Low nitrogen fertilizer use efficiency in irrigated cotton and winter wheat constrains yields and farm income in Uzbekistan. Therefore nitrogen use inefficiencies under farmers’ production practices were quantified and compared to those obtained with higher or lower nitrogen application rates, different fertilizer types and application times. Also the crop quality was assessed for the different practices. Modifications particularly in the timing of the application, e.g. at budding in cotton or an additional dose at wheat heading, could increase the nitrogen use efficiency, help reduce nitrogen losses and thus the cost of fertilizer application. This would render agriculture more environmentally sound.240