrient use efficiency were dependent on the fertilizer types used as well as soil type. Diammonium phosphate and new Mavuno were the best fertilizer types. Core Ideas: Potato yields are influenced by inherent soil properties and fertilizer type.Fertilizer application is inevitable on Nitisol and Planosol for meaningful potato production.Addition of K into fertilizers should be carefully considered. [ABSTRACT FROM AUTHOR]

Low nutrients have been reported in potato-growing areas of Kenya, prompting a need for nutrient management research. A study was designed to determine the effect of omitting nutrients on potato growth, yield and harvest index. On-farm nutrient omission trials were set during the long rains (LR) and short rains (SR) of 2016 in which the treatments involve the judicious omission of N, P, K, S and B. Additional two treatments were included with one receiving all the nutrients and a control where no nutrients were added. The treatment was laid in a randomized complete block design with three replications. Potato yields reduced by 6.6 and 11.2 t ha−1 in N-omitted treatments in LR and SR, respectively, when compared to the one receiving all the nutrients, while omitting P resulted in respective yield reductions of 3.8 and 2.0 t ha−1. Stability analysis revealed that omission of N was more stable with a regression coefficient of 0.5; it was followed by P with a value of 1. Potassium, S and B were limiting nutrients only in some farms. N and P should continue to be included in potato nutrient management, while K, S and B should be added based on soil test. [ABSTRACT FROM AUTHOR]

Inherent low soil fertility remains a hindrance to potato production in Kenya and continues to pose a threat to food security. A study was conducted in Nyandarua and Meru counties to assess the soil fertility status in smallholder potato farms. Soil and plant tissue samples were collected and analysed for selected nutrients (pH, OC, N, P, K, S, Ca, Mg, Zn, B and Cu) from 198 farms. Critical nutrient levels were used to assess the sufficiency levels of nutrients for potato growth. Soils in the sampled farms were weakly to strongly acidic (pH-CaCl2 3.9–6.6) and had low to high soil organic matter content (1.5–97.5 g Kg−1). The percent of farms in Meru and Nyandarua with nutrient contents below critical levels were 66% and 20% for N, 46% and 85% for P, 67% and 31% for S, 9% and 51% for Cu, and 87% and 80% for B, respectively. Low tissue nutrient concentrations were observed for N, P, K, and S irrespective of the sites. Soil pH correlated strongly with majority of the analyzed soil and tissue nutrients. These results affirm the need to design integrative soil fertility management strategies to correct the impoverished soil fertility status in the study area. [ABSTRACT FROM AUTHOR]