Phosphorus is often an important limiting factor for crop yields, and in addition, low soil fertility and crop nutrient imbalances are major obstacles preventing Ethiopian farmers from realizing high agricultural productivity. Effect of the sole and combined application of farmyard manure (FYM) and inorganic fertilizers on tuber yield, nitrogen (N) uptake and use efficiency of Irish potato (Solanum tuberosum L.) was assessed in a field experiment carried out in Arbegona district of Sidama zone in Southern Ethiopia. The studied nutrient management practices were control (without fertilizer) and farmyard manure (FYM), recommended N and phosphorus (P), blended (17.3 N 3 , 4.7 P 2 O 5 , 7.41 S 2 , 23 Zn0, 3 B within 100 kg) plus potassium (K) fertilizers and combined half FYM and recommended NP and combined half FYM and blended plus K fertilizer. Treatments arranged in randomized complete block design with three replications. The experimental soil was loamy and very strongly acidic, low in organic carbon and available P and medium in total N and available K. Results showed that the applied FYM and inorganic fertilizer individual and in combination were resulted positive N balances. Potato plants amended with sole blended fertilizer, combined half recommended NP and FYM, and combined half FYM and blended fertilizers improved total dry tuber yield and total N uptake more than twofold (100%) as compared to the control. In the amendments, average agronomic and physiological efficiency of N supply and uptake were 48 and 46 kg dry tuber, respectively. Furthermore, 112% of apparent recovery efficiency of N was obtained across the treatments. Soil amendments resulted the highest net benefits with acceptable marginal rate of return (above 100%). Generally, soil amendments either in sole or combined inorganic and organic fertilizers could be considered to improve soil fertility status and potato yield in the study area.

The soils of Jinka in Southern Ethiopia were studied based on the detail works on soil pit description, characterizing and classification following the FAO and USDA guidelines. For this, along with the toposequence and landscape, six soil profiles were opened on an area of 100 ha of research field to make them suit for sustainable soil management practices. The soils were generally described as dark reddish brown to very dark brown and deep. These soils were characterized as slightly (4.87) to moderately acidic (6.18). The OC and available phosphorus were found to range from low to medium. All micronutrients were found to be highly associated with lower soil reaction. These soils group can be classified as Cambisols. Therefore, amending the soil with lime based on exchangeable acidity, essential and deficient nutrients will be vital for supplying food and feed crops in the region. However, continuous assessment of the nutrient status at every five to seven years is necessary to make sure that the soil quality is maintained.

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