investigation of nitrogen use efficiency in wheat-based double cropping systems under different rate of nitrogen and return of crop residue

crop rotation affect on crop nitrogen uptake and nitrogen use efficiency (nue). crop rotations with high nue decrease energy use and increase level of sustainability in agro ecosystems. the objectives of this research were to determine the suitable double cropping system for enhancing nue and evaluate the effects of crop rotation, n fertilizer rate and return of crop residue on nue. this study was conducted under cold temperate climate condition in khorasan-razavi during 2006-2008 growing seasons. a randomized complete block design in split-split plot arrangement with three replicates was used. main plots were crop rotation with five different rotations (wheat:wheat, potato:wheat, silage corn:wheat, clover:wheat and sugar beet:wheat) and sub plots were n fertilizer rates in preceding crop with four levels (without n (control), 50% lower than optimum n rate, optimum n rate and 50% more than optimum rate). the sub-sub plots were preceding crop residue return with two levels including no residue return (control) and 50% return of crop residue. results showed that nitrogen use efficiency, nitrogen uptake efficiency and nitrogen utilization efficiency were significantly affected by crop rotation and n fertilizer rates. the highest and lowest nue recorded for corn: wheat and wheat:wheat rotations, respectively. the highly nue in the corn: wheat rotation is due to the higher nute in this rotation. nue indices in all crop rotations reduced with increasing n fertilizer rate. nue in potato:wheat rotation showed highest response to n fertilizer rate. return of crop residue had no significant effect on nue indices.