Variability in crop response and nutrient use efficiencies to fertilizer application is quite common under varying soil and climatic conditions. Understanding such variability is vital to develop farm- and area- specific soil nutrient management and fertilizer recommendations. Hence the objectives of this study were to assess maize grain yield response to nutrient applications for identifying yield-limiting nutrients and to understand the magnitude of nutrient use efficiencies under varying soil and rainfall conditions. A total of 150 on-farm nutrient omission trials (NOTs) were conducted on farmers’ field in high rainfall and moisture stress areas. The treatments were control, PK, NK, NP, NPK and NPK+ secondary and micronutrients. Maize grain yield, nutrient uptake, agronomic and recovery efficiencies of N and P differed between fertilizer treatments and between the contrasting agro-ecologies. The AEN ranged from 24.8 to 32.5 kg grain kg-1 N in Jimma area and from 1.0 kg grain kg-1 N (NK treatment) to 10.2 kg grain kg-1 N (NPK treatment) at Adami Tullu and from 0.1 kg grain kg-1 N (NK treatment) to 8.3 kg grain kg-1 N (NPK treatment) at Bulbula. The differing parameters between the agro-ecologies were related to difference in rainfall amount and not to soil factors. Grain yield response to N application and agronomic efficiencies of N and P were higher in the high rainfall area than in the moisture stress areas. Grain yield responded the most to nitrogen (N) application than to any other nutrients at most of the experimental sites. Owing to the magnificent yield response to N fertilizer in the current study, proper management of nitrogen is very essential for intensification of maize productivity in most maize growing areas of Ethiopia.

Two sets of pot experiments were conducted to investigate the effect of different compost types (market compost, home compost and vermicompost) and their rates on growth of pot grown tomato. During the first experiment, two compost types (market and home composts) each applied at four rates (0, 200, 400 and 800 g/pot) were evaluated while during the second experiment all the three compost types including vermicompost each applied at five rates (0, 200, 400, 600 and 800 g/pot) were evaluated. The chemical compositions of the composts were analyzed using appropriate laboratory procedures. Results revealed that market compost had the highest available P, exchangeable K and total S content whereas vermicompost had the highest organic matter and total N content followed by market compost. Growth parameters increased with increasing rates of home compost and vermicompost, but decreased with increasing rate of market compost. Shoot nutrient content varied much between compost types than compost rates. Shoot nitrogen and potassium concentration was higher with the application of market compost; phosphorus concentration was higher with the application of vermicompost while sulphur concentration was the highest with the application of home compost. Growth reduction at the highest market compost application could be ascribed to higher pH and total soluble salt content, especially chloride and potassium. Key words: Compost, salt stress, tomato, toxicity, vermicompost.