Dear DSSAT list, In my previous email I asked some questions about prediction of maize yields, as the simulated results did not match observed trial results. The DSSAT list recommended I change the soil fertility factor level to better match my observed data. This was also to take account of the addition of phosphorous fertilizer in my actual trials. At present I do not have values for initial soil N. So I have used the default value in Xbuild of 0.1 ppm of ammonium, 1.2 ppm of nitrate. Then I changed fertility factor to range from 1 to 0.60 for a 3-year study to see the results. Year 1 had the fertility factor of 0.6 to simulate the first year of fertilizer application where there had been none previously. The fertility factor values for year 2 and 3 were increased to account for the increased base fertilizer levels due to the previous year’s applications of fertilizer. I found a better match of simulated to observed results. I also then changed the initial N values together with a change in soil fertility factor and found the best match between simulated and observed My question is which would be the appropriate factor to adjust in this case between soil fertility factor and initial N value? It seems that soil fertility factor is very sensitive to the prediction of above ground biomass yields. I have not yet analyzed my own initial soil N. But when I have this real data I will use them instead of an automatic/estimated value. I am wondering if I should keep the value for the fertility factor the same for each year then. Can anyone provide more information about the function of soil fertility factor in the DSSAT model? I have read some papers but there seems to be little information on this and I would like to understand its use in DSSAt a little better. I appreciate everyones comments on my approach. Thanks for your kindness Sutisa