Optimal irrigation and N-fertilizer management for sustainable winter wheat production in Khorezm, Uzbekistan

Abstract

The efficiency of the nitrogen (N) application rates 0, 120, 180 and 240 kg N ha-1 in combination with low or medium water levels in the cultivation of winter wheat (Triticum aestivum L.) cv. Kupava was studied for the 2005-2006 and 2006-2007 growing seasons in the Khorezm region of Uzbekistan. The results show an impact of the initial soil Nmin (NO3-N + NH4-N) levels measured at wheat seeding on the N fertilizer rates applied. When the Nmin content in the 0-50 cm soil layer was lower than 10 mg kg-1 during wheat seeding in 2005, the N rate of 180 kg ha-1 was found to be the most effective for achieving high grain yields of high quality. With a higher Nmin content of about 30 mg kg-1 as was the case in the 2006 season, 120 kg N ha-1 was determined as being the technical and economical optimum. The temporal course of N2O emissions of winter wheat cultivation for the two water-level studies shows that emissions were strongly influenced by irrigation and N-fertilization. Extremely high emissions were measured immediately after fertilizer application events that were combined with irrigation events. Given the high impact of N-fertilizer and irrigation-water management on N2O emissions, it can be concluded that present N-management practices should be modified to mitigate emissions of N2O and to achieve higher fertilizer use efficiency.