Restoring soil fertility in smallholder farming systems is essential to sustain crop production. An experiment was conducted in 2011 and 2012 to study the effect of compost and inorganic fertilizer application on soil chemical properties and wheat yield in northwest Ethiopia. Full factorial combinations of four levels of compost (0, 4, 6, 8 t ha -1 ) and three levels of inorganic fertilizers (0-0, 17.3-5, 34.5-10 kg N-P ha -1 ) were compared in a randomized complete block design with three replications. In 2012, two sets of trials were conducted: one was the repetition of the 2011 experiment on a new experimental plot and the second was a residual effect study conducted on the experimental plots of 2011. Results showed that in the year of application, applying 6 t compost ha -1 with 34.5-10 kg N-P ha -1 gave the highest significant grain yield. In the residual effect trial, 8 t compost ha -1 with 34.5-10 kg N-P ha -1 gave 271 % increase over the control. Grain protein content increased 21 and 16 % in the current and residual effect trials, respectively, when 8 t compost ha -1 was applied; it increased 11 and 14 % in the current and residual effect trials, respectively, when 34.5-10 kg N-P ha -1 was applied. Under the current and residual effects of 8 t compost ha -1 , SOM increased 108 and 104 %; available P 162 and 173 %; exchangeable Ca 16.7 and 17.4 %; and CEC 15.4 and 17.1 %, respectively. Applying 6 t compost ha -1 with 34.5-10 kg N-P ha -1 is economically profitable with 844 % MRR.

Scarcity of water is the most severe constraint for development of agriculture in arid and semi-arid areas. Under this condition, irrigation management has to be improved while still achieving high yield. This study was conducted in North Gondar zone in 2010/2011 to investigate deficit irrigation scheduling on potato yield and yield components. Nine treatment combination: Irrigation frequency based on Cropwat model output, two modified irrigation frequency and two deficit irrigations of 25 and 50% were laid out with three replications in randomized complete block design (RCBD) in factorial combinations. It was found that irrigation scheduling significantly affected yield and some yield components. The highest marketable tuber yields was obtained from 0% deficit irrigation and frequency of F1-2 days (T9) which was 26.33 t ha -1 , whereas 25% deficit irrigation with F1-2 days frequency (T8) gave 25.68 t ha -1 . The lowest marketable yield was 3.4 t ha -1 from T4. The highest water use efficiency (WUE) were obtained from T7 and T8 which were 6.61 and 5.59 kg mm -1 , respectively. Therefore, applying 75% of full irrigation depth throughout the whole growing season with frequency based on Cropwat model scheduling -2 days resulted better potato yield and saved significant depth of water which improved WUE.

Groundwater is a vital resource for human welfare. However, due to various factors, groundwater pollution is one of the main environmental concerns facing. Yet, it is challenging to simulate groundwater quality dynamics due to the insufficient representation of nutrient percolation processes in the soil and Water Assessment Tool model. The objectives of this study were extending the SWAT module to predict groundwater quality. The results proved a linear relationship between observed and calculated groundwater quality considering No3 and TDS with R2, NSE and PBIAS values in the satisfied ranges, albeit underestimation and overestimation were observed due to limited data availability. These results highlight that nitrate and TDS concentrations and variability in groundwater may used as a tool in surface water quality that have to be assumed for designing adaptive management scenarios. Hence, extended SWAT model could be a powerful tool for future regional to global scale modelling of nutrient loads supporting effective surface and groundwater management.

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