Crop rotation is effective on nitrogen uptake by plants, the efficiency use of nitrogen fertilizer and seed amount. Thus, the selection of a rotation system with high efficiency of nitrogen at reduces energy consumption and increase the level of ecological sustainability of cropping systems is effective. In order to determine correlations between some traits and yield components as well as causal relationships between them in wheat-wheat and sugar beet-wheat rotation, an experiment was conducted in factorial based on randomized complete design with three replications in the favorable and relatively humid climate of Golestan (Gonbad Kavous) during 2012-2013. The treatments were included: density at three levels (300, 350, 400 seeds m^-2) and nitrogen at four levels (0, 50, 100, 150 kg ha^-1). Results showed that the highest seed yield was observed in the density of 350 seeds per square meter and 100 N kg ha^-1. The interaction between nitrogen and density on biological yield was significant. In rotation of wheat-wheat and sugar beet-wheat, seed yield and biological yield correlated significantly and positively. In general and with respect to the correlations calculated at this rotation, one can rely on a trait such as biological function to obtain maximum yield. In sugar beet-wheat rotation, the number of seeds per spike due to effect of positive direct and the indirect effect of the number of spikes per square meter, and seed number per spike can be considered as the most important trait for increasing yield.