Adoption of conservation agriculture (CA) is increasingly being promoted as a way of adapting agricultural systems 
to increasing climate variability, especially for areas such as Africa where rainfall is projected to decrease. The DSSAT 
(Decision Support System for Agro Technology) crop simulation models can be a valuable tool in evaluating the effects of 
CA, which are viable both economically and environmentally. Our objectives were to evaluate the ability of DSSAT to 
predict the combined effect of tillage system and fertilizer rates through wheat/soybean rotation on crop yield. DSSAT 
v.4.6.1 (CERES-wheat and CROPGRO-soybean) was utilized for the study to simulate crop yield. Observed field data 
revealed that, the effect of tillage systems during the summer season of 2013 did not differ significantly due to studied 
Soybean traits. Related to, winter season of 2013/2014, the results revealed that, CA tillage system increased significantly 
all studied wheat traits as compared with the other tillage systems. Referring to, the summer season of 2014, CA system 
scored the significant high values for the studied Soybean traits. As for the effect of studied NPK fertilizer levels, results 
showed that, 100% of the recommended doses of NPK favored the values of the studied soybean and wheat traits 
significantly during summer 2013 and winter 2013/2014, as compared by 50% of the recommended dose of it, in addition, 
there are no-significant difference between the two fertilizer levels for soybean traits in the third season (summer, 2014). 
Regarding, the interaction effect between the tested factors, results of the three trial seasons revealed that, growing 
soybean or wheat under the condition of conservation agriculture (CA) and fed by 100% or 50% of the recommended dose 
of NPK fertilizers scored the greatest values for most of soybean and wheat traits. On contrast, the lowest value was 
resulted under the condition of conventional tillage (CT) and fed by the 50% of the recommended dose of NPK fertilizers. 
The DSSAT– CERES-wheat and CROPGRO-soybean models also reflected this trend. These results indicated that, The 
DSSAT program exposed powerful for stimulation for grain yield/fed., harvest index as affected by interaction effect 
between tillage systems and fertilizer rats, which there RMSE ranged between good and excellent, RMSE = (12.44, 12.29) 
and (7.92, 1.76) and (1.68, 16.24) for summer 2013, winter 2013/2014 and summer 2014 seasons respectively, through 
(soybean→ wheat→ soybean) crop sequence.